Stereo- and regiocontrol in ene-dimerisation and trimerisation of 1-trimethylsilyl-3-phenylcyclopropene

Article abstract of DOI:10.1016/j.tet.2009.10.077

1-Trimethylsilyl-3-phenylcyclopropene and its 2D-analog undergo a highly stereocontrolled ene-reaction to give a single dimer. Further reaction leads to one or more trimers derived through two ene-reactions. The dimer formed easily undergoes cycloaddition

Full text of DOI:10.1016/j.tet.2009.10.077

Tetrahedron 65 (2009) 10552–10564
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Stereo- and regiocontrol in ene-dimerisation and trimerisation of 1-trimethylsilyl-
3-phenylcyclopropene
,
,
a
c
Andrey E. Sheshenev a y, Mark S. Baird b , Ivan G. Bolesov , Alexandre S. Shashkov
*
a Department of Chemistry, Moscow State University, Moscow 119992, Russia
b School of Chemistry, Bangor University, Bangor, Gwynedd, Wales, UK LL 57 2UW, UK
c N.D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, Moscow 117913, Russia
a r t i c l e i n f o
a b s t r a c t
Article history:
1-Trimethylsilyl-3-phenylcyclopropene and its 2D-analog undergo a highly stereocontrolled ene-re-
action to give a single dimer. Further reaction leads to one or more trimers derived through two ene-
reactions. The dimer formed easily undergoes cycloaddition with active dienes and nitrile oxides while
the trimers do not react under the same conditions. The first enantioselective example of an ene-reaction
of cyclopropene derivatives using optically active 1-trimethylsilyl-3S-phenylcyclopropene is also
discussed.
Received 9 August 2009
Received in revised form
13 October 2009
Accepted 22 October 2009
Available online 25 October 2009
Ó 2009 Elsevier Ltd. All rights reserved.
Keywords:
Cyclopropene
Ene-reaction
Oligocyclopropanes
Chirality
Stereoselectivity
Cycloaddition
1. Introduction
cyclopropene (only one possible regio- and stereochemistry is
shown) to be considerably faster than the dimerisation of these
Three membered carbocycles, both saturated and unsaturated,
are of interest for synthetic chemists, theoreticians and biochemists
due to their unique structure resulting from the unusual geometry
and high strain energy of a small ring.1 There has been considerable
recent interest in biologically active compounds containing an ar-
ray of contiguous cyclopropanes.2,3 Stereocontrolled synthesis of
these compounds is usually based on the successive introduction of
each small ring.2,4 Cyclopropenes bearing a hydrogen atom at the C-
3 position often undergo ene-dimerization to give cyclopropyl-
cyclopropenes 1 (Scheme 1), which are the possible precursors of
bi- and oligocyclopropanes. Formally, the further addition of
starting cyclopropene molecules to the dimer 1 can lead to the
formation of a single polycyclopropane. However, a high level of
stereocontrol (endo- or exo-transition state) and regiocontrol dur-
ing each step of the process is necessary to realize this sequence of
selective transformations. In addition, such selective trans-
formation would require the rate of reaction of the dimer 1 with
species themselves. The known examples of such reactions for
substituted cyclopropenes suggest that, although the regiochem-
istry in dimerisations can be largely controlled by appropriate in-
troduction of substituents, the stereochemistry (and particularly
the absolute stereochemistry) is more difficult to control.5
?
H
H
H
H
1
H
Scheme 1.
It is not possible to determine the diastereoselectivity of the
ene-reaction in the case of a monosubstituted cyclopropene or
cyclopropene itself,6 but asymmetrically substituted derivatives,
particularly1,3-disubstituted cyclopropenes, are suitable for this
purpose. Moreover, the application of enantiopure or enriched
cyclopropenes in this type of reaction could be useful for the syn-
thesis of chiral bi- and polycyclopropanes as well as providing
a better understanding of the whole process.
* Corresponding author. Tel.: þ44 1248 382374; fax: þ44 1248 370528.
E-mail addresses: chs028@bangor.ac.uk (M.S. Baird), ivbolesov@mail.ru (I.G.
Bolesov).
We have recently reported the preparation and studies of the
chemistry of 3-phenylcyclopropene,7 and some of its derivatives
including 1-trimethylsilyl-3-phenylcyclopropene 2 (Scheme 2).
y
Current address: Institute of Organic Chemistry and Biochemistry, Czech
Academy of Sciences, Flemingovo nam. 2, Prague 6, 16610, Czech Republic.
0040-4020/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2009.10.077

A.E. Sheshenev et al. / Tetrahedron 65 (2009) 10552–10564
10553
Investigation of its properties showed that under mild conditions
cyclopropene 2 undergoes stereocontrolled ene-reaction giving
a single dimer and two trimers in a ratio of 5:3:1, respectively. For
further analysis of this ene-process, 2D-analog 3 and enriched
cyclopropene (S)-2 were also prepared.
the corresponding (Z)- or (E)-1-phenyl-2-trimethylsilylethenes (Z)-,
(E)-10 available from acetylene 9 by stereoselective reduction with
DIBAL-H.12
Reaction of cis-11 with methyllithium was expected to lead di-
rectly to cyclopropene 2. However, when the reaction was carried
out at ꢀ90 ꢁC and quenched with water at ꢀ50 ꢁC, an essentially
quantitative yield of allene 12 (Scheme 5) was obtained. At 20 ꢁC in
ether or in THF medium, the major product was the acetylene 13,
together with allene 12 and a small amount of the dimer 7. Thus the
formation of cyclopropene 2 in this way was not useful, as con-
firmed by the low yield (maximum 13%) of 7.
TMS
TMS
TMS
S
Ph
Ph
Ph
D
2
3
(S)-2
Scheme 2.
The situation improved dramatically when the dibromide trans-
11 was subjected to reaction with MeLi under the same conditions
(Et2O, ꢀ90 ꢁC to ꢀ50 ꢁC, 20 min) (Scheme 6). This reaction resulted
in almost quantitative formation of cyclopropene 2 together with
ca. 4% of the allene 12. The cyclopropene 2 was again unstable but
Initial results in this area (namely, generation and ene-trans-
formations of cyclopropenes 2, 3 and (S)-2, Scheme 2) have been
represented in a short communication;8 we now provide the
details.
1
could be detected directly by H NMR spectroscopy at ꢀ40 ꢁC.
Addition of cyclopentadiene (Cpd) to the reaction mixture at
ꢀ50 ꢁC allowed a single [4þ2]-adduct 14 to be isolated in 92% yield
based on starting trans-11.
2. Results and discussion
The results represented in Schemes 5 and 6 show that the for-
mal cis- and trans-2,3-disubstituted trimethylsilylcyclopropylidene
intermediates 16 (generated from 11 and MeLi) transform primarily
either into allene 12 or 1-trimethylsilylcyclopropene 2, re-
spectively, and the balance is determined by the stereochemistry of
Ph and TMS substituents in the starting dibromides 11 (Scheme 7).
The formation of 2 from trans-11 apparently occur through in-
termediates 15 and 16 by a lithium–bromine exchange followed by
a formal loss of lithium bromide to give a cyclopropylidene, which
rearranges by a 1,2-trimethylsilyl shift. The different outcomes from
the cis- and trans-isomers 11 may simply reflect a steric effect of the
Ph group slowing the migration of the trimethylsilyl-group in the
Tribromocyclopropane 4 was treated with 2.2 mol equiv of MeLi
at ꢀ80 ꢁC, allowed to reach room temperature for 30 min to form
the 1-lithio-3-phenylcyclopropene
5 by lithium–halogen ex-
change,9 and then quenched with trimethylsilyl chloride to gen-
erate cyclopropene 2. This could be trapped in 30% yield (from 4) as
[4þ2]-cycloadduct 6 by reaction with 1,3-diphenylisobenzofuran
(1,3-DPIBF).10 In the absence of the trap, cyclopropene 2 was
detected directly by 1H NMR spectroscopy of the crude reaction
mixture with a ca. 30% yield together with a single dimer 7, which
could be isolated in 40% yield after 12 h at room temperature
(Scheme 3). The regio- and stereochemistry of 7 is established later
(from now only the (S)-enantiomeric series is shown).
Li
TMS
Br
Ph
Br
Br
1.3 mol eq. TMSCl
2.2 mol eq. MeLi
Et2O, -80°Cto r.t.
Ph
O
Ph
-60°C tor.t., 1 h
2 (30% by 1H NMR)
5
4
1,3-DPIBF
r.t., 12 h
r.t., 1 h
Ph
TMS
Ph
TMS
6 (30%)
H
Ph
Ph
H
H
Ph
TMS
H
7 (40%)
Scheme 3.
In order to better understand ene-process, a route to the
cyclopropene 2 was required, which could be carried out at low
temperature to minimize the rate of its dimerization and to avoid
undefined byproduct formation. It is known that reaction of 1,1-
dibromo-2-trialkylsilylcyclopropanes with MeLi in ether at 20 ꢁC or
ꢀ90 ꢁC leads to the formation of 1-trialkylsilylcyclopropenes due to
the 1,2-trialkylsilyl shift in the intermediate cyclopropylidene.11 To
exploit this route, individual stereoisomeric dibromides cis-11 and
trans-11 (Scheme 4) were prepared by dibromocyclopropanation of
cis-case and allowing the normal cyclopropylidene–allene rear-
rangement,13 to compete to form 12. A more subtle effect based on
the stereochemistry of the lithium–bromine exchange in 15 or on
the formation of a more complex intermediate such as carbenoids
rather than ‘free’ carbenes is also possible.
The structure of adduct 14 was in accordance with its NMR
spectra. The endo-configuration of the cyclopropane was de-
termined based on an NOESYexperiment, which showed the spatial
interaction of the TMS group and the bridge protons at C7. The anti-
Ph
Ph
Ph
Ph
Br
50% NaOH, CHBr3
1. n-BuLi
2. TMSCl
DIBAL-H
a) or b)
Cetrimide
Br
H
TMS
TMS
TMS
8
9 (90%)
cis-11 (90%);
trans-11 (88%).
a) ether-hexane: (Z)-10 (97%);
b) pentane-hexane: (E)-10 (91%).
Scheme 4.

10554
A.E. Sheshenev et al. / Tetrahedron 65 (2009) 10552–10564
Br
Ph
Br
TMS
TMS
1.15 mol eq. MeLi
a), b) or c)
7
+
+
TMS
Ph
Ph
13
12
cis-11
-
a) Et2O, -90°C to -50°C,30 min:
b) Et2O, 20°C,1 h:*
1%
12%
13%
97%
31%
38%
56%
49%
c) THF, -90°C to -50°C,20 min:*
* yields by 1H NMR spectroscopy
Scheme 5.
Ph
Ph
Ph
Cpd
1.15 mol eq. MeLi
TMS
+
Br
1. -50°C;
2. r.t., 2 h.
-90°C to -50°C, Et2O
20 min
TMS
Ph
14 (92%)
TMS
2 (96%)
Br
trans-11
TMS
12 (4%)
by 1H NMR at -40°C
Scheme 6.
Ph
Ph
Ph
Ph
Ph
MeLi
Et2O
- LiBr
or
Br
Li
TMS
TMS
TMS
TMS
Br
Br
TMS
12 from
cis- or
trans-11
2 from
trans-11
15
16
cis-11
Scheme 7.
orientation of the phenyl substituent was determined based on the
trans-stereochemistry of H2 and H8 (J¼3.2 Hz) and the interaction
between TMS group and ortho-phenyl protons in the NOESY spec-
trum (Table 1).
lithiocyclopropene 17. This was trapped by electrophiles (methyl
iodide, trimethylsilyl chloride or carbon dioxide) to give the cor-
responding 3-phenylcyclopropenes 18–20, mostly in good yields
(Scheme 8). Quenching of lithiocyclopropene 17 with MeOD or D2O
afforded the unstable cyclopropene 3 in a high yield, proved by the
analysis of its further ene-reaction products (see below), while the
reaction of 17 with methyl chloroformate failed to lead to the cor-
responding cyclopropene ester.
Table 1
The results of NOESY experiment for adduct 14
If the cyclopropene 2 was worked up at 20 ꢁC in the absence of
a trap, the dimer 7 was again obtained, in this case accompanied by
two trimers, 21 and 22 (Scheme 9). Compound 2 was relatively
stable at ꢀ40 ꢁC (an 11% solution in CDCl3 of 50:41:5 monomer 2/
dimer 7/trimer 21 immediately after reaction rearranged to
a 23:56:14 mixture in 27 h) but had reacted completely in 12 h at rt
either neat or as a 7% ethereal solution. Products 7 and 21 were
isolated as individual compounds in 49% and 31% yield, re-
spectively, while the minor trimer 22 was characterized only as
a mixture with 21.
The dimer 7 was efficiently trapped by reaction with cyclo-
pentadiene to give a crystalline endo-adduct 23, which was used for
X-ray analysis (Fig. 1); this, in turn, allowed the relative stereo-
chemistry of parent 7 to be determined. Compound 7 appeared to
be inactive toward 1,3-DPIBF and furan at 20 ꢁC; however, it easily
formed single [3þ2]-adducts 24 and 25 in reactions with benzo-
and p-nitrobenzonitrile oxides generated in situ from the corre-
sponding chlorides of hydroxamic acids and triethylamine.14 Under
7
H
H
4H
TMS
H2
H5
6 H
3
H1
H8
Ph
14
Proton
TMS
H1
H2
H4
H8
w
H2
w
s
s
m
H4
H7
s
w
s
s
o-Ph
m
Successful generation of cyclopropene 2 from trans-11 provided
a simple one pot route to 2-substituted 1-trimethylsilyl-3-phenyl-
cyclopropenes. The trans-isomer 11 reacted with methyllithium
(2.15 mol equiv, ether, ꢀ90 ꢁC to 20 ꢁC), leading to a lithium–hy-
drogen exchange in the intermediate
2
to produce
Ph
TMS
TMS
2.15 mol eq. MeLi, Et2O
E-X
-60°C to 20°C
Br
1. -90°C to 20°C;
2. 20°C, 30 min.
TMS
Ph
E
Ph
Li
Br
trans-11
17
18-20
19
No 18
20
E-X: MeOD (D2O), MeI, TMSCl, CO2, ClCO2Me.
E
Me TMS COOH
%
97
90
57
Scheme 8.

A.E. Sheshenev et al. / Tetrahedron 65 (2009) 10552–10564
10555
TMS
Ph
H
TMS
H
TMS
H
Ph
H
Ph
H
20°C,12 h
H
+
Ph
TMS
H
H
Ph
TMS
Ph
TMS
H
H
2
7 (49%)
21 (31%)
(racemic)
+
ArCNO,
Et2O
Cpd
H
TMS
H
Ph
TMS
H
Ar
PhH,
18 h
H
H
Ph
Ph
N
TMS
H
TMS
H
TMS
O
Ph
H
Ph
Ph
H
H
H
22 (10% by 1H NMR)
Ph
TMS
TMS
H
H
23 (88%)
Ar = Ph, 18 h, 24 (50%);
p-NO2-Ph, 40 h, 25 (30%).
Scheme 9.
The cis-orientation of protons H1, H2 and H4 relative to C1–C2–C3
of the cyclopropane ring of dimer 7 was confirmed by an NOESY
experiment (Table 2). The strong interaction between H3 and H4 as
well as the small coupling constant (J¼4.1 Hz) are evidence for
a deviation (up to 45ꢁ) of dihedral angle H3–C3–C4–H4 from
a transoid conformation (180ꢁ) about the C3–C4 bond in solution.
Table 2
The results of an NOESY experiment for dimer 7
TMS
5
H
4
3
6
Ph
2
H
Ph
TMS
H
1
H
7
Proton
TMS1
w
H1
H2
H3
H2
s
s
H4
s
s
m
s
s
o-Ph2
o-Ph6
In comparison with the above situation for 7, the preferred
conformation around the C3–C9 bond in the cyclopentadiene ad-
duct 23 (Table 3) is found to be trans- (angle H3–C3–C9–H9 close to
180ꢁ), both in the solid state (based on X-ray data, Fig. 1) and in
solution (based on NMR experiments). In the latter case, this was
determined from the relatively high coupling constant (J¼9.7 Hz)
between H3 and H9 along with the absence of spatial contact be-
tween them in the NOESY spectrum. Moreover, the NOESY data
Figure 1. X-ray crystal structure of cyclopentadiene cycloadduct 23.
these conditions neither of the trimers 21, 22 reacted with the
cyclopentadiene, 1,3-DPIBF, furan, diazomethane, and Ar-nitrile
oxides.
The X-ray crystal structure of the adduct 23 showed that the
dimer 7 was formed from two identical molecules of 2, rather than
two enantiomeric molecules, and that the reaction occurred
through an endo-transition state (Scheme 10, the only difference
between the structures is marked bold). This, together with de-
tailed NMR analysis allowed the correct structure of compounds 7,
24 and 25 to be established.
Table 3
The results of an NOESY experiment for Cpd-adduct 23
8
Ha
Hb
Ph
5
4
6
H
TMS
1
7
2
H
9
H
3
H
11
H
Ph
H
H
TMS
H
TMS
H
S
H
TMS
H
Ph
TMS
Ph
10
23
H
H
endo-
exo-
H
H
H3
H8a
H9
H10
Ph
Ph
Proton
TMS2
m
TMS10
H
S
Ph
H
H1
TMS
H
Ph
TMS
TMS
ene
H
7
H6
m
H
H8a
m
m
H
H
H
TMS
Ph
H9
w
w
Ph
TMS
Ph
Scheme 10.
Ph
H10
H11
o-Ph11
o-Ph4
m
s
H
R
H
S
H
s
TMS
TMS
s
s
s
m
s
s

10556
A.E. Sheshenev et al. / Tetrahedron 65 (2009) 10552–10564
Table 5
afforded another confirmation, namely long-distance contacts be-
tween protons of TMS2/ortho-Ph11 and TMS10/ortho-Ph4 groups.
The structure of adducts 24 and 25 was assigned on the basis of
HSQC, HMBC and NOESY data. In particular, HMBC spectra of these
compounds revealed the location of TMS groups at C2 and C6 due to
the presence of correlation peaks CH3–Si2/C2 and CH3–Si6/C6
(Table 4). The location of phenyl residues was also established by
HMBC-correlations between corresponding ortho-protons with
carbon atoms C3, C30 and C5. The above results showed the forma-
tion of [3þ2]-adducts occurred regiospecifically with the attack of
the TMS-substituted atom of the cyclopropene double bond by the
O-side of the nitrile oxide. The cis-orientation of H4, Ph3 and TMS2
relative to C1–C2–C3 ring and H5, H6 relative to C4–C5–C6 was
confirmed by NOESY experiments (Table 4). The absence of spatial
contact H1/H4 revealed that the predominant conformer about the
C1–C4 bond had a trans-orientation of protons H1 and H4 just as in
the case of 23. This conclusion was in agreement with the rather
large values of the 3J1,4 coupling constant (10 Hz). Thus, the addition
of the nitrile oxide occurred stereospecifically from the less hin-
dered side of the cyclopropene fragment of dimer 7.14a
The results of an NOESY experiment for trimer 21
H
TMS
TMS
Ph
4
7
H
3
5
8
9
1
6
H
Ph
H
Ph
TMS
H
2
H
21
Proton
TMS5
TMS2
s
TMS7
H1
s
H3
H4
H5
H6
H2
H3
H4
s
s
s
H6
s
o-Ph1
o-Ph6
o-Ph9
s
m
s
s
s
s
m
m
m
Ph9 were spatially close (Table 5). Groups of substituents Ph1, TMS2,
H3 and H4, TMS5, Ph6 were cis-oriented relative to the C1–C2–C3 and
C4–C5–C6 carbons of the cyclopropane rings, respectively. This in-
formation was in good agreement to the proposed ene-scheme of
21 formation, however at the same time it was not possible to
determine the correct location of the TMS5 and Ph6 pair in the
C4–C5–C6 ring precisely (Scheme 11).
The situation with the minor trimer 22 was similar to that dis-
cussed above for 21. Thus the proposed scheme of its formation again
included two possible routes starting from 2 and 7 (Scheme 12, the
only difference between the structures is marked in bold) but all
attempts to exactly establish the regiochemistry of the TMS/Ph pair
in the unsaturated ring failed.
Table 4
The results of NOESY experiments for [3þ2]-adducts 24, 25
N
H
3'
H
5
O
1
H
3
2
Ph
4
6
R
TMS
Ph
TMS
H
R = H, 24;
NO2, 25.
To determine the correct routes to the trimers, it was decided to
apply another approach resulting from Schemes 10–12. This re-
quired the introduction of chirality into the parent cyclopropene 2,
that in turn could clarify the details for the reaction between 7 and
2. Since the formation of dimer 2 occurs within one enantiomeric
series of 2, then the formation of 21 from chiral 2 via 7 would re-
quire an endo-ene-process; the absence of 21 would suggest the
opposite exo-transition state. The same picture can be observed for
minor product 22. Moreover, the formation of one isomer of 7 from
2 would create eight chiral centers in 23 from the single chiral
center in 2.
In order to exploit the above, the trimethylsilylcyclopropene (S)-
2 was obtained from the optically active acid (-)-(1S, 3S)-26, itself
produced by resolution of racemic acid 26 using (þ)-dehy-
droabiethylamine (Scheme 13).15 The main steps of the resolution
process included: a) formation and separation of a diastereomeric
salt 27, which was almost insoluble in common solvents and
therefore wasn’t subjected to recrystallization; b) recovery of
enriched acid (þ)-26 (62% ee) from 27 and its subsequent further
optical enrichment up to 89% ee by crystallization of racemic acid
Proton
H1
H4
H5
s
TMS2
H5
m
s
H6
TMS2
TMS6
o-Ph3
o-Ph5
s
w
m
s
w
s
m
m
Unfortunately, neither of the trimers 21 or 22 was obtained as
a crystalline derivative suitable for X-ray. However, as long as these
products resulted from the reaction between 7 and 2, then un-
derstanding the correct structure of 7 made the determination of
the relative configuration of the trimers easier. For instance, after
careful analysis of NMR data of the major trimer 21 it was found
that there were only two possibilities for its formation from 7 and 2
(Scheme 11, the only difference between the structures is marked
bold), but all attempts to solve this problem by NMR failed.
In accordance with the NOESY spectrum, protons H1 and H2
were cis-oriented relative to the C1–C2–C3 ring; protons H5, H6 and
H
TMS
H
TMS
Ph
S
H
Ph
endo-
TMS
Ph
TMS
H
H
Ph
Ph
H
H
ene
H
H
H
H
H
Ph
TMS
TMS
Ph
H
H
H
H
Ph
21
TMS
H
H
TMS
TMS
Ph
TMS
TMS
H
H
Ph
TMS
TMS
H
Ph
Ph
H
H
H
Ph
exo-
H
H
Ph
TMS
H
TMS
Ph
H
H
H
H
H
Ph
TMS
H
H
H
H
TMS
R
Ph
TMS
Ph
Scheme 11.

A.E. Sheshenev et al. / Tetrahedron 65 (2009) 10552–10564
10557
H
TMS
H
H
H
H
H
H
H
TMS
H
TMS
H
H
TMS
exo-
TMS
Ph
TMS
H
TMS
TMS
Ph
S
H
TMS
H
H
Ph
H
Ph
Ph
Ph
22
Ph
Ph
ene
Ph
H
TMS
TMS
Ph
TMS
TMS
TMS
H
H
H
H
H
H
H
H
H
H
TMS
TMS
endo-
TMS
Ph
H
H
R
H
TMS
H
H
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Scheme 12.
CH2NH3
Ph
O2C
1R
Br
Br
Ph
Br
CO2H
1/4 eq. of amine*
MeOH
3R 1. 5% HCl-Et2O
2. benzene-hexane, 1:2.5
Br
CO2H
Ph
Br
Br
26
CHMe2
(Salt)
(1R, 3R)-26, 31%,
89% ee, [a]D +86°**
* (+)-dehydroabietylamine
** c ~ 1.0 in CHCl3
27, 84%, 62% de
Ph
Br
Ph
benzene-hexane, 1:2
(1S, 3S)-26, 34%,
Br
91% ee, [a]D -88°**
HO2C
HO2C
Br
Br
(Mother liquid)
(-)-(1S, 3S)-26, ~10% ee
Scheme 13.
26 from benzene/hexane mixture; c) the acid (-)-26 (10% ee) re-
covered from mother liquid was enriched to 91% ee analogously by
precipitating of the parent racemate 26 from a benzene/hexane
solution.
The absolute configuration of optically active acid (þ)-26 [(1R,
3R)-] was established by its two step transformation to methyl ester
(-)-29 with known [(1R, 2R)-] absolute stereochemistry.16a The
enantiomeric excesses of chiral acids (þ)- and (-)-26 (89% and 91%
ee, respectively) were determined based on the 1H NMR spectros-
copy data of their diastereomeric amides with L-b-phenylalanine
methyl ester generated in situ from corresponding hydrochloride
salt and triethylamine (Scheme 14).
Optically active cyclopropene (S)-2 was generated starting from
acid (1S, 3S)-26 (91% ee) according to Scheme 15, which included
the preparation of tribromide (3R)-4 followed by reaction with
methyllithium and chlorotrimethylsilane.
Surprisingly, the dimer (þ)-7 was isolated in only low yield;
trimers 21 and 22 were identified by NMR spectroscopy in a com-
plex mixture with other undefined products. The reason for the
difference between the reactions of the racemic and optically active
cyclopropenes is the subject of further analysis and remains un-
known up to now. However, the presence of two trimers derived
from optically active monomer (S)-2 indicates that they are made
up of three identical monomer molecules, not of enantiomeric
molecules. Trapping of (þ)-7 with cyclopentadiene gave a 64% yield
of the adduct (þ)-23 of the corresponding enantiomerically
enriched cyclopropene possessing eight chiral centers (Scheme 15).
According to NMR data the structure of dimer (þ)-7 derived
from the ene-reaction of (S)-2 was that of one enantiomer of ra-
cemic 7 above, therefore the mechanisms of formation of (þ)-7
from (S)-2 and 7 from 2 were the same and included an endo-
transition state in the reaction between identical enantiomers of
cyclopropene 2 (Scheme 10). The regiochemistry of the major tri-
mer 21 was assigned based on an endo-transition state as in the
ene-dimerisation, on the basis of the above requirement that the
same enantiomer of the cyclopropene 2 must add to the dimer 7
(Scheme 11). On the other hand, the structure of the minor trimer
22 appears to require an exo-transition state (Scheme 12).
Ph
Br
Ph
Br
Ph
Br
Ph
Bn
1R
1R
1R
1R
4.
3.
2.
S
CO2Me
COX
CONH
CO2Me
CO2Me
Br
Br
Br
(+)-30 (78%),
89% de by 1H NMR
(+)-26, 89% ee
(+)-28 (99%)
(-)-29 (100%)
[known compound]
X = OH
1.
X = Cl
Ph
Br
Ph
Br
Bn
S
1S
1S
1, 4
(+)-31 (77%),
91% de by 1H NMR spectroscopy
Br
XOC
MeO2C
HNOC
Br
(-)-26, 91% ee
1. SOCl2, 20oC, 15 h; 2. MeOH, 20oC, 2.5 h; 3. Bu3SnH, C6H6, 55oC, 6 h;
4. L-β-phenylalanine methyl ester hydrochloride, NEt3, CH2Cl2, 0 to 20oC, 3 5
. h.
Scheme 14.

10558
A.E. Sheshenev et al. / Tetrahedron 65 (2009) 10552–10564
TMS
Ph
TMS
Ph
Br
Ph
Br
R
20oC
S
HgO/Br2
CH2Cl2
S
1. MeLi
Br
H
R
R
Br
Ph
2. TMSCl
HO2C
Br
S
H
Ph
H
TMS
S
H
(-)-4 (44%),
2R:2S = 6:1
(-)-26, 91% ee
(S)-2
(+)-7 (9%)
Cpd, PhH
20oC, 24 h
Ph
R
R
TMS
S
R
H
R
R
S
H
Ph
TMS
H
H
S
(+)-23 (64%)
Scheme 15.
TMS
TMS
D
D
TMS
Ph
Ph
Ph
H
-60oC to 20oC
D
MeOD
-60oC
D
+
Ph
Ph
TMS
D
H
Ph
TMS
Ph
Li
TMS
D
TMS
H
H
17
3
H
32 (52%)
33 (25%)
Scheme 16.
TMS
H
TMS
H
S
D
TMS
H
Ph
Ph
D
D
endo-
D
D
Ph
Ph
D
H
Ph
TMS
S
H
TMS
Ph
TMS
ene
H
32
H
TMS
H
D
TMS
S
Ph
D
Ph
endo-
TMS
D
Ph
TMS
Ph
Ph
D
D
D
D
Ph
TMS
TMS
Ph
H
D
H
H
Ph
33
H
H
H
ene
TMS
D
H
TMS
TMS
Ph
Scheme 17.
Attempts to trap the intermediate 17 with MeOD or D2O, how-
ever, did not produce the deuterated cyclopropene 3. Instead, the
dimer 32 and trimer 33 were observed (Scheme 16). Even under the
same conditions under which 2 had been observed directly by 1H
NMR spectroscopy (ꢀ40 ꢁC, CDCl3), no 3 could be observed, sug-
gesting that the ene-dimerisation of the 2-D compound proceeds
somewhat faster than that of the 2-H compound. It is worth also
noting that only one trimer was observed from 3, whereas two
were formed in 3:1 ratio from 2.
a single enantiomer, seven new chiral centers are generated by ene-
dimerisation/[4þ2] cycloaddition sequence. The introduction of
a deuterium at the 2-position of the cyclopropene leads to unusual
changes in the stability of the cyclopropene and the balance of
dimeric and trimeric products.
4. Experimental
4.1. General details
The structures of compounds 32, 33 were similar to non-deu-
terated analogs 7 and 21, respectively, and their formation appar-
ently included the same endo-steps during the ene-sequence. One
of the possible explanations of this unexpected reaction rate of 2-D-
derivative 3 compared to 2 might be that it results from deuterium
isotope effects. Thus, an inverse secondary isotope effect could be
responsible for this in the dimerisation, which converts two
pseudo-sp C–H(D) bonds into cyclopropane C–H(D) bonds.6b,8 Ob-
viously the formation of trimer 33 from 32 and 3 is more compli-
cated process including the transfer of a D-atom from ene to
enophile containing another deuterium at C-2 of the small ring
(Scheme 17).
Commercial reagents were used without further purification
unless stated. Diethyl ether and THF were distilled over sodium
wire. Petroleum was of boiling point 40–60 ꢁC. Benzohydrox-
iminoyl and p-nitrobenzohydroximinoyl chlorides were prepared
by NCS–DMF chlorination of the corresponding oximes.17 Reactions
requiring anhydrous conditions were performed using oven dried
glassware (250 ꢁC) that was cooled under either dry nitrogen or
argon; experiments were conducted under a positive atmosphere
of argon. Unless stated, organic solutions were dried over anhy-
drous magnesium sulfate and evaporated at 14 mm Hg; yields
quoted are for purified compounds and any ratios given are cal-
culated by comparing integrals in the 1H NMR spectrum or by GLC
data.
3. Conclusion
New compounds were homogenous by GLC or TLC. GLC was
conducted using a Carlo Erba HRGC 5300 F.I.D. on a capillary col-
umn (30 mꢂ0.32 mm id Phase, DB5 split ratio of 50:1) with ni-
trogen carrier gas. TLC was performed using Aldrich silica plates
The introduction of a 1-trimethylsilyl-substituent leads to ene-
dimerisation and trimerisation of 3-phenylcyclopropenes with
a high degree of regio- and stereochemical control. By starting with

A.E. Sheshenev et al. / Tetrahedron 65 (2009) 10552–10564
10559
coated with silica gel 60 (F254). Column chromatography was
conducted with Matrex Silica 60 (Fisher Scientific Int. Co.) and
Merck LiChroprep Si 60 under medium pressure. Melting points are
uncorrected. Unless stated, infrared spectra were obtained as so-
lutions in CHCl3 or as liquid films on a Perkin Elmer 1600 FTIR
spectrometer. Low resolution mass spectra were measured using
a Finnigan 8430 spectrometer using EI 70 eV unless stated. Accu-
rate mass measurements were carried out on a MicromassÔ GCT
spectrometer. Microanalyses were performed on a Carlo Erba
Model 1106 CHN analyzer. Optical rotation was measured using
IGP-01 polarimeter. NMR spectra were recorded in CDCl3, using
Bruker AC250 or A500 spectrometers at 250 MHz or 500 MHz (1H)
and 62.9 MHz or 125 MHz (13C). 13C spectra were broad-band
decoupled and in most cases corresponding DEPT spectra were also
recorded. All previously described compounds were characterized
by IR, 1H and 13C NMR spectroscopy and gave data identical to those
in the literature.
10 min at ꢀ60 ꢁC and 1 h at rt, cooled to ꢀ40 ꢁC and quenched with
water (2 mL). The organic layer was separated, the aqueous layer
was extracted with ether (2ꢂ7 mL). The combined organic layers
were washed with brine (5 mL), dried and evaporated. This gave an
orange oil (241 mg), which contained by 1H NMR monomer 2 (30%),
dimer 7 (20%) and cyclopropene 19 (10%). After 12 h at rt the neat
sample was columned on silica (pentane) to yield dimer 7 (98 mg,
0.26 mmol, 40%, Rf 0.52, Rt 14.84 min) (Found Mþ: 376.2035.
C24H3228Si2 requires: 376.2043) and cyclopropene 19 (19 mg,
0.07 mmol, 5%, Rf 0.57) as colorless oils. Compound 7 showed dH
:
ꢀ0.28 (9H, s, TMS-20), ꢀ0.01 (1H, dd, J¼7.3, 10.4 Hz, H-20), 0.36 (9H,
s, TMS-2), 1.45 (1H, ddd, J¼4.1, 4.7, 7.3 Hz, H-10), 1.96 (1H, d,
J¼4.1 Hz, H-1), 2.20 (1H, dd, J¼4.7, 10.4 Hz, H-30), 7.23–7.62 (10H, m,
Ph-3, Ph-30); dC: ꢀ0.9, ꢀ0.6, 14.4, 23.5, 25.9, 27.6, 116.8, 125.6, 127.8,
128.63, 128.65, 129.2, 129.4, 130.7, 136.9, 141.5; ymax: 3079 w, 3059
w, 3026 w, 2954 s, 2897 m, 1944 w, 1768 m, 1602 m, 1488 m, 1446
m, 1406 w, 1248 s, 1025 w, 930 m, 912 m, 840 s, 756 s, 691 s cmꢀ1
;
m/z (GC/MS), %: 378 (Mþ, 0.6), 377 (Mþ, 28Siþ29Si, 1.3), 376 (Mþ,
28Si2, 4), 375 (Mþ–1, 0.6), 319 (6), 304 (8), 303 (92), 302 (14), 288
(69), 287 (58), 273 (55), 271 (12), 230 (8), 229 (19), 228 (11), 211
(12), 187 (55), 159 (9), 145 (11), 135 (31), 128 (16), 74 (16), 73 (100),
59 (22). Compound 7 began to decompose after one night at ꢀ20 to
20 ꢁC under an Ar atmosphere, but it was stable for months as
a hexane solution at ꢀ20 ꢁC. The spectral data of cyclopropene 19
were identical to those obtained in Section 4.6.3.
4.2. Generation and trapping of 1-trimethylsilyl-3-
phenylcyclopropene (2) from tribromide 4
4.2.1. 9-Trimethylsilyl-1,8,10-triphenyl-12-oxatetracyclo[6.3.1.02,7.09,11]-
dodeca-2,4,6-triene (6). Methyllithium in ether (1.42 mL, 1.85 mmol,
1.30 M, 2.2 mol equiv) was added dropwise to tribromide 4 (300 mg,
0.84 mmol) in dry ether (10 mL) at ꢀ82 to ꢀ80 ꢁC over 3 min. The
solution was stirred for 5 min at ꢀ80 ꢁC and allowed to reach rt
(20 min). After a further 30 min at rt the mixture was cooled to
ꢀ60 ꢁC and chlorotrimethylsilane (0.15 mL, 128 mg, 1.18 mmol,
1.4 mol equiv) was added dropwise. The mixture was stirred for
10 min at ꢀ60 ꢁC and 30 min at rt, cooled to ꢀ50 ꢁC, quenched with
methanol (0.1 mL) and then 1,3-DPIBF (251 mg, 0.93 mmol,
1.1 mol equiv) in dry THF (4 mL) was added. The resulting solution
was allowed to reach rt (15 min), stirred for 1 h and quenched with
water (3 mL). The organic layer was separated, the aqueous layer was
extracted with ether (2ꢂ5 mL). The combined organic layers were
washed with brine (5 mL), dried and evaporated to give an orange oil
(450 mg), which was dissolved in dry THF (4 mL) and added to
a mixture of maleic anhydride (92 mg, 0.93 mmol) and Et3N (310 mg,
3.07 mmol) in dry ether–THF mixture (1:1, 5 mL). The mixture was
stirred for 35 min at rt, quenched with water (4 mL) and diluted with
ether (5 mL). The organic layer was separated, the aqueous layer was
extracted with ether (10 mL). The combined organic layers were
extracted with 8% aq NaOH (4ꢂ10 mL), washed with brine (5 mL),
dried and evaporated. Chromatography of the residue (214 mg) on
silica (petrol–ether, 20:1, Rf 0.30) gave adduct 6 (115 mg, 0.25 mmol,
30%) as a white powder, mp 155–156 ꢁC (aq MeOH) (Found Mþ:
458.2049. C32H30O28Si requires: 458.2066), which showed dH: ꢀ0.53
(9H, s, TMS), 2.62 (1H, d, J¼3.8 Hz, H-11), 3.77 (1H, d, J¼3.8 Hz, H-10),
7.15–7.91 (19H, m, Ar); dC: 0.5, 29.9, 35.6, 37.5, 88.7, 94.3, 119.6, 122.0,
125.2, 126.1, 126.5, 128.2, 128.3, 128.44, 128.46, 129.0, 129.8, 136.1,
136.4, 138.9, 148.8, 151.3; ymax (CHCl3): 3061 m, 3029 m, 2952 m, 2894
w, 1952 w, 1811 w, 1604 m, 1497 s, 1454 s, 1339 w, 1298 s, 1250 s, 1217
m, 1110 w, 1075 w, 1050 w, 1024 m, 982 s, 871 m, 837 s, 750 s, 698 s
cmꢀ1; m/z, %: 460 (Mþ, 30Si, 0.7), 459 (Mþ, 29Si, 2), 458 (Mþ, 28Si, 4.5),
386 (6), 385 (21), 353 (12), 352 (54), 339 (5), 338 (19), 337 (100), 322
(11), 321 (48), 291 (17), 276 (16), 263 (4), 215 (6), 202 (6), 160 (6), 107
(2), 106 (12), 105 (19), 77 (19), 73 (21), 59 (12).
4.3. Synthesis of individual stereoisomers of dibromides cis-
11 and trans-11
4.3.1. 1-Phenyl-2-(trimethylsilyl)ethyne (9). n-BuLi in hexane
(35.4 mL, 53.8 mmol, 1.52 M, 1.1 mol equiv) was added dropwise to
a freshly distilled phenylacetylene 8 (5.00 g, 49.0 mmol) in dry THF
(50 mL) at ꢀ78 to ꢀ65 ꢁC over 10 min. The mixture was stirred for
30 min at ꢀ78 ꢁC and then chlorotrimethylsilane (7.5 mL, 6.4 g,
58.8 mmol, 1.2 mol equiv) was added dropwise at ꢀ78 to ꢀ65 ꢁC
over 10 min. After a further 30 min at ꢀ78 ꢁC and 1 h at rt the so-
lution was cooled to 0 ꢁC and quenched with satd aq NH4Cl (20 mL).
The organic layer was separated, the aqueous layer was extracted
with ether (2ꢂ30 mL). The combined organic phases were washed
with brine (20 mL), dried and evaporated. Distillation afforded
acetylene 918 (7.68 g, 44.1 mmol, 90%) as a colorless oil, bp 79–80 ꢁC
at 2 mm Hg, which showed dH: 0.33 (9H, s, TMS), 7.35 (3H, m, Ph),
7.53 (2H, m, Ph); dC: ꢀ0.03, 94.0, 105.1, 123.1, 128.2, 128.4, 131.9;
ymax: 3080 m, 3057 m, 3032 m, 2958 s, 2898 s, 2488 w, 2158 s, 1948
w, 1893 w, 1804 w, 1753 w, 1598 s, 1573 m, 1488 s, 1444 s, 1408 m,
1343 w, 1281 m, 1249 s, 1219 s, 1176 w, 1156 w, 1069 s, 1027 s, 999 w,
931 m, 914 s, 862 s, 757 s, 690 s, 644 s cmꢀ1
.
4.3.2. cis-1-Phenyl-2-(trimethylsilyl)ethylene [(Z)-10]. DIBAL-H in
hexane (46 mL, 46 mmol, 1.0 M, 1.4 mol equiv) was added dropwise
to a solution of acetylene 9 (5.75 g, 33.0 mmol) in dry ether (30 mL)
over 10 min. The reaction mixture was stirred for 50 h at rt and
carefully quenched with ice-cold 10% aq H2SO4 (250 mL). The or-
ganic layer was separated, the aqueous layer was extracted with
ether (3ꢂ50 mL). The combined organic layers were washed with
brine (30 mL), dried and evaporated. Distillation of the residue gave
alkene (Z)-1012 (5.67 g, 32.2 mmol, 97%, Rt 2.82 min) as a colorless
oil, bp 69–70 ꢁC at 2 mm Hg, which showed dH: 0.15 (9H, s, TMS),
5.91 (1H, d, J¼15.1 Hz, ]CH), 7.32–7.39 (5H, m, Ph), 7.44 (1H, d,
4.2.2. 3,30-Diphenyl-2,20-bis-trimethylsilylbicyclopropyl-2-ene
(7). Methyllithium in ether (2.05 mL, 2.87 mmol, 1.40 M,
2.2 mol equiv) was added dropwise to tribromide 4 (464 mg,
1.30 mmol) in dry ether (15 mL) at ꢀ82 to ꢀ80 ꢁC over 4 min. The
solution was stirred for 5 min at ꢀ80 ꢁC and allowed to reach rt
(20 min). After a further 30 min at rt the mixture was cooled to
ꢀ60 ꢁC and chlorotrimethylsilane (0.22 mL, 184 mg, 1.69 mmol,
1.3 mol equiv) was added dropwise. The mixture was stirred for
J¼15.1 Hz, ]CH); dC: 0.2, 127.3, 127.9, 128.1, 132.8, 140.1, 146.6; ymax
3058 w, 3023 w, 2957 s, 2897 w, 1592 m, 1571 m, 1492 m, 1444 w,
1247 s, 1072 w, 1027 w, 840 s, 773 m, 761 m, 702s cmꢀ1
:
.
4.3.3. trans-1-Phenyl-2-(trimethylsilyl)ethylene [(E)-10]. DIBAL-H in
hexane (26.5 mL, 26.5 mmol, 1.0 M, 1.15 mol equiv) was added
dropwise to a solution of acetylene 9 (4.0 g, 23.0 mmol) in dry

10560
A.E. Sheshenev et al. / Tetrahedron 65 (2009) 10552–10564
pentane (5 mL) over 5 min. The reaction mixture was stirred for 21 h
at rt and carefully quenched with ice-cold 5% aq H2SO4 (100 mL). The
organic layer was separated, the aqueous layer was extracted with
ether (2ꢂ50 mL). The combined organic layers were washed with
brine (30 mL), dried and evaporated. Distillation of the residue gave
alkene (E)-1012 (3.69 g, 20.9 mmol, 91%) as a colorless oil, bp 85–
86 ꢁC at 2 mm Hg, which showed dH: 0.23 (9H, s, TMS), 6.53 (1H, d,
J¼19.2 Hz, ]CH), 6.92 (1H, d, J¼19.2 Hz, ]CH), 7.29–7.51 (5H, m,
Ph); dC: ꢀ1.2, 126.4, 127.9, 128.5, 129.5, 138.4, 143.6; ymax: 3101 w,
3077 m, 3059 m, 3023 m, 2988 m, 2955 s, 2896 m, 1940 w, 1874 w,
1801 w, 1605 s, 1574 s, 1493 s, 1447 s, 1332 w, 1247 s, 1214 m, 1196 m,
dropwise to dibromide cis-11 (300 mg, 0.86 mmol) in dry ether
(10 mL) at ꢀ92 to ꢀ90 ꢁC over 2 min. The mixture was stirred for
30 min at ꢀ90 ꢁC, allowed to reach ꢀ50 ꢁC (20 min) and carefully
quenched with water (2 mL). The organic layer was separated, the
aqueous layer was extracted with ether (5 mL). The combined or-
ganic layers were washed with brine (3 mL), dried and evaporated
to give allene 1219 (157 mg, 0.83 mmol, 97%, Rt 7.87 min) as a col-
orless oil, which showed dH: 0.22 (9H, s, TMS), 5.46 (1H, d,
J¼6.7 Hz,¼CH), 5.90 (1H, d, J¼6.7 Hz,¼CH), 7.15–7.36 (5H, m, Ph);
dC: ꢀ0.8, 87.0, 87.9, 125.9, 128.6, 135.1, 210.2; ymax: 3061 m, 3028 s,
2956 s, 2896 s, 1923 s, 1597 s, 1495 s, 1455 s, 1408 m, 1375 m, 1248 s,
1181 s, 1078 m, 1027 m, 907 s, 842 s, 768 s, 697 s, 631 s cmꢀ1; m/z
(GC/MS), %: 190 (Mþ, 30Si, 0.8), 189 (Mþ, 29Si, 2.9), 188 (Mþ, 28Si,
14.4), 173 (3), 145 (8), 115 (9), 89 (5), 75 (5), 74 (10), 73 (100); Rf 0.57
(pentane). The presence of w1% of dimer 7 in 12 was determined by
GC/MS.
1070 w, 1028 w, 988 s, 869 s, 756 s, 723 s, 690 s cmꢀ1
.
4.3.4. cis-1,1-Dibromo-2-trimethylsilyl-3-phenylcyclopropane (cis-
11). Alkene (Z)-10 (4.18 g, 23.7 mmol) was added to a mixture of
bromoform (4.2 mL, 12.0 g, 47.4 mmol, 2 mol equiv), dichloro-
methane (10 mL) and n-hexadecyltrimethylammonium bromide
(444 mg, 1.19 mmol, 5 mol %). The mixture was stirred vigorously
and sodium hydroxide (9.5 g, 237 mmol, 10 mol equiv) in water
(10 mL) was added over 5 min at below 31 ꢁC. After 17 h at rt water
(40 mL) was added and the mixture was extracted with dichloro-
methane (4ꢂ40 mL). The combined organic layers were washed
with water (30 mL) and solvent was removed. The residue was
dissolved in petrol–ether mixture (1:1, 200 mL) and filtered
through Celite. Removal of the solvent and unreacted bromoform at
30–40 ꢁC and 0.5 mm Hg gave a brown oil (9.46 g), which was
columned on silica (petrol, Rf 0.45, Rt 7.03 min) to yield dibromide
cis-11 (7.40 g, 21.2 mmol, 90%) as a colorless oil (Found Mþ:
4.4.2. The same reaction at rt, 1-trimethylsilyl-3-phenyl-3-methyl-
propyne-1 (13). Methyllithium in ether (0.72 mL, 1.0 mmol,
1.40 M, 1.15 mol equiv) was added dropwise to dibromide cis-11
(300 mg, 0.86 mmol) in dry ether (10 mL) at rt over 3 min. The
mixture was stirred for 1 h at rt and carefully quenched with
water (2 mL). The organic layer was separated, the aqueous layer
was extracted with ether (5 mL). The combined organic layers
were washed with brine (3 mL), dried and evaporated. This gave
an yellowish oil (159 mg), which contained compounds 12 (31%),
13 (56%) and dimer 7 (12%). Part of the residue (124 mg) was
columned on silica (pentane) to give allene 12 (38 mg, 23%, Rf
0.57) and a mixture of acetylene 1320 and dimer 7 (34 mg, 17%,
ratio 13/7¼4/1 by 1H NMR, Rf 0.44) as colorless oils. Acetylene 13
showed dH: 0.23 (9H, s, TMS), 1.53 (3H, d, J¼6.9 Hz, Me), 3.83 (1H,
q, J¼6.9 Hz, CHMe), 7.24–7.62 (5H, m, Ph); dC: 0.2, 24.6, 32.8, 86.2,
109.5, 126.6, 126.9, 128.5, 143.0; ymax: 3084 w, 3062 w, 3028 m,
2958 s, 2897 m, 2166 s, 1601 m, 1494 s, 1450 s, 1407 w, 1296 w,
1249 s, 1098 m, 1007 m, 917 s, 844 s, 759 s, 735 s, 698 s cmꢀ1; m/z
(GC/MS), %: 204 (Mþ, 30Si, 1), 203 (Mþ, 29Si, 3.3), 202 (Mþ, 28Si,
19), 189 (4), 188 (15), 187 (80), 161 (2), 160 (6), 159 (34), 147 (2),
146 (3), 145 (22), 128 (11), 115 (6), 86 (21), 83 (30), 73 (100), 59
(31), 53 (9); Rt 7.58 min.
347.9335. C12H1630Si79Br2 requires: 347.9356), which showed dH
:
0.13 (9H, s, TMS), 1.48 (1H, d, J¼13.2 Hz, CHTMS), 3.24 (1H, d,
J¼13.2 Hz, CHPh), 7.28–7.46 (5H, m, Ph); dC: ꢀ0.06, 30.4, 32.3, 38.9,
127.3, 127.9, 130.2, 135.8; ymax: 3085 m, 3058 m, 3026 m, 2955 s,
2897 s,1939 w, 1879 w,1804 w, 1602 m,1496 s,1445 s, 1409 m,1364
m, 1311 w, 1253 s, 1168 w, 1145 m, 1076 w, 1062 m, 1030 s, 1019 s,
965 s, 914 w, 842 s, 803 s, 766 s, 732 s, 697 s, 654 s cmꢀ1; m/z, %: 352
(Mþ, 81Brþ81Brþ30Si, 0.12), 350 (Mþ, 0.04), 348 (Mþ, 0.04), 346 (Mþ,
79Brþ79Brþ28Si, 0.14), 273 (1),188 (20),173 (10),145 (9),115 (64), 86
(11), 84 (18), 73 (100).
4.3.5. trans-1,1-Dibromo-2-trimethylsilyl-3-phenylcyclopropane
(trans-11). Dibromide trans-11 was prepared in a similar way to the
previous experiment from alkene (E)-10 (3.0 g, 17.0 mmol), bro-
moform (3.0 mL, 8.59 g, 34.0 mmol, 2 mol equiv), n-hexadecyl-
trimethylammonium bromide (310 mg, 0.85 mmol, 5 mol %)
dissolved in dichloromethane (7 mL) and sodium hydroxide (6.8 g,
170 mmol, 10 mol equiv) in water (7 mL). After 15 h of vigorous
stirring at rt and standard work up the organic residue (7.01 g) was
columned on silica (petrol, Rf 0.34) to yield trans-11 (5.19 g,
14.9 mmol, 88%) as a greenish oil, wþhich crystallized in a white
crystal mass, mp 20–21 ꢁC (Found M : 347.9346. C12H1630Si79Br2
requires: 347.9356) and showed dH: 0.30 (9H, s, TMS), 1.36 (1H, d,
J¼10.7 Hz, CHTMS), 2.85 (1H, d, J¼10.7 Hz, CHPh), 7.29–7.42 (5H, m,
Ph); dC: ꢀ1.33, 27.4, 34.5, 39.1, 127.5, 128.2, 128.7, 137.1; ymax: 3086
w, 3060 m, 3029 m, 2953 s, 2896 m, 1943 w, 1872 w, 1798 w, 1602
m, 1496 s, 1448 s, 1409 w, 1368 m, 1312 w, 1250 s, 1207 m, 1176 w,
1105 w, 1080 m, 1054 m, 1034 s, 1024 s, 1002 w, 954 s, 911 w, 846 s,
814 m, 785 m, 755 s, 717 m, 695 s, 620 m cmꢀ1; m/z, %: 350 (Mþ,
0.004), 348 (Mþ, 0.003), 346 (Mþ, 79Brþ79Brþ28Si, 0.001), 270 (1),
269 (4), 268 (3), 267 (4), 266 (2), 196 (12), 194 (13), 188 (46), 173
(20), 145 (27), 139 (30), 137 (29), 115 (100), 89 (12), 73 (96).
4.4.3. The same reaction in THF at ꢀ90 ꢁC. Methyllithium in ether
(0.72 mL, 1.0 mmol, 1.40 M, 1.15 mol equiv) was added dropwise to
dibromide cis-11 (300 mg, 0.86 mmol) in dry THF (10 mL) at
ꢀ90 ꢁC over 2 min. The mixture was stirred for 20 min at ꢀ90 ꢁC,
allowed to reach ꢀ50 ꢁC (20 min) and quenched with water
(2 mL). The organic layer was separated, the aqueous layer was
extracted with ether (5 mL). The combined organics were washed
with brine (3 mL), dried and evaporated. It gave yellowish oil
(160 mg), which contained allene 12 (38%), acetylene 13 (49%) and
dimer 7 (13%).
4.5. Generation and trapping of 1-trimethylsilyl-3-
phenylcyclopropene (2) from dibromide trans-11
4.5.1. 1-Trimethylsilyl-3-phenylcyclopropene (2). Methyllithium in
ether (0.72 mL, 1.0 mmol, 1.40 M, 1.15 mol equiv) was added drop-
wise to dibromide trans-11 (300 mg, 0.86 mmol) in dry ether
(10 mL) at ꢀ92 to ꢀ90 ꢁC over 3 min. The mixture was stirred for
15 min at ꢀ90 ꢁC, allowed to reach ꢀ50 ꢁC (10 min) and carefully
quenched with water (1 mL). The organic layer was quickly dec-
anted and concentrated at ꢀ20 ꢁC. It gave a colorless oil (161 mg),
1
4.4. Reactions of cis-1,1-dibromo-2-trimethylsilyl-3-
phenylcyclopropane (cis-11) with MeLi
which contained by H NMR at ꢀ40 ꢁC 50% of monomer 2, 41% of
dimer 7, 5% of trimer 21 and 4% of allene 12. Cyclopropene 2
showed at ꢀ40 ꢁC (11% solution in CDCl3) dH: 0.28 (9H, s, TMS), 2.61
(1H, s, H-3), 7.17–7.56 (6H, m, H-2, Ph); dC: ꢀ1.3, 20.2, 116.7, 119.6,
124.7, 125.0, 127.7, 148.4; ymax: 3079 w, 3059 w, 3025 m, 2955 s,
4.4.1. 1-Trimethylsilyl-3-phenylpropadiene-1,2 (12). Methyllithium
in ether (0.72 mL, 1.0 mmol, 1.40 M, 1.15 mol equiv) was added

A.E. Sheshenev et al. / Tetrahedron 65 (2009) 10552–10564
10561
2897 m, 1693 s, 1602 m, 1492 m, 1446 s, 1407 w, 1248 s, 1070 w, 841
s, 756 s, 698 s cmꢀ1. The optimized syntheses of allene 12 and ene-
products 7 and 21 see in Sections 4.4.1 and 4.7.1 correspondingly.
showed dH: 0.20 (18H, s, 2ꢂTMS), 2.42 (1H, s, H-3), 7.00–7.24
(5H, m, Ph); dC: ꢀ1.0, 22.0, 124.1, 124.9, 127.5, 130.8, 149.6; ymax
:
3078 w, 3060 w, 3024 m, 2957 s, 2897 m, 1940 w, 1879 w, 1725 s,
1597 s, 1492 s, 1451 m, 1406 w, 1250 s, 1212 w, 1078 w, 928 m, 902
m, 840 s, 757 s, 698 s cmꢀ1; m/z, %: 264 (Mþ, 30Siþ30Si, 0.2), 261
(Mþ, 28Siþ29Si, 0.2), 260 (Mþ, 28Siþ28Si, 0.8), 230 (2), 229 (5), 207
(8), 172 (5), 159 (5), 135 (5), 105 (8), 77 (17), 75 (30), 73 (100); Rf 0.57
(pentane).
4.5.2. 2-Trimethylsilyl-3-anti-phenyltricyclo[3.2.1.02,4]octene-6
(14). Methyllithium in ether (1.0 mL, 1.03 mmol, 0.97 M,
1.2 mol equiv) was added dropwise to dibromide trans-11 (300 mg,
0.86 mmol) in dry ether (10 mL) at ꢀ92 to ꢀ90 ꢁC over 2 min. The
mixture was stirred for 15 min at ꢀ90 ꢁC, allowed to reach ꢀ50 ꢁC
(20 min), carefully quenched with methanol (0.15 mL), and then
freshly distilled cyclopentadiene (0.36 mL, 284 mg, 4.3 mmol,
5 mol equiv) was added dropwise. The resulting solution was stir-
red for 2 h at rt and quenched with water (2 mL). The organic layer
was separated, the aqueous layer was extracted with ether (3 mL).
The combined organic phases were washed with water (3 mL),
dried and evaporated. Chromatography of the residue (260 mg) on
silica (petrol, Rf 0.57) afforded adduct 14 (202 mg, 0.79 mmol, 92%)
as a colorless oil (Found: C 80.05, H 8.91, Si 11.48%. C17H22Si re-
quires: C 80.25, H 8.72, Si 11.03%), which showed dH: ꢀ0.25 (9H, s,
TMS), 1.56 (2H, s, 2ꢂH-bridge), 1.77 (1H, d, J¼3.2 Hz, H-3), 2.04 (1H,
t, J¼3.8 Hz, H-4), 2.88 (1H, s, H-1), 2.95 (1H, s, H-5), 5.78 (1H, m,
]CH), 5.88 (1H, m, ]CH), 7.07–7.22 (5H, m, Ph); dC: ꢀ0.8,16.1, 22.6,
4.6.4. 1-Trimethylsilyl-3-phenylcyclopropene-2-carboxylicacid(20). Dry
gaseous CO2 was passed through the stirred ethereal solution of 17
for 20 min at ꢀ60 ꢁC and 20 min during for which the reaction
mixture was allowed to reach 5 ꢁC. Then the solution was cooled to
ꢀ40 ꢁC and quenched with water (4 mL). The organic layer was
separated, the aqueous layer was extracted with ether (5 mL),
acidified with cold 1 M aq HCl, and the product was extracted with
ether (2ꢂ10 mL). The combined organic layers were washed with
brine (5 mL), dried and evaporated to give acid 20 (113 mþg,
0.48 mmol, 57%) as a white powder, mp 75–77 ꢁC (Found M :
232.0927. C13H16O228Si requires: 232.0920), which showed dH: 0.26
(9H, s, TMS), 3.07 (1H, s, H-3), 7.09–7.31 (5H, m, Ph), 11.77 (1H, br s,
CO2H); dC: ꢀ1.6, 27.1, 123.4, 125.6, 125.9, 128.1, 138.8, 144.1, 167.1;
ymax (CHCl3): 3500–2350 br s, 3061 s, 3028 s, 2960 s, 2900 s,1945 w,
1873 w, 1784 s, 1681 s, 1604 s, 1493 s, 1453 m, 1405 s, 1252 s, 1217 s,
1138 s, 1074 w, 1014 m, 951 m, 907 m, 848 s, 761 s, 698 s cmꢀ1; m/z,
%: 234 (Mþ, 30Si, 0.08), 233 (Mþ, 29Si, 0.2), 232 (Mþ, 28Si, 1.3), 231
(1), 217 (1.5), 216 (1), 202 (6), 188 (21), 187 (86), 173 (62), 172 (83),
159 (19), 145 (26), 142 (17), 130 (6), 128 (9), 115 (12), 114 (43), 105
(19), 102 (10), 77 (17), 75 (100), 73 (84).
38.1, 42.9, 47.2, 61.9, 125.7, 127.7, 129.4, 130.7, 131.3, 140.4; ymax
:
3135 w, 3090 w, 3065 m, 3035 m, 2975 s, 2940 s, 2880 s, 1600 m,
1500 m, 1452 m, 1406 w, 1382 w, 1331 m, 1255 s, 1195 w, 1170 m,
1120 w, 1091 m, 1080 w, 1030 m, 993 m, 962 m, 943 w, 915 m, 890 s,
880 s, 860 s, 842 s, 800 w, 758 s, 748 s, 710 s.
4.6. Synthesis of 1-trimethylsilyl-2-R-3-phenylcyclopropenes
18–20
4.7. Ene-di- and trimerisation of 1-trimethylsilyl-3-
4.6.1. Preparation of an ethereal solution 1-trimethylsilyl-2-lithio-3-
phenylcyclopropene (17). Methyllithium in ether (1.32 mL,
1.85 mmol, 1.40 M, 2.15 mol equiv) was added dropwise to trans-11
(300 mg, 0.86 mmol) in dry ether (10 mL) at ꢀ92 to ꢀ90 ꢁC over
3 min. The mixture was stirred for 20 min at ꢀ90 ꢁC and allowed to
reach rt. After a further 30 min at rt the prepared solution of 17 was
cooled to ꢀ60 ꢁC and used directly for reactions with electrophiles
(MeI, TMSCl, CO2, and ClCO2Me).
phenylcyclopropene (2) and its 2-
D-derivative 3
4.7.1. 3,30-Diphenyl-2,20-bis-trimethylsilylbicyclopropyl-2-ene
(7),
2,10,200-triphenyl-3,30,300-tris-trimethylsilyl[1,10;20,100]tercyclopropan-20-
ene (21) and 3,30,300-triphenyl-2,10,200-tris-trimethylsilyl[1,10;20,100]-
tercyclopropan-2-ene (22). Methyllithium in ether (2.9 mL,
3.2 mmol,1.12 M,1.15 mol equiv) was added dropwise to dibromide
trans-11 (970 mg, 2.79 mmol) in dry ether (15 mL) at ꢀ92 to ꢀ90 ꢁC
over 3 min. The mixture was stirred for 15 min at ꢀ90 ꢁC, allowed
to reach ꢀ50 ꢁC (20 min) and carefully quenched with water
(3 mL). The organic layer was separated, the aqueous layer was
extracted with ether (7 mL). The combined organic layers were
washed with brine (5 mL), dried, and evaporated to give brown oil
(534 mg), which was left for overnight (12–15 h) at rt under Ar
atmosphere. This material was then columned on silica (hexane,
ratio 21/22¼3:1 by 1H NMR before the column) to give allene 12
(19 mg, 0.1 mmol, 4%, Rf 0.57), dimer 7 (257 mg, 0.67 mmol, 49%, Rf
0.52) as colorless oils; and trimer 21 (163 mg, 0.29 mmol, 31%, Rf
0.38) (Found Mþ: 565.3054. C36H4828Si229Si requires: 565.3060) as
viscous colorless oil. The major trimer 21 showed dH: ꢀ0.37 (9H, s,
TMS-3), ꢀ0.16 (1H, dd, J¼6.9, 10.4 Hz, H-3), ꢀ0.14 (9H, s, TMS-300),
0.14 (9H, s, TMS-30), 0.78 (1H, dd, J¼6.6, 10.7 Hz, H-300), 1.80 (1H, dd,
J¼5.1, 6.9 Hz, H-1), 2.12 (1H, dd, J¼5.1, 10.4 Hz, H-2), 2.59 (1H, dd,
J¼4.7, 6.6 Hz, H-100), 2.79 (1H, dd, J¼4.7, 10.7 Hz, H-200), 7.12–7.59
(15H, m, Ph-2, Ph-10, Ph-200); dC: ꢀ0.96, ꢀ0.72, ꢀ0.65, 13.1, 17.78,
17.84, 23.2, 26.1, 28.8, 31.6, 110.6, 123.3, 125.6, 126.5, 126.8, 127.8,
128.1, 128.2, 128.6, 129.3, 131.0, 131.1, 139.2, 141.6; ymax: 3060 w,
3027 w, 2953 s, 2896 w, 1940 w, 1840 m, 1601 m, 1496 m, 1445 m,
1402 w, 1247 s, 1155 w, 1009 w, 980 m, 909 s, 839 s, 756 s, 735 s, 699
s cmꢀ1; m/z, %: 567 (Mþ, 0.08), 566 (Mþ, 28Siþ29Si2, 0.3), 565 (Mþ,
28Si2þ29Si, 0.8), 564 (Mþ, 28Si3, 2), 492 (12), 491 (38), 418 (5), 417
(14), 403 (20), 401 (13), 375 (6), 344 (23), 313 (12), 287 (33), 286
(20), 270 (9), 265 (6), 159 (8), 135 (30), 91 (4), 75 (71), 73 (100), 59
(11). The minor trimer 22 (10% yield by 1H NMR of the crude re-
action mixture, Rf 0.35) was inseparable from 21 therefore was
4.6.2. 1-Trimethylsilyl-2-methyl-3-phenylcyclopropene (18). Methyl
iodide (0.5 mL, 1.14 g, 8.0 mmol, 9.3 mol equiv) was added drop-
wise to an ethereal solution of 17 at ꢀ60 ꢁC. The mixture was
allowed to reach rt, stirred for 5 h, cooled to 0 ꢁC and quenched
with water (2 mL). The organic layer was separated, the aqueous
layer was extracted with ether (2ꢂ5 mL). The combined organic
layers were washed with brine (3 mL), dried and evaporated to
afford cyclopropene 18 (169 mg, 0.84 mmol, 97%) as a colorless oil
(Found Mþ: 202.1178. C13H1828Si requires: 202.1178), which showed
dH: 0.19 (9H, s, TMS), 2.23 (3H, s, Me), 2.48 (1H, s, H-3), 7.04–7.29
(5H, m, Ph); dC: ꢀ0.9, 11.5, 24.5, 108.3, 124.4, 125.1, 127.8, 128.6,
148.3; ymax: 3060 m, 3024 s, 2956 s, 1807 s, 1597 m, 1492 s, 1451 m,
1249 s, 1157 m, 1024 w, 999 w, 841 s, 758 s, 698 s cmꢀ1; m/z, %: 204
(Mþ, 30Si, 3), 203 (Mþ, 29Si, 10), 202 (Mþ, 28Si, 100), 187 (49), 185
(29), 169 (9), 159 (46), 143 (10), 129 (8), 128 (47), 127 (15), 114 (10);
Rf 0.50 (pentane).
4.6.3. 1,2-Ditrimethylsilyl-3-phenylcyclopropene
(19). Chlorotri-
methylsilane (0.13 mL, 112 mg, 1.03 mmol, 1.2 mol equiv) was
added dropwise to an ethereal solution of 17 at ꢀ60 ꢁC. The mixture
was allowed to reach rt, stirred for 2 h, cooled to 0 ꢁC and quenched
with water (2 mL). The organic layer was separated, the aqueous
layer was extracted with ether (2ꢂ5 mL). The combined organic
phases were washed with brine (3 mL), dried and evaporated to
provide cyclopropene 19 (202 mg, 0.78 mmol, 90%) as yellowish oil
(Found Mþ: 262.1394. C15H2428Si30Si requires: 262.1385), which

10562
A.E. Sheshenev et al. / Tetrahedron 65 (2009) 10552–10564
characterized only as a mixture with latter and showed dH: ꢀ0.19
(9H, s, TMS), 0.20 (9H, s, TMS), 0.30 (1H, dd, J¼6.9, 10.4 Hz, H-200),
0.37 (9H, s, TMS), 1.53 (1H, ddd, J¼4.4, 4.7, 6.9 Hz, H-100 1.59 (1H, dd,
J¼4.4, 8.8 Hz, H-20), 1.79 (1H, d, J¼8.8 Hz, H-30), 2.28 (1H, dd, J¼4.7,
10.4 Hz, H-300), 2.48 (1H, s, H-1), 7.13–7.65 (15H, m, Ph-3, Ph-30, Ph-
300); dC: ꢀ0.28, ꢀ0.06, 0.83, 18.9, 19.4, 20.6, 26.9, 28.4, 29.6, 32.9,
115.2, 125.62, 125.75, 130.9, 136.5, 139.7, 140.4. The spectral data of
dimer 7 and allene 12 were identical to that obtained above in
Sections 4.2.2 and 4.4.1, respectively.
cmꢀ1): 3084 w, 3060 w, 3031 m, 2965 s, 2899 m, 1602 m, 1497 m,
1450 m, 1443 m, 1324 m,1259 m,1249 s,1150 w, 1027 w, 999 m, 912
m, 890 s, 838 s.
4.7.4. 4,5-Diphenyl-exo-6-(2-phenyl-3-trimethylsilylcyclopropyl)-1-
trimethylsilyl-2-oxa-3-azabicyclo[3.1.0]hexene-3 (24). A solution of
Et3N (21 mg, 0.21 mmol, 1.0 mol equiv) in dry ether (0.5 mL) was
added dropwise to a stirred mixture of dimer 7 (80 mg, 0.21 mmol)
and benzohydroximinoyl chloride (33 mg, 0.21 mmol, 1.0 mol e-
quiv) in dry ether (2 mL) at ꢀ15 ꢁC over 1 min. The mixture was
stirred for 30 min at ꢀ15 ꢁC and 18 h at rt, then quenched with 1 M
HCl (1 mL), diluted with water (2 mL) and ether (5 mL). The organic
layer was separated and the aqueous layer was extracted with ether
(5 mL). The combined organics were washed with water (5 mL),
dried and evaporated. Chromatography of the residue (110 mg) on
silica (hexane–ether, 10:1) gave adduct 24 (53 mg, 0.11 mmol, 50%,
Rf 0.29) and unreacted dimer 7 (15 mg, 0.04 mmol, 19%, Rf 0.82) as
colorless oils. Compound 24 (Found MþNaþ: 518.2306.
C31H37NNaOSi2 requires: 518.2306) showed dH: ꢀ0.20 (9H, s, TMS-
6(3)), 0.18 (9H, s, TMS-1), 0.43 (1H, dd, J¼10.6, 6.9 Hz, H-6(3)), 0.89
(1H, d, J¼10.0 Hz, H-6), 1.52 (1H, ddd, J¼10.0, 6.9, 4.7 Hz, H-6(1)),
2.54 (1H, dd, J¼10.6, 4.7 Hz, H-6(2)), 7.17–7.22 (8H, m, Ph), 7.25–
7.33 (3H, m, Ph), 7.52–7.54 (4H, m, Ph); dC: ꢀ1.5, ꢀ0.3, 18.3, 19.0,
29.3, 37.2, 50.9, 75.9, 126.2, 127.7, 128.1, 128.2, 128.5, 128.7, 131.0,
131.5, 134.5, 139.4, 163.0; ymax (CHCl3, cmꢀ1): 3087 w, 3063 w, 3032
m, 3010 m, 2958 m, 2901 m, 1954 w, 1888 w, 1810 w, 1602 m, 1591
m, 1579 m, 1549 w, 1498 s, 1445 s, 1422 m, 1353 m, 1323 m, 1310 m,
1260 s, 1251 s, 1180 w, 1094 w, 1025 m, 975 m, 912 m, 845 s.
4.7.2. 1,10-Dideutero-3,30-diphenyl-2,20-bis-trimethylsilylbicyclo-
propyl-2-ene (32) and 1,2,100-trideutero-3,10,300-triphenyl-2,30,200-tris-
trimethylsilyl[1,10;20,100]tercyclopropan-20-ene (33). MeOD (0.15 mL)
was added dropwise to an ethereal solution of 17 (Section 4.6.1) at
ꢀ60 ꢁC, allowed to reach rt and diluted with water (1 mL). The
organic layer was separated, the aqueous layer was extracted with
ether (5 mL). The combined organic layers were washed with
brine (3 mL), dried and evaporated. Chromatography of the part of
residue (101 mg from 161 mg) on silica (pentane) gave pure dimer
32 (53 mg, 0.14 mmol, 52%, Rf 0.39) (Found Mþ: 381.2141.
C24H30D229Si30Si requires: 381.2148) and trimer 33 (26 mg,
0.046 mmol, 25%, Rf 0.26) (Found Mþ: 567.3243. C36H45D328Si3
requires: 567.3252) as viscous colorless oils. Compound 32
showed dH: ꢀ0.26 (9H, s, TMS-20), ꢀ0.01 (1H, d, J¼10.4 Hz, H-20),
0.37 (9H, s, TMS-2), 2.21 (1H, d, J¼10.4 Hz, H-30), 7.18–7.64 (10H,
m, Ph-3, Ph-30); dC: ꢀ0.8, ꢀ0.6, 14.3, 22.9 (t, J¼25.7 Hz), 25.4 (t,
J¼23.5 Hz), 27.5, 116.6, 125.6, 127.8, 128.63, 128.65, 129.2, 129.4,
130.7, 136.8, 141.5; ymax: 3078 w, 3059 w, 3026 w, 2954 s, 2896 m,
2166 w, 1944 w, 1766 s, 1602 s, 1488 m, 1446 m, 1406 w, 1248 s,
1098 w, 1028 w, 1000 w, 979 m, 916 m, 841 s, 755 s, 698 s cmꢀ1
;
4.7.5. 4-(p-Nitrophenyl)-5-phenyl-exo-6-(2-phenyl-3-trimethylsi-
lylcyclopropyl)-1-trimethylsilyl-2-oxa-3-azabicyclo[3.1.0]hexene-3
(25). Compound 25 was prepared in a similar method to the pre-
vious experiment from dimer 7 (70 mg, 0.19 mmol), p-nitro-
benzohydroximinoyl chloride (38 mg, 0.19 mmol, 1.0 mol equiv) in
dry ether (2 mL) and Et3N (19 mg, 0.19 mmol, 1.0 mol equiv) in dry
ether (0.5 mL). After 30 min at ꢀ15 ꢁC and 40 h at rt subsequent
work up and chromatography of the residue (110 mg) on silica
(hexane–ether, 10:1) afforded adduct 25 (30 mg, 0.055 mmol, 30%,
Rf 0.26) and unreacted dimer 7 (23 mg, 0.06 mmol, 33%, Rf 0.82) as
viscous colorless oils. Compound 25 (Found MþNaþ: 563.1929.
C31H36N2NaO3Si2 requires: 563.2157) showed dH: ꢀ0.20 (9H, s,
TMS-6(3)), 0.18 (9H, s, TMS-1), 0.44 (1H, dd, J¼10.7, 6.9 Hz, H-6(3)),
0.89 (1H, d, J¼10.2 Hz, H-6), 1.50 (1H, ddd, J¼10.2, 6.9, 4.9 Hz, H-
6(1)), 2.53 (1H, dd, J¼10.7, 4.9 Hz, H-6(2)), 7.18–7.25 (6H, m, Ph),
7.34 (2H, t, J¼7.5 Hz, Ph), 7.50 (2H, d, J¼7.5 Hz, Ph), 7.65 (2H, d,
J¼8.7 Hz, p-NO2-Ph), 8.01 (2H, d, J¼8.7 Hz, p-NO2-Ph); dC: ꢀ1.5,
ꢀ0.3, 17.9, 19.0, 29.3, 36.7, 49.9, 77.7, 123.5, 126.3, 128.1, 128.2, 128.6,
128.8, 128.9, 131.4, 133.3, 135.0, 138.9, 148.1, 161.2; ymax (CHCl3,
cmꢀ1): 2959 m,1603 m,1521 s,1498 m,1348 s,1251 m, 914 w, 856 s,
846 s.
m/z, %: 381 (Mþ, 29Siþ30Si, 0.4), 380 (Mþ, 2), 379 (Mþ, 28Siþ29Si,
4.6), 378 (Mþ, 28Si2, 13), 377 (Mþ–1, 7), 376 (6), 318 (5), 306 (9),
305 (43), 304 (34), 303(33), 290 (34), 289 (53), 288 (44), 275 (27),
274 (19), 273 (34), 272 (15), 271 (12), 232 (49), 231 (90), 230 (100),
229 (88), 228 (50), 216 (30), 215 (22), 203 (20), 202 (17), 159 (35),
135 (36), 105 (19). Compound 33 showed dH: ꢀ0.37 (9H, s, TMS),
ꢀ0.14 (9H, s, TMS), 0.15 (9H, s, TMS), 0.77 (1H, d, J¼10.7 Hz, H-200),
2.13 (1H, s, H-3), 2.79 (1H, d, J¼10.7 Hz, H-300), 7.13–7.47 (15H, m,
Ph-3, Ph-10, Ph-300); dC: ꢀ0.97, ꢀ0.75, ꢀ0.68, 12.9, 17.6, 17.7, 22.9,
26.0, 28.6, 31.5, 110.5, 123.2, 125.5, 126.4, 126.8, 127.8, 128.06,
128.16, 128.6, 129.3, 131.0, 131.1, 139.2, 141.5; ymax: 3079 m, 3059
m, 3027 s, 2952 s, 2895 m, 2212 w, 1942 w, 1840 s, 1601 s, 1496 s,
1445 s, 1403 m, 1247 s, 1155 w, 1071 m, 1030 m, 1001 w, 984 m,
966 m, 894 m, 837 s, 756 s, 698 s cmꢀ1; m/z, %: 570 (Mþ, 29Si3,
0.06), 569 (Mþ, 28Siþ29Si2, 0.2), 568 (Mþ, 28Si2þ29Si, 0.5), 567 (Mþ,
28Si3, 1), 566 (Mþ–1, 0.8), 565 (0.3), 564 (0.06), 495 (3), 494 (12),
493 (8), 419 (3), 405 (5), 404 (7), 403 (3), 345 (2), 328 (2), 316 (3),
315 (3), 301 (2), 288 (3), 254 (1), 159 (2), 135 (23), 105 (10), 77 (20),
75 (77), 73 (100).
4.7.3. 2-Phenyl-anti-3-(2-phenyl-3-trimethylsilylcyclopropyl)-4-tri-
methylsilyltricyclo[3.2.1.02,4]oct-6-ene (23). The mixture of dimer 7
(70 mg, 0.19 mmol) and freshly distilled cyclopentadiene (40 mg,
0.56 mmol, 3.0 mol equiv) in benzene (2 mL) was stirred for 18 h at
rt and then evaporated to dryness. Chromatography of the residue
(90 mg) on silica (hexane, Rf 0.37) gave adduct 23 (72 mg,
0.16 mmol, 88%) as a white powder, mp 141–142 ꢁC (Found: C
78.80, H 8.70%. C29H38Si2 requires: C 78.66, H 8.65%), which showed
dH: ꢀ0.36 (9H, s, TMS-3(3)), 0.10 (1H, dd, J¼10.4, 7.0 Hz, H-3(3)),
0.19 (9H, s, TMS-4), 0.34 (1H, d, J¼9.5 Hz, H-3), 1.03 (1H, ddd, J¼9.5,
7.0, 4.4 Hz, H-3(1)), 1.48 (1H, d, J¼6.9 Hz, H-bridge), 1.99 (1H, d,
J¼6.9 Hz, H-bridge), 2.10 (1H, dd, J¼10.4, 4.4 Hz, H-3(2)), 2.60 (1H, s,
H-1), 2.94 (1H, s, H-5), 5.73 (1H, s, H-6), 5.95 (1H, s, H-7), 6.80 (2H,
m, Ph), 7.09 (3H, m, Ph), 7.19 (3H, m, Ph), 7.37 (2H, m, Ph); dC: ꢀ0.2,
0.6, 17.67, 17.73, 19.8, 29.9, 39.9, 45.1, 48.6, 54.0, 58.9, 125.5, 126.1,
127.4, 128.0, 129.3, 131.2, 131.3, 131.9, 140.1, 142.0; ymax (CHCl3,
4.8. Resolution of trans-2,2-dibromo-3-
phenylcyclopropanecarboxylic acid (26) with
(D)-dehydroabietylamine
4.8.1. Diastereomeric salt of acid (ꢃ)-26 and (þ)-dehydroabietyl-
amine (27). A hot solution of (þ)-dehydroabietylamine (5.72 g,
20.0 mmol, 0.25 mol equiv) in methanol (100 mL) was added to
a hot (60 ꢁC) solution of racemate 26 (25.67 g, 80.2 mmol) in
methanol (100 mL). The combined solution was stirred until pre-
cipitation of the salt 27 occurred (w10 min), then allowed to slowly
cool to rt and left overnight. The product was filtered off from
mother liquid, washed with cold methanol (2ꢂ20 mL) and dried on
air, giving salt 27 (10.17 g, 16.8 mmol, 84%) as a white powder, 62%
de, mp 199–201 ꢁC (dec) (Found: C 59.75, H 6.41, N 2.43%.
C30H39Br2NO2 requires: C 59.51, H 6.49, N 2.31%), which showed

A.E. Sheshenev et al. / Tetrahedron 65 (2009) 10552–10564
10563
ymax (Nujol): 3300–2000 br s, 1640 s, 1585 s, 1560 s, 1510 s, 1470 s,
1370 s, 1325 m, 1310 m, 1270 m, 1245 m, 1220 m, 1180 m, 1163 m,
1142 m, 1090 m, 1055 m, 1040 w, 1030 w, 1010 m, 980 m, 930 w, 890
Filtration of the residue (340 mg) on silica (petrol–ether, 5:1, Rf
0.56) afforded methyl ester (þ)-28 (311 mg, 0.93 mmol, 99%) as
25
a white powder, mp 94–96 ꢁC, [
a
]
þ90 (c 1.0, CHCl3) (Found: C
D
m, 870 m, 830 s, 790 m, 775 s, 720 s, 702 s cmꢀ1. It was not possible
39.88, H 2.95%. C11H10Br2O2 requires: C 39.56, H 3.02%), which
showed dH: 2.89 (1H, d, J¼8.5 Hz, H-1), 3.43 (1H, d, J¼8.5 Hz, H-3),
3.84 (3H, s, OMe), 7.24–7.39 (5H, m, Ph); dC: 28.6, 37.2, 40.8, 52.8,
128.1, 128.4, 128.6, 133.9, 167.6; ymax (CHCl3): 3090 w, 3065 m, 3033
s, 2955 s, 2855 w, 1741 s, 1605 m, 1585 w, 1499 s, 1440 s, 1406 s, 1319
s, 1290 s, 1270 s, 1199 s, 1171 s, 1105 w, 1081 m, 1051 m, 1013 m, 930
m, 909 m, 857 m, 694 s, 670 s.
25
to obtain good NMR data, measure [
a]
and recrystallize salt 27
D
due to its low solubility in common solvents.
4.8.2. (þ)-trans-2,2-Dibromo-3-phenylcyclopropanecarboxylic acid
[(þ)-26]. 5% Aq HCl (92 mL) was added to a suspension of salt 27
(8.0 g, 13.2 mmol) in ether (80 mL). The resulting mixture was
effectively stirred for 15 min at rt, then diluted with ether
(50 mL) and filtered using Buchner funnel. The precipitate was
washed with ether (3ꢂ30 mL) [after drying on air it gave 4.0 g of
pure (þ)-dehydroabietylamine hydrochloride (12.4 mmol, 91%),
which was further used for recovering of a chiral (þ)-amine]. The
filtrate was transferred into a separating funnel, the ethereal
layer was separated and the water layer was extracted with ether
(20 mL). The combined organics phases were washed with water
(10 mL) and brine (10 mL), dried and evaporated to give optically
4.8.5. (-)-trans-2-Phenylcyclopropanecarboxylic acid methyl ester
[(-)-29]. A mixture of (þ)-28 (200 mg, 0.6 mmol) and Bu3SnH
(611 mg, 2.1 mmol, 3.5 mol equiv) in dry benzene (4 mL) was
maintained for 6 h at 55 ꢁC overnight at rt. Then solvent was
evaporated, the residue (815 mg) was columned on silica (petrol–
ether, 10:1, Rf 0.33), giving methyl ester (-)-(1R, 2R)-2916 (105 mg,
25
0.6 mmol, 100%) as a colorless liquid, [
a
]
ꢀ260 (c 1.0, CHCl3),
D
which showed dH: 1.33 (1H, ddd, J¼8.4, 6.5, 4.6 Hz, H-3), 1.60 (1H,
ddd, J¼9.6, 5.1, 4.6 Hz, H-3), 1.90 (1H, ddd, J¼8.4, 5.1, 4.2 Hz, H-1),
2.53 (1H, ddd, J¼9.6, 6.5, 4.2 Hz, H-2), 3.71 (3H, s, OMe), 7.08–
7.29 (5H, m, Ph); dC: 16.9, 23.9, 26.2, 51.8, 126.2, 126.5, 128.5,
140.0, 173.8; ymax: 3445 w, 3095 m, 3070 m, 3037 s, 2960 s, 2938
s, 2864 m, 2100 w, 2040 w, 1960 w, 1895 w, 1840 w, 1733 s, 1610
m, 1500 m, 1464 s, 1445 s, 1405 s, 1348 s, 1331 s, 1275 s, 1210 s,
1182 s, 1125 m, 1085 m, 1062 m, 1010 w, 1000 m, 938 m, 918 m,
852 m, 790 m, 769 s, 732 m, 710 s. Since methyl ester (-)-29 had
(1R, 2R)-configuration therefore the absolute stereochemistry of
(þ)-26 was (1R, 3R)- and other enantiomer (-)-26 had (1S, 3S)-
configuration.21
active acid (þ)-26 (3.40 g, 11 mmol) as a white powder, mp 120–
25
121 ꢁC, [
a
]
þ60 (c 1.0, CHCl3), 62% ee. Further enantiomeric
D
enrichment was achieved by slow recrystallization of this sample
from benzene–hexane (1:2.5, 130 mL). After 24 h at 5 ꢁC the
precipitate of racemate (ꢃ)-26 (1.17 g, 3.7 mmol, 5%) was sepa-
rated and mother liquid was evaporated to provide (þ)-26 (2.17 g,
6.8 mmol) as a white powder, yield 31% based on recovering of
25
64% of starting racemate (ꢃ)-26, mp 117–118 ꢁC, [
a
]
þ86 (c 1.0,
D
CHCl3), 89% ee. Acid (þ)-26 (Found: C 37.71, H 2.65%. C10H8Br2O2
requires: C 37.54, H 2.52%), which showed dH: 2.81 (1H, d,
J¼7.8 Hz, H-1), 3.34 (1H, d, J¼7.8 Hz, H-3), 7.15–7.32 (5H, m, Ph);
dC: 28.3, 37.0, 41.5, 128.3, 128.6, 128.7, 133.7, 172.4; ymax (CHCl3):
3200–2200 br s, 3060 m, 2591 m, 1950 w, 1708 s, 1603 w, 1496 w,
1442 s, 1311 m, 1170 m, 1082 w, 950 m, 899 m, 862 m, 702 s, 690 s
4.8.6. Amide of (þ)-trans-2,2-dibromo-3-phenylcyclopropanecarboxylic
acid (þ)-26 with
L
-
b
-phenylalanine methyl ester [(þ)-30]. A mixture of
cmꢀ1
.
SOCl2 (0.5 mL, 0.81 g, 6.8 mmol) and (þ)-26 (200 mg, 0.62 mmol, 89%
ee) was stirred for 15 h at rt and then excess SOCl2 was removed in
4.8.3. (-)-trans-2,2-Dibromo-3-phenylcyclopropanecarboxylic acid
[(-)-26]. 7% Aq NaHCO3 solution (100 mL) was added to the mother
liquid (Section 4.8.1), which was evaporated to ca. w100 mL and
diluted with chloroform (70 mL). The resulting mixture was stirred
for 20 min, then the water layer was separated and the organic
layer was extracted with 5% aq NaHCO3 solution (20 mL). The
combined bicarbonate layers were extracted with chloroform
(2ꢂ30 mL), acidified with 10% aq HCl and subsequent extracted
with ether (3ꢂ50 mL). The combined ethereal layers were washed
with water (50 mL), dried, and evaporated. It gave optically active
vacuo. The residue was dissolved in dry CH2Cl2 (3 mL) and L-b-phe-
nylalanine methyl ester hydrochloride (135 mg, 0.62 mmol,
1.0 mol equiv) was added followed by cooling of the resulting sus-
pension to 0 ꢁC and subsequent addition of triethylamine (0.19 mL,
136 mg,1.4 mmol, 2.2 mol equiv). The reaction mixture was stirred for
3.5 h at rt and then diluted with ether (2ꢂ5 mL). The organic layer
was extracted with satd aq NaHCO3 (2ꢂ5 mL), 10% aq HCl (2ꢂ6 mL),
washed with water (5 mL), dried and evaporated. Filtration of the
yellow residue (260 mg) on silica (petrol–ether, 1:1, Rf 0.47) afforded
amide (þ)-30 (232 mg, 0.48 mmol, 78%) as a yellowish amorphous
25
acid (-)-26 (18.37 g, 57 mmol) as a white powder, mp 140–142 ꢁC,
mass, 89% de by 1H NMR, [
a]
þ100 (c 1.0, CHCl3) (Found: C 50.20, H
D
25
[
a]
ꢀ10 (c 1.0, CHCl3), w10% ee. Further enantiomeric enrichment
4.00, N 2.94%. C20H19Br2NO3 requires: C 49.92, H 3.98, N 2.91%), which
showed dH: 2.66 (1H, d, J¼8.2 Hz, H-1), 3.17 (1H, dd, J¼13.9, 5.7 Hz,
CHPh), 3.25 (1H, dd, J¼13.9, 6.0 Hz, CHPh), 3.45 (1H, d, J¼8.2 Hz, H-3),
3.77 (3H, s, OMe), 4.97 (1H, ddd, J¼7.5, 6.0, 5.8 Hz, CHBn), 6.52 (1H, d,
J¼7.5 Hz, NH), 7.12–7.14 (2H, m, Ph), 7.23–7.39 (8H, m, Ph); dC: 29.0,
37.7, 38.3, 39.7, 52.4, 54.0, 127.2, 127.9, 128.3, 128.6, 128.7, 129.2, 134.4,
135.7, 165.0, 171.7; ymax: 3450–3200 br s, 3095 m, 3075 m, 3040 m,
2972 m, 2940 m, 2870 m, 1745 s, 1660 s, 1610 m, 1545 s, 1505 m, 1450
m, 1420 m, 1370 m, 1220 m, 1185 m, 1120 m, 1090 s, 1040 s, 930 w, 865
m, 800 s, 770 s, 710 s. This procedure was also used for the de-
termination of ee for acid (þ)-26 isolated directly from the salt 27
(Section 4.8.2); in this case corresponding amide (þ)-30 showed 62%
de by 1H NMR.
D
was achieved by slow recrystallization of this sample from ben-
zene–hexane (1:2, 150 mL). After 24 h at 5 ꢁC the precipitate of
racemate (ꢃ)-26 (15.17 g, 47 mmol, 59%) was separated, mother
liquid was evaporated to provide (-)-26 (3.03 g, 9.5 mmol) as
a white powder, yield 34% based on recovering of 64% of starting
25
racemate (ꢃ)-26, mp 118–119 ꢁC, [
a]
ꢀ88 (c 1.0, CHCl3), 91% ee. All
D
analytical and spectral data were identical to those obtained for
acid (þ)-26.
4.8.4. (þ)-trans-2,2-Dibromo-3-phenylcyclopropanecarboxylic acid
methyl ester [(þ)-28]. A mixture of SOCl2 (0.5 mL, 0.81 g, 6.8 mmol)
and (þ)-26 (300 mg, 0.94 mmol, 89% ee) was stirred for 15 h at rt
and then excess SOCl2 was removed under reduced pressure. The
residue was dissolved in dry CH2Cl2 (3 mL) and methanol (0.5 mL)
was added dropwise followed by cooling to 0 ꢁC and subsequent
addition of triethylamine (0.13 mL, 95 mg, 0.94 mmol). The result-
ing solution was stirred for 2.5 h at rt and diluted with ether (5 mL).
The organic layer was extracted with satd aq NaHCO3 (2ꢂ5 mL),10%
aq HCl (2ꢂ5 mL), washed with water (5 mL), dried, and evaporated.
4.8.7. Amide of (-)-trans-2,2-dibromo-3-phenylcyclopropanecarboxylic
acid (-)-26 with
L
-
b
-phenylalanine methyl ester [(þ)-31]. Compound
(þ)-31 was prepared in a method similar to that in the previous
experiment from acid (-)-26 (100 mg, 0.31 mmol, 91% ee), SOCl2
(0.25 mL, 0.4 g, 3.4 mmol),
L-b-phenylalanine methyl ester hy-
drochloride (68 mg, 0.31 mmol, 1.0 mol equiv) and triethylamine

10564
A.E. Sheshenev et al. / Tetrahedron 65 (2009) 10552–10564
(0.10 mL, 68 mg, 0.7 mmol, 2.2 mol equiv). After filtration on sil-
requires: C 78.66, H 8.65%). The 1H, 13C NMR spectra were identical
ica (petrol–ether, 1:1, Rf 0.44) the procedure gave amide (þ)-31
to those obtained for racemic 23 (Section 4.7.3).
(115 mg, 0.24 mmol, 77%) as a yellowish firm film, 91% de by 1H
25
NMR, [
a
]
24 (c 0.62, CHCl3) (Found: C 50.09, H 4.03, N 2.97%.
D
Acknowledgements
C20H19Br2NO3 requires: C 49.92, H 3.98, N 2.91%), which showed
dH 2.72 (1H, d, J¼8.2 Hz, H-1), 3.19 (2H, d, J¼5.7 Hz, CH2Ph), 3.49
(1H, d, J¼8.2 Hz, H-3), 3.75 (3H, s, OMe), 5.02 (1H, dd, J¼8.0,
5.7 Hz, CHBn), 6.55 (1H, d, J¼8.0 Hz, NH), 7.22–7.34 (10H, m, Ph);
dC: 29.2, 38.3, 38.7, 39.4, 52.4, 53.8, 127.3, 128.0, 128.4, 128.7,
128.8, 129.5, 134.3, 135.4, 164.7, 171.8; ymax: 3475–3160 br s, 3092
m, 3070 m, 3040 m, 2975 m, 2940 m, 2870 m, 1737 s, 1655 s, 1603
m, 1540 s, 1500 m, 1448 m, 1410 m, 1365 m, 1245 m, 1225 m, 1200
m, 1185 m, 1120 m, 1090 m, 1040 m, 980 m, 925 w, 860 m, 795 w,
762 m, 710 m.
The authors are grateful for the financial support of INTAS
program.
References and notes
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Ed.; Wiley: New York, NY, 1987; p 1; (b) Salau¨ n, J. Top. Curr. Chem. 2000, 207, 1–
67; (c) Liu, H.-W.; Walsh, C. T. In The Chemistry of Cyclopropyl Group; Rappoport,
Z., Ed.; Wiley: New York, NY, 1987; Chapter 16, pp 959–1025; (d) Halton, B.;
Banwell, M. G. In The Chemistry of Cyclopropyl Group; Rappoport, Z., Ed.; Wiley:
New York, NY, 1987; Chapter 21, pp 1223–1339; (e) Billups, W. E.; Moorehead,
A. W. In The Chemistry of Cyclopropyl Group; Rappoport, Z., Ed.; Wiley: New
York, NY, 1987; Chapter 24, pp 1533–1574; (f) Rademacher, P. Chem. Rev. 2003,
103, 933–975.
4.9. Generation and ene-reaction of 1-trimethylsilyl-3S-
phenylcyclopropene (S)-2
2. Pietruszka, J. Chem. Rev. 2003, 103, 1051–1070.
4.9.1. (2RS, 3R)-1,1,2-Tribromo-3-phenylcyclopropane [(-)-4]. Bromine
(0.42 mL, 1.31 g, 8.2 mmol, 1.05 mol equiv) in dry CH2Cl2 (30 mL)
was added dropwise to a solution of optically active acid (-)-26
(2.50 g, 7.8 mmol, 91% ee) and red silver (II) oxide (1.27 g, 5.9 mmol,
0.75 mol equiv) in dry CH2Cl2 (30 mL) under Ar atmosphere at
0–5 ꢁC over 10 min. After 1 h at 0 ꢁC and 24 h at rt the reaction
suspension was filtered through a glass filter and the residue was
washed with dichloromethane (30 mL) and hexane (50 mL). The
combined organics were concentrated under reduced pressure,
diluted with hexane (10 mL) and filtered through a pad of silica
(hexane, 3ꢂ50 mL). The solvent was removed to give tribromide
3. de Meijere, A.; Kozhushkov, S. I.; Schill, H. Chem. Rev. 2006, 106, 4926–4996.
4. See, for example: Verbicky, C. A.; Zercher, C. K. Tetrahedron Lett. 2000, 41,
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Lee, G.-A.; Arney, B. E.; Whitmire, K. H. J. Am. Chem. Soc. 1991, 113, 7980–7984;
Billups, W. E.; Luo, W.; Lee, G.-A.; Chee, J. J. Org. Chem. 1996, 61, 764–770;
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17–27.
(-)-4 (1.22 g, 3.4 mmol, 44%, mixture of isomers, 2R:2S¼6:1 by 1H
25
NMR) as a colorless oil, [
a
]
ꢀ6 (c 1.7, CHCl3), Rf 0.48 (petrol). All
D
analytical and spectral data were identical to those obtained for
racemic tribromide 4.7
4.9.2. (þ)-3,30-Diphenyl-2,20-bis-trimethylsilylbicyclopropyl-2-ene
[(þ)-7]. Methyllithium in ether (2.0 mL, 1.85 mmol, 0.92 M,
2.2 mol equiv) was added dropwise to tribromide (-)-4 (300 mg,
0.84 mmol) in dry ether (10 mL) at ꢀ82 to ꢀ80 ꢁC over 2 min. The
solution was stirred for 5 min at ꢀ80 ꢁC and allowed to reach rt
(20 min). After a further 30 min at rt the mixture was cooled to
ꢀ60 ꢁC and chlorotrimethylsilane (0.14 mL, 119 mg, 1.09 mmol,
1.3 mol equiv) was added dropwise. The resulting solution was
stirred for 5 min at ꢀ60 ꢁC and 1 h at rt, cooled down to ꢀ40 ꢁC and
quenched with water (2 mL). The organic layer was separated, the
aqueous layer was extracted with ether (5 mL). The combined or-
ganic layers were washed with water (5 mL), dried, and evaporated.
The orange residue (170 mg) was diluted with ether (4 mL) and left
overnight under Ar atmosphere. Then the solvent was removed,
chromatography on silica (hexane, Rf 0.41) afforded dimer (þ)-7
(14 mg, 0.037 mmol, 9%) as a colorless oil, [a]
25 149 (c 0.47, hexane).
D
The 1H, 13C NMR spectra of (þ)-7 were identical to racemic dimer 7
(Section 4.2.2), however attempts to obtain a good microanalysis
for the title compound failed.
4.9.3. (þ)-2-Phenyl-anti-3-(2-phenyl-3-trimethylsilylcyclopropyl)-4-
trimethylsilyltricyclo[3.2.1.02,4]oct-6-ene [(þ)-23]. The mixture of
dimer (þ)-7 (10 mg, 0.027 mmol) and freshly distilled cyclo-
pentadiene (16 mg, 0.24 mmol, 9.0 mol equiv) in benzene (1 mL)
was stirred for 24 h at rt, then evaporated under reduced pressure.
Chromatography of the residue (15 mg) on silica (petrol, Rf 0.34)
20. Klein, J.; Brenner, S. J. Org. Chem. 1971, 36, 1319–1320.
21. Wang, M.-X.; Feng, G.-Q.; Zheng, Q.-Y. Tetrahedron: Asymmetry 2004, 15,
347–354.
gave adduct (þ)-23 (7.5 mg, 0.017 mmol, 64%) as a colorless film,
25
[
a]
þ40 (c 0.25, hexane) (Found: C 78.8, H 8.7%. C29H38Si2
D