Enantio- and diastereotopos differentiation in the palladium(II)-catalyzed hydrosilylation of bicyclo[2.2.1]alkene scaffolds with silicon-stereogenic silanes

Article abstract of DOI:10.1002/ejoc.200800107

The palladium(II)-catalyzed hydrosilylation of meso-configured bicyclo[2.2.1]alkene scaffolds proved to be an invaluable model reaction for the development of reagent-controlled asymmetric transformations based on silicon-stereogenic silanes as stereoinducers. In the present investigation, the subtle structural requirements of the silane substitution pattern in enantiotopos-differentiating single hydrosilylations of a norbornene-type substrate are disclosed. Extension of this chemistry to a double hydrosilylation of norbornadiene entails a significant increase in stereochemical complexity. Although differentiation of enantiotopic positions by the chiral reagent is demanded in the first hydrosilylation, the same reagent must then differentiate diastereotopic positions in the second. Remarkably high stereocontrol was found in this double hydrosilylation with several silanes first used in the hydrosilylations of the norbornene-type system. Depending on the enantiomeric purity of the silane, C₂- and C_s-symmetric adducts, respectively, were obtained. The identity of the key quaternary silanes was revealed by crystallographic analysis. By this method, the relative and absolute configurations were also assigned, which, in turn, imply that all enantiospecific substitutions at silicon proceed with stereoretention. On the basis of these solid-state structures, we also discuss the structural implications of silane substitution for the diastereoselectivity-determining step of this palladium(II)-catalyzed hydrosilylation reaction. Wiley-VCH Verlag GmbH & Co. KGaA, 2008.

Full text of DOI:10.1002/ejoc.200800107

FULL PAPER
DOI: 10.1002/ejoc.200800107
Enantio- and Diastereotopos Differentiation in the Palladium(II)-Catalyzed
Hydrosilylation of Bicyclo[2.2.1]alkene Scaffolds with Silicon-Stereogenic
Silanes
[a]
[a][‡]
and Manfred Keller,[b][‡‡] and Martin Oestreich*[a]
Sebastian Rendler, Roland Fröhlich,
Keywords: Asymmetric catalysis / Chirality / Hydrosilylation / Silicon / Palladium
The palladium(II)-catalyzed hydrosilylation of meso-config-
ured bicyclo[2.2.1]alkene scaffolds proved to be an invalu-
able model reaction for the development of reagent-con-
trolled asymmetric transformations based on silicon-stereo-
genic silanes as stereoinducers. In the present investigation,
the subtle structural requirements of the silane substitution
found in this double hydrosilylation with several silanes first
used in the hydrosilylations of the norbornene-type system.
Depending on the enantiomeric purity of the silane, C - and
-symmetric adducts, respectively, were obtained. The
identity of the key quaternary silanes was revealed by crys-
tallographic analysis. By this method, the relative and abso-
2
C
s
pattern in enantiotopos-differentiating single hydro- lute configurations were also assigned, which, in turn, imply
silylations of a norbornene-type substrate are disclosed. Ex- that all enantiospecific substitutions at silicon proceed with
tension of this chemistry to a double hydrosilylation of nor- stereoretention. On the basis of these solid-state structures,
bornadiene entails a significant increase in stereochemical
complexity. Although differentiation of enantiotopic positions
by the chiral reagent is demanded in the first hydrosilylation,
the same reagent must then differentiate diastereotopic posi-
tions in the second. Remarkably high stereocontrol was
we also discuss the structural implications of silane substitu-
tion for the diastereoselectivity-determining step of this pal-
ladium(II)-catalyzed hydrosilylation reaction.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2008)
Introduction
formation reactions, their mechanism of action must not
proceed through hypervalent intermediates at any stage. Lit-
erature precedent indeed hinted that the presence of hyper-
valent silicon would thwart enantiospecific substitution at
Asymmetric transformations using stereogenic silicon as
the sole source of chirality constitute a largely undeveloped
area in organic synthesis.[1] Aware of a number of asymmet-
ric methods involving organosilicon compounds, we were
attracted by the prospect of rendering catalyst-controlled
processes stereoselective by using silicon-stereogenic rea-
[
1,6,8–10]
chiral silicon.
This fundamental aspect led us to con-
[
2]
sider unconventional transition-metal-catalyzed silicon–hy-
drogen bond activation of chemically and configurationally
[
4]
stable triorganosilanes A (Scheme 1). The related strate-
gies outlined in Scheme 1 are based on the silicon–hydrogen
bond activation of A in an enantiospecific σ-bond metathe-
sis in which hypervalent silicon might only be, if at all, pres-
ent in a transition state (D or E) and not in an intermediate.
In one scenario (right, Scheme 1), a transition-metal
alkyl, generated by insertion of a prochiral alkene into the
silicon–metal bond of a transition-metal silyl complex, un-
dergoes concerted silicon–hydrogen bond activation via
[
3,4]
gents.
From our initial efforts directed towards the prep-
aration and subsequent transformations[6] of enantiopure,
asymmetrically substituted silanes, we learned that, first
and foremost, the success of this chemistry will rely on a
distinctive feature of silicon, its tendency to racemize by
pseudorotational processes when extracoordinate.[ As the
silicon atom is both carrier of stereogenic information and
reactive site in any of the envisioned silicon–element bond
[5]
7]
[
11]
four-centered transition state D (AǞB). Overall, this se-
[
12]
quence facilitates diastereoselective
alkene hydro-
[
a] Organisch-Chemisches Institut,
[
13]
Westfälische Wilhelms-Universität Münster
Corrensstrasse 40, 48149 Münster, Germany
Fax: +49-251-83-36501
silylation. In another scenario (left, Scheme 1), dehydro-
[14]
genative silicon–oxygen coupling
also makes use of an
enantiospecific σ-bond metathesis. Chiral silane A reacts
with a chiral transition-metal alkoxide via transition state
E to form silyl ether C and the catalytically active metal
E-mail: martin.oestreich@uni-muenster.de
b] Institut für Organische Chemie und Biochemie,
Albert-Ludwigs-Universität Freiburg
[
Albertstrasse 21, 79104 Freiburg im Breisgau, Germany
Si Si
[
‡] X-ray crystal structure analyses of rac-11, ( R, R)-13a, and hydride (AǞC). The latter is subsequently transformed into
meso-13a.
a transition-metal alkoxide upon reaction with an alcohol
accompanied by the liberation of dihydrogen. This dia-
stereoselective silicon–oxygen coupling is a chiral recogni-
[
‡‡]X-ray crystal structure analysis of rac-7a.
Supporting information for this article is available on the
WWW under http://www.eurjoc.org/ or from the author.
582
2
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Palladium-Catalyzed Hydrosilylation of Bicyclo[2.2.1]alkenes
Si
Si
tion, that is, preferential reaction of A with either of the termediate ( S)-6a and not the diastereomeric epi-6a [( S)-
Si
enantiomeric alcohols that inevitably leads to their kinetic 5aǞ( S)-6a]. Step (iii): σ-bond metathesis, likely to be
[
15]
[11a]
Si
Si
resolution.
rate-limiting,
of ( S)-6a with the chiral silane ( R)-2a
Si
in a matched scenario to give the quaternary silane ( S)-7a
Si
Si
[
( S)-6aǞ( S)-3a]; a mismatched scenario is also possible
[
12,18]
(see below).
The diastereomeric excess corresponds to
chirality transfer from the stereogenic silicon atom onto the
carbon skeleton of the substrate to form three new stereo-
centers. We note here that the irreversible σ-bond metath-
esis is not diastereoselectivity- but enantioselectivity-de-
termining. Remarkable asymmetric inductions were seen
when racemic β-silylalkylpalladium(II) intermediates were
treated with chiral nonracemic silanes. This situation with a
fast reacting (matched case) and a slow reacting enantiomer
Scheme 1. Synthetic strategies for silicon-stereogenic silanes based
on enantiospecific σ-bond metathesis.
(mismatched case) is nothing but a dynamic kinetic resolu-
tion within the catalysis, which also rationalizes the positive
[
12]
nonlinear effects
silane.
when using scalemic mixtures of the
[
18]
Within the first scenario, the utilization of a racemiza-
tion-free σ-bond metathesis in stereoselective alkene hydro-
silylation had set the stage for our efforts towards intermo-
So far, our research devoted to the palladium(II)-cata-
lyzed hydrosilylation of bicyclo[2.2.1]heptenes has allowed
us to gain an in-depth understanding of the mechanistic
boundaries needed for the development of catalytic pro-
cesses using silicon-stereogenic silanes as stereoinducers. In
this full account, we present our synthetic efforts to further
illuminate the structural features of the chiral silane unit
essential for achieving high diastereoselectivities in the en-
[
3,12,16,17]
lecular chirality transfer from silicon to carbon.
Needless to say, apart from the enantiospecificity of the
overall catalysis, we were mainly interested in the carbon–
silicon bond formation event which must bring about a high
level of stereoinduction.[
3,4]
For this, the substitution
pattern of the chiral silane and, importantly, its role in and
the nature of the diastereoselectivity-determining step
emerge as crucial points.[ A while ago, we accomplished
[
19]
antiotopos-differentiating hydrosilylation of 4. Moreover,
3,4]
extension of the substrate scope to bicyclo[2.2.1]heptadiene
the enantiospecific hydrosilylation of bicyclo[2.2.1]heptene
(norbornadiene) underlines the strong reagent control of
Si
4
using privileged silane ( R)-2a with immaculate dia-
our privileged silanes in enantio- and diastereotopos-differ-
Si
[12]
[
20]
stereocontrol [4Ǟ( S)-7a, Scheme 2].
entiating double hydrosilylations.
We also provide crys-
tallographic data of several quaternary silanes obtained by
hydrosilylation, thereby allowing unambiguous assignment
of the stereochemical course of the reaction pathway.
Results and Discussion
Exploration of the Silane Substitution Pattern
Initial studies using norbornene as a substrate revealed
that most of the asymmetrically substituted triorgano-
silanes previously described are poor stereoinducers in pal-
[
12]
ladium(II)-catalyzed hydrosilylation reactions. From this
preliminary silane screening, only 1-silatetralins decorated
with a sterically demanding exocyclic alkyl substituent
emerged as effective reagents for the desired chirality trans-
[
3,12,18]
fer.
Consequently, we surveyed this general motif in
[21]
Scheme 2. Catalytic cycle for the palladium(II)-catalyzed hydro- greater detail using benzannulated bicycloalkene 4
as a
silylation reaction.
substrate (4Ǟ7, 10, 11, Table 1); bicycloalkene 4 was gen-
erally preferred over its parent compound, norbornene, as
Subsequent mechanistic investigations revealed the intri- it reacted cleanly without the formation of oligomeric side-
cate stereochemical features of the three-step catalytic cycle products. Substrate 4 was subjected to hydrosilylation ac-
[
18]
(Scheme 2).
Step (i): Reversible coordination of bicyclic cording to the protocol developed by Brookhart and co-
[
11a]
alkene 4 to the highly electrophilic cationic silylpalladi- workers.
um(II) complex ( S)-3a [( S)-3aǞ( S)-5a]. Step (ii): De- (OEt )] (BAr ) [phen: 1,10-phenanthroline; Ar: 3,5-bis(tri-
Cationic palladium(II) catalyst [(phen)PdMe-
Si
Si
Si
+
–
2
4
termination of the diastereoselectivity of the overall process fluoromethyl)phenyl] was generated in situ by mixing the
[
22]
+
–[23]
in a reversible and thermodynamically controlled alkene in- precursors [(phen)PdMe2]
and [H(OEt ) ] (BAr )
in
2 2
4
sertion; this preferentially produces alkylpalladium(II) in- CH Cl ; the reactants were then added to this mixture. As
2
2
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S. Rendler, R. Fröhlich, M. Keller, M. Oestreich
FULL PAPER
Si
[5b]
no detectable temperature effect on the diastereoselectivity using ( S)-2a
in almost enantiopure form, the chiral in-
was observed, reactions were usually performed at 0 °C formation at the silicon was completely preserved in the
Si
with a catalyst loading of 2.0 mol-% (full conversion in 0.5– product ( R)-7a (Table 1, entry 2). In order to evaluate the
4.0 h).
steric demands of the exocyclic substituent, we prepared the
isopropyl-bearing congener rac-2b which was also available
Table 1. Effect of silane substitution on the hydrosilylation of 4.[a]
Si
[18]
in enantioenriched form as ( R)-2b. A slight decrease in
diastereoselectivity led, for the first time, to detectable
amounts of the minor diastereomer of rac-7b (dr = 99:1,
Si
Table 1, entry 3). As expected, enantioenriched ( R)-2b
Si
produced the corresponding quaternary silane ( R)-7b en-
antiospecifically (Table 1, entry 4). Impressed by this very
minor effect on diastereoselectivity, we decided to assess the
influence of the size of the ring in which the silicon atom is
embedded. We therefore prepared the racemic strained 1-
[
24]
[25]
silaindane derivatives rac-8a and rac-8b in analogy to
[
5b]
a previously reported procedure.
a) as well as isopropyl-substituted 1-silaindanes (rac-8b)
showed distinctly reduced diastereoselectivity at slightly in-
Both tert-butyl- (rac-
8
[
15c]
creased reactivity
(dr = 96:4, 92% ct for rac-10a and dr
=
95:5, 90% ct for rac-10b, Table 1, entries 5 and 6). The
structural alterations had, however, only a minor influence
on the diastereoselectivity compared with the replacement
of the tert-butyl by a phenyl group in the related norbor-
[
12]
nene hydrosilylation (dr Ͼ 99:1 vs. dr = 65:35). We then
[
26,27]
directed our interests towards acyclic silane rac-9
ing an almost identical substitution pattern to that of rac-
a and rac-8a. Corroborating the aforementioned findings,
excellent chirality transfer (dr Ͼ 99:1, 99% ct) was observed
Table 1, entry 7). This outcome is particularly noteworthy:
bear-
2
(
It provides further evidence for alkene insertion and not σ-
bond metathesis as the diastereoselectivity-determining step
(see above) because acyclic rac-9 is completely ineffective
(
dr = 59:41) in the mechanistically related silicon–oxygen
[
19]
coupling, a σ-bond metathesis.
Hydrosilylation of Norbornadiene
All the hydrosilylations of alkene 4 in Table 1 turned out
to give exceptionally high chirality transfer. These promis-
ing findings encouraged us to explore the scope of this dia-
stereoselective transformation in reactions using norborna-
[
20a]
diene (12) as the substrate
(12Ǟ13, 14, Table 2). In this
double hydrosilylation sequence, the silicon-stereogenic si-
lane will have to meet a “higher level” of stereodifferenti-
ation. After enantiotopos-differentiating hydrosilylation of
the first double bond of diene 12, which is comparable to
that of alkene 4, competition between substrate and reagent
control arises in the second hydrosilylation of the chiral and
[
a] All reactions were carried out in 0.1  solutions using 1.1–
1
.2 equiv. of the silane until complete conversion of 4, as monitored
1
by H NMR spectroscopy. [b] Enantiomeric excesses were deter-
mined by HPLC on a chiral stationary phase. [c] Relative configu-
rations were assigned according to X-ray crystal structure analysis thus unsymmetric (C
of rac-7a and rac-11. [d] Isolated yield of analytically pure material Scheme 3, see below).
after flash column chromatography. [e] Diastereomeric ratios were
) alkene intermediate 15 (cf.
1
We started our investigations of the double hydro-
silylation of norbornadiene (12) by using a slight excess of
racemic silane rac-2a (2.2 equiv.) (Table 2, entry 1). Clean
conversion to products rac- and meso-13a was observed in
determined by NMR spectroscopy, GLC (SE-54 column), or
HPLC analysis using chiral stationary phases; chirality transfer =
diastereomeric excess.
Privileged silane rac-2a[5b] decorated with an exocyclic the presence of 5.0 mol-% of Brookhart’s palladium(II) cat-
tert-butyl substituent afforded perfect chirality transfer alyst. Analytical data obtained by NMR spectroscopy as
(
99% ct, dr Ͼ 99:1) (Scheme 2, Table 1, entry 1). When well as GLC showed that C -symmetric rac-13a was formed
2
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Palladium-Catalyzed Hydrosilylation of Bicyclo[2.2.1]alkenes
Table 2. Double hydrosilylation of norbornadiene (12).[a]
[
a] All reactions were carried out in 0.1  solutions using 2.2 equiv. of the silane until complete conversion of 12, as determined by GLC
analysis (SE-54). [b] Enantiomeric excesses of the silanes were determined by HPLC on a chiral stationary phase. [c] Relative configura-
tions were assigned according to X-ray crystal structure analysis of ( R, R)-13a. [d] Enantiomeric excesses of the products were deter-
Si Si
mined by HPLC on a chiral stationary phase. [e] Relative configurations were assigned according to X-ray crystal structure analysis of
meso-13a. [f] Determined by analytical GLC analysis (SE-54). [g] Isolated yield of analytically pure material after flash column chromatog-
raphy. [h] Diastereomeric ratios were determined by GLC (SE-54 column) or HPLC using chiral stationary phases; chirality transfer =
Si
2
Si Si
2
diastereomeric excess. [i] ( R)-[ H]-2a (99% D) and ( S, S)-13a (99% D ) by mass spectrometry.
along with approximately equal amounts of C -symmetric observed when other racemic mixtures of chiral silanes such
s
meso-13a. Notably, no other stereoisomer was detected, as rac-2b and rac-8a were converted into the corresponding
which again demonstrated excellent silicon-to-carbon chi- hydrosilylation products rac-13b/meso-13b (C /C = 59:41)
2
s
rality transfer in both hydrosilylation steps (dr Ͼ 99:1, 99% and rac-14a/meso-14a (C /C = 60:40), respectively (Table 2,
2
s
ct). The C /C ratio of 46:54 indicated that the influence of entries 4 and 6). Comprehensive chromatographic (GLC
2
s
1
13
29
substrate control was fully overridden in the second hydro- and HPLC) and spectroscopic ( H, C, Si NMR) analy-
silylation step. A comparable product distribution was also ses revealed almost complete chirality transfer for both 1-
Eur. J. Org. Chem. 2008, 2582–2591
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S. Rendler, R. Fröhlich, M. Keller, M. Oestreich
FULL PAPER
silatetralin (dr Ն 98:2 for 13b) and 1-silaindane (dr = 99:1 if any substrate control is absent. If, however, enantiopure
Si
for 14a). These results compare well within experimental silane, for example, the R enantiomer (left, Scheme 3) is
Si Si
error with the asymmetric induction that is observed in the used, only a single enantio- and diastereomer, ( R, R)-13
hydrosilylation of 4.
having C symmetry, is produced by double hydrosilylation,
2
Based on the product distribution of the reactions of ra- which also underlines the racemization-free overall reaction
cemic silanes, we predicted that enantiopure silanes should pathway. In fact, the silane is not completely enantiopure.
lead exclusively to the C -symmetric diastereomers. To test Thus, two processes become relevant: i. A matched/mis-
2
Si
[18]
for this we subjected ( S)-2a (97% ee) to the same reaction matched scenario for σ-bond metathesis
conditions (Table 2, entry 2); highly enantioenriched to observable asymmetric amplification
R, R)-13a (Ն97% ee) with C symmetry was formed amounts of meso-13 might be formed.
may give rise
and ii. minor
[
12,28]
Si Si
(
2
with excellent diastereocontrol (C /C = 98:2). Analogously,
2
Si
s
2
enantioenriched deuteriosilane ( R)-[ H]-2a (94% ee) gave
Si Si
2
X-ray Crystallographic Study
chiral ( S, S)-[ H ]-13a with the expected complete chiral-
2
ity transfer (Table 2, entry 3). The deuterium label in
In our initial report, the relative configurations of hydro-
Si Si
2
(
S, S)-[ H ]-13a assisted the NMR spectroscopic verifica-
2
silylation product rac-7a and the congeners thereof were as-
tion of the exo selectivity. In this case, HPLC analysis using
a chiral stationary phase showed that the enantiopurity of
[12]
signed inconclusively by NMR measurements.
Our
attempts to solve this issue by X-ray crystallographic analy-
sis of quaternary silanes were hampered by their reluctance
to solidify. Quite by chance, rac-7a crystallized from a sol-
vent mixture of acetonitrile, ethanol, and water over pro-
longed storage at 4 °C (Figure 1). Gratifyingly, the solid-
state molecular structure confirmed our NOE assignment.
Si Si
2
(
S, S)-[ H ]-13a (Ͼ99% ee) was higher than that of the
2
Si
2
parent silane ( R)-[ H]-2a (94% ee). The use of a slight
Si
2
excess of ( S)-[ H]-2a might account for this because in the
closely related hydrosilylation of norbornene (12) we had
already detected a notable asymmetric amplification (see
[
12,28]
above).
Similar observations were made with isopro-
The relative configuration of the quaternary silane rac-7a
Si
pyl-substituted silane ( R)-2b (96% ee). Selective double
addition yielded C -symmetric ( R, R)-13b with excellent
Si
(
1R*,2R*,4S*, S*) seems to represent the thermodynami-
Si Si
2
cally favored product in which the sterically demanding
exocyclic tert-butyl group is arranged in such a manner that
unfavorable steric interactions are minimized. The assump-
tion that rac-7a is the thermodynamically favored dia-
stereomer is in agreement with the diastereoselectivity de-
termination in step (ii) of the catalytic cycle (cf. Scheme 2)
in which thermodynamic control is operative. This might be
concluded if the energetic conditions of the β-silylalkylpal-
diastereoselectivity (dr = 99:1) and enantioselectivity
(Ͼ99% ee) (Table 2, entry 5).
The observed ratio of chiral (C ) and achiral (C ) prod-
2
s
ucts can be rationalized as shown in Scheme 3.[ After en-
29]
antiotopos-differentiation (a) in the first carbon–silicon
Si
bond formation [e.g, 12Ǟ( R)-15], a second, now dia-
stereotopos-differentiating (b) carbon–silicon bond forma-
Si
Si Si
tion [e.g., ( R)-15Ǟ( R, R)-13] involving an unsymmetric
alkene 15 is required. If the reaction is performed with race-
mic silane, both enantiomeric forms of the silanes are avail-
able for step (b). Predominant reagent control consequently
Si
ladium(II) intermediates ( S)-6a and epi-6a match those of
their corresponding products after σ-bond metathesis.
not only results in the formation of the C -symmetric prod-
2
Si Si
uct ( R, R)-13 (left, Scheme 3), and likewise enantiomeric
S, S)-13 (right, Scheme 3), but also the C -symmetric
Si Si
(
s
Si Si
diastereomer ( R, S)-13 (ϵ meso-13, center, Scheme 3).
Marginal substrate control might account for the slight ex-
perimental deviation from the expected C /C ratio of 50:50
2
s
Figure 1. Molecular structure of rac-7a.
As it turned out, rac-11 derived from the acyclic silane
rac-9 is a white solid that was recrystallized from hexanes
at 4 °C to yield single crystals suitable for X-ray diffraction
(Figure 2). Strikingly, the conformations around the newly
formed carbon–silicon bonds in rac-7a and rac-11 are al-
most identical in the solid state. This is exemplified by their
respective dihedral angles of 78.5° for C21–Si1–C31–C40 in
rac-7a compared to 71.1° for C1b–Si–C2–C1 in rac-11.
Scheme 3. (a) Enantiotopos- and (b) diastereotopos-differentiating
steps in the hydrosilylation of norbornadiene.[
29]
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Palladium-Catalyzed Hydrosilylation of Bicyclo[2.2.1]alkenes
Having a similar β-silylalkylpalladium(II) intermediate in representation of meso-13a shows C symmetry after two-
s
mind, this might also explain the equally high chirality fold exo-selective, highly diastereoselective addition of two
transfer using acyclic silane rac-9.
different enantiomers of silane 2a.
Figure 4. Molecular structure of meso-13a.
Figure 2. Molecular structure of rac-11.
Conclusions
In this synthetic and X-ray crystallographic study, we ex-
plored the structural requirements for the intermolecular
chirality transfer from silicon to carbon in a palladium(II)-
catalyzed enantiotopos-differentiating hydrosilylation of a
bicyclo[2.2.1]alkene, namely, benzannulated alkene 4. These
investigations demonstrate that structural alteration around
the silicon atom is tolerated to some extent without affect-
ing the diastereoselectivity. It has been demonstrated that
the steric differences of the three substituents at silicon are
Enantiomerically enriched samples of 7, 10, and 11 failed
to afford single crystals of sufficient quality to assign their
absolute configurations. Conversely, this problem did not
Si
arise in the double addition of virtually enantiopure ( S)-
Si Si
2
a to 12. High-molecular-weight compound ( R, R)-13a
readily solidified. Single crystals were obtained by
recrystallization at room temperature using a mixture of
acetonitrile, ethanol, and water as solvent (Figure 3). As de-
termined by NMR spectroscopy, the two-fold exo addition
[
12]
Si Si
crucial to obtain high diastereoselectivity,
whereas inte-
indeed delivered the C -symmetric product ( R, R)-13a.
2
gration of the silicon atom into a rigid cyclic framework is
not essential. The subsequent extension of this methodol-
ogy to the double hydrosilylation of norbornadiene (12) has
provided an insight into the unusually pronounced reagent
control of our privileged silanes. Equally high chirality
transfer was seen in both steps, the enantiotopos-differen-
tiating followed by the diastereotopos-differentiating hydro-
silylation.
X-ray crystallographic data of several quaternary silanes
obtained from these hydrosilylations has allowed the unam-
biguous verification of their relative and absolute configu-
rations. The structurally closely related products seem to
represent the thermodynamically favored diastereomers,
which is in agreement with the thermodynamically con-
trolled alkene insertion step being diastereoselectivity-de-
termining.
The third-row element silicon also enabled the absolute
configuration to be assigned based on anomalous disper-
[
30]
sion. As the absolute configuration of the starting silane
Si
(
S)-2a is known from previous work by correlation with
[5b]
its precursor, the (–)-menthyl ether, retention of configu-
ration for this hydrosilylation is proved.[ The enantio-
specific silicon–hydrogen bond activation with retention of
configuration at silicon coincides with literature precedent
for homogeneous transition-metal-catalyzed hydro-
silylations. Finally, X-ray diffraction also delivered struc-
tural proof of the achiral meso-13a (Figure 4). Single crys-
tals were again obtained by recrystallization from ethanol,
acetonitrile, and water at room temperature. The structural
31]
[
32]
In summary, these studies complement previously re-
ported research on intermolecular chirality transfer from
silicon to carbon. Our investigations of the palladium(II)-
catalyzed hydrosilylation reaction provide both a mechan-
istic and a synthetic basis for future developments in the
still underrated chemistry of silicon-stereogenic reagents.
Experimental Section
General Information: [(phen)PdMe
2
],[ [H(OEt
22]
2
)
2
]+(BAr)
4
– [23]
,
rac-
Si
[5b] Si
2
Si
[18] [21]
[24]
2
a, ( S)-2a, ( R)-[ H]-2a, rac-2b, ( R)-2b, 4, rac-8a, and
[26]
rac-9
were prepared according to known procedures. All reac-
Si Si
Figure 3. Molecular structure of ( R, R)-13a.
tions were performed in flame-dried Schlenk tubes under a static
Eur. J. Org. Chem. 2008, 2582–2591
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
2587

S. Rendler, R. Fröhlich, M. Keller, M. Oestreich
FULL PAPER
pressure of argon. Liquids and solutions were transferred with sy-
= 96:4 by GLC, exo/endo Ͼ 99:1 by GLC) was obtained as a color-
ringes. CH
2
Cl
2
was dried by continuous distillation from CaH
2
less, highly viscous oil. R
= 22.8 (minor diastereomer), 23.5 min (major diastereomer). 1H
NMR (500 MHz, CDCl ): δ = 0.98–1.07 (m, 1 H), 1.01 (s, 9 H),
1.10–1.28 (m, 3 H), 1.43–1.49 (m, 2 H), 2.06 (ddd, J = 11.7, J =
6.5, J = 3.8 Hz, 1 H), 3.18 (m , 2 H), 3.32–3.37 (m, 2 H), 7.07–7.13
f R
= 0.35 (cyclohexane); GLC (SE-54): t
prior to use. Melting points were determined using a Stuart Scien-
tific SMP3 melting point apparatus (uncorrected values). Analyti-
cal thin-layer chromatography (TLC) was performed on silica gel
SIL G-25 glass plates (Macherey–Nagel, Germany). Flash column
chromatography was performed on silica gel 60 (40–63 µm, 230–
3
c
(m, 2 H), 7.17–7.23 (m, 3 H), 7.29 (br. d, J = 7.7 Hz, 1 H), 7.33
4
00 mesh, ASTM, Merck, Germany) with cyclohexane as solvent.
(ddd, J = 7.3, J = 7.3, J = 1.3 Hz, 1 H), 7.58 (br. d, J = 7.1 Hz, 1
H) ppm. C NMR (100 MHz, CDCl ): δ = 5.9, 18.4, 23.4, 27.4,
3
1
13
29
13
H, C, and Si NMR spectra were recorded in CDCl
3
with
Bruker AV 400, Varian INOVA 500, and Varian Unity plus 600
spectrometers. GLC analyses were performed using a Shimadzu
GC-17A instrument equipped with a SE-54 capillary column
30.8, 32.5, 44.6, 45.8, 48.1, 119.1, 121.0, 125.3, 125.5, 125.6, 125.8,
2
9
129.3, 133.6, 136.9, 147.2, 150.8, 154.3 ppm. Si NMR (99.3 MHz,
CDCl ): δ = 25.3 (minor), 25.7 (major) ppm. IR (ATR): ν˜ = 3053
3
(
30 mϫ0.32 mm, 0.25 µm, N
2
carrier gas, 250 °C injection tem-
(m), 2949 (s), 2926 (s), 2854 (s), 1590 (w), 1559 (w), 1469 (s), 1440
(s), 1389 (w), 1361 (m), 1312 (m), 1261 (m), 1195 (w), 1155 (w),
1118 (s), 1064 (m), 1012 (m), 975 (s), 940 (m), 909 (s), 885 (m), 822
(s), 792 (w), 753 (s), 742 (s), 724 (s), 694 (m), 674 (m), 633 (m), 556
perature, detector temperature 300 °C; temperature program: start
–1
temperature 40 °C for 1 min, heating rate 10 °Cmin , 300 °C end
temperature for 25 min). HPLC analyses were performed with an
Agilent 1200 instrument on a chiral stationary phase using a Daicel
–
1
+
(w), 515 (m) cm . HRMS (EI): calcd. for C23
275.1256; found 275.1239. C23 28Si (332.6): calcd. C 83.07, H 8.49;
spectra were recorded with a Waters Micromass MAT 8200 GC- found C 82.98, H 8.39.
4 9
H28Si [M – C H ]
Chiralcel OD-RH column (MeCN/H
2
O mixtures as solvent). Mass
H
TOF (EI/HRMS) instrument. IR spectra were recorded with a Var-
ian 3100 FT-IR instrument equipped with an ATR unit. Optical
rotations were measured in a 1 dm cuvette with a Perkin-Elmer 341
polarimeter. Elemental analyses were conducted with a Vario EL
III instrument from Elementaranalysensysteme GmbH. Analytical
Si
(
2
1R*,2R*,4S*, R*)-1-Isopropyl-1-(1,2,3,4-tetrahydro-1,4-methano-
-naphthyl)-1-silaindane (rac-10b): See Table 1, Entry 6. According
to GP 1, starting from 4 (142 mg, 1.00 mmol), rac-8b (199 mg,
+
1
.13 mmol), [(phen)PdMe
2
] (6.3 mg, 0.020 mmol), and [H(OEt
) (20 mg, 0.020 mmol), compound rac-10b (223 mg, 70%, dr
95:5 by GLC, exo/endo = 99:1 by GLC) was obtained as a color-
= 0.38 (cyclohexane); GLC (SE-54): t
22.2 (endo isomer), 22.5 (minor diastereomer), 23.2 min (major
2 2
) ] -
–
(BAr
4
Si
Si
data for quaternary silanes rac-7a, ( R)-7a, rac-7b, ( R)-7b, and
=
rac-11 were included in preliminary reports.[
12,18,19]
less, highly viscous oil. R
f
R
=
General Procedure for the Hydrosilylation of 4 (GP 1): A Schlenk
1
diastereomer). H NMR (600 MHz, CDCl
9.7, J = 6.5, J = 1.7 Hz, 1 H), 1.05 (d, J = 7.2 Hz, 3 H), 1.06 (d, J
7.2 Hz, 3 H), 1.08–1.15 (m, 1 H), 1.16–1.25 (m, 2 H), 1.30 (ddd,
J = 8.9, 2ϫ J = 1.4 Hz, 1 H), 1.42 (ddd, J = 11.6, J = 9.7, J =
.8 Hz, 1 H), 1.51 (ddddd, J = 8.7, 4ϫ J = 1.9 Hz, 1 H), 2.01 (ddd,
J = 11.6, J = 6.6, J = 3.3 Hz, 1 H), 3.18 (m , 2 H), 3.31 (br. s, 1
3
): δ = 0.99 (ddd, J =
tube was charged with a mixture of [(phen)PdMe
and [H(OEt ) ] (BAr
2 2 4
2
] (0.02 equiv.)
) (0.02 equiv.) under argon. The solids were
dissolved in anhydrous degassed CH Cl at 0 °C forming a pale-
yellow solution. At this temperature, a solution of bicyclic alkene
(1.00 equiv.) and silane (2, 8, or 9) (1.20 equiv.) in CH Cl was
+
–
=
2
2
1
4
2
2
added in one portion by syringe. The resulting bright-yellow solu-
c
H), 3.39 (br. d, J = 2.6 Hz, 1 H), 7.06–7.13 (m, 2 H), 7.16–7.22 (m,
3 H), 7.29 (br. d, J = 7.7 Hz, 1 H), 7.33 (ddd, 2ϫ J = 7.4, J =
.3 Hz, 1 H), 7.56 (d, J = 7.0 Hz, 1 H) ppm. C NMR (150 MHz,
CDCl ): δ = 6.4, 13.2, 18.2, 18.3, 24.2, 30.0, 32.5, 44.5, 45.3, 48.1,
19.0, 121.0, 125.2, 125.5, 125.6, 125.8, 129.4, 133.4, 137.0, 147.2,
50.8, 154.2 ppm. Si NMR (99.3 MHz, CDCl
3.3 (major) ppm. IR (ATR): ν˜ = 3052 (m), 2950 (s), 2862 (s), 1590
w), 1460 (s), 1440 (s), 1261 (m), 1195 (w), 1118 (s), 1063 (w), 995
w), 974 (w), 942 (m), 909 (s), 881 (s), 792 (w), 726 (s), 699 (m),
tion (0.1  in 4) was maintained at 0 °C until complete consump-
1
tion of the reactants (0.5–4 h) as monitored by H NMR analysis.
1
3
1
After addition of cyclohexane (10 mL) and a small portion of silica
gel the solvents were evaporated. Purification by flash column
chromatography on silica gel (cyclohexane) afforded the analyti-
cally pure products (7, 10, or 11) as colorless, highly viscous oils.
3
1
1
2
(
(
2
9
3
): δ = 23.7 (minor),
Si
(
2
1R*,2R*,4S*, S*)-1-tert-Butyl-1-(1,2,3,4-tetrahydro-1,4-methano-
-naphthyl)silatetralin (rac-7a): See Table 1, Entry 1.[ According
12]
to GP 1, starting from 4 (71.1 mg, 0.500 mmol), rac-2a (112 mg,
–1
6
74 (w), 638 (s), 557 (w), 518 (m) cm . HRMS (EI): calcd. for
+
0
(
.550 mmol),[(phen)PdMe
2
](3.2 mg,0.010 mmol),and[H(OEt
2 2
) ] -
26Si [M]+ 318.1804; found 318.1782. C22
C H H26Si (318.5): calcd.
22
–
BAr ) (10 mg, 0.010 mmol), compound rac-7a (165 mg, 95%, dr
4
C 82.96, H 8.23; found C 82.82, H 8.23.
Ͼ 99:1 by HPLC, exo/endo Ͼ 99:1 by HPLC) was obtained as a
colorless oil that solidified upon prolonged storage at 4 °C.
Si
(
1
1R*,2R*,4S*, S*)-(tert-Butyl)(methyl)(phenyl)(1,2,3,4-tetrahydro-
[
19]
,4-methano-2-naphthyl)silane (rac-11): See Table 1, Entry 7. Ac-
cording to GP 1, starting from 4 (99.5 mg, 0.700 mmol), rac-9
X-ray Crystal Structure Analysis for rac-7a: Formula C24
H
30Si, M
346.57, colorless crystal, 0.20ϫ0.15ϫ0.15 mm, a = 8.1125(2), b
10. 6 3 6 0 (4 ), c = 2 2 . 99 2 1 (8 ) Å, α = β = γ = 9 0 °, V =
=
=
(
[
(
137 mg, 1.10 mmol), [(phen)PdMe
2
] (6.7 mg, 0.021 mmol), and
(21 mg, 0.021 mmol), compound rac-11
157 mg, 70%, dr Ͼ 99:1 by NMR, exo/endo Ͼ 99:1 by NMR) was
+
–
2 2 4
H(OEt ) ] (BAr )
3
–3
–1
1
983.86(11) Å , ρcalcd. = 1.160 gcm , µ = 1.031 mm , semi-empiri-
cal absorption correction (0.917ՅTՅ0.983), Z = 4, orthorhombic,
space group P2 (No. 19), λ = 0.71073 Å, T = 100(2) K, ω
and φ scans, 14742 reflections collected (Ϯh, Ϯk, Ϯl), [(sinθ)/λ] =
obtained as a white solid; m.p. 69 °C (cyclohexane).
1 1 1
2 2
X-ray Crystal Structure Analysis for rac-11: Formula C22
320.53, colorless crystal, 0.35ϫ0.35ϫ0.30 mm, a = 14.799(1), b
H28Si, M
=
=
=
–1
0.67 Å , 2831 independent (Rmerge = 0.0568) and 2394 observed
3
7.776(1), c = 18.138(1) Å, β = 112.56(1)°, V = 1927.5(3) Å , ρcalcd.
reflections [IՆ2σ(I)], 229 refined parameters, R = 0.0350, wR
2
=
–
3
–1
1.105 gcm , µ = 1.031 mm , empirical absorption correction
/n (No. 14),
–
3
0.0838, max./min. residual electron density: 0.283/–0.418) eÅ , hy-
(
0.714ՅTՅ0.747), Z = 4, monoclinic, space group P2
1
drogen atoms calculated and refined as riding atoms.
λ = 1.54178 Å, T = 223 K, ω and φ scans, 13632 reflections col-
lected (Ϯh, Ϯk, Ϯl), [(sinθ)/λ] = 0.60 Å , 3384 independent (Rmerge
Si
–1
(
1R*,2R*,4S*, S*)-1-tert-Butyl-1-(1,2,3,4-tetrahydro-1,4-methano-
2-naphthyl)-1-silaindane (rac-10a): See Table 1, Entry 5. According
= 0.031) and 3241 observed reflections [IՆ2σ(I)], 212 refined pa-
2
to GP 1, starting from 4 (142 mg, 1.00 mmol), rac-8a (228 mg, rameters, R = 0.044, wR = 0.124, max. (min.) residual electron
+
–3
1
.20 mmol), [(phen)PdMe
2
] (6.3 mg, 0.020 mmol), and [H(OEt
2
)
2
] -
density: 0.37 (–0.19) eÅ , hydrogen atoms calculated and refined
as riding atoms.
–
(BAr
4
) (20 mg, 0.020 mmol), compound rac-10a (277 mg, 83%, dr
2588
www.eurjoc.org
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2008, 2582–2591

Palladium-Catalyzed Hydrosilylation of Bicyclo[2.2.1]alkenes
General Procedure for the Hydrosilylation of 12 (GP 2): A Schlenk
2
X-ray Crystal Structure Analysis for meso-13a: Formula C33H48Si ,
tube was charged with a mixture of [(phen)PdMe
and [H(OEt ) ] (BAr
2 2 4
2
] (0.05 equiv.)
) (0.05 equiv.) under argon. The solids were
dissolved in anhydrous degassed CH Cl at 0 °C forming a pale-
yellow solution. At this temperature, a solution of bicyclic diene 12
1.00 equiv.) and silane (2 or 8) (2.20 equiv.) in CH Cl was added
in one portion by syringe. The resulting bright-yellow solution
0.1  in 12) was maintained at 0 °C until complete consumption
M = 500.89, colorless crystal, 0.25 ϫ 0.15 ϫ 0.03 mm, a =
25.4207(9), b = 7.6862(2), c = 15.8275(5) Å, β = 105.177(2)°, V =
2984.65(16) Å , ρcalcd. = 1.115 gcm , µ = 1.198 mm , empirical
absorption correction 0.754ՅTՅ0.965, Z = 4, monoclinic, space
+
–
3
–3
–1
2
2
(
2
2
group P2 /c (No. 14), λ = 1.54178 Å, T = 223 K, ω and φ scans,
1
–1
26089 reflections collected (Ϯh, Ϯk, Ϯl), [(sinθ)/λ] = 0.60 Å , 5220
independent (Rmerge = 0.111) and 3369 observed reflections
(
of the reactants (4–8 h), as monitored by GLC analysis. After ad-
dition of cyclohexane (10 mL) and a small portion of silica gel the
solvents were evaporated. Purification by flash column chromatog-
raphy on silica gel (cyclohexane) afforded the analytically pure
products (13 or 14) as colorless, highly viscous oils.
2
[IՆ2σ(I)], 322 refined parameters, R = 0.066, wR = 0.154, max.
(min.) residual electron density: 0.26 (–0.25) eÅ , hydrogen atoms
calculated and refined as riding atoms.
–
3
Si
(
[
1R,2S,4R,5S)-2,5-Bis[( R)-1-tert-butyl-1-silatetralin-1-yl]bicyclo-
Si Si
2.2.1]heptane [( R, R)-13a]: See Table 2, Entry 2. According to
GP 2, starting from 12 (27.6 mg, 0.300 mmol), ( S)-2a (135 mg,
0.660 mmol, 97% ee), [(phen)PdMe ] (4.8 mg, 0.015 mmol), and
) (15 mg, 0.015 mmol), compound ( R, R)-13a
/C = 98:2 by GLC, dr Ͼ 99:1 by GLC, exo/endo
Ͼ 99:1 by GLC, Ն97% ee by HPLC) was obtained as a white solid;
Si
Si
(
1R*,2S*,4R*,5S*)-2,5-Bis[( R*)-1-tert-butyl-1-silatetralin-1-yl]-
Si
bicyclo[2.2.1]heptane (rac-13a) and (2R,6S)-2-[( S)-1-tert-Butyl-1-
silatetralin-1-yl]-6-[( R)-1-tert-butyl-1-silatetralin-1-yl]bicyclo- [H(OEt
2
Si
+
–
Si Si
2
)
2
] (BAr
4
[2.2.1]heptane (meso-13a): See Table 2, Entry 1. According to GP
(137 mg, 91%, C
2
s
2
0
, starting from 12 (36.9 mg, 0.400 mmol), rac-2a (180 mg,
+
20
20
.880 mmol),[(phen)PdMe
2
](6.3 mg,0.020 mmol),and[H(OEt
2
)
2
] -
D 3
m.p. 134 °C (cyclohexane). [α] = –6.15 (c = 0.585, CHCl ), [α]578
–
20
20
20
(BAr
4
) (20 mg, 0.020 mmol), a mixture of compounds rac-13a and = –6.84, [α]546 = –8.03, [α]436 = –14.9, [α]365 = –24.1. HPLC analysis
meso-13a (156 mg, 78%, C
exo/endo Ͼ 99:1 by GLC) was obtained as a white solid. Repeated
2
/C
s
= 46:54 by GLC, dr Ͼ 99:1 by GLC,
on a chiral stationary phase (see above) did not allow separation
of meso-13a and the minor enantiomer ( S, S)-13a (integration of
Si Si
flash chromatography on silica gel (cyclohexane) furnished separate
2 s
this peak: 1.5%). According to GLC data (C /C = 98:2, see above)
fractions of rac-13a (56 mg, 28 %, C
34 mg, 17%, C /C = 2:98). GLC (SE-54): t
9.3 min (rac-13a); HPLC (Daicel Chiralcel OD-RH, 20 °C,
2
/C
s
= 99:1) and meso-13a
this minor peak should exclusively consist of meso-13a. Thus,
Ͼ99% ee emerges for ( R, R)-13a.
Si Si
(
3
2
s
R
= 37.1 (meso-13a),
Si
Si
–1
X-ray Crystal Structure Analysis for ( R, R)-13a: Formula
, M = 500.89, colorless crystal, 0.30ϫ0.15ϫ0.05 mm, a
= 8.1786(1), b = 14.4813(2), c = 13.2245(2) Å, β = 103.588(1)°, V
2 R
MeCN/H O, 90:10, flow rate = 0.80 mLmin , λ = 230 nm): t =
Si Si
Si Si
33 2
C H48Si
9
.8 [( S, S)-13a], 10.0 (meso-13a), 11.8 min [( R, R)-13a]; no sep-
Si Si
aration of ( S, S)-13a and meso-13a.
3
–3
–1
=
1522.43(4) Å , ρcalcd. = 1.093 gcm , µ = 1.174 mm , empirical
absorption correction (0.720ՅTՅ0.944), Z = 2, monoclinic, space
(No. 4), λ = 1.54178 Å, T = 223 K, ω and φ scans, 12632
Analytical Data for rac-13a: R
f
= 0.44 (cyclohexane). 1H NMR
(
500 MHz, CDCl ): δ = 0.92–1.10 (m, 2 H), 1.01 (s, 18 H), 0.94– group P2
.03 (m, 2 H), 1.09 (br. s, 2 H), 1.14 (dd, 2ϫ J = 8.7 Hz, 2 H), reflections collected (Ϯh, Ϯk, Ϯl), [(sinθ)/λ] = 0.60 Å , 4906 inde-
.39–1.45 (m, 4 H), 1.71 (m , 2 H), 2.04 (m, 2 H), 2.29 (s, 2 H), pendent (Rmerge = 0.050) and 4620 observed reflections [IՆ2σ(I)],
.66 (ddd, J = 15.7, J = 10.1, J = 2.8 Hz, 2 H), 2.72 (ddd, J = 15.5, 322 refined parameters, R = 0.045, wR = 0.109, Flack parameter
3
1
–
1
1
1
2
c
2
–
3
J = 6.3, J = 2.8 Hz, 2 H), 7.08 (br. d, J = 7.4 Hz, 2 H), 7.15 (br.
dd, 2ϫ J = 7.2 Hz, 2 H), 7.23 (ddd, 2ϫ J = 7.5, J = 1.7 Hz, 2 H),
= 0.02(3), max. (min.) residual electron density: 0.21 (–0.19) eÅ ,
hydrogen atoms calculated and refined as riding atoms.
7
.47 (dd, J = 7.2, J = 1.4 Hz, 2 H) ppm. 13C NMR (125 MHz,
2
Si
(
2
1S,2R,4S,5R)-[3,6- H ]-2,5-Bis[( S)-1-tert-butyl-1-silatetralin-1-yl]-
CDCl
1
3
): δ = 7.2, 18.5, 23.9, 24.3, 27.7, 36.0, 38.4, 36.8, 39.0, 124.8,
Si Si
2
28.4, 128.5, 132.8, 135.5, 150.1 ppm. 2 Si NMR (99.3 MHz,
9
bicyclo[2.2.1]heptane [( S, S)-[ H
cording to GP 2, starting from 12 (27.6 mg, 0.300 mmol), ( S)-
2
]-13a]: See Table 2, Entry 3. Ac-
Si
CDCl
3
): δ = –5.51 ppm. IR (ATR): ν˜ = 3055 (w), 2999 (w), 2926
2
0
a (136 mg, 0.660 mmol, 99% D, 94% ee), [(phen)PdMe
2
] (4.8 mg,
) (15 mg, 0.015 mmol), com-
]-13a (112 mg, 74%, 99% D by MS, C /C
(
(
(
s), 2855 (s), 1471 (s), 1435 (s), 1361 (m), 1293 (w), 1264 (w), 1216
m), 1142 (m), 1127 (m), 1074 (m), 1007 (w), 973 (w), 865 (m), 820
+
–
2 2 4
.015 mmol), and [H(OEt ) ] (BAr
Si Si
2
–
1
pound ( S, S)-[ H
2
2
s
=
s), 754 (s), 738 (w), 693 (m), 674 (m), 645 (w), 608 (m) cm
.
+
97:3 by GLC, dr Ͼ 99:1 by GLC, exo/endo Ͼ 99:1 by GLC, Ն99%
ee by HPLC) was obtained as a white solid; m.p. 132 °C (cyclohex-
HRMS (EI): calcd. for C33
43.2632. C33 48Si (500.9): calcd. C 79.13, H 9.66; found C 78.88,
H 9.71.
2 4 9
H48Si [M – C H ] 443.2590; found
4
H
2
2
0
ane); R
[
f
= 0.44 (cyclohexane). [α]
D
= +5.36 (c = 0.560, CHCl
3
),
α]578 = +5.54, [α]546 = +6.43, [α]436 = +10.4, [α]365 = +15.9. HPLC
= 0.35 analysis on a chiral stationary phase (as for unlabeled 13a, see
): δ = 0.85–1.10 (m, 6 above) did not allow separation of meso-13a and the major enanti-
H), 0.96 (s, 18 H), 1.27 (dd, J = 9.5, J = 6.8 Hz, 2 H), 1.42–1.55 omer ( S, S)-[ H
m, 4 H), 1.75 (m , 2 H), 2.08 (m , 2 H), 2.14 (br. t, J = 3.7 Hz, 1 Ͼ99 % ee emerges for ( S, S)-[ H
H), 2.59 (br. s, 1 H), 2.68 (ddd, J = 15.8, J = 10.7, J = 3.0 Hz, 2 CDCl ): δ = 0.85–0.93 (m, 2 H), 0.94–1.03 (m, 2 H), 0.95 (s, 18 H),
H), 2.75 (ddd, J = 16.0, J = 6.8, J = 2.8 Hz, 2 H), 7.10 (dd, J = 1.08 (br. s, 2 H), 1.13 (br. d, J = 9.5 Hz, 2 H), 1.39 (br. d, J =
.5, J = 0.7 Hz, 2 H), 7.16 (ddd, 2ϫ J = 7.5, J = 1.5 Hz, 2 H), 7.24 9.5 Hz, 2 H), 1.71 (m , 2 H), 2.04 (m , 2 H), 2.28 (s, 2 H), 2.65
2
0
20
20
20
Analytical Data for meso-13a: M.p. 110 °C (cyclohexane). R
f
1
(cyclohexane). H NMR (500 MHz, CDCl
3
Si Si
2
2
]-13a. As no minor enantiomer was detectable,
Si Si
2
1
(
c
c
2
]-13a. H NMR (500 MHz,
3
7
c
c
(
ddd, 2ϫ J = 7.5, J = 1.5 Hz, 2 H), 7.49 (dd, J = 7.3, J = 1.4 Hz,
(ddd, J = 15.5, J = 10.2, J = 2.8 Hz, 2 H), 2.71 (ddd, J = 15.5, J
= 6.5, J = 2.8 Hz, 2 H), 7.08 (br. d, J = 7.5 Hz, 2 H), 7.15 (ddd,
2ϫ J = 7.3, J = 1.2 Hz, 2 H), 7.23 (ddd, 2ϫ J = 7.4, J = 1.6 Hz, 2
2
3
1
H) ppm. 13C NMR (125 MHz, CDCl
1.9, 34.0, 36.0, 37.3, 38.0, 41.4, 124.8, 128.4, 128.6, 132.8, 135.6,
50.1 ppm. 29Si NMR (99.3 MHz, CDCl
): δ = –7.24 ppm. IR
3
): δ = 7.9, 18.5, 23.9, 27.7,
13
3
H), 7.47 (dd, J = 7.3, J = 1.6 Hz, 2 H) ppm. C NMR (125 MHz,
1
(
(
(
(
ATR): ν˜ = 3051 (w), 2995 (w), 2925 (s), 2876 (m), 2855 (s), 1470 CDCl
3
): δ = 7.2, 18.5, 23.9, 24.2, 27.7, 36.0, 38.3, 38.7 (t, JC,D
=
s), 1435 (s), 1360 (m), 1292 (w), 1267 (w), 1185 (w), 1140 (m), 1128 19 Hz), 38.7, 124.8, 128.4, 128.5, 132.8, 135.5, 150.1 ppm. 29Si
m), 1074 (m), 1031 (w), 971 (w), 937 (m), 866 (m), 822 (s), 781 NMR (99.3 MHz, CDCl ): δ = –5.60 ppm. IR (ATR): ν˜ = 3054
w), 738 (s), 699 (s), 649 (w), 605 (m), 574 (w) cm . HRMS (EI): (w), 2925 (s), 2854 (s), 2127 (w) (C–D), 1589 (w), 1466 (s), 1434
3
–1
+
calcd. for C33
H48Si
2
[M – C
4
H
9
]
443.2590; found 443.2609.
(s), 1407 (w), 1389 (w), 1361 (m), 1293 (w), 1264 (m), 1216 (m),
Eur. J. Org. Chem. 2008, 2582–2591
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
2589

S. Rendler, R. Fröhlich, M. Keller, M. Oestreich
FULL PAPER
Si
1179 (w), 1141 (m), 1127 (m), 1074 (m), 1008 (w), 974 (m), 865
(1R*,2S*,4R*,5S*)-2,5-Bis[( R*)-1-tert-butyl-1-silaindan-1-yl]bicy-
Si
(
m), 820 (s), 755 (s), 763 (s), 727 (m), 712 (m), 693 (m), 674 (m), clo[2.2.1]heptane (rac-14a) and (2R,6S)-2-[( S)-1-tert-Butyl-1-si-
–
1
Si
6
C
71 (m), 643 (w), 608 (m), 575 (w) cm . HRMS (EI): calcd. for
laindan-1-yl]-6-[( R)-1-tert-butyl-1-silatetralin-1-yl]bicyclo[2.2.1]-
+
33
H
46
D
2
Si
2
[M – C
4
H
9
] ] 445.2716; found 445.2719.
heptane (meso-14a): See Table 2, Entry 6. According to GP 2, start-
ing from 12 (27.6 mg, 0.300 mmol), rac-8a (126 mg, 0.660 mmol),
Si
(
1R*,2S*,4R*,5S*)-2,5-Bis[( S*)-1-isopropyl-1-silatetralin-1-yl]-
+
–
[
(
1
(phen)PdMe
2
] (4.8 mg, 0.015 mmol), and [H(OEt
15 mg, 0.015 mmol), a mixture of compounds rac-14a and meso-
4a (124 mg, 87%, C /C = 60:40 by GLC, dr = 99:1 by GLC,
2 2 4
) ] (BAr )
Si
bicyclo[2.2.1]heptane (rac-13b) and (2R,6S)-2-[( R)-1-Isopropyl-1-
Si
silatetralin-1-yl]-6-[( S)-1-isopropyl-1-silatetralin-1-yl]bicyclo-
2
s
[2.2.1]heptane (meso-13b): See Table 2, Entry 4. According to GP
exo/endo Ͼ 99:1 by GLC) was obtained as a white solid that was
inseparable by flash chromatography; m.p. 114 °C (cyclohexane);
2
0
, starting from 12 (27.6 mg, 0.300 mmol), rac-2b (126 mg,
+
.660 mmol),[(phen)PdMe
2
](4.8 mg,0.015 mmol),and[H(OEt
) (15 mg, 0.015 mmol), a mixture of compounds rac-13b and
meso-13b (124 mg, 87%, C /C = 59:41 by GLC, dr Ն 98:2 by GLC,
exo/endo Ͼ 99:1 by GLC) was obtained as a colorless, highly vis-
cous oil that was inseparable by flash chromatography. R = 0.46
= 33.2 (minor diastereomer), 34.1
meso-13b), 37.1 min (rac-13b); HPLC (Daicel Chiralcel OD-RH,
2 2
) ] -
R
f
= 0.46 (cyclohexane); GLC (SE-54): t
R
= 29.8 (minor dia-
–
(BAr
4
stereomer), 30.3 (meso-14a), 32.2 min (rac-14a). IR (ATR): ν˜ =
055 (w), 2995 (w), 2926 (s), 2854 (s), 1591 (w), 1470 (s), 1440 (s),
388 (w), 1361 (m), 1312 (w), 1185 (w), 1159 (w), 1117 (s), 1058
2
s
3
1
(
5
7
f
w), 1030 (w), 1007 (w), 962 (w), 908 (s), 735 (s), 678 (m), 619 (m),
(cyclohexane); GLC (SE-54): t
R
–1
70 (w) cm . C31
8.45, H 9.21.
H44Si
2
(472.9): calcd. C 78.74, H 9.38; found C
(
–
1
2
0 °C, MeCN/H
2
O, 85:15, flow rate = 0.80 mLmin , λ = 230 nm):
1
t
R
= 18.7 (meso-13b), 20.2 [(SiR, R)-13b], 23.2 (minor dia-
Si
Analytical Data for rac-14a: H NMR (500 MHz, CDCl ): δ = 0.70
3
Si Si
(br. s, 2 H), 0.94–1.03 (m, 4 H), 0.97 (s, 18 H), 1.10 (dd, 2ϫ J =
.6 Hz, 2 H), 1.50–1.65 (m, 4 H), 2.19 (br. d, J = 2.4 Hz, 2 H),
stereomer), 24.7 (minor diastereomer), 28.6 min [( S, S)-13b]. IR
8
3
7
(
(
ATR): ν˜ = 3053 (w), 2995 (w), 2921 (s), 2860 (s), 1589 (w), 1463
s), 1434 (s), 1293 (w), 1266 (w), 1216 (m), 1141 (m), 1127 (m),
.00–3.07 (m, 4 H), 7.10–7.16 (m, 2 H), 7.17–7.23 (m, 2 H), 7.23–
1
3
.29 (m, 2 H), 7.48 (d, J = 7.3 Hz, 2 H) ppm. C NMR (125 MHz,
1074 (m), 995 (m), 972 (m), 908 (s), 881 (s), 781 (m), 754 (s), 707
–1
3
CDCl ): δ = 5.6, 18.4, 24.5, 27.4, 32.4, 37.6, 38.1, 39.5, 125.2, 125.6,
(s), 685 (m), 650 (m), 624 (s), 609 (s) cm . C31
H
44Si
2
(472.9): calcd.
2
9
1
2
33.5, 137.0, 154.4 ppm. Si NMR (99.3 MHz, CDCl
3
): δ =
C 78.74, H 9.38; found C 78.51, H 9.67.
+
4.27 ppm. HRMS (EI): calcd. for C31 [M – C H ]
H44Si
2
4 9
1
Analytical Data for rac-13b: H NMR (500 MHz, CDCl
3
): δ = 415.2277; found 415.2308.
0
.82–0.94 (m, 2 H), 0.90 (br. s, 2 H), 0.96 (d, J = 7.2 Hz, 6 H), 1.03
1
Analytical Data for meso-14a: H NMR (500 MHz, CDCl
3
): δ =
(
(
d, J = 7.2 Hz, 6 H), 0.98–1.04 (m, 4 H), 1.06–1.14 (m, 2 H), 1.42
br. dd, J = 10.9, J = 8.5 Hz, 2 H), 1.52 (ddd, J = 11.8, J = 7.9, J
0
9
1
7
.74 (br. s, 2 H), 0.94–1.03 (m, 4 H), 0.99 (s, 18 H), 1.20 (dd, J =
.5, J = 6.3 Hz, 2 H), 1.50–1.65 (m, 4 H), 2.12 (br. t, J = 3.5 Hz,
H), 2.37 (br. s, 1 H), 3.00–3.07 (m, 4 H), 7.10–7.16 (m, 2 H),
.17–7.23 (m, 2 H), 7.23–7.29 (m, 2 H), 7.48 (d, J = 7.3 Hz, 2
H) ppm. C NMR (125 MHz, CDCl
2.5, 33.3, 37.4, 38.0, 41.5, 125.3, 125.6, 129.1, 133.4, 137.2,
=
3.2 Hz, 2 H), 1.79–1.87 (m, 2 H), 1.88–1.96 (m, 2 H), 2.23 (br.
d, J = 2.8 Hz, 2 H), 2.65–2.75 (m, 4 H), 7.08 (dd, J = 7.5, J =
0
2
.6 Hz, 2 H), 7.14 (ddd, 2ϫ J = 7.3, J = 1.0 Hz, 2 H), 7.22 (ddd,
ϫ J = 7.5, J = 1.4 Hz, 2 H), 7.42 (dd, J = 7.2, J = 1.2 Hz, 2
1
3
3
): δ = 5.7, 18.4, 27.5, 31.1,
3
1
13
3
H) ppm. C NMR (125 MHz, CDCl ): δ = 7.3, 12.9, 18.1, 18.3,
2
9
54.2 ppm. Si NMR (99.3 MHz, CDCl
3
): δ = 22.90 ppm. HRMS
415.2277; found 415.2287.
2
1
3.6, 25.8, 35.9, 37.6, 37.8, 38.6, 125.0, 128.5, 132.9, 135.0,
+
(
EI): calcd. for C31
H44Si
2
[M – C
4
H
9
]
49.9 ppm. 29Si NMR (99.3 MHz, CDCl
): δ = –7.07 ppm. HRMS
429.2434; found 429.2394.
3
+
(EI): calcd. for C31
H44Si
2
[M – C
3
H
7
]
Crystallographic Data: Data sets were collected with a Nonius-
KappaCCD diffractometer. Programs used: data collection COL-
1
Analytical Data for meso-13b: H NMR (500 MHz, CDCl
0
1
(
3
): δ =
[33]
LECT (Nonius B.V., 1998), data reduction Denzo-SMN, absorp-
.83–1.16 (m, 22 H), 1.38–1.46 (m, 2 H), 1.49–1.53 (m, 2 H), 1.79–
.96 (m, 4 H), 2.17 (br. t, J = 3.6 Hz, 1 H), 2.43 (s, 1 H), 2.66–2.74
[34]
[35]
tion correction Denzo, structure solution SHELXS-97, struc-
[36]
[37]
ture refinement SHELXL-97,
graphics SCHAKAL.
CCDC-
m, 4 H), 7.06–7.10 (m, 2 H), 7.12–7.17 (m, 2 H), 7.20–7.25 (m, 2
6
67979 (for rac-7a), -668281 (for rac-11), -668282 (for meso-13a),
13
H), 7.40–7.45 (m, 2 H) ppm. C NMR (125 MHz, CDCl
3
): δ =
.6, 13.0, 18.2, 18.4, 23.6, 32.7, 33.0, 35.9, 37.4, 37.5, 40.4, 125.0,
28.5, 133.0, 135.1, 149.9 ppm. 29Si NMR (99.3 MHz, CDCl
): δ
–8.51 ppm. HRMS (EI): calcd. for C31 [M – C
Si Si
and -668283 [for ( R, R)-13a or rac-13a] contain the supplemen-
tary crystallographic data for this paper. These data can be ob-
tained free of charge from The Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/data_request/cif.
7
1
3
+
=
H
44Si
2
3 7
H ]
429.2434; found 429.2451.
Supporting Information (see also the footnote on the first page of
this article): Copies of NMR spectroscopic data, HPLC and GLC
(if any) traces of new compounds, and experimental details for the
Si
(
[
1S,2R,4S,5R)-2,5-Bis[( R)-1-isopropyl-1-silatetralin-1-yl]bicyclo-
2.2.1]heptane [( R, R)-13b]: See Table 2, Entry 5). According to
Si Si
Si
GP 2, starting from 12 (29.5 mg, 0.320 mmol), ( R)-2b (133 mg, preparation of rac-8b.
0
.700 mmol, 96% ee), [(phen)PdMe ] (5.1 mg, 0.016 mmol), and
2
+
–
Si Si
[H(OEt
2
)
2
] (BAr
4
) (16 mg, 0.016 mmol), compound ( R, R)-13b
/C = 98:2 by GLC, dr = 99:1 by GLC, exo/endo
Acknowledgments
(143 mg, 95%, C
2
s
Ͼ 99:1 by GLC, Ն99% ee by HPLC) was obtained as a colorless,
20
20
This research was funded by the Deutsche Forschungsgemeinschaft
(DFG) (Emmy Noether-Program, Oe 249/2-3 and Oe 249/2-4), the
Aventis Foundation (Karl-Winnacker-Stipendium to M. O., 2006–
2008) and the Fonds der Chemischen Industrie (predoctoral fellow-
ship to S. R., 2005–2007).
highly viscous oil. [α]
D
= –33.2 (c = 0.600, CHCl
3
), [α]578 = –34.7,
20
20
20
[
α]546 = –39.7, [α]436 = –71.3, [α]365 = –121. The minor enantiomer
Si Si
(
S, S)-13b was not detected by HPLC analysis on a chiral station-
Si Si
ary phase (see above). Thus, Ͼ99% ee emerges for ( R, R)-13a.
IR (ATR): ν˜ = 3054 (w), 2996 (w), 2921 (s), 2859 (s), 1589 (w),
1463 (s), 1434 (s), 1406 (w), 1293 (w), 1264 (m), 1216 (m), 1158
(
(
(
w), 1141 (m), 1127 (m), 1074 (m), 993 (m), 972 (m), 912 (s), 880
s), 804 (m), 781 (m), 755 (s), 738 (s), 7.26 (s), 706 (s), 680 (m), 628
s), 597 (m), 562 (m), 518 (m) cm .
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–1
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www.eurjoc.org
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2008, 2582–2591

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[
[
[
[
[
[
[
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[
16] “Chirality transfer from silicon to carbon” requires that a co-
valent bond is cleaved and formed at the chiral silicon center
in a reagent-controlled reaction involving functionalized silanes
with silicon-centered chirality and prochiral substrates. Any in-
Published Online: April 2, 2008
Eur. J. Org. Chem. 2008, 2582–2591
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
2591