O
conclusion was further supported by the observation that only a
trace of the carbene dimer ( < 1%) could be detected by H
NMR analysis of the crude reaction mixtures. Finally, perform-
ing the reaction at 80 °C simply lead to an increased rate without
a change in product outcome or ratio.
1
Ph
1 + 2
OH
R
H
The reaction of equimolar amounts of 1a and 2a in C6D6 was
monitored by 31P NMR spectroscopy. At no time could any
‘free’ triphenylphosphine or zwitterionic intermediates be
10
Michael
addition
1
detected. Careful H NMR analysis of the crude mixture after
cessation of the reaction revealed the presence of 3a, 9a, Ph3PO
and unreacted 2a. All 1a had been consumed affording 3a and
9a in a 77:22 ratio. The remaining 1% constituted the cis-
cyclopropane. Formation of Ph3PO (75%) parallels the yield of
the cyclopropane as expected. Most important was the observa-
tion that 22% unreacted 2a remained and parallels 9a formation
(22%). This observation suggests that formation of 9a is
catalytic in ylide. Indeed, analysis of all crude reaction mixtures
Ph
H+
R1
R2
O
–
Cyclisation
–Ph3P=O
H
Cyclopropanes
R
H
Ph3P
O
11
Scheme 1
1
by 31P and H NMR spectroscopies showed the same trend.
Blank reactions showed that formation of 9a–c was not
promoted by Ph3PO. We have evidence that the rearrangement
1a ? 9a is not promoted by ‘free’ Ph3P liberated during the
ylide reaction, e.g. addition of excess Ph3P to the reaction
mixture containing 1a and 2a failed to dramatically change
product outcome. Based on these initial findings we suggest that
formation of 9a in the reaction of 1a with 2a is promoted by the
ylide acting as a weak base5 in a catalytic manner. Base
catalysed rearrangement (Kornblum–De La Mare decomposi-
tion) of cyclic peroxides has been reported previously and is
initiated by removal of a proton from the carbon adjacent to the
O–O linkage.6 Finally, the observation that the more sterically
hindered 2c affords less cyclopropane 3c when compared to that
for 2b in identical solvents suggests that there is a steric
component to the two competing processes.
Financial support in the form of set-up grants (Adelaide and
Monash Universities, D. K. T.) and the ARC (E. R. T. T.) is
greatly acknowledged. Assistance from Dr S. M. Pyke (Ade-
laide) in NMR spectral analysis is also acknowledged while Dr
P. Perlmutter (Monash University) is thanked for co-super-
vision of T. J. R.
Notes and References
* E-mail: dtaylor@chemistry.adelaide.edu.au
† All new compounds have been fully characterised by elemental analysis,
spectroscopy and mass spectrometry.
¯
‡ Crystal data: C20H20O3, triclinic, space group P1 with a = 7.952(3),
18.417(4), c 5.680(2) Å, a 90.51(2), b 92.28(3),
b
=
=
=
=
g = 85.25(3)°, U = 828.4(4) Å3, Z = 2, Dc = 1.236 g cm23 and m = 0.82
cm21. Single-crystal X-ray diffraction data were collected at 293 K on a
Rigaku AFC6R diffractometer (Mo-Ka radiation) with q/2w scans, 3 < q
< 27.5°. The structure was solved with SIR92 and refined with the
TEXSAN Structure Analysis Package (Molecular Structure Corporation,
1985) of crystallographic programs. A total of 937 reflections with I !
3.0s(I) were used in the refinement which converged with R = 0.063 and
A significant mechanistic finding was the observation of the
1
trans-alcohol 10 intermediate during H NMR monitoring of
these reactions. Indeed, we were able to isolate a quantity of 10
from the reaction mixture and demonstrate that it lead to the
observed cyclopropanes and no 1,2-diketone upon addition of
ylid. Although the reaction manifold is complicated by many
factors, Scheme 1 depicts a general mechanistic overview.
Interaction of 1 and 2 leads in a rate-limiting step to the
formation of the key intermediate 10. Michael addition of the
ylide to 10, followed by cyclisation, proton transfer and
extrusion of triphenylphosphine oxide from 11 affords the
observed cyclopropanes. In competition with this process is the
known cyclisation6 of (Z)-10 via the hemi-acetal and rearrange-
ment leading to formation of 9.
Synthetically, this novel reaction has several advantages over
existing methods7 for cyclopropane formation involving phos-
phorus ylides, as functionalised cyclopropanes are formed in a
highly diastereoselective manner in excellent yields. We are
currently evaluating the reactions of various 1,2-dioxines, alkyl
hydroperoxides and disulfides with a variety of stabilised and
non-stabilised ylides (phosphorus, sulfur etc.) and full mecha-
nistic details will be presented in due course.
Rw
=
0.050 {1/[s2(F) + 0.006F2]}. CCDC 182/708.
1 W. Adam and A. Treiber, J. Org. Chem., 1994, 59, 840.
2 W. Adam, H. M. Harrer and A. Treiber, J. Am. Chem. Soc., 1994, 116,
7581.
3 M. Matsumoto, S. Dobashi, K. Kuroda and K. Kondo, Tetrahedron,
1985, 41, 2147.
4 G. Rio and J. Berthelot, Bull. Soc. Chim. Fr., 1969, 5, 1664.
5 A. W. Johnson, in Organic Chemistry, (Ylid Chemistry), ed. A. T.
Bloomquist, Academic Press, New York, 1966, vol. 7, pp. 64–70.
6 N. Kornblum and H. E. De La Mare, J. Am. Chem. Soc., 1951, 73, 881;
M. G. Zabgorski and R. G. Salomon, J. Am. Chem. Soc., 1980, 102, 2501;
M. E. Sengul, Z. Ceylan and M. Balci, Tetrahedron, 1997, 53, 10 401.
7 D. B. Denny, J. J. Vill and M. J. Boskin, J. Am. Chem. Soc., 1962, 84,
3944; ref. 5, pp. 111–113 and 116–120 and references cited therein.
Received in Cambridge, UK, 13th, October 1997; 7/07360G
334
Chem. Commun., 1998