Efficient enantioselective synthesis of cyclopropanes from sulfonylpyrazolines

Full text of DOI:10.1080/10426500590913014

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Phosphorus, Sulfur, and Silicon
and the Related Elements
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Efficient Enantioselective
Synthesis of Cyclopropanes
from Sulfonylpyrazolines
Jose´ L. Garci´a Ruano a , Ana M. Marti´n Castro a
Esther Torrente a a
&
a Departamento de Qui´mica Orga´nica ,
Universidad Auto´noma de Madrid , Madrid, Spain
Published online: 16 Aug 2006.
To cite this article: Jose´ L. Garci´a Ruano , Ana M. Marti´n Castro & Esther Torrente
(2005) Efficient Enantioselective Synthesis of Cyclopropanes from Sulfonylpyrazolines,
Phosphorus, Sulfur, and Silicon and the Related Elements, 180:5-6, 1445-1446, DOI:
10.1080/10426500590913014
To link to this article: http://dx.doi.org/10.1080/10426500590913014
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Phosphorus, Sulfur, and Silicon, 180:1445–1446, 2005
Copyright © Taylor & Francis Inc.
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426500590913014
Efficient Enantioselective Synthesis of Cyclopropanes
from Sulfonylpyrazolines
´
´
´
Jose L. Garcıa Ruano
Ana M. Martın Castro
Esther Torrente
Departamento de Qu´ımica Orga´nica, Universidad Auto´noma de Madrid,
Madrid, Spain
INTRODUCTION
Sulfinyl acrylonitriles have been shown to be the best monoactivated
vinylsulfoxides in asymmetric Diels–Alder reaction,1 and very efficient
as chiral dipolarophiles in their reactions with diazoalkanes,2 which
afford sulfinylpyrazolines in a completely regioselective and stereose-
lective manner in high yields.
RESULTS
We herein report the use of our previously synthesized enantiopure
sulfinyl cyanopyrazolines (1)2 as the starting products for the prepara-
tion of enantiomerically pure cyclopropane derivatives in a short syn-
thetic sequence. The transformation involves the completely stereose-
lective extrusion of the nitrogen from sulfonyl pyrazolines as the key
step.
Reaction of compounds 1 with m-CPBA readily afforded sulfones 2.
When they were refluxed in toluene, they evolved into cyclopropanes 3
in almost quantitative yields. These reactions took place with a com-
plete retention of the configuration at all the chiral centers, even in
case of the tert-butyl derivatives. The presence of both sulfonyl and
cyano groups seems to be necessary to complete this reaction success-
fully. Elimination of the sulfonyl group with Mg/MeOH provided opti-
cally pure cyanocyclopropyl derivatives 4. The presence of the SO2Tol
moiety in 3 was applied to the synthesis of alkylidene cyclopropanes
such as 5 by treatment of 3 under the conditions reported by Julia.
Received July 9, 2004; accepted October 5, 2004.
Address correspondence to Esther Torrente, Departamento de Qu´ımica Orga´nica,
Universidad Auto´noma de Madrid, Cantoblanco, 28049 Madrid, Spain. E-mail: esther.
torrente@uam.es
1445

1446
J. L. Garc´ıa Ruano et al.
Both transformations of cyclopropanes 3 proceeded in moderate to high
yields with complete retention of the configuration at all the chiral cen-
ters of the resulting molecules.3
REFERENCES
[1] J. L. Garc´ıa Ruano, C. Alemparte, A. M. Mart´ın Castro, H. Adams, and J. H. Rodr´ıguez
Ramos, J. Org. Chem., 65, 7938 (2000).
[2] J. L. Garc´ıa Ruano, D. Blanco, A. M. Mart´ın Castro, S. A. Alonso, M. R. Mart´ın, and
J. H. Rodr´ıguez Ramos, Org. Lett., 3, 3173 (2001).
[3] J. L. Garc´ıa Ruano, A. M. Mart´ın Castro, S. A. Alonso, M. R. Mart´ın, and E. Torrente,
Org. Lett., 6, 4945 (2004).