Organocatalyzed cyclopropanation of alpha-substituted alpha,beta-unsaturated aldehydes: enantioselective synthesis of cyclopropanes bearing a chiral quaternary center.
An enantioselective cyclopropanation of alpha-substituted alpha,beta-unsaturated aldehydes with bromomalonate has been successfully developed through a domino Michael/alpha-alkylation strategy. The method allows the efficient formation of cyclopropanes bearing a quaternary carbon stereocenter at the alpha-position of the aldehydes by using iminium/enamine catalysis and gives a nice extension on the organocatalytic cyclopropanation of bromomalonate and alpha,beta-unsaturated aldehydes previously reported by other groups. Very good yields (up to 81%) and enantioselectivities (up to 97% ee) have been obtained. The optically active cyclopropane derivatives are of high synthetic interest as useful targets for further elaboration into more complex structures.
Institut Charles Gerhardt Montpellier, UMR 5253 CNRS-UM2-UM1-ENSCM, Ecole Nationale Supérieure de Chimie, 8 Rue de l'Ecole Normale, 34296 Montpellier Cedex 5, France.
Vincent
V
Terrasson
Arie
A
van der Lee
Renata Marcia
RM
de Figueiredo
Jean Marc
JM
Campagne