Nitrogen ylide-mediated cyclopropanation of lactams and lactones

Cyclopropanation of alpha,beta-unsaturated delta-lactams and delta-lactones mediated by nitrogen ylides is described. The process tolerates different alkyl halides and gives efficiently bicyclo[4.1.0]heptanes in a totally stereoselective manner. On the other hand, epsilon-lactams under our experimental conditions suffer a novel process involving a skeletal reorganization to give a bicyclic[3.3.0] system. (C) 2010 Elsevier Ltd. All rights reserved.