Sterelospecific and stereoselective alkyl and silylcyclopropanation of α,β-unsaturated amides

A novel chromium-promoted alkyl-and silyl cyclopropanation of (E)- or (Z)-alpha,beta-unsaturated amides in which the C-C double bond is di-, or trisubstituted is described. This process takes place with total stereospecificity, and the new stereogenic center is generated with high or total stereoselectivity. A mechanism is proposed to explain the cyclopropanation reaction.