Stereospecific and Stereoselective Alkyl and Silylcyclopropanation of α,β-Unsaturated Amides

A novel chromium-promoted alkyl- and silyl cyclopropanation of (E)- or (Z)-α,β-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.