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