(E)-Alpha,beta-unsaturated esters can be obtained with complete stereoselectivity by reaction of different aldehydes and ethyl dibromoacetate promoted by SmI(2) or CrCl(2). The transformation takes place as two sequential reactions: an aldol-type reaction and a beta-elimination reaction.

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.

We describe herein a CrCl(2)-promoted cyclopropanation of alpha,beta-unsaturated amides. This reaction can be carried out on (E)- or (Z)-alpha,beta-enamides in which the C-C double bond is di-, tri-, or tetrasubstituted. In all cases the process is completely stereospecific and only a single diastereoisomer is obtained. In addition, cyclopropyl ketones were readily prepared by reaction of the cyclopropanecarboxamides (derived from morpholine) obtained with a range of organolithium compounds. A mechanism has been proposed to explain the cyclopropanation reaction.

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