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CrCl2-Promoted Stereospecific and Stereoselective Alkyl- and Silylcyclopropanation of α,β-Unsaturated Amides

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posted on 16.05.2008 by José M. Concellón, Humberto Rodríguez-Solla, Carmen Méjica, Elena G. Blanco, Santiago García-Granda, M. Rosario Díaz
An efficient chromium-promoted alkyl- or silylcyclopropanation of α,β-unsaturated amides is described. These reactions can be carried out on (E)- or (Z)-α,β-enamides in which the C−C double bond is di-, or trisubstituted. This process takes place with total stereospecificity and the new stereogenic center is generated with high or total stereoselectivity. Some synthetic applications of the obtained silylcyclopropyl amides are also reported. Two mechanisms based on the generation of carbenoid or carbene complexes have been proposed to explain this cyclopropanation reaction.