Intermolecular cyclopropanation versus CH insertion in Rh-II-catalyzed carbenoid reactions

The product ratio of intermolecular insertion and cyclopropanation in trans ition metal-catalyzed diazo decompositions depends strongly upon the metal, its ligands and upon the substituents of the diazo compound. Ethyl diazoac etate (2a) reacts with cyclohexene (1) almost exclusively by cyclopropanati on. However, diazomalonate (2d) and methyl 2-diazophenylacetate (2e) in the presence of Rh-II catalysts exhibit a marked tendency towards allylic CH i nsertion. With 1,4-cyclohexadiene (6), methyl 2-diazophenylacetate (2e) in the presence of chiral Rh-II catalysts affords the allylic insertion produc t 7 in almost quantitative yield and with up to 74% ee. (C) 2000 Elsevier S cience Ltd. All rights reserved.