Reactivite des β-cyclopropyl α-enones—II : Etude de l'addition des diorganocuprates

Abstract

The lithium dimethylcuprate addition on six substituted bicyclo[3.1.0]hex-3-en-2-ones was studied. For five ketones, both expected 1,4-addition compound and 1,6-addition compounds are obtained. The last products result from a cyclopropane bond cleavage. There is no evidence for a correlation between the radical anion half-lives and the formation of ring opened compounds. In many case, the broken bond is different from that which is concerned in the reduction by solvated electrons in liquid ammonia. So the 1,6-addition products do nor probably arise through an electron transfer mechanism. However, a nucleophilic attack of the substrate by a copper atom followed by a reductive elimination inside the complex can be supposed; then both the nature and stereochemistry of reaction products can be explained.