Reactions of 2,2-dibromocyclopropyl carboxylic acids with methyllithium

Abstract

For reactions of 2,2-dibromocyclopropyl carboxylic acids with methyllithium, the course of reaction depends mainly on the position of the carboxyl group. When the COOH group is directly attached to the gem-dibromocyclopropane ring MeLi generally attacks the gem-dibromo moiety and gives the corresponding monobromocyclopropane as the principal product. When the reaction is performed above −80 °C the monobromides are formed stereospecifically in the trans configuration. The highest yields, as high as 80–90%, are obtained at 0 °C. When the carboxyl group is not directly attached to the cyclopropane ring most of the MeLi is consumed in an acid–base reaction with the COOH group.