Stereoselective Synthesis of Secondary Alkyllithiums and Their Application to Stereoselective Cuprations or Intramolecular Carbolithiations for the Stereoselective Synthesis of Alkylidene­cyclobutanes

Abstract

Secondary alkyllithium reagents were prepared stereoselectively via an iodo–lithium exchange by using tert-butyllithium. The resulting secondary alkyllithiums were converted directly into the corresponding alkylcopper reagents by transmetalation with copper(I) bromide–triethyl phosphite [CuBr·P(OEt)3] with retention of configuration and without significant loss of stereoselectivity. The resulting alkylcopper reagents were used for carbocupration or acylation reactions. In addition, a new intramolecular carbolithiation of secondary alkyllithium reagents possessing a remote alkyne moiety was also investigated, allowing the stereoselective production of alkylidenecylobutane derivatives with very high stereocontrol.