Vinyl copper(I) compounds Part I: Stereospecific addition of heterocuprates to 1‐alkynes in tetrahydrofuran

Abstract

Abstract In this paper a study on the reactivity of various heterocuprates [RCuY]MgX 1 towards 1‐alkynes R′−C≡CH 2 in tetrahydrofuran is presented. In most cases a smooth cis addition was observed in this solvent generally leading, after protic work‐up, to terminal alkenes RR′CCH 2 4a or sometimes to mixtures of alkenes 4a and non‐terminal E ‐alkenes R′CHCHR 4b in excellent yields. Except for the reaction of [ t ‐BuCuBr]MgCl with Ph−C≡C−H no evidence was obtained of proton abstraction from the terminal alkynes 2 by the cuprates. The influence of CuBr and LiBr on the course of the addition reaction was studied in some cases.