ALLENES AND ACETYLENES .28. ON THE MECHANISM OF REDUCTION OF PROPARGYLIC ETHERS AND ACETATES WITH ORGANOCUPRATES

The amounts of substitution and reduction products from the reactions of 2 types of propargylic methyl ethers and acetates with organocuprates were determined. The methyl ethers give rise to more of the reduction products than the acetates. Reduced allenes are formed by hydrolysis of an organometallic intermediate whereas reduced acetylenes are formed mainly by another mechanistic pathway. The mechanisms of these reduction reactions are discussed in terms of stabilized, transient Cu(III)-intermediates and concerted .beta.-hydride transfer in the formation of the acetylene. [These reactions can be applied to the synthesis of allenic prostaglandins and amines.].