Monophasic Catalytic System for the Selective Semireduction of Alkynes

A highly efficient semireduction of alkynes has been developed. Using 0.5–2 mol % of a copper catalyst, semireduction can be accomplished with a wide range of substrates, including both internal and terminal alkynes without over-reduction. The new method has excellent chemoselectivity, and the semireduction can be accomplished even in the presence of nitro and aryl iodo groups. Finally, commercial availability of a catalyst precursor adds to the appeal of the new catalytic system.