Cobalt-Catalyzed Chemo- and Enantioselective Hydrogenation of Conjugated Enynes.

Asymmetric hydrogenation is one of the most powerful methods for the preparation of single enantiomer compounds. However, the chemo- and enantioselective hydrogenation of the relatively inert unsaturated group in substrates possessing multiple unsaturated bonds remains a challenge. We herein report a protocol for the highly chemo- and enantioselective hydrogenation of conjugated enynes while keeping the alkynyl bond intact. Mechanism studies indicate that the accompanying Zn 2+ generated from zinc reduction of the Co II complex plays a critical role to initiate a plausible Co I /Co III catalytic cycle. This approach allows for the highly efficient generation of chiral propargylamines (up to 99.9% ee and 2000 S/C) and further useful chemical transformations.