An Iridium Catalytic System Compatible with Inorganic and Organic Nitrogen Sources for Dual Asymmetric Reductive Amination Reactions

Asymmetric reductive amination (ARA) is one of the most promising methods for the synthesis of chiral amines. Herein we report our efforts on merging two ARA reactions into a single-step transformation. Catalyzed by a complex formed from iridium and a steric hindered phosphoramidite, readily available and inexpensive aromatic ketones initially undergo the first ARA with ammonium acetate to afford primary amines, which serve as the amine sources for the second ARA, and finally provide the enantiopure C₂ -symmetric secondary amine products. The developed process competently enables the successive coupling of inorganic and organic nitrogen sources with ketones in the same reaction system. The Brønsted acid additive plays multiple roles in this procedure: it accelerates the formation of imine intermediates, minimizes the inhibitory effect of N-containing species on the iridium catalyst, and reduces the primary amine side products.

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 Zn²⁺ 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.