Enantioselective Iridium-Catalyzed Imine Vinylation: Optically Enriched Allylic Amines via Alkyne−Imine Reductive Coupling Mediated by Hydrogen

Abstract

The first asymmetric iridium-catalyzed C−C bond forming hydrogenation is described. By simply hydrogenating alkynes in the presence of N-arylsulfonyl imines using an iridium catalyst modified by (R)-Cl,MeO-BIPHEP, one may obtain the corresponding allylic amines 1b−21b in highly optically enriched form (92−99% ee). This protocol circumvents the use of preformed vinyl metal reagents and is applicable to aromatic, heteroaromatic, and aliphatic N-arylsulfonyl aldimines 1a−16a. The reductive coupling products, allylic amines 1b−21b, are produced as single geometrical isomers (≥99:1, E:Z). Nonsymmetric alkynes couple to imines 8a and 12a under standard conditions with excellent levels of regioselection. Absolute stereochemical assignment of allylic amines 1b−21b is based upon single-crystal X-ray diffraction analysis of 22b, the p-bromophenylsulfonyl analogue of adduct 1b, using the anomalous dispersion method. A stereochemical model accounting for the observed sense of absolute stereoinduction and regioselectivity is provided.