Allylic amines via iridium-catalyzed C-C bond forming hydrogenation: Imine vinylation in the absence of stoichiometric byproducts or metallic reagents

Exposure of aromatic, heteroaromatic, and aliphatic N-arylsulfonyl aldimines 1a-12a in toluene solution at 60 degrees C to 2-butyne and hydrogen at ambient pressure in the presence of a cationic iridium(I) catalyst modified by BIPHEP enables formation of reductive coupling products, allylic amines 1b-12b, in good isolated yields as single geometrical isomers (> 95:5, E:Z). The nonsymmetric alkynes 4-methyl-2-pentyne couple to imines 1b-12b under standard conditions with complete levels of regioselection. Hydrogenative coupling of 2-hexyne to imines 6a, 12a, and 13a delivers allylic amines 15b, 16b, and 18b in 10:1 regioisomeric ratios in each case. As revealed by H-2 NMR analysis, reductive coupling of 2-butyne to imine 2a under an atmosphere of elemental deuterium provides deuterio-2b, which incorporates deuterium at the vinylic position (83% H-2) and at the allylic methyl groups (5% H-2). An equal distribution of deuterium at the allylic methyl groups suggests H-D exchange at the propargylic positions of 2-butyne in advance of C-C coupling.