Rhodium-Catalyzed Reductive Mannich Coupling of Vinyl Ketones to <i>N</i>-Sulfonylimines Mediated by Hydrogen

Catalytic hydrogenation of methyl vinyl ketone (MVK) and ethyl vinyl ketone (EVK) in the presence of N-(o-nitrophenylsulfonyl)imines 8a−13a at ambient pressure with tri-2-furylphosphine-ligated rhodium catalysts enables formation of Mannich products 8b−13b and 8c−13c with moderate to good levels of syn-diastereoselectivity. As revealed by an assay of various N-protecting groups, excellent yields of reductive Mannich product also are obtained for N-arylimines 1a−4a, although diminished levels of syn-diastereoselectivity are observed. Coupling of MVK to imine 8a under a deuterium atmosphere provides deuterio-8b, which incorporates a single deuterium atom at the former enone β-position.