Asymmetric Reduction of Aromatic Ketones. I. Enantioselective Synthesis of Denopamine

Abstract

Asymmetric reduction of the N-protected amino ketone (2) with serveral chiral reducing agents, i.e., (R)-(+)-2-amino-3-methyl-1, 1-diphenylbutanol (6)-borane complex (method A), (S, S')-N, N'-dibenzoylcystine (7)-LiBH₄-ROH complex (method B), and sodium (S)-prolinate-borane complex (8) (method C), was investigated in an attempt to synthesize denopamine (1) enantioselectively. Reduction of 2f by method B in tetrahydrofuran at 2-3°C gave the best result (88% ee with 95% chemical yield).