ASYMMETRIC REDUCTION OF AROMATIC KETONES .1. ENANTIOSELECTIVE SYNTHESIS OF DENOPAMINE

Asymmetric reduction of the N-protected amino ketone (2) with several chiral reducing agents, i.e., (R)-(+)-2-amino-3-methyl-1,1-diphenylbut anol (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 denopamin e (1) enantioselectively. Reduction of 2f by method B in tetrahydrofur an at 2-3-degrees-C gave the best result (88% ee with 95% chemical yie ld).