Enantiodivergent reduction of alpha-keto amides catalyzed by high valent, chiral oxido-vanadium(v) complexes

Chemoselective enantiodivergent reduction ofN-benzyl-alpha-keto amides catalyzed by chiral oxido-vanadium(v) complexes derived from a reduced form ofN-salicylidenel-tertleucinate can be achieved with good yields and good to high enantioselectivities. These chiral complexes were utilized in catalyzing the enantioselective synthesis of (R)-N-benzyl-mandelamide with pinacolborane and (S)-N-benzyl-mandelamide with catecholborane from the corresponding ketone precursors. A series of 12 different solvents and 8 different reducing agents were examined. By the use of pinacolborane (Risomer, 74-99% ee) or catecholborane (Sisomer, 60-90% ee), a handy approach for complementary asymmetric reduction of alpha-keto amides can be attained.