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

Abstract

Chemoselective enantiodivergent reduction of N-benzyl-α-keto amides catalyzed by chiral oxido-vanadium(V) complexes derived from a reduced form of N-salicylidene L-tert leucinate 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 (R isomer, 74–99% ee) or catecholborane (S isomer, 60–90% ee), a handy approach for complementary asymmetric reduction of α-keto amides can be attained.