Design of new axially chiral NADH mimics. Mechanistic investigation of the enantioselective hydride transfer

This paper reports the design of a new axially chiral NADH model which relies on the configurational control around the C3-CO chiral axis by means of a chiral relay installed on the cyclic structure. The conformational and configurational control of the lactam moiety was successfully achieved affording two conformational diastereoisomers (aS,S)-1 and (aR,S)-1 in a ratio of 95:5, respectively. Reduction of methyl benzoylformate with model 1 afforded (R)-methyl mandelate in up to 84% e.e. The stereoselective synthesis of 4-deuterated model 1 allowed us to establish that this enantioselective reduction arises from the migration of the syn-oriented hydrogen with regard to the carbonyl dipole.