Chiral NADH models with restricted or blocked rotation at the amide function: attempts to interpret the mechanism of the enantioselective hydrogen transfer to methyl benzoylformate

Various NADH models with the following characteristics were studied and compared with previously reported models: (1) use of (S)-phenylalaninol as chiral auxiliary; (2) orientation in or out of the plane of the amide carbonyl. Despite the occurrence of apparently similar characteristics, they gave very different results in the asymmetric reduction of methyl benzoylformate. A detailed NMR study was performed in order to explain the behaviour of these models.