Reduction by a Model of NAD(P)H. 32. Stereoselective Reduction of Camphoroquinone by a Chiral NAD(P)H Model

Abstract (+)-, (−)-, and racemic camphoroquinones (CQ) were reduced by each of four NAD(P)H-models such as N-(α-methylbenzyl)-1-propyl-2,4-dimethyl-1,4-dihydronicotinamide (Me2PNPH) in the presence of magnesium ion in acetonitrile with a view to elucidating the intermolecular arrangement in the transition state for asymmetric reduction. Partial rate factors for each attacking mode were calculated. Electronegative substituents in the substrate prefer to facing the carbamoyl group in Me2PNPH, which is the most important factor determining the stereochemical course of the reduction. 1-Methyl group in CQ has a tendency to interfere with the dihydropyridine moiety in Me2PNPH approaching the C2-carbonyl group in CQ. This interference is more important for the selectivity than the intrinsic exo/endo reactivity difference.