Asymmetric Reduction with 5-Deazaflavin. III. : Reduction of Ethyl Benzoylformate in the Presence of Chiral Ligand

A nonenzymatic asymmetric reduction of ethyl benzoylformate with an achiral 1, 5-dihydro-5-deazaflavin derivative in chiral media was investigated as a model system for reruced nicotinamide adenine dinucleotide (phosphate)-dependent dihydrogenase. The chiral media include chiral nuclear magnetic resonance shift reagent, chiral Lewis acid, and a combination of metal ion an chiral ligand (additive). Of these reductions, a substantial asymmetric induction was observed in the presence of tris-[3-(heptafluoropropylhydroxymethylene)(+)-camphorato]europium to give ethyl mandelate possessing prediominantly S-configuration, in a optical yield of 24 to 36%. These values are among the highest so far reported in nonenzymatic reduction of ethyl benzoylformate with a 5-deazaflavin model. The discrimination of the prochiral face of the carbonyl compound was effectvie even when a catalytic amount of the chiral shift reagent was employed.