Asymmetric Reactions. II. Anomalous Stereoselectivity of the Grignard Reaction with N-Benzyl-2,3-O-isopropylidene- d -glyceraldimine

Stereoselectivity of the organomagnesium reaction with N-benzyl-2,3-O-isopropylidene-d-glyceraldimine was examined under various conditions (change of molarity, solvent, and composition ratio of reagents). The selectivity was not effected by the molarity of the reagents but by the solvent. When the substrate was treated with a mixture of various ratio of magnesium bromide and diphenylmagnesium, a remarkable effect of the ratio on the stereoselectivity was observed. Maximum ratio of erythro/threo was obtained at the point of equimolar mixture of magnesium bromide and diphenylmagnesium in ether. The structure of the transition intermediate was discussed.