Stereoselective reduction of benzoin by the NADH model 3‐(dimethylcarbamoyl)‐1,2,4‐trimethyl‐1,4‐dihydropyridine

The Mg(ClO4)2‐induced reduction of racemic benzoin by the racemic NADH model compound 3‐(dimethylcarbamoyl)‐1,2,4‐trimethyl‐1,4‐dihydropyridine (1), in accordance to Cram's rule, leads exclusively to meso‐1,2‐diphenyl‐1,2‐ethanediol. However, while R‐1 equally reduces 5‐benzoin to afford meso‐1,2‐diphenyl‐1,2‐ethanediol, S‐1 is reluctant to react with S‐benzoin. The intermediacy of a strictly organized transition state, composed of chelated substrate, dihydropyridine and magnesium ion is involved.