Modified chiral triazolium salts for enantioselective benzoin cyclization of enolizable keto-aldehydes: synthesis of (+)-sappanone B.

Asymmetric synthesis of (+)-sappanone B (1), a natural product with a 3-hydroxy chromanone structure, was achieved via enantioselective benzoin cyclization by using a modified Rovis catalyst and triethylamine. This catalyst enabled the successful benzoin cyclization of readily enolizable keto-aldehydes.