A highly stereo-divergent Mannich-type reaction catalyzed by Brّnsted acid in aqueous media

anti And syn stereoselectivity on the HBF4-catalyzed Mannich-type reaction of ketene silyl acetal derived from α-oxy esters with aldimines were investigated. Whereas use of ketene silyl acetal derived from aryl ester in aqueous 2-propanol gave anti β-amino-α-siloxy ester with excellent stereoselectivity, use of ketene silyl acetal derived from methyl ester in water in the presence of sodium dodecyl sulfate gave the syn isomer preferentially.