Effects of Substituents in the β-Position of 1,3-Dicarbonyl Compounds in Bromodimethylsulfonium Bromide-Catalyzed Multicomponent Reactions: A Facile Access to Functionalized Piperidines

w1,3-Dicarbonyl compounds can be converted to Mannich-type products A or highly functionalized piperidines B in the presence of a catalytic amount of bromodimethylsulfonium bromide (BDMS). The combination of aromatic aldehyde, amine, and 1,3-dicarbonyl compounds in the presence of a catalytic amount of BDMS leads to the formation of Mannich-type product A when R is a non-enolizable carbon or an alkoxy group, whereas in cases when R = CH3, the same combination yielded highly functionalized piperidines B. A synthetic study and mechanistic proposal are presented.