Highly efficient one-pot, three-component Mannich reaction catalysed by boric acid and glycerol in water with major 'syn' diastereoselectivity

Boric acid and glycerol efficiently catalysed the one-pot, three-component Mannich reaction of aldehydes, aromatic amines and cyclic ketones in water at ambient temperature to afford the corresponding β-amino carbonyl compounds in good yields. All but one reaction proceeded with moderate 'syn' diastereoselectivity. This observation is just the reverse of the major anti diastereoselectivity obtained in most of the earlier reported procedures. The methodology is mild and efficient using minute quantities of catalyst with no side products and a very simple work-up procedure.