Enantioselective Direct anti-Selective Mannich-type Reactions Catalyzed by 3-Pyrrolidinecarboxylic Acid in the Presence of Potassium Carbonate: Addition of Potassium Carbonate Improves Enantioselectivities

Mannich-type reactions of cyclohexanone and related six-membered-ring ketones with N - p -methoxyphenyl-protected imines of arylaldehydes catalyzed by 3-pyrrolidinecarboxylic acid in the presence of K 2 CO 3 hat afford anti -isomers of the Mannich products with high diastereo- and enantioselectivities are reported. Addition of K 2 CO 3 improved the enantioselectivities of the reactions catalyzed by 3-pyrrolidinecarboxylic acid while retaining the anti -selectivity of the reaction. Thus, the use of K 2 CO 3 expands the scope of these organocatalytic reactions for providing the products with high enantioselectivities.