Asymmetric Mannich Reaction of Dicarbonyl Compounds with α-Amido Sulfones Catalyzed by Cinchona Alkaloids and Synthesis of Chiral Dihydropyrimidones

The highly enantioselective cinchona alkaloid-catalyzed Mannich reaction of dicarbonyl compounds with
α-amido sulfones as acyl imine precursors is described. The reaction requires 10 mol % of the cinchona
alkaloid catalyst, which serves as a general base to generate acyl imines in situ, and aqueous Na2CO3 to
maintain the concentration of free alkaloid catalyst. The reaction products are obtained in good yields
and high enantioselectivities, and in diastereoselectivities that range from 1:1 to >95:5. The cinchonine-catalyzed reactions provide practical access to highly functionalized building blocks which have been
employed in the synthesis of chiral dihydropyrimidones, a class of compounds rich in diverse biological
activity. Dihydropyrimidone modifications include a highly diastereoselective hydrogenation of the enamide
moiety, using an H-Cube flow hydrogenator and a Rh(II)-mediated 1,3-dipolar cycloaddition to afford
highly functionalized complex heterocycles.