Phase-Transfer-Catalyzed Enantioselective Mannich Reaction of Malonates with alpha-Amido Sulfones

The highly enantioselective reaction between in situ generated, Cbz-protected azomethines and malonates in the presence of 150 mol% of potassium carbonate (50% w/w) and 1 mol% of quinine-derived quaternary ammonium bromides as phase-transfer organocatalysts has been developed. This study reports a novel approach for the asymmetric Mannich-type reaction and a wide range of azomethines, including those derived from enolizable aldehydes, is tolerated by the present system. The adducts, obtained in excellent yields with ee up to 98%, are suitable precursors of optically pure beta-amino acids.