Direct organocatalytic asymmetric α-sulfenylation of activated C-H bonds in lactones, lactams, and β-dicarbonyl compounds

The application of cinchona alkaloid derivatives as catalysts for enantioselective alpha-sulfenylation of activated C-H bonds in lactones, lactams, and beta-dicarbonyl compounds by different electrophilic sulfur reagents is presented. Optically active products are obtained in good to excellent yields and up to 91 % ee. Furthermore, the diastereoselective reduction of alpha-sulfenylated P-keto esters to give optically active alpha-sulfenylated beta-hydroxy esters has been studied. A model for the intermediate is presented, in which the protonated cinchona alkaloid interacts with the substrate leading to face-shielding in accordance with the enantioselective alpha-suffenylation step.