P,S Ligands for the Asymmetric Construction of Quaternary Stereocenters in Palladium-Catalyzed Decarboxylative [4+2] Cycloadditions.

A new hybrid P,S ligand was exploited by combining a chiral β-amino sulfide and a simple diphenyl phosphite. The resultant ligand performs extremely well in a palladium-catalyzed asymmetric decarboxylative [4+2] cycloaddition reaction, thus generating multiple contiguous stereocenters and a chiral quaternary center. By doing so, a straightforward route to highly functionalized tetrahydroquinolines was developed with yields of up to 99 %, as well as 98 % ee and greater than 95:5 d.r. Moreover, mechanistic insights into this transformation and the possible stereocontrol are discussed.