Enantioselective rearrangement of proline sulfonamides: an easy entry to enantiomerically pure α-aryl quaternary prolines

(Figure Presented) Enantiopure quaternary prolines have been prepared by stereoselective rearrangement of N-(arylsulfonyl)proline tert-butyl esters under basic conditions (see scheme), without any external source of stereochemical information. The sulfonamide aromatic ring must contain an electron-withdrawing group (EWG), which stabilizes an intermediate Meisenheimer complex. The overall process provides easy entry to a series of optically pure a-aromatic prolines.