Enantioselective base-free phase-transfer reaction in water-rich solvent.

The development of enantioselective phase-transfer catalysis for preparing important natural products or physiologically active compounds is quite attractive and challenging in terms of environmental consciousness. Although quaternary ammonium salts as phase-transfer catalysts are believed to require base additives for phase-transfer reactions, we have discovered that even without any base additives, the enantioselective phase-transfer conjugate addition of 3-phenyloxindole to beta-nitrostyrene proceeded smoothly in the presence of a chiral bifunctional ammonium bromide under neutral conditions in water-rich solvent with both high diastereo- and enantioselectivity.