"One-Pot" Access to 4 H-chromenes with formation of a chiral quaternary stereogenic center by a highly enantioselective iminium-allenamine involved oxa-Michael-aldol cascade

An unprecedented organocatalytic highly enantioselective cascade Michael-aldol reaction has been developed in high yields under mild reaction conditions. The "one-pot" process affords an efficient approach to the synthetically and biologically important chiral 4H-chromenes bearing a quaternary stereogenic center. The study significantly expands the scope of less explored organocatalytic iminium-allenamine chemistry.