Asymmetric Formal Vinylogous Iminium Ion Activation for Vinyl-Substituted Heteroaryl and Aryl Aldehydes.

The vinyl group tethered to furfurals could be LUMO-lowered by forming formal vinylogous iminium ion intermediates catalyzed by a chiral secondary amine and underwent asymmetric [3 + 2] cycloaddition reactions with N-trifluoroethyl-substituted isatin imines, furnishing a variety of spirooxindoles incorporating a 3,2'-pyrrolidine motif with excellent stereoselectivity. In addition, this strategy has been successfully expanded to a number of vinyl-substituted electron-rich heteroaryl aldehydes and even some specific aryl aldehydes.