Diastereoselective synthesis of polycyclic indolines via dearomative [4 + 2] cycloaddition of 3-nitroindoles with ortho -aminophenyl p -quinone methides.

A formal [4 + 2] cycloaddition of 3-nitroindoles with ortho -aminophenyl p -quinone methides via a dearomatization process was developed. This method provides a facile approach for preparing tetrahydro-5 H -indolo[2,3- b ]quinolones with good results. With the bifunctional Cinchona alkaloid-squaramide as the catalyst, the asymmetric version of the reaction successfully afforded the corresponding chiral products with moderate to good enantioselectivities. This work represents the first dearomative cycloaddition of electron-deficient heteroarenes triggered by aza-Michael addition from p -QMs.