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-5H-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.

Automated summary

A formal [4 + 2] cycloaddition reaction between 3-nitroindoles and ortho-aminophenyl p-quinone methides was developed through a dearomatization process. This method provides an efficient approach for the synthesis of tetrahydro-5H-indolo[2,3-b]quinolones with satisfactory results. The use of bifunctional Cinchona alkaloid-squaramide as the catalyst enabled the asymmetric version of the reaction, leading to the formation of 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.