Metal-Free Oxidized Carbon Nitride/l-Proline Synergistic Catalysis: Highly Enantioselective Direct Synthesis of C2-Quaternary Indolinones via Dearomative Oxyalkylation Cascades

Abstract

Herein, we report a metal-free, cooperative oxidized graphitic carbon nitride/l-proline catalysis for enantioselective dearomative oxyalkylation of 2-arylindoles. The developed method leverages the band structure of g-C3N4 to efficiently generate singlet oxygen (1O2) under visible light and aerobic conditions, driving an oxidative dearomatization cascade. The resulting intermediates are intercepted via an l-proline-mediated Mannich addition, providing direct access to C2-quaternary indolin-3-ones in high yields (up to 88%) and with enantioselectivities (up to 99% ee). By integrating heterogeneous carbon nitride photocatalysis with asymmetric organocatalysis, this protocol offers a robust, recyclable alternative to traditional noble-metal catalysis for enantioselective synthesis of C2-quaternary indolin-3-ones.