Herein, we present an intrinsic CaTiO3-photoredox/chloranil dual catalytic system for the cascade radical sulfonylation/cyclization of 2-alkynyl biaryls with sulfonyl hydrazides. This protocol demonstrates broad substrate compatibility, enabling the efficient synthesis of sulfonyl phenanthrenes (31 examples) in good to excellent yields under mild and eco-friendly conditions. The process is readily scalable to gram quantities and allows for the facile recovery and repeated use of a CaTiO3 semiconductor photocatalyst. Mechanistic studies reveal the dual role of chloranil as both an HAT catalyst to generate RSO2̇ from RSO2NHNH2 and a redox catalyst to enhance the intrinsic photocatalytic performance of intrinsic CaTiO3.
Lu et al. (Tue,) studied this question.