Generation of alkene radical cation for thioxanthone-TfOH complex-catalyzed intramolecular cyclization using a photoredox catalysis strategy

Abstract

Photo catalysis has comprehensively become a powerful tool in organic synthesis, and organic molecules are thriving as catalyst. The thioxanthone-TfOH complex (9-HTXTF) as photoredox catalyst with high oxidative capacity can be applied in single electron reduction of alkene affording alkene radical anion as a key intermediate. To transform this intermediate from radical anion to radical cation, a well-designed strategy is proposed with N-arylacrylamides as substrate. Based on its single electron transfer (SET) with 9-HTXTF*, N-radical cation is generated and then transformed to alkene radical cation by intramolecular conjugated system. By using this photoredox catalysis strategy, we developed a 9-HTXTF-catalyzed photochemical cyclization of alkenes, which further expands the applications of this catalyst. The entire cyclization is metal-free and without sacrificing agents, which conforms to atom economy and environmental friendliness.