Strongly Oxidizing Thiapyrylium Salt for Organophotoredox Catalysis

Photoredox catalysis has garnered significant attention in organic chemistry for its ability to promote chemical transformations under visible-light irradiation. To date, research on salt-based organophotoredox catalysts has mainly concentrated on the development of oxygen- and nitrogen-based catalysts such as acridinium and pyrylium salts, whereas sulfur-containing catalysts have received far less attention. Herein, we report a strongly oxidizing <i>tert</i>-butyl-substituted thiapyrylium organophotoredox catalyst (^<i>t</i>Bu-TTPP) that exhibits a high excited-state reduction potential (<i>E</i>_1/2(C*/C^•-) = +2.23 V vs SCE) and can be activated by blue LEDs. The ^<i>t</i>Bu-TTPP catalyst provided promising results in various photoredox reactions, such as radical-cation Diels-Alder reactions, trifluoromethylations, the [4 + 2] annulation of alkynes and thiophene, and the C-N cross-coupling of fluoroarenes, demonstrating its potential in photoredox catalysis.