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 tert-butyl-substituted thiapyrylium organophotoredox catalyst (^tBu-TTPP) that exhibits a high excited-state reduction potential (E_1/2(C*/C^•–) = +2.23 V vs SCE) and can be activated by blue LEDs. The ^tBu-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.