Energy-transfer-enabled photocatalytic transformations of aryl thianthrenium salts

Abstract

Aryl thianthrenium salts are valuable in photocatalysis but traditionally require external electron donors for activation. This study introduces an energy transfer (EnT) strategy for the activation of aryl thianthrenium salts using 2,3,4,5,6-penta(carbazol-9-yl)benzonitrile (5CzBN) as a metal-free photocatalyst, eliminating the need for external donors. Utilizing this EnT approach, we achieve C-H deuteration of arenes under visible light with CDCl₃ as a deuterium source to synthesize various deuterated aromatic compounds, including important natural products and pharmaceuticals. Additionally, this strategy enables diverse functionalizations including borylation, arylation, cyanation, and selenylation, enhancing the applicability of aryl sulfonium salts in environmentally friendly photocatalysis.

Fig. 1. Visible-light activation of aryl thianthrenium salts to aryl radicals.

a Single electron transfer (SET) process. b Electron donor-acceptor (EDA) complexes. c This work: energy transfer strategy.

Fig. 2. Substrate scope and the sensitivity assessment.

^aReaction conditions: aryl thianthrenium salts (0.2 mmol), 5CzBN (5 mol%), water (1 mL), and CDCl₃ (1 mL) were irradiated with 427 nm blue LED for 6 h. ^bIrradiated for 24 h. ^c5-(aryl)dibenzothiophenium triflate was used.

Fig. 3. Deuteration of bioactive molecules.

^aReaction conditions: aryl thianthrenium salts (0.2 mmol), 5CzBN (5 mol%), water (1 mL), and CDCl₃ (1 mL) were irradiated under 427 nm blue LED for 6 h. ^bIrradiated for 24 h.

Fig. 4. Synthetic applications and mechanistic investigations.

a Diverse transformations of our methods. See Supplementary Methods for specific reaction details. b The synthesis of dideuterated biphenyl. c Fluorescence quenching experiment. d UV-Vis and fluorescence spectra. e Catalyst evaluation with different triplet stale energies. f Transient absorption spectrum of thianthrenium salt 1 in the presence of 5CzBN. g Parallel and competitive kinetic isotope experiments. h Radical quenching experiments. i Mechanistic proposal, DAA = deuterium atom abstraction.