Blue Light-Promoted Synthesis of Thiochromenopyrroledione Derivatives via Titanium Dioxide-Catalyzed Dual Carbon-Carbon Bond Formation with Thioanisole and Maleimide Derivatives

Under anaerobic conditions, thioanisole derivatives bearing a thiomethyl group participated in dual carbon-carbon bond-forming reactions with maleimide derivatives in the presence of titanium dioxide. Blue light irradiation facilitated these reactions, producing thiochromenopyrroledione derivatives and nearly equimolar quantities of succinimide derivatives. Specifically, a thiochromenopyrroledione derivative formed from thioanisole and N-benzylmaleimide was achieved with a 43% yield after 12 hours of blue light exposure (>420 nm), approaching its theoretical maximum yield of 50%. Without titanium dioxide, the reaction remained dormant. Our investigations with five varieties of 4-substituted thioanisoles and four N-substituted maleimides as precursors resulted in the synthesis of 20 distinct thiochromenopyrroledione derivatives with moderate to high yields. From observed substituent effects, we postulate that this reaction proceeds through a charge transfer from thioanisole to the conduction band of titanium dioxide during blue light irradiation, initiating the one-electron oxidation of thioanisole and subsequent generation of alpha-thioalkyl radicals via deprotonation.

Automated summary

In this study, it was found that thioanisole derivatives can undergo dual carbon-carbon bond-forming reactions with maleimide derivatives in the presence of titanium dioxide under blue light irradiation. This reaction leads to the synthesis of thiochromenopyrroledione derivatives and succinimide derivatives. The reaction yield and selectivity can be influenced by the substituents on the starting materials, suggesting a charge transfer mechanism involving one-electron oxidation.