Visible-Light Photoredox Catalysis Enabled Triazole Annulation of Azidophilic Michael Acceptors

Fully substituted 1,2,3-triazoles are key functional units in modern organic chemistry owing to their diverse scientific utility. Though ene-azide cycloaddition emerged as a reliable strategy for their synthesis, it often requires metal catalysts and/or high temperature. To tackle this challenge, we herein disclose our approach of visible-light photoredox catalysis (VLPC) by employing Rose Bengal (RB) as a organo-photocatalyst. The chemistry works under blue light-emitting diode illumination by generating a solvent radical intermediate through the cooperation of RB and DMF. The reaction works well for various organic azides and Michael acceptors generating a library of substituted triazoles (50 examples) in excellent regio- and product control. The scope of the methodology is highlighted through the formal synthesis of rufinamide, an antiepileptic drug. From a technoeconomic perspective, our procedure holds sustainable advantages like room temperature, an ambient atmosphere, no byproducts, good to excellent yields, extension to gram-scale synthesis, and a safe and inexpensive catalyst.