TiO2–Photocatalyzed Cyclization of Azobenzenes with Methanol To Access 1,2,4,5-Tetraaryl 1,2,4,5-Tetrazinanes

A photoredox-catalyzed cyclization of azobenzenes with methanol as the C1 source has been developed. Using anatase TiO₂ as the photocatalyst, the reaction proceeded smoothly at room temperature in the absence of any additives, affording 1,2,4,5-tetraaryl 1,2,4,5-tetrazinanes in high yields. The photocatalyst TiO₂ can be readily recycled and reused. Mechanistic studies indicated that the reaction proceeds via a photoredox-catalyzed radical pathway and that H₂O acts as a hydrogen atom transfer (HAT) reagent.