Photocatalysis by 3,6-Disubstituted‑<i>s</i>‑Tetrazine: Visible-Light Driven Metal-Free Green Synthesis of 2‑Substituted Benzimidazole and Benzothiazole

Abstract

<i>s</i>-Tetrazine based molecules were prepared for visible-light-driven organic transformations. The 3,6-di­(pyridin-2-yl)-1,2,4,5-tetrazine (<b>pytz</b>) derivative shows visible light absorption and reversible one-electron reduction behavior. In the presence of <b>pytz</b> and aerial oxygen, aldehyde reacts with <i>o</i>-phenylenediamine or <i>o</i>-aminothiophenol under visible light irradiation at ambient temperature to produce corresponding 2-substituted benzimidazoles and benzothiazoles, respectively. <b>Pytz</b> catalyst demonstrates excellent catalytic activity for alkyl, aryl, organo-metallic substituted aldehydes and reducing sugar. The reaction yield is high for both the electron-donating and electron withdrawing substituents in aromatic aldehydes. The use of a metal-free catalyst and visible light energy, along with the mild reaction conditions, makes this reaction an environmentally benign and energy-saving chemical process