Aerobic cross-dehydrogenative coupling of toluenes and o-phenylenediamines by flavin photocatalysis for the facile synthesis of benzimidazoles

Abstract

Herein, we demonstrate green atom-economical synthesis of benzimidazoles via the flavin-photocatalysed aerobic oxidative cross-dehydrogenative coupling of toluenes and o-phenylenediamines. The proposed metal-free reaction proceeds in methanol/H2O under visible light irradiation...

Aerobic oxidative synthesis of benzimidazoles by flavin photocatalysis

“…11 Recently, we demonstrated a riboflavin-based photocatalysis for the synthesis of benzimidazoles via aerobic cross-dehydrogenative coupling between toluenes and o -phenylenediamines (Scheme 1A). 12 This metal-free system afforded the facile and atom-economical synthesis of benzimidazoles, but it suffered from a narrow substrate range; only electron-rich toluenes with alkoxy substituents worked as the starting materials. As an alternative useful method with a broader substrate scope, we herein report the efficient synthesis of benzimidazoles under mild conditions via the aerobic oxidative reaction of various benzylamines and o -phenylenediamines using riboflavin-based photocatalysis (Scheme 1B).…”

“…10 The in situ -generated hydrogen peroxide is likely to decompose into water and oxygen under the present reaction conditions, but some hydrogen peroxide may promote the oxidation of 10 into 3 . 12,24 Therefore, the flavin photocatalytic reaction allows metal-free synthesis of benzimidazoles 3 via an aerobic oxidative multistep reaction of 1 and 2 , consuming only molecular oxygen, which is a sustainable oxidant produced by plants.…”