Metal-Free Synthesis of N-Containing Heterocycles from o-Substituted Aniline Derivatives via 2,4,6-Trihydroxybenzoic Acid-Catalyzed Oxidative Dehydrogenation of Benzylamines under Oxygen Atmosphere

A series of N-heterocycles, i.e., benzimidazoles, benzoxazoles, and benzothiazoles, can be conveniently synthesized by the oxidative cyclization of benzylamines with o-substituted aniline derivatives, i.e., o-phenylenediamines, o-aminophenols, and o-aminothiophenols, using 2,4,6-trihydroxybenzoic acid as an organocatalyst under an oxygen atmosphere. This approach provides a mild and efficient tool towards benzimidazoles and benzothiazoles with good yields and a broad substrate scope. The developed synthesis of N-heterocycles might proceed via the oxidative dehydrogenation of benzylamines (ArCH2NH2), generating the corresponding imines (ArCH=NH) as key intermediates.