Synthesis of 2-substituted benzoxazoles and benzimidazoles based on mass spectral ortho interactions

Abstract

The ortho interactions of the hydroxy and amino groups with the amide function in N-(2-hydroxyphenyl)and N-(2-aminophenyl)-benzamides on electron impact lead to the elimination of H₂O from the molecular ions resulting in the formation of 2-substituted benzoxazoles and benzimidazole radical cations, respectively. This mass spectrometric reaction has been successfully mimicked in the laboratory to synthesise these heterocyclic compounds in excellent yields by the thermolysis of the corresponding N-(2-hydroxyphenyl)- and N-(2-aminophenyl)-benzamides. The mechanisms and ion structures proposed in the mass spectral study are supported by high-resolution data, B/E and B²/E linked-scan spectra, Collision-Activation-Decomposition (CAD)-B/E linked-scan spectra, chemical substitution and ²H-labelling.