Acid Catalyzed Direct-Amidation-Dehydrocyclization of 2-Hydroxy-acetophenones to Benzoxazoles by a One-Pot Sustainable Synthesis

A series of 2-methyl-benzoxazoles have been synthesized starting from 2-hydroxy-acetophenones via a one-pot three steps reaction. Hydroxylamonium salt has been used as amidation agent. The reaction occurs with different anions, but the best results is achieved with hydroxylamonium hydrchloride. Despite the number of consecutive stages, the reaction is highly selective. Mild reaction conditions and various solvents can be used, but trifluoroacetic acid is the preferred. Almost, complete recovery of the trifluoroacetic acid can be achieved by vacuum distillation. The role of trifluoroacetic acid, as well as, of the hydroxylamonium salt suggests a cooperative effect leading to high selective formation of 2-methyl-benzoxazoles. Graphical Abstract: One-pot TFA catalyzed synthesis of benzoxazoles starting from 2-hydroxyacetophenones. (Chemical Equation Presented).A series of 2-methyl-benzoxazoles have been synthesized starting from 2-hydroxy-acetophenones via a one-pot three steps reaction. Hydroxylamonium salt has been used as amidation agent. The reaction occurs with different anions, but the best results is achieved with hydroxylamonium hydrchloride. Despite the number of consecutive stages, the reaction is highly selective. Mild reaction conditions and various solvents can be used, but trifluoroacetic acid is the preferred. Almost, complete recovery of the trifluoroacetic acid can be achieved by vacuum distillation. The role of trifluoroacetic acid, as well as, of the hydroxylamonium salt suggests a cooperative effect leading to high selective formation of 2-methyl-benzoxazoles. Graphical Abstract: One-pot TFA catalyzed synthesis of benzoxazoles starting from 2-hydroxyacetophenones. (Chemical Equation Presented)