Metal-Free Oxidative Condensation of Catechols, Aldehydes and NH4OAc towards Benzoxazoles

Benzoxazoles extensively exist in biologically active compounds, natural products, pharmaceuticals and functional materials. Thus, facile and green synthesis of such valuable compounds from easily available substrates will make a contribution to drug, material, and fine chemistry. A method for the synthesis of benzoxazoles from catechols, aldehydes and ammonium acetate is developed using NaIO4 as oxidant under metal- and additive-free conditions. A broad range of benzoxazoles including some fluorescent whitening agents, JTP-426467 and tafamidis analogues are synthesized in 56-95% yields with outstanding functional group tolerance. Mechanistic investigations suggest that an interesting o-iminocyclohexa-diene alcohol intermediate is involved in the reaction. These salient features of the protocol make it an alternative for the synthesis of benzoxazoles.

Automated summary

A simple and green method for the synthesis of benzoxazoles from catechols, aldehydes, and ammonium acetate using NaIO4 as an oxidant under metal- and additive-free conditions has been developed. The protocol results in high yields of benzoxazoles with excellent functional group tolerance, with mechanistic investigations revealing the involvement of a unique intermediate.