Direct transition-metal-free intramolecular C-O bond formation: synthesis of benzoxazole derivatives

A direct base-mediated intramolecular carbon-oxygen bond formation has been developed without a transition-metal catalyst. In the presence of 2.0 equiv of K2CO3 in DMSO at 140 degrees C, the intramolecular cyclization of o-haloanilides affords benzoxazoles in high yields. A mechanism via an initial formation of a benzyne intermediate followed by nucleophilic addition to form the C-O bond has been proposed.