A Sustainable Visible Light-Mediated Synthesis of Benzoxazole 2-Carboxylates/Carboxamides

The development of novel methods for the synthesis of substituted benzoxazoles is of wide interest, since such heterocyclic compounds exhibit various bioactivities. We report herein an efficient photochemical protocol for the oxidative cyclization of glycine derivatives to produce 2-substituted benzoxazoles bearing ester or amide moieties. Cheap and commercially available 1,8-dihydroxyanthraquinone serves as the organocatalyst in the presence of a nonprecious salt (CuI), while Kessil LED 427 nm is the source of irradiation. An extended substrate scope proves the generality of the method, which operates under mild conditions and in line with the principles of green chemistry. Direct infusion-high resolution mass spectrometry studies supported the proposal of the reaction mechanism. Furthermore, ease derivatization of selected benzoxazole 2-carboxylates/carboxamides demonstrates their utility as versatile intermediates for the synthesis of a wide range of compounds, thereby highlighting the value and broader applicability of the new photochemical protocol.