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Catalytic Copper-Mediated Ring Opening and Functionalization of Benzoxazoles

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posted on 07.11.2014, 00:00 by Macarena Corro, Maria Besora, Celia Maya, Eleuterio Álvarez, Juan Urbano, Manuel R. Fructos, Feliu Maseras, Pedro J. Pérez
A novel reaction involving benzoxazole, ethyl diazoacetate, and water has been discovered, with TpBr3Cu­(NCMe) (TpBr3 = hydrotris­(3,4,5-tribromopyrazolyl)­borate) as the catalyst. The fused azoles are converted into highly functionalized substituted benzenes bearing aldehyde, amine carboxylate and hydroxyl groups. The protocol has been applied for a series of benzoxazoles with several diazo compounds. Experimental data and theoretical calculations have led to a mechanistic proposal that includes carbene addition, ylide formation, and water addition to the latter, all those steps being catalyzed by the copper center.