Regioselective Formation of 2,5-Disubstituted Oxazoles Via Copper(I)-Catalyzed Cycloaddition of Acyl Azides and 1-Alkynes

The reaction of 1-alkynes with acylazides in the presence of [Tpm*,BrCu(NCMe)]BF4 (Tpm*,Br = tris(3,5-dimethyl-4-bromopyrazolyl)methane) as the catalyst provides 2,5-oxazoles in moderate to high yields. This is a novel transformation of CuAAC type, that constitutes a significant variation of the commonly observed [3+2] cycloaddition reaction to yield 1,2,3-triazolesMEC (Proyecto CTQ2008-00042/BQU, Consolider Ingenio 2010, Grant No. CSD2006-003) and the Junta de Andalucía (Proyecto P07-FQM-02745).This work is dedicated to Prof. Jose Barluenga on the occasion of his retirement. This research was financially supported by MEC (Proyecto CTQ2008-00042/BQU, Consolider Ingenio 2010, Grant CSD2006-003) and the Junta de Andalucia (Proyecto P07-FQM-02745). I.C. thanks MEC for a research fellowship. We gratefully acknowledge Prof. Antonio Echavarren for helpful discussions. Dr. Ana Caballero and Dr. Tomas R. Belderrain are thanked for assistance with GC MS and NMR studies