An Efficient [2 + 2 + 1] Synthesis of 2,5-Disubstituted Oxazoles via Gold-Catalyzed Intermolecular Alkyne Oxidation
Weimin He, Chaoqun Li and Liming Zhang*
*Department of Chemistry and Biochemistry, University of
California, Santa Barbara, California 93106, United States, Email: zhang
chem.ucsb.edu
W. He, C. Li, L. Zhang, J. Am. Chem. Soc., 2011, 133, 8482-8485.
DOI: 10.1021/ja2029188
Abstract
An efficient intermolecular reaction of gold carbene intermediates generated via gold-catalyzed alkyne oxidation using nitriles as both the reacting partner and the reaction solvent offers a generally efficient synthesis of 2,5-disubstituted oxazoles with broad substrate scope. The overall reaction is a [2 + 2 + 1] annulation of a terminal alkyne, a nitrile, and an oxygen atom from an oxidant.
see article for more examples
General procedure for the gold-catalyzed oxazoles formation
8-Methylquinoline N-oxide (0.39 mmol, 62.0 mg) and Au(PPh3)NTf2 (11.1 mg, 0.015 mmol) were added to a solution of an alkyne (0.30 mmol) in a nitrile (3 mL) at 60 °C. The reaction mixture was stirred at 60°C, and the progress of the reaction was monitored by TLC. The reaction typically took 3 h or overnight. Upon completion, the mixture was concentrated and the residue was purified by chromatography on silica gel (eluent: hexanes/ethyl acetate) to afford the oxazole products.
Key Words
Oxazoles, 8-methylquinoline N-oxide
ID: J48-Y2011-1750
