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Paper | Special issue | Vol 74, No. 1, 2007, pp.553-568
Published online, 12th October, 2007
DOI: 10.3987/COM-07-S(W)34
Synthesis of Amide-Substituted Isoxazoles and Pyrazoles via Regioselective [3+2] Cycloadditions of Terminally Unsubstituted Ynamides

Hongyan Li, Lingfeng You, Xuejun Zhang, Whitney L. Johnson, Ruth Figueroa, and Richard P. Hsung*

*Department of Chemistry, Division of Pharmaceutical Sciences, University of Wisconsin, 777 Highland Aenue, Madison, WI 53705-2222, U.S.A.

Abstract

A series of regioselective [3 + 2] cycloadditions of terminally unsubstituted ynamides with nitrile oxides and ethyl α-diazoacetate is described here. These reactions provide an excellent synthetic entry to de novo 5-amide-substituted isoxazoles via a Cu(I)-catalyzed pathway and 3-amide-substituted pyrazoles via a thermally driven cycloaddition.