Synthesis of Amide-Substituted Isoxazoles and Pyrazoles via Regioselective [3+2] Cycloadditions of Terminally Unsubstituted Ynamides

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.