Efficient regioselective synthesis of 4‐ and 5‐substituted isoxazoles under thermal and microwave conditions

Abstract magnified image The [2+3] cycloaddition reaction between nitrile oxides 2 and the captodative olefins 1 or the methyl crotonate derivatives 4 is regioselective and leads to the formation of the 5‐substituted amino‐isoxazole 3 or the 4‐substituted methoxycarbonyl‐isoxazole 5 derivatives, respectively. All these reactions are greatly accelerated by microwave irradiation without changing their regioselectivity with respect to the thermal conditions.