Cascade Reaction of α, β-Unsaturated Keto-carboxylic Acid for the Formation of 5-Substituted Isoxazole using NaN ₃ /I ₂ /TBHP

An efficient and regioselective synthesis of 5-substituted isoxazoles has been developed via the reaction of α, β-unsaturated keto-carboxylic acids with sodium azide in the presence of iodine and TBHP. The transformation proceeds at room temperature to afford the desired products in moderate to good yields across a broad substrate scope. The strategy features the use of readily available starting materials, operational simplicity, and excellent regioselectivity. A plausible mechanistic pathway for isoxazole formation is also proposed.