A convenient microwave-assisted method for the synthesis of isoxazoline-functionalized isoquinolines via the n-Bu₄NI (TBAI) catalyzed radical cascade cyclization of vinyl isocyanides with β,γ-unsaturated ketoximes has been described. The methodology presented here achieves a wide substrate scope and good to excellent yields. A radical mechanism is proposed, which is supported by the intermolecular competing kinetic isotope effect (KIE) experiment and the radical trapping experiment.