Solvent-Regulated Cyclization of Arylidene Isoxazolones with Amidines for Regiodivergent Synthesis of 4- and 5-Acylimidazoles

N-Iodosuccinimide-promoted cascade reactions of arylidene isoxazolones with amidines in p-xylene were accomplished, affording 5-acylimidazoles in good to excellent yields. Interestingly, when the reactions were performed by employing acetonitrile as the solvent, 4-acylimidazoles were efficiently obtained. Mechanistic studies indicate that the formation of imidazolyl and acyl moieties may undergo a spiroannulation-ring opening aromatization-hydrolysis cascade reaction sequence. Based on this solvent-regulated tandem reaction strategy, a powerful protocol for switchable and regiodivergent synthesis of structurally diverse 4-acylimidazoles and 5-acylimidazoles was successfully established.