Synthesis of 4H-Benzo[e][1,3]oxazin-4-ones by a Carbonylation–Cyclization Domino Reaction of ortho-Halophenols and Cyanamide

A mild and convenient one-step preparation of 4H-1,3-benzoxazin-4-ones by a domino carbonylation–cyclization process is developed. Readily available ortho-iodophenols are subjected to palladium-catalyzed carbonylative coupling with Mo(CO)₆ and cyanamide, followed by a spontaneous, intramolecular cyclization to afford 4H-1,3-benzoxazin-4-ones in moderate to excellent yields. Furthermore, the scope of the reaction is extended to include challenging ortho-bromophenols. Finally, to highlight the versatility of the developed method, Mo(CO)₆ is successfully replaced with a wide array of CO-releasing reagents, such as oxalyl chloride, phenyl formate, 9-methylfluorene-9-carbonyl chloride, and formic acid, making this an appealing strategy for the synthesis of 4H-benzo[e][1,3]oxazin-4-ones.