Synthesis of Benz[d]oxazolones Involving Concomitant Acetyl Migration from Oxygen to Nitrogen

Heating of o-acetoxybenzoyl azides 6–10 in toluene leads to the Curtius reaction, which, when followed by closure of oxazolone ring with concomitant migration of acetyl group from oxygen to nitrogen, produces 3-acetoxybenzd]oxazol-2(3H)-ones 11–15, which undergo hydrolysis with hot dilute hydrochloric acid to furnish benzd]oxazol-2(3H)-ones 17–21. Thermal reaction of 2-hydroxy-5-nitrobenzoyl azide (22) in toluene finally yields a mixture of 5-nitrobenzd]oxazol-2(3H)-one (20) and 5-nitrobenzd]isoxazol-3(2H)-one (23).