Synthesis of a new polycyclic heterocyclic ring system. Part III. Benzo[b] imidazo[1,5-d][1,4] oxazepine-1,4(2H, 5H)-diones

A series of novel tricyclic benzoxazepines with fused imidazolone ring was prepared in five steps start-ing from the corresponding benzoxazolones 1-3. The key to the reported synthetic approach is transformation of 3-(2-oxopropyl)-2(3H)-benzoxazolones 4-6 to 1-(2-hydroxyphenyl)-4-methyl-1,3-dihydro-2H--imidazol-2- ones 7-12, and their subsequent conversion to the phenoxy-acetic acids 19-24, which were finally acylated in polyphosphoric acid to form the oxazepine ring.