2.3- Benzoxazepin-l-one system

The unstable dibenz[c,/][l,2]oxazepines (312 R = CN, Cl) have been isolated as the major products of the UV irradiation of 9-cyano- and 9-chloro-acridine 10-oxides (310) in benzene (c/. the analogous Af-imide to 1,2-diazepine conversion on p. 598). Although none of the oxaziridine tautomer (311) was detectable by UV spectroscopy, the subsequent deoxygenation of (312) to acridine suggests the existence of a thermal equilibrium between (311) and (312) (79T1273). These dibenzo compounds (312) are the only fully unsaturated oxazepines yet isolated but the 2,3-benzoxazepin-l-one system (314) has recently been prepared by the reaction of benzonitrile oxide with the benzopyranone (313) (80JCS(Pl)846). 

The 2,3-benzoxazepin-l-one system (436) is prepared by the reaction of benzonitrile oxide with the benzopyranone (435) (80JCS(P1)846). The tetrahydro-3,2-benzothiazepine 3,3-dioxide (438) was prepared from (437) by intramolecular sulfonamidomethylation (76CC470). 

An alternative ring expansion process involving the benzopyranone (77) and the 1,3-dipole benzonitrile oxide, generated in situ from A-a-chlorobenzylidenehydroxylamine, affords access in low yield (8.4%) to the functionalized 2,3-benzoxazepin-l-one system (78) (m.p. 155-156°C). An analogous reaction is demonstrated by A-benzylideneaniline A-oxide to give (79) (m.p. 266-267°C) in 16% yield (Scheme 9) <80JCS(Pi)846>. 

---