Benzoxazepins

It was claimed3 that heating the oxime 2-[2-(hydroxyimino)propanyl]benzoic acid above its melting point resulted in dehydration to give 4-methyl-2,3-benzoxazepin-l(5//)-one (2, R = Me), as orange-red needles,4 but the color of the compound indicates that it has a different structure. 

The 2,3-benzoxazepin-l(3//)-one 4 (NR2 = pyrrolidin-l-yl), a stable colorless solid, is obtained in low yield in the reaction of benzonitrile oxide with 3-(pyrrolidin-l-yl)-l//-2-benzopyran-l-one (3).5... 

Both 1,3- and 3,1-benzoxazepines are known. The parent compounds are unstable oils, which decompose on attempted chromatography 17 cyano or phenyl substituents on the oxazepine ring stabilize the systems. 

Two intramolecular aza-Wittig reactions leading to 1,3-benzoxazepines have been described. In the first,19 ethyl (Z)-3-(2-acyloxyphenyl)-2-azidoprop-2-enoates 1 are treated with triphenyl-phosphane under argon at 20°C for 3-4 hours when 2-substituted ethyl 1,3-benzoxazepine-4-carboxylates 2 are obtained in 85-90% yield. 

In a sequence of cycloaddition and cycloreversion, 3-phenyl-l, 2,4-triazine 1-oxides react with benzyne, generated from 2-aminobenzoic acid (see Houben-Weyl, Vol. 5/2 b, p 622 ff), to give 2-phenyl-l, 3-benzoxazepines in moderate yield.419... 

The photochemical ring expansion of A-oxides when applied to isoquinoline 2-oxides leads to 1,3-benzoxazepines 5.2122 The yield was reported for 5b only. 

Treatment of 2-phenyl-l,3-benzoxazepines with hydrochloric acid in acetic acid gives benzo-furans by hydrolytic opening of the oxazepine ring, followed by loss of benzamide and re-cyclization.23... 

The photochemical ring enlargement of quinoline 1-oxides provides 3,1-benzoxazepines 1 (see Houben-Weyl, Vol.4/5b, p 12971T).24... 

Irradiation of quinoline 1-oxide itself yields the parent 3,1-benzoxazepine (2), accompanied by quinolin-2(l//)-one (3).17... 

The reaction of sodium azide with 2-benzopyrylium perchlorates 4 gives unstable l-azido-2-benzopyrans 5, which lose nitrogen on heating to give mixtures of 3,1-benzoxazepines 6 and anils 7.25... 

The parent 1,4-benzoxazepine is very unstable it and its simple derivatives have been reported only recently. 

The acetal 1, obtained from salicylamide and bromoacetaldehyde diethyl acetal, cyclizes on heating to provide l,4-benzoxazepin-5(4//)-one (2).32... 

The reaction of 5-chloro-l,4-benzoxazepine (4), whose preparation is described below, with tributyltin hydride catalyzed by tetrakis(triphenylphosphane)palladium(0) gives 1,4-benzox-azepine (5).32... 

---