Oxazepine photochemically

Another photochemical ring enlargement leading to a 1,3-oxazepine is the formation of 2-phenyl-l,3-oxazepine (13) by irradiation of 4-phenyl-2-oxa-3-azabicyclo[3.2.0]hepta-3,6-diene (11).12 It is proposed that the process involves the azirine 12 as an intermediate. 

The 1,3-oxazepine (848) is thermally labile the main products are formylpyrroles but some 3-hydroxy-2-phenylpyridine is obtained (75TL1067). The benzoxazepines of type (849) are intermediates in the photochemical breakdown of quinoline iV-oxides and can sometimes be isolated. They normally break down to give 3-hydroxyquinolines (66TL2145, 67CPB663), but compound (849) can be converted by methylamine into the diaminoquinoline (850) (67TL5237). The benzoxazepinone (851) with sodamide forms a mixture of three isoquinoline... 

A number of monocyclic and benzo-annelated examples of 1,2- and 1,3-thiazepines have been prepared but there has been little systematic study of these systems. The interesting photochemical interconversions of pyridine N-imides into 1,2- and 1,3-diazepines and of pyridine Af-oxides into 1,2- and 1,3-oxazepines regrettably lack parallels in thiazepine chemistry. There has been more interest in 1,4-thiazepines, as both rearrangement products and possible biogenetic precursors for penicillins and because of the pharmacological value of the benzo- and dibenzo-[l,4]thiazepines as antidepressants and coronary vasodilators. The only review (70ZC361) is excellent but not very recent. 

The preparation of 3,1-benzoxazepines by photochemical isomerization of quinoline A-oxides constitutes a rather general entry into this class of seven-membered heterocycles. Since the structure of the photoisomer of 2-phenylquinoline A-oxide was first recognized as 2-pheny 1-3,1-benzoxazepine by Buchardt et al.,3 the scope of this method for oxidative ring expansion of six-membered heterocyclic A-oxides to 1,3-oxazepines has been extensively explored.4 For example, irradiation of 2-cyano-, 2-phenyl-, and 2-methoxyquinoline A-oxides affords the corresponding 2-substituted 3,1-benzoxazepines in 70-90% yield.5 However, isolation of the moisture-sensitive parent compound was only recently accomplished in the submitters laboratories.6... 

The photochemical behavior of the W-oxides of the Cinchona alkaloids has been examined 49). Photolysis (> 300 nm) of the aromatic mono-iV-oxides 183 of the dihydro derivatives of quinine, quinidine, cincho-nidine, and cinchonine in alcoholic solvents gave the expected carbo-styrils 186 in yields of 70-85%. The same results were obtained with the corresponding AjiV-dioxides 184. An interesting rearrangement was observed in the case of the iV,A -dioxides of dihydrocinchonine and dihydrocinchonidine. Photolysis in benzene solution afforded, in addition to the carbostyrils, the iV -formylindole methanols 188 in 30% yield. The hydrolysis-sensitive benz[d]-l,3-oxazepines 185 were proposed as the probable intermediates. 

Photochemical intramolecular (2 + 2)-cycloaddition within the framework of a heterocyclic seven-membered ring has further been observed in l//-l,2-diazepines, 1,3-oxazepines, and 1,2-phosphazepines. 

In the above examples only the E isomers of azirine 107 could be prepared. It is noteworthy that the photochemical conversion of the bicyclic isoxazoline 114 to oxazepin 117 is believed to involve the Z isomer of azirine llj 98,99 species could not be isolated but goes on to give nitrile ylide 116. 1,7-Electrocyclization of 116 leads to oxazepin 117 in 80% yield. Because of steric constraints it is clearly impossible for the JE-vinylnitrile ylide 107 (R = CHO) to undergo 1,7-cyclization. 

Whereas the photochemically induced reactions of pyridine JV-oxides can yield a wide range of products, the substitution of phenyl groups results in the isolation of 1,3-oxazepines (663) and (664), formed via the isomeric oxaziridines (661) and (662), The irradiation of polychlorinated p3rridine... 

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