Photochemical and thermal reactions of some heterocycles containing C=N-O or N=C-O group

Abstract

-In connection with photochemistry of the nonconstra1ned Ph-C=N-0 system, those of severa1 2-isoxazo1ine derivatives containing cyc1obutene, cyc1obutane, cyclopropane and cyc1ohexane rings, have been investigated as the mode1s of the rigid and constrained Ph-C=N-0 system. In most cases, such 2-isoxazo1ines, upon irradiation, underwent the nitrogenoxygen bond fission as the primary process, and produced a variety of products depending on the structures of the starting materia1s. For instance, the irradiation of 4~ary1-2-oxa-3-azabicyc1o[3.2.0]hepta-3,6-dienes afforded 2-ary1-1,3-oxazepines, sometimes accompanied by pyrro1e a1dehydes, whereas 2-isoxazo1ines fused with sma11 ring yie1ded ß-aminoa1dehydes, oxazo1ines, azirine a1dehydes, and sma11 fragments such as benzonitri1e. The photochemica1 reaction mechanismsof severa1 2-isoxazo1ines have been studied using 1ow-temperature technique. In addition, the pyro1ytic reactions of 4-pheny1-2-oxa-3-azabicyc1o[3.2.0]heptadiene and 1,3-oxazepines as we11 as their va1ence isomers have been examined to compare with their photochemica1 behavior. It was found that in pyro1ysis of bicyc1o[3.2.0]heptadiene derivatives containing the C=N-0 or N=C-0 gnoup, the cyc1obutene ring fission occurs prior to the nitrogen-oxygen or carbon-oxygen bond c1eavage. Reaction mechanisms for the deep-seated rearrangements of the 1,3-oxazepines and of 2-oxa-3-azabicyclo[3.2.0]hepta-3,6-dienes to pyrro1e a1dehydes were discussed. The resu1ts indicate the major differences in the chemica1 behaviors of the photo1yti-ca11y and therma11y excited states for those heterocyc1es.

Synthesis and Characterization of 1,2-disubstituted -3-(pyrimidine-2-yl)-2,3- dihydro-1H-1,3-diazepine-4,7-dione

“…The 7-membered heterocyclic ring system: 1, 3-oxazepine has already been reported in the literature. Irradiation of 4-phenyl-2-oxa-3-azabicyclo [3.2.0] hepta-3, 6-diene in nhexane gave 2-phenyl-1, 3-oxazpeine in 80% yield [3][4][5][6][7][8] . Many of the benzodiazepines and their oxides show interesting sedatives, muscle relaxant, and anticonvulsant properties in animals [9].…”