Oxaziridines photochemical formation

Koyano and Tanaka found that E-to-Z- and Z-to- -photoisomerization takes place upon the irradiation of a solution of a-cyano-a,iV-diphenylnitrone in the presence of a triplet sensitizer, while the irradiation of E- or Z-forms of the nitrone in the absence of a sensitizer resulted in the formation of the corresponding oxaziridine. These results indicated that photochemical —> Z and Z —> isomerization take place from the triplet-excited nitrone, while the photochemical formation of the oxaziridine takes place from a singlet-excited nitrone (Scheme 8). 

Oxaziridines, the products of photochemical isomerization of polymeric nitrones, are characterized by high stability. The formation of an intramolecular hydrogen bond stabilizes the nitrone group with respect to UV-irradiation... 

The photochemical rearrangement of nitrones to amides often involves initial formation of oxaziridine intermediates. These oxaziridines can be isolated in good to excellent yields (Table 31). 

Acylaminyloxides 90 were obtained in photolysis of 81 c and 89 respectively99. The mechanism of formation of these radicals is not yet known. It is suggested that formation of acylaminyloxides 90 occurs from photochemically excited oxaziridines since 90a is also formed by irradiation of oxaziridine 91. On the other hand heating of 81 c in presence of oxygen gives acylaminyloxide 90a and an aminyloxide for... 

Spectroscopic evidence has been obtained for the formation of an oxaziridine intermediate (194) in the photochemical conversion of 6-cyanophenanthridine 5-oxide (193) into 5-ethoxyphenanthridone (195) (Scheme 79). ... 

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