SENSITIZED PHOTO-OXYGENATIONS OF DELTA-2-OXAZOLIN-5-ONES AND RELATED STUDIES

Sensitized photooxygenations of a few Δ2-oxazolin-5-ones such as 2, 4-diphenyl-Δ2-oxazolin-5-one (3a), 4-benzyl-2-phenyl-Δ2-oxazolin-5-one (3b), and 4-benzylidene-2-phenyl-Δ2-oxazolin-5-one (17) have been studied, using Rose Bengal as a sensitizer. The photooxygenation of 3a in a mixture of benzene and methanol for 0.25 h gave a mixture of bi-4, 4'-(2, 4-diphenyl-Δ2-oxazolin-5-one) (9a, 44%) and benzamide (28%), whereas the photooxygenation of 3a in methanol for 0.5 h gave a mixture of dibenzamide (8a, 40%) and benzamide (49%). In contrast, the irradiation of 3a in either benzene or cyclohexane gave only benzamide. Nickel peroxide oxidation of 3a gave a 38% yield of the bioxazolinone 9a. Direct irradiation of 9a in either benzene or acetone gave benzamide, whereas the thermolysis of 9a in refluxing o-dichlorobenzene gave a 3% yield of 2, 3, 5, 6-tetraphenylpyrazine (16). Photooxygenation of 3b gave a 42% yield of IV-benzoylphenylacetamide (8b), whereas the direct irradiation of 3b gave only benzamide. Nickel peroxide oxidation of 3b gave bi-4, 4'-(4-benzyl-2-phenyl-Δ2-oxazolin-5-one) (9b, 40%). Direct irradiation of 9b gave exclusively benzamide. The photooxygenation of 17 in methanol gave a mixture of the -benzamidocinnamate 18 (53%) and benzamide (29%), whereas the direct irradiation of 17 gave a mixture of a-benzamidocinnamic acid (20) (31%) and benzamide (52%). Resonable mechanisms have been suggested for the formation of the different products in these reactions. Copyright © 1979, American Chemical Society. All rights reserved.