5-Phenylisoxazole (4) and 4-phenylisoxazole (22) underwent phototransposition to 5-phenyloxazole (5) and 4-phenyloxazole (24) respectively. Labeling with deuterium or methyl confirmed that these phototranspositions occurred via the P 4 pathway which involves only interchange of the N2 and C3 ring position. Thus, 4-deuterio-5-phenylisoxazole (4-4d), 4-methyl-5-phenylisoxazole (10), and 5-methyl-4-phenylisoxazole (23) phototransposed to 4-deuterio-5-phenyloxazole (5-4d), 4-methyl-5-phenyloxazole (11), and 5-methyl-4-phenyloxazole (25) respectively. In addition to phototransposition, isoxazoles 4, 10, and 23 also underwent photo-ring cleavage to yield benzoylacetonitrile (9), α-benzoylpropionitrile (15), and aceto-α-phenylacetonitrile (26) respectively. Irradiation of 5-phenyl-3-(trifluoromethyl)isoxazole (16) in acetonitrile led to 5-phenyl-2-(trifluoromethyl)oxazole (17), the P 4 phototransposition product. Irradiation of 16 in methanol led to a substantial decrease in the yield of 17 and to the formation of a mixture of (E) and (Z)-2-methoxy-2-(trifluoromethyl)-3-benzoylaziridines 18a and 18b.

undergo phototransposition via a pathway involving only interchange of the N-2 and C-3 ring position. Additionally, the phototransposition of isoxazoles (I), (VI), and (IX) is accompanied by a photo-ring cleavage. The effect of a trifluoromethyl substituent on the photochemistry of 5-phenylisoxazole (I) is demonstrated with compound (XII). Irradiation of (XII) in methanol leads to a substantial decrease in the yield of phototransposition product (XIV) and to the formation of a mixture of the diastereomeric aziridines (XV) and (XVI). However, upon irradiation in acetonitrile, the only product obtained is (XIV). -(PAVLIK*, J. W.; MARTIN, H. S.; LAMBERT, K. A.; LOWELL, J. A.; TSEFRIKAS, V. M.; EDDINS, C. K.; KEBEDE, N.; J. Heterocycl. Chem. 42 (2005) 2, 273-281; Dep. Chem. Biochem., Worcester Polytech. Inst., Worcester, MA 01609, USA; Eng.) -H. Hoennerscheid 32-132