PHOTOCHEMICAL NITRATION BY TETRANITROMETHANE - PART XLIII - PHOTOLYSIS OF SOME STYRENE DERIVATIVES WITH TETRANITROMETHANE - MECHANISM OF ISOXAZOLIDINE FORMATION

The photochemical reaction of tetranitromethane in dichloromethane or acetonitrile with 4-methylstyrene (2a), styrene (2b), 4-chlorostyrene (2c), 3-chlorostyrene (2d) or 4-acetoxystyrene (2e) gives two stereois omeric isoxazolidines, henyl)ethoxy-3,3-dinitro-5-(X-phenyl)isoxazolid ine (3 and 4, X=4-Me, H, 4-Cl, 3-Cl or 4-AcO), a nitro ketone, nitrome thyl X-phenyl ketone (5, X=4-Me, H, 4-Cl, 3-Cl or 4-AcO) and a nitroni c ester, 3-nitro-5-(X-phenyl)-2-isoxazoline N-oxide (6, X=4-Me, H, 4-C l or 4-AcO). In each case, the (RS,RS)-stereoisomer 4 is the major iso xazolidine formed. The first step of the reaction is the photogenerati on of the triad [2(.+) NO2 (NO2)(3)C-]. In the formation of isoxazolid ines 3 and 4, and of the nitronic esters 6, the key intermediate is as sumed to be the substituted aminoxyl, 3,3-dinitro-4-(X-phenyl)isoxazol idin-N-oxyl (8, X=4-Me, H, 4-Cl, 3-Cl or 4-AcO) formed by reaction of the substituted styrene radical cation (2(.+)) with trinitromethanide ion followed by cyclization of the resulting carbon radical 7. Loss of nitrogen dioxide from 8 gives nitronic eaters 6, and trapping of the 1-(X-phenyl)-2-nitroethyl radical, formed by addition of NO2 at the be ta-carbon of 2, by aminoxyl 8, gives the isoxazolidines 3 and 4 direct ly.