Photochemical nitration by tetranitromethane. Part XLIV. † Some reactions of 2-phenylpropene and 2,4,6-trimethylstyrene with tetranitromethane: Competition between the radical chain addition reaction and isoxazolidine formation: Nitrogen inversion in some isoxazolidines

Reaction of 2-phenylpropene with tetranitromethane in dichloromethane occurs either slowly in the dark or more rapidly photochemically to give 1-nitro-2-phenyl-2-trinitromethylpropane (1) and the two diastereomers of 5-methyl-2-(2′-nitro-1′-phenyl)ethoxy-3,3-dinitro-5- phenylisoxazolidine (5 and 6). In diethyl ether solution these products are also formed, but the yields of 5 and 6 are increased at the expense of the nitro-trinitromethyl adduct 1. At 23°C in [²H]chloroform solution each isoxazolidine 5 and 6 exists as two N-invertimers. Variable temperature ¹H NMR studies of 5 and 6 revealed band broadening and coalescence of all signals in the temperature range 50-100°C; the rate constants and corresponding free energies of activation were identical for the two isoxazolidines 5 and 6, ΔG‡ = 74.7(5) kJ mol^-1 at 353 K. A single-crystal X-ray analysis of isoxazolidine 5 is reported. Photolysis of 2,4,6-trimethylstyrene with tetranitromethane in either dichloromethane or acetonitrile gives the nitro-trinitromethyl adduct, 2-(2′,4′,6′-trimethylphenyl)-1-nitro-2-trinitromethylethane (9), and nitromethyl 2,4,6-trimethylphenyl ketone (10). Base-catalysed eliminations of nitroform from adducts 1 and 9 give the corresponding (E)-nitro alkenes 7 and 11, respectively, kinetic studies showing that the rate of elimination from the secondary but sterically more compressed trinitromethyl compound 9 was greater (x15) than for the tertiary trinitromethyl compound 1. The modes of formation of adducts 1 and 9, isoxazolidines 5 and 6, and nitro ketone 10 are discussed.