Photochemical nitration by tetranitromethane. Part XVIII. The regiochemistry of nitrito/trinitromethyl and nitro/trinitromethyl addition to 2,3-dimethylnaphthalene: Thermal 1,3-dipolar additions of nitro groups to alkenes

The photolysis of the 2,3-dimethylnaphthalene-tetranitromethane charge-transfer complex gives 2,3-dimethyl-1-nitronaphthalene, 2,3-dimethyl-5-nitronaphthalene and adducts: epimeric pairs of 6,7-dimethyl-1-nitro-4-trinitromethyl-1,4-dihydronaphthalene 7 and 8, 1-hydroxy-6,7-dimethyl-4-trinitromethyl-1,4-dihydronaphthalene 11 and 12, 2,3-dimethyl-1-nitro-4-trinitromethyl-1,4-dihydronaphthalene 13 and 14, and the structurally similar trans-6,7-dimethyl-2-nitro-1-trinitromethyl-1,2- dihydronaphthalene 9 and trans-2-hydroxy-6,7-dimethyl-1-trinitromethyl-1,2- dihydronaphthalene 10. At +20 °C in either dichloromethane or acetonitrile the adducts 7-14 comprise some 70% of the product mixture, but at -20 °C in either solvent the total adduct yield is reduced to ca. 31%. In adduct formation trinitromethanide ion reacts preferentially at C-5 in the 2,3- dimethylnaphthalene radical cation. Adducts 9 and 10 undergo thermal cycloaddition in (²H)chloroform at 22 °C to give the nitro cycloadduct 16 and hydroxy cycloadduct 15, respectively. An X-ray crystal structure is reported for hydroxy cycloadduct 15, as are preliminary results of a single crystal X-ray analysis of adduct 7.