Photochemical nitration by tetranitromethane. Part XLI. Addition ipso to a methoxy group and the effect of methanol in the photochemical reaction between 1,4-dimethoxynaphthalene and tetranitromethane

The photolysis of the charge transfer complex between 1,4-dimethoxynaphthalene and tetranitromethane in dichloromethane gives mainly 1,4-dimethoxy-2-nitronaphthalene (1), 1,4-dimethoxy-2-trinitromethylnaphthalene (2) and 4-methoxy-2-(dinitromethylene)-1(2H)-naphthalenone (3) together with smaller amounts of the labile adducts 1,4-dimethoxy-2-trinitromethyl-1,2-dihydronaphthalen-1-ol (4), 1,4-dimethoxy-2-nitro-1-trinitromethyl-1,2-dihydronaphthalene (5) and 1,4-dimethoxy-1-nitro-2-trinitromethyl-1,2-dihydronaphthalene (6). Photolysis in acetonitrile gives higher yields of adducts 4 and 5. Photolysis in dichloromethane containing methanol gives mainly 1,1,4-trimethoxy-2-trinitromethyl-1,2-dihydronaphthalene (7) and 1,1,4-trimethoxy-2-nitro-1,2-dihydronaphthalene (8). Photolysis in acetonitrile containing methanol gives high yields of 8 and 4,4-dimethoxy-3-nitro-3,4-dihydro-1(2H)-naphthalenone (9). The formation of adducts via attack of trinitromethanide ion or nitrogen dioxide ipso to a methoxy group during the photolysis of 1,4-dimethoxynaphthalene and tetranitromethane is discussed, and arguments are presented that such adducts give compounds 2 and 3 via rearrangement and/or elimination reactions. The effect of methanol and the mode of formation of compounds 7-9 via nucleophilic addition or nucleophilic displacement are discussed. X-Ray crystallographic structures are reported for 1,4-dimethoxy-2-trinitromethylnaphthalene (2) and 4-methoxy-2-(dinitromethylene)-1(2H)-naphthalenone (3).