Photochemical nitration by tetranitromethane part XXX. Product isolation and identification in the photochemical reaction of dibenzofuran

The photolysis of the charge-transfer complex of dibenzofuran (1) and tetranitromethane in either dichloromethane or acetonitrile gives t-2-nitro-r-1-trinitromethyl-1,2-dihydrodibenzofuran (4), the epimeric 4-nitro-1-trinitromethyl-1,4-dihydrodibenzofurans 5 and 7, the epimeric 4-hydroxy-1-trinitromethyl-1,4-dihydrodibenzofurans 6 and 8, 3-trinitromethyldibenzofuran (13), and the four isomeric nitrodibenzofurans 9-12. The five adducts 4-8 are formed via attack by trinitromethanide ion at C1 of the dibenzofuran radical cation, while 3-trinitromethyldibenzofuran is formed by decomposition of an adduct, itself formed via initial attack of trinitromethanide ion at C3 of the dibenzofuran radical cation. The regiochemistry of attack of trinitromethanide ion on the radical cation of the non-alternant dibenzofuran system is in keeping with earlier theoretical predictions. In 1,1,1,3,3,3-hexafluoropropan-2-ol solution the analogous photolysis of the charge-transfer complex of dibenzofuran (1) and tetranitromethane gives only the four nitrodibenzofurans 9-12, the attack of trinitromethanide ion on the radical cation of dibenzofuran being suppressed by the solvent. X-Ray crystal structures are reported for compounds 4, 6 and 13, compound 6 representing the first hydroxytrinitromethyl adduct to be unambiguously assigned this structure.