Ipso nitration studies

Abstract

Reaction of pentamethylphenol (19) with nitrogen dioxide in benzene gives the 4-nitrodienone (21), the four isomeric 2,5,6,-trinitrocyclohex-3-enones (23-26), three isomeric 4,5,6-trinitrocyclohex-2-enones (32), (33), [(34) or (35)] and a 2-hydroxy-5,6-dinitrocyclohex-3-enone (36). Nitration of pentamethylphenol (19) with fuming nitric acid in dichloromethane, in contrast, gives no 4-nitrodienone (21) but yields instead the 4-nitratomethy1-2,5,6-trinitrocyclohex-3-enones (49-52), in addition to compounds (23), (24), (26), (32) and (36). The 4-nitratomethyl-2,5,6-trinitrocyclohex-3-enones (49-52) are formed via the quinonemethide (56). Reaction of 4-nitrodurenol (58) with nitrogen dioxide in benzene gives the four isomeric 2,4,5,6-tetranitrocyclohex-3-enones (67-70) and hydroxynitrocyclohex-3-enones (71-73) and (77).The mode of formation of the 6-hydroxy ketones (72), (73) and (77) was demonstrated by addition of nitrogen dioxide to the 6-hydroxycyclohexa-2,4-dienone (66). The mode of formation of the above compounds and the acyloin rearrangement products (74-76) are discussed Nitration of 4,6-dibromo-2-phenylphenol (105a) and 4-bromo-6-methyl-2-phenylphenol (106a) with fuming nitric acid in acetic acid, results in extensive nitro-debromination. The fuming nitric acid nitration of 6-methyl-4-nitro-2-phenylphenol (106c) gives complex mixtures, but reaction with nitrogen dioxide gives only six compounds, two of which (114,115) were isolated from the reaction mixture. The remaining four compounds (116), (121-123) were identified tentatively by spectroscopic methods. The mode of formation of compounds (114-116) and (121-123) are discussed. Reaction of 4-methyl-2,6-diphenylpheno1 (125) with nitrogen dioxide in benzene gives a complex mixture, from which the cyclohex-2-enones (126-131) were isolated. The mode of formation of these compounds is discussed. In the above reaction studies, the structures of products were assigned on the basis of their spectroscopic data and single-crystal X-ray analyses of selected compounds. X-ray crystal structures are reported for twenty compounds viz. (23), (24), (25), (32), (33), (36), (49), (67), (68), (71), (72), (74), (77), (114), (115), (126), (127), (128), (130) and (131).