Ipso nitration studies

In the first part of the thesis the reaction of 1,3,5- trichloro-2,4,6-trimethylbenzene (32) with fuming nitric acid is shown to give the C2-epimeric pair of 6-hydroxy-2,5- dinitrocyclohex-3-enones (42) and (43). Rearrangement of each of those hydroxydinitro compounds under mildly basic conditions gives mixtures of the Cl-epimeric 2,5-dinitrocyclopent-3-en-1-ols. Similar acyloin rearrangement studies are reported for the hydroxydinitro compounds (8), (10), (29) and (30). During the course of these base-catalysed rearrangements an unusual rearrangement was observed of 1-acetyl-3,t-5-dichloro-2,4- dimethyl-c-2,5-dinitrocyclopent- en-r-1-ol (50) in acetone to give the unexpected C6-epimeric compound, 3,t-5-dichloro-t-6- hydroxy-2,4,6-trimethyl-r-2,5-dinitrocyclohex-3-enone (54). Nitration of the polysubstituted 6-methylphenols, 2,3,4,5- tetrabromo-6-methylphenol (2), 2,4,5-tribromo-3,6-dimethylphenol (5), 3,4,5-tribromo-2,6-dimethylphenol (28), 3,5-dichloro-2,4,6- trimethylphenol (41) and 2,4-dibromo-3,5,6-trimethylphenol (57), with fuming nitric acid in acetic acid had been shown earlier to give 6-hydroxy-2,5-dinitrocyclohex-3-enones. In the second part of the thesis the corresponding reactions of these phenols with nitrogen dioxide in either cyclohexane or acetic acid are discussed. For most compounds the reaction products are identical with those obtained from the fuming nitric acid nitration, except that for 2,4-dibromo-3,5,6-trimethylphenol (57) 2,5,6-trinitrocyclohex-3-enones are obtained in the nitrogen dioxide reactions. In the third part of the thesis the study of the reactions of phenols with nitrogen dioxide, in cyclohexane or benzene, is extended to the 2,4,6-trialkylphenols, 4-t-butyl-2,6- dimethylphenol (66), 2-t-butyl-4,6-dimethylphenol (79), 2,4-di-t-butyl-6-methylphenol (84), 2,6-di-t-butyl-4-methylphenol (62) and 2,4,6-tri-t-butylphenol (98). These compounds give a diverse range of products arising from initial ipso substitution, but the structures of the products which are formed can be accommodated within a mechanistic scheme which is discussed. In the final part of the thesis is described the formation of a phenol coupling product, 4-t-butyl-r-2-(4'-t-butyl-2' ,6'-dimethylphenoxy)- t-6-hydroxy-2,6-dimethyl-t-5-nitrocyclohex-3- enone (109), in a reaction mixture derived from the reaction of 4-t-butyl-2,6-dimethylphenol (66) with one molar-equivalent of nitrogen dioxide. The structure of this compound is determined. Throughout the thesis extensive use is made in product structure determination of single crystal X-ray analysis and, in all, seventeen crystal structures are reported