Ipso-nitration studies (1989)
AuthorsWaller, A. G.show all
Reaction of 2,4,6-trialkyl phenols with nitrogen dioxide in organic solvents is known to yield trinitro and dinitro hydroxy cyclohexenones as major products of reaction. These compounds have been postulated as forming via the transient intermediacy of 6-nitrocyclohexa-2,4-dienones. In the first part of the thesis the reactions of the C6-benzyl analogues of 4-t-butyl-2,6- dimethylphenol (206) and 2-t-butyl-4,6-dimethylphenol (216), compounds (229) and (230) respectively, with nitrogen dioxide are shown to give products analogous to those observed in the reactions of the parent phenols. Reaction of 6-benzyl-4-t-butyl-2,6-dimethylcyclohexa-2,4-dienone (229) with nitrogen dioxide in benzene solution is shown to give all four stereoisomeric 2,5-dinitrocyclohex-3-enones (240)-(243), and three of the four possible stereoisomeric 2-hydrox:y-5-nitrocyclohex-3-enones (244)(246). In contrast, reaction of 6-benzyl-2-t-butyl-4,6-dimethylcyclohexa- 2,4-dienone (230) with nitrogen dioxide in dichloromethane solution is shown to yield cyclohex-2-enones as the major products of reaction - namely, the four stereoisomeric 4,5-dinitrocyclohex-2-enones (231)-(234). The cyclohex-3-enones (235)-(238) are isolated as minor products of reaction. In the second part of the thesis, the reactions of p-cymene (401) with nitrogen dioxide in acetic anhydride and dichloromethane solutions are explored. In dichloromethane solution, all the products of reaction, with the exception of 2-nitro-p-cymene (403) and p-nitrotoluene (405), can be accounted for in terms of a mechanism involving initial hydrogen atom abstraction from the iso-propyl group of the p-cymene molecule. In contrast, the reaction of p-cymene in acetic anhydride solution is shown to yield a multitude of products, including 2-nitro-p-cymene (403) and p-nitrotoluene (405), the two substituted aromatic compounds (414) and (415), and the eleven substituted cyclohexenes (410)-(413), (416)-(421) and (434). The mode of formation of these cyclohexenes in particular, is discussed in terms of an overall mechanistic scheme for the reaction of p-cymene in acetic anhydride solution. Throughout the thesis, extensive use is made of single crystal X-ray structure analysis, and high field Fourier transform n.m.r. techniques, in determining molecular structure. The structures of fifteen compounds have been determined by single crystal X-ray structure analyses.