Reactivities of Stable Rotamers. XXXIX. Thermal Decomposition of t-Butyl 3-Methyl-3-(substituted 9-triptycyl)peroxybutanoate Rotamers

Article abstract of DOI:10.1246/bcsj.70.457

The ap and sc rotamers of the title compound, where substituents are 1,4-dimethyl, 1,4-dimethoxy, 1,2,3,4-tetrafluoro, and 1,2,3,4-tetrachloro, were thermolyzed in toluene solutions to examine the effects of interactions between the radical center and the substituent. The rates of thermolyses were affected neither by the substituent nor by the rotameric positions, but the product distributions showed dependence on the substituent. In the ap-forms, the effectively bulkier the substituent at the 1-position, the higher the yields of the 5-membered ring compound. This was attributed to the degree of the tilting of the 9-substituent, which forces the radical center to be pushed into the triptycene skeleton. For the sc-forms, the chloro and the methyl substituents exhibited special effects, the former affording a colligation product between benzyl and 2-(1,2, 3,4-tetrachloro-9-triptycyl)-2-methylpropyl radicals and the latter showing a tendency of radical migration to the benzylic position. Comparison of the results of thermolyses of the 1,4-dimethyl peroxyester with those of 2(1H)-thioxo-1-pyridyl 3-(1,4-dimethyl-9-triptycyl)-3-methylbutanoate indicates that, although it is believed that these precursors afford the same 2-(1,4-dimethyl-9-triptycyl)-2-methylpropyl radicals, the product distributions were significantly different from each other. These results were attributed to the stabilizing effects of the sulfur compound on the radical in the solvent cage in the latter.