Self-Initiated Autoxidation of a Sterically Crowded Cycloheptatriene Derivative via Norcaradienyloxyl Radicals
作者:Toshikazu Kitagawa、Atsushi Miyabo、Hideki Fujii、Takao Okazaki、Tetsuya Mori、Masaki Matsudou、Takeshi Sugie、Ken'ichi Takeuchi
DOI:10.1021/jo961321p
日期:1997.2.1
An extremely crowded cycloheptatriene derivative, 1,3,5-tri-tert-butyl-7-(9-phenyl-9-fluorenyl)-1,3,5-cycloheptatriene (1), underwent autoxidation at 25 degrees C in cyclohexane to give 4-tert-butyl-2-pivaloylphenol (3) (33%), 5-tert-butyl-2-pivaloylphenol (4) (11%), 1,3,5-tri-tert-butylbenzene (5) (5%), tert-butyl 9-phenyl-9-fluorenyl peroxide (6) (44%), bis(9-phenyl-9-fluorenyl) peroxide (7) (7%), 1,1',3,3',5,5'-hexa-tert-butyl-7,7'-bicycloheptatriene (8) (2%), and carbon monoxide (4%). ESR studies showed that 1 dissociates into 1,3,5-tri-tert-butyltropyl radical (II) and 9-phenylfluorenyl radical (12) at 25-85 degrees C. The enthalpy and entropy of dissociation were determined to be 23.3 kcal/mol and 22.0 cal/mol . K, respectively. The formation of 3-5 can be explained by a mechanism involving attack of molecular oxygen to 11 and subsequent valence tautomerism of cycloheptatrienyloxyl radicals to norcaradienyloxyl radicals.