FRIEDEL–CRAFTS REARRANGEMENTS IN BRANCHED CONDENSED RING SYSTEMS: I OCTAMETHYLOCTAHYDROANTHRACENE

Treatment of 1,1,4,4,5,5,8,8-octamethyl-1,2,3,4,5,6,7,8-octahydroanthracene (C22H34, I) with aluminum chloride produced a new hydrocarbon (C22H32, II) containing a conjugated olefinic double bond. Hydrocarbon II was proved to be 1,1,5,5,8,8-hexamethyl-3-isopropyl-5,6,7,8-tetrahydrobenzindene by spectral data, by oxidative studies, and by a synthesis of its reduction product, 1,1,5,5,8,8-hexamethyl-3-isopropyl-5,6,7,8-tetrahydrobenzindane (III). A benzenonium ion mechanism is postulated to explain the 1,2-phenyl shift accompanied by dehydrogenation in the formation of II from I. The detection of hydrogen in the off gas of the rearrangement supports this mechanism. A similar benzenonium ion mechanism can be applied to elucidate the mechanism of isomerization of tertiary to secondary alkylbenzenes reported in the literature.