Friedel–Crafts rearrangements. IV. Cyclialkylations and hydride transfers on phenylalkyl chlorides

Abstract

A number of phenylalkyl chlorides werc synthesized for a comparative study of Friedel-Crafts cyclialkylations and competing reactions involving hydride exchange. Thc synthetic work showed that phenylbutyl alcohols, especially a tertiary alcohol, may cyclize directly with chlorinating agents to yleld tetralins. Cyclialkylation prod~~cts from phenylpcntyl chloridc include I-methyltetralin (4), 11-pentylbenzene, 1-methyl-3,4-dihydronaphthalene, and methylnaphthalene. A reaction sequence is given involving dealkylation of 4 and hydride transfers. Phenylbutyl chloride yiclded tetralin, N-butylbenzene, and naphthalene.I-Chloro-4-methyl-4-phenylpentane yielded 1,l-dimethyltetralin (lo), 2-methyl-5-phenylpentane ( l l ) , and a small amount of 2-n1etliyl-2-pl~enylpentanc (12). Hydrocarbon 11 formed from 10 after cyclialkylation, while 12 formed by hydride transfer preceding cyclization. Phenylpropyl chloride yielded mainly a hydride transfer product (propylbenzene) and not indane. Treatment of this chloride containing deuterium labels at C-1 and C-2 showed that the hydride ion rearranges from the carbon adjaccnt to the halogen. I-Chloro-3-nlethyl-3-phenylbutane yielded a co~nplex mixture including t-pentylbenzene, 2-phenyl-3-methylbutane, and products of higher molecular weight.