FRIEDEL–CRAFTS REARRANGEMENTS: II. REARRANGEMENTS DURING CYCLIALKYLATION OF ε-ARYL-SUBSTITUTED COMPOUNDS

Friedel–Crafts cyclialkylation of aromatics such as 1,1,4,4-tetramethyltetralin with 2,6-dichloro-2,6-dimethylheptane does not yield a benzsuberane as previously reported. Several 5-phenyl-substituted chlorides, alcohols, and olefins were synthesized for cyclialkylation studies. These included 2-chloro-2,6-dimethyl-6-phenylheptane (Xa), 3-chloro-3,7-dimethyl-7-phenyloctane (Xb), 2,6-dimethyl-6-phenyl-2-heptanol, 2,6-dimethyl-6-phenyl-2-hepten-4-one (XX), 2-chloro-6-methyl-6-phenylheptane, and 1-chloro-5-phenylpentane (XXIV). Cyclialkylation of Xa (and the corresponding alcohol), Xb, 2-chloro-6-methyl-6-phenyl-heptane, and XXIV produced alkyltetralins instead of benzsuberanes. Evidence is presented and discussed which indicates that the alkyltetralins form by rearrangements in the side chains of the aryl-substituted systems. The alternative mechanism involving rearrangement of a benzsuberane intermediate via a phenonium ion mechanism was unequivocally ruled out in at least one case—the cyclization of Xb. Nuclear magnetic resonance evidence is presented for the structural assignments.