Kwo-Hrong Lai

Rearrangements in polysubstituted cyclohexadienyl carbonium ions

Abstract Allyl migration in the 2,6-di-t-butyl-1,4-dimethylcyclohexadienyl carbonium ion initially proceeds by an apparently normal [1,2] shift to give the expected aromatic product. In moderately concentrated acid, however, the initial rearrangement product undergoes further rearrangements in which migration of a methyl group rather than an allyl group is the major process. This is accounted for by assuming that protonation occurs most rapidly at the position between the two t-butyl groups, thus minimizing steric strain between the substituents on the aromatic ring. Studies on migration of a deuterium labelled allyl group indicate that the allyl group can undergo processes involving allylic inversion as well as [1,2] shifts.

Carbon versus oxygen alkylation in reactions of phenoxide ions with cyclopropylmethyl bromide

Suspensions of phenoxide salts in toluene react with cyclopropylmethyl bromide to give appreciable amounts of alkylation at the ortho- and para-positions, as well as at the oxygen atom, although cyclopropylmethyl bromide reacts no faster than do simple alkyl bromides, and show no scrambling of the methylene carbons.

Allylic inversion of the migrating group in the acid-catalysed rearrangement of a 2,6-di-t-butylcyclohexa-2,5-dienone

The acid-catalysed migration of an allyl group from C-4 to C-2 of a 2,6-di-t-butylcyclohexa-2,5-dienone proceeds with essentially complete allylic inversion, while migration to C-3 proceeds without inversion.