Rearrangements Involving the Phenonium Ion:  A Theoretical Investigation

Abstract

Rearrangements involving the phenonium ion were investigated by means of a B3LYP/6-311G(d,p) study in which the effect of solvent has been incorporated by using a PCM solvation model. A rationalization of the whole set of experimental facts reported both in the gas phase and in solution was possible thanks to the characterization of protonated benzocyclobutene as a minimum energy structure and, particularly, to the important preferential stabilization in solution of the TS for the isomerization of the phenonium ion to the alpha-methylbenzyl ion, which reduces the Gibbs energy barrier of 26.6 kcal/mol for this process in the gas phase to a more accessible one of 18.7 kcal/mol in solution.

Copper‐Catalyzed Direct Transformation of Secondary Allylic and Benzylic Alcohols into Azides and Amides: An Efficient Utility of Azide as a Nitrogen Source

“…It was also observed that an aryl group migration is preferable over that of a vinyl group, which might be from the stabilization of azidonium intermediate II by a phenonium ion. Therefore, the overall observed migratory aptitude is: aryl group > vinyl group 37b,37c…”

Looking for a Paradigm for the Reactivity of Phenonium Ions

“…The β‐stabilization effect of the aryl group in phenethyl cations and the attending formation of a σ‐bridged intermediate, the phenonium ion, was first evidenced by Cram1 through pioneering studies on the stereochemical course of the solvolysis of optically active phenethyl sulfonates. The role of such an intermediate has since been explored from both the experimental2 and computational points of view 3. Recent work favours a continuum of situations in between the phenethyl cation I and the σ‐bridged structure III , and the possible role of a weak π complex II (see Scheme ) 4.…”

Photochemical Arylation of Alkenols: Role of Intermediates and Synthetic Significance

“…Thus, in the key step the C 2 –C 3 bond can freely rotate (Scheme ), in accord with the idea that the first intermediate from the triplet cation is single‐bonded (formulae 17 / 17′ ) and ISC and intramolecular cyclization on the OH group follow. Should a doubly bonded (phenonium) cation be the first intermediate, a stereospecific arylation would take place,1,4 as equilibration of stereoisomeric phenonium ions over an open‐chain isomer is too slow 28. The exclusive formation of the trans isomers is determined by the steric hindering by the ethyl group.…”