Intramolecular electrophilic aromatic substitution in gas-phase-protonated difunctional compounds containing one or two arylmethyl groups

✍ Scribed by M. Edelson-Averbukh; A. Mandelbaum

• Book ID: 102377541
• Publisher: John Wiley and Sons
• Year: 2003
• Tongue: English
• Weight: 191 KB
• Volume: 38
• Category: Article
• ISSN: 1076-5174
• DOI: 10.1002/jms.537

✦ Synopsis

Abstract

A variety of dibenzyl esters and ethers undergo a rearrangement process upon isobutane chemical ionization and collision‐induced dissociation of their MH^+^ ions, whereby a new bond is formed between the two benzyl groups, giving rise to abundant [C~14~H~13~]^+^ (m/z 181) ions. This rearrangement has been explained as an intramolecular electrophilic substitution in the gas phase occurring in an ion–neutral complex formed by the cleavage of one of the benzyl–oxygen bonds. A similar highly efficient intramolecular electrophilic substitution takes place in di‐α‐ and β‐naphthylmethyl adipates affording m/z 281 [C~22~H~17~]^+^ ions, but not in the sterically hindered di‐9‐anthracylmethyl adipate. An analogous efficient rearrangement occurs in benzyl α‐ and β‐naphthylmethylcyclohexane‐1,4‐dicarboxylates and in benzyl α‐ and β‐phenylethylcyclohexane‐1,4‐dimethanol ethers. The analogous rearrangement is much less efficient in benzylallyl, benzylpropargyl and benzyl‐9‐anthracylmethyl derivatives, even less in benzylisopropyl and benzylacetyl analogs, and it is absent in benzyltetrahydropyranyl derivatives. The distinctive behavior of the protonated difunctional benzyl derivatives is interpreted in terms of the energy requirements of the O—R bond heterolysis of the protonated functionalities, the ability of the neutral R′ groups (non‐dissociated from the oxygen atom) to play the role of the nucleophile in the intramolecular electrophilic substitution processes and the electrophilicity of the R^+^ ions. Copyright © 2003 John Wiley & Sons, Ltd.