Phenoxonium Ion Research Articles

Intramolecular cyclisation of phenolic oximes. Part I. Cyclisations with manganese(III) tris(acetylacetonate)

Reactions of a series of p-hydroxyarylpropan-2-one oximes with manganese(III) tris(acetylacetonate) resulted in intramolecular cyclisation to the corresponding spiro-isoxazolines by a two-electron oxidation in which an incipient phenoxonium ion is trapped by the oxime hydroxy-group. o-Hydroxyarylpropan-2-one oximes did not react in this way but gave instead benzofurans and the parent ketones.

Anodic oxidation of phenolic compounds. Part III. Anodic hydroxylation of phenols. A simple general synthesis of 4-alkyl-4-hydroxycyclo-hexa-2,5-dienones from 4-alkylphenols

The oxidation of simple, monohydric phenols at a lead dioxide anode in aqueous sulphuric acid has been studied. The effects of current density, electrolysis time, pH, concentration of phenol, and method of anode preparation on conversion and product distribution have been investigated, and optimal conditions for anodic hydroxylation of simple phenols have been deduced. In all cases studied the hydroxy-group entered the 4-position: thus 4-substituted phenols gave 4-substituted 4-hydroxycyclohexa-2,5-dienones, and phenols without substituents at C-4 gave p-benzoquinones. The former reaction provides a simple and efficient synthesis of these cyclohexa-2,5-dienone derivatives. A mechanism involving hydrolysis of an anodically generated phenoxonium ion is suggested. Evidence is presented which indicates that the phenoxonium ion is formed by ‘chemical’ oxidation with anodically generated lead dioxide. The lead dioxide anode is superior to carbon, nickel, and platinum anodes for hydroxylation.

Coupling of phenols via an anodically generated phenoxonium ion

Anodic oxidation of 2,6-di-t-butyl-p-cresol (I) in the presence of phenol, anisole, or 2,6-di-t-butylphenol gives the unsymmetrically coupled cyclohexa-2,5-di-enones (VIII), (IX), and (X)via a mechanism involving the phenoxonium ion (III).

Nouvelle voie d'accès aux dérivdś méthyl β- D-lyxofuranosiques à partir du méthyl 2,3,5-tri- O- p-tolylsulfonyl-β- D-ribofuranoside

The synthesis of derivatives of methyl β- D-lyxofuranoside has been accomplished starting from methyl tri- O-p-tolylsulfonyl-β- D-ribofuranoside. Treatment of this compound with sodium benzoate in N,N-dimethylformamide displaced the tosyloxy groups at C-3 and C-5. The resulting trans-benzoyloxysulfonate was further transformed stereospecifically into methyl 3,5-di- O-benzoyl-β- D-lyxofuranoside, after hydrolysis of the intermediate phenoxonium ion. A minor product, methyl tri- O-benzoyl-β- D-lyxofuranoside, was formed by benzoylation of the major product with N,N-dimethylformamide-sodium benzoate.

Anodic Reactions of Simple Phenolic Compounds

A study of the anodic reactions of phenols was made using the techniques of voltammetry, coulometry, and controlled potential electrolysis. It was shown that two entirely different anodic reactions are possible with phenolic compounds. The first is an electrophilic attack on the aromatic nucleus of the nonionized phenol with the irreversible removal of two electrons to give a mesomeric phenoxonium ion. As an example of this process an electrolysis of 2,6‐di‐tert‐butyl‐p‐cresol in acetonitrile at a platinum anode resulted in the addition of methanol to form 2,6‐di‐tert‐butyl‐4‐methyl‐4‐methoxy‐cyclo‐hexadienone in 65% yield. The second possible electrode reaction is the reversible removal of one electron from the phenoxide anion to give a phenoxy free radical. This process was illustrated by the electrolysis of the vanillinate anion in acetonitrile at a platinum anode to give dehydrodivanillin in 65% yield. It was found that half‐wave potentials for both electrode reactions could be correlated by Hammett‐type equations. Brief voltammetric experiments in 50% aqueous isopropanol on a carbon electrode indicated that both reactions could also occur in this system, depending on the pH and on the of the phenol being investigated.