The anodic oxidation in methanol of a series of alkylanisoles and hydroquinone ethers, and of p-xylene has been studied. It was established that the initial step in the product formation always involves direct anodic oxidation of the aromatic compound to the corresponding cation radical. If the electrolysis is conducted under conditions where formation of methoxyl radicals also takes place (platinum anode, supporting electrolyte NaOMe) nuclear methoxylation dominates. Substitution in the nucleus of the aromatic compound presumably occurs either by nucleophilic attack of a methoxide ion on the anodically generated cation radical or by a coupling reaction between the latter and an anodically generated methoxyl radical. If the electrolysis is conducted under conditions where formation of methoxyl radicals does not take place (carbon or platinum anode with supporting electrolyte LiBF4) side-chain oxidation of p-alkylanisoles and p-xylene, with the formation of benzyl ethers, benzaldehyde dimethyl acetals, or ortho-esters of benzoic acids becomes important. This side-chain oxidation occurs via nucleophilic attack of methanol on a benzyl cation formed by deprotonation-anodic oxidation of the initially formed cation radical. Phenol ether cation radicals without p-alkyl substituents under these conditions either dimerise or undergo nuclear methoxylation via nucleophilic attack of methanol on the cation radical.For a review of previous work see N. I,. \Yeinberg, ' 'I'ecliniques of Electro-organic Synthesis,' P a r t I , 1' . 2 3 7 ; vol. \ r .of ' Technique5 of Organic Chemistry,' ed. :I. \Vt.issbc.rger,

Anodic oxidation in acetonitrile of a series of diarylalkanes (1-13) substituted with a phenol ether group (E) at one end and a phenolic group (P) at the other end was investigated. High yields of spirodienones (14-19) can always be obtained from the diarylpropanes when E is 3,4-dimethoxyphenyl (1-6). This anodic cyclization reaction follows three mechanistic pathways: electrophilic attack by the cation radical product from the ether moiety on the unoxidized phenolic part, intramolecular coupling between the cation radical product from the ether moiety and the radical product from the phenolic moiety, or electrophilic attack by the phenoxonium ion product from the phenolic moiety on the unoxidized ether part. When E is 3methoxyphenyl, high yields of spirodienones are obtained only if the 3 and 5 positions of the phenolic part are blocked (8).The cyclization then follows the phenoxonium ion pathway. When E is 3,4,5-trimethoxyphenyl, the product is a polymer obtained via the cation radical of the ether part. Diarylethanes or -butanes did not cyclize on anodic oxidation. Oxidation of the compounds (1-13) using thallium tris(trifluoroacetate) (TTFA) was also investigated. The diarylethanes and -butanes gave no cyclization products with this reagent, but all the diarylpropanes (1-9) gave high yields of the corresponding spirodienones (14-24). The high selectivity of TTFA appears to be due to initial formation of a thallium phenolate.

The products and yields obtained on anodic oxidation in methanol of a series of phenols (la-h) have been investigated as a function of anode material, anode potential, methanol concentration, supporting electrolyte, temperature, and substituents ortho-and para-Methoxylated and dimeric products were observed However, experimental conditions w e r e found which, in favourable cases, allow selective formation of para-methoxylated products (isolated as a para-dienone or para-benzoquinone), ortho-methoxylated products (isolated as an orthodienone or the Diels-Alder adduct of this dienone), or dimeric products. The methoxylated products are formed via nucleophilic attack of methanol on an anodically generated phenoxylium ion, the dimeric products are probably formed by dimerisation of anodically generated phenoxyl radicals. QUINONES (13), quinone acetals (8), and dienones [(Z) and(4)] are of great interest both in themselves and as versatile synthetic precursors. In a previous publication dealing with the anodic hydroxylation of phenols we described a simple synthesis of quinones and 4-alkyl-4-hydroxycyclohexa-2,5-dienones. In this paper we describe a systematic investigation of the anodic methoxylation of phenols and the use of this reaction for the synthesis of quinones, quinone hemiacetals, 4-alkyl-4-methoxycyclohexa-2,5-dienones, and 2-alkyl-2met hoxycyclohexa-3,5-dienones. A similar invest igation of the oxidation with thallium(II1) nitrate of a number of phenols in methanol solution has been published recent 1 y .

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