Methoxyarenes

On the basis of experience with dediazoniations as discussed in previous sections, one is surprised that in a methanolic solution of sodium methoxide practically no methoxyarene is formed directly but, in most cases, a plentitude of other primary compounds is detectable. 

We observed that the reduction side-reaction can be suppressed substantially by applying CO2 as the carrier gas (ref. 31). Perhaps the adduct of CO2 and NH3 acts as a Cu(I) ligand and protects the Cu(I) for reduction towards Cu(0). Recently a similar CO2 promoting effect was reported (ref. 32) for the liquid phase conversion of aromatic bromides towards methoxyarenes. 

Although no new method for formation of simple pyridazino[3,4-f]pyridazines has appeared since the publication of CHEC-II(1996), a further method for the construction of benzo-fused derivatives has been described <1997CHE750>. Electrophilic attack of the diazonium salts formed from aromatic amines 5, with sodium nitrite in acetic acid, upon the neighboring methoxyarene results in formation of pyridazino[3,4-f]cinnolines 1. 

During photolysis in methanol, fluoro- and methoxyarenes are formed without products resulting from hydrogen abstraction from the solvent.249... 

Poly(4-vinylpyridine)-supported bromate in nonaqueous solution has been used in the bromination of aromatic compounds with potassium bromide <2005SC1947>. This bromination method is simple, efficient, mild, and selective for methoxyarenes, anilines, and phenols. 

When the methoxyarene rings are tethered by carbon-heteroatom chains, as in 104, such oxidations proceed in intramolecular fashion and afford the benzo-annulated seven-membered heterocycles 105 (Scheme 33) (96CC1481, 98JOC7698, 01T345). Selected coupling reactions of the types shown in Schemes 32 and 33 have also been demonstrated with the polystyrene analogs of BTIB and DAIB (01T345). 

Selective demethylation of methoxyarenes. Boron trichloride is generally useful for selective cleavage of the more hindered methoxy group of polymethoxybenzenes and of peri-methoxynaphthalenes. 

Cerium(IV) ammonium nitrate has been used increasingly during the last decade in the synthesis of quinones, particularly as a means of effecting oxidative demethylation of methoxyarenes. 

The reaction can be extended to different methoxyarenes and mesi-tylene with different aliphatic and aromatic acyl chlorides and anhydrides (48%-91% yield). Some cases merit special comment the benzoylation of... 

Methoxyarenes. Phenols u DMF. 150°). Comparing to dime iher alkyl group larger than propy... 

Methoxyarenes. Phenols undergo O-methylation with methyl carbonates (K2CO3-D. 1F, 150°). Comparing to dimethyl carbonate the unsymmetrical carbonates with the. then alkyl group larger than propyl can be used in an open flask. 

De-O-benzylation. The oxidative ther functional groups, including second Oxidation of aromatic and heterm methoxyarenes to afford p-quinones reqi Benzofurans and substituted indoles u -ange readily to give benzannulated lactoa malealdehyde, which can be trapped I... 

Oxidation of aromatic and heteroaromatic compounds. The oxidation of methoxyarenes to afford p-quinones" requires acid catalysts. 

Demethylation of methoxyarenes NaOMe, and the demethylation occur dinone at 180 C. Certain phenolates i dibenzofuran derivatives. ... 

Demethylation of methoxyarenes. Me.iSiSNa is prepared from (MejSiljS and NaOMe, and the demethylation occurs in the presence of l,3-dimethyl-2-imidazoli-dinone at 180°C. Certain phenolates thus generated can undergo cyclization to give dibenzofuran derivatives. ... 

Benzoquinones were derived from the oxidation of electron-rich methoxyarenes by magnesium monoperoxyphthalate with a water-soluble iron porphyrin as catalyst (ref.45). 

The finding (ref. 126) that methoxyarenes complexed with chromium hexacarbonyl, thus forming arene chromium tricarbonyls, then undergo 3- rather than the anticipated 2-/4- substitution with certain nucleophiles has a potential application in the synthesis of cardanols and cardols. The method has a number of variants (refs. 127, 128) and is shown in the following scheme. Salicylates formed two isomers. 

Trifluoroacetylation/ Cobalt(II) chloride is a mild Lewis acid that catalyzes the uifluoroacetylation of methoxyarenes with the use of trifluoroacetic anhydride. 

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