Anisole rearrangement

Ciesol and xylenol can be prepared by the methylation of phenol with methanol over both acid and base catalysts. It is postulated that phenol methylation on acid catalysts proceeds through the initial formation of anisole (methoxybenzene [100-66-3]) followed by intramolecular rearrangement of... 

Sulfation by sulfamic acid has been used ia the preparation of detergents from dodecyl, oleyl, and other higher alcohols. It is also used ia sulfating phenols and phenol—ethylene oxide condensation products. Secondary alcohols react ia the presence of an amide catalyst, eg, acetamide or urea (24). Pyridine has also been used. Tertiary alcohols do not react. Reactions with phenols yield phenyl ammonium sulfates. These reactions iaclude those of naphthols, cresol, anisole, anethole, pyrocatechol, and hydroquinone. Ammonium aryl sulfates are formed as iatermediates and sulfonates are formed by subsequent rearrangement (25,26). 

Bis(trimethylsilyl)sulfate 559, which is readily available from TCS 14 and H2SO4 in 76% yield [94], reacts on heating with anisole to form the trimethylsilyl ester of p-methoxybenzenesulfonic acid 1331 in 92% yield [95]. The hexamethyldi-siloxane (HMDSO) 7 and H2O formed are removed during the reaction by azeotropic distillation [95]. On heating of acetyl chloride with 559 the probable intermediate 1332 rearranges to give 1333 in 63% yield. The last reaction can be extended to other acid chlorides [95] (Scheme 8.37). 

The addition of anisole to cyclopentene gives an 1,3-adduct which rearranges to tricycloundecenone in the presence of traces of acid (4.41)446). 

In the field of fine chemical synthesis there is an urgent need to substitute the cleaner technologies for the old polluting ones. It is hoped that the large economic and environmental benefits brought by the recently developed catalysis processes—acetylation of anisole and of veratrole, Beckmann rearrangement, and so forth—will initiate great strides in this field. 

Molenaar-Langeveld, T.A. Ingemann, S. Nibbering, N.M.M. Skeletal Rearrangements Preceding Carbon Monoxide Loss From Metastable Phenoxymethylene Ions Derived From Phenoxyacetic Acid and Anisole. Org. Mass Spectrom. 1993, 28, 1167-1178. 

A minor variant of this, method makes use of the reaction between an anisole and a 3-halogenopropanoyl chloride (14CB2585). These same 3-substituted acid chlorides react with phenols to give esters and a Fries rearrangement is now a prerequisite of chromanone formation (58JCS1190). 

There is, as is well known, a close similarity between the crystalline and porous structures of silicalite-1 and silicalite-2. The same similarity therefore exists between TS-1 and TS-2, and it appears logical that they should have very similar catalytic properties. TS-2 has been evaluated as a catalyst for many different reactions, such as Beckmann rearrangement of cyclohexanone oxime with vapor-phase reactants H202 oxidation of phenol, anisole, benzene, toluene, n-hexane, and cyclohexane and ammoximation of cyclohexanone. As described in detail in Section V.C.3, differences that had been claimed between the catalytic properties of TS-1 and those of TS-2 have not been substantiated. Later investigations have shown that, when all the relevant parameters are identical, the catalytic activities of TS-1 and TS-2 are also identical. The small differences in the crystalline structure between the two materials have no influence on their catalytic properties (Tuel et al., 1993a). 

A similar transformation was observed with the rhodium trifluoroacetate catalyzed decomposition of diazo ketones in the presence of benzene (Scheme 32).130 The cycloheptatrienes (147) formed in this case were acid labile and could be readily rearranged to benzyl ketones (148) on treatment with TFA. The reaction was effective even when the side chain contained reactive halogen and cyclopropyl functionality, but competing intramolecular reactions occurred with benzyl diazomethyl ketone. A more exotic example of this reaction is the rhodium(ll) trifluoroacetate catalyzed decomposition of the diazopenicillinate (149) in the presence of anisole, which resulted in the formation of two cycloheptatriene derivatives (150) and (151) (equation 35).m... 

Triflic acid is also efficient in the alkylation of electron-rich aromatics (anisole, 1,3-dimethoxybenzene, 2-methylfurane, pyrrole, benzofurane, indole) with secondary benzylic alcohols and 3-phenylallyl alcohols (50°C, 1-9 h, 66-95% yield).201 Benzene, toluene, and halobenzenes are also alkylated with hydroxy-biindantetraone 53 in triflic acid within 1-2h202 [Eq. (5.78)]. Suprisingly, however, the primary products (with the exception of the 4-methylphenyl-substituted compound) undergo rearrangement upon prolonged treatment to yield alkenes... 

Nafion-H is also very efficiently catalyzes the rearrangement of anisole, methy-lanisoles, and phenetole to ring-alkylated phenols and products of transalkylation when vapors of the alkyl aryl ethers are passed over it at temperatures higher than 160°C. At these reaction temperatures, some of the starting alkyl phenyl ethers... 

When adduct 88a was heated in an anisole solution, a thermal rearrangement took place and the thiophene derivative 89 formed (Equation 9) <1999HAC167>. 

Figure 17.50 shows how a benzyl alkoxide can be reduced in this way. Here, the reduction is part of the synthesis of an alkylated aromatic system. The target molecule contains a primary alkyl group. It is not possible to introduce this alkyl group by way of a Friedel-Crafts alkylation into the ortho-position of anisole in a regioselective fashion and without rearrangements (see Section 5.2.5). 

In view of the importance of 2-nitroimidazoles as antibiotics e.g. 2-nitroimidazoIe azomycin ) and the problems involved in their synthesis (usually via the 2-aminoimidazole) it seemed worthwhile to attempt to prepare these compounds by thermal rearrangement of the (V-nitro compounds (by analogy with the well-known reactions of 1-nitro-pyrazoles and -indazoles) (Chapter 4.04). Thus, when 1,4-dinitroimidazole (16) is heated at 140 °C in chlorobenzene, benzonitrile or anisole there is conversion into 2,4- and 4,5-dinitroimidazoles, but considerable denitration can also occur, giving 4-nitroimidazole (Scheme 6). 2-Methyl-l,4-dinitroimidazole rearranges smoothly to 2-methyl-4,5-dinitroimidazole, but 5-methyl-l,4-dinitroimidazole appears to denitrate in preference to any other reaction. Further study of these reactions is indicated. 

The migration of an N-nitro substituent to a ring carbon has also been noted thus at 115-120°C in chlorobenzene" or anisole l,4(5)-di-nitroimidazole gives 2,4-dinitroimidazole " and 4,5-dinitroimid-azole. There is also considerable denitration. 2-Methyl-l,4(5)-di-nitroimidazole also gives the 4,5-dinitro isomer on thermolysis, but 4-methyl-l,5-dinitroimidazole fails to rearrange. ... 

---