Ethers aryl methyl

EtSNa, DMF, reflux, 3 h, 94-98% yield.Potassium thiophenoxide has been used to cleave an aryl methyl ether without causing migration of a double bond. odium benzylselenide (PhCH2SeNa) and sodium thiocre-solate (p-CH3C6H4SNa) cleave a dimethoxyaryl compound regioselec-tively, reportedly as a result of steric factors in the former case and electronic factors in the latter case. ... 

Lithium diphenyphosphide (THF, 25°, 2 h HCl, H2O, 87% yield) selectively cleaves an aryl methyl ether in the presence of an ethyl ether.It also cleaves a phenyl benzyl ether and a phenyl allyl ether to phenol in 88% and 78% yield, respectively. ... 

Boron tribromide is reported to be more effective than iodotrimethylsilane for cleaving aryl methyl ethers. ... 

Selective cleavage of an aiyl methylenedioxy group, or an aryl methyl ether, by boron trichloride has been investigated. 

Sodium ethanethiolate has been examined for the selective cleavage of aryl methyl ethers. Methyl ethers para to an electron-withdrawing group are cleaved preferentially. ... 

Sodium sulfide in A -methylpyrrolidone, NMP, (140°, 2-4 h) cleaves aryl methyl ethers in 78-85% yield. ... 

Either an aryl methyl ether or a methylenedioxy group can be cleaved with boron trichloride under various conditions. ... 

The cyclohexylidene ketal, prepared from a catechol and cyclohexanone (AI2O3/TSOH, CH2CI2, reflux, 36 h), is stable to metallation conditions (RX/BuLi) that cleave aryl methyl ethers." The ketal is cleaved by acidic hydrolysis (coned. HCl/EtOH, reflux, 1.5 h, —> 20°, 12 h) it is stable to milder acidic hydrolysis that cleaves tetrahydropyranyl ethers N HCl/EtOH, reflux, 5 h, 91% yield). ... 

Xn. Demethylation of Aryl Methyl Ethers by Boron Tribromide... 

Horner and Stohr (1952) found that in methanol the photolytic formation of the aryl methyl ether is rather a minor process, the main reaction being a hydro-de-di-azoniation. In a comparison between thermal and photolytic dediazoniation in water, Lewis et al. (1969 b) analyzed the percentages of chloro-de-diazoniations for three arenediazonium chlorides in aqueous solution in the presence of various concentrations of NaCl under both thermal and photolytic conditions. The authors came to the conclusion that these processes do not involve the same intermediates. 

A solution of the sodium salt of yV-methylaniline in HMPA can be used to cleave the methyl group from aryl methyl ethers ArOMe + PhNMe —> ArO + PhNMca- This reagent also cleaves benzylic groups. In a similar reaction, methyl groups of aryl methyl ethers can be cleaved with lithium diphenylphosphide (PH2PLi). " This reaction is specific for methyl ethers and can be carried out in the presence of ethyl ethers with high selectivity. 

Lewis acids are also used in conjunction with acyl halides. The reagent Nal—BF3 etherate selectively cleaves ethers in the order benzylic ethers > alkyl methyl ethers > aryl methyl ethers. 

This reaction is similar to 13-1 and, like that one, generally requires activated substrates. With unactivated substrates, side reactions predominate, though aryl methyl ethers have been prepared from unactivated chlorides by treatment with MeO in HMPA. This reaction gives better yields than 13-1 and is used more often. A good solvent is liquid ammonia. The compound NaOMe reacted with o- and p-fluoronitrobenzenes 10 times faster in NH3 at — 70°C than in MeOH. Phase-transfer catalysis has also been used. The reaction of 4-iodotoluene and 3,4-dimethylphenol, in the presence of a copper catalyst and cesium carbonate, gave the diaryl ether (Ar—O—Ar ). Alcohols were coupled with aryl halides in the presence of palladium catalysts to give the Ar—O—R ether. Nickel catalysts have also been used. ... 

The use of iodotrimethylsilane for this purpose provides an effective alternative to known methods. Thus the reaction of primary and secondary methyl ethers with iodotrimethylsilane in chloroform or acetonitrile at 25—60° for 2—64 hours affords the corresponding trimethylsilyl ethers in high yield. The alcohols may be liberated from the trimethylsilyl ethers by methanolysis. The mechanism of the ether cleavage is presumed to involve initial formation of a trimethylsilyl oxonium ion which is converted to the silyl ether by nucleophilic attack of iodide at the methyl group. tert-Butyl, trityl, and benzyl ethers of primary and secondary alcohols are rapidly converted to trimethylsilyl ethers by the action of iodotrimethylsilane, probably via heterolysis of silyl oxonium ion intermediates. The cleavage of aryl methyl ethers to aryl trimethylsilyl ethers may also be effected more slowly by reaction with iodotrimethylsilane at 25—50° in chloroform or sulfolane for 12-125 hours, with iodotrimethylsilane at 100—110° in the absence of solvent, " and with iodotrimethylsilane generated in situ from iodine and trimcthylphenylsilane at 100°. ... 

Aryl methyl ethers. A great deal of attention has been directed to the demethylation of aryl methyl ethers on account of interest in the degradation of lignin and related compounds by both aerobic and anaerobic organisms. 

Good yields are generally observed, especially for methyl ethers. The combination of boron tribromide with dimethyl sulfide has been found to be particularly effective for cleaving aryl methyl ethers.91... 

In connection with another project being developed we needed large quantities of a biaryl phenol or biaryl aryl methyl ether which was being prepared by a Suzuki coupling reaction (Scheme 6). 

Periodic acid dihydrate, with iodine and durene to give iododurene, 51, 94 Phenols, from aryl methyl ethers, 53, 93 Phenylacetaldehyde, from 2-lithio-1,3,5-trithiane and benzyl bromide, 51, 43 Phenylacetic acid, bromination, 50, 31... 

Lithium derivatives of dialkylamines react with aryl methyl ethers in refluxing THF by substitution to afford TV-aryldialkylamines (equation 10). Similarly, lithium piperidide and veratrole give 7V-(2-methoxyphenyl)piperidine (15)40. 

The O-methylated extract was derivatized with 99 percent C-enriched methyl iodide. The NMR spectrum of the extract showed a strong absorption at 56 ppm (relative to TMS), which can be attributed to unhindered aryl methyl ethers (67%), a smaller absorption at 60 ppm, attributable to hindered aryl methyl ethers (23%), and a resonance at 51 ppm, assignable to methyl esters derived from carboxylic acids (10%).(16) TTiese results are consistant with those of Liotta l al, who studied the alkylation of whole Illinois No. 6 coal.(12)... 

Good yields are generally observed, especially for methyl ethers. The combination of boron tribromide with dimethyl sulfide has been found to be particularly effective for cleaving aryl methyl ethers.87 Trimethylsilyl iodide cleaves methyl ethers in a period of a few hours at room temperature.85 Benzyl and /-butyl systems are cleaved very rapidly, whereas secondary systems require longer times. The reaction presumably proceeds via an initially formed silyl oxonium ion ... 

Use of this coupling for synthesis of a number of isoquinoline alkaloids also has been published.2 VOF is usually used in this coupling, but this reagent can lead to overoxidation and oxidative demcthylation of aryl methyl ether groups. 

The three-step sequence used to convert enone 65 to miltirone (56) is shown in Scheme 5.7 and consists of, first, a Wolff-Kishner reduction to convert the C(5) carbonyl moiety into a methylene, followed by deprotection of the aryl methyl ethers and oxidation to an ortho-quinone using ceric ammonium nitrate. The physical and spectroscopic data of our synthetic miltirone are identical with those reported for the natural material. 

This procedure is characterized by the easy isolation of a high-purity product in excellent yield. The reaction illustrates a general method6 for the conversion of aryl methyl ethers to the corresponding phenols, and has proved to be of special advantage with acid-sensitive substrates.6 7... 

Deprotection of aryl methyl ethers may be effected under strongly acidic conditions (e.g. hydriodic acid, Section 9.6.11, p. 1253), but the milder methods employing either iodotrimethylsilane in chloroform solution at 20-50 °C for several hours,40 or boron tribromide at room temperature may be preferable.41... 

This BI3 complex cleaves aryl methyl ethers to phenols at room temperature in good yield. Dialkyl ethers are converted into iodinated products. It also converts terminal gem-diacetates into aldehydes.3... 

Cyclohexanone (202) was converted to compound (203) whose transformation to cyclohexanone (204) was accomplished in three steps. It underwent cyclialkylation with boron trifluoride etherate affording the cyclized product (205) (R=R,=OMe) in 64% yield along with naphthalene (206) (R=Ri= H,H). Compound (205) on heating under reflux with DDQ in benzene produced ketone (207) whose tosylhydrazone on treatment with sodium cyanoborohydride afforded reduced product (208). Deprotection of the aryl methyl ethers and oxidation with ceric ammonium nitrate led to the formation of miltirone (197). 

The first reaction step is most probably hydrolysis of the aryl methyl ether by hydrobromic and acetic acid. Such a mixture is very efficient because one of the products, methanol, is continuously removed from the reaction mixture by esterification with acetic acid, and thus the reaction equilibrium between the starting material and the product is shifted toward the product. 

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