Ethers, alkyl methyl

AIBt3, EtSH, 0°, 0.5-1 h, 73-78% yield. Aluminum bromide cleaves aryl and alkyl methyl ethers in high yield methyl esters are stable. 

Me2Br, CH2CI2, 70°, 30-36 h, 72-96% yield." Alkyl methyl ethers are also cleaved, but tertiary methyl ethers are converted to the bromide. 

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. 

Figure 11.8 THM GC trace of bleached beeswax. FAME, fatty acid methyl ester obtained with a resistively heated filament pyrolyser at 550°C MeO FAME, methyl ester of methoxy fatty acid ME, alkyl methyl ether DiME, dimethoxyalkane EtC, hydrocarbon X Y, carbon chain length number of double bonds. Reprinted from J. Anal. Appl. Pyrol., 52, Asperger et al., 1, 13, Copyright 1999 with permission from Elsevier...

Schulz, S. and Toft, S. (1993a). Branched long chain alkyl methyl ethers a new class of lipids from spider silk. Tetrahedron 49 6805-6820. 

Methyl ethers are stable to acidic and basic conditions, and oxidising or reducing reagents. Deprotection to regenerate the alcohol is difficult (see Section 9.6.10, p. 1254) a convenient mild procedure uses iodotrimethylsilane in chloroform solution at room temperature.768 The alkyl methyl ether under these conditions gives the alkyl silyl ether and methyl iodide the former on treatment with methanol gives the deprotected alcohol. 

The preparation of alkyl methyl ethers may be readily effected under PTC conditions from the alcohol, dimethyl sulphate and 50 per cent w/w aqueous sodium hydroxide, employing tetrabutylammonium hydrogen sulphate as catalyst.95 The usefulness of this procedure has been extended, and optimum conditions have been described for the alkylation of a range of aliphatic alcohols using, for example, 1-chlorobutane or benzyl chloride.96 The PTC preparative examples described in Expt 5.73 are for the methylation, allylation, but-2-enylation and benzylation of, for example, 2-hydroxymethyl-l,4-dioxaspiro[4.5]decane (Expt 5.63), and have been developed in the editors laboratories. These methods have also been applied to the alkylation of protected monosaccharide derivatives (p. 652). 

Naruse, Y. Kido, K. Inagaki, S. Ethylation of the indole dianions by alkyl methyl ethers. 

Selective complexation of ethers.1 This aluminum reagent shows remarkable selectivity in formation of complexes with ethers. Thus it effects virtually complete complexation of alkyl methyl ethers without effect on alkyl ethyl ethers. In general, ethers with less-hindered alkyl substituents form complexes more easily with MAD than their more bulky counterparts and the more basic etheral oxygens coordinate more readily to MAD than the less basic oxygen. The two bulky phenoxy groups are essential for this selective complexation, since methylaluminium bis(2,6-diisopro-pylphenoxide) does not form complexes with ethers under similar conditions. This selective complexation can be used to separate ethers by chromatography with MAD as the stationary phase. 

When primary alkyl phenyl tellurium or secondary alkyl phenyl tellurium compounds in methanol were treated with an excess of 3-chloroperoxybenzoic acid at 20, the phenyltelluro group was eliminated and replaced by a methoxy group. This reaction, which converts alkyl halides used in the synthesis of alkyl phenyl telluriums to alkyl methyl ethers, produced the ethers in yields as high as 90%3-4 Olefins are by-products in these reactions4 With ethanol as the solvent, ethyl ethers were formed. Other oxidizing agents (hydrogen peroxide, ozone, (ert.-butyl hydroperoxide, sodium periodate) did not produce alkyl methyl ethers. 

RSeCJIi — ROCHi. Oxidation of an alkyl phenyl selenide with m-chloroperben-zoic acid (2-5 equiv.) in methanol affords the corresponding alkyl methyl ethers in high yield. Oxidation of selenides with a vicinal phenyl group is accompanied by rearrangement of the phenyl group. vtc-Methoxy selenides derived from cycloalkenes are oxidized under these conditions to dimethyl acetals of ring-contracted aldehydes. 

Cleavage of methyl ethers. Alkyl methyl ethers are converted into acetates in high yield on contact with these two reagents. Both alkyl and aryl methylthiomethyl ethers are cleaved in 60-70% yield by this system. Tertiary alcohols can be acetylated by this reaction (two examples, 90% yield)... 

Reaction of C1-C3 alcohol with tertiary alkyl alcohol M-B ( M= Cr, Fe, V, Al, Si Ga). High conversion of dialkyl tertiary alkyl methyl ethers. ... 

Solvolysis in methyl alcohol converts an alkyl halide to an alkyl methyl ether. 

Methyl alcohol Alkyl halide Dialkyloxonium halide Alkyl methyl ether Hydrogen halide... 

Phenols substituted by the 2-hydroxymethyl group represent the monomers of phenol/formaldehyde polymers and their regio specific synthesis has received extensive experimental study. A number of preparations are Used in Table 6.3 (refs.27-33). The alkyl methyl ether of o-methylsalicyl alcohol [2-(1 -methoxyethyl)phenol] has been formed in a yield of 12% from a mixture of phenol and 1,1-dimethoxyethane (1 10) by passage at 250 C with helium as carrier gas through a fixed bed catalyst of an H-ZSM-5 zeolite proton exchangeable) supported on glass wool with a contact time of 6.9 secs. (ref.34). 

Oxidative cleavage of alkyl methyl ethers. Methyl ethers are cleaved to carbonyl compounds by treatment with NOa BF4 in CH2CI2. 

Demethylation of ethers. Primary and secondary alkyl methyl ethers and aryl methyl ethers are cleaved to alcohols by BF3 etherate in several thiols (ethanethiol is particularly effective). The reaction occurs at room temperature, but requires 1-12 days. Retention of stereochemistry is observed. ... 

Cleavage of ethers and ketals. Hydrogen iodide in acetonitrile, generated from Nal and diiodomethyl methyl ether, is an effective reagent for cleavage of primary and secondary alkyl methyl ethers (20", 30 minutes). Hydrogen iodide generated from Nal and T.sOH is. somewhat less reactive. In other solvent.s, HI... 

Reactions.—New methods for the synthesis and cleavage of benzyl and trityl ethers, and for the cleavage of allyl ethers have been discussed in an earlier section (Protection of Alcohols). Primary and secondary alkyl methyl ethers have been demethylated by the combination boron tribromide-sodium iodide-15-crown-5 The reagent methyltrichlorosilane-sodium iodide is a new combination for regioselective ether cleavage for example aliphatic methyl ethers undergo predominant demethylation to alcohols (for primary or secondary alkyl groups) or iodides (in tertiary cases). 

A full paper has appeared on the use of UFe for the regiospecific oxidative cleavage of alkyl methyl ethers. Oxonium ions are formed as intermediates and these species can be trapped with the appropriate dithiol to give 1,2-dithiolans or 1,3-dithiolans. ... 

Preparation.—Routes to primary alkyl methyl ethers from iodides, and to allylic methyl ethers from alkynes, have been mentioned elsewhere in this Report. 

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