By the methoxy group

Oxidation of alkyl phenyl telluride with excess meto-chloroperbenzoic acid (MCPBA) (3-5 equiv) in methanol affords the replacement of the phenyltellurium moiety by a methoxy group, giving the corresponding methyl ethers - (method A). This reaction. 

Improved yields are obtained by the similar treatment of telluroxides (prepared by hydrolysis of the parent dibromides) and different alcohols such as ethanol, propanol and isopropanol can be employed to give the corresponding ethers (method B). 

The detellurative methoxylation of the telluroxides also proceeds in high yields by treatment with trifluoroperoxyacetic acid (generated in situ from TFA and (method C). 

Finally, alkyl phenyl tellurones (prepared by oxidation of telluroxides with Nal04 are susceptible to similar conversions (method D). 

In the above procedures, the telluroxide xyn-elimination (see Section 4.7.1) was observed as a competitive interference only in the case of cycloheptyl phenyl telluride, where cycloheptene is formed in a yield of 45%. 

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Another example of enhanced sensitivity to substituent effects in the gas phase can be seen in a comparison of the gas-phase basicity for a series of substituted acetophenones and methyl benzoates. It was foimd that scnsitivtiy of the free energy to substituent changes was about four times that in solution, as measured by the comparison of A( for each substituent. The gas-phase data for both series were correlated by the Yukawa-Tsuno equation. For both series, the p value was about 12. However, the parameter r" ", which reflects the contribution of extra resonance effects, was greater in the acetophenone series than in the methyl benzoate series. This can be attributed to the substantial resonance stabilization provided by the methoxy group in the esters, which diminishes the extent of conjugation with the substituents. 

The methyl ether of eugenol, CjjHj 02, is found in calamus oil, cassie oU, betel oil, bay oil, and various other essential oils. It can be prepared artificially by the action of methyl iodide on eugenol sodium. Its constitution is identical with that of eugenol, except that the phenolic group, OH, has been replaced by the methoxy group, O. CHg. 

Carbene reactivity is strongly affected by substituents.117 Various singlet carbenes have been characterized as nucleophilic, ambiphilic, and electrophilic as shown in Table 10.2 This classification is based on relative reactivity toward a series of both nucleophilic alkenes, such as tetramethylethylene, and electrophilic ones, such as acrylonitrile. The principal structural feature that determines the reactivity of the carbene is the ability of the substituent to act as an electron donor. For example, dimethoxycarbene is devoid of electrophilicity toward alkenes because of electron donation by the methoxy groups.118... 

With the exception of adamantane and few related compounds [1-5] in which dichlorocarbene reacts at the tertiary C-H centre, the yields for the majority of insertion reactions into hydrocarbons are low and of little synthetic value (Table 7.1). Reaction also occurs in low yield at benzylic C-H sites [1, 6, 7] and, in the case of simple alkanes, the insertion reaction is promoted by alkoxy groups [1,6-14], Thus, whereas methylcyclohexane produces only 4% yield of the l-dichloromethyl-l-methylcyclohexane, the corresponding yield with 1-methoxycyclohexane is 13% [6], Similarly, the low yielding reaction of 1-methoxyadamantane with dichlorocarbene produces l-dichloromethyl-3-methoxyadamantane by insertion into the tertiary C-H site and (2,2-dichioroethoxy)adamantane by reaction at the primary C-H site, which is activated by the methoxy group. No reaction occurs at the secondary C-H sites [2],... 

An additional offAo-directing effect by the methoxy group at C-1 certainly contributes to the specific reactivity of 4-nitroveratrole 101.124) [ gee above in Section a)]. 

The anchimeric assistance by the methoxy group of P(o-MeOPh)3 in determining the selectivity of C=0 hydrogenation, with OMe coordination to Ir and an increase in electron density, was further verified by replacing the oxygen atom... 

However, in contradistinction to the meta-activation by the nitro-group, there is no attractive simple rationalization of the ortho-activation by the methoxy group. 

When a phenyl group is linked at a vicinal position to tellurium, the replacement of tellurium by the methoxy group is accompanied by phenyl migration. - ... 

A procedure for enantioselective synthesis of carboxylic acids is based on sequential alkylation of the oxazoline 8 via its lithium salt. Chelation by the methoxy group leads preferentially to the transition state in which the lithium is located as shown. The lithium acts as a Lewis acid in directing the approach of the alkyl halide. This is reinforced by a steric effect from the phenyl substituent. As a result, alkylation occurs predominantly from the lower face of the anion. The sequence in which the groups R and R are introduced... 

While protonation regioselectivity in the parent systems corresponded to the energetically most favored carbocations computed by DFT, selectivity in the OMe-substituted derivatives was strongly controlled by the methoxy group. Benzofiuorenes 81,83,84, and 85, and dibenzofluorenes 86 and 88 were nitrated under very mild conditions. Nitration... 

A method for synthesis of anthraquinones is by reaction of cyanophthalide carban-ions with benzynes [162], It is particularly useful for the access of 2 aza-l,3,8-trimeth-oxyanthraquinone because of the high regioselectivity imposed by the methoxy groups and the nitrogen atom of the pyridine. 

Evidently, hydrogen facilitates the nucleophilic replacement of fluorine by the methoxy group more efficiently than the halogens fluorine < chlorine < bromine < iodine < hydrogen.83,84 1,2,4,5-Tetrafluorobenzene when treated with sodium methoxide in methanol yields 1,2,4-tri-fluoro-5-methoxybenzene (7).83... 

Deprotonation occurs veiy regioselcctivcly at the aliylic position and ortho to the methoxy group Resonance stabili/ation of the anion by the double bond, together with eoordinalive stabilization of the lithium atom by the methoxy group, is responsible for selective lormation of intermediate 29... 

The successful preparation of isomers IX and X as well as the different reactivities of the chlorine atoms in the two rings of compound VIII and different tendency to hydrolysis shown by the methoxy groups in compound XIII provide further evidence in favour of an unsymmetrical structure of the azoxy group, in accordance with Angeli s view. 

The ring was built up from a cetyl a ted (S)-lactic acid, and a cy clization step introduced the second chiral centre—the methyl group goes pseudoequatorial while the pseudoaxial position is preferred by the methoxy group because of the anomeric effect (Chapter 42). 

The regioselective nudeophUic attack of the arylamine at the 2-methoxy-substituted iron complex salt is controlled by the methoxy group, which directs the arylamine to the para-position. Moreover, electrophilic attack takes place at the sterically less-hindered orfho-amino position. Iron-mediated oxidative cyclization of the resulting iron complex to the carbazole followed by proton-catalyzed aimulation of the furan ring provides 8-methoxyfurostifoline. Oxidation with 2,3-dich]oro-5,6-dicyano-l,4-benzoquinone (DDQ) to O-methylfurodausine-A followed by deavage of the methyl ether provides furoclausine-A (five steps, 9 % overall yidd). 

Lewis acid-mediated cleavage of p-methoxybenzyl ethers is much easier than benzyl ethers because of the additional resonance stabilisation afforded by the methoxy group in the p-methoxybenzyl carbocation. Consequently, p-methoxybenzyl ethers can be removed from sensitive substrates as in the final step of a synthesis of the anti-HIV-1 sulfolipid 186.2 [Scheme 4.186] wherein three p-methoxybenzyl ethers were expelled on treatment with excess iodotrimethyl-silane.342 Similarly, a synthesis of 1,2-diacylglycerols 187.2 [Scheme 4.187]343... 

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