Ether exchange

They are colourless liquids with characteristic odours, and are prepared by the condensation of ketones with alkyl orthoformates in the presence of alcohols, or by the reaction of acetylenes with alcohols in presence of HgO and BF3. In some cases trichloroethanoic acid is used as the catalyst. They lose alcohol when heated and form vinyl ethers. Exchange of alcohol groups occurs when the ketals of the lower alcohols are boiled with alcohols of greater molecular weight. See acetals. 

Liquid coating resins are prepared by reacting methanol or butanol with the initial hydroxyme-thylureas. Ether exchange reactions between the amino resin and the reactive sites on the polymer produce a cross-linked film. 

Along with tertiary hydroperoxide of ether, the BDE of the O—H bonds of alkoxy hydroperoxides are higher than that of similar hydrocarbons. Very valuable data were obtained in experiments on ether oxidation (RiH) in the presence of hydroperoxide (RiOOH). Peroxyl radicals of oxidized ether exchange very rapidly to peroxyl radicals of added hydroperoxide ROOH and only R02 reacts with ether (see Chapter 5). The rate constants of alkylperoxyl radicals with several ethers are presented in Table 7.18. The reactivity of ethers in reactions with peroxyl radicals will be analyzed in next section. 

Palladium-catalyzed cross-coupling of 19 with allyl bromide occurs exclusively at the vinylstannane moiety to give 1-ethoxy-1-silyl-1,4-diene 20. The following ether exchange with allyl alcohol causes the Glaisen rearrangement to give an acylsilane derivative 21 (Scheme 64).2... 

The procedure described illustrates a new general synthetic method for the preparation of (E)-3-allyloxyacryl ic acids and their conversion to a-unsubstituted y,5-unsaturated aldehydes by subsequent Claisen rearrangement-decarboxyl at ion. Such aldehydes are traditionally prepared by Claisen rearrangements of allyl vinyl ethers. Allyl vinyl ethers are typically prepared by either mercury-catalyzed vinyl ether exchange with allylic alcohols or acid-catalyzed vinylation of allylic alcohols with acetals. The basic conditions required for alkoxide addition to the betaine to produce carboxyvinyl allyl ethers, as described in this report, nicely complements these two methods. In addition, this Claisen rearrangement is an... 

An alcohol/ether exchange reaction can be written for the peroxide collection as in equation 12. 

Internal ether exchange would then eliminate dioxane until the oxonium ion is destroyed in one or both of the following termination steps. 

The etherate exchanges quickly with the trioxane in a reaction of low heat of reaction 82) ... 

Noyori and Kurimoto [330] have found an interesting anodic ether exchange reaction of aryl glycosides. They described that this is a rate example of SoNl-type transformation reaction, but the reaction may be EGA (electrogenerated acid)-catalyzed. The reaction is also stereoselective but not always stereospecific. 

The pyrolysis of allyl vinyl ethers derived by acid- or mercuric ion-catalyzed ether exchange of ethyl vinyl ether or substituted vinyl ethers with allylic alcohols produces the corresponding y, 8-unsaturated aldehydes or ketones, respectively. 

The phenoxy-linked compounds 29 and 30 were isolated from both the reaction of 27 with 21 and 23. Such phenoxy compounds were not observed in the reaction of ortho-quinone methide 31 with any of the phenol and methylphenols. When the ether 28 was heated in the presence of D2O, it decomposed slowly to 27. When mixed with 21, the phenoxy compound 29 was rapidly generated, along with 27 and 26. From this, it was concluded that the phenolic OH undergoes an ether exchange (Scheme 22), and it is the subsequent reaction of 27 with 21 which generates 26. 

SCHEME 22. Ether exchange between 28 and 21 generates 27 and the phenoxy derivative 29. 27 will either self-react, regenerating 28, or react with 21 to give the methylene 26... 

Reaction of allyl and benzyl alcohols with 1-dimethylamino-1-methoxy-ethene 2 leading to acetamidation-rearrangement, proceeding via ether exchange followed by Claisen rearrangement (enamine SN2 displacement). 

Allyl ethers. Conversion of allylic alcohols to ethers (and ether exchange also) and transpositional allylic methoxylation have been effected by the CAN-ROH sys... 

Deacetalization and dethioacetalization. Dimethyl acetals, 4-p-methoxy-phenyl-l,3-dioxolanes are cleaved withDDQ in the presence of water. For deprotection of thioacetals under mild conditions photochemical assistance seems advantageous. The same reaction principle of deacetalization can be extended to ether exchange. Thus alcohol protection is possible by mixing with 2,2-dimethoxypropane in the presence of DDQ, and proximal diols are converted to acetonides. Replacement of anomeric arylmethoxyl groups by this method complements other glycosylation procedures. 

D -ethyl acetals, 4-p-methoxy-re-e. e of water. For deprotection 1. i">tance seems advantageous. in -e extended to ether exchange. It - Z 2-dimethoxypropane in the Tea to acetonides. Replacement C -plements other glycosylation... 

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