Demercuration alkoxymercuration

Problem 14.6 Give the alkene and alcohol needed to prepare the following ethers by alkoxymercuration-demercuration (a) diisopropyl ether, (b) 1-methyl-l-methoxycyclopentane, (c) 1-phenyl-1-ethoxypropane, (d) di-f-butyl ether. ... 

Problem 14.12 Use any needed starting material to synthesize the following ethers, selecting from among intermolecular dehydration, Williamson synthesis, and alkoxymercuration-demercuration. Justify your choice of method. 

The alkoxymercuration-demercuration of alkenes, dienes and alkynes in the presence of alcohols provides an even more versatile approach to the corresponding ethers than the acid-catalyzed process. This reaction has been extensively studied and thoroughly reviewed recently.415 The reaction of alkenes is best carried out using meicury(II) acetate or, for more highly substituted alcohols or alkenes, mercury(II) trifluoroacetate (equation 257).416,417... 

One major advantage of the alkoxymercuration-demercuration approach to ethers over the acid-catalyzed process is the fact that carbon skeleton rearrangements are seldom observed. Only unsaturated cyclopropanes,42S>426 or aryl-substituted alkenes427 428 in the presence of highly electrophilic mercury salts afford rearranged products. 

Mechanism 8-4 Acid-Catalyzed Hydration of an Alkene 338 8-5 Hydration by Oxymercuration-Demercuration 340 Mechanism 8-5 Oxymercuration of an Alkene 340 8-6 Alkoxymercuration-Demercuration 342 8-7 Hydroboration of Alkenes 343... 

Synthesis of Ethers by Alkoxymercuration-Demercuration 636 14-7 Industrial Synthesis Bimolecular Condensation of Alcohols 637 Summary Syntheses of Ethers (Review) 638 14-8 Cleavage of Ethers by HBr and HI 638... 

When mercuration takes place in an alcohol solvent, the alcohol serves as a nucleophile to attack the mercurinium ion. The resulting product contains an alkoxy (—O—R) group. In effect, alkoxymercuration-demercuration converts alkenes to ethers by adding an alcohol across the double bond of the alkene. 

Show the intermediates and products that result from alkoxymercuration-demercuration of 1-methylcyclopentene, using methanol as the solvent. 

The alkoxymercuration-demercuration process adds a molecule of an alcohol across the double bond of an alkene (Section 8-6). The product is an ether, as shown here. 

Show how the following ethers might be synthesized using (1) alkoxymercuration-demercuration and (2) the Williamson synthesis. (When one of these methods cannot be used for the given ether, point out why it will not work.)... 

Addition of an alcohol across a double bond alkoxymercuration-demercuration (Sections 8-6 and 14-6)... 

The reaction mechanism of alkoxymercuration/demercuration of an alkene is similar to other electrophilic additions we have studied. First, the cyclopentene n electrons attack Hg2+ with formation of a mercurinium ion. Next, the nucleophilic alcohol displaces mercury. Markovnikov addition occurs because the carbon bearing the methyl group is better able to stabilize the partial positive charge arising from cleavage of the carbon-mercury bond. The ethoxyl and mercuric groups are trans to each other. Finally, removal of mercury by NaBH4 by a mechanism that is not fully understood results in the formation of 1-ethoxy-1-methylcyclopentane. 

Alkoxymercuration-demercuration- has all the advantages we saw for its counterpart speed, convenience, high yield, and the virtual absence of rearrangement. Compared with the Williamson synthesis, it has one tremendous advantage there is no competing elimination reaction. As a result, it can be used for the... 

Ethers are prepared either by a Williamson synthesis or by alkoxymercuration/demercuration sequence. The Williamson ether sy thesis involves S -2 attack of an alkoxide ion on a primary alkyl halide. The alkoxymercuration reaction involves the formation of an intermediate organomercury compound, followed by NaBH4 reduction of the C-Hg bond. The net result is Markovnikov addition of an alcohol to an alkene. 

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