Mechanism alkoxymercuration

The mechanism of the alkoxymercuration reaction is similar to that described in Section 7.4 for hvdroxymercuration. The reaction is initiated by electrophilic addition of Iig2+ to the alkene, followed by reaction of the intermediate cation with alcohol and reduction of the C-Hg bond by NaBH4. A variety of alcohols and alkenes can be used in the alkoxymercuration reaction. Primary, secondary, and even tertiary alcohols react well, but ditertiary ethers can t be prepared because of steric hindrance to reaction. 

I Review the mechanism of oxymercuration shown in Figure 7.4 (p. 225), and then i write the mechanism of the alkoxymercuration reaction of 1-methylcvclopentene with ethanol. Use curved arrows to show the electron flow in each step. 

Addition of alcohol to alkenes hy alkoxymercuration-reduction produces ethers via Markovnikov addition. This addition is similar to the acid-catalysed addition of an alcohol. For example, propene reacts with mercuric acetate in aqueous THF, followed hy reduction with NaBFl4, to yield methyl propyl ether. The second step is known as demercuration, where Flg(OAc) is removed hy NaBH4. Therefore, this reaction is also called alkoxymercura-tion-demercuration. The reaction mechanism is exactly the same as the oxymercuration-reduction of alkenes. 

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... 

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. 

Problem 17.9 Write all steps of a likely mechanism for alkoxymercuration. 

The mechanism of the alkoxymercuration reaction is similar to that described in Section 7.4 for hydroxymercuration. The reaction is initiated by electrophilic addition of to the alkene, followed by reaction of the... 

The mechanisms for oxymercuration and alkoxymercuration are essentially identical the only difference is that water is the nucleophile in oxymercuration and an alcohol is the nucleophile in alkoxymercuration. Therefore, the product of oxymercuration-reduction is an alcohol, whereas the product of alkoxymercuration-reduction is an ether. 

A variation of this reaction is known as alkoxymercuration. It simply involves using an alcohol as the solvent rather than water. The mechanism is identical to that given before except that ROH replaces water. For example, the reaction of 3-methyl-l-pentene with mercuric acetate and ethanol, followed by reaction with sodium borohydride, leads to 2-methyl-l-ethoxycyclopentane (76). Many alcohols can be used in this reaction, but alcohols such as methanol, ethanol, 2-propanol, etc. that are commonly used as solvents are used most often. 

Suggest a mechanism for the formation of the mercuric-alcohol precursor to 76 via alkoxymercuration. 

In Chapter 15, we saw that we can convert an alkene to an alcohol by oxymercuration-demercuration. If we perform oxymercuration-demercuration of an alkene in an alcohol as the solvent, the product is an ether. In this reaction, the alcohol, rather than water, acts as the nucleophile. This process, called alkoxymercuration, occurs by a mechanism analogous to oxymercuration. First, electrophihc addition of Hg(OAc)2 to the carbon-carbon double bond forms a mercurinium ion intermediate, which is subsequently attacked by the nucleophilic oxygen atom of the alcohoL... 

---