Alkoxy mercuration- Demercuration

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. 

As we have seen, an alkene reacts to form a mercurinium ion that is attacked by the nucleophilic solvent. Attack by an alcohol solvent gives an organomercurial ether that can be reduced to the ether. 

The solvent attacks the mercurinium ion at the more substituted end of the double bond (where there is more S charge), giving Markovnikov orientation of addition. The Hg(OAc) group appears at the less substituted end of the double bond. Reduction gives the Markovnikov product, with hydrogen at the less substituted end of the double bond 

Mercury and its compounds were used for centuries as ingredients in antibacterial drugs, skin creams, and antiseptics. Mercury compounds are quite toxk, however. In the body, mercury combines with the thiol groups of critical enzymes, inactivating them. Mercury poisoning causes brain and kidney damage, often leading to death. 

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

---

Alcohols add directly to alkenes under acid or metal catalysis, or under photoinitiated conditions to give dialkyl ethers. Although these additions provide certain ethers under rather mild conditions, alkoxy-mercuration-demercuration is generally a superior method. 

The threo stereoisomer was the major product obtained by the synthesis in Scheme 13.14. This stereochemistry was established by the conjugate addition in Step A, where a significant (4-6 1) diastereoselectivity was observed. The C(4)-C(7) stereochemical relationship was retained through the remainder of the synthesis. The other special features of this synthesis are in Steps B and C. The mercuric acetate-mediated cyclopropane ring opening was facilitated by the alkoxy substituent.19 The reduction by NaBH4 accomplished both demercuration and reduction of the aldehyde group. 

Addition of mercury and an alkoxy group to a double bond, usually by a solution of mercuric acetate in an alcohol. Alkoxymercuration is usually followed by sodium borohydride reduction (demercuration) to give an ether, (p. 636)... 

---