Demercuration acyloxymercuration

Carboxylic esters are produced by the addition of carboxylic acids to olefins, a reaction that is usually acid-catalyzed (by proton or Lewis acids182) and similar in mechanism to 5-4. Since Markovnikov s rule is followed, hard-to-get esters of tertiary alcohols can be prepared from olefins of the form R2C=CHR.183 When a carboxylic acid that contains a double bond in the chain is treated with a strong acid, the addition occurs internally and the product is a y- and/or a 8-lactone, regardless of the original position of the double bond in the chain, since strong acids catalyze double bond shifts (2-2).184 The double bond always migrates to a position favorable for the reaction, whether this has to be toward or away from the carboxyl group. Carboxylic esters have also been prepared by the acyloxymercuration-demercuration of olefins (similar to the procedures mentioned in 5-2 and 5-4).185... 

The acyloxymercuration-demercuration of alkenes provides an alternative route to esters which is probably less prone to caibon skeleton rearrangements than the direct addition of carboxylic acids to alkenes (equation 282). This reaction has recently been reviewed.477 The reaction is most commonly run using mercury(II) acetate in acetic acid, though other mercury salts may be used and aprotic solvents can also be employed. Equilibria have been measured for the reaction of mercury(II) trifluoroacetate and alkenes in tetrahydrofuran, and were found to be solvent dependent.478... 

The acyloxymercuration of alkynes has been reported to produce a wide variety of products. Terminal alkynes afford either dialkynylmercurials516,517 or polymercurated products whose structures have not been well established (equation 290). Internal alkynes usually afford vinylic mercurials in which the mercury(II) salt has added in an anti fashion (equation 291 ).518-520 Only sodium borohydride has been used to demercurate a few of these mercurials.520... 

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