Oxymercuration-demercuration procedure

Ammonia can be added to double bonds (even ordinary double bonds) in an indirect manner by the use of hydroboration (15-16) followed by treatment with NH2CI or NH2OSO2OH (12-29). This produces a primary amine with anti-Markovnikov orientation. An indirect way of adding a primary or secondary amine to a double bond consists of aminomercuration followed by reduction (see 15-3 for the analogous oxymercuration-demercuration procedure), for example. 

Markownikoff hydration of olefins (2, 265-267). Brown and Geoghegan1 have reported a detailed study of the oxymercuration-demercuration procedure. Yields of alcohols in the case of terminal olefins, RCH=CH2 and R2C=CH2, and disubstituted internal olefins, RCH=CHR are practically quantitative. Tri-substituted olefins of the type R2C=CHR show a wide variation in reactivity. 1 -Phenylcyclopentene and 1 -phenylcy clohexene, for example, are unreacti ve. 

Hydration of the double bond in 3,4-unsaturated sugars by the oxymercuration-demercuration procedure should lead either to 3- or to 4-deoxy sugars. It was found that this reaction applied to methyl 3,4-dideoxy- and 3,4,6-trideoxy-a-DL-hex-3-enopyranosides proceeded regio- and stereospecifically and furnished methyl 3-deoxy- and 3,6-dideoxy-DL-hexopyranosides. From substrates of the a-erythro configuration only a-xylo products (374) were obtained, a-threo substrates gave products (375) of the lyxo configuration. 

The overall oxymercuration-demercuration procedure is highly regioselective, with the nucleophile being introduced at the most highly substituted carbon ... 

A shorter but less selective route to la-hydroxycholesterol has been described by Kaneko (90). Cholesta-l,4-dien-3-one (90) was deconjugated to its -isomer and then reduced with borohydride to give 3P-hydroxy-cholesta-1,5-diene (91). Selective hydroboration followed by alkaline peroxide treatment afforded a 30% yield of a separable 1 1 mixture of la- and 2a-hydroxycholesterol (89) and (93). If the acetate (92) was hydrated by an oxymercuration-demercuration procedure, a mixture of the 2 3-hydroxycholesterol (94) (14%) and la-hydroxycholesterol (89) (26%) was isolated after saponification (118). When starting with the readily available cholesta-l,4,6-trien-3-one, the deconjugation and reduction afforded 3P-hydroxycholesta-l,5,7-triene (95) (59). The 5,7-diene system was then protected as its 4-phenyl-l,2,4-triazoline-3,5-dione (PTD) adduct (96). Treatment of (96) with m-chloroperbenzoic acid gave a 5 3 mixture of the lp,2p- and la,2a-epoxides (98). More recently, Whalley and his co-workers have found that if the dimethyl-t-... 

In the laboratory, alkenes are often hydrated by the oxymercuration-demercuration procedure. Oxymercuration involves electrophilic addition of Hg2+ to the alkene on reaction with mercury(II) acetate [(CH3C02)2Hg, often abbreviated Hg(OAc)2] in aqueous tetrahydrofuran (THF) solvent. When the intermediate organomercury compound is then treated with sodium borohydride, NaBH4, demercuration occurs to produce an alcohol. For example ... 

Oxymercuration-demercuration is a useful laboratory method for the synthesis of small quantities of alcohol. Like the catalytic hydration reaction, this process is an example of Markovnikov addition. It s a useful procedure because it tends to result in high yields and rearrangements rarely occur. 

The products obtained from the oxymercuration-demercuration of alkenylacetates under standard conditions (NaBH4/NaOH 3 M) are diols. However, the yields are significantly lower than with methoxy-and hydroxy-alkenes because of competitive deoxymercuration.Increasing the amount of base results in major increases in the yield of hydrated products. A less basic procedure has been developed, which allows for the survival of the acetate group. 

Brown, H. C. and Geoghegan, P. J., Jr. (1970) Solvomercuration-demercuration. 1. Oxymercuration-demercuration of representative olefins in an aqueous system. Mild procedure for the Markovnikov hydration of the carbon-carbon double bond. J. Org. Chem. 35, 1844-1850. 

Among the synthetically useful reactions of Hg(II) salts with organic compounds, the most familiar is a two-stage procedure for alkene hydration called oxymercuration-demercuration. Its application in the conversion of 3,3-dimethyl-l-butene to 3,3-dimethyl-2-butanol illustrates the procedure. 

The problems that follow explore various synthetic aspects of oxymercuration-demercuration. Experimental procedures sometimes vary depending on the particular transformation. The source of the electrophile may be a mercury(II) salt other than Hg(OAc)2, the nucleophile may be other than H2O, and the reaction may be intramolecular rather than intermolecular. 

Oxymercuration-demercuration A two-stage procedure for alkene hydration. 

Oxonium ion The species H30 (also called hydronium ion). Oxymercuration-demercuration A two-stage procedure for alkene... 

A new procedure for the identification and analysis of A -, A -, and A -unsaturated alcohols and acids has been reported intramolecular participation of the alcohol function (after reduction of the acid) in an oxymercuration-demercuration sequence affords 2-alkyltetrahydropyranyl and/or 2-alkyl... 

Oxymercuration/demercuration has thus been suggested as a mild procedure for the Markovnikov hydration of carbon-carbon double bonds. As shown in Chapter 3, hydroboration followed by oxidation can be used for their hydration contrary to Markovnikov s rule. The two reaction sequences are compared below for 1-hexene ... 

The methanol can be replaced by other nucleophilic solvents such as ethanol, acetic acid, or water (in tetrahydrofuran as cosolvent) to give the corresponding ethoxy-, acetoxy-, or hydroxy-esters. Cyclic ethers (substituted tetrahydrofurans and tetrahydropyrans) are formed by intramolecular reaction when the unsaturated ester also contains an appropriately placed hydroxy-group, even in the presence of a reactive solvent. This has been developed into a procedure for the identification, analysis, and isolation of long-chain alcohols and acids having alkene unsaturation in positions 3 (trans only), 4 (cis or tram), or 5 (cis or trans) Such acids (or natural mixtures in which they are present) are reduced to alcohols and subjected to oxymercuration (in DMF as a non-participating solvent) and demercuration. Cyclic ethers are formed only when there is unsaturation at positions 3,4, or 5 other double bonds are unaffected. For example, methyl arachidonatc... 

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