Organomercury compounds addition reactions

Addition of several organomercury compounds (methyl, aryl, and benzyl) to conjugated dienes in the presence of Pd(II) salts generates the ir-allylpalladium complex 422, which is subjected to further transformations. A secondary amine reacts to give the tertiary allylic amine 423 in a modest yield along with diene 424 and reduced product 425[382,383]. Even the unconjugated diene 426 is converted into the 7r-allyllic palladium complex 427 by the reaction of PhHgCI via the elimination and reverse readdition of H—Pd—Cl[383]. 

Other Cyclopropanation Methods. Haloalkylmercury compounds are also useful in synthesis. The addition reactions are usually carried out by heating the organomercury compound with the alkene. Two typical examples are given in Section C of Scheme 10.9. 

Several other examples of addition reactions involving organomercury compounds are given in Section B of Scheme 10.16 at the end of this section. 

In contrast to another investigation,9 repetition of the methoxymercuration reaction of dimethyl tricyclo[4.2.2.02,5jdeca-3,9-diene-7,8-dicarboxylate gave a crystalline organomercurial, whose structure was reassigned as dimethyl 3-chloromercurio-4-methoxytrieyelo[4.2.2.02-5]dec-9-ene-7,8-dicarboxylate (4).1,5 Some representative electrophilic addition reactions of compounds la-d are summarized in Table l.1,3-7... 

Mercuric trifluoroacetate, Hg(02CCF3)2i Adds to alkenes in the presence of alcohol, giving a-alkoxy organomercury compounds that can be reduced with NaBH4 to yield ethers. The overall reaction effects a net addition of an alcohol to an alkene (Section 18.2). 

Biphosphines may be formed by several methods involving the treatment of phosphinous halides with either electropositive metals or organomercury compounds. An additional intriguing approach involves the reaction of metal organophosphides (see Section 3.2) with 1,2-dibromoethane to form the phosphorus-phosphorus bond and extrude ethylene (equation 17). 

Alkene oxymercuration is closely analogous to halohydrin formation. The reaction is initiated by electrophilic addition of (mercuric) ion to the alkene to give an intermediate mercurinium ion, whose structure resembles that of a bromonium ion (Figure 7.5). Nucleophilic attack of water, followed by loss of a proton, then yields a stable organomercury addition product. The final step, reaction of the organomercury compound with sodium boro-hydride, is not fully understood but appears to involve radicals. Note that... 

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. 

Treatment of an alkene with mercuric acetate in aqueous THF results in the electrophilic addition of mercuric ion to the double bond to form an intermediate mercuri-um ion. Nucleophilic attack by H2O at the more substituted carbon yields a stable organomercury compound, which upon addition of NaBH4 undergoes reduction. Replacement of the caiton-mercury bond by a carbon-hydrogen bond during the reduction step proceeds via a radical process. The overall reaction represents Markovnikov hydration of a double bond, which contrasts with the hydroboration-oxidation process. 

Oxymercuration of simple alkyl- and acyl-substituted cyclopropenes generally results in ring opening.Addition of mercury(II) acetate to 3-methyl-3-phenylcyclopropene, however, gave a low yield of a cyclopropane containing organomercury compound (15-20%), which was converted into an isomeric mixture of 1 -methoxy-2-methyl-2-phenylcyclopropanes by reduction with lithium aluminum hydride. Reaction of 5 with mercury trifluoroacetate in methanol and then sodium hydroxide led predominantly to one cylopropane. ... 

Grignard reagents are also synthesized by addition reactions of alkynes, addition reactions of unsaturated compounds having C=S groups, reactions of cycloalkanes, reactions with organolithium compounds or organomercury compounds, etc. [4,15,27,28],... 

Hg(II) induced SCEs only slightly in CHO cells but a greater response was seen in human lymphocytes (Howard et al. 1991 Morimoto et al. 1982). Chromosomal aberrations have been induced by Hg(II) and by organomercury compounds in a variety of cells (Leonard et al. 1983 Howard et al. 1991). In addition to its clastogenic effects, mercury compounds cause a disturbance of mitosis due to their reactions with the sulfhydryl groups in the spindle fiber proteins. Deleterious effects on the spindle apparatus were seen with Me-Hg-Cl in a number of studies (Watanabe et al. 1982 Curle et al. 1987). Effects on the spindle apparatus are likely to lead to errors of chromosomal segregation (i.e., aneuploidy) (Ramel and Magnusson 1979 Verschaeve et al. 1984). 

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