Radicals organomercury compounds

For a review of this and other free-radical reactions of organomercury compounds, see Barluenga, J. Yus, M. Chem. Rev., 1988, 88, 487. 

The reductive decomposition of alkylmercury compounds is also a useful source of radicals.300 The organomercury compounds are available by oxymercuration (see Section 4.1.3) or from organometallic compounds as a result of metal-metal exchange (see Section 7.3.3). 

Alkyl radicals generated by reduction of organomercury compounds can also add to alkenes having EWG groups. Radicals are generated by reduction of the organomercurial by NaBH4 or a similar reductant. These techniques have been... 

Organomercury compounds are also sources of alkyl radicals. Organomercurials can be prepared either by solvomercuration (Section 4.3) or from organometallic reagents (Section 7.3.3). 

Examples of radical-mediated C-alkylations are listed in Table 5.4. In these examples, radicals are formed by halogen abstraction with tin radicals (Entries 1 and 2), by photolysis of Barton esters (Entry 3), and by the reduction of organomercury compounds (Entry 4). Carbohydrate-derived, polystyrene-bound a-haloesters undergo radical allylation with allyltributyltin with high diastereoselectivity (97% de [41]). Cleavage from supports by homolytic bond fission with simultaneous formation of C-H or C-C bonds is considered in Section 3.16. 

Irradiation of phenyliodonium salts lead to the formation of phenyl radicals. In the presence of C60 these radicals are efficiently trapped under formation of pheny-lated C6o derivatives, mainly the monoadduct. In reaction mixtures of C6o, phenyliodonium salts and spin traps like nitroso-tert-butane ( BuNO) or nitroso-durene (ND) no phenyl adducts with the spin traps could be observed after irradiation. This suggests that C6o is a more efficient scavenger for phenyl radicals than the spin traps [177], Other investigations yielded similar results, e.g., the photolysis of organomercury compounds in the presence of fullerenes leads to fullerene-derived radical adducts. These radical adducts can combine to form dimers that are thermally stable and accumulate in the samples [Eq. (7)] [178],... 

Organometallic compounds with covalent, sparsely polarized C-M bonds do not usually epimerize readily. Thus, organoaluminum or organomercury compounds are configurationally stable up to 150 °C [540, 541] if oxidants or other radical chain... 

Syntheses with Radicals C-C Bond Formation via Organotin and Organomercury Compounds"... 

Organometallic compounds of less active metals and metalloids (e.g., silicon," antimony, and bismuth, are quite inert to water. Organomercury compounds (RHgX or R2Hg) can be reduced to RH by H2, NaBITj, or other reducing agents." The reduction with NaBH4 takes place by a free-radical mechanism." Alkyl-Si... 

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... 

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. 

Carbon-carbon bond formation via free radicals formed from organotin or organomercury compounds. 

Organomercury compounds can also be obtained in preparatively useful quantitites by the action of radicals on metallic mercury. For example, aryl-mercuric compounds are formed on decomposition of arenediazonium salts in the presence of metallic mercury 28 and when 3-iodopropionitrile is reduced electrolytically at a mercury cathode, the radicals produced react with the cathode material forming bis-(2-cyanoethyl)mercury.202 Organomercury compounds are also obtained analogously on reduction of ketones at a mercury cathode.203... 

Oxidation of organomercury compounds via formation of TEMPO derivatives and cleavage with Zn-HOAc completes the functionalization of alkenes. Without TEMPO the oxidative capture of a primary radical generated from organomercurial is inefficient, and the reductive pathway (loss of functionality) becomes competitive. 

Pyranold Compounds.- A review on the formation of C-C bonds by radical reactions Involving organotin or organomercury compounds includes instances of the synthesis of C-glycosides by this approach. 

An alkenylplatinum complex, 180, which is able to support a Geo radical as the cr-bonded ligand, has been prepared by transmetallation using an organomercury compound.The complex with carbomethoxy and hydroxy ligands trans disposed 181 has been obtained and characterized. 

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