Radicals alkylmercury hydrides

Free-radical decomposition of the alkylmercury hydride then occurs to replace the C-Hg bond with a C-O bond, with the O coming from O2. The free-radical reaction gives a hydroperoxide C-OOH. 

The reductive decomposition of alkylmercury compounds is also a useful source of radicals.205 206 207 The organomercury compounds are available by oxymercuration (Section 4.3) or from an organometallic compound as a result of metal-metal exchange (Section 7.3.3). The mercuric hydride formed by reduction undergoes chain decomposition to generate alkyl radicals. 

There is a great diversity of initiating and propagation steps for radical substitution reactions. Bond homolyses, fragmentations, atom abstraction reactions, and addition reactions to C=C double bonds are among the possibilities. All of these reactions can be observed with substituted alkylmercury(II) hydrides as starting materials. For this reason, we will examine these reactions as the first radical reactions in Section 1.6. 

The radicals produced during the decomposition of alkylmercury(II) hydrides can also be added to molecular oxygen (Figure 1.16). A hydroperoxide is first produced in a chain reaction, which again comprises three propagation steps. However, it is unstable in the presence of NaBH4 and is reduced to an alcohol. 

Unfortunately, radicals derived from alkylmercuries are even more limited in what they will react with than radicals made from alkyl halides by the tin hydride method. Styrene, for example, cannot be used to trap alkylmercury-derived radicals efficiently because the radicals react more rapidly with the mercury hydride (which has an even weaker metal-H bond than Bi SnH) than with the styrene. 

That epoxides are formed as by-products supports the assumption of 3-peroxyalkyl radicals as intermediates, and tributyltin hydride itself will be the principal hydrogen donor. A mechanism has been suggested which involves a hitherto unreported Sh2 displacement of alkylmercury by tributyltin, but another radical mechanism has also been proposed. ... 

Hex-5-enyl-l-mercuric bromide (III) is reduced to 1-hexene (IV) by sodium amalgam, whereas sodium borohydride, lithium aluminum hydride, and tri-77-butyltin hydride gave a mixture of IV and methylcyclopentane. This is taken as evidence that sodium amalgam reduction of alkylmercury salts does not proceed via a free radical pathway [72]. 

For studies on organotin-centered radicals, [(PhMe2CCH2)3Sn]2Hg is prepared from (PhMe2CCH2)3SnH and t-BujHg in a 2 1 hydride alkylmercury ratio. The yellow, crystalline product, mp 114°C, is a source of the [(PhMe2CCH2)3Sn] radical . 

The free radical chain reaction between PhCOCHjHgCl and 1-morpholinocyclohex-cne has been reported to involve addition of the acceptor radical PhCOCHj- to the jS-position of the enamine followed by electron transfer to regenerate the attacking radical (Scheme 19). Photostimulated reactions of simple alkylmercury halides failed since an electrophilic radical is required. Photolysis of p-nitrobenzyl chloride in the presence of enamines gave the -/>-nitrobenzyl ketone on hydrolysis . Radical mediated reductive alkylation of acyclic-enamines has also been reported with radical precursors such as PhSCH2CN, PhS02CH2Cl and Me3CS02CH2SePh . Reductive alkylation also occurred with chloromethyl p-tolyl sulphone in the presence of tributyltin hydride and azobis(isobutyronitrile) (AIBN) (Scheme 20). 

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