Mercury hydride radical addition reactions

Radical addition reactions conducted by the mercury(II) hydride method were also pioneered by Giese and are very similar in principle to the tin hydride method. The radical is generated from an organomer-curial (rather than a halide) and removed by hydrogen transfer from a mercury(II) hydride (rather than a tin hydride). Mercury(II) hydride reductions have been covered in several recent reviews.3,5,81,82... 

Cyclopentyl radicals substituted in the /1-position relative to the radical center are formed during the solvomercuration/reductive alkylation reaction of cyclopentene34. The organomer-curial produced in the first solvomercuration step is reduced by sodium borohydride and yields free cyclopentyl radicals in a radical chain mechanism. Addition of alkenes can then occur tram or cis to the / -alkoxy substituent introduced during the solvomercuration step. The adduct radical is finally trapped by hydrogen transfer from mercury hydrides to yield the tram- and ris-addition products, The transicis ratio depends markedly on the alkene employed and it appears that the addition of less reactive alkenes occurs with higher trans selectivity. In reactions of highly substituted alkenes, this reactivity control is compensated for by steric effects. Therefore, only the fnms-addition product is observed in reactions of tetraethyl ethenetetracarboxylate. The choice of alcohol employed in the solvomercuration step has, however, only a small influence on the stereoselectivity. 

The functionalization of H—Si(l 11) surfaces has been extended to the reaction with aldehydes. Indeed, H—Si(lll) reacts thermally (16 h at 85 °C) with decanal to form the corresponding Si—OCH2R monolayer that has been characterized by ATR-FTIR, XPS and atomic force microscopy (AFM) [63]. The reaction is thought to proceed either by a radical chain mechanism via adventitious radical initiation or by nucleophilic addition/hydride transfer. On the other hand, the reaction of H—Si(lll) with octadecanal activated by irradiation with a 150W mercury vapour lamp (21 h at 20-50 °C) afforded a R... 

When (/3-hydroxyalkyl)mercury(II) acetates are treated with NaBH4 and no additional reagent, they first form (( - h y d roxy a Iky 1) me rcu ry (II) hydrides. These decompose via the chain reaction shown in Figure 1.12 to give a mercury-free alcohol. Overall, a substitution reaction R—Hg(OAc) — R—H takes place. The initiation step for the chain reaction participating in this transformation is a homolysis of the C—Hg bond. This takes place rapidly at room temperature and produces the radical Hg—H and a /3-hydroxylated alkyl radical. As the initiating radical, it starts the first of the two... 

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