Organomercury hydrides

Of the other metals or metalloid hydrides that could be conceivably participate in radical processes, by far the most important from the synthetic point of view are organomercury hydrides. Interest in the free radical chemistry of organomercurials blossomed when it was established that the classical demer-curation reaction with sodium borohydride was in fact a radical chain reaction (Scheme 4.1).2... 

Scheme 4.1 Radical chain reduction using organomercury hydride.

As described in Scheme 4.3, the influence of a labile organomercury hydride which gives rise to a carbon radical appears to be a logical explanation. Aliphatic organomercury hydrides are so labile that there is usually no need to add any initiator traces of oxygen (or even some metallic impurities) are sufficient to trigger the radical chain. 

The use of TEMPO to effect oxidative demercuration was originally demonstrated by Whitesides [16], and is attractive because it gives a functional handle for further structural elaboration. This technique was invoked by Kang in the syntheses of (-t-)-lactacystin and (-l-)-furanomycin [17]. For example, alkene 10 was subjected to mercurioamidation conditions to afford the cyclized organomercury intermediate 11 (Scheme 4). Treatment with lithium borohydride in the presence of TEMPO forms the unstable organomercury hydride. This fragments to release the primary carbon radical, which is trapped by TEMPO to yield the masked alcohol product 12, an intermediate in the synthesis of the neurotropic factor (-l-)-lactacystin. 

In a set of organomercury hydrides, RHgH, J(Hg,H) couphngs were found to correlate linearly both with the corresponding proton chemical shift... 

Giese and co-workers " developed a special technique for studying the effects of the substituents upon the relative reactivity of vinyl monomers toward free radicals. Briefly it is as follows. Free radicals are produced by reducing organomercury halides with sodium borohydride. The radicals undergo competitive additions to pairs of various substituted olefins. The adducts in turn are trapped by hydrogen transfers from the formed organomercury hydrides. Relative quantities of each product are then determined ... 

Kanpp M, Malkina O (1998) Density functional analysis of C and H chemical shifts and bonding in mercrtrimethanes and organomercury hydrides The role of scalar relativistic, spin-orbit and substituent... 

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