Bis xanthates

The reduction of thiocarbonyl derivatives by EtsSiH can be described as a chain process under forced conditions (Reaction 4.50) [89,90]. Indeed, in Reaction (4.51) for example, the reduction of phenyl thiocarbonate in EtsSiD as the solvent needed 1 equiv of dibenzoyl peroxide as initiator at 110 °C, and afforded the desired product in 91 % yield, where the deuterium incorporation was only 48% [90]. Nevertheless, there are some interesting applications for these less reactive silanes in radical chain reactions. For example, this method was used as an efficient deoxygenation step (Reaction 4.52) in the synthesis of 4,4-difluoroglutamine [91]. 1,2-Diols can also be transformed into olefins using the Barton-McCombie methodology. Reaction (4.53) shows the olefination procedure of a bis-xanthate using EtsSiH [89]. 

Wc-Diols can also be deoxygenated indirectly, through sulfonate ester derivatives. For example, vic-dimesylates and Wc-ditosylates have been converted to alkenes by treatment, respectively, with naphthalene-sodium271 and with Nal in dimethylformamide.272 In another procedure, the diols are converted to bisdithiocarbonates (bis xanthates), which undergo... 

There is a radical analogy to the above method, which involves reacting a radical with a bis-xanthate. If the radical precursor is a diazo derivative, an interesting situation occurs, since in principle nothing is wasted except for one molecule of nitrogen. This approach is summarised in Scheme 6 for the synthesis of tertiary xanthate 13 by the reaction of a bis-xanthate with an... 

Scheme 5 Xanthates prepared by nucleophilic substitution on a bis-xanthate...

Unsaturated derivatives of cellulose containing double bonds directly in the pyranose ring have b n synthesized by the thermal decomposition of cellulose methylxanthate or bis-xanthate (39,40), which proceeds as follows ... 

Barton and coworkers developed a very useful procedure for the deoxygenation of alcohols, which involves conversion of the alcohol to the corresponding xanthate derivative followed by reaction with BuaSnH. When applied to the bis(xanthates) derived from v/ c-diols the reaction gives alkenes, as illustrated in equation (17). Once again alkene formation is independent of the stereochemistry of the starting diols. 

Among the recent reports on metal xanthate chemistry the following are mentioned, dealing with the structural diversity of nickel(II),213 zinc(II),214 mercury(II), 15 and tellurium(II) bis (xanthate) complexes,216 based upon different coordination patterns and supramolecular self-assembly. 

The crystal structures of several mercury bis(xanthates),267,268 and organomercury derivatives, including methylmercury xanthates, MeHg(S2COR) and their supramolecular self-assembly,269 and phenylmercury xanthates, PhHg(S2COR) (R = Me, Pr1,270 Et,271 have been reported. 

This methodology was applied to synthesis of 2/,3/-didehydro-2/,3/-dideoxy-nucleosides, potent anti-HIY agents. The bis-xanthate of the V3-methyluridine derivative was subjected to radical reaction conditions in water, giving the corresponding alkene in 82% yield. Similar results were also achieved in the case of the adenosine derivative (76% yield). However, Kita et al. found that the combination of a water-soluble radical initiator, 2,2 -azobis[2-(2-imid-azolin-2-yl)propane] (VA-061), a water soluble chain carrier, 1-ethylpiperidine hypophosphite (EPHP), and a surfactant, cetyltrimethylammonium bromide (CTAB), resulted in a radical cyclisation that occurred in water with a variety of hydrophobic substrates16 (Table 5.2). 

Dideoxygenation via 1,2-dixanthate elimination is also possible and, in acyclic systems, will usually generate the more stable trans olefin. For example, treatment of the bis(xanthate) 22 with tin hydride in refluxing toluene gave selective formation of the -alkene 23. 

It was also determined that these phosphine-borane reagents show specific reactivity towards reduction of xanthates over bromide and chloride groups in a substrate. Bis(xanthates) could also be reduced to olefins without the necessity of adding a sacrificial olefin acceptor to protect the deoxygenation product. 

Method 1. Polymerization of Bis(xanthates) with Metal Salts... 

Bis(xanthates) are a readily accessible class of bis(ligands), but surprisingly little research has been published about their coordination polymers with metals 3, 7). This could be due to the fact that thermal stability screening studies showed them to be inferior in this respect (i). A series of polymeric nickel bis(xanthates) have been prepared from reaction of bis(potassium xanthates) with nickel salts (7) (see Table X.3, p. 315). Only meager information about their properties has been published. 

A series of reports describing the catalytic activity of a variety of chelates, including poly[metal bis(xanthates)], has appeared. Their utility as catalysts for the decomposition of hydrazine (7, 10), isopropanol (7), formic acid (7), hydrogen peroxide (77), and the oxidation of cumene to cumene hydroperoxide (5) has been studied. These ligands, especially when linked to copper, were among the most active classes of polymeric chelates that were evaluated in these studies. 

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