Thiocarbonyl derivatives

C=Sst 1275-1030 Subranges 1075-1030 1210-1080 Strong, narrow. In Raman, strong Thioketones Thioesters  

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Exobidentate Coordination Dienic, Carbonyl, and Thiocarbonyl Derivatives... 

The removal of the hydroxy group is easily achieved by radical chemistry starting from the appropriate thiocarbonyl derivative or selenocarbonate. 

The second problem involves the measurement of pKa values for carbonyl and thiocarbonyl derivatives. Grieg and Johnson (157) have pointed out that the measurement of pKa values for very weak bases (11) is an inaccurate and arbitrary process. Of particular difficulty for our purposes is the fact that different carbonyl derivatives may require different acidity functions. As a result of this situation, no attempt was made to make correlations of pKa data for carbonyl and thiocarbonyl derivatives with eq. (2). Because accurate pKa values can be measured for imines, these values were correlated with eq. (2), although the conformational problem remains. The imine sets were first studied by Charton and Charton (73), who correlated them with eq. (2). No correlations of data for carbonyl or thiocarbonyl derivatives with eq. (2) are extant in the literature. Bhaskar, Gosavi, and Rao (158) have reported that AG values for complex formation of substituted thioureas with iodine are a linear function of the Taft a values. Drago, Wenz, and Carlson (159) have reported similar results for complex formation between iodine and substituted amides. Oloffson (160) has reported a linear relationship between -AH for the complex of substituted N,N-dimethylamides with SbCls and the ffj constants. 

Scheme 6.14 Transformation of thiocarbonyl derivatives of flavonoids with clayfen and clayan.

Fragments N-N-C and S-C Hydrazides, amidrazones and diazo compounds with thiocarbonyl derivatives... 

An unexpected C-arylation was observed by Sherburn et al. in an attempted radical deoxygenation of a homoallylic secondary alcohol 83 via its thiocarbonyl-derivative 84 (scheme 17).1511 Thus, reaction of 84, obtained from 83 with ArOC(=S)Cl, with nBu3SnH yielded the 10-aiyl compound 87 As inter-... 

Some thiocarbonyl derivatives of 68 have been shown to have analgesic activity <2005BMC3185>, whereas certain thiocarbonyl derivatives of imidazo[l,5-tf]pyrimidine 69 have antitumor activity <1999JME1661>. 

Acyloin condensation of diester 30a with sodium in liquid ammonia, followed by direct hydrogenation in the presence of Adam s catalyst, furnished the diol 32 in 49% yield. Diol 32 was transformed into the cyclic thiocarbonyl derivative (80% yield) which after heating with trimethylphosphite [14] afforded twistene 33 in 50% yield. Hydrogenation of 33 gave a compound identical in all respects with twistane 1. From the diester (-)-30a (+)-twistene was obtained, m.p. 35.5-36.5 °C, +... 

When thiocarbonyl derivatives are treated with an excess of electrophilic carbene complex, alkenes are usually obtained [1333-1336], The reaction is believed to proceed by the mechanism sketched in Figure 4.18, closely related to the thiocarbonyl olefination reaction developed by Eschenmoser [1337], Few examples have been reported in which stable thiiranes could be isolated [1338], The intermediate thiocarbonyl ylides can also undergo reactions similar to those of carhonyl ylides, e.g. 1,3-dipolar cycloadditions or 1,3-oxathiole formation [1338], Illustrative examples of these reactions are given in Table 4.22. 

From this hypersurface survey, incomplete with respect to approxir mate barriers for kinetic aspects e.g. concerning the ready polymerization of thiocarbonyl derivatives (19g), we tentatively concluded that the PE spectroscopic detection of thioacroleine (18) should be feasible, that it would be less stable than its oxygen analogue, acroleine, and that it could be identified by its PE spectroscopic ionization pattern because of the considerable differences in MNDO eigenvalue sequences to all nearby C4H3S isomers (Figure 2). 

A relevant reductive process, which has found wide application in organic synthesis, is the deoxygenation of alcohols introduced in 1975 by Barton and McCombie [58]. Reaction (4.28) shows that the thiocarbonyl derivatives, easily obtained from the corresponding alcohol, can be reduced in the presence of BusSnH under free radical conditions. The reactivity of xanthates and thiocarbonyl imidazolides [58] was successfully extended to 0-arylthiocarbonates [59] and (9-thioxocarbamates [60]. Several reviews have appeared on this subject, thus providing an exhaustive view of this methodology and its application in natural product synthesis [61-64]. 

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]. 

The addition of silyl radicals to thiocarbonyl derivatives is a facile process leading to a-silylthio adducts (Reaction 5.37). This elementary reaction is the initial step of the radical chain deoxygenation of alcohols or Barton McCombie reaction (see Section 4.3.3 for more details). However, rate constants for the formation of these adducts are limited to the value for the reaction of (TMS)3Si radical with the xanthate c-C6HuOC(S)SMe (Table 5.3), a reaction that is also found to be reversible [15]. Structural information on the a-silylthio adducts as well as some kinetic data for the decay reactions of these species have been obtained by EPR spectroscopy [9,72]. 

Radical decarboxylation via the corresponding thiocarbonyl derivatives of the carboxylic acids. 

Deoxygenation of alcohols by means of radical scission of their corresponding thiocarbonyl derivatives. 

Oxidation with bis(p-methoxyphenyl) telluroxide (general procedure All the reactions are performed at room temperature under Nj in CHCI3 or CHjClj. Approximately 10 mL of solvent is used for every 100 mg of substrate. For thiocarbonyl derivatives, 1.1 equiv of the reagent is used, for thiols 0.55 equiv. The mixtures are concentrated by evaporation and submitted to thin layer or column chromatography to isolate the products. An2Te is always recovered in a yield of 64-96%, while sulphur or selenium is always recovered in near quantitative yields from reaction with thio- or selenocarbonyl derivatives. 

Tri-/ -butyltin hydride also serves as a hydrogen-atom donor in radical-mediated methods for reductive deoxygenation of alcohols.131 The alcohol is converted to a thiocarbonyl derivative. These thioesters undergo a radical reaction with tri-w-butyltin... 

Reaction of the bicyclic 1,3,4-oxadithiolane (113) with triphenylphosphine in refluxing toluene led to an equilibrium mixture of the 1,3-oxathietane (114) and the thiocarbonyl derivative (115) (Scheme 29) <93BCJ1714>. Raney nickel can be used to desulfurize both 1,2,4-trithiolanes (to methylene compounds) and 5,5-disubstituted 1,2,4-oxadithiolane 2-oxides (116) which give rise to secondary alcohols (Equation (20)) <90BSB265>. 

Oxidative desulfurization of the thiourea moiety is known to occur by an in vivo metabolism which forms the corresponding carbonyl compound, although there is no direct evidence for involvement of any activated oxygen species like superoxide, which is distributed widely in living cells. It was found that various thiocarbonyl derivatives such as thioureas, thioamides and thiocarbamates were readily desulfurized with 51 to the corresponding carbonyl compounds in almost quantitative yields at —35°C in CH3CN (equation 82). Desulfurization of thiourea with 02 was previously reported but the yields were comparatively low. ... 

Scheme 4.18 Addition of thiocarbonyl derivatives to carbonyl ylides.

N-acyl derivatives of /V-benzoylpyrrolidines is believed (68JOC3627) to be a factor in the better adaptability of the molecule to biological processes when employed as a drug. In the thiocarbonyl derivative [in which R = l-(2-OMe-naphthyl)] the barrier around the R—C(S) bond seems exceptionally high, allowing chemical separation (76TL4573) of two rotational isomers below room temperature. 

A variety of thiocarbonyl derivatives, in addition to xanthate esters,... 

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