Heterocyclic thione

Compared to other heterocyclic thiones (S3, SS, 56), A-4-thiazoiine-2-thione (54) is among the most reactive (43, 117). The observed order of reactivity is kgg > kn... 

In contrast to the above, the reaction of a heterocyclic thione with an a-halogenoketone (Scheme 3) has been widely exploited as a route to [5,6] ring-fused systems with a heteroatom at a ring fusion point. 

Neutral Au(I) pentafluorophenyl complexes with heterocyclic thiones can be prepared by displacement of the tht ligand in [Au(QF5)(tht)] with a thione [49] as shown in Equation 3.6. 

P. W. Austin. Heterocyclic thione compounds and their use as biocides. Patent EP 249328, 1987. 

An example of thione coordination is demonstrated with the thiocarbonyl donor ligand 2,6-dimethyl-4H-pyran-4-thione, that gives a complex with zinc chloride of the form ZnL2Cl2-The crystal structure shows the zinc is tetrahedrally coordinated by two chloride and two sulfur donors and the compound was further studied by 3H NMR and IR spectroscopy.573 Both monomeric and dimeric heterocyclic thione complexes have been formed with zinc.5 4,575... 

Refluxing a mixture of hydrazonoyl halides 13 and heterocyclic thiones 14 in ethanol in the presence of triethylamine resulted in the formation of 3-arylazo-l,4-dihydro-l,7-disubstituted-pyrimido[l,2,-3]-l,2,4,5-tetrazin-6-ones 8. The reaction starts with the initial formation of the hydrazidine derivatives 15, which in turn undergo cyclization with the elimination of thiolate to give the desired product 8 (Scheme 1)<2004JCM399>. 

Anodic oxidation of heterocyclic thiones leads generally to disulfides. Thus cyclic voltammetric data at a pyrolytic graphite anode of purine-2,6-dithione show three peaks. The first and second correspond to a disulfide formation from the 6- and 2-thione groups, respectively, whereas the third is due to an oxidation to purine-2,6-disulfonic acid.432 Similarly, the electrochemical oxidation of benzthiazole-2-thione and benzimidazole-2-thione in CH3CN-NaC104 at a platinum electrode afforded the corresponding disulfides in good yield.433... 

Heterocyclic thiones have been extensively studied because of their facility to yield coordination complexes. All the ligands contain thione and occasionally thiol (mer-capto) groups directly attached to the carbon atoms of heterocyclic molecules. They have been previously reviewed by Raper in 1985576, and very recently the same author has reviewed28 the copper complexes of heterocyclic thioamides and related ligands. 

An important factor in realizing such potential is that of prototropic tautomerism and, in particular, which tautomer is present in solution immediately prior to the formation of the metal-ligand bond576. A common feature of all nitrogen-containing heterocyclic thiones is thione (157c)-thiol (157b) tautomerism. 

Deprotonation of heterocyclic thiones (157c) produces the corresponding thionate ion (157d) in which an electron pair on the heterocyclic trigonal nitrogen and three electron pairs on the thionate sulfur generate considerable coordination potential (158). 

Among the heterocyclic thiones, we present in Tables 20-25 the metal complexes of some of the thiocarbonyl ligands most widely used, which are represented in Figure 3. In these tables, data are given from 1988. In the case of copper, only complexes reported since Raper s review28 are given. 

Heterocyclic thiones l,3-dithiole-2-thione-4,5-dithiolate (DMIT). N. Svenstrup and J. Becher, Synthesis, 215 (1995). 

Complexes of heterocyclic thione donors. Coord. Chem. Rev. 61, 115 (1984). 

Benzothiazolyl alkyl sulfides, prepared from the corresponding alcohols, are easily desulfurized (87-99%) by TBTH-AIBN. This reaction constitutes a good indirect deoxygenation of alcohols. Desulfurization of dithioketals may be controlled. Thus 1,3-dithiolanes with 1 mol equiv. of TBTH lead to 3-alkyl (or 3-aryl) thiols (64-82%), while 4 mol equiv. of TBTH leads to the completely desulfurized derivative. Desulfurization of heterocyclic thiones is also performed with this reagent. In passing, it should be noted that generation of radicals from C—S bonds and tin hydrides in the presence of radical initiators is of large synthetic interest. ... 

The formation of four-membered chelate rings involving N and S donors is not unusual and has been observed in several complexes of 2-thiol- or 2-thione-substituted N heterocycles. Foye and Lo reported this form of coordination for a variety of metal chelates of antibacterial heterocyclic thiones. 2-Mercaptobenzimidazole (35 X = NH) was reported to form such chelates with Cu , Al and Fe . Complexes of 2-thiouradl (36), and substituted forms, also have been reported with this bonding mode to these metal ions. The tetrakis chelate of W" with 2-mercaptopyrimidine has been shown to adopt a symmetrical dodecahedral geometry. The mercapto S atom is thought to act as the better t-electron donor with the corresponding aromatic N atom acting as a tc acceptor. 

With heterocyclic thiones [Co 2-(S=)C3H5NS J(CIO )2 295 10150 4.98 Gouy 68S32... 

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