Dithioles and Related Compounds

A useful general method has been described for the synthesis of 1,3-di-thiole-2-ones from easily available starting materialsxanthate esters of type (52) undergo cyclization with loss of the isopropyl group when treated 

Irradiation of 4,5-bis-p-dimethylaminophenyl-l,3-dithiole-2-one in benzene yields the dark red, stable, a-dithione (57 Ar = p-Me2NC6H4), which appears to exist, in solution, partly in the cyclized form (58).  

The stereospecihc conversion of selenadiazoles (59) into diselenafulvenes (60) by the action of bases is thought to proceed via a selenaketen. A 

Beiner, D. Lecadet, D. Paquer, A. Thuillier, and J. Vialle, Bull. Soc. chim. France, 1973, 1979. 

Isothiathiophthen-Iike structures (63) are produced when 3-dimethyl-amino-5-phenacylthio-4-phenyl-l,2-dithiolium bromide is heated with phosphorus pentasulphide in pyridine.  

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Much interest has been generated in various properties of metal derivatives of dithioketones, ethylene (1, 2) dithiolates, and related compounds in recent years (17,18,29, 43, 65, 66). There are many interesting facets of these fascinating compounds, and the previously mentioned references cover them in some detail. We limit ourselves here to the structures of the Pt group metals of these engrossing ligands. Unfortunately, some of the more interesting properties of the transition metals... 

The chemistry of the 1,2-dithioles and related compounds was covered in the first edition of Comprehensive Heterocyclic Chemistry (CHEC-I), and a review, published in 1990, of some systems containing the 1,2-dithiolane ring <90SR257>. Reviews of other 1,2-dithioles were published in the early 1980s <80SRi, 82AHC(3i)63>. Since 1985 there has been a marked increase in published applications of 1,2-dithioles. 

Bismorpholino disulfide (35) and related compounds are prepared from the corresponding amine (or imide) and disulfur dichloride. An elegant synthesis of the 1,3-dithiole-2-thione (36) from 35 is shown this is an example of two transfer reagents acting in concert.40... 

There are few examples of the preparations of heterocyclic compounds containing two or more heteroatoms which involve cyclization with formation of a bond between two heteroatoms. The best known instances of this type of reaction, all of which are [6 + 0] reactions, are the preparations of benzocinnolines as outlined in equations (l)-(4). A similar type of approach to that outlined in equation (4) has been used for the direct preparation of the di-N-oxide (2) from the dioxime (1 equation 5). The naphthotriazine betaine (4) is obtained as one of the products of the thermal decomposition of the azidoazo compound (3 equation 6). 1,2-Dithiins and their dibenzo derivatives have been prepared by oxidation of appropriate dithiols and related starting materials as outlined in equation (7). All of these reactions are, however, somewhat specialized and there has been essentially no systematic study of the preparation of six-membered heterocycles via formation of a bond between two heteroatoms. 

Dithiolo-l,2-dithioles, thermolysis and photolysis of 91PS(58)179. Structure of trithispentalenes and related compounds 91PS(58)17. Synthesis and properties of new functionalized tetrathiafulvalene jr-... 

The 1,2-dithiole system and related compounds possess two adjacent sulfur atoms in a five-membered ring. The types are known respectively as 1,2-dithiolanes (1), 1,2-dithioles (2), l,2-dithiol-3-ones (3a), l,2-dithiole-3-thiones (3b), 3-iminodithioles (3c), l,2-dithiol-3-ylidenes (3d) and 1,2-dithiolylium (4) ions. 

The parent 1,2-dithiolylium ion (4) is readily prepared by treatment of l,2-dithiole-3-thione (3b R = R = H) with hydrogen peroxide in acetic acid (65JCS32). The method may be applied to the alkyl and aryl derivatives with equal success. For cations with 3- and 5-substitution the acid catalyzed reactions of j8-dicarbonyl compounds with hydrogen disulfide or equivalent are best (80AHC(27)l5i), whereas the benzo-1,2-dithiolylium ion (172) and related compounds are best prepared by ring contraction of benzo-l,3-dithiins (171) (63LA(661)84>. 

This section is divided into reactions of fully unsaturated rings like 1,3-dithiolylium ions, mesoionic 1,3-dithiolones, l,3-dithiol-2-ones and l,3-dithiole-2-thiones, and reactions of the saturated 1,3-dithiolanes. As a consequence of the positive charge in 1,3-dithiolylium ions, the main reactions of this class of compounds consist of nucleophilic attack at the 2-position, whereas the mesoionic 1,3-dithiolones undergo cycloaddition reactions. Reactivity of the benzo ring in benzo-l,3-dithiole and related systems has not been studied to any extent. 

In accordance with the format of the two preceding reviews in CHEC(1984) and CHEC-II(1996) <1984CHEC(6)783, 1996CHEC-II(4)569> covering the chemistry of 1,2-dithioles, 1,2-dithiolanes, and related compounds, this chapter follows basically the same concept. Thus, the review aims to describe (1) the various reactivity aspects of these compounds (2) strategies to obtain them, not only by previously developed synthetic pathways but also via application of new routes and (3) their diverse applications. Much effort has been directed to structural and spectroscopic characterization of particular compounds, containing the basic 1,2-dithiole 1 or 1,2-dithiolane core 2, which possess projected physicochemical properties. There are several reasons for interest in these compounds. First, some are isolated natural compounds from medicinal plants, and second they are expected to possess some degree of activity. 

Dithioles and Related Systems. - Base-catalysed condensation of the 1,2-dithiolium salt (195) with ethylidenemalononitrile yields the dithiole (196). The action of potassium borohydride on the enamine (197) results in the rearranged thiopyranthione (199), presumably via compound (198). Deprotonation of the bisulphate (200) or heating the tosylhydrazone (201) produces the thienothiophen (202). It has been reported that the dihydrodithiolone (203) is desulphurized by hexaethylphosphoric triamide to yield the thietanone (204). 1,2-Dithiole-3-thiones (205 X = S =... 

Dithioles, Diselenoles, and Ditelluroles 245 Tetrathiafulvalenes and Related Compounds 248 Pyrazoles 250... 

Most of the compounds studied in this group are dithiolate and related complexes. Their spectra are interpreted using the spin Hamiltonian Eq. (16) and assuming S=j, their bonding is discussed in [66],... 

The studies discussed earlier in this chapter focused on the photophysics of met-allo-l,2-enedithiolates and possible applications for these complexes. In addition to being emissive, several (diimine)Pt(dithiolate) complexes photochemically activate molecular oxygen. Recent reports by Srivastava and co-wwkers showed that (bpy)Pt(tdt) and related compounds are sensitizers for the formation of singlet oxygen [81 -83], the generation of which leads to decompositirai of the parent metal complex. The end-products from these reactions are similar to those obtained from the thermal and photochemical oxidation of Ni(II) and Pd(II) dithio-lates [84-87]. These reactions give stable metal-sulfinate (M[SQ2R]) and metal-sulfenate (M[SOR]) derivatives. Collectively, this work parallels the photo- and thermal oxidation of thioethers (RSRO [88-90]. 

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