Of 1,2-dithiolium salts

The reaction of 1,2-dithiolanes with 2- and 4-picolyllithium has been examined <96PS(112)101> and the reactions of thioanhydrides such as 94 with both thiols <95JOC3964> and amines <96TL5337> have been reported. Treatment of 1,2-dithiolium salts with lithium or thallium cyclopentadienide results in formation of a variety of bi-, tri- and tetracyclic products <96LA109>. Reaction of 95 with trimethyl phosphite gives some of the desired coupling product but also the phosphonates 96 <96PS(109)557>. 

Judging from these early results, it appears that the reaction of 1,2-dithiolium salts with ammonia offers an elegant synthesis of certain substituted isothiazoles that are difficult to obtain by other methods.98 The reaction of the unsubstituted 1,2-dithiolium salt with NH8, however, does not yield the parent isothiazole system. Moreover, in the case of the 3(5)-methyl salts, the abstraction of a methyl proton activated by the positive charge of the ring successfully competes with this reaction (Section II,B,4).14a... 

The literature at present contains very few NMR data for 1,2-dithiolium salts. The results of systematic NMR studies on a number of 1,2-dithiolium salts and on many Baumann-Fromm disulfides and trithiones are presented in a Dissertation by Dr. E. Futterer (Freiburg-im-Breisgau, 1964). Most of the data in the following tables were taken from this dissertation. 

An example of the formation of 1,2-dithiolium salts by protonation of an alkylidene-l,2-dithiole is the decarboxylation of 1,2-dithiol-3-ylidene malonic acids (14) in the presence of perchloric acid. In this particular case, a strongly acidic reaction medium is necessary for obtaining satisfactory yields because the corresponding 3-aryl-5-methylene-l,2-dithiole is unstable and undergoes an autocondensation reaction leading to an a-(thiopyran-2-ylidene)thioketone (cf. Ref. 1 p. 83). 

Recent Bond-Length Determinations of 1, 2-Dithiolium Salts... 

The electrochemical reduction of 1,2-dithiolium salts (3) gives bis-l,2-dithiole dimers (72) via radicals, whose stability depends on their substitution <80SRi>. Further reduction gives a 3-thio-... 

The three or five protons on 1,2-dithiolium salts are exchanged by deuterium under various conditions <66AHC(7)3i, 66T2ii9>. Probably carbene intermediates are involved in these, and in the conversion of 1,2-dithiolium salts (3) to the thiones (2b) by sulfur in pyridine <82AHC(3l)63,89CC1716>. 

Because of structural contributors such as (101), ring substituents on dithiole rings with exocyclic double bonds at C(3) or C(5) should have a reactivity similar to that of 1,2-dithiolium salts (3). 

Ring transformations of 1,2-dithiolium salts with primary amines and oxidative cyclizations ... 

Ring Transformations of 1,2-Dithiolium Salts with Primary Amines and Oxidative Cyclizations... 

The specific reaction pathway of 1,2-dithiolium salts 39 was determined by the substituent in the 5-position. Primary aromatic amines reacted with monocyclic 5-aryl-3-ethoxy-1,2-dithiolium salts 39a but did not give 3-phenylamino-thioacrylicacid-(9-ethylesters because the attack of the amines on 5-position in 39a is hindered. In contrast, the 4-aryl salts 39b reacted very easily to produce thioesters 40, which were converted to salts 41 by cyclization with Br2 in CC14 (75ZC478). After treatment of... 

The treatment of 1,2-dithiolium salts 43 with methylamine gave 3-methyl-aminothiopropenones 44, which were oxidized by iodine to form the TV-methyl-isothiazolium salts 27a,45a, isolated as their perchlorates (73CJC3081). The yields of products were rather poor but the reaction is a very quick synthesis of TV-methyl-isothiazolium salts 27a,45a from the 1,2-dithiolium salts 43 (Scheme 12). 

The reduction of 1,2-dithiolium salt 158 with sodium borohydride followed by oxidation yields the 4,5-bis(methylthio) derivative 159 in 95% yield (Scheme 34)... 

The well-known synthesis of enamino-thioketones (21) using the reaction of 1,2-dithiolium salts with primary or secondary amines has been the subject of renewed investigation. " Duguay and Quiniou observed that the action of p-methylaniline on unsymmetrical 3,5-diaryI-l,2-dithiolium... 

Further recent papers concerning metal complexes of thio-analogues of j3-diketones deal with the preparation of the cobalt(n) complex of 1,3-diacetylthioacetone, the synthesis and properties of a series of metal complexes of dithioacetylacetone, the synthesis of the nickel(n) complexes of monothio- and dithio-dibenzoylmethane (67) by the nucleophilic cleavage of 1,2-dithiolium salts by hydroxide or mercaptide ions in the presence of nickel(ii) ions, the bromination of the cobalt(m) complex of monothioacetylacetone (68) with iV-bromosuccinimide to yield (69), and the application of monothiodibenzoylmethane as an analytical reagent for quantitative determination of copper. ... 

The synthesis of 1,2-dithiolium salts from /3-diketones has been modified by the use of diacetyl disulphide in place of hydrogen disulphide. Precursors of the general type (30), where Y = O, S, (OEt)a, or N+MCg, and Z = OH, Cl, or OEt, are treated with the diacyl disulphide and a strong acid. This versatile synthesis has been applied to the preparation of a wide range of alkyl- and aryl-substituted dithiolium salts. 

Further examples have been given of the reaction of 1,2-dithiolium salts (both 3,4-dialkyl and 3,5-dialkyl) with ammonia to give isothiazoles, and the formation of ring-opened products, (45) and (46), from 3-aryl-l,2-dithiolium perchlorates and excess of dimethylamine has been reported. The reactions of 3-methylthio-l,2-dithiolium salts with amines continue to be of interest. With primary aliphatic amines, 5-aryl-3-methylthio-l,2-dithiolium iodides give j8-alkylaminodithioacrylates (47) and isothiazoline-3-thiones (48) as well as the demethylated compounds (l,2-dithiole-3-thiones). Similar products are obtained with secondary amines, except that the isothiazole derivatives are replaced by 3-dialkylamino-l,2-dithio-lium iodides (49), the n.m.r. spectra of which indicate restricted rotation... 

Synthesis.—3,5-Diaryl- and 3,5-dialkyl-1,2-dithiolium salts (121 R = Ar or Bu ) can be prepared in good yield by the sulphurization of diketones (Scheme 9). Treatment of these salts (121) with pyridine affords the corresponding 4-olates (122), which can be O-alkylated with iodomethane and similar compounds. With ammonia, ring scission and re-cyclization occurs, and the corresponding iso-thiazolium-4-olates are formed. An unusual synthesis of 1,2-dithiolium salts (124) is by the photolysis of l,2-dithiole-3-thiones (123) in benzene or acetonitrile, in the presence of aryl or alkenyl bromides or iodides. 

Mixtures of 1,2-dithiolium salts and CigTCNQ were subjected to the homodoping metiiod [93], Although different counteranions (I , TCNQ and F4TCNQ ) were used, die LB films obtained were independent of the anion. It was suggested that a chemical reaction occurred at the air-water interface and mixed-valence clusters were spontaneously formed. Detailed discussions on IR spectra have been reported [94-96],... 

Dimeric products (21), previously obtained electrochemically, have been prepared by reduction of 1,2-dithiolium salts with zinc. These products oxidize, either in air or with selenium dioxide, to highly coloured products of type (22). 

The reaction of l,2-dithiole-3-thiones with enamines gave substituted thio-pyranthiones such as (12). Another synthesis of (12) employed the reaction of 1,2-dithiolium salts with CNCHgCSNHg. Various syntheses of substituted thiopyranylidenes (18) have been reported and their photoisomerization about the exocyclic double bond has been studied. The thermal isomerization of... 

S(2p) Binding energies for 3,5-dimethyl-, 3,5-diphenyl-, and 3-methyl-5-phenyl-dithiolium cations have been measured by X-ray photoelectron spectroscopy, and some mass spectral data for the thermolysis products of 1,2-dithiolium salts have been recorded. ... 

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