1.2- Dithiolium salts 1.2- dithiole-3-thiones

Phosphonates based on (1), i.e., (PI), can be prepared simply by heating 1,3-dithiole-2-thiones with a trialkyl phosphite at high dilution [215]. They react with aldehydes, ketones, 2-iminium-I,3-dithioles or dithiolium salts and selenium analogs to give larger molecules, precursors of extended tetrachalcogenaftil-valenes (see below). The reactions take place in the presence of a base, such as butyllithium (BuLi) or LDA. Some aldehydes and ketones, which have... 

The reaction of substituted 4-(2-hydroxyaryl)-2-(T,T-dialkylamino)-l,3-dithiolium salts 166 (NR2 = pyrrolidine, piperidine, morpholine) with sodium sulfide in EtOH at room temperature afforded the corresponding 1,3-dithiole-2-thiones 167, whereas reaction in boiling EtOH led to formation of 2-hydroxyacetophenones 168 (Scheme 16) <2003SC3071>. 

Dialkylamino and 2-ethylthio-I,3-dithiolium salts are cleaved by hydrogen sulfide,or sodium hydrosulfide,giving l,3-dithiole-2-thiones in excellent yields. Sodium sulfide and sodium hydrosulfide react with 1,3-benzodithiolium salts in methanol giving the sulfide 158 and the dithiole 159. 

Alkylthio-1,2-dithiolium salts (17) also lose alkyl groups to form thiones (2b) under the conditions of mass spectroscopy. For other 1,2-dithiolium salts (3), radicals are initially formed whose masses correspond to the molecular ions. Certain 1,2-dithiolium salts (3) form 1,2-dithiole-3-thiones under mass spectrometry conditions, presumably by thermal degradation <80SRl>. 

Dithiolium cations (3) form radicals under the thermal conditions of mass spectroscopy (Section 3.11.3.4), and carbenes may be involved in the formation of l,2-dithiole-3-thiones and thieno[3,2-Z>]thiophenes by thermolysis of 2-iodo-l,2-dithiolium salts (29a) <8ILA1729>. 

The reactions of 1,2-dithiole-3-thiones (2b) with various types of halogen reagents forming 3-halo-l,2-dithiolium cations (29b) <76PS(1)185> can be treated as a nucleophilic attack of a halide ion, or a halogen source on a type of initially formed 3-halothio-1,2-dithiolium salt (69b). 

Dithioles with hydroxy and thiol substituents are protonated forms of l,2-dithiole-3-ones (2a) and -3-thiones (2b) respectively, which are regenerated on deprotonation. The reactions with nucleophiles of 3-alkoxy and 3-alkylthio-1,2-dithiolium salts give dealkylation products only in minor amounts. Instead, nucleophilic attack occurs on the ring (Section 3.11.4.2(iv)). A l,2-dithiolium-4-thiolate (98) readily acylates on an amine function to form a l,2-dithiolo-l,2-dithiole (99). This unusual reactivity is explained by the relative preferences for cyclic and acyclic forms of mesoionic forms <91EGP293120>. 

Various reagents, including oxalyl chloride and thionyl chloride, convert 1,2-dithiole-3-ones (2a) and -3-thiones (2b) into 3-chloro-l,2-dithiolium salts, types (56a), some via cyclic intermediates <87PS(3l)i09>. The oxygen atom on l,2-dithiolium-3-olates (20) can be protonated or alkylated to form 4-hydroxy or 4-alkoxy-l,2-dithiolium salts respectively <86MCLC373>. 

Dithiole-3-thiones (2b) readily alkylate to form 3-alkylthio-l,2-dithioUum salts (19). Aryl halides are usually unreactive but react photochemically to form 3-arylthio-l,2-dithiolium salts... 

The required C3S unit also exists in 2-thio derivatives of benzoic acid. Thus, thionation of diphenyl disulfide-2,2 -dicarboxylic acid gives benzo-l,2-dithiole-3-thione (37b). This approach can be also applied to thienodithioles and to dithiolopyridines <82AHC(3l)63>. In a conversion of thiosalicylic acid to benzo-l,2-dithiole-3-thione, the extra sulfur atom is provided by thiolacetic acid <920PP488>. The necessary units also appear in some palladium complexes, which by treatment with thiocyanate give benzo-l,2-dithiolium salts and other fused dithioles (Equation (10)) <90JCS(Pl)288l>. 

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 =... 

A similar 3-adduct was formed by only the ethanethiolate ion with 3,5-diphenyl-1,2-dithiolium salts. Other thiols, except ethanethiol, which did not react, convert to 3-alkylthio-5-phenyl-l,2-dithiolium cations (62) into l,2-dithiole-3-thione (63). 

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... 

The syntheses of bis-l,3-dithiolylidene compounds noted above, involving treatment of 1,3-dithiolium salts with bases, are thought to proceed through carbene intermediates. These may be generated in other ways, for example, by the action of carbon disulphide on acetylenes (81 R = CF3) and by the action of triphenylphosphine on the l,3-dithiole-2-thione (83 R = CF3). In the first of these two methods, more complex products. 

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. 

Tetrathiafulvalenes and Selenium Analogues. A review on organic metals has been published. The photoelectron spectra of tetrathiafulvalene (388) and the corresponding di- and tetra-selenium compounds have been determined " and the H n.m.r. spectra of tetrathiafulvalene in nematic liquid-crystalline solvents have been measured. Synthetic procedures for symmetrically substituted tetrathiafulvalenes include the reduction of 1,3-dithiolium hexafluorophosphate with zinc dust, the reductive coupling of l,3-dithiole-2-thiones [cf. (379)] with derivatives of tervalent phosphorus, and a five-stage synthesis of tetraethyl-tetrathiafulvalene, starting from the dithiocarbamate (389). Treatment of a mixture of the dithiolium salts (390 R, R = H, Me, or Et) and (391) with triethylamine results in three products, two symmetrical tetrathiafulvalenes and the crossed compounds (392). The conversion of the bisdithiolone (393) into... 

---