1.3- Dithiolium - from

Dithiolium from 1,3-dithiene ring Ring contraction of S-heterocyclics s. 19, 648 0)... 

Aryl-l,2-dithiolium salts are a source of either dithiatricyclodecadienes (29) or cyclopenta[fc]thiopyrans (30) depending on whether the initial ring opening resulting from reaction with a metal cyclopentadienide is followed by an intramolecular cycloaddition or a condensation <96LA109>. 

Dichloro-bis-dithiolium salt 85 obtained from M-ethyldiisopropylamine, S2CI2 and DABCO in chloroform at room temperature reacted with arenesulfonamides and their Af,N-dichloro derivatives with the formation of Ahhf -bis(arylsulfonyl)-dithiolothiazine diimines 90 in modest yields (2001JCS(P1)2409 Scheme 42). 

Somewhat earlier, Souizi and Roberts (63) reported mesoionic heterocycle interconversions leading to l,3-thiazolLum-4-thiolates, l,3-thiazolium-4-olates, and l,3-dithiolium-4-thiolates from l,3-dithiolium-4-olates. This elegant chemistry, which involves cycloaddition reactions, is presented in Section 10.3.8. 

Regitz and co-workers (140,142) continued their exploration of the chemistry of mesoionic heterocycles with phosphaalkynes. Thus, 339 (R = R =Ph) reacts with tert-butyl- and mesitylphosphaacetylene to give 1,3-thiaphospholes (346). This same 2,5-diphenyl-l,3-dithiolium-4-olate reacts with 2,3,4-tri-tert-butylazete to give 347 in low yield (143). This reaction is believed to proceed via diphenylthiir-ene by loss of carbonyl sulfide from 339. 

Reaction with acetylenic dipolarophiles represents an efficient method for the preparation of 2,5-dihydrothiophenes. These products can be either isolated or directly converted to thiophene derivatives by dehydration procedures. The most frequently used dipolarophile is dimethyl acetylenedicarboxylate (DMAD), which easily combines with thiocarbonyl ylides generated by the extrusion of nitrogen from 2,5-dihydro-1,3,4-thiadiazoles (8,25,28,36,41,92,94,152). Other methods involve the desilylation (31,53,129) protocol as well as the reaction with 1,3-dithiolium-4-olates and l,3-thiazolium-4-olates (153-158). Cycloaddition of (S)-methylides formed by the N2-extrusion or desilylation method leads to stable 2,5-dihydrothiophenes of type 98 and 99. In contrast, bicyclic cycloadducts of type 100 usually decompose to give thiophene (101) or pyridine derivatives (102) (Scheme 5.37). 

The 1,2-dithiolium (158) and 1,3-dithiolium ions (159) are iso-Tr-electronic with the tropylium ion, from which they may be formally derived by replacing two pairs of double bonds by sulfur atoms. Structural data and calculations demonstrate that the rings are substantially stabilized by -ir-electron delocalization. 

The first recorded attempt to prepare a thio derivative of a /1-diketone resulted in the isolation of the colourless dimer (57 R = R = Me) from the reaction of acetylacetone and hydrogen sulfide in hydrochloric acid.243 Similar dimers with various R and R groups have been reported244 and the structure (57) has been confirmed from NMR and MS data.245 Other attempts to prepare dithio-/ -diketones (58) yielded 1,2-dithiolium salts (59).246... 

The MS fragmentation patterns of dithio-/J-diketonato complexes differ from those of both /J-diketonato and monothio-/J-diketonato complexes. The mass spectra of bivalent dithioacetyl-acetonato complexes are characterized by a molecular ion peak M and a much stronger peak for L+ due to the formation of the 3,5-dimethyl-l,2-dithiolium ion another peak at tn/e 96 is due to the loss of HS from the dithiolium cation. The mass spectra of nickel complexes of dithio-/ -diketones are dominated by fragmentation products of the uncomplexed oxidized ligand, which is consistent with the low stability of dithio-/J-diketones and the greater stability of the 1,2-dithiolium... 

Martin and Stewart1199 first described the preparation of the deep-violet complex [Co(SacSac)2] (363 R = Me) from the reaction of CoCl2 with acetylacetone (acacH) and H2S. A similar synthesis1200 where CF,acac is substituted for acac yields [Co(CF3SacSac)2] (363 R = CF3). The preparation of [Co(PhSacSac)2] via BHf reduction of the dithiolium salt (364) in the presence of CoCl2 has also been reported.1201... 

The 1,2- and 1,3-dithiolium ions (1 and 2) are unsaturated five-membered ring cations in which each of the two ring sulfur atoms can contribute a free pair of Zpn electrons to the mesomeric bond system. Thus both systems possess a potential aromatic sextet, and are therefore iso-7r-electronic with the tropylium ion (3), from which they... 

Thus the leuco bases expected from the reaction of aryl-substituted 1,2-dithiolium salts with tertiary aromatic amines can only occasionally be obtained as such (e.g., 19b). The 1,2-dithiole derivatives (19) generally suffer rapid loss of hydride ion by the unreacted 1,2-dithiolium salt or by added oxidizing agent.23 It has recently been shown24 that 1,2-dithiole derivatives can be isolated only if the ring is stabilized by several aryl substituents. The compounds are then reasonably stable, and can be reconverted into the starting salts by the action of strong acids (Section II, B, 3). 

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