1.2- Dithietes reactions

All unexpected reaction is the formation of dithiete 175, thiirene 1-oxide 185, and thioketone 186 by the treatment of di-l-adamantylacetylene with S2CI2 (99UPl).Tlie yield of each compound is 30% at most. 

Tile a-dithione 158 (dithiete 159) underwent a [4 + 2] cycloaddition with fra s-(l,2-dimethoxy)ethylene to give 197 in addition to reactions with HCN and CH2N2, which yielded 198 and 199, respectively (74JA3502). 

Tile preparation of beiizo-l,2-dithiete (264) had been claimed by oxidation of 1,2-benzenedithiol (25JIC318). However, later work has shown that the reaction product was probably a polymeric mixture (61JOC4782). Subsequently, compound 265 was irradiated to give a mixture of CO, sulfur, and dithiin and thiophene derivatives, which could, at least in part, be explained by the formation of 266 (72JHC707). Results of the thermolysis of 267 were also rationalized in terms of the intermediacy of o-dithiobenzo-quinone (the tautomer of 264) (78JOC2084). 

A solution of 10.5 g. (0.046 mol) of freshly distilled bis(tri-fluoromethyl)-l,2-dithiete (Note 2) in 200 ml. of n-pentane is cooled to —10° in a 1-1. round-bottomed flask equipped with an efficient reflux condenser and protected from moist air by a dry nitrogen blanket. A solution of 3.0 ml. (0.023 mol) of nickel carbonyl dissolved in 100 ml. of w-pentane is added down the condenser in one portion to this solution. The mixture is swirled to mix. An intense blue-violet color develops in about 15 to 20 seconds and after 1 to 2 minutes, vigorous evolution of carbon monoxide occurs. This evolution subsides in 10 minutes and the deep violet solution is allowed to warm to 0° during 2 hours to ensure complete reaction. Most of the pentane is removed by distillation at atmospheric pressure, the remaining 50 to 60 ml. is removed in vacuo (0.1 mm.), and the resultant crystalline mass is evacuated (0.1 mm.) at 50° for 4 hours. The crude product consists of shiny black-purple needles and weighs 11.8 g. (98%). Recrystallization from dry benzene (Note 3) gives shiny black crystals, m.p. 134 to 135° (sealed tube). The complex is air-stable but should be kept out of contact with moist air. 

Krespan and McKusick have studied the addition reaction of dithietenes to various oleflnes and acetylenes. Thus, the reaction of 3,4-bis(trifluoromethyl)-l,2-dithiete (378) with DMAD gives a dithiin derivative (379), which loses sulfur on heating to give 2,5-dicarbomethoxy-4,5-bis(trifluoromethyl)thiophene (380) [Eq. (57)]. 

The 1,2-dithiete 34 has been prepared <98JOC8192> and X-ray crystal structure determination shows the ring to be planar as had previously been shown for sterically hindered 1,2-dithietes <98BCJ1181>. Prolonged reaction of (alkylthio)chloroacetylenes (RSC i CCl) with NaiS in DMSO yields 1,3-dithietanes 35 <99SUL57>. 

The stereospecific formation of 5,6-dihydro-l,4-dithiins from the reaction of the 13-dithiete 60 with alkenes has been shown to proceed through its valence isomer, l,2-bis(methoxycarbonyl)ethane-13-dithione (Scheme 42) <99JOC8489>. 

Related indolocarbazoles have been synthesized using a Diels-Alder/retro-Diels-Alder approach. The rigid dithiete intermediate 172 produced in the initial cycloadduct reaction undergoes sulfur extrusion and dehydrogenation under the reaction conditions to produce the fully aromatized product (Equation 106) <1999TL3795>. 

Formal substitution of two benzene double bonds by sulfur atoms leads to the four-membered heterocycle 1,2-dithiete (37). This compound has not been synthesized, although derivative 38 is known,59,80 and dicyano-l,2-dithiete (39) is very probably an intermediate in some reactions of thiacyanocarbons (see below). Models of both compounds have been studied theoretically,23,91 but the calculations are... 

An example of the photodecomposition of a dithiin to give a stable dithiet, with elimination of ethylene, has been reported.206 A different reaction is preferred in the dithiins (261), which on irradiation, are converted to benzene derivatives (262) via the 1,4-dithiocins (263).207 The cyclic trimer of thio-acetophenone on irradiation in cyclohexane yields thioacetophenone.208 An initial carbon-sulfur bond homolysis is also responsible for the conversion, on irradiation in methanol, of a 3-cephem to two thiazoles,209 whereas a 1,2-alkyl migration followed by a further photochemically induced carbon-sulfur bond homolysis has been proposed to account for the photorearrangement of the sulfonium ylides (264) to the pyrimido-l,4-benzo[h]thiazepines (265).210 The novel photorearrangemenl of a 1,3-thiazine to a cyclopro-pathiazolidine has also been rationalized in terms of an initial carbon-sulfur... 

Theoretical and experimental studies on the reaction of 3,4-bis(methoxycarbonyl)-1,2-dithiete with alkenes and alkynes yielding cycloadducts have been carried out. The activation energy of the interconversion of the 1,2-dithiete to 1,2-dithione was estimated by MO calculations. These calculations (MP2/6-31G(d)) show that the dithiete 19f is 5.8 kcal mol-1 more stable than the ethane-1,2-dithione cis-20f, and the tautomerization energy is 28.5 kcal mol-1 from the thiete 19f and this value of the activation energy supports the possibility of the tautomerization between the 1,2-dithiete 19f and ethane-1,2-dithione cis-20f, at least at high temperature <1996IJQ859>. 

Theoretical studies on the ring-opening reaction of 1,2-dithiete by using unrestricted density functional theory (DFT) with fractionally occupied frontier orbitals were reported. The topic addressed in these studies was the question of the relative energies of the sulfur species 1,2-dithiete 19a and dithioglyoxal trans-20a <1999JCP7705>. 

The reaction of 1,2-dithietes with unsaturated compounds has also been investigated. 1,2-Dithietes were found to react with alkenes and alkynes to give the cycloadducts stereospecifically, which indicates the concerted reaction between ethane-1,2-dithione, the valence isomer of 1,2-dithiete, and dienophiles <2000JOM(611)106, 1999JOC8489>. 

Thus the reaction of 3,4-bis(methoxycarbonyl)-l,2-dithiete 19f with alkenes and alkynes gave the corresponding dihydrodithiins or thiophenes 120-126, respectively (Scheme 14). This reaction was considered as a reverse electron-demand hetero-Diels-Alder process (see Section 2.18.2) <2000JOM(611)106, 1999JOC8489>. 

Dithiete can be used as an oxidant for the thiometalates and oxythiometalates, and thus induced internal electron-transfer reactions provide an efficient method for synthesizing selected metal dithiolene and oxo-containing... 

Dithiolene complex 138 (having a 1 1 ratio) was also formed in the reaction of 3,4-di(l-adamantyl)-l,2-dithiete 135 or its valence tautomer 136 with ethylenebis(triphenylphosphine)platinum(0) 137 (Scheme 16) <2003JA12114>. 

An analogous reaction, which leads to the bicyclic dithietanes 160 and also to the dithietes 161 and 162 (Equation 21), has also been reported <2003JA14290>. 

The reaction of 1,2-diadamantylacetylene with disulfur dichloride led to the formation of the dithiete 232 (mentioned above), l,2-diadamantyl-2-thiooxoethanone 233, and the thiirene 1-oxide derivative 234 in 21%, 33%, and 27% yield, respectively (Equation 50) <2000TL8349, 2003JA12114, 1998BCJ1181 >. 

The gas-phase thermolysis at 850°C under 1.5 x 10-3 Torr of 243 led to a mixture of 1,2-dithiete 244 in 70% yield accompanied by two heterocyclic products <2006HCA991> (Scheme 30). The authors suggested a possible mechanism of the reaction. 

Figure 12. Representative complexation reactions involving l,2-bis(trifluoromethyl)dithiete.

Oxidation of complex Cp2Ti(S2C2Z2) (Z = C02Me) with sulfuryl chloride affords 1,2-dithiete and its oligomers (132). The reaction, if proved general, could be employed as a synthetic route to dithietes (Eq. 29). 

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