L,3-Diselenole-2-thione

The synthesis of halogenated TTF is most often based on the lithia-tion/electrophilic halogenation of either the TTF core itself [50] or the five-membered l,3-dithiole-2-thione [36,51]. This procedure has been recently expanded to the analogous l,3-diselenole-2-thione [52,53], allowing for the formation of a wide variety of iodo- and bromotetraselenafulvalenes or dithiadiselenafulvalenes shown in Schemes 6 and 7. 

The reaction of selenadiazole 121a with titanocene pentaselenide in xylene at 140 °C (15 min) affords titanocene complex 194 in 34% yield (Scheme 22) <1999SM1703>. The titanocene complex 194 was treated with CSC12 to afford the l,3-diselenole-2-thione 195. 

An interesting side reaction was observed when certain l,3-diselenole-2-thiones were heated with trimethyl phosphite (77CC835). Instead of formation of tetraselenafulvalenes, thiatriselenafulvalenes were formed as shown in Scheme 7. The phosphite most likely initiates a rearrangement of the l,3-diselenole-2-thiones to l,3-thiaselenole-2-selenones. 

Scheme 7 Thiatriselenafulvalenes from l,3-diselenole-2-thiones and trimethyl phosphite...

The photochemical couplings of 4,5-diphenyl- and 4-phenyl-l,3-diselenole-2-thione to give tetraphenyl- and diphenyl-tetraselenafulvalene, respectively, and elemental sulfur have been reported (79ZC192). In this same report the irradiation of 4,5-diphenyl-l,3-thiaselenol-2-one (52) in the presence of nickel tetracarbonyl gave the nickel thiaselenane (53). 

Decarboxylation of 4,5-dicarboxy-l,3-diselenole-2-thione 189 upon treatment with iodomethane in nitromethane gave the salt 190-D (Scheme 11) <2003CC1940>. Subsequent refluxing with pyridine in benzene gave 1,3-diselenole-2-thione 112. 

The thiadiazole route to l,3-dithiole-2-thiones and l,3-diselenole-2-thiones or selones is quite versatile as 1,2,3-thia- (184) or selenadiazoles (185) are readily prepared from an appropriate methyl ketone semicarbazone (183) (Scheme 48). 

Tetrathiafulvalenes.—Preparations of ever more elaborate compounds of this class have been announced. Coupling of the dithiolethiones (293 n = 2 or 3) by means of triethyl phosphite affords the tetracyclic derivatives (294) °° mixtures of the dithioleselones (295) and (296) give good yields of the crossed product (297) in this reaction.The tetraselenafulvalene (299) is obtained by photolysis of 3,4-diphenyl-l,3-diselenole-2-thione (298). Even cyclophanes containing the tetrathiafulvalene structure have been reported thus compound (300), on sequential treatment with methyl iodide, sodium borohydride, and fluoroboric acid-acetic anhydride, affords a mixture of the tetrathiafulvalenophanes (301) and (302), ° and the paracyclophanes (304) and (305) result from the para-substituted benzene (303). 

Other complexes of thiocarbonyl compounds related to dmit, such as 1,2-dithiole-3-thione-4,5-dithiolate (dmt, 161)741,744,752, l,3-dithiole-2-thione-4,5-diselenolate (dsit, 162)687,753-758 or l,3-thiaselenole-2-thione-4,5-dithiolate (dmits, 163)699 have been described. 

Very few structural investigations have been made for five-membered heterocycles containing selenium or tellurium and one other chalcogen atom by either theoretical methods or X-ray diffraction. The lone theoretical treatment <8lJST(7l)l) was a MINDO/3 optimization of molecular geometry for l,3-thiaselenole-2-thione and -2-selenone and for 1,3-diselenole-2-selenone (8) and -2-thione. These molecules were predicted to be planar. The calculated bond lengths and angles for (8) are shown in Scheme 3. 

V,Ar-Dialkylamino)-l,3-diselenolylium salts react with hydrogen selenide and hydrogen sulfide to give l,3-diselenole-2-selenones and -2-thiones, respectively (74CC937,80CC866, 80CC867). Examples of these transformations include the conversion of (67) and (68) into selenone (25) and thione (69). 

Diselenolane (81) has been prepared by the condensation of paraformaldehyde with ethane-1,2-diselenol (79JOC4689). The condensation of ethane-1,2-diselenol with (thiocar-bonyl)diimidazole (82) gave l,3-diselenolane-2-thione (72) (80JOC2632). 

The 1,2,3-selenadiazole route to l,3-diselenole-2-chalcogenones (i.e., l,3-thiaselenole-2-thione <1980JOC2632>) was described in detail in CHEC-11(1996). Here one more recent example is shown. 1,2,3-Selenadiazole 254 was treated with isoselenocyanatobenzene and potassium tert-hutoxide in A)A -dimethylformamide and /7-butanol to provide 2-phenylimino-l,3-diselenole 25 in 50% yield (Equation 61) <1996RJC1641, 1996RJ01812>. Compounds 37, 38, and 255 were made in a similar way by cycloaddition reactions <1996RJ01812>. 

Dithioles. Diselenoles. and Dltelluroles.- Treatment of ethyl benzoylacetate with Lawesson s reagent (188) gives the l,2-dithiole-3-thione (189) 197 the latter reacts with arenediazonium fluoroborates to yield the 1,2-dithioliua salts (190 R = aryl). The action of -methylbenzylidenemalononitrile, PhMeC C(CN)2, on the methylthio-analogue (190 R = Me) leads to a mixture of the condensation product (191) and the thieno[3,2-b]thiopyranimine (192).199 The mesoionic dithiolium oxide (193) has been prepared from -dichloroacetone and sulphur, followed by methylation. 

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