Benzo-1,3-dithiole-2-thiones

Synthesis of fused D-A systems such as 665 involved /-butyldiphenylsilyl protection of 4,7-dihydroxy-l,3-benzo-dithiole-2-thione 661, then the Horner-Wittig reaction of the resulting 662 with the carbanion derived from phosphonate 663 and finally deprotection of the TTF 664 to the required 665, obtained as green crystals (Scheme 94) <2003AG2871, 2004JOC2164>. 

Ring.—Monocyclic Compounds and their Benzo-analogues. Calculated coupling constants in the e.s.r. spectra of the radical ions of the dithiole-thiones (356) and... 

Some years later, the first stable thiocarbonyl ylides 9 and 10 were prepared by the reaction of thiourea with cyano-substituted oxiranes (19,20) or by addition of Rh-di(tosyl)carbenoid to benzo-l,2-dithiole-3-thione (21), respectively. Enhanced stability and the low reactivity of 9 and 10, which enables their isolation in crystalline form, results from the push-pull substitution at the two termini [cf. also (22)]. Another class of stable thiocarbonyl ylides that are also able to afford [3 + 2]-cycloaddition products are the mesoionic 1,3-dithiole-4-ones of type 11 (23,24). 

The 8 + 2-cycloaddition of 2//-cy c I o h cpta[h ] furan -2 - one (155) with acyclic 1,3-dienes provides a facile route to bicyclo[5.3.0] ring systems (156) (Scheme 61).291 2H-Benzo[Z>]thiete in the o-quinoid form undergoes 8 + 2-cycloaddition with 1,3-dithiolane-2-thione, l,3-dithiole-2-thiones, and adamantanethione to produce 4//-1,3-benzoditliianes.292... 

Explicitly included are species with carbonyl (>CO) groups such as the isomeric phthalimide (VIII) and isatin (IX), and with thiocarbonyl (>CS) groups such as the isomeric benzo-l,2-dithol-3-thione (X) and benzo-l,3-dithiol-2-thione (phenylene trithiocarbonate) (XI). Conversely, species with the isoelectronic >BF (and the related >BH) are ignored. Thus the question of the aromaticity in carboranes never arises in this chapter, even had we been explicitly interested in three-dimensional aromaticity (another issue we will ignore here). 

Finally, we turn to sulfur-containing species. Many indane derivatives may be suggested. However, there are only a few for which the enthalpy of formation has been determined phenylene trithiocarbonate (benzo-l,3-dithiole-2-thione) (X = Z = S, Y = CS) (XI), the isomeric benzo-l,2-dithiole-3-thione (X = Y = S, Z = CS) (X) [50],... 

Benzo-l,2-dithiole-3-thione+2C2H6 — oC6H4(CH3)2 + CH3C(S)SSCH3 (21)... 

Benzo[7]thiete 41 reacts in the ortho-qumoiA isomer 41 with cyclic trithiocarbonates such as l,3-dithiolane-2-thione, (ethylene trithiocarbonate), l,3-dithiole-2-thiones, and adamantanethione <1997LA1603>. In boiling toluene, 1,3 dithiolane and dithiole derivatives formed the spiro compound 42 and 43 in good yield. The related l,3-dithiole-2-thiones reacted chemoselectively at the C=S double bond. The use of adamantanethione yielded the polycyclic adduct 44 in a smooth and quantitative reaction (Scheme 3). 

The photolysis of 4-phenyl-l,2-dithiole-3-thione (71) gives a dimer (72) (73TL1561), but benzo-l,2-dithiolane 2,2-dioxide (73a) gives an o-thioquinone methide (74) (78JOC3374). 

The reduction of benzo-l,2-dithiole-3-thiones (77b) to various polythiols (74ACS(B)827, 63LA(661)84) may be accomplished by lithium (78BEP867155), lithium aluminum hydride, or by catalytic hydrogenation, and Raney nickel hydrodesulfurization gives products by complete elimination of sulfur (B-66MI43100). 

Benzo-l,2-dithiole-3-thione (77b) also reacts, but the monoadducts corresponding to (95) have o-thioquinone methide structures (cf. structure 104) and form diadducts rapidly. The use of dehydrobenzene (benzyne) gives 2-thioacylmethylenebenzo-l,3-dithioles (95 R3, R4 = (CH=CH)2). 

For alkanes, alkenes and their aryl derivatives, direct sulfurization gives thiones (3b). Typical examples are the preparation of 4-methyl- (10), 5-(4-methoxyphenyl)- (129) and 4-phenyl-l,2-dithiole-3-thiones (71) and benzo-l,2-dithiole-3-thione (77b) (Scheme 22) (B-66MI43100). 

The readily accessible enamines react with carbon disulfide and sulfur under mild conditions to produce l,2-dithiole-3-thiones (3b) via 3-amino dithioacids (Scheme 24), The nucleophilic character of the enamines is necessary for the initial reaction and to activate the sulfur (from Sg) for further insertion (67AG(E)294). Modified procedures produce other heterocycles. The yields of thiones (3b) may be low but this versatile reaction produces thiones that may be otherwise difficultly accessible, especially by direct sulfurization procedures, e.g. 1-morpholinocyclohexene may be converted into tetrahydrobenzo-1,2-dithiole-3-thione (142) in 40% yield. By contrast, direct sulfurization of 1-methylcyc-lohexene gives benzo-l,2-dithiole-3-thione (77b). Even dihydronaphtho-l,2-dithiole-3-thione (143) may be made by this procedure, although this compound may be dehydrogenated readily by sulfur at 220 °C. 

Benzo-l,3-thioxin-4-thione (148) reacts with phenylhydrazine to form the dithiole hydrazone (149), which must arise by initial nucleophilic attack at the thione function (80T3309). The l,3-thiazine-2,4-dione (150) possesses a three-carbon unit with an attached sulfur atom. Thionation with phosphorus pentasulfide gives the unsubstituted l,2-dithio e-3-thione (3b) (70AjC5l>. 

The parent 1,2-dithiolylium ion (4) is readily prepared by treatment of l,2-dithiole-3-thione (3b R = R = H) with hydrogen peroxide in acetic acid (65JCS32). The method may be applied to the alkyl and aryl derivatives with equal success. For cations with 3- and 5-substitution the acid catalyzed reactions of j8-dicarbonyl compounds with hydrogen disulfide or equivalent are best (80AHC(27)l5i), whereas the benzo-1,2-dithiolylium ion (172) and related compounds are best prepared by ring contraction of benzo-l,3-dithiins (171) (63LA(661)84>. 

Quantum mechanical calculations for the 1,3-dithiolylium ion, benzo-1,3-dithiolylium ion, l,3-dithiol-2-one and l,3-dithiole-2-thione have been carried out with the simple LCAO MO method <66AHC(7)39). According to these calculations, the lowest electron density was found at the 2-position of the 1,3-dithiolylium cation, and the C(4)—C(5) bond order corresponded approximately to that of an isolated C—C double bond. A delocalization energy of 105 kJ mol-1 has been calculated for this cation. For the benzo-l,3-dithiolylium ion it was found that nucleophilic attack should take place in the 2-position but electrophilic substitution at the 4-position. 

This section is divided into reactions of fully unsaturated rings like 1,3-dithiolylium ions, mesoionic 1,3-dithiolones, l,3-dithiol-2-ones and l,3-dithiole-2-thiones, and reactions of the saturated 1,3-dithiolanes. As a consequence of the positive charge in 1,3-dithiolylium ions, the main reactions of this class of compounds consist of nucleophilic attack at the 2-position, whereas the mesoionic 1,3-dithiolones undergo cycloaddition reactions. Reactivity of the benzo ring in benzo-l,3-dithiole and related systems has not been studied to any extent. 

J. B. Guttenplan, T. E. Spratt, M. Khmelnitsky, W. Kosinska, D. Desai, K. El-Bayoumy, Effects of 3H-l,2-dithiole-3-thione, l,4-phenylenebis(methylene)sele-nocyanate, and selenium-enriched yeast individually and in combination on benzo[a]-pyrene-induced mutagenesis in oral tissue and esophagus in lacZ mice, Mutat. Res., 559 (2004), 199 D210. 

Thione-l,3-dithiole-benzo [Pg.469]

Benzo-l,3-dithiole-2-thiones (254) are cleaved to thiocatechols (256) by treatment with DIBAL-H, or diborane-dimethyl sulfide. Sodium borohydride, LAH or Red-Al are much less efficient reagents for this purpose. Under more controlled conditions it is possible to obtain good yields of the intermediate ben-zodithiolanes (255). ... 

Thiete structures have been suggested as fragmentation products in the mass spectra of a thietane fused to a 3-lactam, an ortho disulfide of a thiolbenzoate ester, -propanethiol, thiirane carboxylic acid esters, isothiazoles, thiazoles, 1,3-dithiole 2-thiones, 1,3-dithiolene-2-ones, S-ethyl thio-benzoate, and thianaphthene sulfones. Tetramethylthiete may have been formed on thermolysis of the p-toluenesulfonyl-hydrazone of 2,2,4,4-tetramethyl-3-thietanone. " Thiete 2-thione may be an intermediate in the decomposition of 1,2-ditholium salts by the action of bases. " 2,2-Diphenyl-2H-thiete is suggested as an intermediate in the reaction of diphenyldiazomethane with 1,2,3-benzo-thiadiazole which yields 9-phenylthioxanthene and three other products. ... 

Reduction of l,3-dithiole-2-thione yields an anion-radical (150) whose ESR spectrum at low temperature has been measured the very low proton splitting (indicated in gauss) implies the spin population to be highly concentrated in the trithiocarbonate moiety. Consistent with this, no proton hyperfine splittings were resolved in the ESR spectrum of the anion-radical of benzo-l,3-dithiole-2-thione. ... 

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