1.2- Dithiole-3-thiones ketones

From the reactions of sulfur and carbon disulfide with cyclic ketone-derived enamines (570-573) 3H-l,2-dithiole-3-thiones were obtained, whereas the addition of carbon disulfide to other enamines gave a-dithio-pyrones (574), through initial dimerization of the enamine. 

SM(68)1914>. Trimethyl phosphite 102 (lOequiv) mediated cross-coupling between the l,3-dithiole-2-thiones 103 and the ketone 40 yielded unsymmetrical TTF derivatives 45-48, in moderate yields (Scheme 7)<1997SM(86)1871>. Similar reaction between the 2-thione 104 and the TTF derivatives 105 yielded the pentacycles 88 (yields were not recorded) (Equation 2) <1997SM(86)1821>. 

Pyran-4-thiones reacting with potassium hydrogen sulfide lead to a-(l,2-dithiol-3-ylidene) ketones and/or thiopyran-4-thiones (Eq. 

Thiopyran-4-thiones give adducts with mercury dichloride which, by reaction with aqueous sodium carbonate, give a mixture of a-(l,2-dithiol-3-ylidene)ketone and thiopyran-4-one (Eq. 2).9> 10... 

A better synthesis of a-(l,2-dithiol-3-ylidene)ketones from thio-pyran-4-thiones consists in the reaction with sodium hydroxide in dimethylformamide (DMF), followed by ferricyanide oxidation (Eq. 3).11... 

With 4-aryl-1,2-dithiole-3-thione.s, a dithiopyrone is obtained24 probably because the dithiole ring of the dithiolylidene ketone is less stabilized by a 4-aryl than by a 5-aryl group (see Section IV,B). 

At 150°C, a-diazoketones react with l,2-dithiole-3-thiones, giving a-(l,2-dithiol-3-ylidene)ketones (Scheme 6). This may be done either with cyclic or acyclic diazoketones28 a-diazo esters react similarly.28... 

Bromoacetone or phenacyl bromide react with 1,2-dithiole-3-thiones giving a 3-acetonylthio- or a 3-phenacylthio-l,2-dithiolium bromide, which yields a dithiolylidene ketone, through sulfur extrusion, by moderate heating.43... 

This transposition explains why the condensation in alkaline media of 4-aryl-l,2-dithiole-3-thiones with acenaphthenone gives a y-dithiopyrone instead of a dithiolylidene ketone.24 A possible mechanism is as in Scheme 19. 

A further efficient and general synthesis of l,3-dithiole-2-thiones (169) with a variety of functional groups is the acid-catalyzed ring closure of j8-keto f-butyl trithiocarbonates of type (261) which are readily available from a-halo ketones and sodium t-butyl trithiocarbon-ate. The intermediates (262) fragment into isobutene and l,3-dithiole-2-thiones (169) (80JOC175). 

Thiiranes are assumed to be intermediates in the formation of l-oxa-6,6aA4-dithiapen-talenes from l,2-dithiole-3-thiones reacting either with diazo ketones or with a-halogeno ketones with subsequent desulfuration in basic medium (71AHC(13)161, pp. 177-179). 

In the presence of acetic acid and pyridine, 5-phenyl- or 5- eri-butyl-3-methylthio-l,2-dithiolium ions have been reacted with cyanoacetone to give, in the usual way, an a-(l,2-dithiol-3-ylidene) ketone. A similar reaction has been observed with 4-hydroxy-6-methylpyran-2-one and with 4-hydroxy-coumarin (Eq. 23). In the same way, 4-hydroxy-6-methylchromene-2-thione and 3-methylthio-5-phenyl-l,2-dithiolium cation gave the fused trithiapentalene 59. ... 

One of the most versatile methods for the synthesis of 5-substituted 1,2-dithiole-3-thiones is the reaction of a-methylene groups of ketones with base... 

Aryl-substituted ketones react directly with elemental sulfur in hexa-methylphosphorus triamide with formation of l,2-dithiole-3-thiones.46,47 Aryl-substituted acetaldehydes can condense likewise with carbon disulfide to give the analogous 4-aryl-substituted l,2-dithiole-3-thiones.48 The same reaction was observed with aryl-substituted acetic acid esters, in which a methylthio group is incorporated into the reaction product (26).49 Thioketones and enthioles react analogously. 50,51 The parent l,2-dithiole-3-thione (27) has been prepared from the tetra-methyl acetal of malondialdehyde and phosphorus pentasulfide.52 In the presence of ammonia the reaction of cyclohexanone or cycloheptanone with carbon disulfide and sulfur gives as by-products the condensed 1,2-dithiole-3-thiones 28a and 28b, respectively.53... 

When ketones 32a react with elemental sulfur mixtures of thiophenes (33) and l,2-dithio e-3-ylidene ketones (34) are obtained.65 When R = Me (32b), the resulting product is a l,2-dithiole-3-thione. 

Beside their ability to form TTF, l,3-dithiole-2-thiones (172) have been coupled in the presence of trimethyl phosphite with ketones to afford (174) or with phenacylbromide to yield (175) and... 

Not for general application is the reaction of enamines with tetramethylthiuram disulfide/ triethylamine/hydrogen sulfide since the enamines of aliphatic aldehydes do not react at all and the ketimines of acyclic dialkylketones give only moderate yields (10-35%), whereas the enamines of cyclic or of aryl substituted ketones give the corresponding l,3-dithiole-2-thiones in fair to good yields (35-90%) <75JPR123>. 

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). 

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