1.3- Benzodithiole-2-thiones

Benzopentathiepin (3, R1 =R2 = H) is produced in 54% yield from 1,2,3-benzothiadiazole and sulfur402 and in 97% yield from 1,3-benzodithiole-2-thione and sulfur in liquid ammonia in the presence of 1,3-dinitrobcnzcnc.403 These methods have also been used for the preparation of various substituted benzopentathiepins 3. 

Figure 8.9 Reaction of an isothiocyanate with 1,2-benzenedithiol which gives rise to a cyclocondensation product (1,3-benzodithiole-2-thione) and an amine (R-NH2).

Method BAOi A titanium autoclave of 50-mL capacity was charged with a l,3-benzodithiole-2-thione (0.5 mmol), sulfur (as S8) (0.128 g, 0.5 mmol) and NH3 (1) (30 mL). The autoclave was closed and the mixture was stirred at 20 C for 30 min. The resulting solution was added dropwise through a needle bulb to benzene (80 mL) containing 1,3-dinitrobenzene (0.084 g, 0.5 mmol) and the mixture was stirred at 20 C until all the NH3 had evaporated (ca. 2h). The resulting solution was evaporated and the residue was chromatographed (silica gel, CC]4/hexane) to give the yellow crystalline product. 

Unexpectedly, upon reacting commercially available ethylene trithiocarbonate 111 with benzyne, the salt 103a was obtained as the major product along with a small amount of l,3-benzodithiole-2-thione 109a, as shown in Equation (31) <1996CC205> and <1996BCJ2349>. 

Reaction of benzodithiol-3-thione (220) with anthranilamide gave a complex mixture of products from which benzisothiazolo[2,3-u]quinazolin-5 one (221) was isolated (75JHC1077). 

These structures may be named as follows 7, l-(l,2-benzodithiol-3-ylidene)propane-2-thione and 8, 6-(5-methyl-l,2-dithiol-3-ylidene)-2,4 -cy clohexadiene-1 -thione. 

Carbon oxysulfide and sodium hydride react with 4,5,6,7-tetra-hydro-l,2-benzodithiole-3-thione in dimethyl sulfoxide (DMSO), giving a dianion (28) which, by action of methyl iodide, gives a dithiolic thio ester (29). On standing, 28 partly isomerizes to 30, which, by methylation gives the dithiolone 31.23... 

Another semidegradative synthesis is the reaction of 3-methylthio-1,2-benzodithiolium sulfate with malonic acid. It does not give, as initially thought,65 a 3-[(l,2-benzodithiol-3-ylidene) methyl]-l,2-benzodithiolium ion, but in fact a 2-(l,2-benzodithiol-3-ylidene)-2JT benzo[6]thiophene-3-thione (45).40... 

A further example of the same type of rearrangement is afforded by the l 2-benzisothiazoline-3-thiones. If the benzisothiazolium salt (40) is treated with thioacetic acid, the product is the 3-arylimino-3/f-1,2-benzodithiole (41), provided R is an aryl group when R is alkyl, the product is the benzisothiazoline-3-thione (42).32 Structures of types 41 and 42 are, however, in equilibrium with each other at 150°, presumably via a dipolar intermediate [Eq. (3)].32 A diradical... 

With the exception of the compounds mentioned in Section II, C, 3, all l,2-benzisothiazoline-3-thiones (46) have been prepared by the reaction between a benzodithiole-3-thione ( trithione ) (45) and a... 

The l,3-benzodithiole-2-thione derivative (290) is obtained by refluxing an aqueous solution of 1,2-benzenedithiol (289) and carbon disulfide in the presence of sodium hydroxide (72S29). 

An approach to nitro-substituted l,3-benzodithiole-2-thiones (325) is based on the reaction of l-chloro-2,6-dinitrobenzenes (323) with sodium f-butyl trithiocarbonate which yields dinitrophenyl f-butyl trithiocarbonates (324). The latter cyclize on heating in acetic acid with formation of nitro-l,3-benzodithiole-2-thiones (325) (80JOC4041). 

The reaction of benzyne with l,3-benzodithiole-2-thione 188 in 1,2-dichloroethane gave the bicyclic sulfonium chloride 190 by trapping of the intermediate 189 (Scheme 21) <1996CC205>. 

Although this reaction gives good results with aryl-1,2-dithiole-3-thiones, it does not work well with aromatic fused rings such as l,2-benzodithiole-3-thione. Some examples of this reaction are given in the preparations of the... 

Benzyne (generated from 7 or from 9) also reacted with l,3-dithiolan-2-thione (163) to give l,3-benzodithiole-2-thione (164) (9-13%).92 Evidence for... 

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