Benzodithioles

The 2-substituted 1,3-benzodithioles 57 are readily lithiated and react as acyl anions with various electrophiles, including alkyl halides, aldehydes, ketones. 

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. 

This reaction is essentially thermoneutral. Although we lack enthalpy of formation data for the corresponding 1,3-benzodithiole, the weakness of 1,3 sulfur-sulfur interactions as manifest by the near equality [52] of the enthalpies of formation of 1,3- and 1,4-dithiane (unlike 1,3- and 1,4-dioxane) suggests no special interaction in this nonaromatic heterocycle. Said differently, the thermoneutrality of the above reaction, as opposed to profound exothermicity (21 kJ mol ) for indane (six n electrons) and the endothermicity (29 kJ mol1) for benzimidazolinone (ten n electrons), suggests phenylene trithiocarbonate (ten n electrons) has an intermediate degree of aromaticity. For the latter two species, analysis of the related reactions ... 

The CD induced in 2-(2,4,6-cycloheptatrien-l-ylidine)-4-cyclopentene-l,3-dione upon its inclusion in 6-cyclodextrin was used to obtain full assignment of the observed absorption bands [49]. It was concluded that the low energy band system was composed of three electronic transitions, two of which were polarized perpendicular, and one parallel, with respect to the long molecular axis of the solute. The higher energy band system was found to also consist of three allowed electronic transitions, but two of these were polarized parallel, and one perpendicular, to the long axis of the solute molecule. These deductions were supported by a series of CNDO/S-CI calculations performed on the system. A similar approach was taken to assign the polarizations of the various transitions associated with 2-thioxo-l,3-benzodithiole and 2-selenoxo-1,3-benzodithiole [50]. 

Grignard reagents rapidly add to 1,3-benzodithiolylium perchlorate in dry ether to produce 2-substituted 1,3-benzodithioles which can be hydrolyzed in high yields to aldehydes <76JCS(P1)1886>. 

Activated methylene compounds may react with one or two molecules of 1,3-dithiolylium salts to produce (60) or (61), respectively. For example, malononitrile and 1,3-benzodithiol-ylium ion (54) yields a product of type (61), whereas methyl acetate forms the one-to-one product (60) <80AHC(27)151>. 

A preparation of 2,2-disubstituted 1,3-benzodithiole derivatives (278) involves the reaction of benzene-1,2-dithiols (273) with alkynic ketones in the presence of piperidine or potassium carbonate (80S115,81KGS329). 

The reactions of 1,3-dithioles with strong bases have been reported for 1,3-benzodithioles (78TL2345) and 2-(0,0-dimethylphosphonyl) or 2-tributylphosphonium substituted 1,3-... 

DMTrT = 5 -O-di-p-methoxy tritylthymidine mTHPT = 5 -0-(4-methoxytetrahydropyran-4-yl)thymidine BDTT = 5 -0- 1,3-benzodithiol-2-yl)thy midine MMTrT = 5 -0-mono-p-methoxytritylthy midine THPT = 5 -tetrahydropyranylthy midine TBDT = 3 -0-(l,3-benzodithiol-2-yl)thy midine... 

Benzodithioles 285 (R1 = H) and 7,8-dimethyl-l,5-dihydro-2,4-benzodithiepins286 (R = H) have been used as precursors of formyl and acyl anion derivatives. The lithiation of compounds 285 takes place at —30 °C with n-BuLi and these anions are stable for long periods of time at this temperature454. They react with alkyl iodides, carbonyl compounds and epoxides, the addition to cyclohex-2-enone taking place at the carbonyl group. The deprotection has also been carried out with mercury(II) oxide and BF3 OEt2-... 

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