Dithiole-2-thiones and Selenium-containing Analogues

The reaction of dithiocarbamates and diselenocarbamates with a-halogenated carbonyl compounds has proved to be a useful first step in the synthesis of l,3-dithiole-2-thiones and their analogues. Thus 2-dimethylamino-l,3-dithiolium salts (38) and diselenolium salts (39) are readily obtainable by this route, and these salts are converted into thiones (40 X = Y = S or Se, Z = S) or selones (40 X = Y = S or Se, Z = Se) with hydrogen sulphide or hydrogen selenide. The dihydroxybenzo-l,3-dithiole-2-thione (41) has been prepared from p-benzoquinone and dithiocarbamic acids.  

The Mayer-Gebhardt procedure (involving sodium acetylide, sulphur, and carbon disulphide) has been extended to the synthesis of l,3-diselenole-2-selone 

Acetylenic starting materials have also been used in the preparation of a series of amidine derivatives of l,3-dithiole-2-thione and some related compounds, and in the synthesis of l,3-dithiole-4-carboxylic acids.  

The reaction of ethylene trithiocarbonate with dimethyl acetylenedicarboxylate has been modified so as to provide useful syntheses of the l-selena-3-thiole-2-selone (40 R = C02Me, X = S, Y = Z = Se), the l,3-diselole-2-selone (40 R = COaMe, X = Y = Z = Se), and other analogues.  

Chemical reduction of carbon disulphide, and electrochemical reduction of carbon diselenide lead to dianions (40 R = S, X = Y = Z = S) or (40 R = Se, X = Y = Z = Se), which on methylation yield the corresponding bis(methylthio)- or bis(methylseleno)-compounds. 

---