Z-bis Methylthio Ethene

Apparatus 3-1 round-bottomed, three-necked flask provided with a dropping funnel, a mechanical stirrer and a vent. 

If stirring is carried out too vigorously, part of the solution of sodium chloroacetylide may splash into the upper part of the flask or into the necks. If air and moisture enter during the removal of the stirrer, dropping funnel and vent, or in the last stage of work-up water is added, the presence of this unreacted Cl—C=C—Cl may give rise to an explosion. 

Vinyl propargyl sulfide (0.30 mol (29.4 g), see Ref. [6]) is added dropwise over 20 min to purified HMPT (Chap. 1-2, 120 ml) at 115 °C (Note 1). During this addition the solution is stirred at a moderate rate, while the temperature is kept between 115 and 120 °C by occasional cooling or heating. The rearrangement is strongly exothermic and careful control of the temperature is necessary. When the exothermic reaction has subsided after the addition, the temperature is raised to 

Cautious heating with a free flame is preferred to using an oil bath, since it allows a better control of the temperature. 

Cl2C=CHCl + NaNH2 Me2NH Cl—C=C—Cl + NaCl j + NH31 

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The lithio derivatives of 1,4-dithiin [88] and Z-bis(methylthio)ethene [89] are stable only at very low temperatures fragmentation and elimination of thiol occur if the temperature of the solutions is allowed to rise above — 90 °C. The electron-withdrawing action of chlorine in 5-chloro-2,3-dihydropyran permits a fast and quantitative lithiation with BuLi [89,90] ... 

Treatment of Z-bis-thioethers RS—CH=CH—SR with alkali amides or organo-lithium result s in a smooth elimination of thiol with formation of metallated ethynyl sulfides M—C=C—SR [203]. If Z-bis(methylthio)ethene and the reactive basic system BuLi TMEDA in THF are allowed to interact at very low temperatures, no elimination occurs, but a precipitate of the lithio derivative is formed. It has a reasonable stability below — 100°C, thus permitting functionalizations... 

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