A NEW APPROACH TO THE SYNTHESIS OF SYMMETRICAL BIS(ORGANYLCHALCOGENO)ACETYLENES - SCOPE AND LIMITATIONS

A new general method to prepare bis(organylchalcogeno)acetylenes R-Y-C =C-Y-R (Y = S, Se, Te) by dehydrochlorination of the corresponding 1,2 -bis(organylchalcogeno) chloroethylenes R-Y-CH=CCl-Y-R with tert-BuOK/ tert-BuOH and/or KOH/DMSO is developed. Dechlorination of 1,2-bis(orga nylchalcogeno)-1,2-dichloroethylenes R-Y-CCl=CCl-Y-R (Y = S: Se, Te) w ith BuLi in ether or THF is effective only for sulfur derivatives. Wit h Y = Se and alkyl substituents, substitution of the chlorine atom by a butyl group takes place giving rise to 5,6-bis(alkylseleno)dec-5-ene [Bu-C(SeR)=C(SeR)-Bu]. With aryl substituents, an attack of the ArSe- group by the Bu-radical is observed leading to an aryl butyl selenide. In the case of the tellurium compound Ph-Te-CCl=CCl-Te-Ph, there is a competition between dechlorination to give Ph-Te-C=C-Te-Ph, and subst itution to produce the phenyl butyl telluride.