Condensation of o-phenylenediamine with phenylpropiolic acid

Attempted condensation of o-phenylenediamine with phenylpropiolic acid with a view to preparing 2-beta-phenylacetylenylbenzimidazole under a variety o f conditions such as in refluxing methanol, in hot PPA, in refluxing benzen e with Dean-stark removal of water etc., leads to the recovery of starting materials. However, condensation of o-phenylenediamine dihydrochloride and dihydrobromides with phenylpropiolic acid in refluxing ethylene glycol yiel d the respective 2-haloarylvinylblenzimidazoles: The latter are dehydrohalo genated under basic conditions to obtain the desired 2-beta-phenylacetyleny lbenzimidazole. The mechanism of formation of 2-haloarylvinylbenzimidazoles has been discussed.