The heterocyclization of unsaturated nitriles and ethyne catalyzed by cyclopentadienyl - ١،٥ - cis, cis-cyclooctadiene-cobalt (I) and promoted by light has been studied in toluene as solvent. Acrylonitrile and substituted acrylonitriles gave satisfying results interesting for the preparation of ٢-vinylpyridines. No reaction was observed using fumaronitrile, maleonitrile and allycyanides. (E)/(Z)-ratio of reactants and products seems not to be influenced within the reaction.