Eight new complexes with the formula [PhC_2C(OH)R~2R~2]Co_2(CO)_6 were prepared fromphenyl substituted propargylic alcohols and dicobalt octacarbonyl.The reactions of these propargylioalcohol complexes with active methylene compounds,2,4-pentanedione or ethyl acetoacetate,in thepresnce of an acid,HBF_4(40％)+P_2O_5(in excess)or BF_3·Et_2O,at room temperature in dichlorome-thane were investigated.From the 1-alkyl substituted tertiary propargylic alcohol complexes,threenew conjugated ene-yne complexes produced by intramolecular dehydration reaction were isolated inhigh yields(82—95％).On the other hand,four new alkylated complexes were obtained withsatisfactory yields(44—66％)from the secondary propargylic alcohol complexes.The influence ofother acids,phosphorus pentoxide and polyphosphoric acid,on both dehydration reaction andalkylated reaction was also studied. Eight new complexes with the formula [PhC_2C (OH) R ~ 2R ~ 2] Co_2 (CO) _6 were prepared from phenyl substituted propargylic alcohols and dicobalt octacarbonyl. These reactions of these propargylioalcohol complexes with active methylene compounds, 2,4-pentanedione or ethyl acetoacetate, in the plasma of an acid, HBF_4 (40%) + P_2O_5 (in excess) or BF_3 · Et_2O, at room temperature in dichlorome- thane were investigated. From the 1-alkyl substituted tertiary propargylic alcohol complexes, complexes produced by intramolecular dehydration reaction were isolated in high yields (82-95%). On the other hand, all four new alkylated complexes were obtained with satisfactory yields (44-66%) from the secondary propargylic alcohol complexes. and polyphosphoric acid, both both dehydration reaction and alkylated reaction was also studied.