Preparation of phenyl substituted propargylic alcohol dicobalt hexacarbonyls and their reactions with active methylene compounds in the presence of acid

Abstract

Eight new complexes with the formula [PhC2C(OH)R1R2]Co2(CO)4 were prepared from phenyl substituted propargylic alcohols and dicobalt octacarbonyl. The reactions of these propargylic alcohol complexes with active methylene compounds, 2,4-pentanedione or ethyl acetoacetate, in the presence of an acid, HBF4(40%) + P2O5 (in excess) or BF2·Et2O, at room temperature in dichloromethane were investigated. From the 1-alkyl substituted tertiary propargylic alcohol complexes, three new conjugated ene-yne complexes produced by intramolecular dehydration reaction were isolated in high yields (82–95%). On the other hand, four new alkylated complexes were obtained with satisfactory yields (44–66%) from the secondary propargylic alcohol complexes. The influence of other acids, phosphorus pentoxide and polyphosphoric acid, on both dehydration reaction and alkylated reaction was also studied.