Synthesis of ferrocenyl pyrazoles by the reaction of 3-ferrocenylpropynal with hydrazinium salts

Synthesis of ferrocenyl-substituted pyrazoles via the reaction between 3-ferrocenylpropynal and hydrazinium salts is described. Depending upon the substitution pattern of hydrazine derivative, the reaction affords 1-alkyl/aryl-5-ferrocenylpyrazoles and/or 1-alkyl/aryl-3-ferrocenylpyrazoles. Structures of 5-ferrocenyl-1-phenyl-1H-pyrazole, 1-benzyl-5-ferrocenyl-1H-pyrazole and 2-(3-ferrocenylpyrazol-1-yl)ethanol were identified by X-ray crystallography.