REGIOSELECTIVE SYNTHESIS OF 1-METHYL-3-HYDROXY-5-PERFLUOROALKYLPYRAZOLES BY THE ADDITION OF METHYLHYDRAZINE TO PERFLUOROALKYLACETYLENIC ESTERS

A regioselective route to 1-methyl-3-hydroxy-5-perfluoroalkyl(1H,3H)pyrazoles has been developed. Treatment of perfluoroalkylacetylenic esters with methylhydrazine in methanol-water at 0° or in methylene chloride at low temperature leads to 1-methyl-3-hydroxy-5-perfluoroalkyl(1H,3H)pyrazoles in a regioselective manner. Structural assignments of the regioisomers are based on 13C nmr chemical shifts, long range carbon-fluorine and carbon-proton coupling. The effect of the acetylene structure on the regioselectivity of the reaction is discussed. © 1990.