The N-Alkylation and N-Arylation of Unsymmetrical Pyrazoles

Abstract

Unsymmetrical pyrazoles with alkyl, aryl, nitro and carboxyl substituents at C3 or C5 have been methylated with dimethyl sulfate in methanol, dimethyl sulfate in basic medium, and with diazomethane. The ratios of the isomeric N-methylpyrazoles have been determined by N.M.R. and g.l.c. analysis. The modified Ullmann phenylation has also been applied to these pyrazoles. Explanations for the observed product orientations involve considerations of electronic and steric effects, the possible intermediacy of quaternary salts, and, in some instances, the likelihood that the dominant tautomer is reacting.