The N-Alkylation and N-Arylation of Unsymmetrical Pyrazoles

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