Reactivity of indazoles and benzotriazole towards N-methylation and analysis of the 1H nuclear magnetic resonance spectra of indazoles and benzotriazoles

Abstract

Methylation of some simple 3-, 7-, and 3,7-substituted indazoles in alkaline solution leads to mixtures of both 1- and 2-methyl compounds, in which the 1-methyl isomer predominated in all except the 7-monosubstituted cases. Steric effects are less marked in this series than in cinnolines. INDO Calculations of the electron density at the nitrogen were performed in an attempt to account for the relative reactivities. The ¹H n.m.r. spectra of the 1- and 2-methylindazoles are sufficiently different for this to be used as a diagnostic tool for the positions of methylation. A detailed ABCD analysis of various indazole and benzotriazole spectra has been carried out and the results assessed in terms of degree of aromatic character.