Reactions of 1,2-dimethylimidazole, particularly its metallation

Abstract

A re-examination of the metallation of 1,2-dimethylimidazole has shown that, after quenching of reaction mixtures with suitable reagents, single products may arise from substitution either in the 2-methyl group or in the 5-position or mixtures of both products may arise, depending on the metallating reagent, solvent, and reaction conditions. 1,2-Dimethylimidazol-5-yl-lithium was prepared by reaction of 1,2-dimethyl-5-trimethylstannylimidazole (13) with n-butyl-lithium in tetrahydrofuran at –100 °C. The corresponding 5-trimethylsilyl compound (12) was metallated by n-butyl-lithium exclusively in the 2-methyl group. 1,2-Dimethylimidazol-5-yl-lithium was shown to undergo transmetallation reactions at temperatures higher than –100 °C. An improved procedure is given for the synthesis of 1,2-dimethylimidazole-5-carbaldehyde via hydroxymethylation of 1,2-dimethylimidazole and oxidation of the 5-hydroxymethyl group with nitric acid.