Intramolecular cyclization of alkylimidazoles

Abstract

1,2-Dialkylimidazoles can be converted to nucleophilic 2-alkylidene imidazolines upon treatment with (BOC)2O under mild conditions. Incorporation of a β-keto amide carbonyl electrophile in the 2-alkylimidazole side chain results in intramolecular aldol-like cyclization to afford imidazole-functionalized γ-lactams. Positioning of a ketone electrophile in a 1-alkyl side chain results in cyclization at the 2-position to afford fused ring imidazoles through a similar reaction manifold. Efficient transfer of a BOC group from an intermediate N-acyl imidazolium species to a nucleophilic center in the cyclized product appears to be an important feature of these reactions.