Azoles. Part II. Synthesis of imidazole-2(and -5)-carbaldehydes and derivatives of imidazo[1,2-b]isoquinoline; transmetallation of imidazol-5-yllithium compounds

Abstract

The transmetallations of 1-protected 4-bromoimidazol-5-yllithium derivatives have been studied using DMF as the quenching reagent. 4-Bromoimidazole-2-carbaldehydes are usually the major products and not the -5-carbaldehydes as reported previously. Various attempts to prevent or inhibit these transmetallations are described. Cyclisation of 4-bromo(and 4,5-dibromo)-1-(3,4-dimethoxybenzyl)imidazole-2-carbaldehyde and 1-(3,4-dimethoxybenzyl)benzimidazole-2-carbaldehyde in TFA gave the corresponding imidazo- or benzimidazo-[1,2-b]isoquinoline.