Functionalized Imidazo[4,5-b]pyridinium Salts: Synthesis and Use as M/NHC Precursors

A simple method was developed for the preparation of 7-hydroxyimidazo[4,5-b]pyridinium salts via the two-step reaction of readily available 4-amino-1,3-diarylimidazolium salts with 1,3-biselectrophiles in the presence of BF3·Et2O. The reactivity of the prepared bicyclic compounds was studied through alkylation with various reagents, leading to the synthesis of both O- and N-alkylated derivatives. The applicability of these bicyclic salts as N-heterocyclic carbene (NHC) precursors was demonstrated by their selective C2–H metallation, which afforded the corresponding Pd and Au complexes.