Extending the Carbon Skeleton of Biomass‐Derived Furaldehydes via Benzoin Condensation and Synthesizing Novel 2,4,5‐trisubstituted Imidazoles Thereof

This study reports the synthesis of furoins from biorenewable 5‐substituted‐2‐furaldehydes, using tertiary amines as homogeneous bases and thiamine hydrochloride (vitamin B1)‐derived N ‐heterocyclic carbene as the innocuous catalyst. The effect of various bases on the efficiency (kinetics, selectivity) of the benzoin condensation reaction was explored under conventional heating and microwave irradiation (MWI). The benzoin condensation reaction of 5‐substituted‐2‐furaldehydes under MWI afforded significantly better isolated yields of the furoin products compared to the conventional heating method. The relative amounts of furoin and furil products were controlled using suitable reaction conditions. Moreover, the renewable furoin (and furil) derivatives were transformed into novel 2,4,5‐trisubstituted imidazoles, following a multicomponent reaction using gluconic acid aqueous solution as an effective and innocuous biogenic acid catalyst. Under the optimized conditions, all the imidazole derivatives were obtained in good to excellent isolated yields.