Groebke-Blackburn-Bienaymé Multicomponent Reaction Catalysed by Reusable Brϕnsted-Acidic Ionic Liquids

In the present work, the use of Brϕnsted acidic ionic liquids (BAIL) as catalysts for Groebke-Blackburn-Bienaymé (GBB) multicomponent reactions was systematically investigated. A series of four 1-(butyl-4-sulfonic)-3-methylimidazolium salts bearing different anions was easily prepared and screened as acidic catalysts for this transformation. The best reaction conditions were stablished as 20 mol % of catalyst [(SO3H)4C4C1Im][OTf] in refluxing EtOH or MeOH under conventional heating and in sealed tube at 150 °C for 1–4 hours under microwave heating, affording a series of imidazo-fused heterocycles in moderate to excellent yields (42–93 %). The homogeneous BAIL catalyst could be recycled and reused in four consecutive reaction cycles, despite of a laborious recovery procedure employed. This approach represents the first example of a task-specific reusable homogeneous Brϕnsted acidic catalyst in GBB reactions and opens new opportunities for the exploration of acidic ionic liquid phases as catalysts for this fascinating multicomponent reaction