A Comparative Study on the Groebke-Blackburn-Bienaymé Three-Component Reaction Catalyzed by Rare Earth Triflates under Microwave Heating

Over the last twenty years, the Groebke-Blackburn-Bienaymé (GBB) reaction has been emerged as a powerful tool to access different nitrogen-based heterocycles as privileged scaffolds in medicinal chemistry. This multicomponent reaction is usually catalyzed by ordinary Brønsted or Lewis acid catalysts. Herein, we present a comparative study on the catalytic efficiencies of different rare earth triflates in GBB reactions under microwave heating, involving 2-aminopyridine or 2-aminothiazole, as aminoazole component, and different aldehydes and aliphatic isocyanides. The use of gadolinium(III) triflate as cheaper alternative catalyst for the most commonly used scandium(III) triflate was acknowledged for the first time, and a library of twenty three imidazo[1,2-a]pyridines and imidazo[2,1-b]thiazoles could be obtained in good to excellent yields.