Heterogeneous Copper-Catalyzed Cascade Three-Component Reaction Towards Imidazo[1,2-a]pyridines: Efficient and Practical One-Pot Synthesis of Alpidem

The heterogeneous cascade three-component reaction of 2-aminopyridines, aldehydes and terminal alkynes was achieved in toluene at 120 degrees C in the presence of 3-(2-aminoethylamino)propyl-functionalized MCM-41-immobilized copper(I) complex [MCM-41-2 N-CuCl] (5 mol%) and copper(II) complex [MCM-41-2N-Cu(OTf)(2)] (5 mol%), yielding a wide variety of imidazo[1,2-a]pyridines in mostly good to excellent yields. These two heterogeneous copper catalysts can be facilely prepared via a simple procedure from readily available and inexpensive reagents, and recovered by filtration and recycled up to eight times with almost consistent activity.