Efficient and “Green” Synthetic Route to Imidazo[1,2-<i>a</i>]pyridine by Cu(II)–Ascorbate-Catalyzed A³-Coupling in Aqueous Micellar Media

Abstract

An efficient and environmentally sustainable method for the synthesis of imidazo[1,2-<i>a</i>]pyridine derivatives by domino A³-coupling reaction catalyzed by Cu(II)-ascorbate was developed in aqueous micellar media in the presence of sodium dodecyl sulfate (SDS). The catalyst, a dynamic combination of Cu(II)/Cu(I), was generated in situ in the reaction mixture by mixing CuSO₄ with sodium ascorbate and aided a facile 5-<i>exo</i>-dig cycloisomerization of alkynes with the condensation products of 2-aminopyridines and aldehydes to afford a variety of imidazo[1,2-<i>a</i>]pyridines in good overall yields. A simple experimental setup, water as the "green" medium, and inexpensive catalyst and auxiliary are some of the merits of this protocol.