Zinc Aluminate (ZnAl2O4) Supported and Catalyzed Highly Effective Sonogashira Cross-Coupling and Cyclization Reaction Under Microwave Irradiation Used in One-Pot Tandem Synthesis of Furo[3,2-H]Quinolines

Abstract

The Sonogashira reaction (SR) which forms a C–C bond by cross-coupling a vinyl/aryl halide with a terminal alkyne, uses a palladium species as a catalyst, with a copper species as co-catalysts and a phosphine/amine as ligand/base in its actual form. This efficient reaction is beneficial in synthesizing heterocycles, nanomaterials, medicines and other complex molecules with biological functions. However, in this study, we were able to successfully execute the SR under microwave irradiation, using zinc aluminate (ZnAl2O4) as the catalyst, without using palladium, phosphines/amine as a ligand/base. This method, therefore, particularly useful for adhering to green chemistry principles and achieving atom-friendly reaction. In order to do this, we adopted a straightforward and concise method involving the development of a convergent protocol for sequential coupling and cyclization from Acetylenic 8-quinolinols generated in situ by the microwave-assistance SR to synthesize furo[3,2-h]quinolines, using ZnAl2O4 as a catalyst.