Hierarchically Porous Sphere-Like Copper Oxide (HS-CuO) Nanocatalyzed Synthesis of Benzofuran Isomers with Anomalous Selectivity and Their Ideal Green Chemistry Metrics

Abstract

Development of nanocatalysts for a chemical reaction with ideal values in green chemistry metrics is considered to be a challenging task to achieve sustainable chemistry. With this aim, we herein report a hierarchically porous sphere-like copper oxide (HS-CuO) nanocatalyst to afford benzofuranamine and dihydro-benzofuranamine isomers with anomalous selectivity via O-annulated A3 coupling among salicylaldehydes, secondary amines, and alkynes followed by cycloisomerization in the absence of base and solvent. The anomalous selectivity of benzofuran isomers was dependent on the electronic factors of substituents on salicylaldehyde and the type of secondary amines used in the coupling reaction. The HS-CuO nanocatalyst was recycled five times without significant loss in its catalytic activity. The present method offers several advantages over the reported methods such as wide substrate scope with anomalous selectivity in the products, high yields in short reaction time, avoided the usage of extra reagents such as additives/bases, and showed ideal values of green chemistry metrics such as low E-factor and process mass intensity (PMI), high atom economy (AE), reaction mass efficiency (RME), and carbon efficiency (CE).