CuONPs exhibiting excellent catalytic activity are developed following a green and sustainable approach, transforming agrowaste material into wealth. The reusable nanostructure effectively catalyzed the CN bond-forming reactions, facilitating the aza-Michael addition and the synthesis of quinoxaline derivatives offering excellent yields, wide substrate scope, and hassle-free route.

A simple, green, and cost-effective method is reported for the synthesis of copper oxide nanoparticles (CuONPs) using waste cotton shell (WCS) ash extract, which serves as a natural base (pH 12), replacing conventional inorganic bases. The green-synthesized CuONPs exhibit excellent catalytic activity in heterogenous catalysis facilitating CN bond formation, a key strategy for accessing various bioactive nitrogen heterocycles. TEM analysis reveals spherical morphology of the CuO nanostructure with an average particle size of 15.5 nm. The catalyst efficiently promotes the synthesis of quinoxaline derivatives via cyclization of terminal alkynes and o-phenylenediamine, offering broad substrate scope (17 quinoxaline derivatives), good yields, and recyclability. This methodology is also applicable to aliphatic terminal alkynes. Additionally, CuONPs also catalyzed the aza-Michael addition reactions of amines with α,β-unsaturated compounds at room temperature, affording excellent yields. The protocol tolerates a wide range of amines, including acyclic, cyclic (up to seven-membered rings), primary, secondary, and heterocyclic amines. Synthesis of 14 aza-Michael addition products is reported. Furthermore, the CuO nanostructures exhibit high stability and reusability for up to five cycles with minimal loss of activity.