Eco-friendly synthesis of indole-4-hydroxy-chromen-2-ones using green zinc oxide nanocatalyst and its assessment of anti-cancer studies against A549 cells

[Display omitted] •Green ZnO nanocatalyst was prepared using Celastruspaniulatus leaf extract as a green fuel.•ZnO characterized using PXRD, FT-IR, UV, SEM and TEM analysis.•Developed green ZnO nanocatalyst for the Synthesis of novel indole-4-hydroxy-chromen-2-ones.•Synthesized indole-4-hydroxy-chromen-2-ones derivatives characterized by Spectral Analysis.•The synthesised chrome compound 4f and 4g are active compounds against A549 cells. Zinc oxide (ZnO) nanoparticles have significant attention in the field of photocatalyst, super capacitor, battery and biomedicine due to their versatile potential and diverse applications. In the present study, ZnO was synthesized using Celastruspaniulatus leaf extract as a green fuel through combustion method. The morphological and structural studies of ZnO were characterized using XRD, FTIR, UV–Vis, SEM and TEM analysis. The PXRD pattern of ZnO as shown diffraction peaks of ZnO planes (100), (002), (102), (110), (103) and (112) are hexagonal Wurtzite ZnO structure. ZnO is formed in a discrete irregular hexagonal shape was confirmed by SEM analysis. The application of ZnO is achieved for the synthesis of (4-hydroxy3-(1H-indol-3-yl)-phenyl-methyl-chromen-2-one) and its derivatives via Knoevenagel/Michael addition reaction. All synthesized compounds showed good yield and are characterized using 1H NMR, 13C NMR and ESI-MS spectral studies. The reusability of the ZnO catalyst is tested and documented. Some of the synthesized chromenone compounds show promising anticancer activity against A549 cells with less concentration.