Ultrasonication‐Assisted Synthesis of 3‐Substituted Indoles in Water Using Polymer Grafted ZnO Nanoparticles as Eco‐Friendly Catalyst

Abstract Indole based heterocyclic molecules are important and valuable structural unit that are present in various biologically active natural products, pharmaceuticals and agrochemicals. In this paper, zinc oxide nanoparticles were explored as catalyst for the synthesis of 3‐substituted indoles in water via ultra‐sonication. The stability of ZnO nanoparticles and their dispersion in water was enhanced by grafting it with a biodegradable polymer (poly lactic acid). The proposed methodology is capable of providing desired products in good yield (83‐97%) and 25 derivatives of indoles were synthesized. The green reaction metrics such as E‐factor (0.16) and atom economy (97%) show that the present protocol is sustainable and economical. Also, the reactions were carried out in water under environmentally benign conditions that avoids use of any additives or hazardous solvents.