Single Step Upgradation of Isatin to Bioactive Fused Heterocycles via Ring Expansion Reactions

Abstract

Isatin, also known as indoline‐2,3‐dione, is a fused, N‐heterocyclic aromatic compound first isolated and purified in 1841. Since then, isatin and its derivatives emerged as a hot research topic for the scientific community. The number of research publications on isatin justifies their popularity. Researchers explored isatins and their derivatives as potential candidates in multidisciplinary research areas, including medicinal chemistry, synthetic organic chemistry, and polymer science. Synthetic chemists’ perspective of tailoring isatin and its family members led to more efficient synthesis strategies in which ring‐opening reactions of isatins were particularly significant due to the product's importance. Our investigation aims to group the different types of cascade ring expansion reactions of isatin to synthesise fused heterocyclic compounds such as derivatives of quinolines, quinazolinones, acridines, acridones, and few spiro heterocyclic compounds, all of which highlight an inevitable role in the field of medicinal chemistry.