Synthesis of Heterocyclic Compounds Based on Isatins

Isatin (1H-indole-2,3-diones) and its derivatives are a unique structure of heterocyclic molecules with great synthetic versatility and enormous biological activities of interest. Isatins have been broadly used as building blocks for the formation of a wide range of N-heterocycles. These applicable compounds undergo various reactions to form new heterocyclic compounds. The focus of this review is to summarize the recent literature and key reactions published about Pfitzinger, ring-opening, and ring expansion reactions of isatin and its derivatives during the period from 2018 to 2020. We believe this gives some insight and helps to bring about new ideas for further research.