Indoles are extremely important and versatile building blocks in the field of chemistry. This review highlights the advance made in the three-component reactions of indoles between 2011-2021. The reaction types are classified into three categories based on the trigger mechanisms.Reactions with alkenes, alkynes, aldehydes, imines, ketones, S, Se, etc are discussed. In order to highlight the mechanisms involved, this review has provided specific analysis inside a gray box in each scheme. We hope these studies will promote future research in the indole area.

This review discussed the synthetic applications of propiolic acids in the preparation of diverse N-heterocycles. 3~9-membered rings like azirines, β-lactams, oxazolidin-2-ones, 2-oxindoles, indoles, isoindolin-1-ones, imidazo[1,2-a]pyridines, triazoles, 2-pyridones, 2-quinolones, 1,4-benzothiazines, thiazinones, spiroindolines et al could be constructed via radical addition, four-component Ugi reactions, 1,3-dipolar cycloadditions, or Diels-Alder reaction mechanism. We hope this review will promote future research in this area. • Introduction