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Indole, a ubiquitous and structurally versatile aromatic compound, has emerged as a key player in the synthesis of diverse heterocyclic frameworks via cycloaddition reactions. These reactions are completely atom-economical and, hence, are considered as green reactions. This review article provides a comprehensive overview of the pivotal role played by indole in the construction of complex and biologically relevant heterocyclic compounds. Here we explore the chemistry of indole-based cycloadditions, highlighting their synthetic utility in accessing a wide array of heterocyclic architectures, including cyclohepta[b]indoles, tetrahydrocarbazoles, tetrahydroindolo[3,2-c]quinoline, and indolines, among others. Additionally, we discuss the mechanistic insights that underpin these transformations, emphasizing the strategic importance of indole as a building block. The content of this article will certainly encourage the readers to explore more work in this area. [ABSTRACT FROM AUTHOR]

Reaction of barbituric acids with aldehydes and dihydropyridines in one pot under microwave (MW) irradiation in the absence of solvent, affords 55-82% of the 5-benzylated barbituric acids. Use of alkyl nitriles or barbituric acids with indole-3-aldehyde and dihydropyridine (DHP) afforded 3-alkylated indoles in 57-76 % yield. In each case DHPs are converted to pyridines. [ABSTRACT FROM AUTHOR]