In situ generation and protonation of the isocyanide/acetylene adduct: a powerful catalyst-free strategy for multicomponent synthesis of ketenimines, aza-dienes, and heterocycles

In addition to isocyanide-based Ugi, Passerini, van Leusen, and Orru multicomponent reactions (IMCRs), a new class of isocyanide/acetylene-based multicomponent reactions (IAMCRs), through a zwitterionic adduct, have emerged as powerful and elegant methods for the synthesis of biologically interesting molecules. Coupling reaction between in situ generated Huisgen-type zwitterions of the isocyanide/acetylene adduct and CH-, OH- and NH-acids provide a powerful synthetic pathway to obtain ketenimines, aza-dienes, and heterocycles. This review focuses on the chemistry and applications of the isocyanide/acetylene adduct in multicomponent reaction conditions.