Ynamides as Linear Building Blocks for Aromatic N-Heterocycles in Metal-Catalyzed Transformations

Abstract Alkyne is one of the most exploited synthetic equivalent in organic synthesis due to easy accessibility and electron-rich nature. Subsequently, their excellent coordinating ability with metals make them an indispensable synthon in organic reactions. Notably, alkynes directly attached to a heteroatom (N, O, S) at C–C triple bond end have emerged as an alternative class of reactant that are able to generate structural diversity. In this context, ynamides where one end of C–C triple bond is attached with an amide unit have emerged as a versatile building blocks in chemical transformations over the past 20 years. The natural polarization of C–C triple bond in ynamides mobilizes a broad spectrum of chemical transformations under both metal-catalyzed and metal-free conditions. Few interesting review articles on ynamide chemistry have been appeared recently that cover synthetic potential and mechanistic insights. However, this review highlights the application potential of ynamides and bisynamides chemistry for the synthesis of aromatic N-heterocycles such as isoquinolines, quinolines, pyrroles, pyrrolo[2,3-b]quinolines, and diaryl[c,h][1,6]naphthyridines through metal-catalyzed cycloisomerization, annulation, and skeletal editing strategies, respectively. We have further shown that how ortho substitution in anilines yields different N-heterocycles upon varying reaction conditions. Notably, we have mostly used inexpensive and earth abundant metal salts for transformations.