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Environmentally friendly acid-catalyzed ynamide N–Csp bond cleavage, skeletal rearrangement and chemo-, regio- and stereospecific functionalization with nucleophiles are of great interest in synthetic chemistry. However, such transformations present remarkable regio- and stereospecific challenges due to the biased carbon–carbon (α and β) triple bonds in ynamides. Herein, we developed a greener and faster acid-catalyzed ynamide N–Csp bond fission, skeletal rearrangement and stereospecific functionalization with nucleophilic anisole derivatives to produce thermodynamically unstable challenging cis-alkene tethered indole scaffolds in a very short reaction time (5–10 min). The key features of this transformation are its transition-metal-free nature, broad scope, ease of handling, simple setup, mild reaction conditions, atom/step/time economy, and the gram-scale experiment. Most importantly, 13C-isotope labeling experiments in mechanistic studies confirmed the alkyne-carbon position in the rearrangement process. The green chemistry metrics evaluation and EcoScale score (75 on a scale of 0–100) indicate that our transformation is safer, environmentally friendly, and economically feasible. [ABSTRACT FROM AUTHOR]

The radical chemistry of ynamides has recently drawn the attention of synthetic organic chemists to the construction of various N-heterocyclic compounds. Nevertheless, the ynamide-radical chemistry remains a long-standing challenge for chemists due to its high reactivity, undesirable byproducts, severe inherent regio- and chemoselective problems. Importantly, the ynamide C(sp)-N bond fission remains an unsolved challenge. In this paper, we observe Photoinduced radical trigger regio- and chemoselective ynamide bond fission, structural reshuffling and functionalization of 2-alkynyl-ynamides to prepare synthetically inaccessible/challenging chalcogen-substituted indole derivatives with excellent step/atom economy. The key breakthroughs of this work includes, ynamide bond cleavage, divergent radical precursors, broad scope, easy to handle, larger-scale reactions, generation of multiple bonds (N-C(sp2), C(sp2)-C(sp2), C(sp2)-SO2R/C-SR, and C-I/C-Se/C-H) in a few minutes without photocatalysts, metals, oxidants, additives. Control experiments and 13C-labeling experiments supporting the conclusion that sulfone radicals contribute to ynamide structural reshuffling processes via a radical pathway. Although ynamides have emerged as a versatile class of compounds for organic synthesis, the radical chemistry of ynamides usually proceeds with the expected connectivity largely intact. Here the authors show a methodology by which the C(sp)–N bond undergoes scission, alkyne migration and functionalization under blue LED light in the absence of metals or additives. [ABSTRACT FROM AUTHOR]