Green and rapid acid-catalyzed ynamide skeletal rearrangement and stereospecific functionalization with anisole derivatives

Abstract

Environmentally friendly acid-catalyzed ynamide N–C_sp 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–C_sp 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.