Metal- and Solvent-Free, One-Pot Synthesis of 3-Unsubstituted Benzoindolizines

A simple one-pot, solvent-free method for the synthesis of 3-unsubstituted indolizines is presented. Conversely to the output from standard classical cycloaddition approaches, an unconventional connectivity is achieved with excellent chemoselectivity under neat conditions without requiring any metal catalyst or additional additive. Hence, various abundant (iso)quinolines and propiolic esters were transformed into the corresponding benzoindolizines in synthetically useful yields. This straightforward and simplistic transformation expands the synthetic tool kit for the preparation of valuable 3-unsubstituted indolizines, which have been shown to be highly versatile synthetic intermediates with a broad bioactivity spectrum.