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

Abstract

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.

Divergent access to fused N-heterocycle-thiazolines by solvent-dependent reaction of isoquinolinium thiolates with silylketene acetals

“…Based on these precedents and our previous studies on cycloaddition reactions of (iso)quinolinium 1,3-zwitterionic species, 10 we sought to investigate the unrevealed use of the barely explored isoquinolinium 1,4-zwitterionic thiolates in cyclization reactions 11 towards novel N , S -containing heterocycles (Scheme 1c). We envisioned that upon reacting this species with nucleophilic silyl ketene acetals, a similar mechanism involving a nucleophile addition/cyclization would be possible.…”