Domino Approach for the Synthesis of Pyridinium Salts and 1,2,3,8a‑Tetrahydroimidazo[1,2‑a]pyridines from 2‑Imidazolines and Propiolic Acid Esters

• Published in: Journal of organic chemistry 2023-08, Vol.88 (16), p.11603-11617
• Main Authors: Golantsov, Nikita E., Golubenkova, Alexandra S., Festa, Alexey A., Novikov, Anton P., Varlamov, Alexey V., Voskressensky, Leonid G.
• Format: Article
• Language: English
• ISSN: 0022-3263; 1520-6904
• DOI: 10.1021/acs.joc.3c00916

Adducts of 1-alkyl-2-imidazolines and two molecules of alkyl propiolate, possessing an N-propargyl-β-enaminoester fragment, easily undergo a domino reaction to form pyridinium salts with β-(alkylammonio)­ethyl group at the nitrogen atom in the presence of 2 equiv of a protic acid. Treatment of the above reaction mixture with a base gives 1,2,3,8a-tetrahydroimidazo­[1,2-a]­pyridines. Reaction of the latter compounds with acid chlorides affords pyridinium salts with β-(alkylamido)­ethyl moiety at the nitrogen atom.