ChemInform Abstract: Alkynyl Acylammoniums as Electrophilic 3C Synthons in a Formal [3 + 3] Annulation: Access to Functionalized 4H‐Pyran‐4‐ones.

Construction of Functionalized 2H-Pyran-2-ones via N-Heterocyclic Carbene-Catalyzed [3 + 3] Annulation of Alkynyl Esters with Enolizable Ketones

“…We previously reported a formal [3 + 3] annulation of alkynyl acylammoniums I generated in situ from alkynyl acids with enolizable ketones for regioselective synthesis of functionalized 4H-pyran-4-ones (Scheme 1b). 9 Recently, we found that the regioselectivity could be controlled to exclusively afford 2Hpyran-2-ones if the alkynyl esters and an NHC precursor were used as the substrates and activator, respectively (Scheme 1c). Herein, we report a new strategy for the synthesis of trisubstituted 2H-pyran-2-ones 3 via an NHC-catalyzed [3 + 3] annulation of alkynyl esters 1 with enolizable ketones 2.…”