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

Alkynyl acylammoniums generated in situ from alkynyl acids are first used as electrophilic 3C synthons in a formal [3 + 3] annulation with 1,3-dicarbonyl compounds for regioselective synthesis of functionalized 4H-pyran-4-ones via a 4-(dimethylamino)pyridine/Lewis acid dual-activation strategy. This protocol paves the way for further investigation of alkynyl acylammoniums as 3C synthons for construction of diverse heterocyclic skeletons.