Unexpected reactivity of pyridinium salts toward alkynyl Fischer complexes to produce oxo-heterocycles

The unprecedented reaction of ketone-containing aromatic pyridinium salts 3a-e and alkynyl Fischer complexes 1a-f proceeds via a mild domino process to provide 4,6-disubstituted pyran-2-ones 5a-k and 2,3,5-trisubstituted furans 6a-h (45-97%). According of the results of isotopic labeling experiments, a mechanism involving an initial Michael addition appears to be the key step, obtaining a mesomeric structure responsible for the formation of both products.