Dual-action catalyst: A Brønsted acid catalyzed regioselective cycloisomerization was found to be highly effective for the preparation of structurally diverse 2,3-dihydro-4H-pyran-4-ones in a 6-exo-trig manner from the corresponding 5,2-enyne-1-ones. In this reaction, the Brønsted acid acts as a dual catalyst activating both the carbonyl and alkene moieties in a cascade manner (see scheme).
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