Heteroannulation of 4-oxo-4H-1-benzopyrans (chromones) via the conjugate addition of haloalkanols in the presence of base

Chromones (4-oxo-4H-1-benzopyrans) bearing electron-withdrawing substituents at C-3 react with 2-haloethanols and potassium carbonate in acetone to produce tetrahydrofuro[2,3-b][1]benzopyran-4-ones, the heteroannulation proceeding via the conjugate addition of the haloethanol to the chromone, followed by intramolecular alkylation. Under the conditions of the reaction, the products derived from chromone-3-carbaldehydes undergo in situ...