Ring opening and ring closure reactions of chromone-3-carboxylic acid: unexpected routes to synthesize functionalized benzoxocinones and heteroannulated pyranochromenes

Unexpected routes to synthesize functionalized benzoxocinones and heteroannulated pyranochromenes were achieved via transformations of the γ -pyrone ring in chromone-3-carboxylic acid throughout its reactions with some acyclic and cyclic carbon nucleophiles. A key part of the reaction mechanisms is discussed. Structures of the new synthesized products were established on the basis of elemental analysis and spectral data (IR, MS, and 1H and 13C NMR).