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 7-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 (II)-I-1 and C-13 NMR).