Synthesis of zwitterionic 4-hydroxycoumarin derivatives through a unique reaction of 4-hydroxycoumarins with p- benzoquinone and pyridine.

[reaction: see text] A unique reaction of 4-hydroxycoumarins with p-benzoquinone and pyridine was found, and through the reaction, six zwitterionic 4-hydroxycoumarin derivatives were synthesized. The structures of these compounds were determined by IR, MS(ESI), 1H NMR, 13C NMR, and single-crystal X-ray diffraction studies.