Reinvestigation of the supposed enediol diacetate derived from dihydroquercetin 5,7,3′,4′-tetramethyl ether: Novel ring-fission of dihydroquercetin 5,7,3′,4′-tetramethyl ether to α,2′-diacetoxy-3,4,4′,6′-tetramethoxychalcone.