Flavan derivatives. XV. Reinvestigation of the supposed enediol diacetate derived from dihydroquercetin 5,7,3',4'-tetramethyl ether: Novel ringfission of dihydroquercetin 5,7,3',4'-tetramethyl ether to α,2'-diacetoxy-3,4,4',6'-tetramethoxychalcone

Abstract

Boiling acetic anhydride and sodium acetate is shown to convert (±)- dihydro-quercetin tetramethyl ether into (α,2?-diacetoxy-3,4,4?,6?- tetramethoxychalcone, the first chalcone derivative to be isolated from base-catalysed ring fission of a dihydro-flavonol. 7,3?,4?- Trimethoxydihydroflavonol under similar conditions gave the 3-acetate as the only characterizable product, so that a methoxylated phloroglucinol-type A ring appears necessary for fission of a dihydroflavonol to the corresponding chalcone diacetate. The dihydrochalcone obtained by hydrogenation of α,2?-diacetoxy-3,4,4?,6?- tetramethoxychalcone was also prepared by unambiguous synthesis in nine stages from phloroglucinol (33% over-all yield), and was converted in low yield by N-bromosuccinimide into α,2?-diacetoxy-3?(or 5?)-bromo- 3,4,4?,6?-tetramethoxychalcone. Infrared and nuclear magnetic resonance data are recorded for the compounds described.