Dihydroflavonols (flavonolones) are 3-hydroxy flavanones and are found to occur in nature, e.g. Fustin in the young fustic and the yellow cedar, Ampelopsin in the Ampelopsio melioefolia, etc. From the point of view of biogenesis dihydroflavonols seem to occupy an important place in the evolution of anthoxanthins.A number of methods have been evolved for the synthesis of dihydroflavonols: (a) from an o-hydroxy chalkone or flavanone by the action of alkaline hydrogen peroxide [Murakami (1) 1935], (b) by converting a chalkone dibromide into its diacetate and further cyclization with hydrochloric acid [Oyamada (2) 1939], (c) by the action of lead tetraacetate on flavonones and subsequent deacetylation by HC1 gas in a nitrogen atmosphere, [Oyamada (3) 1943], and (d) recently by reduction of flavonols to dihydroflavonols with sodium hydrosulphide as a reducing agent [Geissman (4) 1952],Dihydroflavonols have now been synthesized from o-hydroxy-or o-acetoxychalkone dibromides of the type RCOCHBrCHBrR', where R' contains a methoxy or benzyloxy group in the para position, by the action of aqueous acetone and sodium carbonate. Formation of a dihydroflavonol was proposed to take place through a 0-hydroxy derivative formed by the action of water on the 0-bromine atom [Marathey (5) 1952; Marathey (6) 1953]. These 0-hydroxy derivatives have been isolated in a few cases and the postulation made in the earlier work has been found to be correct [Marathey (7) 1954], Thus the reaction could be represented as follows:rX\0H Br Br R Rf J\
Die durch Veresterung der o‐Hydroxy‐acetophenone (I) mit den aromatischen Säuren (II) erhaltenen Ester (III) werden mit CuBr, in Dioxan oder THF zu den Derivaten (IV) (38‐77% Ausbeute) bromiert; diese werden nach Baker‐Venkataraman (Erhitzen in THF oder Dioxan in Gegenwart von KOH) zu den Benzoylcumaranonen (V) 60‐40%) cyclisiert.
2566 KUTUMBE und MARATHEY Jahrg. 94 Versuche, den auf die obige Weise hergestellten Ester mit wasserfreiem Hydrazin in absol. Methanol bei Raumtemperatur in das zugehorige Hydrazid Uberzufiihreo, ergaben immer nur N.N-Phtholy/-hydrarin6), das quantitativ in farblosen, sehr feinen Nadeln vom Schmp. 344-347" (Zers.) aus Athanol anfiel. C&,NzOz (162.1) Ber. N 17.28 Gef. N 17.58 6 ) TH. CURTIUS und A. DAVIDS, J. prakt. Chem. [2] 54, 72 [1896]. KUNDA RAMKRISHNA KUTUMBE und MADHAV GAJANAN MARATHEY Reaktivitat von Pyridin, 111 1)Bildung von 6-Brom-7-methyl-4'-methoxy-flavon
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