Synthesis of 5-subsituted flavonols via the Algar-Flynn-Oyamada (AFO) reaction: The mechanistic implication
Herein, we report a synthetic method with improved selectivity for 5-substituted flavonols via the Algar-Flynn-Oyamada reaction (AFO), by using of sodium carbonate/hydrogen peroxide A series of 5-substituted flavonols was obtained with moderate to high yields. The mechanism of the AFO reaction was elucidated. LCMS analysis and in situ 1H NMR analysis indicated that the epoxide was involved in the transformation from chalcone to flavonol and/or aurone under alkaline base/peroxide conditions.
Shen, Xianyan,Zhou, Qiang,Xiong, Wei,Pu, Wenchen,Zhang, Wei,Zhang, Guolin,Wang, Chun
supporting information
p. 4822 - 4829
(2017/07/17)
Kinetics and Mechanism of the Cyclisation of Some 2'-Hydroxychalcone Epoxides and Subsequent Elimination Reactions of Aurone Hydrates
Analysis of the pH-rate profile for the cyclisation of the monoanion of 2'-hydroxychalcone epoxide which gives 3-hydroxyflavanone and of some 6'-alkoxy-substituted analogues which give mostly aurone hydrate, gives rate coefficients which quantify the preference for α over β cyclisation when 6'-substituents are present.These are considered in terms of stereoelectronic factors which may be responsible for the preference.Also reported are rate coefficients for the subsequent reaction of aurone hydrates in which aurones and coumaranones are formed.
Adams, Christopher J.,Main, Lyndsay
p. 9929 - 9938
(2007/10/02)
Cyclisation and subsequent reactions of 2′-hydroxy-6′-methoxychalcone epoxide and related compounds
2′-Hydroxy-6′-methoxychalcone epoxide reacts in neutral aqueous acetonitrile solution to give a 6:1 ratio of the α- and β-cyclisation products, erythro-4-methoxyaurone hydrate [erythro-2-(α-hydroxybenzyl)-4-methoxycoumaran-3-one] and trans-3-hydroxy-5-methoxyflavanone: the dominance of α-cyclisation may be associated with a stereoelectronic preference for a conformation favourable for α- but not β-cyclisation when the carbonyl group is forced by the 6′-substituent to lie out-of-plane with the aromatic ring. In more basic solutions, erythro-threo isomerisation of aurone hydrate occurs, and 4-methoxycoumaran-3-one and 4-methoxyaurone are formed. Other 6′-substituted 2′-hydroxychalcone epoxides show a similar strong preference for α- over β-cyclisation.
Adams, Christopher J.,Main, Lyndsay
p. 4979 - 4990
(2007/10/08)
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