Water-mediated phosphorylative cyclodehydrogenation: An efficient preparation of flavones and flavanones

Structural derivatization strategies of natural phenols by semi-synthesis and total-synthesis

“…However, excess iodine and reaction time will give rise to the formation of 3-iodoflavones [170], while novel iodine sources such as iodine monochloride [171] and ammonium iodide [172] have been developed to solve this problem. In a water-mediated phosphorylative cyclodehydrogenation, flavones and flavanones can be synthesized in the same condition with the product type controlled by dosage of reagent [173]. As the oxidative state of flavones, flavonols can be produced from flavones by the oxidation with 3,3-dimethyldioxirane (DMDO) [174] or Algar-Flynn-Oyamada reaction in the presence of base and hydrogen peroxide [175,176], which may generate by-product of aurone due to the different attacking position of epoxide [177].…”

Synthesis of Flavones through NaI‐Mediated Electrochemical Cyclization of Chalcones

“…Among these approaches, the oxidative cyclization of 2'-hydroxychalcones (1) (Scheme 1 bottom) is widely used because of the simplicity of the starting material preparation via simple aldol condensation between 2'-hydroxyacetophenones and benzaldehydes. [28] Various reagents have been used to furnish this transformation such as InBr 3 , [29] Ce(SO 4 ) 2 , [30] CuI, [31] FeCl 3 , [32] ZnCl 2 , [33] Pd(TFA) 2 , [34] I 2 -DMSO, [35] NH 4 I, [36] POCl 3 [37] and oxalic acid. [38] Even though the aforementioned methods are effective, those processes still face one or more following limitations such as long reaction time, high temperature, requirement of inert conditions or harmful solvents, and the use of toxic heavy metal reagents or strong oxidizing reagents.…”

Divergent synthesis of flavones and flavanones from 2′-hydroxydihydrochalcones via palladium(ii)-catalyzed oxidative cyclization

“… 8 In addition, such flavanones can be readily converted into flavones via further oxidation processes ( Scheme 1 ). 9 Thus, these types of flavonoid synthesis involving intramolecular conjugate addition have been generally used for flavonoid synthesis, 10 but they generally have drawbacks of requiring harsh conditions such as acidic or basic reflux conditions for cyclization, indicating that chemically labile compounds may in some cases not be tolerable in reaction conditions. 11 Additional oxidation steps in which flavanones are transformed into flavones often require the use of strong oxidants such as I 2 that enable side reactions to occur.…”