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

Abstract

Divergent and versatile synthetic routes to flavones and flavanones via efficient Pd(ii) catalysis are disclosed.

Synthesis of Xanthones via Copper(II)-Catalyzed Dehydrogenative Cyclization and Successive Aromatization in a One-Step Sequence

“…Recently, an intramolecular link between a nucleophilic heteroatom and a β-site of a carbonyl group via dehydrogenative synthesis of a core scaffold in xanthone was reported by both our group as well as others (Scheme a). This dehydrogenative cyclization strategy might provide an atom-economic route toward xanthone from cyclohexyl­(2-hydroxy­phenyl)­methanone via hexa- or tetrahydro xanthone as an intermediate, assuming the reaction condition enables the intermediate to be successively aromatized into xanthone.…”

“…Homolytic cleavage of the Cu­(II)–enolate bond then affords radical intermediate B , which is captured by TEMPO to form α-TEMPO-substituted ketone C . It then undergoes TEMPOH elimination, resulting in enone 4a , which is then transformed into product 5a via intramolecular conjugate addition under copper catalysis. , The cyclohexane ring of 5a undergoes successive dehydrogenation, so that it is transformed into xanthone 2 . Meanwhile, hydroxybenzophenone byproduct 3a is also produced through direct successive dehydrogenation of 4 before conjugate addition of phenol to the α,β-unsaturated ketone.…”

Crossing borders: On‐Water Synthesis of Flavanones

“…Owing to flavanones are found to exhibit a large number of important biological and pharmacological activities, [12,13] for example: antiviral, [14] anticancer, [15–17] antioxidant, [18–21] anti‐inflammatory, [22,23] anti‐HIV, [15–17] antiallergic [24] . antibacterial [25,26] among others, they are considered privileged structures [3] . Some relevant examples of flavanones with biological activities are shown in Figure 1 [27–31] …”

Radical-Induced Cascade Annulation/Hydrocarbonylation for Construction of 2-Aryl-4H-chromen-4-ones

“…The application of palladium-catalyzed protocols, including oxidative arylation of chromones with phenylboronic acids ( Scheme 1 a) [ 35 , 36 , 37 ], and carbonylative cyclization using CO gas as a carbonyl source ( Scheme 1 b) [ 38 , 39 , 40 , 41 , 42 , 43 , 44 ], for the construction of chromones has attracted significant attention for a long time. Additionally, the Pd-catalyzed intramolecular acylation and oxidative cyclization can be used to synthesize 2-aryl-4 H -chromen-4-ones ( Scheme 1 c) [ 45 , 46 ]. Recently, other methods involving intramolecular annulation of 2-alkoxyphenylacetophenones ( Scheme 1 d) [ 47 , 48 ] and 2′-hydroxychalcones ( Scheme 1 e) [ 49 , 50 , 51 , 52 ] via C–O bond formations have also been reported.…”