A new synthesis of novel alkenylated flavones by palladium-catalyzed cross-coupling reactions

Abstract

Bromoflavones were treated with various terminal alkynes in palladium-catalyzed cross-coupling reactions under phosphine-free condions to give the expected alkenylated flavones in moderate to good yields. The presence of two different β hydrogens in the terminal alkene led to the formation of both alkenylated and alkylated products.

Optimization of the Synthesis of Flavone–Amino Acid and Flavone–Dipeptide Hybrids via Buchwald–Hartwig Reaction

“…6-Bromoflavone ( 1 ), 7-bromoflavone ( 2 ), and amino acid methyl ester hydrochlorides were synthesized according to literature procedures.…”

“…The biological assays exhibited that these special structures are promising cytotoxic compounds on different cell lines. 6-Bromoflavone (1), 30 7-bromoflavone (2), 30 and amino acid methyl ester hydrochlorides 31 were synthesized according to literature procedures.…”

Recent advances in the synthesis of 4H-chromen-4-ones (2012 − 2021)

“…The reaction proceeds in a short period of time (15 min to 8 h) and temperatures ranging from 100 °C, 61,62 110 °C, 63,64 120 °C, 65 130 °C, 66,67 140 °C, 68-70 160 °C, 71,72 °C73 to reflux conditions. [74][75][76][77][78][79][80][81][82][83][84][85] The mechanism involves addition of iodine to the CαdCβ double bond; elimination of HI to form the α-iodinated chalcone; cyclization to chroman-4-one via attack of the hydroxyl group to the C-β position and finally elimination of a second HI to afford the desired 4H-chromen-4-one. Iodine can be regenerated through oxidation of HI promoted by DMSO as oxidant (Scheme 6).…”

“…443 5.14 Functionalization at C-2/C-3 of 4H-chromen-4-ones A series of 2-aryl-4H-chromen-4-ones reacted with diluted fluorine in nitrogen at À78 °C in a mixture of chloroform/trichlorofluromethane/ ethanol to afford cis-2-aryl-2,3-difluoro-4H-chroman-4-ones, which underwent facile dehydrofluorination by adsorbing it on a silica gel column to produce 2-aryl-3-fluoro-4H-chromen-4-ones. 347 Using the same starting materials, bromination with NBS in acetic anhydride followed by addition of methanol under reflux conditions, 126 with an excess of NBS and pyridine in dry carbon tetrachloride 74 and with ammonium bromide and ammonium persulfate at room temperature under grinding and solvent-free conditions 151 afforded 2-aryl-3-bromo-4H-chromen-4-ones while iodination with equimolar amounts of molecular iodine in DMSO at 130 °C gave access to 2-aryl-3-iodo-4H-chromen-4-ones in 87-92% yield. 371 The synthesis of Scheme 88…”

New Developments in the Synthesis of (E)-8-Styrylflavones

“…13,14 Under similar conditions, 3-, 6-, or 7-bromoflavones can also be treated with multiple terminal alkenes, including styrene derivatives, to give the corresponding alkenylated flavones in moderate to good yields. 15 Luthman et al have efficiently coupled methyl acrylate to the 3-, 6-, and 8-positions of flavone scaffolds using microwave heating as an alternative energy source. 16 Silva et al performed an efficient Heck cross-coupling reaction of 3-bromoflavones with styrene derivatives, under microwave irradiation, leading to the corresponding (E)-3styrylflavones.…”