Notes-Reactions of Nitrohydroxychalcones. Oxidation by Hydrogen Peroxide in Alkaline Medium.

Modified Algar–Flynn–Oyamada Reaction for the Synthesis of 3-Hydroxy-2-styryl-chromen-4-ones under Solvent-Free Conditions

“…An 1 H-NMR spectrum showed a singlet at δ 9.60, a doublet at δ 8.05, and a multiplet at δ 7.85-7.55, due to the presence of OH, -CH=CH-, and aromatic protons, respectively. Further, the formation of 3hydroxy-2-styrylchromones was confirmed by comparing the melting point with literature values [33,35] (Table 1). The present method is simple, as UHP is used as a source of hydrogen peroxide, which avoids increasing the bulk volume of the reaction and makes handling easy.…”

“…However, the above-mentioned conditions suffer from one or the other limitations, as hydrogen peroxide is only available as aqueous (30-40 %) and its use increases the amount of water in the reaction mixture, the result makes 1-(2 -hydroxy-phenyl)-5aryl-penta-2,4-dien-1-ones insoluble. Further addition of a sufficient amount of pyridine is required to homogenize the reaction mixture and as a result increases the bulk of the reaction mixture [35]. Additionally, as the reaction is carried out under heating conditions, the formation of 2-cinnamylidene-3(2H)-benzofuranones may also accompany the reaction, making the purification of the required 3-hydroxy-2-styrylchromones difficult and lowering the yield.…”