Synthesis of amidoalkylated phenols (3a, b):Ethyl or methyl chloroformate (2 mmol) was added dropwise to a magnetically stirred solution of benzothiazole (0.270 g, 2 mmol, 0.22 mL) in acetonitrile (10 mL), followed immediately by phenol (0.094 g, 1 mmol). The stirring was then continued at 20 o C for 80 h. After that, the solvent was evaporated under reduced pressure, the residue was dissolved in dichloromethane (40 mL) and washed twice with water. The organic layer was dried (Na 2 SO 4 ) and the crude mixture was dry-loaded onto silica gel. The products were isolated by column chromatography on silica gel with mixtures of petrol / diethyl ether as the eluent.Ethyl 2-(4-hydroxyphenyl)benzo [d]thiazole-3(2H)-carboxylate 3a: Obtained using ethyl chlorofomate (0.217 g, 2 mmol, 0.19 mL); Chromatographed on silica gel with petroleum/diethyl ether (4:1, increasing polarity to 2:1), Yield: 83%; M.p. 127 -128 o C;

New quercetin-based derivatives are synthesized in an easily accessible one-pot manner. The method is based on the reaction of quercetin with in situ formed electrophilic N-alkoxycarbonylazolium ions. The position of the newly formed C-C bond and structure were spectrally characterized by 1D, 2D 1H, 13C-NMR, IR, and MS analysis. Thus, in all cases, good regioselectivity in the C-8 position for the obtained products was demonstrated. The obtained compounds were evaluated for their DPPH and ABTS free radical scavenging activity and compared to natural compounds—quercetin and rutin.

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