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The direct acylation of quercetin (I) with 3-chloro-2,2-dimethylpropanoyl chloride (II) gives a complex reaction mixture. The synthesis of different acylated quercetin with from mono- to tetra-O-substituted functions was achieved in a simple procedure wherein the yield of isomers depended on the stoichiometric ratio of reagents. The crude reaction mixtures were analysed (LC-MS) and compared with the isolated products. Unambiguous structural characterisation of isomeric quercetin derivatives was confirmed by NMR analysis. In addition, the quercetin dimer can be obtained in a high yield in the simple procedure. The anti-oxidant activity and aldose reductase inhibition of the compounds were screened with the aim of providing bi-functional remedies to treat diabetic complications and other diseases where oxidative stress and the polyol pathway are key etiological factors.