Synthesis of substituted chalcones based on 1,3-dihydroxy-4-isobornylbenzene
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Russian Chemical Bulletin, International Edition, Vol. 69, No. 11, pp. 2198—2204, November, 2020
Synthesis of substituted chalcones based on 1,3-dihydroxy-4-isobornylbenzene S. A. Popova, E. V. Pavlova, and I. Yu. Chukicheva Institute of Chemistry of the Federal Research Centre Komi Science Centre of the Ural Branch of the Russian Academy of Sciences, 48 ul. Pervomaiskaya, 167000 Syktyvkar, Russian Federation. Fax: +7 (821 2) 21 9916. Е-mail: [email protected] A series of new chalcones containing an isobornyl fragment was synthesized by Claisen— Schmidt condensation of 6-acetyl-1,3-dihydroxy-4-isobornylbenzene with various benzaldehydes. Key words: chalcone, 1,3-dihydroxy-4-isobornylbenzene, acetylation, Claisen—Schmidt condensation.
Chalcones or 1,3-diarylprop-2-en-1-ones are representatives of the open-chain flavonoids, in which two aromatic rings are bound by a three-carbon α,β-unsaturated carbonyl system. Natural and synthetic chalcones have a wide range of biological activities such as anti-inflammatory,1 antibacterial,2 antimicrobial,3 antifungal,4 antiparasitic,5 antiviral,6 antitumor,7 antioxidant,8 antiulcer,9 etc., which makes them an attractive object of research for scientists. The structure of many natural chalcones exerting various biological effects include fragments of isoprenoids.10 The practical use of natural compounds is often limited by rather expensive isolation from plant materials, as well as by the low degree of purification of drugs. Therefore, the synthesis of analogs of natural chalcones is a promising area of research. Various methods for the synthesis of chalcone derivatives are currently available. In each of these methods, the most important part is the condensation of two aromatic systems to form the chalcone scaffold. Chalcones can be synthesized by Claisen—Schmidt condensation, Heck carbonylative cross-coupling,11 Sonogashira12 and Suzuki—Miyaura 13 reactions. But Claisen—Schmidt condensation is one of the most widely used method.14—21 In this reaction, chalcones are formed as a result of the condensation of benzaldehyde and acetophenone derivatives catalyzed, as a rule, by an alkali metal hydroxide or sodium ethoxide,14 as well as by heterogeneous catalysts, 15 hydrotalcites, 16 LiHDMS, 17 piperidine-functionalized silica,18 and Lewis acids.19 In addition, the use in the Claisen—Schmidt reaction of microwave radiation 20 in solutions and without solvents21 reduces the synthesis time and gives high yields of chalcones. The work presents the synthesis of a number of new chalcones based on 1,3-dihydroxy-4-isobornylbenzene.
Results and Discussion 1,3-Dihydroxy-4-isobornylbenzene 1 (a racemate) was used as a starting compound for the synthesis of new chalcones, which was obtained according to the known procedure22 by alkylation of resorcinol with racemic camphene in the presence of aluminum phenolate as a catalyst (Scheme 1). Acetylation of terpenophenol 1 with acetic anhydride in boron trifluoride diethyl etherate at 60 °C for 3 h resulted in 6-acetyl-1,3-dihydroxy-4-isobornylbenz
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