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Abstract
An efficient synthesis of a valuable intermediate of coenzyme Q10 by microwave-assisted Lewis acidic ionic liquid (IL)-catalyzed Friedel-Crafts alkylation is reported. The acidity of six [Etpy]BF4-based ionic liquids was characterized by means of the FT-IR technique using acetonitrile as a molecular probe. The catalytic activities of these ionic liquids were correlated with their Lewis acidity. With increasing Lewis acid strength of the ionic liquids, their catalytic activity in the Friedel-Crafts reaction increased, except for [Etpy]BF4-AlCl3. The effects of the reaction system, the molar fraction of Lewis acid in the Lewis acid ILs and heating techniques were also investigated. Among the six Lewis acid ionic liquids tested [Etpy]BF4-ZnCl2 showed the best catalytic activity, with a yield of 89% after a very short reaction time (150 seconds). This procedure has the advantages of higher efficiency, better reusability of ILs, energy conservation and eco-friendliness. The method has practical value for preparation of CoQ10 on an industrial scale.
Highlights
Isoprenoid natural products containing a p-quinone groups play an important role in biological processes and display many interesting biological properties including anticancer, anti-oxidative, antifungal, antiviral, and anti-inflammatory activities [1,2,3]
In order to study the relationship of acidity and activity of Lewis acid ionic liquid (IL), their acidities need to be characterized first
We have developed a Lewis acid IL-catalyzed synthesis of compound 3, the key intermediate in the synthesis of Co-Q10, by means of microwave irradiation
Summary
Isoprenoid natural products containing a p-quinone groups play an important role in biological processes and display many interesting biological properties including anticancer, anti-oxidative, antifungal, antiviral, and anti-inflammatory activities [1,2,3]. Many methods for the synthesis of this indispensable natural product have been described [6,7,8], the key step is the direct coupling method of the quinone core and the prenyl side chain by a Friedel–Crafts (F-C) reaction to afford the key intermediate 1-[(E)-3-methyl-4-benzenesulfonyl-3-methylbut-2-enyl]-2,3,4,5-tetramethoxy-6-methylbenzene (3, Scheme 1) [9] This reaction has always suffered from low yields, long reaction times, high temperatures, use of solvents hazardous to the environment and so on. Lewis acid ILs play an important role in avoiding the use of toxic or flammable organic solvents, and microwave irradiation can significantly enhance the reaction rates. This procedure, followed by an eco-friendly and simple workup procedure, gave the corresponding products in good yields
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