Browsing by Subject "Catechol"

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Laccase-katalysierte Dominoreaktionen von Brenzcatechinen und Hydrochinonen mit 1,3-Dicarbonylverbindungen
(2012) Hajdok, Szilvia; Beifuss, Uwe
In the present work novel domino reactions have been described which are based on the laccase-catalyzed oxidation of catechols and hydroquinones to the corresponding o- and p-quinones and their subsequent reactions with 1,3-dicarbonyl compounds. In the first part of this thesis an efficient approach to 3,4-dihydro-7,8-dihydroxy-2H-dibenzofuran-1-ones has been developed. The method includes a laccase-initiated domino reaction between cyclohexane-1,3-diones and catechols using air as an oxidant. The reactions can be carried out under mild reaction conditions without using toxic reagents. The products were obtained in yields ranging from 70 to 97% and with high purity. Byproducts were not formed. The structures of all products were unambiguously elucidated by NMR spectroscopic methods. In the second part of this work laccase-initiated domino reactions between catechols and heterocyclic 1,3-dicarbonyls have been presented. Using pyridinones, quinolinones and thiocoumarin as substrates, the corresponding benzofuropyridinones, benzofuroquinolinones and thiocoumestans were being obtained. The reactions could be easily performed to deliver the products regioselctively in yields ranging between 55 and 98%. In contrast, polycyclic dispiropyrimidinones were exclusively formed when barbituric acid derivatives were employed as substrates. The unambiguous and complete structure elucidation of all products has been achieved by NMR spectroscopic methods (HSQMBC and band-selective HMBC) as well as by X-ray crystal structure analysis. In the third part of this work laccase-catalyzed transformations between differently substituted hydroquinones and 1,3-dicarbonyls have been studied. These reactions provide a new and highly selective method for the formation of quinone bisadducts with two adjacent 1,3-dicarbonyl substituents. The only exception is the reaction of 2-chlorohydroquinone with 4-hydroxycoumarin which delivers a trisadduct. It is noteworthy that under different conditions the reaction between hydroquinones and 1,3-dicarbonyls resulted in the formation of benzofuran derivatives. The unambiguous structure elucidation of all products has been achieved by NMR spectroscopic methods including spin pattern analysis of the long-range coupled C=O carbons and 13C satellites analysis in 1H NMR spectra. The domino reactions presented in this thesis allow for the efficient and selective synthesis of numerous heterocyclic systems as well as substituted p-benzoquinones under mild reaction conditions. In most cases the products can be isolated in good to very good yields and with high purity. For the structure elucidation of the products a wide range of NMR methods was used.