Arylnaphthoquinones. 9. adducts diels-alder reaction of 2-aryl-1,4-benzoquinones with cyclopentadiene

The 4+2-cycloaddition reaction of conjugated dienes to 1,4-benzoquinones forms the basis of convenient methods for the synthesis of many natural compounds and their synthetic analogues. The high regioselectivity of the cycloaddition of 1,3-dienes to substituted quinones played a key role in the first synthetic methods for obtaining important natural compounds, such as steroids, alkaloids, vitamin K group, analogues of tetracycline and anthracycline antibiotics and antimalarial drugs, terpenoids, etc. The diene synthesis reaction is also an important step in the construction of various polynuclear carbocyclic compounds. Another practically important area of application of the Diels–Alder reaction is the synthesis of 1,4-naphthoquinone and 9,10-anthraquinone derivatives based on it, which are used both as intermediates in the synthesis of organic dyes and pigments and as important biologically active compounds and drugs. In this work we describe the results of studies carried out during the investigation of the reactivity of monoarylquinones with conjugated dienes, in particular cyclopentadiene. The use of such a diene in the Diels–Alder reaction will allow obtaining promising arylquinones fused with a norbornane fragment for further studies. It has been established that the interaction of 2-aryl-1,4-benzoquinones with cyclopentadiene (Diels–Alder reaction), in a molar ratio of reagents of 1:1, at room temperature occurs stereoselectively and leads to the formation of cycloaddition endo -adducts with yields of 80–90 %. Isomerization of 6-aryl-1,4,4a,8a-tetrahydro-1,4-methanonaphthalene-5,8-diones was carried out at room temperature in toluene in the presence of equivalent of triethylamine to hydroquinones, which, as shown, can be oxidized to the corresponding quinones. The structures of the synthesized compounds were confirmed by the IR-, 1 H-, 13 C NMR spectroscopy and element analysis data. Keywords: 1,4-benzoquinone, 2-aryl-1,4-benzoquinones, сyclopentadiene, 1,4-naphthoquinone derivatives, Diels–Alder reaction.