No abstract

Methods for the synthesis of heteroaryl-substituted 1,4-benzo-and 1,4-naphthoquinones with a C-C bond between the heterocycle and quinone fragments are reviewed.Benzoquinones and their derivatives are widely used in organic synthesis as synthons and reagents [1,2]. They are used as electron-accepting components for the production of charge-transfer complexes and radicalion salts [3,4]. Derivatives of benzoquinones, isolated from natural sources, are subunits in many biological processes, such as electron transport, the photosynthesis of plants, the coagulation of blood, and cell respiration [1, 2, 5]. Reviews have been published on the synthesis of hydroxyquinones [6] and 1,4-benzoquinones condensed with heterocycles [7,8], but methods for the synthesis of heteroaryl derivatives of 1,4-benzoquinones and 1,4-naphthoquinones where the fragments of the heterocycle and the quinone are linked by a C-C bond have not so far been reviewed. Heteroaryl-substituted benzoquinones have demonstrated anticancer [9-11], antifungal, and antibacterial characteristics [11] and antidiabetic activity [12]. The present review is devoted to the analysis and classification of methods for the production of these compounds. Methods for the synthesis of heteroaryl derivatives of quinones can be divided into three groups: The formation of a C-C bond between the quinone and the heterocycle, construction of the heterocycle on the basis of the quinone, and construction of the quinone on the basis of the heterocycle.

No abstract

No abstract

,4series Keywords: 2-(2-aminothiazol-5-yl)-3,6-dichloro-5-diethylaminocthcnyl-l,4-bcnzoquinoncs, 2-(2-aminothiazol-5-yl)-3,5,6-trichloro-l,4-benzoquinoncs, 1,4-bcnzoquinoncs, 2,5-bis(2-aminothiazol-5-yl)-3,6-dichloro-l,4-benzoquinoncs, thiazolc, intramolccular charge transfer.The aim of this work is the synthcsis of 2,5-dihctaryl-l,4-bcnzoquinoncs frorn trichloro-l,4-bcnzoquinonylthiazolcs. These cornpounds arc of intcrcst in conncction with thc prcscncc in the molecule of a strong intrarnolccular charge transfcr bctwccn the electron acccptor quinonc fragmcnt and the electron donor l'ragmcnts of thc thiazolc.Extcnding the work [ I-3] with a study of thc possiblc usc of thc prcviously dcvclopcd rncthod[ 1 ] for thc synthesis of 2,5-dihctaryl-substitutcd 1,4-bcnzoquinoncs showed that, in the case of thiazolc derivatives, thc three component condensation reaction of trichloro-1,4-bcnzoquinonylthiazolcs (I) with acctaldchydc and dicthylaminc in tolucnc givcs thc 5-N,N-dicthylaminocthcnyl dcrivativcs (2a-e).Compounds 2a-e arc dccply colorcd, crystalline materials (thc yiclds in this rcaction being in thc rangc 32-96%). It was lbund that satisfactory rcsults wcrc obtained in thc casc whcrc the amino group protons in thc thiazolc 2 position (compound I) arc substituted. The use of ma6mcsium sulfate in the course of thc reaction increases the yield of the final product.In the rncthod used for prcparation of monohctaryl-substitutcd trichloro-l,4-bcnzoquinoncs [i, 3, 4], the subscqucnt step was the synthesis of 3, 4,6,7-tctrachloro-2,5-dihydroxy-2,3-dihydrobcnzo[h] furan from 3,5,6-trichloro-2-(N,N-dicthylaminoethcnyl)-1,4-bcnzoquinonc. Howcvcr, the separation of its 6-(2-arninothiazol-5-yl)-substituted analog when heating compounds 2a-e with hydrochloric was not successful in our hands. This lowcrs thc yields of thc final product and complicates thc use of thc givcn mcthod for constructing other hctcrocyclcs.Thc reaction of compounds 2a-e with the corrcsponding thiourcas in thc prcscncc of an excess of conccntrated hydrochloric acid lcads to Ibnnation of the hydroquinoncs 3. The best solvcnt Ibr this rcaction provcd to bc acctonitrilc since carrying out thc rcaction in dioxanc give an oily precipitatc which was not susceptible to purification. The hydroquinoncs arc cxtrcmcly difficult to separate in the pure state sincc thcy arc readily oxidizcd in air to thc corrcsponding 1,4-benzoquinoncs. This is indicated by thc prcscncc in thc IR spcctra of compounds 3a and 3b of absorption bands tbr the OH of the hydroquinonc (3000, 3200 cm t) and the C-O group band of tb, c 1,4-bcnzoquinonc (1640, 1630 cm -t rcspcctivcly). Thc prcscncc in thc UV spcctrum of compound 3b of an absorption band typical of hctaryl substitutcd 1,4-bcnzoquinoncs (582 nm) confinncd this proposition. Because thc final target is the prcparation of 1,4-bcnzoquinoncs, thc synthcsizcd hydroquinoncs wcrc irnnlcdiatcly oxidizcd. Oxidation with t~zrric chloridc in aqucous DMF solution occurrcd rcadily and in good yiclds.