Different strategies in electrochemical synthesis of new mono and di-substituted hydroquinone and benzoquinone Davood Nematollahi *, Shima Momeni, Sadegh Khazalpour Faculty of Chemistry, Bu-Ali-Sina University, P. O. Box 65174, Hamedan, Iran A R T I C L E I N F O Article history: Received 8 July 2014 Received in revised form 22 September 2014 Accepted 24 September 2014 Available online 28 September 2014 Keywords: Electrochemical syntheses 2-Indolyl-5-arylsulfonyl-p-benzoquinone Arylsulfinic acid Cyclic voltammetry Hydroquinone A B S T R A C T Electrochemical syntheses of 2-indolyl-5-arylsulfonyl-p-benzoquinone derivatives were carried out in two successive oxidation steps. The first involves the oxidation of hydroquinone, 4-(piperazin-1-yl) phenol) and 1-(4-(4-hydroxyphenyl) piperazin-1-yl) ethanone in the presence of arylsulfinic acids as nucleophiles. Our voltammetric data indicate that electrochemically generated p-benzoquinone participates in Michael addition reaction with arylsulfinic acids leading to the 2-(arylsulfonyl) benzene-1,4-diols. The second consists of the oxidation of 2-(arylsulfonyl) benzene-1,4-diols in the presence of 1,2-dimethylindole and the formation of 2-indolyl-5-arylsulfonyl-p-benzoquinone derivatives as the final products. A plausible mechanism for the synthesis of 2-indolyl-5-arylsulfonyl-p-benzoquinone derivatives is also presented. ã 2014 Elsevier Ltd. All rights reserved. 1. Introduction Hydroquinone is an important organic compound that is widely used in many fields such as pharmaceutical, antioxidant, dye, photography and cosmetic industries [1]. In addition, the biological and clinical significance of indole and its derivatives have been widely reported in literatures [2]. Facile access to substituted indoles is of general interest because indoles are building blocks of many natural products and have applications as pharmaceuticals, as agrochemicals, and in materials science [3]. For example, it is recognized that, the 3-indolylbenzoquinone (Fig. 1A) fragment is a core structure in a number of biologically active natural products such as asterriquinones (Fig. 1B) [4]. The asterriquinones exhibit a wide spectrum of biological activities including antitumor proper- ties and are inhibitors of HIV reverse transcriptase [5–7]. On the other hand diarylsulfones are useful in the practice of medicinal chemistry because the sulfone functional group is found in numerous drugs [8]. Some of diphenylsulfones have been shown to inhibit HIV-1 reverse transcriptase and represent an emerging class of substances able to, address toxicity and resistance problems of nucleoside inhibitors [9,10]. The importance of these compounds has motivated us to synthesize some organic compounds containing diphenylsulfone, hydroquinone and indole moieties (Fig. 1C). Following our experience in electrochemical synthesis of organic compounds based on the in-situ generation of Michael acceptor [11– 16], to achieve this target, we firstly investigated the electrochemical oxidation of hydroquinone (1), 4-(piperazin-1-yl) phenol (2) and 1- (4-(4-hydroxyphenyl) piperazin-1-yl) ethanone (3) in the presence of arylsulfinic acids (4a-4c) as nucleophiles and represent a facile and one-pot electrochemical method for the synthesis of some 2- (phenylsulfonyl) benzene-1,4-diol derivatives (6a-6c). This reaction is carried out in a single step, in ambient conditions and in a divided cell using a carbon electrode. Our data shows that, in acidic solutions, the hydrolysis of electrochemically generated p-quinone- imines 2ox or 3ox causes the production of the same products (6a-6c) in the electrochemical oxidation of 1–3 in the presence of 4a-4c. The results of these studies including the full characteriza- tion of the obtained product is presented and discussed. In order to get the 2-indolyl-5-arylsulfonyl-p-benzoquinone derivatives (Fig. 1C), the electrochemical oxidation of 2-(phenyl- sulfonyl) benzene-1,4-diol derivatives (6a-6c) have also been investigated in the presence of 1,2-dimethylindole (8) as a nucleophile and a facile electrochemical method for the synthesis of new hydroquinone derivatives with two different substituents (10a-10c) has been reported. 2. Experimental 2.1. Apparatus and reagents Cyclic voltammetry, controlled-potential coulometry and pre- parative electrolysis were performed using an Autolab model PGSTAT 30 and a Behpazho potentiostat/galvanostat. The working electrode used in the voltammetry experiments was a glassy carbon * Corresponding author: Tel.: +98 811 8282807; fax: +98 811 8257407. E-mail address: nemat@basu.ac.ir (D. Nematollahi). http://dx.doi.org/10.1016/j.electacta.2014.09.122 0013-4686/ ã 2014 Elsevier Ltd. All rights reserved. Electrochimica Acta 147 (2014) 310–318 Contents lists available at ScienceDirect Electrochimica Acta journal homepa ge: www.elsev ier.com/locate/electacta