Iran. J. Chem. Chem. Eng. Research Article Vol. 39, No. 6, 2020 Archive of SID One-Step Synthesis of Dicyano Imidazoles by (NH4)2Ce(NO3)6/HNO3 Promoted Oxidative Cyclocondensation of an Aldehyde and 2,3-diaminomaleonitrile Kalhor, Mehdi*+; Seyedzade, Zahra Department of Organic Chemistry, Payame Noor University, P.O. Box 19395-4697 Tehran, I.R. IRAN ABSTRACT: The purpose of this study is to obtain a facile, mild, and effective synthetic method for the one-pot synthesis of 2-aryl-4,5-dicarbonitrile imidazole derivatives 3a-q from oxidative cyclo- condensation of aromatic aldehydes and 2,3-diaminomaleonitrile (DAMN) by cerium(IV) ammonium nitrate/nitric acid (CAN/NA) as a novel and efficient oxidation catalyst. This synthetic protocol is cost-effective in addition to other advantages such as rapid transformation with good to excellent yields of products, one-step process and avoiding the pre-functionalization of the starting materials, simple workup procedure and easy operation under mild conditions in comparison previously report. These valuable conditions may be ideally suited for an effective synthesis of dicyano imidazole heterocycles on a larger scale. KEYWORDS: One-step synthesis; Catalytic oxidation; Ceric ammonium nitrate (CAN)/HNO3; Diaminomaleonitrile; Dicyano imidazole. INTRODUCTION Imidazole and its derivatives are one of the most Therefore, in recent years, considerable attention has been important and useful heterocycles among organic focused on the development of synthetic methods of compounds. Imidazole rings are present in some natural substituted imidazoles and also the studies of their products like alkaloids, in many fungicides, antiprotozoal, biological properties, and synthetic applications [7,8]. and antihypertensive medications such as clotrimazole, A number of substituted imidazoles, including 2-aryl- metronidazole and eprosartan, in biological building blocks 4,5-dicarbonitrile imidazoles have attracted much for example histidine [1-3]. These important rings have also attention in medicinal chemistry and organic synthesis. been used for industrial applications Some of them have displayed pharmacological activities like corrosion inhibitor on certain transition metals, and have used in the synthesis of new promising acceptor fire retardant, photography and electronics [4,5]. Salts moiety [9, 10]. There are a few methods for preparation of of imidazole can also be found in the structure of various dicyanoimidazole heterocycles. So far, the four general ionic liquids that are used for catalytic processes [6]. The synthetic methods including the use of Schiff bases structure of some of the drugs and biological molecules and oxidant reagents have been reported [11-14]. The most containing the imidazole ring is shown in Fig. 1. previously methods have some disadvantages such as long * To whom correspondence should be addressed. + E-mail: [email protected] 1021 -9986/2020/6/1-8 8/$/5.08 Research Article 1 www.SID.ir Iran. J. Chem. Chem. Eng. Kalhor M. & Seyedzade Z. Vol. 39, No. 6, 2020 Archive of SID Fig. 1: Some of the drugs and biological molecules containing the imidazole ring. reaction times, hazardous reaction conditions, the use EXPERIMENTAL SECTION of stoichiometric amounts of toxic reagents, tedious work-up Chemical reagents in high purity were purchased and purification and low yield of products. Recently, from the Merck Chemical Company with commercial it has been reported that the use of ceric ammonium nitrate grade. Melting points were determined in open capillaries (CAN) as a reagent is very effective for the synthesis using an electro-thermal digital melting point apparatus of 2-aryl-4,5-dicarbonitrile imidazoles. But the usage of excess and are uncorrected. 1H NMR and 13C NMR spectra amount of CAN reagent (0.45 equiv.) and one-pot, were recorded with a Bruker spectrometer (400 or 500 MHz). two-step procedure of this reaction is not a cost-effective NMR spectra were obtained in DMSO-d6 solution strategy [15]. Therefore, the development of an efficient, and are reported as parts per million (ppm) downfield cost-effective and high-yield synthetic protocol is required from Me4Si as internal standard. FT-IR spectra were obtained in the synthesis of dicyano imidazoles. with potassium bromide pellets in the range CAN is a valuable catalyst and multipurpose reagent 400-4000 cm–1 with a JASCO 4200-A spectrometer. for the synthesis of heterocycles such as tetrahydroindoles [16], A mass spectrum was recorded by an Agilent model: tetrazole [17], chromenes [18], thiadiazoles [19], 5975C VL MSD with a Triple-Axis detector spectrometer hydroxycoumarines [20], and indoles [21]. The extensive at 70 eV. use of CAN as a catalyst and oxidant reagent is due to many advantages like air stable, inexpensive, excellent General one-pot procedure for the synthesis of dicyano solubility in water and reasonably soluble in many organic imidazoles solvents, eco-friendly nature, easy handling and high A mixture of DAMN (0.5 mmol), aromatic aldehyde reactivity [23,24]. (0.5 mmol), and CAN/NA (0.05/0.4 equiv.) was heated However, the use of CAN/HNO3 mixture as a high at 70 °C in acetonitrile (2 mL), for desired time (Table 2). oxidant catalyst in the one-step approach for preparation The reaction was followed by Thin Layer Chromatography (TLC) of 2-aryl-4,5-dicarbonitrile imidazoles has not yet been (ethyl acetate/n-hexane, 2:1). After the completion explored. Therefore, in this investigation and in our further of reaction, the organic solvent was removed. research efforts for the easy catalytic synthesis of heterocyclic The precipitate was dissolved in a small amount of ethanol compounds with valuable biological properties [25-28], and increasing some cold water results in pure product. we report for the first time, CAN/NA catalyzed synthesis Most of the dicyano imidazole products are known and of dicyano imidazoles by oxidative condensation of were characterized by comparison of their physical (Mp) aromatic aldehyde with DAMN under mild conditions and and spectral data (IR, 1H NMR, and 13C NMR) with those high yield in comparison to previously reports. of authentic samples. 2 Research Article www.SID.ir Iran. J. Chem. Chem. Eng. One-Step Synthesis of Dicyano Imidazoles by (NH4)2Ce(NO3)6/HNO3 ... Vol. 39, No. 6, 2020 Archive of SID 2-(3-Chlorophenyl)-1H-imidazole-4,5-dicarbonitrile (3c) 2-(2,5-Dimethoxyphenyl)-1H-imidazole-4,5-dicarbonitrile (3o) FT-IR (KBr) (νmax): 3436, 3179 (N-H), 3090 (C-H), FT-IR (KBr) (υmax): 3277 (N–H), 2234 (C≡N), 1591 2261, 2234 (C≡N), 1644 (C=N), 1466 (C=C), 1120, 799 (C=N), 1543, 1490, 1438, 1307 (C=C), 1281, 1196 (C- -1 1 - (C-Cl), 725 cm ; H NMR (500 MHz, DMSO-d6): δH 7.56- O), 1171, 1146 (O-Me), 1084, 1042, 1018, 811, 743 cm 1 1 7.59 (t br, 2H, H-Ar), 7.92 (d, J = 6.85 Hz, 1H, H-Ar), 7.98 ; H NMR (500 MHz, DMSO-d6): δH 3.78 (s, 3H, (s, 1H, H-Ar), (NH of the imidazole ring was not observed OMe), 3.92 (s, 3H, OMe), 7.10 (dd, J1 = 2.90 Hz, J2 = that probably due to the effect of exchange of this acidic 6.15 Hz, 1H, H–Ar), 7.17 (d, J = 9.05 Hz, 1H, H–Ar), proton with deuterium in small amounts of D2O, which is 7.56 (d, J = 2.80 Hz, 1H, H–Ar), 13.72 (br, 1H, NH) 13 present in DMSO-d6) ppm. ppm; C NMR (125 MHz, DMSO-d6): δC 55.6, 56.0 (OMe), 111.3 (2C), 113.3, 115.6, 118.5 (2C), 147.9, 2-(2,3-Dichlorophenyl)-1H-imidazole-4,5-dicarbonitrile (3f) 150.9, 153.1 ppm. FT-IR (KBr) (νmax): 3289 (N-H), 2240 (C≡N), 1651 (C=N), 1541, 1506, 1446, 1417, 1308 (C=C), 1237, 1193, 2-(3,4,5-Tri methoxyphenyl)-1H-imidazole-4,5- 1156, 1135, 1083, 1055, 975, 804 (C-Cl), 710, 500 cm-1; dicarbonitrile (3p) 1 H NMR (500 MHz, DMSO-d6): δH 7.54 (t, J = 7.92 Hz, FT-IR (KBr) (νmax): 3464, 3299 (N-H), 2939 (C-H), 1H, H-Ar), 7.72 (d, J = 7.65 Hz, 1H, H-Ar), 7.86 (d, J = 2230, 2208 (C≡N), 1617 (C=N), 1584, 1508, 1382, 1332 8.00 Hz, 1H, H-Ar) ppm, (NH of the imidazole ring was (C=C), 1242, 1128 (C-O), 987 cm-1; 1H NMR (400 MHz, 13 exchanged with D2O); C NMR (125 MHz, DMSO-d6): DMSO-d6): δH 3.71 (s, 3H, OMe), 3.83 (s, 6H, OMe), 7.25 13 δC 111.1, 115.8, 128.6, 129.4, 130.1, 130.7, 132.7, 133.0, (d, J = 1.58 Hz, 2H, H-Ar) ppm; C NMR (100 MHz, 148.1 ppm. DMSO-d6): δC 56.0, 60.2 (OMe), 103.6, 111.2, 122.5, 139.6, 145.4, 150.6, 153.3 (C-O) ppm. 2-(4-Bromophenyl)-1H-imidazole-4,5-dicarbonitrile (3h) FT-IR (KBr) (νmax): 3442, 3171 (N-H), 3093 (C-H), RESULTS AND DISCUSSION 2258, 2234 (C≡N), 1600 (C=N), 1557, 1540, 1473, 1424 At the beginning of the research, the condensation (C=C), 1010, 832 (C-Br), 728, 577 cm-1; 1H NMR (500 of 4-chlorobenzaldehyde and DAMN as a model reaction MHz, DMSO-d6): δH 7.77 (d, J = 8.40 Hz, 2H, H-Ar), 7.92 with 0.4:5 eq. of CAN:NA as catalyst was carried out (d, J = 8.40 Hz, 2H, H-Ar) ppm, (NH of the imidazole ring in different solvents, including EtOH, H2O, MeCN and was exchanged with D2O). CH2Cl2 at 70 °C. The results are shown in Table 1. MeCN was chosen to be the best media for this condensation. 2-(4-Nitrophenyl)-1H-imidazole-4,5-dicarbonitrile (3i).