ORIGINAL PAPER a Facile, Highly Efficient and Novel Method For

Chemical Papers 69 (9) 1231–1236 (2015) DOI: 10.1515/chempap-2015-0124

ORIGINAL PAPER

A facile, highly eﬃcient and novel method for synthesis

of 5-substituted 1À-tetrazoles catalysed by copper(I) chloride

aIbrahim˙ Esirden, aErhan Ba¸sar, bMuharrem Kaya*

aChemistry Department, bBiochemistry Department, Faculty of Arts and Science, Dumlupınar University, Evliya C¸ elebi Campus 43100 K¨utahya, Turkey.

Received 18 December 2014; Revised 15 March 2015; Accepted 17 March 2015

The present study on tetrazole compounds, which have a wide area of application, proposes a new, simple and highly eﬀective method. A series of 5-substituted 1H-tetrazoles were synthesised in DMF via the [3 + 2] cycloaddition reaction, in which diﬀerent aryl nitriles with sodium azide were used and copper(I) chloride served as a catalyst. Short reaction times, high yields and simple procedures rendered this method attractive and useful for the organic synthesis of 5-substituted 1H-tetrazoles. A further advantage was the use of an environmentally friendly catalyst. c 2015 Institute of Chemistry, Slovak Academy of Sciences

Keywords: 5-substituted 1H-tetrazoles, copper(I) chloride, sodium azide, [3 + 2] cycloaddition, aryl nitriles

Introduction been increased interest in modifying the methods of the preparation of tetrazoles (Amantini et al., 2004; Tetrazoles are heterocyclic compounds which have Keith, 2006; Lakshmi Kantam et al., 2006a; Su et al., a five-membered ring containing one carbon and 2006; Hajra et al., 2007; Shie & Fang, 2007; Yavuz et four nitrogen atoms. Tetrazoles have a wide range al., 2010; Yildirir et al., 2013). The synthesis of dif- of applications in pharmaceutical chemistry (Butler, ferent types of tetrazoles containing heteroatom has 1984); they exhibit strong activities as anti-candida also become quite common (Ozkan¨ et al., 2007; Di¸sli (Kaplancıklı et al., 2014a), antimicrobial (Yıldırır & Salman, 2009). In practice, the use of sodium azide et al., 2009; Çelik et al., 2013; Di¸sli et al., 2013), as a substrate in the place of hydrazoic acid would be anti-proliferative (Kaplancıklı et al., 2014b), analgesic convenient. However, the [3 + 2] cycloaddition energy (Yavuz et al., 2013) and antifungal preparations (Ah- barrier is significantly lower with hydrazoic acid than mad Malik et al., 2012). Furthermore, these nitrogen- it is with the azide ion and the significant excess of rich ring systems possess many applications in mate- azide ions can be used in the presence of metal cata- rial science, including propellants (Damavarapu et al., lysts to overcome the energy limitation (Wittenberger 2010), explosives (Chen & Xiao, 1999) and photogra- & Donner, 1993). Various methods have been reported phy (Frija et al., 2010). for the synthesis of 5-substituted 1H-tetrazoles, most Although tetrazoles were discovered more than 130 of which are based on the addition of the nitrile years ago, a systematic examination of these com- group of sodium azide (NaN3) and trimethylsilyl azide pounds was only initiated in the latter half of the 20th (TMSN3). These reactions were carried out using cat- century. Tetrazole was first prepared by the reaction of alysts such as Fe(OAc)2 (Bonnamour & Bolm, 2009), anhydrous hydrazoic acid and hydrogen cyanide under Brønsted acid catalyst (Bakunova et al., 2009), AlCl3 harsh reaction conditions. The reactants used in the (Matthews et al., 2000). original method are highly toxic, expensive and water- It was recently reported that nanocrystalline ZnO reactive. In particular, hydrazoic acid is profoundly (Lakshmi Kantam et al., 2005), Zn/Al HT (Lakshmi toxic, explosive and volatile. Accordingly, there has Kantam et al., 2006b), CuSO4 · 5H2O (Akhlaghinia

*Corresponding author, e-mail: [email protected] 1232 I.˙ Esirden et al./Chemical Papers 69 (9) 1231–1236 (2015)

Fig. 1. Synthesis of 5-substituted 1H-tetrazole compounds.

& Rezazadeh, 2012), CdCl2 (Venkateshwarlu et al., Table 1. Comparison of efficiency of various catalysts 2009), γ-Fe2O3 (Qi & Dai, 2010), ZnS (Lang et al., (4 mole %) used in synthesis of 5-phenyl-1H-tetrazole in DMF 2010), Cu2O (Crosignani et al., 2011; Jin et al., 2008) and nano CuO (Yapuri et al., 2013) were used in the Entry Catalyst Time/h Yield/% synthesis of tetrazole compounds as various homoge- neous and heterogeneous catalysts. In addition, metal- 1CuCl6 89 modified montmorillonites and zeolite were widely re- 2CuI9 75 ported, and many metals such as Cu, Mn, Fe, Mo, 3CuSO4 872 4ZnCl 14 70 Al and Co (Clark et al., 1997; Varma, 2002; Carriazo 2 5AlCl3 10 52 et al., 2003; Shinde et al., 2004; Yin & Shi, 2005; Ben 6LiCl1250 Achma et al., 2008; Rama et al., 2011) were commonly used in improving the catalytic abilities of montmorillonites. All these methods require a large excess of sodium azide, a prolonged reaction time and expensive metal catalysts. (2 mL) was stirred at 120 ◦C for the appropriate time In this study, a cheap and harmless catalyst period. The progress of the reaction was monitored copper(I) chloride (CuCl) was used for the synthe- by TLC. After completion, the reaction mixture was sis of 5-substituted 1H-tetrazoles. Also, aryl nitrile cooled and treated with 5 mL of HCl (4 mol L−1) compounds and NaN3 were used along with N,N- and 10 mL of ethyl acetate, successively. The ethyl dimethylformamide (DMF) as solvents in the reac- acetate extract was washed with water, dried over an- tions and a new, simple and convenient way was re- hydrous sodium sulphate and concentrated under reported. duced pressure. The product thus obtained was recrys- tallised from acetic acid to afford pure 5-substituted Experimental 1H-tetrazoles.

The chemicals used in the synthesis of tetrazole Results and discussion derivatives were obtained from Merck (Germany) and Aldrich Chemical Company (USA). All chemicals and The general synthesis method shown in Fig. 1 was solvents used in the synthesis were of spectroscopic employed to prepare the tetrazole compounds. The reagent grade. Melting points were measured on a tetrazole compounds were prepared by a one-pot re- Bibby Scientific Stuart Digital, Advanced, SMP30 action affording high yields and following a simple pro- (UK). Fourier Transform Infrared (FT–IR) spectra cedure. were recorded on a Bruker Optics, ALPHA FT–IR Aryl nitriles I were converted into tetrazoles with spectrometer (Germany). The 1HNMRand13CNMR sodium azide II at the mole ratio of 1 : 1.5 using cop- spectra were obtained with a Bruker DPX-300 in per(I) chloride as the catalyst and various solvents. DMSO-d6 as solvents with tetramethylsilane (TMS) By changing the nature of the substituents present in as the internal reference. Chemical shifts are given in the aryl nitrile components, a rather large chemical di- δ relative to TMS. HRMS spectra were detected using versity could be included in tetrazoles (Fig. 1). These an Agilent Technologies 6530 Accurate-Mass Q-TOF various substituents were subsumed in the compounds (USA) LC/MS at the advanced technology research of nitro, aldehyde, halogen (Cl, Br), methyl, pyridine centre of Dumlupınar University (Kütahya, Turkey) moiety, acetanilide and amino. (ILTEM). The reaction of benzonitrile and sodium azide in the presence of copper(I) chloride catalyst tested in General procedure for preparation of tetrazole DMF was selected as a model reaction. The catalysts derivatives (III–XIV) tested in this model reaction are summarised in Ta- ble 1. The reaction in the presence of LiCl alone af- A mixture of nitrile (1 mmol), sodium azide forded the 5-phenyl-1H-tetrazole product over a long (1.5 mmol) and copper(I) chloride (4 mole %) in DMF time with a very low yield. (Table 1, entry 6). In the I.˙ Esirden et al./Chemical Papers 69 (9) 1231–1236 (2015) 1233

Table 2. Optimisation of reaction conditions for preparation of 5-phenyl-1H-tetrazole

Entry Solvent Temperature/ ◦C Time/h Yield/%

1DMF 120 6 89 2 DMSO 120 10 70 3 methanol 65 12 40 4 THF 66 14 34 5 toluene 110 15 15 6water 100 18 10

Table 3. Optimisation of conditions for preparation of 5-phenyl 1H-tetrazole using copper(I) chloride as catalyst in DMF

Entry 1 2 3 45678910

Catalyst/mole%nonenonenone12345710 Time/h 48 48 48 48 24 18 6 5 4.5 3 Temperature/ ◦C r.t. 60 120 120 120 120 120 120 120 120 Yield/% – 122570808189857265

reaction catalysed by CuCl (Table 1, entry 1), the 5- an efficient synthesis. In conclusion, the optimal cat- phenyl-1H-tetrazole product was obtained in a short alyst amount was determined as 4 mole % copper(I) time with high yields. The reactions in which CuI (Ta- chloride (Table 3, entry 7). ble 1, entry 2), CuSO4 (Table 1, entry 3), ZnCl2 (Ta- To understand the scope and effectiveness of ble 1, entry 4) and AlCl3 catalysts (Table 1, entry 5) the catalyst, CuCl, different substituent benzoni- were tested were performed both over long time pe- triles (Table 4) were selected and used under the riods and with very low yields. All the catalysts of determined conditions. These [3 + 2] cycloaddi- CuI, CuSO4,ZnCl2,AlCl3 andLiClweremuchless tion reactions play a vital role in the nitrile com- effective than CuCl. pound activity. 5-Substituted 1H-tetrazoles were ob- The effects of the solvent on the model reaction tained with very good yields in a shorter time were also investigated (Table 2, entries 1–6). The than with electron-withdrawing substituents con- model reaction was performed in DMF, DMSO, THF, taining benzonitriles (Table 4, compounds V–IX) methanol, toluene and water. The reactions afforded while benzonitriles containing electron-donating sub- poor yields when THF, water, toluene and methanol stituents (Table 4, compounds X–XIV)werecon- were used as solvents. Accordingly, these solvents were verted to tetrazoles in longer reaction times. For ex- determined as being unsuitable for this model re- ample, such aromatic nitriles as –NO2,–Cl,–Brand– action. Although 5-phenyl-1H-tetrazole was obtained CHO, which contain electron-withdrawing groups, re- over a long reaction time with a moderate yield in act faster with better yields than with the nitriles DMSO, the reaction in DMF was performed in a short containing electron-donating substituents like –CH3,– reaction time with the best yield, hence DMF was re- NHAc and –NH2. In effect, pyridine-4-carbonitrile was garded as a superior solvent. transformed into the tetrazole compound in a much The concentration of the catalyst plays a crucial shorter period of time with a very good yield (Table 4, role in the success of the reactions in terms of rate and compound IV). In addition, the aryl nitrile compounds yields. These experiments are summarised in Table 3. containing electron-releasing groups such as amino (– In the absence of a catalyst, 5-phenyl-1H-tetrazole NH2) did not react although the reaction conditions was obtained with 0 % yield at ambient temperature were forced. These compounds were converted to ac- (48 h), 12 % yield at 60 ◦C (48 h) and 25 % yield at etanilide derivatives and, from these derivatives, an 120 ◦C (48 h). Increasing the catalyst to 1 mole %, attempt was made to obtain tetrazoles. The products 2 mole %, 3 mole % and 4 mole % resulted in in- were obtained from the acetanilide compounds with a creases in reaction yields to 70 %, 80 %, 81 %, and yield of less than 50 %. All the products were charac- 89 %, while the reaction times varied from 5 h to terised by melting points, IR, NMR and HRMS anal- 48 h. The 5-phenyl-1H-tetrazole product was obtained yses. in the model reaction in the presence of 4 mole % The disappearance of a strong and sharp absorp- CuCl in DMF in a short time (6 h) with a high yield tion –CN band and the appearance of –NH bands in (89 %). However, increasing the catalyst to 5 mole %, the 2500–3000 cm−1 confirmed the formation of 5– 7 mole % and 10 mole % resulted in reductions in the substituted 1H–tetrazoles. Also, the IR spectra of all reaction yields to 85 %, 72 % and 65 %. The use of the products showed bands at 1515–1606 cm−1 due just 4 mole % CuCl in DMF was sufficient to afford to (N—N) (Ozkan¨ et al., 2007) and 1233–1293 cm−1 1234 I.˙ Esirden et al./Chemical Papers 69 (9) 1231–1236 (2015)

Table 4. Preparation of 5-substituted 1H-tetrazoles in the presence of copper(I) chloridea

Compound Substrate Product Time/h Yieldb/% Mp/ ◦C

III 6 89 214–216

IV 4 88 254–256

V 8 90 220

VI 10 85 183–185

VII 10 84 196–198

VIII 12 90 249–250

IX 12 90 260

X 20 80 248–250

XI 20 47 288

XII 24 40 253–254 decomposition

XIII 24 – –

XIV 24 – –

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