Hindawi Publishing Corporation Journal of Chemistry Volume 2013, Article ID 104690, 6 pages http://dx.doi.org/10.1155/2013/104690 Research Article An Efficient One-Pot Three-Component Synthesis of Novel Sulfanyl Tetrazoles Using Ionic Liquids Sankari Kanakaraju, Bethanamudi Prasanna, and G. V. P. Chandramouli Department of Chemistry, National Institute of Technology, Warangal 506 004, India Correspondence should be addressed to G. V. P. Chandramouli; [email protected] Received 13 June 2012; Accepted 11 August 2012 Academic Editor: Mohamed Afzal Pasha Copyright © 2013 Sankari Kanakaraju et al. is is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. An efficient, simple, and environmentally benign method for the synthesis of novel sulfanyl tetrazoles has been achieved by one- pot three-component reaction of phenacyl bromides/3-(2-bromoacetyl)coumarins with KSCN and NaN using [Bmim]BF ionic liquid. It could be reused and recycled for four runs without signi�cant loss of product yield. 3 4 1. Introduction synthesize the compounds containing coumarin-substituted sulfanyl tetrazoles. Over the years, multicomponent reactions (MCRs) have e most convenient method of synthesizing tetrazoles become increasingly popular tools to ensure sufficient molec- is the addition of azide ions to nitriles. Earlier reported ular diversity and complexity. ey have gained signi�cant methods for the synthesis of 5-substituted tetrazoles suffer popularity in recent years due to their atom-economy and from drawbacks such as the use of strong Lewis acids, straightforward reaction design due to substantial minimiza- or expensive and toxic metals, and the in situ generated tion of waste, labour, time, and cost [1, 2]. hydrazoic acid which is highly toxic and explosive [21–24]. Tetrazoles play an important role in coordination chem- Several syntheses of 5-substituted tetrazoles have been istry as ligands, in medicinal chemistry as stable surro- reported through the [2+3] cycloaddition of nitriles using gates for carboxylic acids and in materials applications, NaN or TMSN in the presence of catalysts such as ZnCl including explosives, rocket propellants, and agriculture [3– [25], AlCl [26], BF -OEt [27], Pd(PPh ) [28], FeCl -SiO 13]. ere is a particular interest for the synthesis of 5- [29],3TBAF [30],3 Zn/Al hydrotalcite [31], ZnO [32], and2 alkyl/arylthiotetrazoles as these thiotetrazoles are having Cu O [33].3 Recently,3 LeBlanc2 and Jursic [34]3 4 and Demko3 and2 powerful activating property than the corresponding 5- Sharpless [35] reported the synthesis of sulfanyl tetrazoles. akyl/aryltetrazoles used for synthesis of DNA and RNA [14, Although2 these methods were quite useful, but having some 15]. e presence of alkylthio group makes the tetrazole ring limitations such as use of toxic solvents and use of homo- more acidic than the corresponding 5-alkyltetrazoles which geneous Lewis acid catalyst like ZnBr which could not be improves its ability to act asan activator [16]. recycled from the reaction mixture. All the above methods On the other hand, coumarins are heterocyclic organic require prolonged reaction times. erefore,2 we thought of compounds which constitute an important group of natural developing more efficient and convenient method which is products having varied biological activities such as antitumor, free from all the above drawbacks. antiin�ammatory, antiviral, CNS, antioxidant, and anti-HIV activities [17–20]. 2. Results and Discussion us, in view of the diverse activity of coumarins and tetrazoles, as a part of our continuing research work on the In recent times, ionic liquids have attracted increasing inter- synthesis of novel heterocyclic compounds, we thought to est in the context of green synthesis. ese ILs have shown 2 Journal of Chemistry great promise as an alternative to conventional solvents due T 1: Synthesis of 6b in various ILs at 100 C. ∘ to their unique properties of nonvolatility, non�ammabil- a b ity, thermal stability, recyclability, and controlled miscibil- Entry Solvent Time h Yield ity [36–40]. Butylimidazolium salts ILs have already been 1 [Bmim]Cl 7 74 ( ) (%) demonstrated as efficient catalysts and solvents for various 2 [Bmim]Br 6.5 66 organic transformations [41–44]. 3 [Bmim]PF6 8 48 Our literature survey revealed that till now there were 4 [Bmim]BF4 2 91 no methods reported in the literature for the synthesis a Time for total completion of the reaction. of sulfanyl tetrazoles via one-pot three-component reac- b tion using ionic liquids. As part of our ongoing research Isolated yield. work on the developments of new routes to heterocyclic system in ionic liquids [45, 46], we, herein, wish to T 2: Recycling of [Bmim]BF4 ionic liquid. report a simple and efficient procedure for one-pot three- a component synthesis of novel sulfanyl tetrazoles by using Entry Cycle Time (h) Yield ( ) 3-(2-bromoacetyl)coumarins/phenacyl bromides, KSCN and 1 1st run 2 91 % NaN in the presence of [Bmim]BF ionic liquid at 100 C to 2 2nd run 2 90 afford title compounds in good yields. (Schemes 1 and 2). ∘ 88 Ionic3 liquids (ILs) based on4 butylimidazolium salts 3 3rd run 2 were tested as solvents. In order to optimize the reac- 4 4th run 2.5 87 a tion conditions, a model reaction was performed using 4- Isolated yield of 6b. chlorophenacyl bromide 5b, KSCN and NaN using various ionic liquids. A mixture of 4-chlorophenacyl bromide 35b and KSCN of novel sulfanyl tetrazoles using [Bmim]BF ionic liquid. in ionic liquid was stirred at RT for 10 minutes. Aer is protocol has the advantages of simple workup, short completion of the reaction, NaN was added and the reaction reaction times, milder reaction conditions, good4 yields, and was continued for 12 h, there was no product formation as environmentally benign reusable solvent. observed by TLC, whereas at 603 C the reaction proceeded but not to completion even aer∘ 8 h. Consequently, the 4. Experimental reaction temperature was optimized at 100 C, which gave the sulfanyltetrazole as the sole product. e∘ results were 4.1. General. Melting points were recorded in open capillary summarized in Table 1. As can be seen from Table 1, the and were uncorrected. Column chromatography was per- best result was obtained when the reaction was carried out formed using silicagel (100–200 mesh size) purchased from in [Bmim]BF at 100 C (Table 1, entry 4). e reaction using omas Baker and TLC was carried out using aluminium [Bmim]BF proceeded∘ in higher yield and shorter reaction sheets precoated with silica gel 60F254 purchased from 4 time than that using another ionic liquids as reaction media. Merck. IR spectra (KBr) were recorded on a Bruker WM- 4 e recyclability of the ionic liquid was also investigated 4(X) spectrometer (577 model). H NMR (300 MHz) and using the above model reaction. Aer completion of the C NMR (75 MHz) spectra were1 recorded on Bruker AC- reaction, the mixture was poured into water and stirred 300 spectrometer in CDCl and DMSO- with TMS as thoroughly. e solid product was isolated by �ltration, and 13 an internal standard. Mass spectra (ESI) were recorded on the �ltrate containing ionic liquid was extracted with ethyl JEOL SX-102 spectrometer. CHN3 analysis was6 done by Carlo acetate ( mL) to remove nonionic organic impurities. Erba EA 1108 automatic elemental analyzer. e chemicals en, the water was evaporated under reduced pressure and and solvents used were of commercial grade and were used the recovered ionic liquid was dried at 80 C under vacuum 2 × 20 without further puri�cation unless, otherwise, stated. for 2 h and reused in the next reaction. e∘ procedure was repeated, and the results indicated that the ionic liquid could be reused for four times without evident loss in the yield of the 4.2. Typical Procedure. A mixture of phenacylbromide 5a–f product (Table 2). e scope and the generality of the present (1 mmol) or 3-(2-bromoacetyl)coumarin 1a–f (1 mmol) and method were further demonstrated by the reaction of various KSCN (1.2 mmol) in [Bmim]BF (3 mL) was stirred at RT phenacylbromides/3-(2-bromoacetyl)coumarins with KSCN for 10 min (in case of 3-(2-bromoacetyl)coumarins; 45 min), and NaN . In all cases, up to quantitative yields in reasonable aer completion of the reaction (single4 spot on TLC), NaN reaction times were obtained (Table 3). All the synthesized (1.2 mmol) was added portion wise to the reaction mixture compounds3 were characterized by m.p, elemental analysis, and then it was stirred at 100 C for appropriate time. Aer3 IR, H NMR, mass, and C NMR data. completion of the reaction (monitored∘ by TLC), it was cooled to RT and poured into ice cold water, the solid separated was 1 13 �ltered, washed with water, dried, and puri�ed by column 3. Conclusion chromatography using silicagel (ethylacetate/n-hexane: 2/8) to afford title compounds 4a–f and 6a–f in good yields. In summary, we have developed an efficient, practically 3-(2-(1H-Tetrazol-5-ylsulfanyl)-acetyl)-chromen-2-one (4a). convenient, and ecologically safe method for the synthesis m.p. 154–156 C; IR (KBr, cm ) 3347, 3073, 1729, 1680, ∘ −1 Journal of Chemistry 3 R1 R1 O O O O N [Bmim]BF HN + KSCN + 4 N NaN3 100∘C, 4–6 h S N R Br R2 2 2 3 4a-f O 1a-f O S 1 O O H S [Bmim]BF N Br + KSCN + 4 NaN3 N 100∘C, 2–4 h N 2 3 R N R 6a-f 5a-f S 2 1551; H NMR (300 MHz, CDCl ) 4.96 (s, 2H, –CH ), 1714, 1677, 1557; H NMR (300 MHz, CDCl ) 4.92 (s, 7.34–7.361 (m, 2H, ArH), 7.95 (d, 2H, ArH), 8.80 (s, 1H, C 2H, –CH ), 7.62 (s,1 1H, ArH), 7.85 (s, 1H, ArH), 8.80 (s, of coumarin); C NMR (75 MHz,3 CDCl ): 42.89, 123.21,2 1H, C of coumarin); C NMR (75 MHz, CDCl3 ) 42.70, 4 2 125.22, 128.32,13 129.65, 130.36, 135.15, 145.16, 148.84, 123.26, 128.71, 129.83,13 131.47, 133.21, 136.31, 143.47, 147.82, 155.18, 158.94, 185.66; MS m/z: 289 (M+1)3 ; Anal.