An efficient one-pot synthesis of new 2-imino-1,3-thiazolidin-4-ones under ultrasonic conditions

Ultrasonics Sonochemistry 18 (2011) 45–48

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Short Communication

An efficient one-pot synthesis of new 2-imino-1,3-thiazolidin-4-ones under ultrasonic conditions Manouchehr Mamaghani *, Azam Loghmanifar, Mohammad Reza Taati Department of Chemistry, Faculty of Sciences, University of Guilan, P.O. Box 41335-1914, Rasht, Iran

a r t i c l e

i n f o

a b s t r a c t

Article history: Received 31 March 2010 Received in revised form 23 May 2010 Accepted 25 May 2010 Available online 2 June 2010

A convenient one-pot protocol was developed for the synthesis of 2-imino-1,3-thiazolidin-4-ones by the reaction of amines, isocyanates, aldehydes, and chloroform in the presence of sodium hydroxide under ultrasonic conditions in high yields (75–91%) and shorter reaction times (12–15 min). Ó 2010 Elsevier B.V. All rights reserved.

Keywords: Iminothiazolidinone One-pot Multicomponent Ultrasound Thiourea

1. Introduction Substituted thiazolidin-4-ones have been used for photography, as synthetic intermediates, dyes and display diverse biological activities such as antiarthiritic, anti-bacterial, anti-viral, inhibitors of bacterial type III secretion, anti-convulsant, anti-inflammatory, anti-diabetic, pesticidal, SHP-2 inhibitor and calcium antagonist [1–4]. For example Troglitazone (1) was used as insulin sensitizing drug for the treatment of type 2 diabetes. 2-imino-4-thiazolidinones 2 (R1 = C3H7, R2 = C6H5) and 3 (R1 = C3H7, R2 = C6H5) proved to have interesting anti-inflammatory activity [5,6]. S O O

O

NH

O

HO 1 R2

N

R1

N R2

R1

N

N

S

S O

O 2

3

* Corresponding author. Tel.: +98 1317270899; fax: +98 1313233262. E-mail address: [email protected] (M. Mamaghani). 1350-4177/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.ultsonch.2010.05.009

This array of properties has resulted in a considerable number of reviews [7,8]. Interestingly, accounts of thiazolidinones are dominated by 4-thiazolidinones [2,9] and in particular 2iminothiazolidinones are prevalent [1,10]. There are many available methods for the synthesis of 2-imino-4-thiazolidinones, but a common synthetic strategy to generate iminothiazolidinones relies on cyclization of thioureas with a-haloesters or acetic acid. For unsymmetrical thioureas regiocontrol in cyclization step is typically influenced by electronic factors that predispose electron-withdrawing substituents (aryl or heteroaryl) to maintain conjugative stabilization with imine nitrogen (R2 in structure 2). This allows regioselective cyclization of thiourea bearing one alkyl, one aryl substituent or two aryl groups [11]. Laurent et al. have reported regioselective cyclization of unsymmetrical thioureas in the absence of base and obtained regioisomer 2 in high ratio (71/29–99/1) by employing R1 as heteroaryl substituent [11]. Pihlaja and co-workers have used a similar method for the preparation of 2-[(anthracen-9-yl)imino]-3ethyl-1,3-thiazolidin-4-one as prevalent regioisomer [1]. Another interesting development in the synthesis of 2-imino-4-thiazolidinones has been reported by Sedlak and co-workers who have used a ‘‘classical ring transformation” for conversion of substituted S-(1-phenyl pyrrolidin-2-one-3-yl)isothiouronium salts (4) to substituted imino-5-[2-(phenylamino)ethyl] thiazolidine-4ones (5) [12].

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M. Mamaghani et al. / Ultrasonics Sonochemistry 18 (2011) 45–48

O

R1

S

N

NHR2

NHR3

4 R2 O

R1

N NR3 N H

S

5

Alternative methods for the synthesis of iminothiazolidinones have been employed by using trichloromethylcarbinols under basic condition [5,13], gem-dicyanoepoxides as dicationic ketene equivalent [14], and recently a-chloro amide derivatives [15]. However some of these methods use expensive starting materials, harsh reaction conditions, and suffer from multi-step synthesis, long reaction times, and low yields. Therefore, the development of an efficient and versatile method is still required. On the other hand, ultrasonic reactions have been increasingly used as clean, green and environmentally benign routes for the preparation of organic compounds of synthetic and biological values [16–21]. A large number of organic reactions can be carried out in higher yield, shorter reaction time and under milder conditions, by using ultrasonic irradiation [22,23]. 2. Results and discussion In continuation of our ongoing program aiming at the development of efficient methods for the synthesis of heterocycles with medicinal applications [24,25], we carried out a simple one-pot reaction for the synthesis of 2-iminothiazolidinones under ultrasonic irradiation (Scheme 1). A common synthetic strategy to generate disubstituted thioureas has typically involved the addition of amines to N-substituted isothiocyanates [6]. In this protocol a suitable amine and isocyanate reacted in CH2Cl2. Subsequent addition of aldehyde in a basic media (NaOH, DME) followed by application of ultrasound (45 kHz, 25 °C) lead to the desired 2-iminothiazolidinones in 75– 91% yields (Table 1). With unsymmetrical thioureas, a mixture of two isomers 8 and 9 is expected (Scheme 1). They conceivably can be originated from the condensation of trichloromethylcarbinol, produced by the reaction of aldehyde and chloroform under basic reaction media, with sulfur atom of thiourea. Under the reaction condition used

in this protocol only the regioisomers 8a–j were formed. However when employing N-cyclohexyl, N0 -ethylthiourea, a mixture of regioisomers 8i and 9i (ratio 1:1 from 1H NMR) were formed. For the synthesis of thiazolidinones 8a, 8h and 8j readily available thioureas were used. The regioselectivity observed in this reaction can be explained by the stereoelectronic effects of the substituents on the in situ formed thioureas. For example for the substrate possessing phenilic system as in the case of for example (8d and 8e) the NH proton flanked by a phenyl moiety is more acidic compared to the other NH proton flanked by benzyl moiety [this is because of the higher basicity of the benzyl amine (pKa 9.41) compared to aniline (pKa 4.61)], therefore enolization of the thiourea from the phenyl side of the substrate is facilitated. Finally to compare the results obtained under ultrasonic conditions with classical method developed by Blanchet and Zhu [5], 2iminothiazolidin-4-ones 8a–c were prepared by using thiourea and in situ prepared unsymmetrical thioureas. The desired products were produced in much longer reaction time (12 h) and lower yields (41–53%) (Table 1). These results support the specific effects of ultrasound. The effect is due to cavitation, a physical process that creates, enlarges, and implodes gaseous and vaporous cavities in an irradiated liquid. The collapse of cavitation bubbles result in the formation of very fine emulsions, thus facilitating the reaction [26]. Full structural assignments of all the synthesized regioisomers were possible by the NMR and elemental analyses. Based on our previous studies with closely related structures which was also supported by X-ray analysis [27], it is quite evident from 1H NMR data that CH2 protons attached to the ring nitrogen compared with those on imino nitrogen are observed in relatively downfields. This is due to more basic nature of exocyclic imino nitrogen.

Table 1 Synthesis of 2-imino-1,3-thiazolidin-4-ones under ultrasonic conditions at room temperature. Entry 8a 8b 8c 8d 8e 8f 8g 8h 8i 8j a b c

R1

R2

H C2H5– C2H5– C6H4CH2– C6H5CH2– CH2@CH–CH2– CH2@CH–CH2– H Cyclohexyl H

R3

H 4-MeC6H4– 4-MeC6H4– C6H5– C6H5– Thiazol-2-yl 4-MeC6H4– 4-MeC6H4– C2H5– H

Time (min)

C6H5– C6H5– H C6H5– H H H C6H5– H 4-MeC6H4–

b

15 (12 h) 15 (12 h)b 12 (12 h)b 15 15 12 15 15 15 15

Isolated yield. Reaction under classical condition at room temperature. Mixture of regioisomers (ratio 1:1).

NR2

NR1

S 2

R1NH2

R NCS CH2Cl2

R1

R2 N H

N H

R3CHO, CHCl3, DBU

NR1

S

+

NR2

NaOH, H2O, DME Ultrasound, rt

6

S

7

R3

R3

8a-j

O

R1 = H, C2H5, C6H5CH2, CH2=CHCH2, cyclohexyl R2 = H, C6H5, 4-MeC6H4, thiazol-2-yl, C2H5 ; R3 = H, C6H5, 4-MeC6H4 Scheme 1. Synthesis of new 2-imino-1,3-thiazolidin-4-ones under ultrasonic conditions.

9a-j O

Yield (%)a,b 88 (53)b 80 (47)b 85 (41)b 90 83 86 85 90 75c 91

M. Mamaghani et al. / Ultrasonics Sonochemistry 18 (2011) 45–48

3. Conclusion We report a convenient one-pot reaction for the synthesis of iminothiazolidinones by using in situ formed unsymmetrical thiourea, aldehydes and chloroform under ultrasound condition at ambient temperature in short reaction time (12–15 min) with high yields (75–91%). At present condition a very high acceleration of the reaction compared with classical condition was also observed (Table 1). Application of this method to newly designed thioureas and heteroaryl aldehydes is underway. 4. Experimental 4.1. General IR spectra were recorded on a Shimadzu FTIR-8400S spectrometer. 1H NMR and 13C NMR spectra were recorded on a 500 MHz Bruker DRX-500 in CDCl3 and DMSO-d6 as solvent and TMS as an internal standard. For the ultrasonic reactions, ultrasound apparatus Astra 3D (9.5 L, 45 kHz frequency, input power with heating, 305 W, number of transducers, 2) from TECNO-GAZ was used. Elemental analyses were done on a Carlo-Erba EA1110CNNO-S analyser and agreed with the calculated values. Melting points were measured on a Buchi melting point B-540 instrument and are uncorrected. All the chemicals were purchased from Merck and used without further purification. General procedure for the preparation of 2-imino-4-thiazolidinone under ultrasonic conditions. The appropriate amine (8.0 mmol) was added to a solution of aryl or alkyl isothiocyanate (8.0 mol) dissolved in CH2Cl2 (24 mL). The mixture was stirred for 2.5 h at room temperature. To this a mixture of aldehyde (4 mmol), CHCl3 (8 mmol) and DBU (4 mmol) in DME (8 mL) was added under nitrogen atmosphere. The reaction mixture was cooled to 0 °C and a solution of 0.5 M aqueous NaOH (32 mL) was added over 30 min. The cloudy monophasic solution was irradiated by ultrasound (45 kHz, 25 °C) for the required reaction times (12–15 min). The progress of the reaction was monitored by TLC (n-hexane/ethyl acetate: 3:1). After completion of the reaction the mixture was neutralized with dilute hydrochloric acid. The aqueous layer was extracted with ethyl acetate (3  30 mL) and the combined organic layers, washed with water and brine, dried over Na2SO4 and evaporated to furnish a slightly coloured solid. Pure 2iminothiazolidinone was obtained by column chromatography (nhexane/ethyl acetate: 3:1) as a solid (75–91%). 4.1.1. 2-Imino-5-phenylthiazolidin-4-one (8a): white solid Mp 102–103 °C; FTIR (KBr, cm1) mmax 3260, 3100, 1650, 1500, 1480, 1380, 1140, 800, 720, 690 cm1; 1H NMR (500 MHz, DMSO-d6) dH: 5.47 (1H, s, CH), 7.26 (2H, d, J = 7.50 Hz, ArH), 7.30 (1H, d, J = 7.0 Hz, ArH), 7.36 (2H, t, J = 7.50 Hz, ArH), 8.97 (1H, s, NH), 9.22 (1H, s, NH) ppm. Anal. Calc. for C9H8N2OS: C, 56.23; H, 4.19; N, 14.57. Found: C, 56.11; H, 4.10; N, 14.37%.

47

CH2CH3), 2.35 (3H, s, CH3–Ph), 3.7 (2H, s, CH2–S), 3.9 (2H, q, J = 7.1 Hz, CH2CH3), 6.9 (2H, d, J = 8.1 Hz, ArH), 7.17 (2H, d, J = 8.1 Hz, ArH) ppm. Anal. Calc. for C12H14N2OS: C, 61.51; H, 6.02; N, 11.96. Found: C, 61.62; H, 6.15; N, 11.87%. 4.1.4. 3-Benzyl-5-phenyl-2-(phenylimino)thiazolidin-4-one (8d): white solid Mp 131–133 °C; FTIR (KBr, cm1) mmax 2954, 2918, 2846, 1670, 1640, 1465, 1386, 1366, 1228, 1070, 730, 690. 1H NMR (500 MHz, CDCl3) dH: 3.75 (2H, s, CH2), 5.14 (1H, s, CH), 6.8–7.54 (15H, m, ArH) ppm. Anal. Calc. for C21H18N2OS: C, 72.78; H, 5.24; N, 8.08. Found: C, 72.62; H, 5.15; N, 8.01%. 4.1.5. 3-Benzyl-2-(phenylimino)thiazolidin-4-one (8e): White solid Mp 66–67 °C; FTIR (KBr, cm1) mmax 3029, 2940, 1718, 1643, 1622, 159, 1485, 1425, 1382, 1321, 1153, 1132, 1074, 966, 896, 754, 696. 1H NMR (500 MHz, CDCl3) dH: 3.82 (2H, s, CH2-Ph), 5.11 (2H, s, CH2S), 7.05 (2H, dd, J = 1.0, 8.3 Hz, ArH), 7.22 (1H, t, J = 7.4 Hz, ArH), 7.37–7.44 (5H, m, ArH), 7.6 (2H, dd, J = 1.4, 8.3 Hz, ArH) ppm. Anal. Calc. for C16H14N2OS: C, 68.06; H, 5.00; N, 9.92. Found: C, 68.12; H, 5.15; N, 9.75%. 4.1.6. 3-Allyl-2-(thiazol-2-ylimino)thiazolidin-4-one (8f): yellow solid Mp 54–57 °C; (KBr, cm1) mmax 2927, 2864, 1728, 1639, 1573, 1423, 1373, 1330, 1282, 1215, 1128, 1072, 931, 750, 704. 1H NMR (500 MHz, CDCl3) dH: 3.90 (2H, s, CH2–S), 4.53 (2H, d, J = 5.85 Hz, N-CH2CH@CH2), 5.28 (1H, d, J = 10.20 Hz, CH@CH2), 5.37 (1H, d, J = 17.09, CH@CH2), 5.95 (1H, m, CH@CH2), 7.12 (1H, d, J = 3.6 Hz, CH–S), 7.63 (1H, d, J = 3.6 Hz, CH–N) ppm; 13C NMR (125 MHz, CDCl3) dC: 172.1 (C@O), 170.0, 159.6, 140.2, 131.0, 119.2, 116.9, 45.8, 33.9 ppm. Anal. Calc. for C9H9N3OS2: C, 45.17; H, 3.79; N, 17.56. Found: C, 45.01; H, 3.58; N, 17.47%. 4.1.7. 3-Allyl-2-(p-tolylimino)thiazolidin-4-one (8g): white solid Mp 133–134 °C; FTIR (KBr, cm1) mmax 2929, 1722, 1633, 1506, 1377, 1336, 1176, 1124, 927, 827. 1H NMR (500 MHz, CDCl3) dH: 2.38 (3H, s, CH3), 3.84 (2H, s, CH2S), 4.50 (2H, d, J = 5.8 Hz, N– CH2CH@CH2), 5.28 (1H, d, J = 10.0 Hz, CH@CH2), 5.37 (1H, d, J = 17.0 Hz, CH@CH2), 5.98 (1H, m, CH@CH2), 6.91 (2H, d, J = 8.19 Hz, ArH), 7.19 (2H, d, J = 8.19 Hz, ArH) ppm; 13C NMR (125 MHz, CDCl3) dC: 171.8 (C@O), 153.8, 145.8, 134.6, 131.2, 130.2, 121.2, 118.7, 45.5, 33.1, 21.4 ppm. Anal. Calc. for C13H14N2OS: C, 63.39; H, 5.73; N, 11.37. Found: C, 63.42; H, 5.58; N, 11.46%. 4.1.8. 5-Phenyl-2-(p-tolylimino)thiazolidin-4-one (8h): yellow solid Mp 142–143 °C; FTIR (KBr, cm1) mmax 3247, 3056, 2929, 2856, 1652, 1627, 1500, 1429, 1272, 1132, 1080, 810, 783, 684. 1H NMR (500 MHz, DMSO-d6) dH: 2.3 (3H, s, CH3), 5.06 (1H, s, CH), 7.35– 7.41 (9H, m, ArH), 9.18 (1H, s, NH) ppm. Anal. Calc. for C16H14N2OS: C, 68.06; H, 5.00; N, 9.92. Found: C, 67.95; H, 4.83; N, 10.12%.

4.1.2. 3-Ethyl-5-phenyl-2-(p-tolylimino)thiazolidin-4-one (8b): white solid Mp 58–60 °C; FTIR (KBr, cm1) mmax 2954, 2918, 2846, 1670, 1640, 1575, 1465, 1386, 1366, 1228, 1070, 821, 721, 690 cm1. 1 H NMR (500 MHz, CDCl3) dH: 1.41 (3H, t, J = 7.12 Hz, CH2CH3), 2.34 (3H, s, CH3–Ph), 4.1 (2H, m, CH2CH3), 5.4 (1H, s, CH), 7.30– 7.40 (9H, m, ArH) ppm. Anal. Calc. for C18H18N2OS: C, 69.65; H, 5.84; N, 9.02. Found: C, 69.74; H, 5.68; N, 9.16%.

4.1.9. 3-Cyclohexyl-2-(ethylimino)thiazolidin-4-one (8i): white solid Mp 63–66 °C; FTIR (KBr, cm1) mmax 2925, 2852, 1646, 1446, 1332, 1236, 1095, 1041, 796, 646. 1H NMR (500 MHz, CDCl3) dH: 1.10 (3H, t, J = 7.08 Hz, CH3), 1.17–1.72 (10H, m, cyclohexyl), 3.14 (1H, m, cyclohexyl CH), 3.68 (2H, q, J = 7.08 Hz, CH2), 3.71 (2H, s, CH2–S) ppm; 13C NMR (125 MHz, CDCl3) dC: 171.7 (C@O), 149.0, 61.5, 38.3, 33.9, 32.8, 26.1, 24.8, 12.7 ppm. Anal. Calc. for C11H18N2OS: C, 58.37; H, 8.01; N, 12.38. Found: C, 58.42; H, 8.21; N, 12.45%.

4.1.3. 3-Ethyl-2-(p-tolylimino)thiazolidin-4-one (8c): yellow solid Mp 43–44 °C; FTIR (KBr, cm1) mmax 3024, 2977, 2937, 1722, 1631, 1605, 1505, 1454, 1434, 1386, 1373, 1338, 1195, 1120, 900, 821, 770; 1H NMR (500 MHz, CDCl3) dH: 1.3 (3H, t, J = 7.1 Hz,

4.1.10. 2-Imino-5-p-tolylthiazolidin-4-one (8j): white solid Mp 119–121 °C; FTIR (KBr, cm1) mmax 3260, 3070, 2931, 2856, 1614, 1510, 1440, 1369, 1301, 1251, 1176, 1029, 833; 1H NMR (500 MHz, DMSO-d6) dH: 2.27 (3H, s, CH3), 5.47 (1H, s, CH), 7.13

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M. Mamaghani et al. / Ultrasonics Sonochemistry 18 (2011) 45–48

(2H, d, J = 7.9 Hz, ArH), 7.24 (2H, d, J = 7.9 Hz, ArH), 8.98 (1H, s, NH), 9.20 (1H, s, NH) ppm. Anal. Calc. for C10H10N2OS: C, 58.23; H, 4.89; N, 13.58. Found: C, 58.15; H, 4.73; N, 13.42%. 4.1.11. 2-Cyclohexylimino-3-ethylthiazolidin-4-one (9i): white solid Mp 85–87 °C; FTIR (KBr, cm1) mmax 2929, 2823, 1637, 1382, 1323, 1209, 1126, 1074, 894, 785, 696. 1H NMR (500 MHz, CDCl3) dH: 1.15 (3H, t, J = 7.0 Hz, CH3), 1.26–1.81 (10H, m, cyclohexyl CH2), 3.05 (1H, m, cyclohexyl CH), 3.82 (2H, s, CH2S), 3.75 (2H, q, J = 7.0 Hz, CH2) ppm; 13C NMR (125 MHz, CDCl3) dC: 171.6 (C@O), 148.6, 61.4, 40.2, 33.9, 32.9, 26.1, 24.7, 12.8 ppm. Anal. Calc. for C11H18N2OS: C, 58.37; H, 8.01; N, 12.38. Found: C, 58.22; H, 8.17; N, 12.23%. Acknowledgements The authors are grateful to the Research Council of University of Guilan for the financial support of this research work.

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