One-pot synthesis of 2-hydrazonyl-4-phenylthiazoles via [PDBMDIm]Br-catalyzed reaction under solvent-free conditions

Mohammad Nikpassand; Leila Zare Fekri; Sina Sanagou

doi:10.1515/hc-2016-0024

Artikel Open Access

One-pot synthesis of 2-hydrazonyl-4-phenylthiazoles via [PDBMDIm]Br-catalyzed reaction under solvent-free conditions

Mohammad Nikpassand , Leila Zare Fekri und Sina Sanagou

Veröffentlicht/Copyright: 27. Juli 2016

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Abstract

A clean and environmentally benign route for the preparation of substituted thiazoles 4a–k via a three component reaction of an aldehyde, thiosemicarbazide and a bromoacetophenone in the presence of 3,3′-(pentane-1,5-diyl)bis(1,2-dimethyl-1H-imidazol-3-ium) bromide is reported. The present methodology offers several advantages such as solvent-free conditions, excellent yields, simple procedure, mild conditions and reduced environmental consequences. The ionic liquid can be recovered and reused. All synthesized compounds were characterized by IR, NMR and elemental analysis.

Keywords: benzothiazole; bromoacetophenone; one-pot reaction; thiosemicarbazide

Introduction

Thiazoles are widely found in medicinal and biochemical compounds. They exhibit various biological activities such as antimicrobial [1], [2], [3], [4], anti-HIV [5] antifungal [6], anticancer [7], [8], [9], anthelmintic [10], antiviral [11], anti-diabetic [12] activities. In particular, 2-arylbenzothiazoles have received much attention in medicinal chemistry [13], [14], [15].

Numerous methods have been reported in the literature for the synthesis of thiazoles. Condensation of 2-aminothiophenols with aldehydes [16], [17], with carboxylic acids [18], [19], with esters [18], [20] or with acid chlorides [21], [22], and Jacobson’s cyclization of thiobenzanilides are the main methods [23], [24]. In this paper we present a new synthetic route to substituted thiazoles 4a–k that is conducted in the presence of an ionic liquid [PDBMDIm]Br (Figure 1). Ionic liquids lack flammability, are easy to recycle, and possess effectively no vapor pressure [25], [26], [27], [28], [29].

Figure 1

Structure of ionic liquid [PDBMDIm]Br.

Results and discussion

In continuation of our studies on the development of efficient and eco-friendly procedures for the synthesis of heterocyclic compounds [30], [31], [32], [33] we now report the synthesis of novel 2-hydrazonyl-4-phenylthiazoles that is conducted in the presence of ionic liquid [PDBMDIm]Br (Figure 1) under solvent-free conditions at room temperature (Scheme 1).

Scheme 1

Synthesis of 2-hydrazonyl-4-phenylthiazoles 4a–k.

For comparison, a model reaction between aldehyde 1a, 2-hydroxyacetophenone and thiosemicarbazide in the presence of a catalytic amount of HCl, SiO₂, montmorillonite K10,montmorillonite KSF, Fe₃O₄, ZnCl₂ or an ionic liquid including [BMIM]Br, [BMIM]OH and [PDBMDIm]Br was carried out. The reaction conducted in the presence of [PDBMDIm]Br furnished the highest yield of the product 4a in a relatively short period of time. Lower yields were obtained in the presence of mono ionic liquid [BMIM]Br or [BMIM]OH and all reactions conducted in the presence of the remaining catalysts were quite inefficient. The optimized amount of the catalyst [PDBMDIm]Br is 0.04 mmol per 1 mmol of aldehyde. The bis ionic liquid is easily separated from the reaction mixture by washing with water. The recovered catalyst can be distilled under reduced pressure for reuse in subsequent reactions. Our experiments showed that after five successive runs there was no loss of efficiency of the recycled ionic liquid with regard to reaction time and yield.

The use of substituted pyrazolecarbaldehydes 1 and bromoacetophenones 3 containing either electron withdrawing groups (such as halide or nitro) or electron releasing groups (such as hydroxyl or alkoxyl) furnished the corresponding 2-hydrazonyl-4-phenylthiazoles 4 with the yields ranging from 85% to 96%. All products are assumed to have E-configuration.

Conclusions

A simple, convenient and efficient protocol for the synthesis of 2-hydrazonyl-4-phenylthiazoles using [PDBMDIm]Br as a catalyst was developed. Good yields of the products, short reaction times, simplicity, easy workup, together with the use of an inexpensive, environmentally friendly and reusable catalyst, are the notable features of this catalytic procedure.

Experimental

Melting points were measured on an Electrothermal 9100 apparatus. Melting points were measured on an Electro-thermal 9100 apparatus and are uncorrected. ¹H NMR (500 MHz) and ¹³C NMR (125 MHz) spectra were obtained on a Bruker DRX 500 Avance spectrometer in CDCl₃ as solvent and with TMS as internal standard. FT-IR spectra were recorded in KBr pellets on a Shimadzu FT-IR-8400S spectrometer. Microwave irradiation was performed using a microwave oven model LG, 4280MCR. Elemental analyses were recorded on a Carlo-Erba EA1110CNNO-S analyzer. An ultrasound apparatus TECNO-GAZ Astra 3D operating at 45 kHz was used.

Synthesis of 3,3′-(pentane-1,5-diyl)bis(1,2-dimethyl-1H-imidazol-3-ium)bromide, [PDBMDIm]Br

A mixture of 1,2-dimethylimidazole (20 mmol, 2.0 g) and 1,5-dibromopentane (10 mmol, 1.8 mL) was stirred under a gentle reflux for 2 h. After cooling to room temperature, the residue was washed with diethyl ether (3×10 mL) and the ether was discarded. The remaining material formed two liquid phases. The ionic liquid was separated using the separator funnel and the remaining solvent in the ionic liquid was removed at 80°C. Finally, the yellow viscous ionic liquid was produced: yield 97%; IR: ν_max 1639, 1695, 1367 cm^-1; ¹³C NMR: δ 23.2, 41.0, 42.1, 52.2, 56.1, 127.7, 129.2, 132.2. Anal. Calcd for C₁₅H₂₆Br₂N₄: C, 42.67; H, 6.21; N, 13.27. Found: C, 42.54; H, 6.32; N, 13.32.

General procedure for the synthesis of 2-hydrazonyl-4-phenylthiazoles 4a–k

A mixture of a pyrazolecarbaldehyde 1 (2.0 mmol), thiosemicarbazide 2 (2.1 mmol), a bromoacetophenone 3 (2.0 mmol) and [PDBMDIm]Br (0.04 mmol) was stirred at room temperature for the period of time indicated below. After completion of reaction, as indicated by TLC analysis, the ionic liquid was removed from the mixture by extraction with water (2×15 mL). The aqueous extract was concentrated under reduced pressure, washed with diethyl ether, and concentrated under reduced pressure to recover the ionic liquid. The residue of 4a–k was kept at 80°C under reduced pressure to remove traces of water and ether and then crystallized from ethanol.

(E)-2-(2-(2-((1-Phenyl-3-p-tolyl-1H-pyrazol-4-yl)methylene)hydrazinyl)thiazol-4-yl)phenol (4a)

Reaction time 60 min; yield 96% of yellow solid; mp 220–222°C; IR: 3573, 3386, 1595, 1537, 1504, 1365 cm^-1; ¹HNMR: δ 7.32 (d, 2H, J = 8.0 Hz), 7.36–7.40 (m, 2H), 7.53–7.58 (m, 5H), 7.63 (d, 1H, J = 8.0 Hz), 7.80 (d, J = 2.0 Hz, 1H), 7.88 (d, J = 8.0 Hz, 2H), 8.0 (d, 1H, J = 7.6 Hz), 8.21 (s, 1H), 8.26 (s, 1H), 8.68 (s, 1H), 9.14 (s, 1H), 9.18 (s, 1H); ¹³C NMR: δ 21.3, 116.8, 117.6, 118.9, 119.3, 127.4, 127.6, 128.0, 128.4, 128.9, 129.4, 129.7, 129.9, 130.1, 135.4, 138.5, 138.7, 139.4, 139.5, 151.8, 153.3, 154.0, 177.9. Anal. Calcd for C₂₆H₂₁N₅OS: C, 69.16; H, 4.69; N, 15.51. Found: C, 69.19; H, 4.72; N, 15.49.

(E)-4-Phenyl-2-(2-((1-phenyl-3-p-tolyl-1H-pyrazol-4-yl)methylene)hydrazinyl)thiazole (4b)

Reaction time 75 min; yield 90% of yellow solid; mp 249–251°C; IR: 1668, 1596, 1533, 1502 cm^-1; ¹H NMR: δ 2.39 (s, 3H), 7.32–7.41 (m, 4H), 7.53–7.59 (m, 4H), 7.64 (d, 2H, J = 8.0 Hz), 7.79 (m, 1H), 7.88 (d, 1H, J = 8.0 Hz), 7.90 (d, 2H, J = 8.0 Hz), 8.22 (s, 1H), 8.68 (s, 1H), 9.13 (s, 1H), 9.17 (s, 1H); ¹³C NMR: δ 20.8, 116.3, 118.4, 118.8, 119.2, 126.8, 127.1, 127.5, 127.9, 128.5, 128.9, 129.6, 129.6, 129.6, 135.0, 138.2, 139.0, 152.8, 153.4, 184.6. Anal. Calcd for C₂₆H₂₁N₅S: C, 71.70; H, 4.86; N, 16.08. Found: C, 71.68; H, 4.83; N, 16.10.

(E)-4-(2-Bromophenyl)-2-(2-((1-phenyl-3-p-tolyl-1H-pyrazol-4-yl)methylene)hydrazinyl) thiazole (4c)

Reaction time 60 min; yield 95% of white solid; mp 259–260°C; IR: 3272, 1622, 1539, 1496 cm^-1; ¹H NMR: δ 2.40 (s, 3H), 7.30–7.43 (m, 6H), 7.54 (t, 1H, J = 8.4 Hz), 7.68 (d, 2H, J = 8.0 Hz), 7.86 (dd, 2H, J = 8.0 Hz, 1.6 Hz), 8.2 (s, 1H), 8.88 (s, 1H), 11.99 (s, 1H); ¹³C NMR: δ 21.4, 104.0, 117.3, 119.2, 126.0, 127.3, 128.0, 128.1, 128.8, 129.1, 129.6, 129.8, 130.0, 134.8, 135.90, 138.4, 139.5, 150.2, 151.4, 168.56. Anal. Calcd for C₂₆H₂₀BrN₅S: C, 60.70; H, 3.92; N, 13.61. Found: C, 60.69; H, 3.95; N, 13.57.

(E)-4-(2-Bromophenyl)-2-(2-((3-(4-chlorophenyl)-1-phenyl-1H-pyrazol-4-yl)methylene)hydrazinyl)thiazole (4d)

Reaction time 75 min; yield 92% of orange solid; mp 265–267°C; IR: 3239, 1618, 1528, 1531 cm^-1; ¹H NMR: δ 7.30–7.32 (m, 1H), 7.36–7.43 (m, 3H), 7.55 (d, 2H, J = 8.4 Hz), 7.57–7.60 (m, 2H), 7.85 (dd, 2H, J = 7.2 Hz, 1.6 Hz), 7.88 (dd, 2H, J = 8.0 Hz, 2.0 Hz), 7.97 (dd, 2H, J = 8.4 Hz, 1.2 Hz), 8.19 (s, 1H); ¹³C NMR: δ 104.0, 117.5, 119.2, 126.0, 127.5, 128.1, 129.0, 129.2, 130.1, 130.8, 131.7, 133.7, 134.9, 135.3, 139.4, 149.9, 168.4. Anal. Calcd for C₂₅H₁₇BrClN₅S: C, 56.14; H, 3.20; N, 13.09. Found: C, 56.16; H, 3.22; N, 13.12.

(E)-2-(2-((3-(4-Chlorophenyl)-1-phenyl-1H-pyrazol-4-yl)methylene)hydrazinyl)-4-(3-methoxyphenyl)thiazole (4e)

Reaction time 90 min; yield 91% of yellow solid; mp 232–234°C; IR: 3280, 1600, 1542, 1504, 1371 cm^-1; ¹H NMR: δ 3.45 (s, 3H), 7.39 (t, J = 7.2 Hz, 1H), 7.55–7.59 (m, 6H), 7.70–7.73 (m, 3H), 7.77 (s, 1H), 7.91 (d, 2H, J = 7.6 Hz), 8.19 (s, 1H), 8.21 (s, 1H), 8.26 (s, 1H), 11.32 (s, 1H); ¹³C NMR: δ 117.1, 118.8, 127.4, 128.4, 129.3, 130.4, 130.3, 131.9, 134.1, 135.2, 138.6, 151.2, 178.7. Anal. Calcd for C₂₆H₂₀ClN₅OS: C, 64.26; H, 4.15; N, 14.41. Found: C, 64.26; H, 4.17; N, 14.37.

(E)-2-(2-((3-(4-Chlorophenyl)-1-phenyl-1H-pyrazol-4-yl)methylene)hydrazinyl)-4-(3-nitrophenyl)thiazole (4f)

Reaction time 60 min; yield 95% of yellow solid; mp 232–234°C; IR: 3440, 3320, 1600, 1500, 1545, 1372 cm^-1; ¹H NMR: δ 7.36 (t, 1H, J = 7.2 Hz), 7.55–7.60 (m, 6H), 7.70–7.73 (m, 3H), 7.78 (s, 1H), 7.89 (dd, 2H, J = 8.4 Hz, 1.2 Hz), 8.21 (s, 1H), 8.27 (s, 1H), 9.20 (s, 1H), 11.33 (s, 1H); ¹³C NMR: δ 117.8, 119.0, 127.6, 128.4, 129.3, 130.2, 130.3, 131.6, 133.8, 135.1, 139.4, 150.6, 178.1. Anal. Calcd for C₂₅H₁₇ClN₆O₂S: C, 59.94; H, 3.42; N, 16.78. Found: C, 59.95; H, 3.44; N, 16.80.

(E)-2-(2-(2-((3-(4-Chlorophenyl)-1-phenyl-1H-pyrazol-4-yl)methylene)hydrazinyl)thiazol-4-yl)phenol (4g)

Reaction time 90 min; yield 87% of yellow solid; mp 274–276°C; IR: 3442, 3330, 3180, 1600, 1542, 1508 cm^-1; ¹H NMR: δ 7.39 (t, 1H, J = 7.2 Hz), 7.55–7.60 (m, 7H), 7.70–7.73 (m, 3H), 7.78 (s, 1H), 7.89 (dd, 2H, J = 8.4 Hz, 1.2 Hz), 8.21 (s, 1H), 8.27 (s, 1H), 9.19 (s, 1H), 11.33 (s, 1H); ¹³C NMR: δ 117.8, 119.0, 127.6, 128.4, 129.3, 130.2, 130.3, 131.4, 133.8, 135.1, 139.4, 150.6, 178.1. Anal. Calcd for C₂₅H₁₈ClN₅OS: C, 63.62; H, 3.84; N, 14.84. Found: C, 63.59; H, 3.86; N, 14.81.

(E)-4-(4-Chlorophenyl)-2-(2-((3-(4-chlorophenyl)-1-phenyl-1H-pyrazol-4-yl)methylene) hydrazinyl)thiazole (4h)

Reaction time 120 min; yield 88% of yellow solid; mp 248–250°C; IR: 3440, 3330, 1600, 1541, 1500 cm^-1; ¹H NMR: δ 7.39 (t, 1H, J = 7.2 Hz), 7.55–7.59 (m, 7H), 7.71 (d, 2H, J = 8.4 Hz), 7.76 (s, 1H), 7.89 (d, 2H, J = 7.6 Hz), 8.21 (s, 1H), 8.24 (s, 1H), 9.18 (s, 1H), 11.3 (s, 1H); ¹³C NMR: δ 117.8, 119.0, 127.6, 128.4, 129.3, 130.2, 130.3, 131.4, 133.8, 135.2, 139.4, 150.6, 178.0. Anal. Calcd for C₂₅H₁₇Cl₂N₅S: C, 61.23; H, 3.49; N, 14.28. Found: C, 61.19; H, 3.51; N, 14.29.

(E)-4-(2-Bromophenyl)-2-(2-((1,3-diphenyl-1H-pyrazol-4-yl)methylene)hydrazinyl)thiazole (4i)

Reaction time 120 min; yield 85% of yellow solid; mp 226–228°C; IR: 3431, 1695, 1573, 1498 cm^-1; ¹H NMR: δ 7.29 (s, 1H), 7.38–7.42 (m, 3H), 7.48–7.57 (m, 5H), 7.79 (dd, 2H, J = 6.8 Hz, J = 1.6 Hz), 7.85 (m, 2H), 7.99 (m, 2H), 8.18 (s, 1H), 8.88 (s, 1H), 11.93 (s, 1H); ¹³CNMR: δ 103.9, 117.4, 119.2, 119.6, 126.0, 127.3, 128.0, 128.1, 128.9, 129.0, 129.4, 129.5, 130.1, 130.2, 130.9, 132.8, 135.1, 135.2, 139.5, 151.3, 168.4. Anal. Calcd for C₂₅H₁₈BrN₅S: C, 60.00; H, 3.63; N, 14.00. Found: C, 60.01; H, 3.65; N, 14.03.

(E)-4-(4-((2-(4-(2-Bromophenyl)thiazol-2-yl)hydrazono)methyl)-1-phenyl-1H-pyrazol-3-yl)phenol (4j)

Sixty minutes, 96% of yellow solid; mp 192–194°C; IR: 3418, 3215, 1607, 1534, 1246 cm^-1; ¹H NMR: δ 6.92 (m, 2H), 7.31 (s, 1H), 7.36–7.49 (m, 3H), 7.52–7.67 (m, 4H), 7.70 (d, 1H, J = 7.6 Hz), 7.84 (d, 1H, J = 7.6 Hz), 7.94–8.02 (m, 2H), 8.15 (s, 1H), 8.30 (d, 1H, J = 8.0 Hz), 8.83 (d, 1H, J = 8.4 Hz), 9.72 (s, 1H), 11.93 (s, 1H); ¹³C NMR: δ 115.8, 119.0, 119.5, 122.5, 123.5, 123.0, 127.2, 127.9, 129.0, 129.5, 130.0, 130.2, 130.2, 130.8, 134.9, 135.5, 158.5, 168.4. Anal. Calcd for C₂₅H₁₈BrN₅OS: C, 58.14; H, 3.51; N, 13.56. Found: C, 58.16; H, 3.53; N, 13.59.

(E)-4-(2-(2-((3-(4-Hydroxyphenyl)-1-phenyl-1H-pyrazol-4-yl)methylene)hydrazinyl)thiazol-4-yl)phenol (4k)

Reaction time 120 min; yield 86% of yellow solid; mp 223–225°C; IR: 3385, 3192, 1592, 1532, 1341; ¹H NMR: δ 7.42 (t, 1H, J = 7.8 Hz), 7.53–7.61 (m, 7H), 7.69- 7.78 (m, 3H), 7.91 (d, 2H, J = 7.8 Hz), 8.26 (s, 1H), 8.21 (s, 1H), 9.41 (s, 1H), 9.63 (s, 1H), 11.42 (s, 1H); ¹³C NMR: δ 118.3, 119.6, 127.4, 128.7, 129.5, 130.5, 130.7, 131.6, 133.9, 135.4, 139.0, 151.3, 178.2. Anal. Calcd for C₂₅H₁₉N₅O₂S: C, 66.21; H, 4.22; N, 15.44. Found: C, 66.18; H, 4.23; N, 15.45.

Acknowledgments

We gratefully acknowledge financial support from the Islamic Azad University, Rasht Branch, Iran.

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Received: 2016-3-17

Accepted: 2016-5-23

Published Online: 2016-7-27

Published in Print: 2016-8-1

This article is distributed under the terms of the Creative Commons Attribution Non-Commercial License, which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Artikel in diesem Heft

https://doi.org/10.1515/hc-2016-0024

Schlagwörter für diesen Artikel

benzothiazole; bromoacetophenone; one-pot reaction; thiosemicarbazide

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