Synthesis and fluorescence of pyrazolines substituted with pyrimidine and ferrocene subunits

Manman Liu; Jian Zhang

doi:10.1515/hc-2015-0129

Article Open Access

Synthesis and fluorescence of pyrazolines substituted with pyrimidine and ferrocene subunits

Manman Liu and Jian Zhang

Published/Copyright: January 9, 2016

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From the journal Heterocyclic Communications Volume 22 Issue 1

Abstract

1,3,5-Trisubstituted 2-pyrazolines were synthesized by the reaction of chalcones with hydrazine in hot ethanol. Their structures were elucidated by ¹H NMR, ¹³C NMR, IR, MS and elemental analysis. The fluorescence spectra were measured in different organic solvents. The emission wavelength is blue shifted with the increase in solvent polarity.

Keywords: ferrocene; fluorescence; pyrazoline; pyrimidine; synthesis

Introduction

Pyrazoline derivatives have attracted increasing attention due to their pharmaceutical properties such as antimicrobial [1–3], antiamoebic [4, 5], antinociceptive [6], anticancer [7] and antidepressant [8] activities. In addition, because of their excellent fluorescence [9, 10], they have been widely used as fluorescent brightening agents, fluorescence chemosensors, hole-transport materials in electrophotography, as components of OLEDs and as novel fluorescent materials [11–21].

Substituted pyrimidines [22–26] are central subunits of interesting pharmacological agents, such as calcium channel modulators, α1 a-adrenergic receptor antagonists, mitotic kinesin inhibitors and hepatitis B virus replication inhibitors [27–31]. Ferrocene has been used for the preparation of small bioactive molecules due to its good biocompatibility [32–34]. Recently, ferrocene containing multichannel chemosensors with electrochemical properties have received considerable attention. In light of these data, we would like to report the synthesis, characterization and fluorescence of novel ethyl 2-(3-ferrocenyl)-5-aryl-4, 5-dihydropyrazol-1-yl)-6-methyl-5-phenylpyrimidine-4- carboxylates 6a-h (Scheme 1).

Scheme 1

Reagents, conditions and yields: (a) AlCl₃, EtOH, reflux 3 h, 78–83%; (b) HNO₃(50–60%), ice-bath 1 h, 68–79%; (c) POCl₃, EtOH, reflux, 3 h, 69–85%; (d) NH₂NH₂, EtOH, reflux 4 h, 77–85%; (e) acetic acid, Ar-CHO, EtOH, reflux 8–12 h, 75–80%.

Results and discussion

Starting compounds 1-5 were prepared by using literature procedures [35]. The desired pyrazoline derivatives 6a-h were obtained by the reaction of ferrocenyl chalcones 5 with pyrimidin-2-ylhydrazine 4 under reflux conditions in 51–82% yields. The structures of products 6a-h were characterized by spectroscopic methods and elemental analysis.

The fluorescence spectra of compounds 6a-h were recorded in chloroform, tetrahydrofuran and dichloromethane (1×10^-5m) at room temperature at the excitation wavelength of 371 nm. The emission wavelengths are from 422 nm to 434 nm. The spectra are shown in Figures 1–3. It can be concluded that different aromatic groups at C5 of the central 4,5-dihydropyrazole moiety have little influence on the emission wavelengths.

Figure 1

Fluorescence emission spectra of compounds 6a-h in CHCl₃.

Figure 2

Fluorescence emission spectra of 6a-h in THF.

Figure 3

Fluorescence emission spectra of compounds 6a-h in CH₂Cl₂.

Experimental

All chemicals were of reagent grade, purchased from commercial sources and used without further purification. Melting points were recorded on electrothermal digital melting point apparatus and were uncorrected. Aromatic aldehydes, ethyl acetoacetate, phosphorus oxychloride and hydrazine were purchased from the Alladin Chemical Company and were used without further purification. All solvents were dried using standard methods before use. ¹H NMR (400 MHz) and ¹³C NMR (100 MHz) spectra were recorded in CDCl₃ on a Bruker AVANCE III 400 instrument. IR spectra were recorded with an FTIR 1730 spectrometer. Fluorescence spectra were obtained on a Sanyo 970CRT spectrofluorometer with the excitation wavelength of 371 nm. Starting materials 1-5 were prepared by using literature procedures [36–39].

Synthesis of compounds 6a-h

To a mixture of ferrocenyl chalcone 5a-h (0.01 mol) and pyrimidine hydrazine 4 (0.012 mol) in ethanol (30 mL) was added sodium hydroxide (0.005 mol) at room temperature, and the resulting mixture was stirred at reflux for 10 h. Then the mixture was cooled to room temperature, poured into ice water and neutralized with hydrochloric acid. The resultant precipitate was filtrated, washed with water and crystallized from ethanol to afford compound 6a-h.

Ethyl 2-(3-ferrocenyl-5-(2-chlorophenyl)-4,5-dihydropyrazol-1-yl)-4-methyl-6-phenylpyrimidine-5-carboxylate (6a)

This compound was obtained as pale yellow powder in 81% yield; mp 250–251°C; ¹H NMR: δ 7.48 (d, J = 6.8 Hz, 1H, aromatic), 7.35 (d, J = 7.4 Hz, 4H, aromatic), 7.25 (d, J = 11.2 Hz, 3H, aromatic), 6.16 (dd, J = 11.9, 4.5 Hz, 1H, pyrazoline), 4.91 (s, 1H, ortho-C₅H₄), 4.61 (s, 1H, ortho-C₅H₄), 4.42 (d, J = 9.7 Hz, 2H, meta-C₅H₄), 4.13 (s, 5H, C₅H₅), 4.08 (m, 2H, methylene), 3.83 (dd, J = 16.9, 11.4 Hz, 1H, pyrazoline), 3.05 (dd, J = 17.9, 4.2 Hz, 1H, pyrazoline), 2.59 (s, 3H, methyl), 1.01 (t, J = 7.1 Hz, 3H, methyl); ¹³C NMR: δ 168.8, 167.7, 165.27, 156.7, 155.4, 155.3, 142.4, 138.8, 131.8, 129.6, 128.3, 127.7, 121.1, 116.2, 75.8, 75.8, 70.4, 70.2, 69.3, 68.0, 67.6, 61.1, 43.7, 23.4, 13.6; IR: 2982(CH, aliphatic), 1704(C=O), 1544(C=N), 1510(C=N), 1466(C=N) cm^-1; MS: m/z 605.1(M⁺+1). Anal. Calcd for C₃₃H₂₉ClFeN₄O₂: C, 65.52; H, 4.83; N, 9.26. Found: C, 65.37; H, 4.64; N, 9.06.

Ethyl 2-(3-ferrocenyl-5-(4-chlorophenyl)-4,5-dihydropyrazol-1-yl)-4-methyl-6-phenylpyrimidine-5-carboxylate (6b)

This compound was obtained as pale yellow powder in 75% yield; mp 218–219°C; ¹H NMR: δ 7.42 (s, 2H, aromatic), 7.38–7.32 (m, 6H, aromatic), 7.31 (s, 1H, aromatic), 5.73 (dd, J = 12.6, 4.4 Hz, 1H, pyrazoline), 4.90 (s, 1H, ortho-C₅H₄), 4.63 (s, 1H, ortho-C₅H₄), 4.44 (d, J = 10.1 Hz, 2H, meta-C₅H₄), 4.15 (s, 5H, C₅H₅), 4.12 – 4.05 (m, 2H, methylene), 3.77 (dd, J = 17.9, 11.9 Hz, 1H, pyrazoline), 3.11 (dd, J = 17.5, 3.7 Hz, 1H, pyrazoline), 2.58 (s, 3H, methyl), 0.99 (t, J = 7.1 Hz, 3H, methyl); ¹³C NMR: δ 168.8, 167.5, 165.3, 156.8, 155.4, 142.1, 138.6, 130.3, 129.6, 128.9, 128.3, 128.1, 127.4, 121.3, 75.9, 70.3, 70.2, 69.3, 68.0, 67.7, 61.2, 57.2, 43.9, 23.4, 13.6; IR: 2977(CH, aliphatic), 1708(C=O), 1547(C=N), 1511(C=N), 1465(C=N) cm^-1; MS: m/z 605.1(M+1). Anal. Calcd for C₃₃H₂₉ClFeN₄O₂: C, 65.52; H, 4.83; N, 9.26. Found: C, 65.45; H, 4.76; N, 9.13.

Ethyl 2-(3-ferrocenyl-5-(thiophene-2-yl)-4,5-dihydropyrazol-1-yl)-4-methyl-6-phenylpyrimidine-5-carboxylate (6c)

This compound was obtained as pale yellow powder in 71% yield; mp199–200°C. ¹H NMR: δ 7.49 (d, J = 6.9 Hz, 5H, aromatic), 7.29–7.18 (m, 1H, aromatic), 7.10 (d, J = 2.9 Hz,1H, aromatic), 7.08 – 6.91 (m, 1H, aromatic), 6.10 (dd, J = 11.4, 3.9 Hz, 1H, pyrazoline), 4.96 (s, 1H, ortho-C₅H₄), 4.59 (s, 1H, ortho-C₅H₄), 4.45 (t, J = 18.4 Hz, 2H, meta-C₅H₄), 4.12 (s, 5H, C₅H₅), 4.10 (m, 2H, methylene), 3.74 (dd, J = 17.1, 11.6 Hz, 1H, pyrazoline), 3.32 (dd, J = 17.1, 4.0 Hz, 1H, pyrazoline), 2.61 (s, 3H, methyl), 1.00 (t, J = 7.1 Hz, 3H, methyl); ¹³C NMR: δ 168.9, 167.7, 165.3, 156.9, 155.6, 146.0, 138.7, 129.6, 128.4, 128.1, 126.6, 124.5, 124.4, 116.2, 75.7, 70.4, 70.1, 69.4, 68.1, 67.5, 61.2, 57.1, 43.9, 23.4, 13.6; IR: 2987(CH, aliphatic), 1702(C=O), 1580(C=N), 1503(C=N), 1469(C=N) cm^-1; MS: m/z 577.1(M⁺+1). Anal. Calcd for C₃₁H₂₈FeN₄O₂S: C, 64.59; H, 4.90; N, 9.72. Found: C, 65.32; H, 4.72; N, 9.54.

Ethyl 2-(3-ferrocenyl-5-(4-bromophenyl)-4,5-dihydropyrazol-1-yl)-4-methyl-6-phenylpyrimidine-5-carboxylate (6d)

This compound was obtained as pale yellow powder in 86% yield; mp 198–199°C; ¹H NMR: δ 7.48 (d, J = 8.2 Hz, 2H, aromatic), 7.39 (d, J = 4.9 Hz, 1H, aromatic), 7.33 (d, J = 5.8 Hz, 3H, aromatic), 7.24 (d, J = 9.5 Hz, 3H, aromatic), 5.69 (dd, J = 12.5, 2.9 Hz, 1H, pyrazoline), 4.87 (s, 1H, ortho-C₅H₄), 4.59 (s, 1H, ortho-C₅H₄), 4.41 (d, J = 10.1 Hz, 2H, meta-C₅H₄), 4.12 (s, 5H, C₅H₅), 4.06 (m, 2H, methylene), 3.75 (dd, J = 16.9, 12.1 Hz, 1H, pyrazoline), 3.09 (dd, J = 17.4, 4.4 Hz, 1H, pyrazoline), 2.56 (s, 3H, methyl), 0.96 (t, J = 7.2 Hz, 3H, methyl); ¹³C NMR: δ 168.8, 167.6, 165.4, 156.9, 155.4, 146.1, 138.9, 129.5, 128.4, 128.1, 126.6, 124.4, 124.3, 116.4, 76.0, 70.3, 70.0, 69.4, 68.1, 67.5, 61.1, 57.1, 43.8, 23.3, 13.1; IR: 2926(CH, aliphatic), 1712(C=O), 1545(C=N), 1513(C=N), 1466(C=N) cm^-1; MS: m/z 649.1(M⁺+1). Anal. Calcd for C₃₃H₂₉BrFeN₄O₂: C, 61.04; H, 4.50; N, 8.63. Found: C, C, 60.91; H, 4.35; N, 8.41.

Ethyl 2-(3-ferrocenyl-5-phenyl-4,5-dihydropyrazol-1-yl)-4-methyl-6-phenylpyrimidine-5-carboxylate (6e)

This compound was obtained as pale yellow powder in 83% yield; mp 195–196°C; ¹H NMR: δ 7.38 (d, J = 4.3 Hz, 5H, aromatic), 7.36–7.29 (m, 5H, aromatic), 5.77 (dd, J = 11.9, 4.8 Hz, 1H, pyrazoline), 4.92 (s, 1H, ortho-C₅H₄), 4.60 (s, 1H, ortho-C₅H₄), 4.42 (d, J = 11.2 Hz, 2H, meta-C₅H₄), 4.14 (s, 5H, C₅H₅), 4.12–4.03 (m, 2H, methylene), 3.77 (dd, J = 17.1, 11.9 Hz, 1H, pyrazoline), 3.16 (dd, J = 17.0, 4.3 Hz, 1H, pyrazoline), 2.59 (s, 3H, methyl), 0.98 (t, J = 7.2 Hz, 3H, methyl); ¹³C NMR: δ 168.9, 167.7, 165.6, 156.8, 155.5, 143.3, 138.8, 129.5, 128.7, 128.3, 128.0, 127.4, 125.9, 115.9, 76.1, 70.3, 70.0, 69.3, 68.1, 67.6, 61.6, 61.1, 43.9, 23.4, 13.6; IR: 2975(CH, aliphatic), 1700(C=O), 1545(C=N), 1515(C=N), 1466(C=N) cm^-1; MS: m/z 571.1(M⁺+1). Anal. Calcd for C₃₃H₃₀FeN₄O₂: C, 69.48; H, 5.30; N, 9.82. Found: C, 69.22; H, 5.15; N, 9.64.

Ethyl 2-(3-ferrocenyl-5-(4-methylphenyl)-4,5-dihydropyrazol-1-yl)-4-methyl-6-phenylpyrimidine-5-carboxylate (6f)

This compound was obtained as pale yellow powder in 81% yield; mp 195–196°C; ¹H NMR: δ 7.37 (s, 3H, aromatic), 7.28 (d, J = 5.4 Hz, 2H, aromatic), 7.18 (d, J = 8.1 Hz, 2H, aromatic), 5.74 (dd, J = 12.4, 4.6 Hz, 1H, pyrazoline), 4.91 (s, 1H, ortho-C₅H₄), 4.60 (s, 1H, ortho-C₅H₄), 4.42 (d, J = 11.2 Hz, 2H, meta-C₅H₄), 4.15 (s, 5H, C₅H₅), 4.11–4.04 (m, 2H, methylene), 3.75 (dd, J = 17.2, 12.2 Hz, 1H, pyrazoline), 3.14 (dd, J = 17.2, 3.8 Hz, 1H, pyrazoline), 2.59 (s, 3H, methyl), 2.36 (s, 3H, methyl), 0.99 (t, J = 7.0 Hz, 3H, methyl); ¹³C NMR: δ 169.9, 167.6, 165.2, 156.8, 155.5, 140.3, 138.9, 137.0, 129.4, 129.3, 128.4, 128.0, 125.9, 115.8, 76.2, 70.3, 70.00, 69.3, 68.0, 67.6, 61.4, 61.1, 43.9, 23.4, 21.1, 13.6; IR: 1703(C=O), 1583(C=N), 1512(C=N), 1469(C=N) cm^-1; MS: m/z 585.1(M+1). Anal. Calcd for C₃₄H₃₂FeN₄O₂: C, 69.87; H, 5.52; N, 9.59. Found: C, 69.65; H, 5.31; N, 9.37.

Ethyl 2-(3-ferrocenyl-5-(4-methoxyphenyl)-4,5-dihydropyrazol-1-yl)-4-methyl-6-phenylpyrimidine-5-carboxylate (6g)

This compound was obtained as pale yellow powder in 79% yield; mp 185–186°C; ¹H NMR: δ 7.38 (s, 4H, aromatic), 7.28 (s, 4H, aromatic), 5.73 (dd, J = 10.4, 4.3 Hz, 1H, pyrazoline), 4.91 (s, 1H, ortho-C₅H₄), 4.61 (s, 1H, ortho-C₅H₄), 4.42 (d, J = 10.2 Hz, 2H, meta-C₅H₄), 4.15 (s, 5H, C₅H₅), 4.12–4.02 (m, 2H, methylene), 3.82 (s, 3H, methoxy), 3.73 (dd, J = 12.0, 3.4 Hz, 1H, pyrazoline), 3.14 (dd, J = 16.0, 4.2 Hz, 1H, pyrazoline), 2.59 (s, 3H, methyl), 0.98 (t, J = 5.8 Hz, 3H, methyl); ¹³C NMR: δ 168.9, 167.3, 166.4, 156.7, 154.8, 141.4, 140.0, 138.0, 128.3, 128.4, 128.2, 127.9, 125.0, 116.9, 76.3, 70.6, 70.0, 69.4, 68.3, 67.4, 62.1, 61.1, 55.8, 43.0, 23.4, 13.6; IR: 1713(C=O), 1584(C=N), 1512(C=N), 1467(C=N) cm^-1; MS: m/z 601.1(M+1). Anal. Calcd for C₃₄H₃₂FeN₄O₃: C, 68.01; H, 5.37; N, 9.33. Found: C, 67.88; H, 5.16; N, 9.14.

Ehyl 2-(3-ferrocenyl-5-furan-2-yl-4,5-dihydropyrazol-1-yl)-4-methyl-6-phenylpyrimidine-5-carboxylate (6h)

This compound was obtained as pale yellow powder in 79% yield; mp 105–106°C; ¹H NMR: δ 7.54 (s, 2H, aromatic), 7.41 (d, J = 19.1 Hz, 3H, aromatic), 7.28 (s, 1H, aromatic), 5.91 (dd, J = 11.2, 3.4 Hz, 1H, pyrazoline), 5.01 (s, 1H, ortho-C₅H₄), 4.55 (s, 1H, ortho-C₅H₄), 4.43 (d, J = 13.1 Hz, 2H, meta-C₅H₄), 4.23 (s, 5H, C₅H₅), 4.15–4.01 (m, 2H, methylene), 3.60 (dd, J = 17.4, 11.3 Hz, 1H, pyrazoline), 3.42 (dd, J = 17.9, 5.1 Hz, 1H, pyrazoline), 2.61 (s, 3H, methyl), 0.99 (t, J = 4.7 Hz, 3H, methyl); ¹³C NMR: δ 168.7, 167.0, 165.4, 157.9, 156.1, 146.2, 139.1, 129.6, 128.5, 128.0, 126.2, 125.3, 124.4, 117.1, 76.2, 70.7, 70.2, 69.6, 68.9, 67.6, 62.1, 56.9, 44.1, 23.6, 13.7;IR: 1715(C=O), 1630(C=N), 1511(C=N), 1468(C=N) cm^-1; MS: m/z 561.1(M+1). Anal. Calcd for C₃₁H₂₈FeN₄O₃: C, 66.44; H, 5.04; N, 10.00. Found: C, 66.21; H, 4.87; N, 9.86.

Conclusions

We have designed and synthesized a series of novel pyrazoline chromophores containing pyrimidine and ferrocene moieties which show a blue emission. This fluorescence is blue shifted with the increase of solvent polarity. The synthetic strategy is straightforward, benefits from high yield and facile purification without tedious silica gel chromatography.

Corresponding author: Jian Zhang, College of Chemistry and materials, South-Central University for Nationalities, Wuhan 430074, P. R. China, e-mail: jianzhangye@gmail.com

Acknowledgments

The authors express their thanks to the Nature Science Foundation of Hubei Province of China (No. 2012FFB07410) for financial support during this investigation.

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Received: 2015-6-1

Accepted: 2015-8-7

Published Online: 2016-1-9

Published in Print: 2016-2-1

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.

Articles in the same Issue

https://doi.org/10.1515/hc-2015-0129

Keywords for this article

ferrocene; fluorescence; pyrazoline; pyrimidine; synthesis

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