ZrOCl2·SiO2-catalyzed synthesis of bis(indoles) via conjugate addition of indole with electron-deficient alkenes in water
-
Tayebeh Jari
und
Zohreh Kheilkordi
Abstract
This report provides a description of an efficient and environmentally benign procedure for the synthesis of bis(indole) derivatives via reaction of indole with electron-deficient alkenes. The remarkable advantages of this method for obtaining bis(indoles) are the simplicity of the experimental procedure, short reaction times, and high yields with the green aspects by avoiding toxic catalysts and solvents.
Introduction
Michael addition is one of the most important reactions for the construction of carbon-carbon bonds in organic reactions [1, 2]. Among the Michael acceptors, (arylmethylidene)malononitriles are attractive because nitrile moiety is an electron-withdrawing group that can be readily transformed into a range of different functionalities.
Bis(indole) derivatives have received much attention because of their synthetic as well as biological applications [3, 4]. The synthesis of this important class of nitrogen heterocycles has been reported via condensation reactions of indole with different carbonyl compounds. A variety of reagents such as I2 [5, 6], hexamethylenetetramine-bromine [7], ZrOCl2 [8], p-toluenesulfonic acid [9], [bnmim][HSO4] [10], NH4Cl [11], AlPW12O40 [12], TPA-ZrO2 [13], Zr(DS)4 [14], ZrCl4 [15], trichloro-1,3,5-triazine [16], ZrOCl2 silica gel [17], and N-bromosuccinimide [18] have been used to accomplish this transformation. Aqueous phase organic synthesis has attracted the attention of chemists as it overcomes the harmful effects associated with the organic solvents and is environmentally benign [19].
In recent years, zirconium salts have been used as catalysts in organic synthesis because these solid acids are relatively nontoxic, easy to handle, inexpensive, and possess good stability [20–23]. Among these, ZrOCl2 has been reported to be an efficient catalyst for many important organic transformations [24–29]. In continuation of our previous work on the development of new synthetic methodologies [30, 31], we report the synthesis of bis(indole) derivatives via reaction of indole with electron-deficient alkenes in the presence of ZrOCl2·SiO2 in H2O under reflux conditions (Scheme 1).
Results and discussion
For optimizing the experimental conditions, the reaction between 1 and 2a was used as a model reaction. To find the best catalyst, several Lewis acids such as ZrCl4, Ni(NO3)2, ZrOCl2, P2O5, Cu(I)Cl, and Cu(OAc)2 were used. The highest yield was achieved with ZrOCl2. The formation of the product was more facile and proceeded in shorter time when the reaction was performed in the presence of ZrOCl2·SiO2. Similar reactions were then attempted in the presence of 10, 15, 20, and 25 mol% of ZrOCl2·SiO2. The results show that the use of 20 mol% of ZrOCl2·SiO2 at reflux in water is sufficient. Greater amounts of the catalyst had no significant influence on the reaction yield. To find the optimum temperature, the reaction was conducted with 20 mol% of ZrOCl2·SiO2 at room temperature, 60°C, and at reflux, which resulted in the isolation of product in a trace amount, 70 and 92% yields, respectively. In addition, CH2Cl2, CHCl3, MeCN, and AcOEt were also tested as solvents. In all these cases, product 3a was formed in lower yields. Solvent-free conditions at different temperatures did not accelerate the reaction. Thus, the reaction is optimally conducted in the presence of 20 mol% of ZrOCl2·SiO2 under reflux conditions.
Bis(indole) derivatives 3a-g were synthesized under the optimized conditions. It can be observed that the process tolerates both electron-donating and electron-withdrawing substituent R1 in the substrates 2a-k. In all cases, the reactions proceed efficiently at reflux in water under mild conditions to afford the corresponding products in high yields. All products were characterized by IR, 1H-and 13C-NMR spectra, and elemental analysis.
Under the optimized conditions, the treatment of (pyridylmethylene)malononitriles (2h and 2i) and ethyl (pyridyl)acrylates (2j and 2k) with indole does not yield bis(indole derivatives. These reactions proceed smoothly, but the products contain only one indole moiety in the molecule. Changes in a molar ratio of the substrates (1:2=1:0.5 or 1:1) do not affect the final structural outcome.
Conclusion
Depending on the structure of electron-deficient alkenes, their addition reactions with indole in the presence of ZrOCl2·SiO2 give rise to bis(indole) or mono-indole adducts.
Experimental
Melting points were determined on a Büchi melting point B-540 B.V.CHI apparatus in open capillaries and are uncorrected. IR spectra were recorded in KBr pellets on a Bruker Eqinox 55 spectrometer. 1H- and 13C-NMR spectra were obtained in CDCl3 on a BrukerAvance 500 MHz spectrometer. Elemental analyses were conducted with a Costech ECS 4010 CHN analyzer. Column chromatography was performed on silica gel (230–400) mesh. Analytical thin-layer chromatography (TLC) was performed on precoated plastic sheets of silica gel G/UV-254 of 0.2 mm thickness. The catalyst ZrOCl2·SiO2 was prepared as previously reported [32].
General procedure for the synthesis of bis(indole) compounds 3a–g and mono adducts 3h–k
A mixture of indole (1, 1 mmol), an electron-deficient alkene [(2a-g, 0.5 mmol) or (2h-k, 1 mmol)], and the catalyst ZrOCl2·SiO2 (20 mol%) in water (8 mL) was heated under reflux until the reaction was completed, as monitored by TLC. After cooling, the mixture was filtered and the filtrate was concentrated. The residue was subjected to column chromatography eluting with chloroform/n-hexane, 9:1.
2-[Di(1H-indol-3-yl)(phenyl)methyl]malononitrile (3a)
Yield 92%; red crystals; mp 89–90°C; IR: 3409, 3050, 2923, 2259, 1619, 1455 cm-1; 1H-NMR: δ 5.94 (s, 1H, CH), 6.67 (s, 2H, CH), 7.07 (t, J = 6.4 Hz, 2H, ArH), 7.23 (t, J = 6.4 Hz, 2H, ArH), 7.27–7.35 (m, 7H, ArH), 7. 45 (d, J = 6.9 Hz, 2H, ArH), 7.88 (s, 2H, NH); 13C-NMR: δ 27.7, 40.6, 111.4, 112.6, 119.6, 120.1, 120.3, 122.3, 124.0, 126.5, 127.5, 128.6, 129.1, 137.1, 144.4. Anal. Calcd for C26H18N 4: C, 80.81; H, 4.69; N, 14.50. Found: C, 80.51; H, 4.49; N, 14.20.
2-[Di(1H-indol-3-yl)(4-nitrophenyl)methyl]malononitrile (3b)
Yield 90%; yellow crystals; mp 243–245°C; IR: 3422, 3047, 2923, 2263, 1592, 1504, 1453, 1339 cm-1; 1H-NMR: δ 5.93 (s, 1H, CH), 6.64 (s, 2H, CH), 6.92 (t, J = 7.4 Hz, 2H, ArH), 7.09 (t, J = 7.4 Hz, 2H, ArH), 7.26 (d, J = 7.9 Hz, 2H, ArH), 7.34 (d, J = 8.1 Hz, 2H, ArH), 7.46 (d, J = 8.3 Hz, 2H, ArH), 8.15 (d, J = 8.3 Hz, 2H, ArH), 9.45 (s, 2H, NH); 13C-NMR: δ 32.0, 45.9, 111.0, 113.0, 113.8, 117.2, 119.8, 120.1, 122.0, 123.8, 124.0, 128.0, 132.4, 148.0, 149.1. Anal. Calcd for C26H17N5O2: C, 72.38; H, 3.97; N, 16.23. Found: C, 72.15; H, 3.65; N, 16.43.
2-[(4-Fluorophenyl)di(1H-indol-3-yl)methyl]malononitrile (3c)
Yield 86%; pink crystals; mp 132–135°C; IR: 3408, 3052, 2923, 2252, 1601, 1416, 1217, 743 cm-1; 1H-NMR: δ 5.90 (s, H, CH), 6.33 (s, 2H, CH), 7.00 (m, 2H, ArH), 7.19–7.27 (m, 4H, ArH), 7.30 (m, 2H, ArH), 7.80 (d, J = 8.1 Hz, 2H, ArH), 8.00 (d, J = 7.9 Hz, 2H, ArH), 9.30 (s, 2H, NH); 13C-NMR: δ 39.9, 48.0, 112.0, 112.8, 113.0, 116.0, 119.0, 120.7, 121.2, 123.8, 128.4, 131.1, 136.8, 138.0, 159.1. Anal. Calcd for C26H17N4F: C, 77.21; H, 4.24; N, 13.58. Found: C, 77.00; H, 4.60; N, 13.44.
2-[(4-Chlorophenyl)di(1H-indol-3-yl)methyl]malononitrile (3d)
Yield 85%; viscous oil; IR: 3411, 3070, 2923, 2257, 1616, 1470, 744 cm-1; 1H-NMR: δ 5.89 (s, 1H, CH), 6.66 (s, 2H, CH), 6.93–7.04 (m, 4H, ArH), 7.21 (d, 2H, J = 8.0 Hz, ArH,), 7.44 (d, 2H, J = 7.3 Hz, ArH), 7.80 (d, 2H, J = 8.0 Hz, ArH), 8.00 (d, J = 7.3 Hz, 2H, ArH), 8.60 (s, 2H, NH); 13C-NMR: δ 37.6, 50.0, 112.1, 113.2, 113.8, 118.5, 120.1, 121.5, 121.7, 125.5, 128.3, 130.1, 131.9, 138.1, 140.0. Anal. Calcd for C26H17N4Cl: C, 74.19; H, 4.07; N, 13.31. Found: C, 74.42; H, 4.28; N, 13.55.
2[(3,4-Dimethoxyphenyl)di(1H-indol-3-yl)methyl]malononitrile (3e)
Yield 81%; light yellow crystals; mp 168–169°C; IR: 3309, 3055, 2926, 2250, 1593, 1580, 1455 cm-1; 1H-NMR: δ 3.80 (s, 3 H, CH3), 3.89 (s, 3H, CH3), 5.88 (s, 1H, CH), 6.67 (d, J = 1.8 Hz, 1H, ArH), 6.71 ( s, 2H, CH), 6.81 (d, J = 8.2 Hz, 1H, ArH), 6.88 (dd, J1 = 8.2 Hz, J2 = 1.8 Hz, 1H, ArH), 7.05 (t, J = 7.5 Hz, 2H, ArH), 7.21 (t, J = 7.5 Hz, 2H, ArH), 7.4 (d, J = 8.0 Hz, 2H, ArH), 7.45 (d, J = 8.0 Hz, 2H, ArH), 7.96 (s, 2H, NH); 13C-NMR: δ 38.0, 50.0, 57.3, 57.4, 110.0, 112.0, 112.8, 115.0, 117.7, 119.7, 120.0, 122.0, 123.01, 123.7, 128.7, 133.0, 136.5, 148.0, 150.0. Anal. Calcd for C28H22N4O2: C, 75.32; H, 4.97; N, 12.55. Found: C, 75.52; H, 4.63; N, 12.22.
2-[(4-Hydroxyphenyl)di(1H-indol-3-yl)methelyl]malononitrile (3f)
Yield 80%; red crystals; mp 87–88°C; IR: 3407, 3055, 2922, 2273, 1611, 1509, 1455 cm-1; 1H-NMR: δ 5.30 (s, 1H, OH), 5.40 (s, 1H, CH), 6.67 (s, 2H, NH), 6.80 (d, J = 8.2 Hz, 2H, ArH), 7.00 (m, 2H, ArH), 7.14 (d, J = 7.9 Hz, 2H, ArH), 7.60 (m, 2H, ArH), 7.90 (d, J = 8.2 Hz, 2H, ArH), 7.97 (d, J = 8.2 Hz, 2H, ArH), 8.30 (s, 2H, NH); 13C-NMR: δ 39.0, 49.1, 111.2, 113.0, 116.1, 119.6, 121.1, 123.0, 128.2, 129.0, 129.3, 132.7, 136.5, 138.1, 155.5. Anal. Calcd for C26H18N4O: C, 77.59; H, 4.51; N, 13.92. Found: C, 77.65; H, 4.71; N, 13.62.
2-[Di(1H-indol-3-yl)(p-tolyl)methyl]malononitrile (3g)
Yield 82%; red crystals; mp 174–176°C; IR: 3380, 3030, 2923, 2267, 1610, 1475 cm-1; 1H-NMR: δ 2.54 (s, 3H, CH3), 5.32 (s, 1H, CH), 6.80 (s, 2H, CH), 7.00–7.25 (m, 4H, ArH), 7.35 (d, J = 7.3 Hz, 2H, ArH), 7. 49 (d, J = 8.1 Hz, 2H, ArH), 7.65 (d, J = 7.3, 2H, ArH), 7. 95 (d, J = 8.1 Hz, 2H, ArH), 8.93 (s, 2H, NH); 13C-NMR: δ 21.4, 37.8, 55.7, 112.6, 113.4, 119.6, 120.1, 120.9, 122.3, 124.0, 126.5, 127.5, 128.6, 129.1, 137.1, 144.4. Anal. Calcd for C27H20N 4: C, 80.98; H, 5.03; N, 13.99. Found: C, 80.71; H, 4.69; N, 14.20.
2-[(1H-Indol-3-yl)(pyridine-3-yl)methyl]malononitrile (3h)
Yield 92%; white crystals; mp 159–161°C; IR: 3407, 3075, 2902, 2258, 1618, 1494; 1H-NMR: δ 4.80 (d, J = 6.9 Hz, 1H, CH), 5.00 (d, J = 6.9 Hz, 1H, CH), 7.50–7.90 (m, 7H, ArH), 8.42 (s, 1H, CH), 8.61 (s, 1H, CH), 10.37 (s, 1H, NH); 13C-NMR: δ 29.5, 42.1, 110.9, 112.2, 112.9, 116.1, 118.6, 120.0, 122.8, 124.0, 127.9, 134.1, 136.1, 136.9, 141.4, 156.1, 165.7. Anal. Calcd for C17H12N4: C, 74.98; H, 4.44; N, 20.58. Found: C, 74.55; H, 4.61; N, 20.55.
2-[(1H-Indol-3-yl)(pyridine-4-yl)methyl]malononitrile (3i)
Yield 91%; white crystals; mp 165–166°C; IR: 3402, 3050, 2930, 2269, 1605, 1472 cm-1; 1H-NMR: δ 4.80 (d, J = 6.9 Hz, 1H, CH), 4.50 (d, J = 6.9 Hz, 1H, CH), 7.10 (s, 1H, ArH), 7.10–7.30 (m, 4H, ArH), 7.28 (d, J = 7.7 Hz, 2H, ArH), 8.61 (d, J = 7.7 Hz, 2H, ArH), 9.37 (s, 1H, NH); 13C-NMR: δ 49.5, 62.1, 110.9, 112.9, 116.1, 118.6, 119.8, 120.7, 123.3, 124.0, 127.3, 134.1, 136.9, 155.0, 163.1. Anal. Calcd for C17H12N4: C, 74.98; H, 4.44; N, 20.58. Found: C, 74.65; H, 4.61; N, 20.65.
Ethyl 2-cyano-3-(1H-indol-3-yl)-3-(pyridine-3-yl)propanoate (3j)
Yield 87%; light pink crystals; mp 147–148°C; IR: 3411, 3040, 2980, 2252, 1732, 1260 cm-1; 1H-NMR: δ 1.06 (t, J = 7.1 Hz, 3H, CH3), 4.08 (q, J = 7.1 Hz, 2H, CH2), 4.34 (d, J = 6.1 Hz, 1H, CH), 5.01 (d, J = 6.1 Hz, 1H, CH), 6.80–7.90 (m, 7H, ArH), 8.45 (d, J = 3.9 Hz, 1H, CH), 8.63 (s, 1H, CH), 10.04 (s, 1H, NH); 13C-NMR: δ 14.1, 38.0, 40.8, 63.4, 111.1, 112.9, 116.1, 118.6, 119.9, 122.1, 122.6, 123.0, 124.0, 133.2, 135.29, 136.9, 148.2, 149.9, 165.2. Anal. Calcd for C19H17N3O2: C, 71.46; H, 5.37; N, 13.16. Found: C, 71.16; H, 5.67; N, 13.36.
Ethyl 2-cyano-3-(1H-indol-3-yl)-3-(pyridine-4-yl)propanoate (3k)
Yield 85%; viscous oil; IR: 3402, 3060, 2981, 2250, 1741, 1599, 1458 cm-1; 1H-NMR: δ 1.06 (t, J = 7.1 Hz, 3H, CH3), 4.08 (q, J = 7.1 Hz, 2H, CH2), 4.34 (d, J = 6.2 Hz, 1H, CH), 5.01 (d, J = 6.1 Hz, 1H, CH), 7.18 (m, 4H, ArH), 7.28 (d, J = 8.0 Hz, 2H), 8.46 (d, J = 8.0 Hz, 2H, ArH), 8.63 (s, 1H, CH), 10.04 (s, 1H, NH); 13C-NMR: δ 14.1, 38.1, 40.1, 63.4, 112.0, 117.4, 120.9, 121.7, 122.6, 123.2, 124.5, 124.7, 137.1, 141.0, 150.0, 153.4, 164.7. Anal. Calcd for C19H17N3O2: C, 71.46; H, 5.37; N, 13.16. Found: C, 71.23; H, 5.14; N, 13.54.
Acknowledgments
The authors thank the Research Council of Yazd University for financial support.
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- Frontmatter
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Artikel in diesem Heft
- Frontmatter
- Preliminary Communication
- Preparation of cysteine adducts by regioselective ring-opening reactions of phenyloxirane
- Research Articles
- Synthesis of hydroxylated tryptanthrins as possible metabolites and characterization
- Tributylhexadecylphosphonium bromide: an efficient reagent system for the one-pot synthesis of 2,4,5-trisubstituted imidazoles
- Synthesis and properties of multifunctional nitroxyl radical hindered-amine light stabilizers
- Photochemical oxidation of N,N-bis- (tert-butoxycarbonyl)-1,4-dihydropyrazine derivatives
- ZrOCl2·SiO2-catalyzed synthesis of bis(indoles) via conjugate addition of indole with electron-deficient alkenes in water
- Synthesis of polysubstituted pyridines as potential multidrug resistance modulators
- Catalyst-free tandem Knoevenagel-Michael reaction of aldehydes and pyrazolin-5-one: fast and convenient approach to medicinally relevant 4,4′-(arylmethylene)bis(1H-pyrazol-5-ol)s
- Synthesis of mono- and bis-1,2,3-triazole derivatives containing 4H-pyran-4-one moiety by 1,3-dipolar cycloaddition reaction
- Synthesis and biological evaluation of novel 2-(1H-imidazol-2-ylmethylidene)hydrazinyl- 1,3-thiazoles as potential antimicrobial agents
