Abstract
New hybrid compounds, thienopyrimidinyl-1H-pyrazolo[3,4-b]pyridine derivatives, were efficiently synthesized by the three-component reaction of 3-phenyl-1-(thienopyrimidin-4-yl)-1H-pyrazol-5-amine, benzoylacetonitrile and an aromatic aldehyde in the presence of FeCl3 on basic alumina.
Introduction
Pyrazolo[3,4-b]pyridines have been reported to posses antioxidant [1], antibacterial [2], antiviral [3] and antitumor activities [4], [5], [6], [7], [8]. Thienopyrimidines and their derivatives have also attracted considerable attention due to important biological properties including anticancer [9], antimicrobial [10], antiviral [11], and anti-inflammatory activities [12]. Fused thienopyrimidines with cycloalkyl substituents are potent antitumor agents [13]. These results prompted us to study the synthesis of thienopyrimidine derivatives substituted with the pyrazolo[3,4-b]pyridine ring system. We have previously reported several biologically active fused thienopyrimidine derivatives [14], [15], [16].
Many synthetic approaches to pyrazolo[3,4-b]pyridines have been developed [17]. Recently, some new pyrazolo[3,4-b]pyridines have been prepared by a multi-component reaction of a substituted 5-amino-1-phenyl-1H-pyrazole, benzoylacetonitrile and an aromatic aldehyde in the presence of a catalyst such as ammonium acetate [18], acetic acid/triethylamine [8], L-proline [19] or FeCl3 [20]. We report here an efficient one-pot three-component synthesis of new pyrazolo[3,4-b]pyridine-thienopyrimidine hybrids with the concept of molecular hybridization [21] by treating 3-phenyl-1-(thienopyrimidin-4-yl)-1H-pyrazol-5-amine with benzoyl acetonitrile and an aromatic aldehyde catalyzed by FeCl3 on basic alumina.
Results and discussion
The synthesis is outlined in Scheme 1 starting from the readily available substrates 1a–c and 2a [22], [23]. Intermediate products 4a–c and 5a were easily prepared in good yields by the reaction of 1a–c or 2a with benzoylacetonitrile (3) in refluxing ethanol using the previously reported method [24]. Initially, the three-component reaction of 4a, arylaldehyde 6a and 3 in refluxing ethanol without catalyst or in the presence of various catalysts such as ammonium acetate, acetic acid, L-proline or FeCl3 was investigated as a model reaction (Table 1, entries 1–5). The desired hybrid product 7a was observed in low to moderate yields (15–61%) for the reactions conducted in refluxing ethanol. With FeCl3 on basic alumina as catalyst (0.2 equiv), compound 7a was obtained in a yield of 86% after heating for 6 h (entry 6). The use of a smaller amount of the catalyst or lowering the reaction temperature resulted in decreased yields (entries 7, 8). No further increase in yield was achieved with the use of different solvents and varying temperatures (entries 9, 10). The reaction of 4a with 6b and 3 under the optimized reaction conditions (using 0.2 equiv FeCl3/basic Al2O3 in refluxing ethanol) gave a corresponding product 7b in 82% yield (Scheme 2). The reaction of cycloalkyl-substituted 4b or 4c with arylaldehyde 6a–c and 3 under the same reaction conditions afforded product 7c–f in good yield (80–83%). When 5a bearing a different thiophene ring was allowed to react with 6a and 3, the corresponding compound 8a was obtained in 85% yield. These results show that cyclocondensation of the three components is not strongly affected by substituent on the arylaldehyde or thienopyrimidine.
Synthesis of reactants 4a–c and 5a.
Optimization of reaction conditions for the synthesis of 7a.a
| Entry | Catalyst (equiv)b | Solvent | Time (h) | Temperature (°C) | Yield (%)c |
|---|---|---|---|---|---|
| 1 | – | EtOH | 10 | Reflux | 32 |
| 2 | NH4OAc (0.2) | EtOH | 6 | Reflux | 40 |
| 3 | AcOH (0.2) | EtOH | 6 | Reflux | 46 |
| 4 | L-proline (0.2) | EtOH | 6 | Reflux | 15 |
| 5 | FeCl3 (0.2) | EtOH | 6 | Reflux | 61 |
| 6 | FeCl3/Al2O3 (0.2) | EtOH | 6 | Reflux | 86 |
| 7 | FeCl3/Al2O3 (0.1) | EtOH | 6 | Reflux | 65 |
| 8 | FeCl3/Al2O3 (0.2) | EtOH | 10 | 25 | 44 |
| 9 | FeCl3/Al2O3 (0.2) | DMF | 6 | 100 | 56 |
| 10 | FeCl3/Al2O3 (0.2) | MeCN | 6 | 80 | 38 |
aReactions were carried out with 4a (1.0 mmol), 6a (1.0 mmol), 3 (1.0 mmol) in an appropriate solvent (10 mL). bEquiv is based on FeCl3. cYield of isolated product.
Three-component synthesis of compounds 7a–f and 8a.
All products were fully characterized by spectroscopy and elemental analysis. To definitively assign the structure of 7a–f and 8a, an authentic sample of 7a was prepared by a stepwise synthesis. Thus, 4a was first allowed to react with 3, and the subsequent reaction of the crude product with 6a gave 7a. This product was identical in all respects (mp, 1H NMR, and MS) with 7a obtained from the three-component reaction. This result is also consistent with the report by Jachak and co-workers [18].
Conclusions
New thienopyrimidinyl-1H-pyrazolo[3,4-b]pyridines were synthesized by the three-component reaction of 3-phenyl-1-(thienopyrimidin-4-yl)-1H-pyrazol-5-amine, benzoylacetonitrile and an aromatic aldehyde in refluxing ethanol in the presence of FeCl3 on basic alumina. The use of the catalyst in this reaction has the advantage of enhanced yields and simple work-up compared to FeCl3 alone.
Experimental
Melting points were measured by using capillary tubes on a Büchi apparatus and are uncorrected. Compounds were purified by column chromatography using Merck silica gel (70–230 mesh). The 1H NMR spectra were recorded on a Unity Inova 400NB FT NMR spectrometer (400 MHz) in CDCl3 with Me4Si as internal standard. Mass spectra were recorded on a HP 59580 B spectrometer (APCI). Elemental analyses were performed on a Carlo Erba 1106 elemental analyzer.
Preparation of the catalyst (FeCl3/basic Al2O3)
A mixture of hydrated ferric chloride (FeCl3 · 6H2O, 4 g) and basic Al2O3 (20 g) in acetone (30 mL) was stirred at room temperature for 1 h and then concentrated under reduced pressure. The resulting yellow powder was dried at 100°C under reduced pressure for 2 h [25].
General procedure for the synthesis of 4a–c and 5a
A mixture of hydrazinylthienopyrimidine 1a–c or 2 (10 mmol) and benzoylacetonitrile 3 (10 mmol) in anhydrous ethanol (20 mL) was heated under reflux for 10 h. The mixture was poured into crushed ice (20 mL) and the precipitated solid product was filtered, washed with water, and crystallized from ethanol to give pure 4a–c or 5a.
3-Phenyl-1-(thieno[2,3-d]pyrimidin-4-yl)-1H-pyrazol-5-amine (4a)
Yield 75%; mp 211–212°C; 1H NMR: δ 8.89 (s, 1H), 8.55 (d, 1H, J=5.5 Hz), 7.97 (d, 1H, J=5.5 Hz), 7.92 (m, 2H), 7.48 (m, 3H), 6.70 (s, 2H), 5.98 (s, 1H); MS: m/z 294.21 (M+). Anal. Calcd for C15H11N5S: C, 61.42; H, 3.78; N, 23.87. Found: C, 61.21; H, 3.82; N, 23.76.
1-(6,7-Dihydro-5H-cyclopenta[4,5]thieno[2,3-d]pyrimidin-4-yl)-3-phenyl-1H-pyrazol-5-amine (4b)
Yield 80%; mp 158–159°C; 1H NMR: δ 8.81 (s, 1H), 7.83 (m, 2H), 7.44 (m, 2H), 7.36 (m, 1H), 6.22 (bs, 2H), 5.95 (s, 1H), 3.17 (m, 2H), 3.05 (m, 2H), 2.31 (m, 2H); MS: m/z 334.21 (M+). Anal. Calcd for C18H15N5S: C, 64.84; H, 4.53; N, 21.01. Found: C, 64.66; H, 4.49; N, 21.14.
3-Phenyl-1-(5,6,7,8-tetrahydrobenzo[4,5]thieno[2,3-d]pyrimidin-4-yl)-1H-pyrazol-5-amine (4c)
Yield 70%; mp 171–172°C; 1H NMR: δ 8.94 (s, 1H), 7.78 (m, 2H), 7.42 (m, 2H), 7.39 (m, 1H), 5.94 (s, 1H), 5.85 (bs, 2H), 2.91 (m, 2H), 2.55 (m, 2H), 1.83 (m, 2H), 1.64 (m, 2H); MS: m/z 348.23 (M+). Anal. Calcd for C19H17N5S: C, 65.68; H, 4.93; N, 20.16. Found: C, 65.89; H, 4.98; N, 20.04.
3-Phenyl-1-(thieno[3,2-d]pyrimidin-4-yl)-1H-pyrazol-5-amine (5a)
Yield 72%; mp 191–192°C; 1H NMR: δ 8.76 (s, 1H), 8.33 (d, 1H, J=5.6 Hz), 7.77 (m, 2H), 7.44 (d, 1H, J=5.6 Hz), 7.30 (m, 3H), 7.20 (bs, 2H), 5.81 (s, 1H); MS: m/z 294.30 (M+). Anal. Calcd for C15H11N5S: C, 61.42; H, 3.78; N, 23.87. Found: C, 61.29; H, 3.80; N, 23.99.
General procedure for the synthesis of 7a–f and 8a
A mixture of thienopyrimidinylpyrazolamine 4a–c or 5a (5 mmol), arylaldehyde 6a–c (5 mmol), benzoylacetonitrile 3 (5 mmol) and FeCl3/basic Al2O3 (1 mmol, based on FeCl3) in anhydrous ethanol (20 mL) was heated under reflux. After completion of the reaction (6 h, monitored by TLC), the mixture was diluted with ethyl acetate and the insoluble substance was filtered out. The solvent was evaporated under reduced pressure and the residue was crystallized from chloroform.
4-(4-Methoxyphenyl)-3,6-diphenyl-1-(thieno[2,3-d]pyrimidin-4-yl)-1H-pyrazolo[3,4-b]pyridine-5-carbonitrile (7a)
Yield 86%; mp 255–257°C; 1H NMR: δ 8.78 (s, 1H), 8.62 (d, 1H, J=5.4 Hz), 7.80 (d, 1H, J=5.4 Hz), 7.59 (m, 3H), 7.51 (m, 3H), 7.35 (m, 3H), 7.25 (m, 3H), 6.83 (d, 2H, J=7.4 Hz), 3.76 (s, 3H); MS: m/z 537.16 (M+). Anal. Calcd for C32H20N6OS: C, 71.62; H, 3.76; N, 15.66. Found: C, 71.50; H, 3.81; N, 15.55.
4-(4-Bromophenyl)-3,6-diphenyl-1-(thieno[2,3-d]pyrimidin-4-yl)-1H-pyrazolo[3,4-b]pyridine-5-carbonitrile (7b)
Yield 82%; mp 190–191°C; 1H NMR: δ 8.75 (s, 1H), 8.60 (d, 1H, J=5.4 Hz), 7.84 (d, 1H, J=5.4 Hz), 7.68 (m, 2H), 7.50 (m, 3H), 7.40 (m, 4H), 7.28 (m, 2H), 7.19 (m, 3H); MS: m/z 586.01 (M+). Anal. Calcd for C31H17BrN6S: C, 63.59; H, 2.93; N, 14.35. Found: C, 63.74; H, 2.90; N, 14.45.
1-(6,7-Dihydro-5H-cyclopenta[4,5]thieno[2,3-d]pyrimidin-4-yl)-4-(4-methoxyphenyl)-3,6-diphenyl-1H-pyrazolo[3,4-b]pyridine-5-carbonitrile (7c)
Yield: 80%; mp 237–239°C; 1H NMR: δ 9.02 (s, 1H), 7.66 (m, 2H), 7.54 (m, 2H), 7.50 (m, 3H), 7.33 (m, 3H), 7.25 (m, 2H), 6.83 (m, 2H), 3.76 (s, 3H), 3.46 (m, 2H), 3.08 (m, 2H), 2.40 (m, 2H); MS: m/z 577.14 (M+). Anal. Calcd for C35H24N6OS: C, 72.90; H, 4.19; N, 14.57. Found: C, 72.77; H, 4.16; N, 14.48.
1-(6,7-Dihydro-5H-cyclopenta[4,5]thieno[2,3-d]pyrimidin-4-yl)-3,6-diphenyl-4-(p-tolyl)-1H-pyrazolo[3,4-b]pyridine-5-carbonitrile (7d)
Yield 83%; mp 270–271°C; 1H NMR: δ 8.65 (s, 1H), 7.66 (m, 2H), 7.55 (m, 2H), 7.51 (m, 3H), 7.33 (m, 3H), 7.25 (m, 2H), 7.10 (m, 2H), 3.46 (m, 2H), 3.09 (m, 2H), 2.42 (m, 2H), 2.29 (s, 3H); MS: m/z 561.16 (M+). Anal. Calcd for C35H24N6S: C, 74.98; H, 4.31; N, 14.99. Found: C, 74.90; H, 4.27; N, 14.88.
4-(4-Bromophenyl)-1-(6,7-dihydro-5H-cyclopenta[4,5]thieno[2,3-d]pyrimidin-4-yl)-3,6-diphenyl-1H-pyrazolo[3,4-b]pyridine-5-carbonitrile (7e)
Yield 81%; mp 280–281°C; 1H NMR: δ 8.63 (s, 1H), 7.65 (m, 2H), 7.53 (m, 5H), 7.50 (m, 2H), 7.40 (m, 3H), 7.21 (m, 2H), 3.44 (m, 2H), 3.07 (m, 2H), 2.39 (m, 2H); MS: m/z 625.97 (M+). Anal. Calcd for C34H21BrN6S: C, 65.28; H, 3.38; N, 13.43. Found: C, 65.40; H, 3.40; N, 13.39.
4-(4-Methoxyphenyl)-3,6-diphenyl-1-(5,6,7,8-tetrahydrobenzo[4,5]thieno[2,3-d]pyrimi-din-4-yl)-1H-pyrazolo[3,4-b]pyridine-5-carbonitrile (7f)
Yield 83%; mp 266–268°C; 1H NMR: δ 9.08 (s, 1H), 7.93 (m, 2H), 7.50 (m, 3H), 7.27 (m, 3H), 7.15 (m, 4H), 6.77 (m, 2H), 3.81 (s, 3H), 2.92 (m, 2H), 2.32 (m, 2H), 1.87 (m, 2H), 1.68 (m, 2H); MS: m/z591.19 (M+). Anal. Calcd for C36H26N6OS: C, 73.20; H, 4.44; N, 14.23. Found: C, 73.33; H, 4.47; N, 14.28.
4-(4-Methoxyphenyl)-3,6-diphenyl-1-(thieno[3,2-d]pyrimidin-4-yl)-1H-pyrazolo[3,4-b]pyridine-5-carbonitrile (8a)
Yield 85%; mp 264–265°C; 1H NMR: δ 8.89 (s, 1H), 8.15 (d, 1H, J=5.5 Hz), 7.72 (m, 4H), 7.60 (d, 1H, J=5.5 Hz), 7.51 (m, 3H), 7.34 (m, 3H), 7.28 (m, 3H), 6.85 (d, 2H, J=7.3 Hz), 3.77 (s, 3H); MS: m/z 537.23 (M+). Anal. Calcd for C32H20N6OS: C, 71.62; H, 3.76; N, 15.66. Found: C, 71.56; H, 3.73; N, 15.60.
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