Application of novel metal–organic framework [Zr-UiO-66-PDC-SO₃H]FeCl₄ in the synthesis of dihydrobenzo[g]pyrimido[4,5-b]quinoline derivatives

Abstract

In the current paper, we produce a new metal–organic framework (MOF) based on Zr metal, [Zr-UiO-66-PDC-SO₃H]FeCl₄, via an anion exchange method, which is fully characterized by FT-IR, SEM with elemental mapping and EDX, FE-SEM and TEM. Furthermore, the use of [Zr-UiO-66-PDC-SO₃H]FeCl₄ as a porous catalyst was examined for the one-pot synthesis of novel dihydrobenzo[g]pyrimido[4,5-b]quinoline derivatives by reaction of 6-amino-1,3-dimethylpyrimidine-2,4(1H,3H)-dione, 2-hydroxynaphthalene-1,4-dione and various aldehydes at 100 °C with good to excellent yields.

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Introduction

Nowadays, porous materials such as metal–organic frameworks (MOFs) are of great interest to scientists.^1,2 These crystalline materials comprise metal and organic compounds as the nucleus and ligands, respectively. MOFs are multifunctional materials that have been used as adsorbents for the storage and separation of gas, drug delivery, catalyst, proton conductivity and heavy metal adsorbents.^3–9 Post- modification and synthesis of MOFs with acid functional groups and metal have been reported for the transportation of organic compounds, oxidation, and synthesis of biological compounds.¹⁰ Lillerud et al. reported the first MOFs based on Zr, such as Zr-UiO-66-PDC.¹¹ Considering this, the new class of porous catalyst with sulfonic and phosphorus acid tag-MOFs have been applied in the preparation of pyrimido[4,5-b]quinolones and dicyanomethylene pyridine derivatives – N-amino-2-pyridone and pyrano [2,3-c]pyrazole derivatives.^12–15

Anion exchange is an architectonic method for the preparation of ionic liquids (ILs) and/or molten salts (MSs) with several opposing ions that cannot be synthesized directly. Our research group has introduced MSs with N–S bonds as a new category of catalyst and reagent based on organic materials.^16–24 Now, we combine the porous materials MOF Zr-UiO-66-PDC with ClSO₃H, to prepare [Zr-UiO-66-PDC-SO₃H]Cl as a novel porous catalyst for ILs.

Recently, N-heterocyclic scaffold compounds have been considered as candidates for the design and discovery of new biologically active compounds. It is very important to supply new and easy methods for the preparation of target compounds with unique features. In this regard, 1,4-dihydropyridine structures containing uracil and henna (2-hydroxynaphthalene-1,4-dione) moieties are suitable candidates for biological and pharmacological purposes.^25–29 These molecules have been used as drugs in furnidipine and alogliptin (Fig. 1).^30,31 Also, scaffolds with uracil moieties have been reported as having antitumour,³² cardiotonic,³³ hepatoprotactive,³⁴ antihypertensive,³⁵ antibronchitic³⁶ and antifungal activity.³⁷ Therefore, the appearance of novel and simple organic synthetic approaches for the efficient preparation of this type of heterocycle is an interesting challenge. Since scaffolds with uracil and henna moieties are of biological interest,^38,39 we synthesize 1,4-dihydropyridine with uracil and henna moieties.

Fig. 1 Biological compounds containing uracil, henna and dihydropyridine moieties in their structures.

In continuation of our investigation on the development and preparation of MOFs with sulfonic acid tags and organic molecules with henna moieties,⁴⁰ in this paper, we prepare [Zr-UiO-66-PDC-SO₃H]FeCl₄ as an efficient and novel porous catalyst for new dihydrobenzo[g]pyrimido[4,5-b]quinoline derivatives by condensation reaction of 2-hydroxynaphthalene-1,4-dione, 6-amino-1,3-dimethylpyrimidine-2,4(1H,3H)-dione and various aldehydes (mono and bis) under solvent free conditions at 100 °C (Fig. 2).

Fig. 2 Preparation of dihydrobenzo[g]pyrimido[4,5-b]quinoline using [Zr-UiO-66-PDC-SO₃H]FeCl₄.

Experimental

Preparation of [Zr-UiO-66-PDC-SO₃H]FeCl₄

Initially, our MOFs [Zr-UiO-66-PDC] were synthesized according to a previously reported methodology.⁴¹ In a round-bottomed flask, 50 mL, a mixture of ClSO₃H (2 mmol, 0.134 mL) and [Zr-UiO-66-PDC] (0.564 g) in dry CH₂Cl₂ (30 mL) at 0 °C was stirred for 2 hours. After this, a white precipitate appeared which was separated (by centrifugation) and dried under vacuum. Then, according to the anion exchange method, a mixture of [Zr-UiO-66-PDC-SO₃H]Cl (2 g) and FeCl₃ (5 mmol, 0.81 g) was stirred in a mortar at 50 °C for 2 hours. After completion of the reaction, the reaction mixture was cooled down to room temperature. Finally, acetone was used to purify the [Zr-UiO-66-PDC-SO₃H]FeCl₄ via trituration (Fig. 3).

Fig. 3 Preparation of [Zr-UiO-66-PDC-SO₃H]FeCl₄.

General procedure for the synthesis of dihydrobenzo[g]pyrimido[4,5-b]quinoline derivatives using [Zr-UiO-66-PDC-SO₃H]FeCl₄

In a 15 mL round-bottomed flask, a mixture of 2-hydroxynaphthalen-1,4-dione (henna, 1 mmol, 0.174 g), 6-amino-1,3-dimethylpyrimidine-2,4(1H,3H)-dione (1 mmol, 0.155 g) and aldehyde (1 mmol) in the presence of 10 mg of [Zr-UiO-66-PDC-SO₃H]FeCl₄ was stirred at 100 °C under solvent-free conditions. After the completion of the reactions which were monitored by the TLC technique (2 : 3 n-hexane : ethyl acetate). The described catalyst was separated from the reaction mixture by centrifugation (1000 rpm) after adding 10 mL of EtOH as solvent. Finally, after the evaporation of the solvent at room temperature, pure product was obtained by washing with hot ethanol and water (Fig. 2).

Spectra data

1,3-Dimethyl-5-(p-tolyl)-5,12-dihydrobenzo[g]pyrimido[4,5-b]quinolone 2,4,6,11(1H,3H)-tetraone (U1). Red solid; Mp: 280 °C dec.; FT-IR (KBr) υ (cm⁻¹) = 3401, 3245, 1702, 1575, 1510. ¹H NMR (400 MHz, DMSO-d₆) δ 7.89 (d, J = 7.5 Hz, 1H), 7.80 (d, J = 7.1 Hz, 1H), 7.69 (t, J = 8.0 Hz, 1H), 7.62 (s, 1H), 7.57 (t, J = 7.6 Hz, 1H), 6.95 (s, 4H), 6.30 (s, 1H), 3.31 (s, 3H), 3.21 (s, 3H), 2.26 (s, 3H). ¹³C NMR (101 MHz, DMSO) δ 180.3, 162.3, 150.6, 135.4, 133.4, 132.5, 131.2, 130.4, 127.9, 126.6, 125.7, 125.4, 125.2, 124.7, 87.0, 34.4, 29.6, 28.1, 20.5. MS: m/z (%) = 413.2.

1,3-Dimethyl-5-(4-nitrophenyl)-5,12-dihydrobenzo[g]pyrimido[4,5-b]quinoline 2,4,6,11(1H,3H)-tetraone (U2). Red solid; Mp: >300 °C; FT-IR (KBr) υ (cm⁻¹) = 3396, 3230, 1694, 1656, 1605, 1576, 1342. ¹H NMR (400 MHz, DMSO-d₆) δ 7.86 (d, J = 7.6 Hz, 1H), 7.77 (d, J = 6.4 Hz, 1H), 7.66 (t, J = 5.6 Hz, 1H), 7.54 (s, 2H), 7.16 (d, J = 7.4 Hz, 2H), 7.03 (d, J = 6.9 Hz, 2H), 6.27 (s, 1H), 3.27 (s, 3H), 3.18 (s, 3H). ¹³C NMR (101 MHz, DMSO-d₆) δ 180.0, 150.7, 135.4, 133.4, 131.3, 130.3, 128.6, 128.2, 127.6, 127.1, 125.4, 124.7, 119.1, 86.4, 34.5, 29.5, 28.1. MS: m/z (%) = 444.1.

5-(4-Chlorophenyl)-1,3-dimethyl-5,12-dihydrobenzo[g]pyrimido[4,5-b]quinoline-2,4,6,11(1H,3H)-tetraone (U3). Red solid; Mp: >300 °C; FT-IR (KBr) υ (cm⁻¹) = 3456, 3336, 1693, 1596, 1508. ¹H NMR (400 MHz, DMSO-d₆) δ 8.00 (d, J = 8.7 Hz, 2H), 7.86 (d, J = 7.5 Hz, 1H), 7.77 (d, J = 7.3 Hz, 1H), 7.66 (t, J = 7.2 Hz, 1H), 7.53 (t, J = 7.3 Hz, 1H), 7.47 (s, 1H), 7.26 (d, J = 8.4 Hz, 2H), 6.39 (s, 1H), 3.26 (s, 3H), 3.17 (s, 3H). ¹³C NMR (101 MHz, DMSO) δ 185.8, 179.6, 161.7, 154.3, 152.6, 150.8, 144.4, 135.4, 133.4, 131.3, 130.3, 127.9, 127.8, 125.4, 124.7, 122.6, 118.6, 85.8, 35.8, 29.5, 27.9. MS: m/z (%) = 433.1[M], 435.2 [M + 2].

5-(3,4-Difluorophenyl)-1,3-dimethyl-5,12-dihydrobenzo[g]pyrimido[4,5-b]quinoline-2,4,6,11(1H,3H)-tetraone (U4). Red solid; Mp:>300 °C; FT-IR (KBr) υ (cm⁻¹) = 3392, 3061, 1691,1669, 1591, 1510. ¹H NMR (400 MHz, DMSO-d₆) δ 7.88–7.85 (m, 1H), 7.77–7.74 (m, 1H), 7.68–7.64 (m, 1H), 7.54–7.50 (m, 1H), 7.44 (s, 1H), 7.16–7.09 (m, 1H), 6.90 (d J = 9.1 Hz, 1H), 6.83–6.77 (m, 1H), 6.27 (s, 1H), 3.25 (s, 3H), 3.16 (s, 3H). ¹³C NMR (100 MHz, DMSO) δ 163.9, 154.4, 152.1, 147.9, 140.9, 133.8, 132.5, 129.5, 124.0, 123.3, 121.2, 120.8, 116.9, 114.3, 93.4, 37.2, 30.4, 29.0. MS: m/z (%) = 435.2.

1,3-Dimethyl-5-(4-(trifluoromethyl)phenyl)-5,12-dihydrobenzo[g]pyrimido[4,5-b]quinoline-2,4,6,11(1H,3H)-tetraone (U5). Red solid; Mp: 290 °C dec.; FT-IR (KBr) υ (cm⁻¹) = 3403, 3247, 1702, 1603, 1575, 1511. ¹H NMR (400 MHz, DMSO-d₆) δ 7.96 (d, J = 7.5 Hz, 1H), 7.87 (d, J = 7.4 Hz, 1H), 7.76 (t, J = 7.3 Hz, 1H), 7.66–7.60 (m, 2H), 7.56 (d, J = 8.1 Hz, 2H), 7.32 (d, J = 7.9 Hz, 2H), 6.45 (s, 1H), 3.36 (s, 3H), 3.27 (s, 3H). ¹³C NMR (101 MHz, DMSO-d₆) δ 185.6, 162.0, 152.9, 150.7, 135.4, 133.4, 131.3, 130.4, 127.3, 126.2, 125.4, 124.7, 124.2, 118.9, 86.1, 35.2, 29.6, 28.1. MS: m/z (%) = 467.1.

5-(3,5-Difluorophenyl)-1,3-dimethyl-5,12-dihydrobenzo[g]pyrimido[4,5-b]quinoline-2,4,6,11(1H,3H)-tetraone (U6). Red solid; Mp: >300 °C; FT-IR (KBr) υ (cm⁻¹) = 3393, 3238, 1691, 1659, 1594, 1509. ¹H NMR (400 MHz, DMSO-d₆) δ 8.00 (d, J = 7.4 Hz, 1H), 7.89 (d, J = 7.1 Hz, 1H), 7.81–7.77 (m, 1H), 7.66 (t, J = 7.4 Hz, 1H), 6.94 (s, 1H), 6.77 (s, 1H), 6.75 (s, 1H), 6.41 (s, 1H), 3.38 (s, 3H), 3.29 (s, 3H). ¹³C NMR (100 MHz, DMSO) δ 183.5, 150.7, 133.8, 133.2, 131.9, 130.9, 128.7, 128.4, 128.1, 125.7, 125.1, 123.3, 121.8, 117.7, 116.4, 115.8, 53.5, 32.5, 29.6, 28.0. MS: m/z (%) = 436.2.

5-(3-Hydroxyphenyl)-1,3-dimethyl-5,12-dihydrobenzo[g]pyrimido[4,5-b]quinoline-2,4,6,11(1H,3H)-tetraone (U7). Red solid; Mp:280 °C dec.; FT-IR (KBr) υ (cm⁻¹) = 3397, 3250, 1674, 1609, 1578, 1512. ¹H NMR (400 MHz, DMSO-d₆) δ 8.83 (s, 1H), 7.92 (d, J = 7.6 Hz, 1H), 7.81 (d, J = 7.2 Hz, 1H), 7.71 (t, J = 7.2 Hz, 1H), 7.60 (s, 1H), 7.57 (d, J = 7.3 Hz, 1H), 6.95 (t, J = 7.7 Hz, 1H), 6.53 (d, J = 7.4 Hz, 2H), 6.45 (d, J = 7.8 Hz, 1H), 6.29 (s, 1H), 3.33 (s, 3H), 3.23 (s, 3H). ¹³C NMR (101 MHz, DMSO-d₆) δ 182.1, 156.7, 135.7, 133.4, 131.3, 130.2, 127.9, 125.4, 124.5, 119.6, 117.7, 113.7, 110.8, 87.0, 34.8, 29.5, 28.0. MS: m/z (%) = 415.1.

1,3-Dimethyl-5-phenyl-5,12-dihydrobenzo[g]pyrimido[4,5-b]quinoline-2,4,6,11(1H,3H)-tetraone (U8). Red solid; Mp: 255–256 °C; FT-IR (KBr) υ (cm⁻¹) = 3407, 3244, 1699, 1605, 1578, 1509. ¹H NMR (400 MHz, DMSO-d₆) δ 13.21 (s, 1H), 8.03 (d, J = 7.4 Hz, 1H), 8.00 (d, J = 8.5 Hz, 1H), 7.87–7.80 (m, 2H), 7.22 (dt, J = 16.9, 5.6 Hz, 5H), 5.86 (s, 1H), 3.38 (s, 3H), 3.15 (s, 3H). ¹³C NMR (101 MHz, DMSO-d₆) δ 181.1, 163.6, 154.3, 150.1, 138.4, 134.3, 133.9, 133.5, 132.0, 131.7, 130.5, 128.0, 127.7, 126.7, 126.0, 125.7, 125.1, 124.8, 123.4, 85.6, 34.7, 30.4, 28.2. MS: m/z (%) = 399.2.

5-(2-Methoxyphenyl)-1,3-dimethyl-5,12-dihydrobenzo[g]pyrimido[4,5-b]quinoline-2,4,6,11(1H,3H)-tetraone (U9). Red solid; Mp: 288 °C dec.; FT-IR (KBr) υ(cm⁻¹) = 3442, 3355, 1696, 1633, 1657, 1504. ¹H NMR (400 MHz, DMSO-d₆) δ 9.02 (s, 1H), 8.06 (s, 1H), 7.99–7.71 (m, 3H), 7.25 (d, J = 100.1 Hz, 2H), 6.96–6.75 (m, 2H), 5.31 (s, 1H), 3.70 (s, 3H), 3.61 (s, 3H), 3.09 (s, 3H). ¹³C NMR (101 MHz, DMSO-d₆) δ 181.8, 160.4, 150.6, 139.4, 135.0, 133.5, 131.6, 128.1, 125.9, 125.8, 125.8, 122.5, 119.7, 111.8, 88.3, 55.4, 33.8, 29.7, 27.6. MS: m/z (%) = 429.2.

5-(2,4-Dichlorophenyl)-1,3-dimethyl-5,12-dihydrobenzo[g]pyrimido[4,5-b]quinoline-2,4,6,11(1H,3H)-tetraone (U10). Red solid; Mp: >300 °C; FT-IR (KBr) υ (cm⁻¹) = 3456, 3336, 1693, 1596, 1508. ¹H NMR (400 MHz, DMSO-d₆) δ 7.96 (s, 2H), 7.89 (s, 1H), 7.77 (s, 1H), 7.69 (s, 1H), 7.41 (s, 1H), 7.35 (s, 1H), 7.27 (s, 1H), 6.51 (s, 1H), 2.90 (s, 3H), 2.74 (s, 3H).¹³C NMR (101 MHz, DMSO-d₆) δ 177.9, 176.9, 158.9, 158.6, 156.4, 153.0, 151.8, 150.5, 150.4, 136.6, 136.6, 135.4, 134.9, 132.6, 132.4, 132.3, 132.1, 131.9, 128.8, 128.2, 127.8, 127.7, 127.2, 127.0, 126.8, 121.3, 104.2, 79.3, 31.3, 30.0, 28.0. MS: m/z (%) = 466.8 [M], 469 [M + 2].

5-(4-Methoxyphenyl)-1,3-dimethyl-5,12-dihydrobenzo[g]pyrimido[4,5-b]quinoline-2,4,6,11(1H,3H)-tetraone (U11). Red solid; Mp: 232–234 °C; FT-IR (KBr) υ (cm⁻¹) = 3398, 3238, 1702, 1607, 1580, 1511.¹H NMR (400 MHz, DMSO-d₆) δ 8.04–7.99 (m, 1H), 7.98 (d, J = 7.3 Hz, 1H), 7.86–7.78 (m, 2H), 7.20 (s, 1H), 7.09 (d, J = 8.3 Hz, 2H), 6.79 (d, J = 8.7 Hz, 2H), 5.80 (s, -1H), 3.71 (s, 3H), 3.36 (s, 3H), 3.14 (s, 3H). ¹³C NMR (101 MHz, DMSO-d₆) δ 163.4, 157.2, 154.2, 150.2, 134.3, 133.8, 133.3, 130.5, 127.7, 126.0, 125.6, 113.4, 85.9, 54.9, 34.0, 30.3, 28.1. MS: m/z (%) = 429.1.

5-(4-(Dimethylamino)phenyl)-1,3-dimethyl-5,12-dihydrobenzo[g]pyrimido[4,5-b]quinoline-2,4,6,11(1H,3H)-tetraone (U12). Red solid; Mp: 230 °C dec.; FT-IR (KBr) υ (cm⁻¹) = 3402, 3357, 1671, 1597, 1574, 1515. ¹H NMR (400 MHz, DMSO-d₆) δ 7.92 (d, J = 7.7 Hz, 1H), 7.82 (d, J = 7.3 Hz, 1H), 7.75–7.68 (m, 1H), 7.61–7.56 (m, 1H), 6.90 (d, J = 8.4 Hz, 1H), 6.86 (s, 2H), 6.62 (d, J = 8.5 Hz, 1H), 4.77 (s, 1H), 3.31 (s, 3H), 3.24 (s, 3H), 3.14 (s, 3H), 2.87 (s, 3H). ¹³C NMR (101 MHz, DMSO-d₆) δ 185.4, 180.6, 163.1, 158.0, 153.9, 149.7, 145.1, 135.1, 133.9, 133.0, 131.2, 130.1, 126.1, 125.5, 125.2, 123.2, 85.2, 40.6, 34.0, 30.0, 27.7. MS: m/z (%) = 441.2.

5-(4-Isopropylphenyl)-1,3-dimethyl-5,12-dihydrobenzo[g]pyrimido[4,5-b]quinoline-2,4,6,11(1H,3H)-tetraone (U13). Red solid; Mp: >300 °C; FT-IR (KBr) υ (cm⁻¹) = 3408, 3130, 2925, 1668, 1590, 1511. ¹H NMR (400 MHz, DMSO-d₆) δ 7.85 (d, J = 7.5 Hz, 1H), 7.73 (d, J = 7.6 Hz, 1H), 7.64 (t, J = 7.4 Hz, 1H), 7.53–7.47 (m, 2H), 6.96 (d, J = 8.1 Hz, 2H), 6.90 (d, J = 7.9 Hz, 2H), 6.24 (s, 1H), 3.25 (s, 3H), 3.15 (s, 3H), 2.82–2.74 (m, 1H), 1.17 (d, J = 6.8 Hz, 6H). ¹³C NMR (101 MHz, DMSO-d₆) δ 185.9, 181.1, 163.6, 158.5, 154.4, 150.1, 145.5, 135.6, 134.3, 133.5, 131.7, 130.6, 126.6, 126.1, 126.0, 125.7, 123.7, 85.6, 34.4, 32.9, 30.4, 28.2, 24.0, 23.9. MS: m/z (%) = 441.2.

5-(4-Hydroxyphenyl)-1,3-dimethyl-5,12-dihydrobenzo[g]pyrimido[4,5-b]quinoline-2,4,6,11(1H,3H)-tetraone (U14). Red solid; Mp: 220 °C dec.; FT-IR (KBr) υ (cm⁻¹) = 3393, 3229, 1671, 1654, 1509. ¹H NMR (400 MHz, DMSO-d₆) δ 8.49 (s, 1H), 7.86 (d, J = 7.7 Hz, 1H), 7.75 (d, J = 7.6 Hz, 1H), 7.65 (t, J = 7.5 Hz, 2H), 7.52 (d, J = 7.5 Hz, 2H), 7.43 (s, 1H), 7.17–7.07 (m, 2H), 6.90 (d, J = 7.8 Hz, 2H), 6.26 (s, 1H), 3.24 (s, 3H), 3.16 (s, 3H). ¹³C NMR (101 MHz, DMSO-d₆) δ 180.0, 150.7, 142.9, 135.4, 133.4, 131.3, 130.3, 128.6, 128.2, 127.1, 125.4, 124.7, 86.4, 34.5, 29.5, 28.1. MS: m/z (%) = 415.2.

1,3-Dimethyl-5-(3-nitrophenyl)-5,12-dihydrobenzo[g]pyrimido[4,5-b]quinoline-2,4,6,11(1H,3H)-tetraone (U15). Red solid; Mp: 300 °C dec.; FT-IR (KBr) υ (cm⁻¹) = 3334, 3508, 1717, 1682, 1562, 1529. ¹H NMR (400 MHz, DMSO-d₆) δ 7.90 (d, J = 7.9 Hz, 1H), 7.87 (d, J = 8.2 Hz, 1H), 7.78 (s, 1H), 7.67 (t, J = 7.1 Hz, 1H), 7.56–7.51 (m, 1H), 7.49–7.39 (m, 3H), 6.39 (s, 1H), 3.27 (s, 3H), 3.17 (s, 3H). ¹³C NMR (101 MHz, DMSO-d₆) δ 185.8, 179.8, 161.7, 152.7, 150.8, 147.6, 147.3, 135.4, 133.8, 133.4, 131.4, 130.3, 128.7, 125.4, 124.7, 121.2, 119.1, 118.4, 85.8, 35.2, 29.5, 28.0. MS: m/z (%) = 444.1.

5,5’-(1,3-Phenylene)bis(1,3-dimethyl-5,12-dihydrobenzo[g]pyrimido[4,5-b]quinoline-2,4,6,11(1H,3H)-tetraone) (U16). Red solid; Mp: >300 °C; FT-IR (KBr) υ (cm⁻¹) = 3396, 3200, 1682, 1608, 1579, 1508.¹H NMR (400 MHz, DMSO-d₆) δ 8.00 (d, J = 7.9 Hz, 2H), 7.97 (d, J = 8.2 Hz, 2H), 7.88 (s, 2H), 7.77 (t, J = 7.1 Hz, 2H), 7.66–7.61 (m, 2H), 7.57 (d, J = 7.2 Hz, 2H), 7.55–7.50 (m, 2H), 6.49 (s, 2H), 3.37 (s, 6H), 3.27 (s, 6H). ¹³C NMR (101 MHz, DMSO-d₆) δ 193.8, 161.7, 152.6, 150.9, 145.8, 135.8, 135.6, 133.4, 131.4, 130.2, 128.1, 127.9, 125.6, 125.4, 124.6, 118.9, 86.2, 35.0, 29.5, 27.9. MS: m/z (%) = 718.1.

5,5’-(1,4-Phenylene)bis(1,3-dimethyl-5,12-dihydrobenzo[g]pyrimido[4,5-b]quinoline-2,4,6,11(1H,3H)-tetraone) (U17). Red solid; Mp: 289 °C dec.; FT-IR (KBr) υ (cm⁻¹) = 3396, 3200, 1682, 1608, 1579, 1508. ¹H NMR (400 MHz, DMSO-d₆) δ 1H NMR (400 MHz, DMSO-d6) δ 9.97 (s, 2H), 7.93 (d, J = 7.5 Hz, 2H), 7.85 (d, J = 7.4 Hz, 2H), 7.74 (d, J = 7.8 Hz, 4H), 7.31 (d, J = 7.7 Hz, 4H), 6.45 (s, 2H), 3.35 (s, 6H), 3.25 (s, 6H). ¹³C NMR (101 MHz, DMSO-d₆) δ 185.8, 153.7, 144.6, 142.9, 137.8, 127.7, 127.5, 125.3, 123.4, 122.1, 120.1, 119.9, 117.5, 117.3, 116.5, 110.8, 78.2, 26.9, 21.5, 19.9. MS: m/z (%) = 718.1.

Results and discussion

To improve the catalytic application of MOFs, we have designed and synthesized [Zr-UiO-66-PDC-SO₃H]Cl. Post-functionalization of [Zr-UiO-66-PDC] occurred by preparing [Zr-UiO-66-PDC-SO₃H]FeCl₄ using FeCl₃ in a mortar at room temperature (Fig. 3). [Zr-UiO-66-PDC-SO₃H]FeCl₄ has a dual role as a Brønsted-Lewis acid catalyst for the preparation of biological compounds. For more detail, full characterization of [Zr-UiO-66-PDC-SO₃H]FeCl₄ as a catalyst was conducted by FT-IR, VSM, EDX, FE-SEM, elemental mapping, SEM and TEM techniques.

Synthesis and characterization of [Zr-UiO-66-PDC-SO₃H]FeCl₄ as a new metal–organic framework (MOF)

The FT-IR analysis of ZrCl₄, [Zr-UiO-66-PDC], [Zr-UiO-66-PDC-SO₃H]Cl and [Zr-UiO-66-PDC-SO₃H]FeCl₄ is shown in Fig. 4. The broad peak at 2700–3500 cm⁻¹ is related to the OH of SO₃H functional group. The aromatic C–H and C=C stretching bands are respectively at 2924 and 1626 cm⁻¹. The absorption bands at 1042 and 1136 cm⁻¹ are related to N–S and O–S bond stretching. Furthermore, the absorption bands at 587 cm⁻¹ are linked to the stretching vibrational modes of Fe–Cl groups in FeCl₄. The FT-IR spectrum difference between starting materials and [Zr-UiO-66-PDC-SO₃H]FeCl₄ verified the structure of the catalyst.

Fig. 4 FT-IR spectra of ZrCl₄, [Zr-UiO-66-PDC], [Zr-UiO-66-PDC-SO₃H]Cl and [Zr-UiO-66-PDC-SO₃H]FeCl₄.

The materials in the structure of [Zr-UiO-66-PDC-SO₃H]FeCl₄ were characterized by energy dispersive X-ray spectroscopy (EDX) (Fig. 5). The [Zr-UiO-66-PDC-SO₃H]FeCl₄ confirmed the existence of Zr, C, O, S, Cl, N and Fe atoms. Furthermore, [Zr-UiO-66-PDC-SO₃H]Cl as a well-dispersed material, was determined and verified by SEM-elemental mapping (Fig. 5).

Fig. 5 Upper: energy dispersive X-ray spectroscopy (EDX) of [Zr-UiO-66-PDC-SO₃H]FeCl₄. Lower: elemental mapping analysis of [Zr-UiO-66-PDC-SO₃H]FeCl₄.

Also, SEM images of [Zr-UiO-66-PDC-SO₃H]FeCl₄ were recorded to investigate the morphology (Fig. 6). The obtained images show the face centred cubic (fcu) structure. In addition, the topography of [Zr-UiO-66-PDC-SO₃H]FeCl₄ was studied more closely using transmission electron microscopy (TEM) as shown in Fig. 7. We can see that [Zr-UiO-66-PDC-SO₃H]FeCl₄ is a fcu topological network with 12-connected Zr clusters.

Fig. 6 FE-SEM images of [Zr-UiO-66-PDC-SO₃H]FeCl₄.

Fig. 7 TEM of [Zr-UiO-66-PDC-SO₃H]FeCl₄.

After the preparation of [Zr-UiO-66-PDC-SO₃H]FeCl₄ via the anion exchange method, it was tested as a catalyst for the synthesis of new dihydrobenzo[g]pyrimido[4,5-b]quinoline derivatives with uracil and henna (2-hydroxynaphthalene-1,4-dione) moieties. The above-mentioned products were obtained by reaction of 4-methoxy benzaldehyde (1.0 mmol, 0.136 g), 2-hydroxynaphthalen-1,4-dione (1 mmol, 0.174 g), and 6-amino-1,3-dimethylpyrimidine-2,4(1H,3H)-dione (1 mmol, 0.155 g) as a model for the optimization of the reaction conditions. The optimized data is listed in Table 1. As shown in Table 1, the best choice for the synthesis of 5-(4-methoxyphenyl)-1,3-dimethyl-5,12-dihydrobenzo[g]pyrimido[4,5-b]quinoline-2,4,6,11(1H,3H)-tetraone was achieved in the presence of 10 mg [Zr-UiO-66-PDC-SO₃H]FeCl₄ under solvent-free conditions (entry 4, Table 1). The model reaction was also studied under different temperatures and several solvents – H₂O, EtOH, DMF, n-hexane, EtOAc, CH₃CN (5 mL) – in the presence of 10 mg of [Zr-UiO-66-PDC-SO₃H]FeCl₄. As is shown, the results of the reaction did not improve (Table 1, entries 10–15).

Table 1 Effect of different amounts of catalyst, solvent and different temperatures, on the synthesis of 5-(4-methoxyphenyl)-1,3-dimethyl-5,12-dihydrobenzo[g]pyrimido[4,5-b]quinoline-2,4,6,11(1H,3H)-tetraone

Entry	Amount of catalyst (mg)	Temp. (^o C)	Solvent (10 mL)	Time (min)	Yield (%)
1	—	100	—	50	Trace
2	5	100	—	50	45
3	7	100	—	50	50
4	10	100	—	50	90
5	15	100	—	50	90
6	10	r.t.	—	50	75
7	10	50	—	50	70
8	10	70	—	50	20
9	15	120	—	50	90
10	10	Reflux	H2O	50	85
11	10	Reflux	EtOH	50	70
12	10	100	DMF	50	40
13	10	Reflux	n-Hexane	50	Trace
14	10	Reflux	EtOAc	50	Trace
15	10	Reflux	CH3CN	50	45

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After optimizing the reaction conditions, [Zr-UiO-66-PDC-SO₃H]FeCl₄ (10 mg) is applied to synthesize a range of novel biological and pharmacological candidate compounds using various aromatic aldehydes such as trephetaldehyde, iso-trephetaldehyde, bearing electron-donating and electron-withdrawing groups, 2-hydroxynaphthalen-1,4-dione and 6-amino-1,3-dimethylpyrimidine-2,4(1H,3H)-dione. As shown in Table 2, the obtained results indicated that [Zr-UiO-66-PDC-SO₃H]FeCl₄ is appropriate for the preparation of target molecules in high to excellent yield (70–90%) with relatively short reaction times (70–120 min).

Table 2 Synthesis of dihydrobenzo[g]pyrimido[4,5-b]quinoline derivatives using [Zr-UiO-66-PDC-SO₃H]FeCl₄

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In the proposed mechanism, the [Zr-UiO-66-PDC-SO₃H]FeCl₄ catalyst activates the carbonyl functional group of aldehyde. To investigate the activation of the aldehyde, 4-methoxy benzaldehyde was reacted with [Zr-UiO-66-PDC-SO₃H]FeCl₄ at room temperature. The FT-IR spectra of the subsequent reaction mixtures were examined.^15,42,43 The absorption bond of C=O of the 4-methoxy benzaldehyde at 1704 cm⁻¹, was changed to 1704, 1705 or 1711 cm⁻¹ by [Zr-UiO-66-PDC], [Zr-UiO-66-PDC-SO₃H]Cl and [Zr-UiO-66-PDC-SO₃H]FeCl₄ (Fig. 8). Then, the henna (2-hydroxynaphthalen-1,4-dione) moiety reacts with the carbonyl of the aldehyde by removing one H₂O molecule, to give intermediate (I) (Fig. 9). In the next step, 6-amino-1,3-dimethylpyrimidine-2,4(1H,3H)-dione reacts with intermediate (I) to give intermediate (II). In the next two steps, intermediate (II) gives the desired product after intramolecular cyclization and the loss of another molecule of H₂O.

Fig. 8 FT-IR spectra of 4-methoxy benzaldehyde in percent of [Zr-UiO-66-PDC], [Zr-UiO-66-PDC-SO₃H]Cl and [Zr-UiO-66-PDC-SO₃H]FeCl₄.

Fig. 9 Proposed mechanism for the synthesis of dihydrobenzo[g]pyrimido[4,5-b]quinoline derivatives using [Zr-UiO-66-PDC-SO₃H]FeCl₄.

To evaluate the performance of [Zr-UiO-66-PDC-SO₃H]FeCl₄ as a catalyst for the synthesis of dihydrobenzo[g]pyrimido[4,5-b]quinoline derivatives, we tested various acid catalysts (organic and inorganic) in the reaction of 4-methoxy benzaldehyde (1.0 mmol, 0.136 g), 2-hydroxynaphthalen-1,4-dione (1 mmol, 0.174 g), 6-amino-1,3-dimethylpyrimidine-2,4(1H,3H)-dione (1 mmol, 0.155 g) as evaluated in Table 3. The obtained results which are collected in Table 3 show that, [Zr-UiO-66-PDC-SO₃H]FeCl₄ is the best catalyst for the synthesis of novel dihydrobenzo[g]pyrimido[4,5-b]quinoline derivatives. The obtained results of catalytic activity and reusability of [Zr-UiO-66-PDC-SO₃H]FeCl₄ are shown in Fig. 10. As mentioned above, [Zr-UiO-66-PDC-SO₃H]FeCl₄ was separated by centrifugation and reused without significant reduction in its catalytic activity. Recyclability of the catalyst was also studied using the one-pot reaction of 4-methoxy benzaldehyde (1.0 mmol, 0.136 g), 2-hydroxynaphthalen-1,4-dione (1 mmol, 0.174 g), 6-amino-1,3-dimethylpyrimidine-2,4(1H,3H)-dione (1 mmol, 0.155 g) as a model under the above-mentioned optimized reaction conditions. We found that [Zr-UiO-66-PDC-SO₃H]FeCl₄ can be reused up to four times without noticeable changes in its catalytic activity.

Fig. 10 Recyclability of [Zr-UiO-66-PDC-SO₃H]FeCl₄ in the synthesis of dihydrobenzo[g]pyrimido[4,5-b]quinoline derivatives.

Table 3 Evaluation of various catalysts for the synthesis of 5-(4-methoxyphenyl)-1,3-dimethyl-5,12-dihydrobenzo[g]pyrimido[4,5-b]quinoline-2,4,6,11(1H,3H)-tetraone with [Zr-UiO-66-PDC-SO₃H]FeCl₄

Entry	Catalyst	Amount of catalyst (mol%)	Time (min)	Yield (%)
1	NaOH	10	60	25
2	Et3N	10	65	—
3	K2CO3	10	70	Trace
4	P-TSA	10	90	—
5	SSA ^44,45	10 mg	120	Trace
6	GTBSA ^46	10 mg	80	45
7	[PVI-SO3H]FeCl4 ^19	10 mg	70	70
8	MIL-100(Cr)–NHEtN(CH2PO3H2)2 ^15	10 mg	60	65
9	Fe3O4@Co(BDC-NH2) ^47	10 mg	50	35
10	CQDs-N(CH2PO3H2)2 ^48	10 mg	80	43
11	TTPA^49	10	100	55
12	MIL-101(Cr)–N(CH2PO3H2)2 ^12	10 mg	60	80
13	FeCl3	10	120	50
14	ZrCl4	10	120	55
15	Zr-UiO-66-PDC	10 mg	120	40
16	[Zr-UiO-66-PDC-SO3H]Cl	10 mg	65	75
17	[Zr-UiO-66-PDC-SO3H]FeCl4	10 mg	50	90

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Conclusion

In this study, we have designed, synthesized and introduced [Zr-UiO-66-PDC-SO₃H]FeCl₄ as a novel mesoporous catalyst, which was fully characterized using various techniques. To the best of our knowledge, this catalyst is the first MOF that was synthesized via the anion exchange method. [Zr-UiO-66-PDC-SO₃H]FeCl₄ is an efficient catalyst. It was tested for the preparation of new dihydrobenzo[g]pyrimido[4,5-b]quinoline derivatives with henna and uracil moieties which have biological interest.

Conflicts of interest

There are no conflicts to declare.

Acknowledgements

We thank Bu-Ali Sina University and the Iran National Science Foundation (INSF) (Grant number: 98001912) for the financial support of our research group.

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Footnote

† Electronic supplementary information (ESI) available. See DOI: 10.1039/d1ra08710j

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