An Efficient, Simple, and Scaleable Domino Reaction to Diverse N-(1-Oxo-1H-inden-2-yl)benzamides Catalyzed by HPW@nano-SiO₂ under Microwave Irradiation

Abstract

A facile, efficient, and large-scale strategy for the synthesis of N-(1-oxo-1H-inden-2-yl)benzamide derivatives via domino reaction between aryl aldehydes, hippuric acid, and acetic anhydride catalyzed by HPW@nano-SiO₂ was accomplished under microwave irradiation. The reaction conditions are very simple and offer easy isolation of the product. Moreover, the catalyst can be re-used up to five times in 86% average yield after simple filtration.

tandem reaction - indenones - heterogeneous catalyst - microwave irradiation - nanosilica - heteropoly acid

References and Notes

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11

The supported H₃PW₁₂O₄₀ on nano-SiO₂ was prepared by the method of incipient wetness. In a typical process, H₃PW₁₂O₄₀ (400 mg) was dissolved in deionized water and impregnated dropwise onto nano-SiO₂ (1600 mg) with constant agitation. The resulting paste was dried for 8 h at 120 ˚C and calcined for 4 h at 250 ˚C.

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14

General Procedure for Synthesis of N -(1-oxo-1 H -inden-2-yl)benzamides
In a high-pressure Teflon reactor equipped with a magnetic stir bar and an IR sensor (for controlling of reaction temperature), a mixture of aryl aldehyde 1 (1 mmol), hippuric acid (0.179 g, 1 mmol), Ac₂O (0.204 g, 2 mmol), and PW@nano-SiO₂ (200 mg, 4 mol%) was submitted to microwave irradiation at 120 ˚C (650 W) using a Micro-SYNTH labstation reactor for 28-45 min. During this time, the power was modulated automatically to hold the reaction mixture at 120 ˚C. After the reaction was complete (monitoring by TLC), the reaction mixture was cooled to r.t., filtered, washed with a hot mixture of EtOAc-EtOH (10:1, 2 × 10 mL) and concentrated in vacuo to give crude 2, which was purified as appropriate by recrystallization with EtOH (95%). N -(6-Chloro-1-oxo-1 H -inden-2-yl)benzamide (2b)
FTIR (KBr, solid): 3235, 1698, 1644, 1470, 1423, 1311, 1277, 1088, 910, 699, 524 cm^-¹. ^¹H NMR (500 MHz, DMSO): δ = 9.54 (s, 1 H), 7.88-7.89 (d, J = 7.55 Hz, 2 H), 7.54-7.56 (t, J = 7.80 Hz, 1 H), 7.47-7.50 (t, J = 7.80 Hz, 2 H), 7.34-7.35 (d, J = 8.10 Hz, 1 H), 7.28-7.29 (d, J = 8.10 Hz, 2 H), 7.16 (s, 1 H). ^¹³C NMR (125 MHz, DMSO): δ = 167.6, 163.5, 149.5, 137.1, 135.8, 134.7, 131.4, 130.9, 130.4, 128.4, 127.6, 127.3, 124.2, 122.9. MS (EI): m/z = 149.94 [M + 2], 104.87, 76.86, 50.9.
N -(6-Bromo-1-oxo-1 H -inden-2-yl)benzamide (2d) FTIR (KBr, solid): 3235.97, 1696, 1644.98, 1477, 1438, 1314, 1279, 1072, 913, 693, 528 cm^-¹. ^¹H NMR (500 MHz, DMSO): δ = 9.92 (s, 1 H), 7.94-7.95 (d, J = 7.35 Hz, 2 H), 7.58-7.60 (m, 4 H), 7.49-7.55 (m, 2 H), 7.37 (s, 1 H). ^¹³C NMR (125 MHz, DMSO): δ = 166.15, 165.83, 149.35, 133.48, 133.17, 131.76, 131.46, 130.98, 130.94, 128.41, 128.22, 127.62, 122.30. MS (EI): m/z = 195.96 [M + 2], 104.98, 76.97, 51. Anal. Calcd for C₁₆H₁₀BrNO₂: C, 58.56; H, 3.07; N, 4.27. Found: C, 58.02; H, 3.56; N, 4.07.
N -(6-Nitro-1-oxo-1 H -inden-2-yl)benzamide (2f) FTIR (KBr, solid): 3216, 1699, 1651, 1518, 1478, 1432, 1343, 1272, 1109, 691, 326 cm^-¹. ^¹H NMR (400 MHz, DMSO): δ = 9.66 (s, 1 H), 7.88-7.90 (d, J = 7.61 Hz, 1 H), 7.56-7.57 (d, J = 6.40 Hz, 1 H), 7.49-7.52 (t, J = 7.20 Hz, 2 H), 7.36-7.38 (d, J = 8.00 Hz, 2 H), 7.29-7.31 (d, J = 7.22 Hz, 2 H), 7.10 (s, 1 H). ^¹³C NMR (125 MHz, DMSO): δ = 166.14, 165.83, 149.35, 133.48, 133.18, 131.76, 131.48, 131.47, 130.98, 130.94, 128.41, 128.22, 127.62, 122.29. MS (EI): m/z = 294.01, 104.98, 77.03, 55.66.
N -(6-Methoxy-1-oxo-1 H -inden-2-yl)benzamide (2g) FTIR (KBr, solid): 3386, 2929, 2839, 1690, 1653, 1439, 1079, 980, 896, 811, 516 cm^-¹. ^¹H NMR (500 MHz, DMSO): δ = 9.42 (s, 1 H), 7.48-7.57 (m, 5 H), 7.36-7.38 (d, J = 8.20 Hz, 2 H), 6.83-6.85 (d, J = 8.41 Hz, 1 H), 6.78-6.80 (d, J = 8.00 Hz, 1 H), 3.73 (s, 3 H). ^¹³C NMR (125 MHz, DMSO): δ = 166.54, 165.82, 158.85, 145.98, 133.47, 133.17, 131.76, 131.5, 131.45, 130.98, 130.94, 128.4, 128.22, 122.3, 55.98. MS (EI): m/z = 264.08 [M - 15], 105.06, 77.03, 55.12. Anal. Calcd for C₁₇H₁₃NO₃: C, 73.11; H, 4.69; N, 5.02. Found: C, 72.99; H, 5.00; N, 4.89.
N , N ′-(1,5-Dioxo-1,5-dihydros-indacene-2,6-diyl)dibenzamide (2j) FTIR (KBr, solid): 3374, 1703, 1610, 1569, 1437, 1266, 1026, 675, 589 cm^-¹.^¹H NMR (400 MHz, DMSO): δ = 9.7 (s, 2 H), 7.94-7.95 (d, J = 7.10 Hz, 2 H), 7.84-7.85 (d, J = 7.10 Hz, 2 H), 7.66 (br s, 2 H), 7.49-7.51 (t, J = 8.40 Hz, 4 H), 7.41-7.44 (t, J = 8.35 Hz, 4 H). ^¹³C NMR (300 MHz, DMSO): δ = 167, 165.93, 152.17, 142.38, 133.22, 131.76, 131.48, 128.41, 127.63, 126.40, 121.48. MS (EI): m/z = 420.19, 105.01, 77.02, 55.04.
N -(2-Methyl-4-oxo-4 H -cyclopenta[ b ]thiophen-5-yl)benzamide (2k) FTIR (KBr, solid): 3395, 1695, 1610, 1539, 1448, 1028, 670, 469 cm^-¹. ^¹H NMR (400 MHz, DMSO): δ = 9.3 (s, 1 H), 7.99 (s, 2 H), 7.33-7.68 (m, 3 H), 7.01 (s, 1 H), 6.71 (s, 1 H), 2.35 (s, 3 H). ^¹³C NMR (125 MHz, DMSO): δ = 166.09, 163.80, 149.89, 144.12, 141.57, 135.82, 130.91, 130.4, 128.46, 127.65, 127.32, 121.99, 17.21. MS (EI): m/z = 148.96 (M-120), 104.94, 76.95, 57.04. Anal. Calcd for C₁₅H₁₁NO₂S: C, 66.89; H, 4.12; N, 5.20. Found: C, 66.45; H, 4.40; N, 5.09.
N -(3,4-Dihydro-3-oxocyclopenta[ b ]indol-2-yl)benz-amide (2l) FTIR (KBr, solid): 3364, 3343, 1698, 1644, 1539, 1079, 962, 889, 792, 437 cm^-¹. ^¹H NMR (300 MHz, DMSO): δ = 10.31 (s, 1 H), 9.98 (s, 1 H), 7.83-7.85 (d, J = 5.58 Hz, 2 H), 7.65 (br s, 3 H), 7.48-7.49 (d, J = 4.40 Hz, 2 H), 7.40-7.43 (t, J = 4.70 Hz, 2 H), 7.30 (s, 1 H). ^¹³C NMR (125 MHz, DMSO): δ = 166.15, 163.73, 149.35, 137.98, 133.48, 133.18, 131.76, 131.47, 131.46, 130.97, 130.84, 128.41, 128.22, 127.63, 122.29, 117.99. MS (EI): m/z = 167.07 [M - 120], 149, 71, 57. Anal. Calcd for C₁₈H₁₂N₂O₂: C, 74.99; H, 4.20; N, 9.72. Found: C, 74.85; H, 4.68; N, 9.01.