A simple conventional method is followed to prepare all the compounds.
Experimental
All the reagents used in the present study were obtained from commercial suppliers. All the solvents were freshly distilled before being used. Melting points were determined using a Buchi melting point B-545 apparatus and are uncorrected. TLC analyses were done on glass plates coated with silica gel GF-254 and spotting was done using iodine/UV lamp. IR spectra were recorded on a Perkin-Elmer model 446 instrument in KBr phase. H1 NMR were recorded by 400 MHz spectrometer, LC–MS spectrometer, model HP5989A. 13C NMR was recorded in DMSO using 100 MHz spectrometer.
General procedure for the synthesis of 2-styrylbenzimidazole derivatives from O-PDA and cinnamic acids (route 1, Scheme 1)
An intimate mixture of o-phenylenediamine 1 (1.08 g, 10 mM) was dissolved in 10 mL of glycerol in a 250 mL round bottom flask. Triacetylborate (0.2 g, 10 mol) and cinnamic acids 3a–3i (10 mM) are added and allowed the solution to boil at 160–180 °C for 3 h using dean-stark apparatus placed in oil-bath. The completion of the reaction was monitored by checking TLC. At the end of this period, the reaction mixtures was poured into ice cold water and adjust the pH of the solution to 8.0–10.0. Filter the compound and recrystallized by using suitable solvent.
General procedure for the synthesis of 2-styrylbenzimidazole derivatives from 2-methylbenzimidazoles and aromatic aldehydes (route 2, Scheme 1)
An intimate mixture of 2-methylbenzimidazoles 6 (1.32 g, 10 Mm) was dissolved in 10 mL of glycerol in a 250 mL round bottom flask was added triacetyleborate (0.2 g, 10 mol) and corresponding aromatic aldehydes 7a–7i (10 Mm) and allowed to boil at 160–180 °C for 3 h using dean-stalk apparatus placed in oil-bath. The completion of the reaction was monitored by checking TLC.
General procedure for the synthesis of 2-styrylbenzimidazole derivatives from 4-nitro benzene di amine and acetic acid (Scheme 2)
4-Nitro benzene di-amine on reaction with acetic acid in 4 N HCl under Phillip’s conditions for 3 h gave the well-known 2-methylbenzimidazole [3]. 2-methylbenzimidazole [3] on condensation with benzaldehydes (4j–4n) at 170–180 °C using dean-stark apparatus placed in oil-bath. The completion of the reaction was monitored by checking TLC.
(E)-phenyl-(2-styryl-1H-benzo[d]imidazol-6-yl)methanone (5a)
Light orange crystals, yield (2.9 g, 88%), m.p 202–204 °C, IR (KBr, ʋ
max cm−1): 3401 (–NH), 2956 (=C–H), 1891 (C=N), 1610 (C=C), 1644 (C=O), 1H NMR (DMSO-d
6
/TMS, 400 MHz) δppm 7.09–7.13 (d, 1H, –C=CH– vinylic proton, J
H-H = 16.4 Hz), 7.33–7.37 (d, 1H, –CH=C, vinylic proton, J
H-H = 16.4 Hz), 7.48–7.67 (m, 8H-aryl, 5H-phenyl), 10.2 (s, 1H, –NH of benzimidazole). 13C NMR (DMSO-d
6
, 100 MHz) δppm 102, 106, 108, 110, 112, 120, 121, 122, 128, 129, 130, 132, 142, 148, 152, 190, MS (m/z): 325.2 (M+).
(E)-(2-(4-fluorostyryl)-1H-benzo[d]imidazol-6-yl)(phenyl)methanone (5b)
Black crystals, yield (3.0 g, 90%), m.p 178–180 °C, IR (KBr, ʋ
max cm−1): 3432 (–NH), 3178 (=C–H), 1909 (C=N), 1628 (C=C), 1700 (C=O). 1H NMR (DMSO-d
6
/TMS, 400 MHz) δppm 7.09–7.13 (d, 1H, –C=CH– vinylic proton, J
H-H = 16.4 Hz), 7.3–7.9 (m, 8H-aryl, 4H-phenyl), 8.09–8.13 (d, 1H, –CH=C–, vinylic proton, J
H-H = 16.4 Hz), 10.2 (s, 1H, –NH of benzimidazole). 13C NMR (DMSO-d
6
, 100 MHz) δppm 102.29, 106.24, 108.53, 110, 112, 120, 121, 122, 128.51, 129, 130, 132, 142, 148, 152, 190.91, MS (m/z): 343.2 (M+).
(E)-(2-(4-chlorostyryl)-1H-benzo[d]imidazol-6-yl)(phenyl)methanone (5c)
Brown crystals, yield (3.2 g, 90%), m.p 130–132 °C, IR (KBr, ʋ
max cm−1): 3426 (–NH), 2898 (=C–H), 1909 (C=N), 1601 (C=C), 1680 (C=O), 1H NMR (DMSO-d
6
/TMS, 400 MHz) δppm 7.09–7.13 (d, 1H, –C=CH– vinylic proton, J
H-H = 16.4 Hz), 7.3–7.9 (m, 8H-aryl, 4H-phenyl), 8.09–8.13 (d, 1H, –CH=C–, vinylic proton, J
H-H = 16.4 Hz), 10.2 (s, 1H, –NH of benzimidazole). 13C NMR (DMSO-d
6
, 100 MHz) δppm 102, 106, 108, 110, 112, 120, 121, 122, 128, 129, 130, 132, 142, 148, 152, 190, MS (m/z): 359.1 (M+).
(E)-(2-(2-(furan-2-yl)vinyl)-1H-benzo[d]imidazol-6-yl)(phenyl)methanone (5d)
Black crystals, yield (2.5 g, 82%), m.p 100–102 °C, IR (KBr, ʋ
max in cm−1): 3423 (–NH), 2921 (=C–H), 1642 (C=N), 1597 (C=C), 1617 (C=O), 1H NMR (DMSO-d
6
/TMS, 400 MHz) δppm 6.6–8.1 (m, 8H-aryl, 3H-furanyl, 2H-vinylic protons, J
H-H = 16.4 Hz), 10.2 (s, 1H, –NH of benzimidazole). 13C NMR (DMSO-d
6
, 100 MHz) δ ppm: 111.00, 112.01, 118.01, 125.12, 128.45, 128.68, 128.91, 129.47, 130.43, 131.85, 132.27, 137.75, 139.96, 152.32, 195.27, MS (m/z): 370.2 (M+).
(E)-phenyl(2-(2-(thiophen-2-yl)vinyl)-1H-benzo[d]imidazole-6-yl)methanone (5e)
Light green crystals, yield (2.6 g, 80%), m.p 108–110 °C, IR (KBr, ʋ
max in cm−1): 3427 (–NH), 3060 (=C–H), 1633 (C=N), 1597 (C=C), 1614 (C=O). 1H NMR (DMSO-d
6
/TMS, 400 MHz) δppm 6.6–8.1 (m, 8H-aryl, 3H-thiophenyl, 2H-vinylic protons, J
H-H = 16.4 Hz), 10.2 (s, 1H, –NH of benzimidazole). 13C NMR (DMSO-d
6
, 100 MHz) δppm 111.00, 112.01, 118.01, 125.12, 128.45, 128.68, 128.91, 129.47, 130.43, 131.85, 132.27, 137.75, 139.96, 152.32, 195.27, MS (m/z): 370.2 (M+).
(E)-(2-(2-(benzo[d][1,3]dioxol-5-yl)vinyl)-1H-benzo[d]imidazol-6-yl)(phenyl)methanone (5f)
Dark brown crystals, yield (3.2 g, 88%), m.p −240 °C, IR (KBr, ʋ
max in cm−1): 3422 (–NH), 2917 (=C–H), 1644 (C=N), 1575 (C=C), 1609 (C=O). 1H NMR (DMSO-d
6
/TMS, 400 MHz) δppm 2.5 (s, 2H, –CH2), 6.2–6.26 (d, 1H, –C=CH–, vinylic proton, J
H-H = 16.4 Hz), 7.0–8.0 (m, 8H-aryl, 4H-phenyl, 1H-vinylic protons, J
H-H = 16.4 Hz), 9.8 (s, 1H, –NH of benzimidazole). 13C NMR (DMSO-d
6
, 100 MHz) δppm 114.30, 115.04, 116.96, 125.42, 128.45, 128.68, 129.12, 129.30, 129.48, 129.59, 131.08, 132.22, 132.33, 133.76, 134.37, 137.58, 137.64, 137.74, 195.17, MS (m/z): 370.2 (M+).
(E)-(2-(2-(1H-indol-2-yl)vinyl)-1H-benzo[d]imidazol-6-yl)(phenyl)methanone (5g)
Light green crystals, yield (1.97 g, 92%), m.p 198–200 °C, IR (KBr, ʋ
max in cm−1): 3405 (–NH), 3101 (=C–H), 1894 (C=N), 1633 (C=C). 1H NMR (DMSO-d
6
/TMS, 400 MHz) δppm 6.91–6.95 (d, 1H, –C=CH vinylic, J
H-H = 16.4 Hz), 7.16–7.18 (t, 1H, thiophenyl), 7.23–7.28 (q, 2H, phenylic), 7.44–7.45 (d, 1H, thiophenyl), 7.57–7.61 (q, 2H, phenylic), 7.67–7.68(d, 1H, thiophenyl), 7.92–7.96 (d, 1H, –CH=C–(vinylic), J
H-H = 16.4 Hz), 10.0 (s, 1H, –NH of benzimidazole). 13C NMR (DMSO-d
6
, 100 MHz) δppm 114.47, 114.50, 122.87, 127.96, 128.51, 129.15, 129.48, 137.39, 140.33, 149.87, MS (m/z): 227.07 (M+).
(E)-(2-(4-nitrostyryl)-1H-benzo[d]imidazol-6-yl)(phenyl)methanone (5h)
Light yellow crystals, yield (3.2 g, 86%), m.p 210–212 °C, IR (KBr, ʋ
max in cm−1): 3410 –NH), 2960 (=C–H), 1680 (C=N), 1620 (C=C), 1670 (C=O). 1H NMR (DMSO-d
6
/TMS, 400 MHz) δppm 7.0–8.3 (m, 8H-aryl, 4H-phenyl, 2H-vinylic protons, J
H-H = 16.4 Hz), 10.2 (s, 1H, –NH of benzimidazole). 13C NMR (DMSO-d
6
, 100 MHz) δppm 102, 106, 108, 110, 112, 120, 121, 122, 128, 129, 130, 132, 142, 148, 152, 190, MS (m/z): 370.2 (M+).
(E)-(2-(2-nitrostyryl)-1H-benzo[d]imidazol-6-yl)(phenyl)methanone (5i)
Light yellow crystals, yield (3.2 g, 86%), m.p 210–212 °C, IR (KBr, ʋ
max in cm−1): 3410 (–NH), 2960 (=C–H), 1680 (C=N), 1620 (C=C), 1670 (C=O). 1H NMR (DMSO-d
6
/TMS, 400 MHz) δppm 7.0–8.3 (m, 8H-aryl, 4H-phenyl, 2H-vinylic protons, J
H-H = 16.4 Hz), 10.2 (s, 1H, –NH of benzimidazole). 13C NMR (DMSO-d
6
, 100 MHz) δppm 102, 106, 108, 110, 112, 120, 121, 122, 128, 129, 130, 132, 142, 148, 152, 190, MS (m/z): 370.2 (M+).
(E)-2-(4-fluorostyryl)-6-nitro-1H-benzo[d]imidazole (5j)
Brown crystals, yield (2.49 g, 88%), m.p 203–206 °C, IR (KBr, ʋ
max in cm−1): 3405 (–NH), 3101 (=C–H), 1894 (C=N), 1633 (C=C), 1340–1520 (NO2), 1H NMR (DMSO-d
6
/TMS, 400 MHz) δppm 6.9–7.9 (q, 4H-aryl protons), 7.71–7.75 (d, 1H-vinylic proton, J
H-H = 16.4 Hz), 7.76–7.79 (q, 2H-aryl protons), 8.80–8.84 (d, 1H-vinylic proton, J
H-H = 16.4 Hz), 8.42 (s, 1H, ArH), 10.0 (s, 1H, NH, benzimidazole). 13C NMR (DMSO-d
6
, 400 MHz) δppm 115.85, 115.93, 115.95, 116.06, 118.10, 129.57, 129.65, 131.73, 131.76, 132.09, 136.36, 142.63, 155.14, 161.47, 190.20, MS (m/z): 284.07 (M+).
(E)-2-(2-(1H-indol-2-yl)vinyl)-1H-benzo[d]imidazole (5k)
Light green crystals, yield (1.97 g, 92%), m.p 198–200 °C, IR (KBr, ʋ
max in cm−1): 3405 (–NH), 3101 (=C–H), 1894 (C=N), 1633 (C=C). 1H NMR (DMSO-d
6
/TMS, 400 MHz) δppm 6.91–6.95 (d, 1H,=CH-vinylic proton, J
H-H = 16.4 Hz), 7.16–7.18 (t, 1H, thiophenyl proton), 7.23–7.28 (q, 2H, phenylic protons), 7.44–7.45 (d, 1H, thiophenyl proton), 7.57–7.61 (q, 2H, phenylic protons), 7.67–7.68(d, 1H, thiophenyl proton), 10.0 (s, 1H, –NH, benzimidazole). 13C NMR (DMSO-d
6
, 100 MHz) δppm 114.47, 114.50, 122.87, 127.96, 128.51, 129.15, 129.48, 137.39, 140.33, 149.87. MS (m/z): 227.07 (M+).
(E)-6-nitro-2-styryl-1H-benzo[d]imidazole (5l)
Brown crystals, yield (2.49 g, 88%), m.p 203–206 °C, IR (KBr, ʋ
max in cm−1): 3405 (–NH), 3101 (=C–H), 1894 (C=N), 1633 (C=C), 1340–1520 (NO2). 1H NMR (DMSO-d
6
/TMS, 400 MHz) δppm 6.9–7.9 (q, 4H-aryl protons), 7.71–7.75 (d, 1H-vinylic proton, J
H-H = 16.4 Hz), 7.76–7.79 (q, 2H-aryl protons), 8.80–8.84 (d, 1H-vinylic proton, J
H-H = 16.4 Hz), 8.42 (s, 1H- aromatic proton), 10.0 (s, 1H, –NH benzimidazole). 13C NMR (DMSO-d
6
, 400 MHz) δppm 115.85, 115.93, 115.95, 116.06, 118.10, 129.57.
(E)-2-(2-(furan-2-yl)vinyl)-6-nitro-1H-benzo[d]imidazole (5m)
Yield 2.04 gm (80%); m.p 240 °C, IR (KBr, ʋ
max in cm−1): 3405 (–NH), 3101 (=C–H), 1894 (C=N), 1633 (C=C), 1340–1520 (NO2,). 1H NMR (DMSO-d
6
/TMS, 400 MHz) δppm 6.5–7.8 (m, 3H-furanyl protons), 6.99–7.03 (d, 1H-vinylic proton, J
H-H = 16.4 Hz), 7.03–7.07 (d, 1H-vinylic proton, J
H-H = 16.4 Hz), 7.6–8.1 (m, 3H-aryl protons), 10.0 (s, 1H, –NH, benzimidazole). MS (m/z): 256.07 (M+).
(E)-2-(2-(benzo[d][1,3]dioxol-5-yl)vinyl)-6-nitro-1H-benzo[d]imidazole (5n)
Dark brown crystals, yield (3.2 g, 88%), m.p >240 °C, IR (KBr, ʋ
max in cm−1): 3422 (–NH), 2917 (=C–H), 1644 (C=N), 1575 (C=C), 1609 (C=O), 1H NMR (DMSO-d
6
/TMS, 400 MHz) δppm 2.5 (s, 2H, –CH2), 6.2–6.26 (d, 1H, –C=CH–, vinylic proton, J
H-H = 16.4 Hz), 7.0–8.0 (m, 8 aryl, 4H-phenyl, 1H-vinylic protons, J
H-H = 16.4 Hz), 9.8 (s, 1H, –NH of benzimidazole). 13C NMR (DMSO-d
6
, 100 MHz) δppm 114.30, 115.04, 116.96, 125.42, 128.45, 128.68, 129.12, 129.30, 129.48, 129.59, 131.08, 132.22, 132.33, 133.76, 134.37, 137.58, 137.64, 137.74, 195.17, MS (m/z): 370.2 (M+).