Development of an imidazole salt catalytic system for the preparation of bis(indolyl)methanes
0.30 (40:10 PE:EA); mp 139–140 oC, lit. mp 141–142 oC [43]; 1H NMR (400 MHz, CDCl3) δ
5.89 (1H, s), 6.67 (2H, dd, J = 2.4, 0.9 Hz), 7.00 (2H, td, J = 7.5, 1.0 Hz), 7.19 (2H, t, J = 7.9 Hz),
7.22–7.25 (1H, m), 7.28–7.30 (2H, m), 7.34–7.39 (4H, m), 7.40–7.43 (2H, m), 7.90 (2H, br s);
13C NMR (100 MHz, CDCl3) δ 40.2, 111.0, 119.3, 119.8, 120.0, 121.9, 123.6, 126.2, 127.1, 128.2,
128.7, 136.7, 144.0; HRMS (ESI+) calcd for C23H19N2 [M+H]+ 323.1543, found 323.1531
(error 3.7 ppm). All spectroscopic data were in agreement with the literature values. [20]
3,3’-((4-Ethylphenyl)methylene)bis(1H-indole) (4b). Condensation of indole and benzalde-
hyde using the general method afforded the title compound (168 mg, yield 96%) as a white
solid. Rf = 0.33 (40:10 PE:EA); mp 161–163 oC; 1H NMR (400 MHz, CDCl3) δ 1.22 (3H, t,
J = 8.5 Hz), 2.61 (2H, q, J = 8.5 Hz), 5.86 (1H, s), 6.66 (2H, s), 7.00 (2H, t, J = 7.5 Hz), 7.11 (2H,
d, J = 9.0 Hz), 7.18 (2H, t, J = 7.5 Hz), 7.26 (2H, d, J = 9.0 Hz), 7.35 (2H, d, J = 7.5 Hz), 7.40
(2H, d, J = 7.5 Hz), 7.86 (2H, br s); 13C NMR (100 MHz, CDCl3) δ 15.5, 28.5, 39.8, 111.0, 119.2,
119.99, 120.01, 121.9, 123.6, 127.1, 127.7, 128.6, 136.7, 141.2, 141.9; HRMS (ESI+) calcd for
C25H23N2 [M+H]+ 351.1840, found 351.1855 (error 4.3 ppm).
3,3’-([1,1’-Biphenyl]-4-ylmethylene)bis(1H-indole) (4c). Condensation of indole and benz-
aldehyde using the general method afforded the title compound (183 mg, yield 92%) as a pink
solid. Rf = 0.34 (40:10 PE:EA); mp 230–232 oC, lit. mp 241–243 oC [44]; 1H NMR (400 MHz,
CDCl3) δ 5.94 (1H, s), 6.62–6.67 (2H, m), 7.02 (2H, t, J = 8.0 Hz), 7.18 (2H, t, J = 7.6 Hz), 7.32
(1H, t, J = 7.3 Hz), 7.34–7.39 (3H, m), 7.40–7.48 (5H, m), 7.52 (2H, d, J = 8.9 Hz), 7.59 (2H, d,
J = 8.9 Hz), 7.92 (2H, br s); 13C NMR (100 MHz, CDCl3) δ 39.9, 111.1, 119.3, 119.7, 120.0,
122.0, 123.6, 126.95, 126.99 (2C), 127.1, 128.7, 129.1, 136.7, 138.9, 141.1, 143.2; HRMS (ESI-)
calcd for C29H21N2 [M−H]− 397.1684, found 397.1699 (error 3.8 ppm). All spectroscopic data
were in agreement with the literature values. [44]
3,3’-((2-Fluorophenyl)methylene)bis(1H-indole) (4d). Condensation of indole and benzal-
dehyde using the general method afforded the title compound (157 mg, yield 92%) as a red
solid. Rf = 0.35 (40:10 PE:EA); mp 80–81 oC, lit. mp 77 oC [28]; 1H NMR (400 MHz, CDCl3) δ
6.24 (1H, s), 6.70 (2H, s), 6.98–7.04 (3H, m), 7.08 (1H, t, J = 9.2 Hz), 7.16–7.22 (4H, m), 7.36
(2H, d, J = 8.2 Hz), 7.41 (2H, d, J = 7.9 Hz), 7.89 (2H, br s); 13C NMR (100 MHz, CDCl3) δ 32.5
(d, J = 4.1 Hz), 111.1, 115.3 (d, J = 22.4 Hz), 118.3, 119.3, 119.8, 122.0, 123.6, 123.9 (d, J = 3.5
Hz), 126.9, 127.8 (d, J = 8.1 Hz), 130.4 (d, J = 3.5 Hz), 130.9 (d, J = 14.0 Hz), 136.7, 160.7 (d,
J = 245.9 Hz); HRMS (ESI+) calcd for C23H18FN2 [M+H]+ 341.1449, found 341.1437 (error
3.5 ppm). All spectroscopic data were in agreement with the literature values. [28]
3,3’-((2-Bromo-6-fluorophenyl)methylene)bis(1H-indole) (4e). Condensation of indole
and benzaldehyde using the general method afforded the title compound (194 mg, yield 93%)
as a red solid. Rf = 0.32 (40:10 PE:EA); mp 113–115 oC; 1H NMR (400 MHz, CDCl3) δ 6.27
(1H, s), 6.64 (2H, dd, J = 2.3, 1.0 Hz), 6.83 (1H, ddd, J = 8.7, 7.8, 3.1 Hz), 6.95 (1H, dd, J = 9.8,
3.1 Hz), 7.04 (2H, t, J = 7.2 Hz), 7.21 (2H, t, J = 7.2 Hz), 7.41–7.39 (4H, m), 7.51–7.61 (1H, m),
7.95 (2H, br s); 13C NMR (100 MHz, CDCl3) δ 39.8, 111.2, 115.2 (d, J = 22.4 Hz), 117.8 (d,
J = 23.5 Hz), 117.9, 118.8 (d, J = 3.0 Hz), 119.5, 119.8, 122.2, 123.8, 126.9, 133.9 (d, J = 7.8 Hz),
136.8, 145.5 (d, J = 6.6 Hz), 162.1 (d, J = 245.8 Hz); HRMS (ESI+) calcd for C23H17FBrN2 [M
+H]+ 419.2889, found 419.2894 (error 1.2 ppm).
3,3’-((3-Hydroxyphenyl)methylene)bis(1H-indole) (4f). Condensation of indole and benz-
aldehyde using the general method afforded the title compound (152 mg, yield 90%) as a red
solid. Rf = 0.20 (40:10 PE:EA); mp 105–107 oC, lit. mp 100 oC [21]; 1H NMR (400 MHz,
CDCl3) δ 5.35 (1H, s), 6.00 (1H, s), 6.78 (2H, d, J = 2.4 Hz), 6.86 (2H, t, J = 7.5 Hz), 7.02 (2H, t,
J = 7.5 Hz), 7.13–7.23 (4H, m), 7.28 (4H, dd, J = 10.8, 8.4 Hz), 7.99 (2H, br s); 13C NMR (100
MHz, CDCl3) δ 35.9, 111.2, 116.7, 117.2, 119.6, 119.9, 120.8, 122.4, 123.6, 126.9, 128.1, 129.1,
130.0, 136.9, 154.6; HRMS (ESI+) calcd for C23H19N2O [M+H]+ 339.1483, found 339.1492
(error 2.7 ppm). All spectroscopic data were in agreement with the literature values. [21]
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