Microwave Synthesis of Benzimidazoles
2823
0
0
0
0
1
12.97 (C-5 ), 121.11 (C-4, C-7), 122.05 (C-1 ), 123.06 (C-3 , C-5 ), 130.38
0 0
(
C-5, C-6), 131.19 (C-2 ), 131.21 (C-4 ), 150.12 (C-3a, C-7a), 156.39 (C-2),
þ
0
1
67.76 (C-6 ) ppm; EIMS: m/z (% rel. int.) 238 (M , 48), 223 (100), 209
15); 194 (85). HRMS: calcd. for C H N O: 238.1106, found: 238.1119.
(
15 14 2
2
2
7
-(4-Methoxyphenyl)-1H-benzimidazole (7): White solid, mp 228.6–
1
30.58C (ethanol). H NMR (300 MHz, DMSO-d ) d 3.82 (s, 3H, CH -O-),
6
3
0
0
.05–7.09 (m, 2H, H-3 , H-5 , J ¼ 8.5, J ¼ 2.2 Hz), 7.21–7.25 (m, 2H,
H-5, H-6, J ¼ 8.5, J ¼ 7.0, J ¼ 1.4 Hz), 7.57–7.61 (m, 2H, H-4, H-7,
0
0
J ¼ 8.5, J ¼ 1.4 Hz), 8.03–8.06 (m, 2H, H-2 , H-6 , J ¼ 8.5, J ¼ 1.4 Hz),
1
3
1
O-), 114.59 (C-3 , C-5 ), 116.08 (C-4, C-7), 123.48 (C-5, C-6), 125.28
0.88 (bs, 1H, N-H) ppm; C NMR (75.5 MHz, DMSO-d ) d 55.43 (CH -
6 3
0
0
0
0
0
0
(C-2 , C-6 ), 125.22 (C-1 ), 139.85 (C-3a, C-7a), 152.12 (C-2), 161.06 (C-4 )
ppm; EIMS: m/z (% rel. int.) 224 (M , 100), 209 (35), 181 (25); HRMS:
þ
calcd. for C H N O: 224.0949, found: 224.0952.
14 12 2
2
-(3-Hydroxy-4-methoxyphenyl)-1H-benzimidazole (9): Pale yellow solid,
1
mp 224.7–225.48C (methanol). H NMR (300 MHz, DMSO-d6) d 3.97
0
(
s, 3H, -OCH ), 6.91(d, 1H, H-5 , J ¼ 8.4 Hz), 7.11–7.16 (m, 2H, H-5, H-6,
3
0
J ¼ 9.6, J ¼ 3 Hz), 7.53 (sa, 1H, H-6 , J ¼ 0.9 Hz), 7.61 (dd, 2H, H-4, H-7,
J ¼ 8.1, J ¼ 1.8 Hz), 7.74 (d, 1H, H-2, J ¼ 1.5 Hz), 9.57 (bs, 2H, N-H,
1
3
O-H). C NMR (75.5 MHz, DMSO-d ) d55.67 (CH ), 110.24 (C-2 ),
0
6
3
0
0
1
16.07 (C-4, C-7), 117.28 (C-5 ), 123.08 (C-1 ), 123.48 (C-5, C-6), 124.72
0
0
0
(C-6 ), 139.73 (C-3a, C-7a), 146.81 (C-4 ), 150.22 (C-3 ), 151.67 (C-2) ppm.
2
2
6
-(5-Methyl-1H-benzimidazol-2-yl)phenol (14): White solid, mp 240–
1
428C (methanol). H NMR (300 MHz, DMSO-d ) d 2.43 (s, 3H, CH ),
6
3
0
.62 (dd, 1H, H-3 , J ¼ 7.8, J ¼ 1.2 Hz), 7.08–7.11 (m, 1H, H-6, J ¼ 8.6,
0
J ¼ 1.8 Hz), 7.09–7.13 (m, 1H, H-5 , J ¼ 7.7, J ¼ 1.3 Hz), 7.18 (td, 1H,
0
H-4 , J ¼ 7.8, J ¼ 7.7, J ¼ 1.8 Hz), 7.24–7.25 (m, 1H, H-4, J ¼ 1.8 Hz),
0
7
.26–7.28 (m, 1H, H-7, J ¼ 8.6 Hz), 7.78 (dd, 1H, H-6 , J ¼ 7.8 Hz), 7.78
0
13
(dd, 1H, H-6 , J ¼ 7.8, J ¼ 1.8 Hz), 10.95 (bs, 2H, N-H, O-H) ppm;
C
0
NMR (75.5 MHz, DMSO-d ) d 21.86 (CH ), 112.34 (C-7), 113.94 (C-1 ),
6
3
0
0
1
1
1
17.56 (C-3 ), 119.58 (C-4), 119.56 (C-4), 120.65 (C-5 ), 124.42 (C-6),
28.77 (C-6 ), 132.86 (C-4 ), 136.68 (C-3a), 137.43 (C-7a), 140.75 (C-5),
0
0
0
þ
56.39 (C-2), 159.60 (C-2 ) ppm; MS: m/z (% rel. int.) 224 (M , 100), 209
(2), 195 (25); HRMS: calcd. for C H N O: 224.0949, found: 224.0953.
14 12 2
2-(4-Methoxyphenyl)-5-methyl-1H-benzimidazole (19): Workup by extrac-
tion with EtOAc and concentration under vacuum left an oil, which was
purified by column chromatography (4 ꢀ 60 cm, 60 g of silica gel,
1
petroleum ether), colorless oil. H NMR (300 MHz, DMSO-d ) d 2.43
(
6
0 0
s, 3H, CH -C-5), 3.86 (s, 3H, CH -O-), 7.06–7.09 (m, 2H, H-3 , H-5 ,
3 3
J ¼ 8.4, J ¼ 2.4 Hz), 7.08–7.11 (m, 1H, H-6, J ¼ 8.6, J ¼ 1.7 Hz), 7.22–
7
.23 (m, 1H, H-4, J ¼ 1.7 Hz), 7.22–7.26 (m, 1H, H-7, J ¼ 8.6,