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4.3. General procedure for homo-coupling of aryl-
diazonium salts without electron-withdrawing groups
1034 cmꢁ1; dH (600 MHz, CDCl3) 7.49–7.46 (4H, m,
arom.), 6.97–6.94 (4H, m, arom.), 3.84 (6H, s, 2ꢂOCH3);
dC (600 MHz, CDCl3) 158.5, 133.3, 127.6, 114.0, 55.2.
To a solution of copper(II) triflate (145 mg, 0.4 mmol,
20 mol %) in anhydrous acetonitrile (10 mL), 2,20-bipyr-
idine (bpy, 62 mg, 0.4 mmol, 20 mol %) was added, and the
resulting mixture was stirred at rt for 1 h under an argon at-
mosphere. Then, copper bronze (0.38 g, 6 mmol, 3 equiv),
and aryldiazonium salt (1j–p, 2 mmol) were added, and
the resulting suspension was stirred at rt under an argon at-
mosphere for the time indicated in Table 3. The reaction
mixture was evaporated to dryness, diluted with water
(20 mL) and then extracted with dichloromethane
(3ꢂ20 mL). The combined organic phases were dried
(Na2SO4), filtered, and evaporated to dryness. Crude prod-
ucts were purified by preparative chromatography on silica
gel (50 g).
4.3.7. trans-4,40-Dimethoxyazobenzene (3m). Yellow nee-
dles; yield 51 mg (21%); Rf (CH2Cl2) 0.59; mp 155.4–
158.7 ꢀC; nmax (KBr) 3016, 2839, 2033, 1599, 1579, 1497,
1457, 1439, 1318, 1244, 1178, 1144, 1103, 1023 cmꢁ1; dH
(600 MHz, CDCl3) 7.91–7.87 (4H, m, arom.), 7.02–6.98
(4H, m, arom.), 3.88 (6H, s, 2ꢂOCH3); dC (600 MHz,
CDCl3) 161.4, 146.9, 124.2, 114.0, 55.4.
4.3.8. 3,30-Dimethoxybiphenyl (2n). Colourless liquid;
yield 170 mg (79%); Rf (CH2Cl2/n-hexane, 2:1) 0.51; nmax
(KBr) 3054, 3029, 3000, 2957, 2939, 2835, 1599, 1575,
1477, 1412, 1317, 1299, 1291, 1235, 1204, 1170, 1092,
1056, 1047, 1031 cmꢁ1; dH (600 MHz, CDCl3) 7.34–7.29
(m, 2H, arom.), 7.17–7.11 (m, 4H, arom.), 6.89–6.85 (m,
2H, arom.), 3.81 (s, 6H, 2ꢂOCH3); dC (600 MHz, CDCl3)
159.7, 142.4, 129.6, 119.5, 112.8, 112.6, 55.0.
4.3.1. Biphenyl (2j). Colourless needles; yield 110 mg
(71%); Rf (CH2Cl2/n-hexane, 1:2) 0.65; mp 67.2–70.0 ꢀC;
lit.26 mp 69–70 ꢀC (corr.); nmax (KBr) 3033, 1569, 1480,
1429, 1344, 1170, 1042, 1007 cmꢁ1; dH (600 MHz,
CDCl3) 7.59–7.56 (4H, m, arom.), 7.44–7.39 (4H, m,
arom.), 7.34–7.16 (2H, m, arom.); dC (600 MHz, CDCl3)
141.1, 128.6, 127.1, 127.0.
4.3.9. N-(3-Methoxyphenyl)acetamide (4n). Colourless
needles; yield 56 mg (17%); Rf (CH2Cl2/2-PrOH, 9.5:0.5)
0.42; nmax (KBr) 3308, 3207, 3147, 3090, 3002, 2961,
2938, 2836, 1668, 1599, 1549, 1494, 1455, 1428, 1371,
1286, 1264, 1198, 1157, 1084, 1045 cmꢁ1; dH (600 MHz,
CDCl3) 8.10 (s, 1H, NH), 7.29–7.28 (m, 1H, arom.), 7.21–
7.08 (m, 1H, arom.), 7.03–7.00 (m, 1H, arom.), 6.67–
6.64 (m, 1H, arom.), 3.75 (s, 3H, OCH3), 2.15 (s, 3H,
NHCOCH3); dC (600 MHz, CDCl3) 168.8, 159.8, 139.1,
129.4, 112.0, 109.7, 105.6, 55.0, 24.3.
4.3.2. trans-Azobenzene (3j). Orange needles; yield 10 mg
(5%); Rf (CH2Cl2/n-hexane, 2:1) 0.44; mp 70.1–73.2 ꢀC;
nmax (KBr) 3062, 2319, 1957, 1898, 1769, 1583, 1483,
1453, 1300, 1222, 1151, 1071, 1020 cmꢁ1; dH (600 MHz,
CDCl3) 7.94–7.92 (4H, m, arom.), 7.53–7.51 (4H, m,
arom.), 7.48–7.46 (2H, m, arom.); dC (600 MHz, CDCl3)
152.6, 130.9, 129.0, 122.7.
4.3.10. 2,20-Dimethoxybiphenyl (2o). Pale yellow needles;
yield 110 mg (51%); Rf (CH2Cl2) 0.70; mp 139.8–142.5 ꢀC;
nmax (KBr) 2962, 2930, 1914, 1601, 1590, 1500, 1482, 1456,
1429, 1299, 1284, 1237, 1164, 1112, 1022, 1001 cmꢁ1; dH
(600 MHz, CDCl3) 7.33–7.30 (2H, m, arom.), 7.24–7.23
(2H, m, arom.), 7.00–6.98 (2H, m, arom.), 6.97–6.96 (2H,
m, arom.), 3.75 (6H, s, 2ꢂOCH3); dC (600 MHz, CDCl3)
156.9, 131.3, 128.5, 127.5, 120.2, 111.0, 55.6.
4.3.3. 4,40-Dimethylbiphenyl (2k). Colourless needles;
yield 110 mg (60%); Rf (CH2Cl2/n-hexane, 1:2) 0.67; mp
121.5–122.0 ꢀC; lit.57 mp 120.7–121.5 ꢀC; nmax (KBr)
2914, 1903, 1562, 1501, 1445, 1311, 1178, 1113,
1036 cmꢁ1; dH (600 MHz, CDCl3) 7.49–7.46 (4H, m,
arom.), 7.24–7.21 (4H, m, arom.), 2.38 (6H, s, 2ꢂCH3); dC
(600 MHz, CDCl3) 138.2, 136.6, 129.3, 126.7, 21.0.
4.3.11. trans-2,20-Dimethoxyazobenzene (3o). Red nee-
dles; yield 42 mg (17%); Rf (CH2Cl2) 0.41; mp 143.1–
147.6 ꢀC; nmax (KBr) 2966, 2839, 2040, 1924, 1593,
1584, 1488, 1467, 1436, 1307, 1279, 1243, 1158, 1119,
1023 cmꢁ1; dH (600 MHz, CDCl3) 7.64–7.62 (2H, m,
arom.), 7.42–7.39 (2H, m, arom.), 7.07–7.05 (2H, m,
arom.), 7.01–6.98 (2H, m, arom.), 4.00 (6H, s, 2ꢂOCH3);
dC (600 MHz, CDCl3) 156.7, 142.8, 132.0, 120.6, 117.4,
112.4, 56.2.
4.3.4. trans-4,40-Dimethylazobenzene (3k). Orange nee-
dles; yield 22 mg (10%); Rf (CH2Cl2/n-hexane, 1:2) 0.48;
mp 137.1–140.8 ꢀC; nmax (KBr) 3021, 2921, 1598, 1501,
1411, 1294, 1208, 1152, 1108, 1035, 1010 cmꢁ1; dH
(600 MHz, CDCl3) 7.83–7.80 (4H, m, arom.), 7.31–7.28
(4H, m, arom.), 2.41 (6H, s, 2ꢂCH3); dC (600 MHz,
CDCl3) 150.7, 141.1, 129.6, 122.6, 21.5.
4.3.5. N-(2-Tolyl)acetamide (4l). Colourless needles; yield
101 mg (34%); Rf (CH2Cl2/2-PrOH, 9.5:0.5) 0.45; mp 105–
108 ꢀC; nmax (KBr) 3294, 1655 (C]O, amide), 1588, 1529,
1486, 1459, 1369, 1287, 1270 cmꢁ1; dH (600 MHz, CDCl3)
7.59 (1H, d, J 8.1 Hz, arom.), 7.45 (1H, s, NH), 7.13 (2H, s,
arom.), 7.07–7.03 (1H, m, arom.), 2.19 (3H, s, COCH3), 2.12
(3H, s, CH3); dC (600 MHz, CDCl3) 168.6, 135.5, 130.3,
130.0, 126.3, 125.3, 123.9, 23.8, 17.6.
4.3.12. 1,10-Binaphthyl (2p). Colourless needles; yield
18 mg (7%); mp 156.1–158.9 ꢀC; lit.59 mp 158–160 ꢀC;
nmax (KBr) 3039, 2963, 1927, 1821, 1568, 1502, 1384,
1327, 1259, 1210, 1130, 1012 cmꢁ1; dH (600 MHz,
CDCl3) 8.00–7.97 (4H, m, arom.), 7.65–7.60 (2H, m,
arom.), 7.55–7.48 (2H, m, arom.), 7.45–7.40 (4H, m,
arom.), 7.35–7.28 (2H, m, arom.); dC (600 MHz, CDCl3)
138.3, 133.4, 132.7, 128.0, 127.8, 127.7, 126.4, 125.9,
125.7, 125.3.
4.3.6. 4,40-Dimethoxybiphenyl (2m). Colourless needles;
yield 101 mg (47%); Rf (CH2Cl2) 0.74; mp 177.2–
180.3 ꢀC; lit.58 mp 182–183 ꢀC; nmax (KBr) 3056, 2923,
1567, 1488, 1463, 1423, 1261, 1241, 1128, 1084, 1057,
4.3.13. trans-1,10-Azobinaphthyl (3p). Pale orange needles;
yield 60 mg (21%); Rf (CH2Cl2/n-hexane, 1:2) 0.52;