MICROWAVE-ASSISTED ARYLATION OF 5-SUBSTITUTED TETRAZOLES
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ratio of 5-benzyl- and 5-(4-chlorobenzyl)-substituted
derivatives IIb:IIIb and IIc:IIIc was 1:2. In these
cases, microwave irradiation did not affect the selec-
tivity of arylation to an appreciable extent, but the
yield of isomeric products was higher. The overall
yields of 1,5- and 2,5-disubstituted tetrazoles IIa–IIc
and IIIa–IIIc under microwave irradiation and in con-
ventional thermal reactions were, respectively, %:
IIa+IIIa, 74, 56; IIb+IIIb, 82, 78; IIc+IIIc, 81, 64.
column chromatography on silica gel using ethyl
acetate–carbon tetrachloride (2:3) as eluent.
5-Benzyl-1-(4-nitrophenyl)tetrazole (IIb).
mp 114–115°C (from ethanol) [11]. IR spectrum, ν,
cm–1: 3439, 3123, 3113, 3095, 3067, 3032, 3007, 2925,
2867, 1615, 1599, 1528, 1507, 1493, 1456, 1427, 1381,
1363, 1347, 1316, 1301, 1280, 1264, 1149, 1113, 1097,
1081, 1074, 1040, 1028, 1012, 1002, 987, 963, 894,
859, 845, 795, 754, 738, 725, 712, 696, 690, 676, 578,
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5-Methyl-1-(4-nitrophenyl)tetrazol (IIa) and
5-methyl-2-(4-nitrophenyl)tetrazole (IIIa). 5-Meth-
yltetrazole (Ia), 0.4 g (5 mmol), was dissolved in
15 ml of DMSO, 0.5 g (3.5 mmol) of 4-nitrofluoro-
benzene and 0.2 g (5 mmol) of sodium hydroxide were
added, and the mixture was stirred for 3 h in a micro-
wave reactor at 90°C (50 W). The mixture was cooled
to 20°C and diluted with 50 ml of cold water, the
resulting suspension was acidified with hydrochloric
acid to pH 2, and the precipitate was filtered off,
treated with 10 ml of a 1% solution of sodium
hydroxide to remove unreacted 5-methyltetrazole,
washed with water, and dried in air. Overall yield 74%.
The isomeric products were separated by column
chromatography on silica gel using ethyl acetate–
carbon tetrachloride (2:3) as eluent.
544, 517, 501. H NMR spectrum (acetone-d6), δ,
ppm: 4.51 s (2H, CH2), 7.18–7.22 m (2H, Harom), 7.24–
7.38 m (3H, Harom), 7.93 d (2H, Harom), 8.50 d
(2H, Harom).
5-Benzyl-2-(4-nitrophenyl)tetrazole (IIIb).
mp 109°C (from propan-2-ol). IR spectrum, ν, cm–1:
3438, 3113, 3084, 3031, 2956, 2853, 1612, 1594, 1525,
1501, 1454, 1426, 1410, 1382, 1367, 1343, 1315, 1293,
1278, 1212, 1172, 1122, 1108, 1092, 1074, 1031, 1011,
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993, 863, 857, 832, 751, 733, 717, 700, 682. H NMR
spectrum (acetone-d6), δ, ppm: 4.43 s (2H, CH2), 7.27–
7.30 t (1H, Harom), 7.34–7.38 t (2H, Harom), 7.43 d (2H,
Harom), 8.44 d (2H, Harom), 8.55 d (2H, Harom). Found,
%: C 59.62; H 3.82; N 24.75. C14H11N5O2. Calculated,
%: C 59.79; H 3.91; N 24.91.
5-(4-Chlorobenzyl)-1-(4-nitrophenyl)tetrazole
(IIc). mp 188–189°C (from acetonitrile). IR spectrum,
ν, cm–1: 3442, 3121, 3110, 3090, 3067, 2977, 2922,
2854, 1613, 1598, 1524, 1508, 1490, 1440, 1429, 1416,
1407, 1361, 1344, 1313, 1294, 1280, 1266, 1165, 1150,
1108, 1092, 1182, 1040, 1014, 1009, 993, 957, 912,
859, 832, 825, 784, 753, 727, 716, 695, 684, 646, 549,
524, 505, 460. 1H NMR spectrum (acetone-d6), δ, ppm:
4.53 s (2H, CH2), 7.26 d (2H, Harom), 7.33 d (2H,
5-Methyl-1-(4-nitrophenyl)tetrazole (IIa).
mp 130°C (from toluene) [10]. IR spectrum, ν, cm–1:
3438, 3118, 3090, 3070, 3004, 2925, 2853, 1926, 1612,
1598, 1530, 1521, 1502, 1411, 1386, 1361, 1344, 1315,
1304, 1290, 1278, 1178, 1122, 1104, 1079, 1041, 1011,
983, 958, 856, 825, 754, 734, 716, 701, 689, 682, 528,
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502. H NMR spectrum (CDCl3), δ, ppm: 2.72 s (3H,
CH3), 7.77 d (2H, Harom), 8.48 d (2H, Harom). 13C NMR
spectrum (CDCl3), δC, ppm: 10.15 (CH3), 125.00
(CHarom), 125.45 (CHarom), 138.58 (Carom),148.20 (C5),
151.46 (Carom).
H
arom), 7.97 d (2H, Harom), 8.52 d (2H, Harom). 13C NMR
spectrum (acetone-d6), δC, ppm: 29.81 (CH2), 125.41
(CHarom), 126.79 (CHarom), 128.89 (CHarom), 130.94
(CHarom), 132.91 (Carom), 133.77 (Carom), 139.11 (Carom),
148.92 (C5), 154.55 (Carom). Found, %: C 53.38;
H 3.43; N 22.11. C14H10ClN5O2. Calculated, %:
C 53.25; H 3.17; N 22.19.
5-Methyl-2-(4-nitrophenyl)tetrazol (IIIa).
mp 155–156°C (from ethanol). IR spectrum, ν, cm–1:
3430, 3119, 3086, 3061, 3042, 3016, 2917, 2853, 2794,
1948, 1806, 1617, 1596, 1527, 1497, 1431, 1377, 1366,
1353, 1339, 1314, 1302, 1258, 1212, 1177, 1110, 1096,
1051, 1016, 971, 862, 853, 751, 743, 711, 693, 682,
5-(4-Chlorobenzyl)-2-(4-nitrophenyl)tetrazole
(IIIc). mp 144°C (from acetonitrile). IR spectrum, ν,
cm–1: 3436, 3115, 3090, 3083, 3055, 2922, 2853, 1615,
1594, 1525, 1507, 1490, 1433, 1421, 1407, 1382, 1368,
1340, 1314, 1293, 1230, 1186, 1173, 1109, 1095, 1084,
1015, 1010, 996, 914, 864, 854, 801, 749, 735, 711,
683, 625, 517, 485. 1H NMR spectrum (acetone-d6), δ,
ppm: 4.44 s (2H, CH2), 7.39 d (2H, Harom), 7.46 (2H,
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533, 504, 496. H NMR spectrum (CDCl3), δ, ppm:
2.67 s (3H, CH3), 8.31–8.34 d (2H, Harom), 8.42–8.45 d
(2H, Harom). 13C NMR spectrum (CDCl3), δC, ppm:
10.98 (CH3), 120.12 (CHarom), 125.40 (CHarom), 140.55
(Carom), 147.55 (Carom), 164.16 (C5). Found, %:
C 46.57; H 3.42; N 34.18. C8H7N5O2. Calculated, %:
C 46.83; H 3.41; N 34.15.
Tetrazoles IIb/IIIb and IIc/IIIc were synthesized in
a similar way. Individual isomers were isolated by
H
arom), 8.42 d (2H, Harom), 8.54 d (2H, Harom). 13C NMR
spectrum (acetone-d6), δC, ppm: 31.06 (CH2), 120.72
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 46 No. 4 2010