Synthesis of 2-Arylamino-2-Imidazolines and 2-Aminobenzimidazoles
Synthesis of amino(phenylimino)methanesulfonic
acid
NH), 3.73 (s, 4H, imidazoline CH2), 6.28 (broad peak,
1H, imidazoline NH), 7.12—8.34 (m, 4H, ArH); IR
(KBr) ν: 3270 (imidazoline N—H stretching), 3262
(N—H stretching), 1665 (C=N stretching), 1542 (N—
Typical procedure A reaction vessel was charged
with 1-phenylthiourea (1.97 g, 0.013 mol), water (6 mL),
sodium chloride (0.29 g, 0.005 mol) and sodium mo-
lybdate dihydrate (0.0484 g, 0.0002 mol), and cooled to
0 ℃ with efficient stirring. Hydrogen peroxide (30%,
4.65 g, 0.041 mol) was added drop wise to the cooled
suspension at a rate to minimize decomposition (fol-
lowed the reaction by TLC). After addition of H2O2, the
reaction mixture was allowed to warm up to 30 ℃ and
stirred for 1 h. The product was isolated by cooling the
reaction to 5 ℃ and collecting the solid sulfonic acid
by filtration (2.33 g, 90%). m.p. 157.5—158.5 ℃
(Lit.14 157—158 ℃); 1H NMR (DMSO-d6, 300 MHz) δ:
3.52 (s, 1H, NH), 7.12—7.85 (m, 4H, ArH), 10.23 (br s,
1H); IR (KBr) ν: 3340 (NH amine), 3350 (OH), 1670
(C=N stretching), 1590 (N—H bending), 1170 (asy
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1
H bending) cm .
N-(4-Bromophenyl)-N-(4,5-dihydro-1H-imidazol-2-
yl)amine: 1H NMR (DMSO-d6, 300 MHz) δ: 3.35 (s, 1H,
NH), 3.68 (s, 4H, imidazoline CH2), 6.04 (broad peak,
1H, imidazoline NH), 7.10—8.51 (m, 4H, ArH); IR
(KBr) ν: 3267 (imidazoline N—H stretching), 3253
(N—H stretching), 1667 (C=N stretching), 1547 (N—
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1
H bending) cm .
2-Aminoimidazoline: 1H NMR (DMSO-d6, 300
MHz) δ: 3.50 (s, 2H, NH2), 3.61 (s, 4H, imidazoline
CH2), 6.02 (broad peak, 1H, imidazoline NH); IR (KBr)
ν: 3258 (imidazoline N—H stretching), 3243, 3250
(NH2 stretching), 1660 (C=N stretching), 1540 (N—H
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1
bending) cm .
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1
SO2), 1040 (sym. SO2), 650 (SO) cm .
Synthesis of 2-amino-5-nitrobenzimidazole
Amino(4-chlorophenylimino)methanesulfonic acid:
1
Typical procedure Aminoiminomethanesulfonic
acid (1.24, 0.01 mol) and 4-nitrophenylenediamine
(1.53 g, 0.01 mol) were mixed in 10 mL of 2-propanol
or water and stirred at room temperature for 5 min. The
reaction mixture was heated at 60 ℃ for 1 h. The mix-
ture was cooled and pH was adjusted between 12—14
with 3 mol/L NaOH. The resulting precipitate was fil-
tered and washed with water. Crude product was re-
crystalized from methanol (1.6 g, 90%), m.p. 207—210
m.p. 147—148 ℃; H NMR (DMSO-d6, 300 MHz) δ:
3.52 (s, 1H, NH), 7.02—7.90 (m, 4H, ArH), 10.22 (br s,
1H); IR (KBr) ν: 3340 (NH amine), 3345 (OH), 1668
(C=N stretching), 1595 (N—H bending), 1170 (asy
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1
SO2), 1040 (sym. SO2), 655 (SO) cm .
Amino(4-bromophenylimino)methanesulfonic acid:
1
m.p. 153—156 ℃; H NMR (DMSO-d6, 300 MHz) δ:
3.40 (s, 1H, NH), 7.02—7.76 (m, 4H, ArH), 10.20 (br s,
1H); IR (KBr) ν: 3340 (NH amine), 3348 (OH), 1668 (C
=N stretching), 1590 (N—H bending), 1174 (asy SO2),
1
℃ (Lit.17 207—211 ℃); H NMR (DMSO-d6, 300
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1
MHz) δ: 6.85 (s, 2H), 7.18 (d, J=8.7 Hz, 1H), 7. 87 (dd,
JAB=8.7 Hz, Jm=2.3 Hz, 1H), 7.95 (d, J=2.3 Hz, 1H).
2-Amino-5-methylbenzimidazole: m.p. 203 — 204
℃; 1H NMR (DMSO-d6, 300 MHz) δ: 2.31 (s, 3H), 6.85
(s, 2H), 7.18 (d, J=8.2 Hz, 1H), 7. 87 (dd, JAB=8.2 Hz,
Jm=2.2 Hz, 1H), 7.95 (d, J=2.2 Hz, 1H).
1045 (sym. SO2), 650 (SO) cm .
Amino(2,6-dichlorophenylimino)methanesulfonic a-
cid: m.p. 264—265 ℃; 1H NMR (DMSO-d6, 300 MHz)
δ: 3.52 (s, 1H, NH), 7.02—8.10 (m, 3H, ArH), 10.18 (br
s, 1H); IR (KBr) ν: 3345 (NH amine), 3350 (OH), 1668
(C=N stretching), 1545 (N—H bending), 1173 (asy
1
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1
2-Amino-5-chlorobenzimidazole: H NMR (DMSO-
SO2), 1046 (sym. SO2), 650 (SO) cm .
d6, 300 MHz) δ: 6.79 (s, 2H), 7.15 (d, J=8.1 Hz, 1H),
7.80 (dd, JAB=8.1 Hz, Jm=2.1 Hz, 1H), 7.90 (d, J=2.1
Hz, 1H).
Synthesis of N-phenyl-N-(4,5-dihydro-1H-imidazol-
2-yl)amine
1
2-Aminobenzimidazole: H NMR (DMSO-d6, 300
Typical procedure Amino(phenylimino)sulfonic
acid (2 g, 0.01 mol) prepared above was added to the
ethylenediamine (1.56 g, 0.026 mol) in 10 mL of
2-propanol or water at room temperature. The reaction
mixture was heated at 60 ℃ for 4 h. The reaction was
worked up by adjusting the pH to range 12—14 with 3
mol/L NaOH and the mixture was extracted with
CH2Cl2 (20 mL×3), dried over Na2SO4 and concen-
trated. The concentrated residue was purified by column
chromatography to afford pure compound (1.38 g, 86%).
MHz) δ: 6.68 (s, 2H), 7.21—7.81 (m, 5H).
References
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1
m.p. 115.5—117 ℃ (Lit.12 m.p. 115—116 ℃); H
NMR (DMSO-d6, 300 MHz) δ: 3.45 (s, 1H, NH), 3.70
(s, 4H, imidazoline CH2), 6.28 (broad peak, 1H, imida-
zoline NH), 7.10—8.15 (m, 5H, ArH); IR (KBr) ν: 3275
(imidazoline N—H stretching), 3254 (N—H stretching),
6
7
Chapleo, C. B.; Butler, R. C.; England, D. C.; Myeres, P. L.;
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1
1660 (C=N stretching), 1539 (N—H bending) cm .
N-(4-Chlorophenyl)-N-(4,5-dihydro-1H-imidazol-2-
yl)amine: 1H NMR (DMSO-d6, 300 MHz) δ: 3.48 (s, 1H,
Chin. J. Chem. 2011, 29, 1055— 1058
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