D
G.-F. Chen et al.
between aldehydes and ethylenediamine using molecular iodine
and potassium carbonate in absolute ethanol under ultrasound
irradiation. The advantages offered by this synthetic method-
ology are the mild reaction conditions, shorter reaction times,
operation simplicity, high product yields, low costs, and low-
toxicity catalyst.
(d, J 8.5, 2H, ArH), 7.37 (d, J 8.5, 2H, ArH), 4.74 (s, 1H, NH),
3.78 (s, 4H, CH2). dC 163.7, 136.6, 129.1, 128.6, 128.3, 50.3. m/z
(ESI) 181 [MþH]þ.
2-(4-Methylphenyl)imidazoline (3d), light yellow crystal.
nmax (KBr)/cmꢁ1 3138, 2921, 1599, 1494, 1271, 984, 828.
dH 7.67 (d, J 7.7, 2H, ArH), 7.20 (d, J 7.4, 2H, ArH), 4.61
(s, 1H, NH), 3.76 (s, 4H, CH2), 2.38 (s, 3H, CH3). dC 164.8,
140.8, 129.1, 127.6, 126.9, 50.2, 21.4. m/z (ESI) 161 [MþH]þ.
2-(4-Methoxyphenyl)imidazoline (3e), light yellow crystal.
nmax (KBr)/cmꢁ1 3121, 2927, 1604, 1492, 1253, 1030, 838.
dH 7.73 (d, J 8.7, 2H, ArH), 6.88–6.90 (m, 2H, ArH), 4.47 (s, 1H,
NH), 3.82 (s, 3H, CH3), 3.74 (s, 4 H, CH2). dC 164.5, 161.5,
128.4, 122.9, 114.0, 55.3, 50.3. m/z (ESI) 177 [MþH]þ.
2-(3-Nitrophenyl)imidazoline (3f), light yellow crystal. nmax
(KBr)/cmꢁ1 3148, 2932, 1597, 1524, 1269, 983, 699. dH 8.58
(s, 1H, ArH), 8.28 (d, J 8.2, 1H, ArH), 8.16 (d, J 7.6, 1H, ArH),
7.59 (t, J 8.0, 1H, ArH), 4.71 (s, 1H, NH), 3.84 (s, 4 H, CH2).
dC 162.1, 148.4, 133.0, 132.3, 129.5, 125.0, 121.9, 49.9. m/z
(ESI) 192 [MþH]þ.
Experimental
Apparatus, Materials, and Measurements
The materials were obtained from commercial suppliers and
used as received. The solvents were dried and freshly distilled
before reactions. All reactions were monitored by TLC plates
and visualised by ultraviolet light (254 nm). Melting points were
determined using a TECH X-4 melting point apparatus and were
uncorrected. Infrared (IR) spectra were recorded with a Bruker
1
VERTEX 70 infrared spectrometer using KBr discs. H NMR
(600 MHz) and 13C NMR (150 MHz) spectra were recorded at
room temperature on a Bruker AVANCE III 600 spectrometer
using TMS as internal standard and CDCl3 or [D6]DMSO as
solvent. Chemical shifts (d) are given in ppm relative to internal
TMS and coupling constants are in Hz. Mass spectrometric data
were determined on a Shimadzu LCMS-2010EV or a Bruker
apex ultra 7.0 T spectrometer (the accuracy was 1 ppm). The
ultrasonic irradiation was generated by a Shanghai Branson
BUG 40–06 or BUG25–06 ultrasonic cleaner (operating at a
frequency of either 40 or 25 kHz and a nominal power 250 W).
2-(4-Nitrophenyl)imidazoline (3g), light yellow crystal. nmax
(KBr)/cmꢁ1 3169, 2874, 1581, 1520, 1336, 983, 862, 699.
dH 8.29 (d, J 8.8, 2H, ArH), 8.06 (d, J 8.7, 2H, ArH), 3.66
(s, 4H, CH2). dC 162.8, 148.7, 136.9, 129.0, 124.2, 50.3. m/z
(ESI) 192 [MþH]þ.
2-(3,4-Dichlorophenyl)imidazoline (3h), white crystal. nmax
(KBr)/cmꢁ1 3191, 2939, 1633, 1508, 1283, 983, 817. dH 7.87
(s, 1H, ArH), 7.59 (d, J 8.3, 1H, ArH), 7.46 (d, J 8.3, 1H, ArH),
4.59 (s, 1H, NH), 3.78 (s, 4H, CH2). dC 162.8, 134.7, 132.8,
130.4, 129.0, 126.2, 50.4. m/z (ESI) 215 [MþH]þ.
Typical Procedure for Preparation of 2-Imidazolines
In a 25-mL conical flask, ethylenediamine (2, 1.1 mmol) was
added to a solution of aromatic aldehydes (1, 1 mmol) in abso-
lute ethanol (5 mL). Then anhydrous K2CO3 (414 mg, 3 mmol)
and I2 (317 mg, 1.25 mmol) were added to the resulting solution.
The reaction flask was placed in the ultrasonic bath; the reaction
mixture was slightly below the level of the water, and irradiated
at 25–308C for the time as indicated in Tables 1–5. The progress
of the reaction was monitored by TLC using ethyl acetate/
triethylamine (40 : 1 v/v) as eluent. After completion of the
reaction, the solvent was evaporated under reduced pressure.
The residue was quenched with saturated aqueous Na2S2O3 until
the iodine colour almost disappeared, and then extracted with
CH2Cl2 (4 ꢀ 10 mL). The organic layer was dried over Na2SO4.
After filtration, the filtrate was concentrated and the residue was
purified by silica gel column chromatography (200–300 mesh)
using ethyl acetate / triethylamine (80 : 1 v/v) as eluent. The
identity of the known compounds 3a–3g, 3i and 3j, and 3l–3o
were confirmed by comparing their melting points with those
2-(2,4-Dichlorophenyl)imidazoline (3i), light yellow crystal.
nmax (KBr)/cmꢁ1 3133, 2921, 1581, 1464, 1275, 978, 797.
dH 7.72 (d, J 8.4, 1H, ArH), 7.41 (d, J 2.0, 1H, ArH), 7.27
(dd, J 8.5, 2.0, 1H, ArH), 4.71 (s, 1H, NH), 3.78 (s, 4H, CH2).
dC 162.6, 136.4, 132.7, 132.2, 130.0, 128.8, 127.3, 50.2. m/z
(ESI) 215 [MþH]þ.
2-(3,4-Piperonyl)imidazoline (3j), light yellow crystal. nmax
(KBr)/cmꢁ1 3182, 2872, 1581, 1466, 1258, 1036, 826. dH 7.31
(s, 1H, ArH), 7.26 (d, J 8.2, 1H, ArH), 6.80 (d, J 8.0, 1H, ArH),
6.00 (s, 2H, OCH2O), 4.38 (s, 1H, NH), 3.75 (s, 4H, CH2).
dC 164.3, 149.6, 147.8, 124.7, 121.3, 108.0, 107.4, 101.4, 50.1.
m/z (ESI) 191 [MþH]þ.
2-(2-Furanyl)imidazoline (3k), white crystal. nmax (KBr)/
cmꢁ1 3075, 2928, 1636, 1506, 1174, 985, 754. dH 7.44 (s, 1H,
FuranH), 6.92 (d, J 3.4, 1H, FuranH), 6.44–6.45 (m, 1H,
FuranH), 4.80 (s, 1H, NH), 3.73 (s, 4H, CH2). dC 156.6, 145.8,
143.6, 111.6, 111.5, 50.0. m/z (ESI) 137 [MþH]þ.
2-(2-Pyridyl)imidazoline (3l), white crystal. nmax (KBr)/
cmꢁ1 3270, 3050, 1594, 1505, 1280, 977, 804. dH 8.48–8.49
(m, 1H, PyH), 8.06 (dd, J 7.9, 0.9, 1H, PyH), 7.67–7.69 (m, 1H,
PyH), 7.26–7.28 (m, 1H, PyH), 5.89 (s, 1H, NH), 3.76 (s, 4H,
CH2). dC 164.3, 148.7, 148.6, 136.5, 125.0, 122.2, 53.4. m/z
(ESI) 148 [MþH]þ.
1
reported in literature, their IR, H NMR, 13C NMR, and mass
spectra. The remaining unknown compounds 3h and 3k were
characterised by IR, 1H NMR, 13C NMR, and mass spectrometry.
2-(Phenyl)imidazoline (3a), light yellow crystal. nmax (KBr)/
cmꢁ1 3197, 2928, 1598, 1508, 1269, 981, 695. dH 7.79–7.80 (m,
2H, ArH), 7.45–7.47 (m, 1H, ArH), 7.40–7.42 (m, 2H, ArH),
3.80 (s, 4H, CH2). dC 164.8, 130.6, 130.5, 128.4, 127.0, 50.2. m/z
(ESI) 147 [MþH]þ.
2-(4-Pyridyl)imidazoline (3m), white crystal. nmax (KBr)/
cmꢁ1 3196, 3036, 1595, 1506, 1276, 980, 835. dH 8.67–8.68
(m, 2H, PyH), 7.63–7.64 (m, 2H, PyH), 4.84 (s, 1H, NH), 3.81
(s, 4H, CH2). dC 162.9, 150.2, 137.8, 121.1, 50.3. m/z (ESI) 148
[MþH]þ.
2-(3-Chlorophenyl)imidazoline (3b), white crystal. nmax
(KBr)/cmꢁ1 3150, 2932, 1564, 1511, 1273, 985, 758. dH 7.77–
7.78 (m, 1H, ArH), 7.63–7.65 (m, 1H, ArH), 7.39–7.41(m, 1H,
ArH), 7.30–7.34(m, 1H, ArH), 4.60 (s, 1H, NH), 3.78 (s, 4H,
CH2). dC 163.7, 134.4, 132.3, 130.6, 129.7, 127.2, 125.1, 50.3.
m/z (ESI) 181 [MþH]þ.
2-(4-Fluorophenyl)imidazoline (3n), white crystal. nmax
(KBr)/cmꢁ1 3133, 2938, 1612, 1493, 1222, 987, 842. dH
7.76–7.79 (m, 2H, ArH), 7.06–7.10 (m, 2H, ArH), 4.55 (s, 1H,
NH), 3.78 (s, 4H, CH2). dC 165.0, 163.8, 163.3, 129.1, 129.0,
126.8, 126.7, 115.6, 115.4, 50.4. m/z (ESI) 165.0823. HRMS
Anal. Calc. for C9H10FN2 [MþH]þ 165.0823. Found: 165.0821.
2-(4-Chlorophenyl)imidazoline (3c), white crystal. nmax
(KBr)/cmꢁ1 3116, 2922, 1607, 1469, 1270, 1012, 838. dH 7.71