376 JOURNAL OF CHEMICAL RESEARCH 2014
Table 2 Synthesis of 1,3-dialkylimidazole-2-selenones in ethanol or
gave the pure product. All the products were characterised by NMR
and HRMS.
acetone
1-Butyl-3-methyl-1H-imidazole-2(3H)-selenone (1b):16 Yellow liquid,
1H NMR (400 MHz, CDCl3): δ 0.96 (t, J=8 Hz, 3H, CH3), 1.34–1.44
(m, 2H, CH2), 1.75–1.86 (m, 2H, CH2), 3.71 (s, 3H, N–CH3), 4.13 (t,
J=7.6 Hz, 2H, N–CH2), 6.88 (br, 1H, J=2 Hz, CH), 6.90 (br, J=2 Hz,
1H, CH). 13C NMR (100 MHz, CDCl3): δ 13.65, 19.70, 29.24, 31.14,
37.05, 49.70, 118.78, 119.92, 154.61 (C=Se). HRMS for C8H14N2Se: (m/z)
calcd: 218.0322; found: 218.0317 [M]+.
Yield/%b
Ethanolc Acetoned
Entrya
R
X
Cmpd
116
216
39
n-Butyl
n-Butyl
n-Propyl
Ethyl
n-Hexadecyl
2-Bromobenzyl
3-Chlorobenzyl
Iso-propyl
n-Butyl
Cl
BF4
Br
Br
Br
Br
Cl
Br
I
1b
1b
2b
3b
4b
5b
6b
7b
1b
8b
96
94
95
91
97
94
97
88
92e
89e
97
90
96
94
89
96
94
90
37
33
49
516
6
3-Methyl-1-propyl-1H-imidazole-2(3H)-selenone (2b):9 Yellow
1
7
liquid, H NMR (400 MHz, CDCl3): δ 0.97 (t, J=8.4 Hz, 3H, CH3),
89
1.83 (m, 2H, CH2), 3.71 (s, 3H, N–CH3), 4.10 (t, J=7.2 Hz, 2H, N–CH2),
6.91 (br, J=2.4 Hz, 2H, CH), 6.93 (br, J=2 Hz, 2H, CH). 13C NMR
(100 MHz, CDCl3): δ 10.61, 21.99, 36.63, 51.03, 118.39, 119.39, 154.52
(C=Se). HRMS for C7H12N2Se: (m/z) calcd: 204.0166; found: 204.0172
[M]+.
916
109
Methyl
I
aReaction conditions: 1,3-dialkylimidazolium salts, 5 mmol; Se, 5 mmol;
solvent: ethanol or acetone, 5 mL; K2CO3, 10 mmol.
bIsolated yields.
1-Ethyl-3-methyl-1H-imidazole-2(3H)-selenone (3b):9 Yellow
liquid, 1H NMR (400 MHz, CDCl3): δ 1.40 (t, J=5.6 Hz, 3H, CH3), 3.71
Refluxing time c3 h; d6–8 h; e6 h.
(s, 3H, N–CH3), 4.18 (q, J=7.2 Hz, 2H, N–CH2), 6.92 (m, 2H, CH). 13
C
NMR (100 MHz, CDCl3): δ 14.08, 36.58, 44.51, 117.56, 119.62, 154.20
(C=Se). HRMS for C6H10N2Se: (m/z) calcd: 190.0009; found: 190.0000
[M]+.
1-Hexadecyl-3-methyl-1H-imidazole-2(3H)-selenone (4b):16 M.p.
71–72 °C, 1H NMR (400 MHz, CDCl3): δ 0.88 (t, J=7.2 Hz, 3H, CH3),
1.25–1.34 (m, 28H, CH2), 1.80 (m, 2H, CH2), 3.71 (s, 3H, N–CH3), 4.11
(t, J=7.6 Hz, 2H, N–CH2), 5.93 (s, 1H, CH), 5.98 (s, 1H, CH). 13C NMR
(100 MHz, CDCl3): δ 14.32, 22.89, 26.75, 29.40, 29.56, 29.68, 29.76,
29.88, 32.13, 37.38, 50.36, 119.23, 120.43, 155.67 (C=Se). HRMS for
C20H38N2Se: (m/z) calcd: 386.2200; found: 386.2201 [M]+.
A possible mechanism for the reaction is shown in Fig. 1 based
on that proposed for the reaction of 1,3-dialkylimidazolium
salts and Se.3–6 The formation of 1-butyl-3-methylimidazole-
2-selenone (1b) may involve two-steps (see Fig. 1): (1)
deprotonation of 1-butyl-3-methylimidazolidine chloride salt
1a by K2CO3 to give the N-heterocyclic carbene intermediate
C and (2) reaction of intermediate C with selenium to produce
1-butyl-3-methylimidazole-2-selenone 1b.
In summary, we have developed an efficient synthetic
1-(2-Bromobenzyl)-3-methyl-1H-imidazole-2(3H)-selenone (5b):
M.p. 110–112 °C, 1H NMR (400 MHz, CDCl3): δ 3.73 (s, 3H, N–CH3),
5.46 (s, 2H, N–CH2), 6.82 (br, J=2.4 Hz, 1H, CH), 6.90 (br, J=2.4 Hz,
1H, CH), 7.19 (m, 2H, 2×ArH), 7.27 (d, J=4.4 Hz, 2H, 2×ArH), 7.58
(d, J=7.6 Hz, ArH). 13C NMR (100 MHz, CDCl3): δ 14.09, 22.51, 26.53,
29.13, 29.68, 30.96, 31.75, 37.05, 49.98, 118.64, 119.71, 155.33 (C=Se).
HRMS for C11H11N2BrSe: (m/z) calcd: 329.9271; found: 329.9279 [M]+.
1-(3-Chlorobenzyl)-3-methyl-1H-imidazole-2(3H)-selenone (6b):
method
for
1,3-dialkylimidazole-2-selenones
from
1,3-dialkylimidazolium salts and selenium in the presence
of K2CO3 in ethanol or acetone. Further studies regarding
the mechanism for the synthesis of 1,3-dialkylimidazole-2-
selenones are underway.
Experimental
All melting points were recorded on a WRS-1A melting-point
apparatus and are uncorrected. All 1H NMR spectra were recorded on
a 400 MHz Bruker AZ 400 spectrometer. Chemical shifts are given as
δ value with reference to tetramethylsilane (TMS) as internal standard.
Carbon monoxide (99.9%) was dried by Zeolite 5A. Elemental
selenium (99.5%) and the reagents were obtained from commercial
suppliers without purification prior to use. All operations should be
carried out in an efficient fume hood.
1
M.p. 97–98 °C, H NMR (400 MHz, CDCl3): δ 3.70 (s, 3H, N–CH3),
5.34 (s, 2H, N–CH2), 6.66 (s, 1H, CH), 6.96 (s, 1H, CH), 7.22–7.27 (m,
3H, 3×ArH), 7.30 (s, 1H, ArH). 13C NMR (100 MHz, CDCl3): δ 30.77,
37.11, 52.15, 118.43, 120.40, 126.15, 127.85, 128.14, 129.97, 134.29,
137.44, 156.26 (C=Se). HRMS for C11H11N2ClSe: (m/z) calcd: 285.9776;
found: 285.9753 [M]+.
1-Isopropyl-3-methyl-1H-imidazole-2(3H)-selenone (7b):9 M.p.
109–110 °C, 1H NMR (400 MHz, CDCl3): δ 1.40 (d, J=8 Hz, 6H,
2×CH3), 3.72 (s, 3H, N–CH3), 5.20 (m, 1H, N–CH), 6.93 (m, 2H,
2×CH). 13C NMR (100 MHz, CDCl3): δ 21.52, 30.54, 36.40, 50.39,
114.53, 119.93, 153.35 (C=Se). HRMS for C7H12N2Se: (m/z) calcd:
204.166; found: 204.0169 [M]+.
Synthesis of 1,3-dialkylimidazole-2-selenones; typical procedure
1-Butyl-3-methylimidazolidine, chloride salt (5 mmol), selenium
(5 mmol), potassium carbonate (10 mmol), ethanol or acetone (5 mL)
and a magnetic stirring bar were placed in a 50 mL, two-necked flask.
Then the reaction mixture was vigorously stirred under reflux for the
given times (see Table 2). After the reaction was complete, the resultant
mixture was filtered, and the solvent evaporated under reduced
pressure. Further purification by column chromatography on silica gel
1,3-Dimethyl-1H-imidazole-2(3H)-selenone (8b):9 M.p. 201–202 °C,
1H NMR (400 MHz, CDCl3): δ 3.70 (6H, 2×CH3), 6.99 (m, 2H, 2×CH).
13C NMR (100 MHz, CDCl3): δ 37.21, 119.68, 155.90 (C=Se). HRMS for
C5H8N2Se: (m/z) calcd: 175.9853; found: 175.9853 [M]+.
K2CO3
KCl
Se
Se
N
N
Cl
N
N
N
N
1a
1b
KHCO3
C
Fig. 1 Proposed pathway to 1,3-dialkylimidazole-2-selenone (1b).
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