A R T I C L E S
Scheme 3
Landry et al.
using fast atom bombardment (FAB). 1-Mesitylimidazole was obtained
by a method analogous to the literature procedure.10
Synthesis of (seimMes)H. A solution of 1-mesitylimidazole (0.5 g,
2.7 mmol) in tetrahydrofuran (THF; 30 mL) was cooled to -78 °C
and treated with BunLi (1.7 mL of a 1.6 M solution in hexane, 2.7
mmol). The solution was stirred at -78 °C for 30 min, allowed to
warm to room temperature, and stirred for 1 h. The solution was cooled
to -78 °C, and powdered selenium (0.43 g, 5.4 mmol) was added.
The mixture was stirred at room temperature overnight and neutralized
using HCl (5%), maintaining a N2 atmosphere. The mixture was filtered,
and water (50 mL) and CHCl3 (50 mL) were added to the filtrate. The
organic layer was separated, washed with brine (50 mL), and dried
with Na2SO4. The solution was separated from the Na2SO4, and the
solvent was removed in Vacuo to give (seimMes)H as a pale yellow
solid (0.35 g, 49%). IR data (KBr pellet, cm-1): 3118 (w), 3053 (s),
2982 (s), 2880 (s), 2700 (w), 1561 (m), 1487 (m), 1459 (s), 1439 (m),
1406 (w), 1373 (w), 1318 (s), 1294 (vs), 1277 (m), 1249 (s), 1128
(w), 1100 (s), 1076 (vs), 1030 (w), 974 (w), 911 (m), 870 (w), 837
(w), 796 (m), 715 (s), 680 (s), 584 (w). Mass spectrum: m/z ) 267.3
{M + 1}+. Anal. Calcd for C12H14N2Se‚0.1(CHCl3): C, 52.4; H, 5.1;
1
N, 10.1%. Found: C, 52.4; H, 4.7; N, 10.0%. H NMR (CDCl3): δ
2.06 [s, 6H of o-Me], 2.34 [s, 3H of p-Me], 6.78 [d, 2JHH ) 2 Hz, 1H
of imidazole ring], 6.99 [s, 2H of aryl ring], 7.04 [d, 2JHH ) 2 Hz, 1H
of imidazole ring], 11.91 [br, N-H]. 1H NMR (Me2SO-d6): δ 1.92 [s,
6H of o-Me], 2.28 [s, 3H of p-Me], 6.99 [s, 2H of aryl ring], 7.15 [d,
JH-H ) 2 Hz, 1H of imidazole ring], 7.24 [d, JH-H ) 2 Hz, 1H of
imidazole ring], 12.8 [br, N-H]. 13C{1H} NMR (CDCl3): δ 18.2
[o-Me], 21.3 [p-Me], 117.7 [C-H of imidazole ring], 120.6 [C-H of
imidazole ring], 129.4 [C-H of mesityl], 133.7 [ipso C of mesityl],
135.7 [C-Me of mesityl], 139.6 [C-Me of mesityl], 152.5 [CdSe of
imidazole ring]. 13C{1H} NMR (Me2SO-d6): δ 17.7 [o-Me of mesityl],
20.6 [p-Me of mesityl], 118.1 [C-H of imidazole ring], 120.9 [C-H
of imidazole ring], 128.6 [C-H of mesityl], 134.2 [ipso C of mesityl],
135.1 [C-Me of mesityl], 138.0 [C-Me of mesityl], 152.4 [CdSe of
imidazole ring, JSe-C ) 231 Hz]. 77Se{1H} NMR (CDCl3): δ 17 ppm.
77Se{1H} NMR (Me2SO-d6): δ 29 ppm.
liberate (seimR)H and form (seimR*)(seimR),39 as illustrated in
Scheme 3.
Conclusions
In summary, 1-mesitylimidazole-2-selone (seimMes)H may be
obtained from 1-mesitylimidazole via (i) deprotonation with Bun-
Li, (ii) treatment with elemental selenium, and (iii) addition of
HCl(aq). Structural characterization of (seimMes)H by X-ray
diffraction demonstrates that the compound exists as the selone
rather than the selenol tautomer, a result that is confirmed by
DFT calculations. A reexamination of the selenium analogue
of methimazole demonstrates that, in contrast to recent reports,
the compound exists in the selone form with a structure that is
analogous to methimazole.
Synthesis of (seimMes)2. Procedure a: A solution of 1-mesitylimi-
dazole (1 g, 5.4 mmol) in THF (50 mL) was cooled to -78 °C and
treated with BunLi (3.4 mL of a 1.6 M solution in hexane, 5.4 mmol).
The solution was stirred at -78 °C for 30 min, allowed to warm to
room temperature, and stirred for 1 h. Powdered selenium (0.85 g, 10.8
mmol) was added to the solution and the mixture stirred at room
temperature overnight. The mixture was filtered, treated with distilled
water (15 mL), and exposed to air, with occasional shaking, for
approximately 2 h. The THF was removed from the solution in Vacuo,
and the remaining aqueous solution was extracted with CHCl3 (2 ×
20 mL). The organic layer was washed with water and dried with Na2-
SO4. The CHCl3 was removed in Vacuo to give (seimMes)2 as an orange
powder (0.73 g, 51%), which may be crystallized from CHCl3. IR data
(KBr pellet, cm-1): 3132 (m), 3104 (m), 2954 (w), 2916 (m), 2848
(w), 1606 (w), 1492 (s), 1483 (s), 1439 (w), 1413 (s), 1376 (w), 1309
(w), 1290 (m), 1264 (w), 1109 (m), 1087 (w), 1034 (vw), 979 (w),
909 (w), 865 (s), 759 (s), 735 (w), 682 (w), 586 (w). Mass spectrum:
m/z ) 531.4 {M + 1}+. Anal. Calcd for C24H26N4Se2: C, 54.6; H,
Experimental Section
General Considerations. All manipulations were performed using
Schlenk techniques under a nitrogen atmosphere unless otherwise
specified. Solvents were purified and degassed by standard procedures.
1H and 13C NMR spectra were measured on Bruker 300 DRX, Bruker
400 DRX, and Bruker Avance 500 DMX spectrometers. H and 13C
1
chemical shifts are reported in ppm relative to SiMe4 (δ ) 0) and were
referenced internally with respect to the protio solvent impurity (δ 7.26
for CHCl3, 2.50 for Me2SO). 77Se chemical shifts are reported in ppm
relative to neat Me2Se (δ ) 0) and were referenced using a solution of
Ph2Se2 in C6D6 (δ ) 460) as external standard.40 Coupling constants
are given in hertz. Infrared spectra were recorded on Nicolet Avatar
370 DTGS spectrometer and are reported in cm-1. Mass spectra were
obtained on a Micromass Quadrupole-Time-of-Flight mass spectrometer
(37) For thiol/disulfide exchange, see: (a) Singh, R.; Whitesides, G. M. J. Am.
Chem. Soc. 1990, 112, 1190-1197. (b) Singh, R.; Whitesides, G. M. J.
Org. Chem. 1991, 56, 6931-6933. (c) Guo, W.; Pleasants, J.; Rabenstein,
D. L. J. Org. Chem. 1990, 55, 373-376. (d) Fernandes, P. A.; Ramos, M.
J. Chem. Eur. J. 2004, 10, 257-266. (e) Lees, W. J.; Whitesides, G. M. J.
Org. Chem. 1993, 58, 642-647. (f) Theriault, Y.: Cheesman, B. V.; Arnold,
A. P.; Rabenstein, D. L. Can. J. Chem. 1984, 62, 1312-1319. (g) Theriault,
Y.; Rabenstein, D. L. Can. J. Chem. 1985, 63, 2225-2231. (h) Rabenstein,
D. L.; Theriault, Y. Can. J. Chem. 1984, 62, 1672-1680. (i) Keire, D. A.;
Guo, W.; Rabenstein, D. L. Magn. Reson. Chem. 1992, 30, 746-753. (j)
Rabenstein, D. L.; Theriault, Y. Can. J. Chem. 1985, 63, 33-39.
(38) For thiol/diselenide exchange, see: Engman, L.; Stern, D. J. Org. Chem.
1994, 59, 5179-5183.
1
5.0; N, 10.6%. Found: C, 54.4; H, 5.0; N, 10.6%. H NMR (CDCl3):
δ 1.87 [s, 12H of o-Me], 2.30 [s, 6H of p-Me], 6.89 [s, 4H of aryl
ring], 6.96 [br, 2H of imidazole ring], 7.35 [br, 2H of imidazole ring].
1H NMR (Me2SO-d6): δ 1.76 [s, 12H of o-Me], 2.26 [s, 6H of p-Me],
6.94 [s, 4H of aryl ring], 7.25 [br, 2H of imidazole ring], 7.34 [br, 2H
of imidazole ring]. 13C{1H} NMR (CDCl3): δ 17.4 [o-Me of mesityl],
20.6 [p-Me of mesityl], 123.5 [C-H of imidazole ring], 128.5 [C-H
of mesityl], 131.4 [C-H of imidazole ring], 132.2 [C-Se of imidazole
ring], 133.3 [ipso C of mesityl], 135.1 [C-Me of mesityl ring], 138.4
[C-Me of mesityl ring]. 77Se{1H} NMR (CDCl3): δ 415 ppm. 77Se-
{1H} NMR (Me2SO-d6): δ 407 ppm.
(39) Calculations suggest that the mechanism of nucleophilic displacement at a
diselenide proceeds by a two-step process involving addition, giving a three-
coordinate T-shaped intermediate, followed by elimination. See: (a)
Bachrach, S. M.; Demoin, D. W.; Luk, M.; Miller, J. V., Jr. J. Phys. Chem.
A 2004, 108, 4040-4046. (b) Bachrach, S. M.; Hayes, J. M.; Dao, T.;
Mynar, J. L. Theor. Chem. Acc. 2002, 107, 266-271.
Procedure b: A solution of (seimMes)H (10 mg, 0.038 mmol) in
CDCl3 (0.7 mL) was exposed to air and monitored by 1H NMR
(40) Lardon, M. J. Am. Chem. Soc. 1970, 92, 5063-5066.
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12496 J. AM. CHEM. SOC. VOL. 128, NO. 38, 2006