L.-Y. Wu et al. / Tetrahedron: Asymmetry 18 (2007) 2086–2090
2089
the reactions. Column chromatography was performed
with silica gel (200–300 mesh). All yields given refer to
4.3.3. (S)-1-Methyl-3-(4-(1-(pyrrolidin-2-ylmethyl)-1,2,3-tri-
azol-4-yl)benzyl)-imidazolium tetrafluoroborate 2. To a
1
isolated yields. H NMR spectra were recorded at 300 or
solvent of (2S)-2-azidomethyl-pyrrolidine
4
(1.00 g,
400 MHz, and 13C NMR spectra at 75 MHz or
100 MHz. Mass spectra were recorded by the EI method
or HRMS method. HPLC analysis was performed on
Varian-ProStar using a ChiralPak AD-H column with 2-
propanol in hexanes as the eluent.
8 mmol) and 7 (1.74 g, 7.5 mmol) in 20 mL THF/H2O
(1:1) was added CuI (10 mol %, 0.75 mmol). The mixture
was stirred for 24 h at ambient temperature. After removal
of the solvent under vacuum, the residue was dissolved in
10 mL methanol and was added to AgBF4 (1.95 g,
10 mmol) with vigorous stirring. After 10 min, the black
precipitate was moved by filtration. The Na2SÆ9H2O
(1.0 g, 4 mmol) was added and stirred for 10 min. The reac-
tion was filtered again and concentrated. The residue was
diluted with CH3CN/CH2Cl2 (2:1) and the insolubles re-
moved by filtration. The clear filtrate was concentrated to
4.2. Typical experimental procedure for the asymmetric
Michael addition of cyclohexanone to nitroolefins
To a mixture of nitroolefins (0.5 mmol), the catalyst
(0.075 mmol) and TFA (0.025 mmol) was added ketone
(10 mmol). The mixture was stirred vigorously at ambient
temperature and monitored by TLC. The homogeneous
reaction mixture was diluted with 5 mL diethyl ether to
precipitate the catalyst. The organic layer was separated
and rotary evaporated. The resulting residue was then puri-
fied by silica gel chromatography (ethyl acetate/petroleum
ether = 1:20 to 2:1) and fractions were collected and
concentrated in vacuum.
dryness under vacuum to afford a pale yellow viscous liquid
20
2 (2.95 g, 90%). ½aꢁD ¼ þ6 (c 1.0, H2O). IR (cmꢀ1): 3422,
1
2962, 1686, 1571, 1061. H NMR (300 MHz, D2O): 1.77
(dd, J = 3.6, 3.0 Hz, 1H), 1.97–2.08 (m, 2H), 2.20 (dd,
J = 3.0, 5.1 Hz, 1H), 3.30–3.41 (m, 2H), 3.73 (s, 3H), 4.07
(m, 1H), 4.67–4.74 (m, 3H), 5.22 (s, 2H), 7.27–7.34 (m,
4H), 7.58 (d, J = 5.4 Hz, 2H), 8.18 (s, 1H), 8.34 (s, 1H).
13C NMR (75 MHz, D2O): d 22.9, 27.6, 35.9, 46.1, 50.4,
52.4, 59.4, 122.2, 123.0, 124.1, 126.3, 129.3, 129.5, 130.1,
þ
134.1, 136.2. HRMS for C18H23N6
323.1979, found 323.1983.
(M+), calcd
The relative configurations of the products (syn and anti)
1
were determined by the comparison of H NMR spectral
data with those reported in the literature. The absolute
configurations of the products were determined by compar-
ison of specific rotation values with those reported in the
literature. All compounds in Tables 2 and 3 are known.9
Acknowledgements
We thank the NSF of China (20021001, 20572038) and the
‘Hundred Scientist Program’ from the Chinese Academy of
Sciences for the financial support of this work.
4.3. Synthesis of IL-supported catalyst 2
4.3.1. p-Ethynylbenzyl chloride 6.16 At 0 ꢁC, a mixture of
(4-ethynylphenyl)methanol 515 (1.98 g, 15 mmol) and pyri-
dine (3.16 g, 40 mmol) in 20 mL CH2Cl2 was added to
SOCl2 (2.94 g, 25 mmol) in 10 min. After stirring overnight
at ambient temperature, the mixture was diluted with
30 mL CHCl3 and washed with 2 N HCl (15 mL · 2), sat-
urated NaHCO3 (20 mL · 2) and brine (20 mL · 1). The
organic phase was dried over Na2SO4, concentrated under
reduced pressure, and purified by column chromatography
(silica gel, ethyl acetate/hexane = 1:10). Compound 6 was
obtained as a colourless oil (1.69 g, 75%). 1H NMR
(300 MHz, CDCl3): d 3.10 (s, 1H), 4.55 (s, 2H), 7.32 (dt,
J = 1.5, 3.3 Hz, 2H), 7.47 (dt, J = 1.5, 3.3 Hz, 2H). 13C
NMR (75 MHz, CDCl3): d 45.6, 77.9, 83.0, 122.1, 128.5,
132.4, 138.0; EI-MS m/z (EI) 150 (M+), 115, 89.
References
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4.3.2. 1-(4-Ethynyl-benzyl)-3-methyl-3H-imidazol-1-ium chlo-
ride 7. A mixture of p-ethynylbenzyl chloride 6 (1.50 g,
10 mmol) and N-methyl imidazole (1.64 g, 20 mmol) in
10 mL CH3CN was refluxed 8 h under argon. After cool-
ing, 60 mL ether was added to the mixture and the standing
crystallization to afford a white solid (2.09 g, 90%), mp
1
183–185 ꢁC. IR (cmꢀ1): 3381, 2959, 2102, 1573, 1162. H
NMR (300 MHz, CDCl3): d 3.16 (s, 1H), 3.68 (s, 3H),
5.17 (s, 2H), 7.46 (s, 2H), 7.52 (m, 2H), 7.68 (s, 2H),
10.58 (s, 1H). 13C NMR (75 MHz, CDCl3): d 36.1, 52.0,
77.4, 78.6, 121.8, 122.6, 123.4, 128.5, 132.3, 133.7, 137.0.
4. (a) Giacalone, F.; Gruttadauria, M.; Marculescu, A. M.;
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HRMS for C13H13N2 (M+), calcd 197.1073, found
þ
`
Jimeno, C.; Pericas, M. A. Org. Lett. 2006, 8, 4653–4655; (c)
197.1077.