Lipase-Catalyzed Enantio- and Regioselective Acylations
J . Org. Chem., Vol. 66, No. 25, 2001 8401
stirred at 70-80 °C (50 °C for EMIM‚BF4) for 1 or 2 days under
nitrogen. The mixture was cooled to room temperature, and
ethyl acetate (70 mL) was added causing precipitation of
1-alkyl-3-methyl imidazolium halide as a white solid. This solid
was recovered by filtration and washed with ethyl acetate
followed by ethyl ether: the crude yield was 90-100%.
To prepare the tetrafluoroborate salts, the 1-alkyl-3-methyl-
imidazolium halide salt (0.40 mol) was added to a suspension
of NaBF4 (1.2 equiv, 52.7 g, 0.48 mol) in acetone (150 mL).
After the mixture was stirred for 48 h at room temperature,
the sodium halide precipitate was removed by filtration and
the filtrate concentrated to an oil (∼100 mL) by rotary
evaporation. This oil still contained some 1-alkyl-3-methyl
imidazolium halide because it gave a precipitate when mixed
with aqueous silver nitrate.
Tr a n sester ifica tion of 1-P h en yleth a n ol. Vinyl acetate
(92 µL, 1.0 mmol) and 1-phenylethanol (120 µL, 1.0 mmol) were
added to a suspension of PCL (20 mg) in solvent (1.0 mL of
either organic solvents or ionic liquids) and stirred at 25 °C.
The reactions were monitored by TLC (ethyl acetate/hexane,
1:3). After 24 h, the reaction mixture was extracted with
hexane (3 mL), and the hexane extract was analyzed by GC
with a chiral capillary column (Chromopak Chiralsil-Dex CB
column (25 m × 0.25 mm, Raritan, NJ )): initial column
temperature 125 °C for 2 min, then ramp to 150 °C over 10
min: 1-phenylethanol (R ) 1.06, kR ) 3.32, kS ) 3.35);
1-methylbenzyl acetate (R ) 1.12, kR ) 2.53, kS ) 2.26) The
conversion, c, was calculated from the enantiomeric excess of
the product, eep, and of the starting material, ees, using the
equation below.24
P u r ifica tion of Tetr a flu or obor a te Sa lts: Meth od A.7b,c
The oil (∼100 mL) was dissolved in methyl alcohol (100 mL),
and an aqueous solution of AgBF4 (generated from Ag2O and
HBF4) was added dropwise until no more precipitate was
formed. The mixture was filtered through Celite (no. 545),
concentrated by rotary evaporation, dissolved in dichloro-
methane (100 mL), and filtered again to remove insoluble
material. The product was purified by column chromatography
in three portions on silica gel (∼400 g) eluted with methylene
chloride/methanol (9:1). The solvent removed under vacuum
yielded pale yellow oil, 60-80% yield.
ees
c )
ees + eep
Tr a n sester ifica tion of â-D-Glu cose. Vinyl acetate (92 µL,
1.0 mmol), â-D-glucose (90 mg, 0.5 mmol), and Novozyme
SP435 (30 mg) were mixed with solvent (1.0 mL of either
organic solvents or ionic liquids) and stirred at 55 °C. After
36 h, pyridine (2 mL), 1,1,1,3,3,3-hexamethyldisilazane (1 mL),
and chlorotrimethylsilane (1 mL) were added to the reaction
mixture, and the mixture was extracted with hexane (5 mL).
The hexane extract was analyzed by gas chromatography on
the column noted above. The derivatives of glucose and acetyl
glucose were separated using the following temperature
program: initially 2 min at 180 °C, then gradient to 190 °C at
1 °C/min, then held at 190 °C for 28 min. In a separate
experiment, we confirmed that this derivatization method does
not cause anomerization of glucose.
P ola r ity Deter m in a tion Usin g Reich a r d t’s P ola r ity
Sca le. Reichardt’s dye (2,6-diphenyl-4-(2,4,6-triphenylpyri-
dinio)phenolate, 0.4 mg) was dissolved in ionic liquid (0.5 mL),
and an aliquot was transferred to a 96-well microplate. The
wavelength of the absorption maximum of the long-wavelength
transition was measured at 25 °C using a microplate reader
(Spectra Max 340, Molecular Devices Co., Sunnyvale, CA).
Normalized polarity values (ENT), which range from 0.0 for
tetramethylsilane to 1.0 for water, were calculated using the
equation
P u r ifica tion of Tetr a flu or obor a te Sa lts: Meth od B.
The crude ionic liquid was diluted with methylene chloride
(200 mL) and filtered through silica gel (∼100 g). This step
removed the 1-alkyl-3-methylimidazolium halide since the
filtrate no longer gave a precipitate mixed with aqueous silver
nitrate. The solution was washed twice with saturated sodium
carbonate aqueous solution (40 mL) and dried over anhydrous
magnesium sulfate. Removal of solvent under vacuum yielded
a pale yellow oil, 50-70% yield. Washing a solution of EMIM‚
BF4 in methylene chloride with aqueous sodium carbonate
yielded three layers: water on the top, EMIM‚BF4 in the
middle, and methylene chloride at the bottom. The two bottom
layers were separated, evaporated to remove water dissolved
in the EMIM‚BF4 layer, diluted with methylene chloride (200
mL), dried over anhydrous magnesium sulfate, and concen-
trated to an oil.
EMIM‚BF 4. 1H NMR: δ 8.98 (1H, s); 7.75 (1H, dd); 7.68
(1H, dd); 4.37 (2H, q); 4.03 (3H, s); 1.54 (3H, t).
MOEMIM‚BF 4. 1H NMR: δ 8.95 (1H, s); 7.71 (1H, dd); 7.68
(1H, dd); 4.51 (2H, t); 4.05 (3H, s); 3.80 (2H, t); 3.34 (3H, s).
P MIM‚BF 4. 1H NMR: δ 8.99 (1H, s); 7.75 (1H, dd); 7.71
(1H, d); 4.31 (2H, t); 4.04 (3H, s); 1.95 (2H, m); 0.95 (3H, t).
BMIM‚BF 4. 1H NMR: δ 8.99 (1H, s); 7.75 (1H, d); 7.70 (1H,
d); 4.35 (2H, t); 4.04 (3H, s); 1.91 (2H, m); 1.37 (2H, m); 0.94
(3H, t).
ET(solvent) - ET(TMS) ET(solvent) - 30.7
EN
)
)
T
32.4
ET(water) - ET(TMS)
where ET(solvent) is the energy, in kilocalories per mole, of
the maximum of the long wavelength transition and is given
by
1
sBMIM‚BF 4. H NMR: δ 9.05 (1H, s); 7.82 (1H, dd); 7.73
(1H, dd); 4.57 (1H, m); 4.04 (3H, s); 1.94 (2H, m); 1.60 (3H, d);
0.87 (3H, t).
BMIM‚P F 6. 1H NMR: δ 8.99 (1H, s); 7.76 (1H, dd); 7.71
(1H, dd); 4.36 (2H, t); 4.06 (3H, s); 1.93 (2H, m); 1.38 (2H, m);
0.94 (3H, t).
28591
max(nm)
ET(solvent)(kcal/mol) )
λ
P MP yr ‚BF 4. 1H NMR: δ 8.95 (2H, d); 8.06 (2H, d); 4.70
(2H, t); 2.73 (3H, s); 2.09 (2H, q); 0.99 (3H, t).
BMP yr ‚BF 4. 1H NMR: δ 8.96 (2H, d); 8.05 (2H, d); 4.73
(2H, t); 2.72 (3H, s); 2.06 (2H, m); 1.42 (2H, m); 0.96 (3H, t).
Ack n ow led gm en t. We thank NSERC (Canada) for
financial support.
1
J O015761E
P P yr ‚BF 4. H NMR: δ 9.13 (2H, d); 8.72 (1H, t); 8.26 (2H,
t); 4.78 (2H, t); 2.13 (2H, m); 1.00 (3H, t).
1
BP yr ‚BF 4. H NMR: δ 9.16 (2H, d); 8.73 (1H, t); 8.27 (2H,
(24) Chen, C. S.; Fujimoto, Y.; Girdaukas, G.; Sih, C. J . J . Am. Chem.
Soc. 1982, 104, 7294-7299.
t); 4.83 (2H, t); 2.10 (2H, m); 1.45 (2H, m); 0.97 (3H, t).
Park
