Materials and methods
HPLC analysis: The sample was diluted with water to 10.0 ml.
A sample of 1.0 ml was taken and 0.2 ml of a phenol stock
All chemicals unless otherwise stated were purchased from
commercial suppliers and used without further purification.
Star anise powder was purchased on a local market and used
as received. N-Methylimidazole was distilled from KOH prior
to use. 1-Methyl-3-(4-sulfobutyl)-imidazolium zwitterion was
solution (250.0 mg in 100 ml H O) were added. The samples
were directly analyzed via HPLC according to Method A.
2
General procedure for the microwave assisted reactive dissolution
of star anise powder
16
prepared following literature methods. Functionalised ionic
20
17
17
21
17
liquids 5, 6, 7,
8
and 9 and the protic ionic liquid 11
A microwave vial (5 ml) was charged with 100.0 mg of star
anise powder, 100 mg of 3-methyl-1-(4-sulfobutyl)imidazolium
were prepared as previously reported, and analytical data were
in accordance with literature. All ionic liquids were dried for
hydrogensulfate [HSO
3
C
4
mim]HSO 5 and 800 mg of anhydrous
4
◦
24–48 h at 80 C and 0.01 mbar with stirring before use and
EtOH, sealed with a Teflon septum and heated for 30 min at
◦
were stored under Argon. Analytical standards of shikimic acid
ethyl ester 2 and ketal intermediate 3 were prepared according
to literature procedures and purified via repeated crystallisation
80 C under microwave irradiation (high absorption level). Water
(50 ml) was added to the resulting black residue and thoroughly
mixed.
HPLC analysis: A sample of 1.0 ml was immediately taken
from the clear supernatent solution and 0.2 ml of a phenol stock
solution (250.0 mg in 100 ml H O) were added. The samples
were centrifuged for 10 min at 13000 min , and the supernatent
7
or preparative HPLC.
Microwave reactions were performed on a BIOTAGE
TM
Initiator
sixty microwave unit. The reported times are
2
-
1
hold times.
1
13
H and C NMR spectra were recorded on a Bruker AC
00 at 200 and 50 MHz, respectively, using the solvent peak as
was directly analysed via HPLC according to Method A.
2
1
3
reference. J values are given in Hz. C NMR spectra were run
in proton-decoupled mode and multiplicities from DEPT were
referred as s (singlet), d (doublet), t (triplet) and q (quartet).
HPLC analysis was performed on a Thermo Finnigan
Surveyor chromatograph equipped with a PDA plus (190–
General procedure for the in situ formation of (3aR,7R,7aS)-
2,2-diethyl-3a,6,7,7a-tetrahydro-7-hydroxy-1,3-benzodioxole-5-
carboxylic acid, ethyl ester 3
A 5 ml screw-cap vial was charged with shikimic acid 1
(
17.4 mg, 1 mmol), 3-methyl-1-(4-sulfobutyl)imidazolium bistri-
3
60 nm) and refractive index (RI) detector. For analysis of
flimide [HSO mim]NTf 8 (49.9 mg, 1 mmol), 0.5 ml of
3
C
4
2
shikimic acid 1 and shikimic ester 2, a Phenomenex Resex
+
anhydrous EtOH and 0.5 ml of 3-pentanone and heated with
RHM-monosaccharide H column (150 ¥ 7.80 mm) was used
◦
stirring for 24 h at 80 C.
as the stationary phase with H O/5% trifluoroacetic acid as
2
-
1
HPLC analysis: A sample of 0.2 ml was immediately taken,
solvent and a flow rate of 0.6 ml min ; detection was done
diluted with 0.8 ml of CH
solution (50.0 mg in 100 ml CH
3
CN and 0.2 ml of a phenol stock
CN) were added. The samples
via refractive index (Method A). For the determination of ketal
3
3, a Phenomenex Luna 10 mm C18(2) 100A column (250 ¥
were directly analysed via HPLC according to Method B.
4
.60 mm) was used with CH CN–H O 50/50 as the solvent
3
2
-
1
and a flow rate of 1 ml min ; detection was done at 210 nm
In situ formation of (3aR,7R,7aS)-2,2-diethyl-3a,6,7,7a-
tetrahydro-7-hydroxy-1,3-benzodioxole-5-carboxylic acid, ethyl
ester 3 from star anise powder
(
Method B).
Preparative HPLC was performed on a Shimadzu LC-8A
device with a SIL-10AP autosampler, SPD-20A dectector and
FRC-10A fraction collector. For separation, a Phenomenex
Luna 10 mm RP18(2) 100A (250 ¥ 21.20 mm) was used with
A large microwave vial (20 ml) with magnetic stirrer flee is
charged with 1.0 g of star anise powder, 1.0 g of IL 5, 4.0 g
of EtOH and 4.0 g of 3-pentanone. The flask is sealed with
-
1
CH
3
CN–H O 40/60 as solvent and a flow rate of 20 ml min .
2
The injection volume was 3 ml and the detection wavelength was
2
◦
a Teflon septum and heated at 80 C (oil bath temperature)
10 nm.
with stirring overnight. The mixture is poured into a saturated
GC–MS analyses were conducted on
a VOYAGER
NaHCO
EtOAc. The combined organic layers are treated with charcoal,
dried over Na SO , filtered over a batch of silica and evaporated
3
solution (50 ml), filtered and extracted 3 times with
Quadrupol (Thermo Finnigan) directly interfaced to a GC 8000
TOP gas chromatograph using a BGB-5 (30 m ¥ 0.32 mm
i.d., 1.0 mm film thickness) cross-bonded dimethyl polysiloxane
capillary column. The oven program temperature was 80
2
4
to dryness. Remaining solvent traces are removed under reduced
pressure (0.01 mbar) to give crude 3 as light yellow oil.
◦
C
◦
-1
◦
(
2 min)//10 C min //280 C (3 min). Source and transfer line
HPLC analysis: The sample was diluted with CH
0.0 ml. A sample of 0.2 ml was taken, diluted with 0.8 ml
of CH CN and 0.2 ml of a phenol stock solution (50.0 mg in
00 ml CH CN) were added. The samples were directly analysed
3
CN to
◦
temperatures were set at 200 and 280 C, respectively.
5
3
1
3
General procedure for the formation of (3R,4S,5R)-3,4,5-
trihydroxycyclohex-1-ene-1-carboxylic acid, ethyl ester 3
(
via HPLC according to Method B.
Isolation: The crude product was further purified via prepar-
ative HPLC to give pure 3 as colourless oil in 10.3% yield.
shikimic acid ethyl ester)
A 5 ml screw-cap vial was charged with shikimic acid 1
d
H
(200 MHz; CDCl
t, J 7.19), 1.64 (4 H, 2q, J 7.53), 2.22 (1 H, m), 2.55 (1 H, m),
2.74 (1 H, dd, J 17.37, J 4.70), 3.89 (1 H, m)), 4.10 (1 H, t,
J 6.96), 4.19 (2 H, q, J 7.20), 4.74 (1 H, m), 6.90 (1 H, m). d
3
, Me
4
Si) 0.87 (6 H, q, J 7.75), 1.27 (3 H,
(
17.4 mg, 1 mmol), 3-methyl-1-(4-sulfobutyl)imidazolium bistri-
flimide [HSO
3
C
4
mim]NTf
2
8 (49.9 mg, 1 mmol) and 1 ml of
1
2
◦
anhydrous EtOH and heated with stirring for 24 h at 80 C.
C
1
446 | Green Chem., 2011, 13, 1442–1447
This journal is © The Royal Society of Chemistry 2011