Enantiopure (9-anthryl)(2-piperidyl)- and (9-anthryl)(2-pyridyl)methanols - Their use as chiral modifiers for heterogeneous hydrogenation of keto esters over Pt/Al2O3

Article abstract of DOI:10.1002/ejoc.200600734

A route toward the synthesis of the erythro isomer of (9-anthryl)(2- piperidyl)methanol is presented as well as resolution and assignment of the structure (through NMR). The use of both the erythro and threo enantiopure isomers of this new amino alcohol, and its precursor [(9-anthryl)(2-pyridyl) methanol], as chiral modifiers for the Pt/Al₂O₃ hydrogenation of ethyl lactate showed that the erythro isomer is not necessarily the most efficient chiral modifier. This is probably because of the 9-anthryl group. The enantioselectivities that this compound provides are not, as one would expect, higher than those observed with the naphthyl group. Wiley-VCH Verlag GmbH & Co. KGaA, 2007.

Full text of DOI:10.1002/ejoc.200600734

FULL PAPER
DOI: 10.1002/ejoc.200600734
Enantiopure (9-Anthryl)(2-piperidyl)- and (9-Anthryl)(2-pyridyl)methanols –
Their Use as Chiral Modifiers for Heterogeneous Hydrogenation of Keto
Esters over Pt/Al O
2
3
[
a]
[a]
[a]
[b]
Arlette Solladié-Cavallo,* Claire Marsol, Khalid Azyat, Marin Roje,
[c]
[c]
[d]
Christopher Welch, Jennifer Chilenski, Philippe Taillasson, and
Hugues D’Orchymont[
e]
Keywords: Amino alcohols / Chiral resolution / Chiral modifiers / Hydrogenation
A route toward the synthesis of the erythro isomer of (9-an-
thryl)(2-piperidyl)methanol is presented as well as resolution
and assignment of the structure (through NMR). The use of
both the erythro and threo enantiopure isomers of this new
amino alcohol, and its precursor [(9-anthryl)(2-pyridyl)meth-
rily the most efficient chiral modifier. This is probably be-
cause of the 9-anthryl group. The enantioselectivities that
this compound provides are not, as one would expect, higher
than those observed with the naphthyl group.
anol], as chiral modifiers for the Pt/Al
ethyl lactate showed that the erythro isomer is not necessa-
2
O
3
hydrogenation of
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2007)
Introduction
cinchonidine 1 (which is also an erythro isomer). Until
2002, it also seemed that the anthryl group had a tendency
Asymmetric heterogeneous hydrogenation of α-keto es- to provide higher enantioselectivities than the naphthyl
ters over supported platinum catalysts with the use of cin- group (when located on the carbon bearing the hydroxy
[1]
chona alkaloids (Orito reaction ) has been known for
about thirty years and has been the subject of numerous
reviews. When we started our work in this field in 1998,[3]
[2]
it was already known that cinchonidine 1 was the most ef-
[2]
ficient chiral modifier and apart from cinchonidine or cin-
chonine derivatives[ the only different modifiers tested
4]
[5]
were type 3 amino alcohols (1994) and type 4 amines
[
6a,6b]
Our target was then amino alcohol 5a[3] which
(1995).
had the same –CH(OH)–CH(N)– link as cinchona alka-
loids and one chiral carbon less. Moreover, both enantio-
mers of both the erythro and threo diastereomers could be
available which would provide straightforward conclusions.
With the use of 5a, for the first time we clearly showed
(
2001) that the erythro isomer was a more efficient chiral
[3]
modifier than the threo isomer and almost as efficient as
[
a] Laboratoire de Stéréochimie Organométallique, ECPM/Uni-
versité Louis Pasteur,
2
5 rue Becquerel, 67087 Strasbourg Cedex 02, France
Fax: +33-3-90242706
E-mail: cavallo@chimie.u-strasbg.fr
b] Laboratory for Stereoselective Catalysis and Biocatalysis, De-
partment of Organic Chemistry and Biochemistry, Rueer Bo sˇ -
kovi c´ Institute,
[
Bijeni cˇ ka 54, 10000 Zagreb, Croatia
c] Merck & Co., Inc.,
[
[
[
Rahway, NJ 07065, USA
d] Sylachim-Finorga,
3
8670 Chasse sur Rhone, France
e] Sanofi-Synthelabo Recherche,
7080 Strasbourg, France
6
826
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2007, 826–830

Enantiopure (9-Anthryl)(2-piperidyl)- and (9-Anthryl)(2-pyridyl)methanols
group). Therefore, we decided to synthesize and study
FULL PAPER
The ratios of I/II have been determined with the use of
erythro and threo amino alcohols 5b. By the time this work the 1-H proton doublets (between δ = 6.0 ppm and
was completed, other results appeared that dealt with the 6.2 ppm, Table 1).
comparison of anthryl and naphthyl groups in the case of
[
6c–6e]
[7]
amines 4
and amino alcohols 6.
Determination of threo/erythro Structure of 5b-I and 5b-II
We present here the synthesis and resolution of both the
erythro and threo diastereomers of anthryl amino alcohol
threo/erythro Structure from NMR
5b, a synthesis of the pure erythro isomer (lower overall
In amino alcohols having the CH(OH)–CH(NH) system
and of known structure, Table 1, the erythro isomer has the
smallest coupling constant. Therefore, the erythro structure
has been assigned to isomer 5b-II, which exhibits the small-
est coupling constant: 7.5 Hz versus 9.5 Hz for isomer 5b-
I.
yield but no difficulty with the separation of diastereomers),
the use of 5b as a chiral modifier for the heterogeneous
hydrogenation of ethyl pyruvate over Pt/Al O , as well as
the use of precursor 7 to test the effect of the possible in
situ hydrogenation of 7 into 5b during hydrogenation of
pyruvate.
2
3
Moreover, the 1-H doublets in the erythro isomers are
always the most deshielded, which is the case here too (δ =
6
.10 ppm compared to δ = 6.03 ppm for the threo isomer in
Synthesis
this case).
Condensation of the 9-anthryl Grignard reagent with 2-
pyridinecarboxaldehyde proceeded smoothly in THF to
provide anthrylpyridyl alcohol 7 in 80% yield (Scheme 1).
erythro Structure from Model
The erythro structure assigned by NMR to isomer II,
the only isomer obtained from hydrogenation over PtO , is
consistent with the model shown in Scheme 3, as it is rea-
sonable to postulate that the hydrogen (located on the cata-
lyst surface) approaches from the less hindered side of the
H-bonded C1 conformer of substrate 7 (1-H side).
Heterogeneous hydrogenation of 7 with the use of PtO
2
2
from Aldrich) in EtOH/HCl (1 equiv.)[
8,9]
(
then provided
pure erythro 5b-II in 40% yield (5b-I/5b-II = 0/100).
Scheme 1.
It is worth noting that threo isomer 5b-I (necessary for
structure determination) can be obtained (as the major iso-
mer) from formamidine 8, Scheme 2, by following Meyers’ Scheme 3.
[
10,11]
procedures,
(overall yield 50%, after chromatographic
purification).
Resolution of Piperidyl Alcohol 5b-I and 5b-II
Table 1. NMR spectroscopic data for threo and erythro configura-
tions.
Diastereomeric separation of the threo isomer from the
erythro isomer was performed first by preparative supercrit-
ical fluid chromatography with a Chromegabond Amine
column (25 cmϫ23 mm ID, 5 µm 60 Å, ES Industries) at a
flow rate of 50 mL/min with a mobile phase of 25% metha-
nol in carbon dioxide (100 bar outlet pressure) with UV
detection at 257 nm.
Analytical separation of racemic pure threo isomer 5b-I
was further performed with a CHIRALCEL OD-RH col-
umn (150ϫ4.6 mm, 5 µm) with acetonitrile/ethanolamine,
Amino alcohol
3J1–2 CDCl
3
∆3J δ(1-H) Configuration
[
Hz]
[Hz] [ppm]
5
5
-I (Ar = Ph)
-II (Ar = Ph)
7.5
5.0
8.2
3.9
6.0
4.0
9.5
7.5
2.5
4.3
2
4.36
4.56
threo[
a]
[
a]
erythro
(
1S,2S)-Pseudoephedrine
threo[
a]
[
a]
(
1R,2S)-Ephedrine
erythro
[
a]
5a-I (67%)
5a-II (33%)
5b-I (80%)
5b-II (20%)
5.24
5.44
6.03
6.10
threo
erythro[
a]
2
threo
erythro
100:0.1, as the mobile phase (flow rate = 0.5 mL/min) and
[
a] Known compounds, cf. refs.[12,13]
UV detection at 235 nm.
Scheme 2.
Eur. J. Org. Chem. 2007, 826–830
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
827

A. Solladié-Cavallo et al.
FULL PAPER
On a preparative scale, a CHIRALCEL OD column Table 2. Ethyl pyruvate hydrogenation over 5% Pt/Al
250ϫ50 mm, 20 µm) and the same mobile phase (100 mL/
2
O
3
at room
temperature for 2 h.
(
min) were then used. After recrystallization from acetoni-
trile (to completely remove ethanolamine as seen from H
Modifier
Conversion
[%]
(R)/(S)
ee
[%]
1
NMR) of the two fractions having the highest ee, the spe-
None
13
–
–
cific rotations of enantiomers threo 5b-I1 and threo 5b-I2 (+)-5b-II2 erythro
100
100
100
100
100
68:32
32.5:67.5
27:73
73.5:26.5
37:63
36
35
46
47
26
(
(
(
–)-5b-II1 erythro
were determined: threo 5b-I1: [α]D = +11.0 (c = 0.45,
CHCl ), ee = 99%; threo 5b-I2: [α] = –10.8 (c = 0.50,
–)-5b-I2 threo
+)-5b-I1 threo
3
D
[a]
CHCl ), ee = 99%.
3
(–)-7
The erythro isomer (5b-II) was obtained pure and the
enantiomers were then preparatively obtained by supercriti-
cal fluid chromatography with the use of a CHIRALPAK
AD column (250ϫ20 mm, 10 µm) at a flow rate of 50 mL/
min with a mobile phase of 16% methanol (containing
[
a] Cf. ref.[3]
It is worth noting that, contrary to the cinchona alka-
loids generally used, 5b-I1 and 5b-I2 (as well as 5b-II1 and
b-II2) are true enantiomers; therefore, the samples of 5b-
5
25 m of isobutylamine) in carbon dioxide (100 bar outlet
I1 and 5b-I2 (as well as 5b-II1 and 5b-II2) that were used
that have identical enantiomeric purities (cf. above) provide
identical (R)/(S) ratios to ethyl lactate, within the reproduci-
bility of the method used, for the determination of these
ratios (compare 68:32 with 32.5:67.5 and 27:73 with
pressure) with UV detection at 257 nm, with the isolation
of two fractions: erythro 5b-II1 negative CD at 263 nm, ee
=
99%; erythro 5b-II2 positive CD at 263 nm, ee = 99%.
[
α]D = +17 (c = 0.24, CHCl3).
73.5:26.5). It appears that (S)-lactate is obtained from (–)-
5
b-II (erythro) and (–)-5b-I (threo) while (+)-5b-II and (+)-
Resolution of Pyridyl Alcohol 7
5b-I provide (R)-lactate. It is also worth noting that the
threo isomers provide slightly higher enantioselectivities
than the erythro isomers (46–47% versus 35–36% ee).
Analytical separation of rac-7 was performed with a
CHIRALCEL OD column (250ϫ4.6 mm, 10 µm) with
hexane/EtOH/diethylamine, 8:2:0.5, as the mobile phase
Precursor 7, which under these conditions undergoes
[14]
slow hydrogenation
probably because hydrogenation of pyruvate is too rapid
and that 7 is a less efficient chiral modifier.
into desired 5b-II, is less efficient
(
flow rate = 1 mL/min) and UV detection at 254 nm. On
preparative scale, CHIRALCEL OD column
0.46ϫ25 cm, 10 µm) and the same mobile phase (120 mL/
min) were used with the isolation of two fractions: (–)-7,
a
a
(
1
chemical purity Ͼ95% (by 400 MHz H NMR). [α]D
=
Conclusions
–
171 (c = 0.36, CHCl ), ee = 100% (from analytical chro-
3
These results show that the erythro isomer is not necessa-
matography); (+)-7, chemical purity Ͼ95% (by 400 MHz
1
rily the most efficient chiral modifier as was suggested from
previous results obtained by using compound 5a and cin-
chona alkaloids
H NMR). [α]D = +97 (c = 0.37, CHCl ), ee = 57% (from
3
[
3]
specific rotation).
[
4,15]
(Table 3).
Table 3. Hydrogenation of ethyl pyruvate with the use of various
chiral modifiers.
Modifier
Conversion
%]
(R)/(S)
ee
[%]
[
Cinchonidine (9R,8S) erythro
Epiquinidine (threo)[
100
?
100
100
100
67
–
93.5:6.5
1:1
86.5:13.5
14:86
27:73
67.5:32.5
6:94
87
0
a]
(
(
(
–)-(1R,2S)-5a-II erythro[
73
72
46
b]
+)-(1S,2R)-5a-II erythro
–)-5a-I threo [
b]
[c]
Asymmetric Pt/Al O Hydrogenation of Ethyl Pyruvate
(+)-5a-I threo
35
88
79
2
3
[d]
(
(
+)-6a-(1S,2R) erythro
+)-6b-(1S,2R) erythro[
d]
–
10.5:89.5
After hydrogenation and distillation, the enantiomeric
excesses of the ethyl lactate samples were determined by gas [a] Cf. ref.[15] [b] Cf. ref. , note that the absolute configuration
[3]
chromatography with a Cyclodex-B capillary column (30 m) of erythro 5a-II was determined from the stereo-outcome of the
with the use of an HP 5890 GC-FID instrument and the ee
values were reproducible within 1%.
hydrogenation of pyruvate and confirmed by VCD (ref.[ ). [c] This
sample of the threo isomer that was used contained 1.8% of one
enantiomer of the erythro isomer (ref. ). [d] Cf. ref.
13]
[13]
[7]
The well-defined catalyst 5% Pt/Al O 4759 from Engel-
2
3
hard was activated before use (3 h, 300 °C, under H flow);
The results also corroborate that the anthryl group is not
2
AcOH was used as the solvent. The reactions were run at necessarily a more efficient modifier than the naphthyl
room temperature for 2 h with stirring at a rate of ca. group, and it may provide lower enantioselectivities for
500 rpm, and the pyruvate, purchased from Aldrich, was both erythro and threo isomers as in the case of type 5
distilled before used. The results are given in Table 2. amino alcohols (compare Table 2 and Table 3) or compara-
828
www.eurjoc.org
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2007, 826–830

Enantiopure (9-Anthryl)(2-piperidyl)- and (9-Anthryl)(2-pyridyl)methanols
FULL PAPER
ble enantioselectivities in the case of type 6 erythro amino ium (1.7 , 8.5 mL, 14.25 mmol, 1.2 equiv.). The solution was
stirred at –20 °C for 1 h, which resulted in the formation of a white
alcohol (Table 3).
precipitate. The reaction mixture was cooled to –78 °C, the desired
As in the case of (–)-5a-II, for which the (1R,2S) configu-
aldehyde (1.1 equiv.) added, and the mixture slowly warmed up to
ration was determined from the stereo-outcome of the reac-
0
°C over 5 h. The solution was poured into 10% HCl (30 mL) and
tion (pyruvate hydrogenation) and corroborated by VCD,
one could postulate from the stereo-outcome of the pyru-
vate hydrogenation reaction that (+)-5b-II, which also pro-
vides (R)-lactate, has the (1R,2S) configuration.
extracted with diethyl ether (2ϫ10 mL). The aqueous layer was
then made basic (pH 12) with 20% NaOH and extracted several
times with dichloromethane. The combined organic phases were
then concentrated under vacuum. A solution of the resulting crude
product in MeOH (25 mL) and water (4 mL) and KOH (4 g) was
heated at 60 °C for 24 h. After cooling, the mixture was extracted
with dichloromethane (5ϫ15 mL). The combined dichlorometh-
Experimental Section
2 4
ane phases were dried with Na SO , the solvents removed under
General Procedure for Anthryl Grignard Addition onto 2-Pyridincar-
boxaldehyde: It is worth noting that the 9-anthryl grignard formed
from 9-bromoanthacene must be generated in THF heated at re-
flux. A solution of bromoanthracene (3.36 g, 13 mmol) in anhy-
drous THF (80 mL) was added dropwise whilst stirring to a suspen-
sion of Mg (0.31 g, 13 mmol) in anhydrous THF (30 mL) and 1,2-
dibromoethane (0.2 mL). The mixture was heated at reflux and stir-
ring was maintained until all of the Mg disappeared. After cooling
to room temperature, a solution of 2-pyridincarboxaldehyde (0.7 g,
reduced pressure, and the amino alcohol isolated and purified by
chromatography on silica gel (CH Cl /MeOH, 4:1).
2
2
General Procedure for Pt/Al O Hydrogenation: A mixture of ethyl
2
3
pyruvate (5 mL, 3500 equiv.) and the desired chiral modifier
(1 equiv.), stirred for 30 min before used, was poured into a glass
tube that exactly fits inside of a stainless steel autoclave. AcOH
(10 mL) and the activated catalyst (50 mg, 1 equiv. in Pt) were then
added successively. After being closed tightly, the device was purged
three times (through successive vacuum-H2 admission), the H2
pressure was fixed at 40 bar, and the mixture was stirred for 2 h.
6
.5 mmol) in anhydrous THF (30 mL) was added dropwise whilst
stirring overnight. Then, a saturated aqueous solution of NH Cl
was added, THF was evaporated under vacuum, and the aqueous
phase was extracted with CH Cl (5ϫ20 mL). The combined or-
ganic phases were dried with Na SO , the solvent removed under
4
1
The conversion was determined by using H NMR of the crude
2
2
products, then ethyl lactate was separated from other components
2
4
through distillation and the ee was determined by chromatography
1
3
reduced pressure, and the amino alcohol isolated and purified by
(cf. text above). 9: H NMR (300 MHz, CDCl ): δ = 1.23 (t, J =
3
1
3
chromatography on silica gel (ether/hexane, 3:2). 7: H NMR
7 Hz, 3 H), 1.35 (d, J = 7 Hz, 3 H) 3.15 (br. s, 1 H, OH), 4.17 (2
3
(
300 MHz, CDCl
3
): δ = 5.9 (br. s, 1 H), 6.72 (d, J = 7.5 Hz, 1 H),
H, CH and 1 H, CH overlapped q).
2
3
7
2
.2 (dd, J = 7.5, 5 Hz, 1 H), 7.29 (s, 1 H), 7.44 (m, 5 H), 8.02 (m,
H), 8.31 (m, 2 H), 8.49 (s, 1 H), 8.71 (d, J = 5 Hz, 1 H) ppm.
3
Resolution of Piperidyl Alcohols 5b-I and 5b-II and Pyridyl Alcohol
1
3
C NMR (75 MHz, CDCl
27.2, 128.9, 129.3, 130.7, 131.8, 132.3, 137.0, 147.6, 161.8 ppm.
15NO (285.22): calcd. C 84.17, H 5.30; found C 84.00, H 5.42.
3
): δ = 69.7, 120.8, 122.1, 124.8, 125.0, 7: Diastereomeric separation of the threo isomer from the erythro
1
isomer was first necessary (cf. above). Analytical separation of race-
mic pure threo isomer 5b-I was then performed further with a CHI-
RALCEL OD-RH (150ϫ4.6 mm, 5 µ) column with acetonitrile/
ethanolamine, 100:0.1 as the mobile phase (flow rate = 0.5 mL/
20
C H
General Procedure for PtO Hydrogenation: To a solution of 7
0.2 g, 0.7 mmol) in EtOH (10 mL) in a glass tube that exactly fits
inside of a stainless steel autoclave were added successively concen-
trated HCl (0.05 mL, 0.7 mmol) and PtO (30 mg). After being
purged twice (vacuum/H admission), the mixture was stirred un-
der 50 bar H and at 0 °C for 6 h. The catalyst was filtered out,
NaOH (1 equiv.) and H O (5 mL) were added, the mixture was
extracted with CH Cl (10ϫ10 mL), the combined organic phases
were dried with Na SO , the solvent was removed under vacuum,
2
(
min), the chromatographic parameters obtained are: Rt1
.15 min, Rt2 = 11.04 min, kЈ = 1.54, kЈ = 2.07, alpha = 1.34.
=
9
1
2
2
Then, on a preparative scale, 483 mg of rac-5b-I was resolved by
using a larger CHIRALCEL OD column (250ϫ50 mm, 20 µm)
and the same mobile phase (100 mL/min), with isolation of three
fractions whose enantiomeric purities were determined by using the
analytical conditions (93% of the starting material was recovered):
2
2
2
2
2
2
4
2
50 mg (52%) threo: enantiomer 1 (5b-I1), chemical purity = 95%,
ee = 100%; 90 mg (19%) threo: enantiomer 2 (5b-I2), ee = 86.8%;
09 mg (22%) threo: enantiomer 2 (5b-I2), chemical purity = 94%,
and the amino alcohol was then purified by chromatography on
1
silica gel (ether/hexane, 9:1). threo 5b-I: H NMR (400 MHz,
1
3
CDCl
3
): δ = 0.81 (br. d, J = 12.0 Hz, 1 H, 2-H
e
), 1.0 (m, 1 H, 3-
ee = 98.5%. The enantiomers of 5b-II were preparatively obtained
H), 1.10 (br. q, 1 H, 2-H
a
), 1.36 (m, 1 H, 4-H), 1.48 (m, 2 H, 3-H,
®
by supercritical fluid chromatography by using a CHIRALPAK
2
3
4
(
4
-H), 2.69 (td, J = 12 Hz, J = 12 Hz, 2.5 Hz, 1 H, 5-H
br. d, J = 12 Hz, 1 H, 5-H
), 3.52 (td, 3J = 9.5 Hz, 9.5 Hz and
Hz, 1 H, 1-H), 3.60 (br. s, 1 H), 6.03 (d, J = 9.5 Hz, 1 H), 7.47
a
), 3.09
AD column (250ϫ20 mm, 10 µm) from Chiral Technologies, Inc.
and recovery of 81% of the starting material (the enantiomeric pu-
rities of the fractions have been determined by using the analytical
e
3
16]
13
(
m, 4 H), 8.00 (m, 2 H), 8.40 (s, 1 H), 8.72 (br., 2 H)[ ppm.
): δ = 24.5, 26.0, 29.4, 46.7, 62.0, 73.5,
25.1, 125.2, 125.7, 128.4, 129.6, 130.7, 132.0, 133.8 ppm.
21NO (291.22): calcd. C 82.44, H 7.26; found C 81.79, H 7.34.
erythro 5b-II: All signals overlapped with those of threo 5b-I, ex-
C
conditions): erythro 5b-II1 (70 mg), first eluted: R
negative CD at 263 nm, ee = 99%; erythro 5b-II2(108 mg), second
eluted: R = 17.31 min, positive CD at 263 nm, ee = 99%. Analyti-
t
= 16.21 min,
NMR (100 MHz, CDCl
3
1
t
20
C H
cal and preparative separation of rac-7 were performed with CHI-
RALCEL OD columns with different sizes (either 250ϫ4.6 mm,
2
3
3
cept: δ = 2.72 (br. t, J = J = 12 Hz, 1 H, 5-H
a
) and 6.10 (d, J =
1
0 µ or 0.46ϫ 25 cm, 10 µ) and the same mobile phase. The
analytic chromatographic parameters obtained are: Rt1
4.50 min, Rt2 = 16.00 min. On the preparative scale, 167 mg of
7
2
1
.5 Hz, 1 H) ppm. 13C NMR (100 MHz, CDCl
8.2, 46.6, 62.2, 73.7, 124.8, 125.7, 128.4, 129.1, 130.2, 131.6,
32.1 ppm.
3
): δ = 24.1, 25.2,
=
1
rac-7 was resolved with isolation of two fractions and recovery of
74% of the starting material (the enantiomeric purities of the frac-
tions have been determined by using the analytical conditions):
General Procedure for Aldolization of Formamidine 8: To a solution
of piperidine formamidine 8 (2.0 g, 11.88 mmol, 1.0 equiv.) in an
ether/THF mixture (15:4 mL) was added (at –78 °C) tert-butyllith-
1
52 mg enantiomer (–)-7, chemical purity Ͼ95% (by 400 MHz H
Eur. J. Org. Chem. 2007, 826–830
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
829

A. Solladié-Cavallo et al.
FULL PAPER
NMR); 71 mg enantiomer (+)-7, chemical purity Ͼ95% (by
C. Marsol, C. Suteu, F. Garin, Enantiomer 2001, 6, 245; d) S.
Diezi, M. Hess, E. Orglmeister, T. Mallat, A. Baiker, J. Mol.
Catal. A 2005, 239, 49; e) E. Orglmeister, T. Bürgi, T. Mallat,
A. Baiker, J. Catal. 2005, 232, 137.
1
400 MHz H NMR).
Acknowledgments
[7] C. Exner, A. Pfaltz, M. Studer, H. U. Blaser, Adv. Synth. Catal.
2003, 345, 1253.
[
[
8] T. S. Hamilton, R. Adams, J. Am. Chem. Soc. 1928, 50, 2260.
We are grateful to Region Alsace and to CNRS for a grant to
C. M. (BDI), to Ministère de L’Enseignement Supérieur et de la
Recherche for a grant (MNERT) to K. A. and Ministère des Af-
faires Étrangères for a grant to M. R.
ˇ
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Received: August 18, 2006
Published Online: December 8, 2006
830
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