Influence of hydroperoxides on the enantioselectivity of metal-catalyzed asymmetric Baeyer-Villiger oxidation and epoxidation with chiral ligands

Article abstract of DOI:10.1016/S0957-4166(01)00417-7

Chiral hydroperoxides have a significant influence on the enantioselectivity of the metal-catalyzed asymmetric Baeyer-Villiger oxidation of cyclic ketones and the epoxidation of allylic alcohols, when chiral ligands are employed. If both the ligand and th

Full text of DOI:10.1016/S0957-4166(01)00417-7

TETRAHEDRON:
ASYMMETRY
Pergamon
Tetrahedron: Asymmetry 12 (2001) 2441–2446
Influence of hydroperoxides on the enantioselectivity of
metal-catalyzed asymmetric Baeyer–Villiger oxidation and
epoxidation with chiral ligands
Carsten Bolm,a,* Oliver Beckmann,a,† Toralf Ku¨hn,a Chiara Palazzi,a Waldemar Adam,b
Paraselli Bheema Raob and Chantu R. Saha-Mo¨llerb
aInstitut fu¨r Organische Chemie der RWTH Aachen, Professor-Pirlet-Straße 1, D-52056 Aachen, Germany
bInstitut fu¨r Organische Chemie, Universita¨t Wu¨rzburg, Am Hubland, D-97074 Wu¨rzburg, Germany
Received 30 August 2001; accepted 24 September 2001
Abstract—Chiral hydroperoxides have a significant influence on the enantioselectivity of the metal-catalyzed asymmetric
Baeyer–Villiger oxidation of cyclic ketones and the epoxidation of allylic alcohols, when chiral ligands are employed. If both the
ligand and the hydroperoxide are enantiopure, the ligand determines the formation of the preferred product enantiomer in both
reactions. © 2001 Elsevier Science Ltd. All rights reserved.
1. Introduction
2. Results and discussion
We have recently reported on a new variant of the
asymmetric Baeyer–Villiger oxidation, mediated by a
chiral Lewis acid that is based on aluminium (Scheme
1).3 The combination of BINOL and an appropriate
aluminium compound (1:1 ratio of ligand and metal
precursor) were found to give optically active lactones
from the racemic cyclobutanones 1. In part, this system
proved to be more efficient than the other metal-based
ones known to date.2,3
Asymmetric epoxidation has gained its place among the
most powerful synthetic methods to obtain chiral inter-
mediates.1 Metal-catalyzed Baeyer–Villiger oxidation
has not yet reached this highly developed level; how-
ever, some promising new developments have recently
been reported.2 For both types of reactions, much
effort has been expended in finding the right combina-
tion of metal and chiral ligand to catalyze these oxida-
tions efficiently. To date, the hydroperoxides tested
were mainly restricted to the commercially available
tert-butyl hydroperoxide (TBHP) or cumene hydroper-
oxide (CHP).
The experiments to examine the influence of the
hydroperoxide were carried out in toluene in the pres-
ence of 0.5 equivalents of Me2AlCl and 0.5 equivalents
of enantiopure BINOL. The reaction mixture was
stirred overnight and allowed to warm from −25°C to
In the course of our search for new methods of asym-
metric catalysis, we have examined the influence of
hydroperoxides in oxidative transformations, viz the
Baeyer–Villiger oxidation of cyclic ketones and the
epoxidation of allylic alcohols. Two different substrates
were investigated for each reaction to allow more gen-
eral conclusions.
room temperature.
O
O
0.5 equiv. Me2AlCl,
0.5 equiv. (S)-BINOL
O
2
1.5 equiv. CHP,
toluene, -25 ˚C -> r.t.
+
1
O
O
* Corresponding author. Tel.: +49 241-8094 675; fax: +49 241-8092
391; e-mail: carsten.bolm@oc.rwth-aachen.de
† Present address: Institut de Chimie, Campus de Beaulieu, Universite´
de Rennes 1.
3
Scheme 1.
0957-4166/01/$ - see front matter © 2001 Elsevier Science Ltd. All rights reserved.
PII: S0957-4166(01)00417-7

2442
C. Bolm et al. / Tetrahedron: Asymmetry 12 (2001) 2441–2446
Based on the results shown in Table 1, no general trend
may be deduced, as long as an achiral hydroperoxide is
employed. Although trityl hydroperoxide (TrOOH,4
entry 4) was the best oxygen source in the case of
lactone 6, the two regioisomeric products 4a and 4b
were formed with the lowest enantioselectivity under
these conditions. Furthermore, the lowest 4a:4b ratio
was not observed with the smallest hydroperoxide,
TBHP, but with the sterically more demanding 1-
methylcyclohexyl hydroperoxide.5 In contrast, the
bulkiest hydroperoxide, TrOOH, led to the highest
4a:4b ratio.
reported,8b with which highly efficient asymmetric oxi-
dations have been achieved. Consequently, the oppor-
tunity presented itself to examine the stereoselectivity of
a combination of a chiral hydroperoxide with each
enantiomer of BINOL in the asymmetric Baeyer–Vil-
liger oxidation (Scheme 1). The incentive was to assess
whether any cooperative effects operate between the
two chiral components, that is, the optically active
hydroperoxide and the optically active ligand simulta-
neously coordinated to the metal catalyst, and to iden-
tify which stereogenic center is responsible for the
formation of the preferred enantiomer of the oxidation
product. Clearly, entries 5 and 6 in Table 1 reveal that
the absolute configurations for the products 4 and 6 are
determined by the chirality of the ligand. Furthermore,
the enantiomeric excess of the oxidation products differ
in both experiments, which implicates cooperative
effects between the chiral ligand and the chiral
hydroperoxide as a result of matched and mismatched
combinations. This is also supported by the marked
change in the 4a:4b ratio from 11.2:1 to 4.5:1. Conse-
With few exceptions, chiral hydroperoxides have so far
been reported to give only moderate enantioselectivities
in asymmetric oxidations.6 We have developed an effec-
tive method to obtain enantiopure (S)-(1-phenyl)ethyl
hydroperoxide by enzymatic kinetic resolution7 and
demonstrated that it serves as an efficient chiral oxygen
source in various asymmetric oxidations.8a Moreover, a
TADDOL-based
hydroperoxide
was
recently
Table 1. Aluminium-promoted Baeyer–Villiger oxidation of 3 and 5 using different hydroperoxides
O
7a
O
O
7a
O
O
O
O
O
+
0.5 equiv. Me2AlCl,
0.5 equiv. BINOL
3a
3a
4a
4b
3
5
1.5 equiv. oxygen source,
toluene, -25 ˚C -> r.t.
Ph
Ph
6
Oxygen
source
BINOL
E.e. of 4b
E.e. of 4a
Entry
Ratio
E.e. of 6
[%]a
[%]a
4a:4bb,c
[%]a
(S)
(S)
(S)
(S)
(S)
(R)
(S)
27 (3aR,7aR)
36 (3aR,7aR)
34 (3aR,7aR)
22 (3aR,7aR)
5 (3aR,7aR)
18 (3aS,7aS)
11 (3aR,7aR)
64 (S)
58 (S)
71 (S)
75 (S)
60 (S)
51 (R)
56 (S)
1
2
95 (3aR,7aS)
94 (3aR,7aS)
96 (3aR,7aS)
80 (3aR,7aS)
89 (3aR,7aS)
92 (3aS,7aR)
89 (3aR,7aS)
3.3
TBHP
OOH
2.1
2.7
4.5
11.2
4.5
8.3
3
CHP
4
TrOOH
OOH
5d
6d
7e
Ph
OOH
OOH
Ph
Ph
a Determined by GC using a chiral column.
b Calculated from area percentages.
c Full conversion of the starting material in each case.
d (S)-(1-phenyl)ethyl hydroperoxide with >99% e.e. was used.
e Oxidant was racemic.

C. Bolm et al. / Tetrahedron: Asymmetry 12 (2001) 2441–2446
2443
the epoxidation of geraniol 12 from 9% e.e. (R,R) to
42% e.e. (S,S) for the corresponding epoxide 13. Again,
it was the chiral ligand which determined the absolute
configuration of the epoxide for both substrates, when
a combination of chiral ligand and chiral hydroperox-
quently, the enantiomeric excess achieved with the
racemic (1-phenyl)ethyl hydroperoxide (entry 7) falls,
after complete oxidation, between the e.e. values of the
experiments with the pure enantiomers in entries 5 and
6.
In order to gain more insight into the generality of the
findings, we extended our studies to the vanadium-cata-
lyzed epoxidation of allylic alcohols 7. We have
reported earlier that the catalyst formed from VO(Oi-
Pr)3 and the chiral hydroxamic acids 9 with a
[2.2]paracyclophane scaffold gave epoxides 8 with up to
71% e.e. (Scheme 2) by asymmetric oxidation.9,10
A survey of various achiral hydroperoxides revealed
that the presence of aryl groups in the oxygen source is
detrimental to the enantiomeric excess (Table 2, entries
1–4). Exchange of the aryl substituents with methyl
groups dramatically increased the enantioselectivity in
Scheme 2.
Table 2. Vanadium-catalyzed epoxidation of 10 and 12 using different hydroperoxides

2444
C. Bolm et al. / Tetrahedron: Asymmetry 12 (2001) 2441–2446
ide was used (entries 5 and 6). Substrate 10 showed a
remarkable difference in the enantioselectivity (63 versus
33% e.e.) with respect to the matched versus the mis-
matched combination. In agreement with our findings for
the Baeyer–Villiger oxidation, the use of racemic (1-
phenyl)ethyl hydroperoxide (entry 7) gave a value
between the ones of the experiments with the single
enantiomer in entries 5 and 6. In addition, the e.e. value
of the remaining hydroperoxide, which was employed in
1.5-fold excess, was determined to be less than 5% after
the reaction11 for both substrates, which indicates that no
kinetic resolution of the racemic hydroperoxide had
taken place. This confirms that both diastereomeric
combinations of the chiral ligand and the chiral
hydroperoxide react at about the same rates. Signifi-
cantly, again the more effective combination, analogous
to the Baeyer–Villiger oxidation, cannot be predicted:
either substrate shows a better selectivity for the opposite
enantiomer combination.
1.00 mmol) and DMF (two drops) in dichloromethane
(2 mL). The resulting mixture was stirred for 1 h at
ambient temperature (ca. 20°C) wherein a light red
solution was obtained. The solvent and excess oxalyl
chloride were removed in vacuo. The remaining car-
boxylic chloride was dissolved in dichloromethane (5
mL) and slowly added to a solution of tert-butylhydroxyl-
amine (115 mg, 1.30 mmol) and NEt3 (0.40 mL, 2.88
mmol) in dichloromethane (5 mL) at −70°C. The mixture
was then allowed to warm to ambient temperature and
stirred for an additional 4 h. Upon completion, aqueous
hydrochloric acid (2 M, 10 mL) was added. The aqueous
layer was extracted with MTBE (2×20 mL). The com-
bined organic layers were washed with water (20 mL) and
brine (20 mL) and dried over MgSO4. Removal of the
solvent provided the crude product, which was purified
by flash column chromatography (silica, petroleum
ether:MTBE, 2:1), followed by recrystallization from
hexane to give (S)-14 as white fibers (145 mg, 45%): mp
146°C; Rf 0.41 (petroleum ether:MTBE, 2:1); [h]2D5=
+73.6 (c 0.5, CHCl3); IR (KBr) 3180, 2928, 2852, 1604,
1558, 1499, 1475, 1454, 1430, 1383, 1364, 1203, 1120
cm−1; 1H NMR (400 MHz, CDCl3) l 1.07 (s, 9H),
2.86–3.03 (m, 4H), 3.08–3.27 (m, 4H), 6.38 (dd, J=8.0,
1.6 Hz, 1H), 6.41 (d, J=7.7 Hz, 1H), 6.45 (d, J=1.6 Hz,
1H), 6.53–6.61 (m, 3H), 7.13 (dd, J=8.0, 1.6 Hz, 1H),
8.80 (br s, 1H); 13C NMR (100 MHz, CDCl3) l 29.2, 33.9,
35.4, 35.6, 35.8, 61.8, 131.6, 132.0, 132.5, 132.6, 133.1,
133.3, 135.0, 135.1, 138.4, 139.3, 139.5, 139.7, 168.9;
HPLC (Chiralcel OD, hexane:i-PrOH, 98:2, 0.6 mL/min,
25°C): tR=38.3 min (S) and 48.4 min (R). Anal. calcd
for C21H25NO2: C, 77.99; H, 7.79; N, 4.33. Found: C,
77.96; H, 7.52; N, 4.25%.
In conclusion, we have demonstrated that the choice of
the hydroperoxide as oxygen source has a pronounced
influence on the stereochemical outcome of the metal-cat-
alyzed asymmetric Baeyer–Villiger oxidation of cyclic
ketones, as well as the epoxidation of allylic alcohols. For
the combination of chiral ligands with chiral hydroperox-
ides, the ligand dominates the formation of the preferred
enantiomer of the oxidation product. A significant coop-
erative effect has been found, but it is difficult to predict
a priori which combination may be the more successful.
The outcome strictly depends on the substrate used.
3. Experimental
3.3. Asymmetric Baeyer–Villiger oxidation
3.1. General information
3.3.1. Synthesis of reactants. ( )-cis-Bicyclo[4.2.0]octan-
7-one 313 and 3-phenylcyclobutanone 514 are accessible
by means of [2+2]-cycloaddition of dichloroketene to an
appropriate olefin and subsequent dehalogenation.
1H NMR spectra were recorded on a Varian VXR 300
(300 MHz) or a Varian Inova 400 (400 MHz). The
chemical shifts are referred to tetramethylsilane. Data are
reported as follows: chemical shift, multiplicity, coupling
constants, integration. 13C NMR spectra were recorded
on a Varian VXR 300 (75 MHz), a Varian Inova 400 (100
MHz) or a Varian Unity 500 (125 MHz) with complete
proton decoupling. The chemical shifts are referenced to
the solvent used. IR spectra were recorded on a Perkin
Elmer spectrometer (PE 1720X, PE 1760 FT). Melting
points were determined on a Bu¨chi B-540 and are
uncorrected. Optical rotation values a were determined
on a Perkin Elmer polarimeter PE-241. All reactions were
carried out under an argon gas atmosphere.
Dichloromethane was distilled from CaH2 under N2,
toluene was distilled from Na under an argon atmo-
sphere; NEt3 and pyridine were distilled from KOH and
stored under argon. Anhydrous DMF was purchased
from Fluka and used without further purification.
1
3.3.2. ( )-cis-Bicyclo[4.2.0]octan-7-one 3. H NMR (400
MHz, CDCl3) l 1.04–1.26 (m, 3H), 1.39–1.48 (m, 1H),
1.52–1.59 (m, 2H), 1.94–1.98 (m, 1H), 2.13–2.19 (m, 1H),
2.44–2.50 (m, 2H), 3.11–3.18 (m, 1H), 3.26–3.30 (m, 1H);
13C NMR (125 MHz, CDCl3) l 21.0, 22.2, 22.3, 22.4,
29.3, 52.0, 56.4, 209.7; GC: Lipodex B (25 m×0.25 mm)
with pre-column (3 m×0.25 mm), 60 kPa N2, either 120°C
isotherm with tR=5.9 min or 120°C, 2°C/min, 150°C, 5
min with tR=4.9 min.
3.3.3. 3-Phenylcyclobutanone 5. 1H NMR (300 MHz,
CDCl3) l 3.15–3.27 (m, 2H), 3.40–3.52 (m, 2H), 3.64
(quin, J=8.2 Hz, 1H), 7.21–7.36 (m, 5H); 13C NMR (75
MHz, CDCl3) l 28.2, 54.5, 126.3, 126.5, 128.5, 143.4,
206.4; GC: Lipodex B (25 m×0.25 mm) with pre-column
(3 m×0.25 mm), 60 kPa N2 at 140°C, 140°C, 15 min,
2°C/min, 160°C, 50 min with tR=15.8 min.
3.2. Synthesis of (S)-N-(1,1-dimethylethyl)-N-hydroxy-
[2.2]paracyclophane-4-carboxylic amide 14
3.3.4. General procedure for the Baeyer–Villiger oxida-
tion. A solution of Me2AlCl in hexane (50 mol%) was
injected into a solution of enantiopure BINOL (50 mol%)
in dry toluene under an argon gas atmosphere. After
A solution of oxalyl chloride in dichloromethane (0.5 M,
3 mL, 1.50 mmol) was slowly added to a suspension of
(S)-[2.2]paracyclophane-4-carboxylic acid12 (252 mg,

C. Bolm et al. / Tetrahedron: Asymmetry 12 (2001) 2441–2446
2445
being stirred for 0.5×1 h at ambient temperature, the
ketone was added to the suspension, which became
more homogeneous after stirring for an additional 15
min. The mixture was cooled to −25°C before addition
of hydroperoxide (1.5 equiv.) and then slowly allowed
to warm to ambient temperature again. After stirring
for 12 h, the mixture was treated with aqueous HCl (0.5
M) and the aqueous layer was extracted with MTBE.
The combined organic layers were washed with a satu-
rated aqueous solution of NaHCO3, dried over anhy-
drous MgSO4, filtered, and directly submitted to GC
analysis.
stirred for 1 h at ambient temperature and then cooled
to −20°C. Subsequently, the allylic alcohol was added
via syringe, followed, after 15 min, by the hydroperox-
ide (1.5 equiv.). After stirring the mixture for 3 days,
the reaction was quenched with aqueous Na2SO3 (1 M),
and the mixture was extracted with MTBE. The com-
bined organic layers were dried over anhydrous
MgSO4, filtered and concentrated under reduced pres-
sure. The epoxide was purified by flash column chro-
matography on silica gel.
When the enantiomeric excess of the remaining (1-
phenyl)ethyl hydroperoxide was to be determined, the
crude reaction mixture was directly submitted to
column chromatography without any work-up.
When yields of isolated products were to be deter-
mined, 1–2 mmol of ketone was employed and the
product was purified by flash column chromatography
(silica, petroleum ether:MTBE, 2:1).
3.4.2. Procedure for the experiments with the shift
reagent Eu(tfc)3. Acetic anhydride (50 mL) was added to
a solution of 2,3-epoxygeraniol 13 (30 mg) in dry
pyridine (0.5 mL). The resulting mixture was stirred at
ambient temperature for 2 h and then diluted with
petroleum ether (0.5 mL). The formed acetate was
purified by flash column chromatography (silica,
petroleum ether:MTBE, 2:1, Rf 0.75). The enantiomeric
3.3.5. ( )-cis-Hexahydro-2(3H)-benzofuranone 4a. 1H
NMR (300 MHz, CDCl3) l 1.20–1.34 (m, 2H), 1.43–
1.54 (m, 2H), 1.58–1.77 (m, 3H), 2.03–2.12 (m, 1H),
2.25 (dd, J=16.4, 2.4 Hz, 1H), 2.35–2.45 (m, 1H), 2.62
(dd, J=16.8, 6.9 Hz, 1H), 4.52 (ddd, J1=J2=J3=4.3
Hz, 1H); 13C NMR (75 MHz, CDCl3) l 19.7, 22.6,
27.0, 27.6, 34.7, 37.3, 79.1, 177.6; GC: Lipodex B (25
m×0.25 mm) with pre-column (3 m×0.25 mm), 60 kPa
N2, either 120°C isotherm with tR=37.7 min [(+)-
(3aR,7aR)] and 41.0 min [(−)-(3aS,7aS)] or 120°C, 2°C/
min, 150°C, 5 min with tR=17.6 min [(+)-(3aR,7aR)]
and 18.2 min [(−)-(3aS,7aS)].15
1
excess was determined by H NMR analysis of a solu-
tion of the acetate and Eu(tfc)3 (8 mg) in C6D6 (1 mL)
by integrating the signal at l 1.04 ppm.
3.4.3. ( )-2,3-Epoxy-2-methyl-3-phenylpropan-1-ol 11. Rf
0.22 (petroleum ether:MTBE, 1:1); 1H NMR (400
MHz, CDCl3) l 1.09 (s, 3H), 2.18 (dd, J=8.5, 4.1 Hz,
1H), 3.76 (dd, J=12.5, 8.7 Hz, 1H), 3.86 (dd, J=12.5,
4.0 Hz, 1H), 4.22 (s, 1H), 7.28–7.39 (m, 5H); 13C NMR
(100 MHz, CDCl3) l 13.7, 60.4, 64.0, 65.2, 126.6, 127.8,
128.3, 135.8; HPLC (Chiralcel OD, hexane:i-PrOH,
97:3, 0.8 mL/min, 25°C): tR=19.0 min (2S,3S) and 26.3
min (2R,3R).
1
3.3.6. ( )-cis-Hexahydro-1(3H)-isobenzofuranone 4b. H
NMR (400 MHz, CDCl3) l 1.19–1.24 (m, 3H), 1.56–
1.67 (m, 3H), 1.77–1.85 (m, 1H), 2.10–2.13 (m, 1H),
2.44–2.51 (m, 1H), 2.63–2.67 (m, 1H), 3.96 (dd, J=9.1,
1.4 Hz, 1H), 4.20 (dd, J=8.8, 5.2 Hz, 1H); 13C NMR
(100 MHz, CDCl3) l 22.5, 22.9, 23.4, 27.2, 35.4, 39.5,
71.7, 178.3; GC: Lipodex B (25 m×0.25 mm) with
pre-column (3 m×0.25 mm), 60 kPa N2, either 120°C
isotherm with tR=24.6 min [(−)-(3aS,7aR)] and 26.1
min [(+)-(3aR,7aS)] or 120°C, 2°C/min, 150°C, 5 min
with tR=14.3 min [(−)-(3aS,7aR)] and 14.7 min [(+)-
(3aR,7aS)].16
3.4.4. ( )-2,3-Epoxygeraniol 13. Rf 0.19 (petroleum
1
ether:MTBE, 1:1); H NMR (400 MHz, CDCl3) l 1.30
(s, 3H), 1.43–1.52 (m, 1H), 1.61 (s, 3H), 1.64–1.72 (m,
1H), 1.69 (d, J=1.1 Hz, 3H), 1.96 (dd, J=7.3, 4.8 Hz,
1H), 2.09 (q, J=8.0 Hz, 2H), 2.98 (dd, J=6.8, 4.3 Hz,
1H), 3.64–3.72 (m, 1H), 3.79–3.87 (m, 1H), 5.06–5.11
(m, 1H); 13C NMR (100 MHz, CDCl3) l 16.7, 17.6,
23.7, 25.7, 38.4, 61.1, 61.4, 62.9, 123.2, 132.0.
3.3.7. ( )-4-Phenyltetrahydro-2-furanone 6. 1H NMR
(400 MHz, CDCl3) l 2.65 (dd, J=17.3, 9.1 Hz, 1H),
2.90 (dd, J=17.3, 8.5 Hz, 1H), 3.78 (quin, J=8.2 Hz,
1H), 4.24 (t, J=8.6 Hz, 1H), 4.64 (t, J=8.5 Hz, 1H),
7.21–7.24 (m, 2H), 7.26–7.31 (m, 1H), 7.34–7.38 (m,
2H); 13C NMR (100 MHz, CDCl3) l 35.5, 40.9, 73.8,
126.5, 127.4, 128.8, 139.2, 176.1; GC: Lipodex B (25
m×0.25 mm) with pre-column (3 m×0.25 mm), 60 kPa
N2 at 140°C, 140°C, 15 min, 2°C/min, 160°C, 50 min
with tR=65.0 min [(+)-(S)] and 66.6 min [(−)-(R)].17
3.4.5. Acetate of ( )-2,3-epoxygeraniol 13. 1H NMR
(400 MHz, C6D6) l 1.04 (s, 3H), 1.31–1.39 (m, 1H),
1.48 (s, 3H), 1.48–1.56 (m, 1H), 1.63 (d, J=1.1 Hz,
3H), 1.66 (s, 3H), 1.96–2.03 (m, 2H), 2.89 (dd, J=6.6,
4.4 Hz, 1H), 3.99 (dd, J=12.1, 6.6 Hz, 1H), 4.19 (dd,
J=12.1, 4.4 Hz, 1H), 5.03–5.09 (m, 1H); 13C NMR
(100 MHz, C6D6) l 16.8, 17.6, 20.2, 23.9, 25.7, 38.5,
1
59.5, 59.8, 63.5, 123.9, 131.6, 169.7; H NMR experi-
ment with the shift reagent Eu(tfc)3: l 1.16 (2S,3S) and
1.19 (2R,3R).
3.4. Asymmetric epoxidation
3.4.1. General procedure for the epoxidation of allylic
alcohols. VO(Oi-Pr)3 (5 mol%) and ligand 14 (7.5
mol%) were dissolved in dry toluene under an argon
atmosphere. The resulting deep red solution was first
3.4.6. ( )-(1-Phenyl)ethyl hydroperoxide. Rf 0.20
(petroleum ether:MTBE, 4:1); HPLC (Chiralcel OD-H,
hexane:i-PrOH, 95:5, 0.5 mL/min, 20°C): tR=23.2 min
(R) and 28.4 min (S).

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C. Bolm et al. / Tetrahedron: Asymmetry 12 (2001) 2441–2446
5. Lauterbach, G.; Pritzkow, W.; Tien, T. D.; Voerckel, V.
Acknowledgements
J. Prakt. Chem. 1988, 330, 933.
We are grateful to the Deutsche Forschungsgemein-
schaft (Schwerpunktprogramm Sauerstofftransfer/Per-
oxidchemie) and the Fonds der Chemischen Industrie
for continuous financial support of this research pro-
ject. P.B.R. thanks the Alexander-von-Humboldt
Foundation for a postdoctoral fellowship (1999–2000).
6. (a) Adam, W.; Korb, M. N. Tetrahedron: Asymmetry
1997, 8, 1131; (b) Adam, W.; Korb, M. N.; Roschmann,
K. J.; Saha-Mo¨ller, C. R. J. Org. Chem. 1998, 63, 3423.
7. (a) Adam, W.; Hoch, U.; Lazarus, M.; Saha-Mo¨ller, C.
R.; Schreier, P. J. Am. Chem. Soc. 1995, 117, 11898; (b)
Adam, W.; Fell, R. T.; Hoch, U.; Saha-Mo¨ller, C. R.;
Schreier, P. Tetrahedron: Asymmetry 1995, 6, 1047.
8. (a) Adam, W.; Rao, P. B.; Degen, H.-G.; Saha-Mo¨ller, C.
R. J. Am. Chem. Soc. 2000, 122, 5654; (b) Aoki, M.;
Seebach, D. Helv. Chim. Acta 2001, 84, 187.
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