A new target for highly stereoselective Katsuki-Sharpless epoxidation - One-pot synthesis of C2-symmetric 2,2′-bioxiranes

Article abstract of DOI:10.1002/ejoc.200600711

The double asymmetric Katsuki-Sharpless epoxidation of a conjugated diallyl alcohol affords excellent enantioselectivity (>97% ee), the product being isolated as the stable p-nitrobenzoate 5a or tosylate 5b. The optical purities of the chiral epoxides were determined by HPLC on chiral columns, while the molecular structures of compounds 5a and 7 and the absolute configuration of mono-epoxide 12 were confirmed by X-ray crystallography. Possible π-π stacking interaction has been evaluated by ab initio calculation. Wiley-VCH Verlag GmbH & Co. KGaA, 2007.

Full text of DOI:10.1002/ejoc.200600711

FULL PAPER
DOI: 10.1002/ejoc.200600711
A New Target for Highly Stereoselective Katsuki–Sharpless Epoxidation –
One-Pot Synthesis of C2-Symmetric 2,2Ј-Bioxiranes
Vitaliy Bilenko,[a,b] Haijun Jiao,[a] Anke Spannenberg,[a] Christine Fischer,[a]
Helmut Reinke,[c] Jutta Kösters,[d] Igor Komarov,[b] and Armin Börner*[a,c]
Keywords: Epoxidation / Asymmetric catalysis / Bis-epoxides / Diols / ab initio calculation
The double asymmetric Katsuki–Sharpless epoxidation of a
conjugated diallyl alcohol affords excellent enantioselectivity
(Ͼ97% ee), the product being isolated as the stable p-nitro-
benzoate 5a or tosylate 5b. The optical purities of the chiral
epoxides were determined by HPLC on chiral columns, while
solute configuration of mono-epoxide 12 were confirmed by
X-ray crystallography. Possible π–π stacking interaction has
been evaluated by ab initio calculation.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
the molecular structures of compounds 5a and 7 and the ab- Germany, 2007)
Introduction
Results and Discussion
1. Synthesis of Diallyl Alcohol
The asymmetric Katsuki–Sharpless epoxidation of allyl
alcohols plays a pivotal role in organic chemistry for the
generation of chiral epoxides,[1,2] which serve as useful chi-
ral building blocks for further transformations. The cata-
lytic reaction does not require expensive reagents or special
equipment, while the mild reaction conditions and the tol-
eration of a range of functional groups are especially note-
worthy. In general, the stereochemistry of the resultant ep-
oxy alcohols can be unambiguously predicted by common
rules. In the case of Lewis acid-sensitive epoxides a facile in
situ derivatization has been suggested.[3]
As a substrate for the epoxidation we chose the hydroxy-
functionalized (E,E)-butadiene 4, which is easily available
by the synthetic route depicted in Scheme 1.
In a few cases, stereoselective bis-epoxidation of prochi-
ral diallyl alcohols has also been investigated.[4] The double
epoxidation also usually proceeds with high diastereo- and
enantioselectivity, but it is interesting to note that conju-
gated dienes have never been subjected to Katsuki–
Sharpless epoxidation. Here we report the first example of
this transformation, which proceeds with high stereoselecti-
vity. The products of such transformations might serve as
building blocks in syntheses of chiral multifunctional com-
pounds, in particular as chiral ligands for enantioselective
catalysts.
[a] Leibniz-Institut für Katalyse e.V.,
A.-Einstein-Str. 29a, 18059 Rostock, Germany
Fax: +49-381-1281-5202
E-mail: armin.boerner@catalysis.de
[b] Kyiv Taras Shevchenko University,
Volodymyrska-Str. 64, 01033 Kyiv, Ukraine
[c] Institut für Chemie der Universität Rostock,
A.-Einstein-Str. 3a, 18059 Rostock, Germany
[d] Institut für Anorganische und Analytische Chemie, Universität
Münster,
Scheme 1. Synthesis of diallyl alcohol 4 used as substrate in the
Katsuki–Sharpless epoxidation.
Corrensstrasse 36, 48149 Münster, Germany
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The synthesis commenced with dimethyl succinate, which
was subjected to Stobbe condensation to give the benzyl-
idene derivative 1.[5] The free carboxylic group in the half
ester 1 was reesterified by treatment with SOCl2 and sub-
sequently with MeOH to give 2. [An alternative synthesis is
the coupling between benzaldehyde and dimethyl maleate
in the presence of (nBu)3P by a modified literature pro-
cedure.[6]] A second Stobbe condensation of 2 afforded the
dibenzylidene hemi-ester 3, which was reduced with LiAlH4
to give the diallyl alcohol 4 in 24–29% overall yield.
The asymmetric epoxidation of 4 was performed in ac-
cordance with the Sharpless procedure in order to avoid
Lewis acid-catalyzed intramolecular epoxide opening.[3]
The reaction was carried out at –30 °C with a catalytic
amount of a TiIV complex based on -(+)-diethyl tartrate
as a chiral ligand (Scheme 2). The chiral product was
trapped by in situ esterification either with p-nitrobenzoyl
chloride or with p-toluenesulfonyl chloride, at low tempera-
ture.
Figure 1. Chromatograms of: a) an approximately equimolar mix-
ture of (all R)-5a and (all S)-5a, and b) the product of the asymmet-
ric epoxidation [(all R)-5a]. Whelk(R,R) column, eluent: n-hexane/
ethanol 8:2, 0.8 mLmin–1.
Scheme 2. Epoxidation of 4 and subsequent trapping of the prod-
uct.
The bis-epoxides 5a and 5b were purified by flash
chromatography on silica gel. The purification of 5a could
also be performed by crystallization, but in this case the
yield decreased by ca. 5%. Compounds 5a and 5b are stable
at room temperature.
2. Determination of Optical Purities and Absolute
Configurations
To determine the optical purities of the bis-epoxides 5a
and 5b the corresponding enantiomers of opposite configu-
ration were synthesized by use of -(–)-diethyl tartrate as a
chiral ligand for TiIV. HPLC analyses on a chiral column
showed extremely high enantioselectivity in the case of 5b
(Ͼ99% ee), with slightly diminished enantioselectivity in
that of 5a (Ͼ97% ee) (Figure 1 and Figure 2).
For the determination of the absolute stereochemistry of
the epoxidation an X-ray structure analysis of 5a was per-
formed. The molecular structure is depicted in Figure 3.
The absolute configuration could not be unambiguously de-
rived only from this analysis, but was confirmed together
by HPLC and X-ray crystallography indirectly after trans-
formation of 5b into the corresponding diol (vide infra).
Figure 2. Chromatograms of: a) an approximately equimolar mix-
ture of (all R)-5b and (all S)-5b, and b) the product of the asymmet-
ric epoxidation [(all S)-5b]. Whelk(R,R) column, eluent: n-hexane/
ethanol 8:2, 0.8 mLmin–1].
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Figure 3. Molecular structure of 5a. The thermal ellipsoids correspond to 30% probability.
Scheme 3. Reduction of 5b.
The bis-O-tosylate 5b was reduced with LiAlH4
In order to study whether the double epoxidation of bu-
(Scheme 3) in a step in which the course of the reaction was tadiene 4 is a consecutive process or proceeds in parallel we
dependent on the conditions. At room temperature and af- studied the reaction with application of only one equivalent
ter 2 h it yielded the monotosylate 6 in 56% yield, and this of tBuOOH instead of an excess as described above
could be converted into the bis-epoxide 7 by further treat- (Scheme 4). Under these conditions and even with pro-
ment with LiAlH4. Compound 7 could also be obtained in longed reaction times the corresponding mono-epoxide was
one step and in 54% yield by heating 5b with LiAlH4 at formed exclusively. After derivatization with p-nitrobenzoyl
reflux for 18 h. Further extended heating of the reaction chloride the epoxide 9 and the diester 10 derived from un-
mixture opened the epoxide rings and furnished the vicinal converted diene 4 were isolated.
diol 8.
The structure of 7 was confirmed by X-ray crystallogra- illustrated in Scheme 5. In the first step, the monoester 11
phy. It is displayed in Figure 4 and shows C2 symmetry. was formed by a selective esterification of one hydroxy
This study provided access to the mixed diester 12, as
The (R,R)-diol 8 had previously been described by group with p-nitrobenzoyl chloride, while subsequent asym-
Sharpless et al., who obtained this compound in 29% ee by metric Katsuki–Sharpless epoxidation of the remaining al-
another method.[7] The optical rotation of the product was lyl alcohol moiety and treatment with p-bromobenzoyl
measured as [α]2D0 = 7.2 (c = 0.98, EtOH). The value of our chloride yielded the α,β-unsaturated epoxide 12.
product 8 was [α]2D0 = –56.5 (c = 10, EtOH), which provides
The molecular structure of the p-bromobenzoyl com-
additional evidence that the all-S isomer is formed under pound 12 is depicted in Figure 5. It gives clear evidence for
the conditions of the Katsuki–Sharpless epoxidation with its absolute configuration – (S) – at C-2 [Flack parameter
-(+)-diethyl tartrate.
in this case is equal to –0.006(15)].
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Scheme 5. Synthesis of a mixed diester monoepoxide.
4. Structure and Reactivity
The epoxides 5 and 7 were found to be less reactive than
expected: for the full conversion of 5b into 8 the reaction
mixture had to be heated with a large excess of LiAlH4 for
48 h, while heating of 5a at reflux in acetonitrile solution
with BnNH2 for 24 h in the presence of a stoichiometric
amount of LiClO4 gave only the starting material. Employ-
ment of PhP(SiMe3)2 as a nucleophile for 7 was also unsuc-
cessful: NMR analysis showed only starting compound,
without any trace of the targeted phospholane, even after
6 h heating at 110 °C in the absence of solvent.
Figure 4. Molecular structure of 7 (two different molecules). The
thermal ellipsoids correspond to 30% probability.
A careful inspection of the X-ray structural analyses of
5a, 7 and 12 reveals nearly parallel alignments of the two
phenyl rings. The angle between the two phenyl planes in
5a, defined by C7–C12 and C13–C18, is 4.39(9) °. More-
over, the positions of the two phenyl rings are staggered
(Figure 6, a), which gives a hint of possible π–π stacking
interactions.[8,9] The smallest distance between two carbon
atoms in different rings (C7 and C13) is 3.158(2) Å (Fig-
ure 6, b), due to which arrangement the O2–C2 and C3–O1
bonds are oriented in an anti conformation.
Indications of possible parallel displaced π–π interac-
tions in solution were provided by some unusual spectro-
Scheme 4. Monoepoxidation of diallyl alcohol 4.
Figure 5. Molecular structure of 12. The thermal ellipsoids correspond to 30% probability.
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Figure 6. Different views of the structure of 5a.
1
scopic data. The H NMR spectra of 7, 5a and 5b each ferent views of the optimized structures for 7 and 7Ј (H
contained a broad four-proton signal, which was shifted to instead of Me groups) are shown in Figure 7.
higher field in relation to the resonances of other aromatic
The MP2/6-31G*-optimized structural parameters given
1
protons. For comparison, the H NMR spectra of cis- or in Table 1 agree reasonably well with the X-ray structural
trans-β-methylstyrene oxide did not show this feature. This analyses of 5a and 7. This agreement between theory, X-ray
broad signal could be assigned to H8, H9, H17 and H18 (Fig- analysis and spectroscopic data in solution indicates that
ure 6, a), which should be influenced by the aromatic ring the relative positions of the two phenyl rings are not caused
current effect. UV spectroscopy showed a bathochromic by crystallization, and therefore that there is no structural
shift of the absorption maximum of 7 by 22 nm in relation difference between gas phase and solid state.
to that of cis-β-methylstyrene oxide.[10] We speculated that
this geometrical arrangement in 5 and 7 could hinder the desmotic equation,[11] in which we used the mono-epoxide
attack of nucleophiles, causing the low reactivity. and ethane as reference molecules. Homodesmotic equa-
To quantify the interaction we employed the homo-
In order to evaluate the strength of such assumed π–π tions have been successfully used to estimate long-distance
stacking interactions we carried out ab initio calculations interactions.[12] For 7 the calculated homodesmotic reaction
at the electron-correlated MP2/6-31G* level of theory. Dif- energy is only –1.80 kcalmol–1 at the MP2/6-31G* level
762
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Figure 7. MP2/6-31G*-optimized structures of 7 (top) and 7Ј (bottom) in different views.
Table 1. MP2/6-31G*-optimized bond parameters and comparison
with the available X-ray data.[a]
7[a]
7Ј
5a[a]
C1–C2
1.510
1.496
[1.521(2)]
[1.522(5)],
[1.518(5)]
1.485
[1.470(4)],
[1.484(4)]
1.449
[1.435(4)],
[1.445(3)]
1.4478
[1.444(4)],
[1.447(3)]
1.509
[1.483(4)],
[1.497(4)]
1.482
[1.485(5)],
[1.487(4)]
3.702
[3.156(6)],
[3.188(3)]
170.95
[168.8(2)],
[169.9(2)]
–93.48
C1–C3
1.480
1.441
1.446
[1.472(2)],
[1.480(2)]
C1–O1
[1.433(2)],
[1.447(2)]
O1–C3
[1.446(2)],
[1.4411(2)]
C1–C7
[1.518(2)],
[1.504(2)]
Scheme 6. Theoretical investigation of π–π stacking phenomena.
C3–C5
1.482
3.158
163.2
[1.487(2),
[1.488(2)]
also very small, and no significant effects of methyl substi-
tution can be found. In addition, the structural parameters
of 7 and 7Ј, especially the length of the shortest C–C bond
and the distance between the phenyl ring centres, are very
similar, and since these distances in 5a are also very similar
to those in 7 and 7Ј, we can conclude that the interaction
of the phenyl rings in 5a should be in the same range as
those of 7 and 7Ј and hence very weak. The observed low
reactivity of the bis-epoxide towards nucleophiles can
hardly therefore be interpreted solely in terms of arguments
based on π–π stacking interactions. In addition, we also
carried out QCISD(T)/6-31G*//MP2/6-31G* single-point
energy calculations on 7Ј and the homodesmotic reaction
energy was found to be +0.97 kcalmol–1, again indicating
negligible interaction between the two phenyl rings. Since
C5–C6[b]
O1–C1–C2–O2
C7–C1–C2–C8
C3–C1–C2–C4
[3.158(2)]
[166.0(1)]
[–99.9(2)]
[–57.8(2)]
[–96.6(3)],
[–94.9(3)]
–54.50
–59.8
[–56.3(5)],
[–56.3(4)]
[a] The X-ray data are given in parentheses. [b] Distance (no bond).
(Scheme 6), which indicates a very weak stabilizing interac- highly correlated calculations with larger basis sets includ-
tion between the two phenyl rings. In order to check the ing polarization and diffuse functions are not possible with
substitution effect of the methyl group we also replaced the present systems, it is to be expected that the energetic inter-
methyl groups by hydrogen atoms (7Ј). However, the calcu- action between the two phenyl rings found on the basis of
lated homodesmotic reaction energy, of –1.31 kcalmol–1, is our calculations is probably not significant.
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wR2 (all data) = 0.116, 369 parameters. The structures were solved
by direct methods [SHELXS-97: G. M. Sheldrick, University of
Göttingen, Germany, 1997.] and refined by full-matrix, least-
squares techniques against F2 [SHELXL-97: G. M. Sheldrick, Uni-
versity of Göttingen, Germany, 1997.] XP (Bruker AXS) was used
for structural representations.
Conclusions
As a first example, the double asymmetric Katsuki–
Sharpless epoxidation of a conjugated diallyl alcohol was
investigated, and was found to afford the desired bis-epox-
ide with excellent enantioselectivity (Ͼ97% ee). The reac-
tion proceeds in a stepwise manner and the product was
CCDC-617872 (for 5a), -617873 (for 7) and -617874 (for 12) con-
trapped by acylation or tosylation. HPLC on chiral col- tain the supplementary crystallographic data for this paper. These
data can be obtained free of charge from The Cambridge Crystallo-
graphic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
umns was used to determine the optical purities of the
products, and X-ray structural analyses were employed to
confirm the relative and absolute configurations. By re-
duction of the bis-O-tosylate 5b with LiAlH4 the corre-
sponding enantiopure vicinal alcohol was obtained. The
synthesized bis-epoxides possess low reactivity towards nu-
cleophiles. One reason for such low reactivity might be π–π
stacking interactions between the phenyl rings, but it might
instead be more convincingly attributed to the sterically
crowded environment of the epoxide units.
Compounds 1 and 4 are known and could be synthesized by the
methods reported in the literature.[5,6,13] For the synthesis of bis-
epoxides 5a and 5b we used the method described by Sharpless for
the formation of monoepoxides followed by in situ derivatization.[3]
Dimethyl (E)-2-Benzylidenesuccinate (2). Method A: SOCl2 (26 mL,
0.354 mol) was added dropwise with stirring at room temperature
to a solution of 1 (52 g, 0.236 mol) in CH2Cl2 (150 mL). The mix-
ture was heated at reflux until the end of gas evolution (approxi-
mately 6 h), the solvent and SOCl2 were evaporated, and MeOH
(100 mL) and Et3N (36 mL) were added consecutively with stirring.
The stirring was continued overnight, the solvent was evaporated,
and the residue was dissolved in EtOAc, washed with water, aq.
NaHCO3 solution, a diluted solution of HCl and brine and dried
with Na2SO4. The solvent was evaporated and the product was
distilled under vacuum (0.8 mbar, 125–130 °C) to give 2 (45 g, 82%
Experimental Section
General: All reagents were purchased from commercial sources and
were used without additional purification unless otherwise men-
tioned. Solvents were dried and freshly distilled under argon before
use. Thin-layer chromatography was performed on precoated TLC
plates (silica gel). Melting points are corrected. The optical rota-
tions were measured on a “Gyromat-HP” instrument. NMR spec-
tra were recorded at the following frequencies: 250.13 MHz (1H),
1
yield). H NMR (CDCl3): δ = 3.92 (s, 2 H), 4.10 (s, 3 H), 4.20 (s,
3 H), 7.68–7.79 (m, 5 H), 8.28 (s, 1 H).
Method B: Tri-n-butylphosphane (95%, 64 mL, 1.4 equiv.) was
added slowly by syringe, under Ar at 20–25 °C, to a stirred solution
of dimethyl maleate (28.8 g, 0.2 mol) and benzaldehyde (21.2 g,
0.2 mol) in dry THF (300 mL), and stirring was continued for 20 h.
The mixture was diluted with CH2Cl2 (1 L) and stirred for 0.5 h.
Water (400 mL) containing H2O2 (30%, 34 mL) was added to oxi-
dise the remaining nBu3P. The organic phase was washed with
NaHCO3 (1 ) and dried (Na2SO4), and the solvents were evapo-
rated. TLC indicated that the residue contained the desired prod-
uct, tri-n-butylphosphane oxide and some starting aldehyde. Flash
chromatography (Merck 60 silica gel; n-heptane/ethyl acetate 2:1)
gave the pure diester as a an oil (33 g, 70% yield).
75.48 MHz (13C), 121.49 MHz (31P). Chemical shifts of 1H and 13
C
NMR spectra are reported in ppm downfield from TMS as an in-
ternal standard, while chemical shifts of 31P NMR spectra are ref-
erenced to H3PO4 as an external standard. Elemental analyses were
performed with a LEGO CHNS-932, mass spectra were recorded
on an AMD 402 spectrometer, and UV/Vis spectra were recorded
with a Perkin–Elmer Lambda 2 spectrometer. The enantiomeric ex-
cesses of compounds 5, 7 and 8 were measured on a Agilent 1100
Series HPLC instrument. The syntheses of only one enantiomer
from each enantiomeric pair are given below.
(2E,3E)-2-Benzylidene-3-(methoxycarbonyl)-4-phenylbut-3-enoic
Acid (3): A solution of benzaldehyde (21.2 g, 0.2 mol) and diester
2 (45 g, 0.192 mol) in anhyd. MeOH (30 mL) was added dropwise
to a solution of LiOMe in MeOH [freshly prepared by slow ad-
dition of finely divided lithium (1.4 g, 0.2 mol) to anhyd. MeOH
(150 mL) with stirring and heating until total dissolution]. The
mixture was heated at reflux for 36 h under argon and then cooled
in an ice bath, and most of the solvent was removed in vacuo. The
residue was acidified to pH 1 with aq. HCl (6 ) and extracted with
EtOAc, the organic phase was washed with sat. aq. NaHCO3 solu-
tion, and the aq. phase was collected. After acidification with aq.
HCl (2 ), the aqueous solution was extracted with EtOAc, and
removal of the solvent gave the corresponding monoester 3 as a
powder (53.2 g, 90% yield). m.p. 151 °C. 150–151 °C.[14] 1H NMR
(CDCl3): δ = 4.13 (s, 3 H), 7.55–7.90 (m, 10 H), 8.31 (s, 1 H), 8.35
(s, 1 H), 10.60–11.70 (brs, 1 H) ppm.
X-ray Crystallographic Study of Complexes 5a: Data were collected
with a Bruker-AXS SMART 6 K diffractometer with use of graph-
ite-monochromated Cu-Kα radiation and ω-scans.
Compound 5a: Space group P212121, orthorhombic, a = 10.5922, b
= 11.9304, c = 21.6245 Å, V = 2732.67 Å3, Z = 4, ρcalcd.
=
1.450 gcm–3,16357 reflections measured, 5077 were independent of
symmetry, of which 4672 were observed [IϾ2σ(I)], R1 = 0.0321,
wR2 (all data) = 0.0809, 397 parameters.
X-ray Crystallographic Study of Complexes 7 and 12: Data were
collected with a STOE-IPDS diffractometer with use of graphite-
monochromated Mo-Kα radiation.
Compound 7: Space group C2, monoclinic, a = 15.243(3), b =
8.861(2), c = 12.800(3) Å, β = 122.77(3)°, V = 1453.6(5) Å3, Z = 4,
ρcalcd. = 1.217 gcm–3, 11744 reflections measured, 3345 were inde-
pendent of symmetry, of which 2017 were observed [IϾ2σ(I)], R1
= 0.051, wR2 (all data) = 0.139, 181 parameters.
(2E,3E)-2,3-Dibenzylidenebutane-1,4-diol (4): A solution of 3 (5.7 g,
18.5 mmol) in THF (40 mL) was added dropwise at 0 °C over
10 min to a suspension of LiAlH4 (1.1 g, 28 mmol) in THF
(70 mL). After addition, the mixture was stirred for 2.5 h at room
temperature and the excess LiAlH4 was then quenched by addition
of H2O (no excess) and EtOH (50 mL). The inorganic compounds
Complex 12: Space group P212121, orthorhombic, a = 6.8896(4), b
= 19.085(2), c = 21.344(2) Å, V = 2806.5(3) Å3, Z = 4, ρcalcd.
=
1.454 gcm–3, 39350 reflections measured, 5522 were independent
of symmetry, of which 2698 were observed [IϾ2σ(I)], R1 = 0.051,
764
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were filtered off through a pad of SiO2 and intensively washed with
EtOH. The product was purified by chromatography on silica gel
(CH2Cl2/EtOAc 1:1) to give compound 4 as a solid (1.87 g, 38%
yield). m.p. 108–110 °C. 111–112 °C.[15] 1H NMR (CDCl3): δ = 4.14
2 H), 7.22–7.34 (m, 3 H), 7.51 (d, J = 8 Hz, 2 H), 7.91 (d, J =
8 Hz, 2 H) ppm. 13C NMR (CDCl3): δ = 22.1 (s, CH3), 60.8 (s,
CH), 61.5 (s, C), 70.2 (s, CH2), 126,5, 128.4, 128.5, 128.7, 130.4
(arom. CH), 132.7, 130.1, 145.6 (arom. C) ppm. MS(EI): m/z =
(d, J = 4.27 Hz, 2 H), 4.49 (t, J = 5.65 Hz, 1 H), 6.82 (s, 1 H), 7.15– 605.8 [M]+ (C32H30O8S2), 514.8, 438.8, 344.9, 314.9, 260.9, 181,
7.31 (m, 3 H), 7.51–7.59 (m, 2 H) ppm. 13C NMR ([D6]acetone): δ
180, 179, 172, 165, 154.9, 143, 105, 91, 77.
= 65.6, 126.5, 128.0, 128.9, 129.4, 138.0, 141.8 ppm.
(2S,3S)-2-[(2S,3S)-2-Methyl-3-phenyloxiran-2-yl]-2-(4-methylphen-
ylsulfonyloxymethyl)-3-phenyloxirane (6): LiAlH4 (0.18 g,
4.7 mmol) was added in three portions (at intervals of 30 min) to
a solution of 5b (2.25 g, 3.7 mmol) in dry THF (10 mL). After the
last addition, the mixture was stirred for another 30 min and di-
ethyl ether (15 mL) was added. The excess of LiAlH4 was quenched
by the addition of H2O, the inorganic residue was filtered off, and
chromatography on silica gel (Merck 60, n-hexane/ethyl acetate 2:1)
afforded 6 (900 mg, 56% yield) as an oil, together with 7 (100 mg,
10% yield) as a solid. [α]2D5 = 4.4 (c = 5, CHCl3). 1H NMR (CDCl3):
δ = 1.46 (s, 3 H), 2.45 (s, 3 H), 3.56 (s, 1 H), 3.76 (s, 1 H), 4.05–
4.22 (m, 2 H), 6.8–7.23 (m, 10 H), 7.35 (d, J = 8 Hz, 2 H), 7.77 (d,
J = 8 Hz, 2 H) ppm. 13C NMR (CDCl3): δ = 22.1 (s, CH3), 22.2
(s, CH3), 61.2 (s, CH), 61.8 (s, C), 63.2 (s, C), 64.3 (s, CH), 70.9 (s,
CH2), 126.5, 126.9, 127.9, 128.2, 128.4, 128.5, 128.5, 130.3 (all s,
arom. CH), 132.9, 133.9, 134.8, 145.5 (all s, arom. C) ppm. MS
(CI, isobutane): m/z = 437 [M + H]+ (C25H24O5S + H), 419, 331,
265, 247, 219, 205, 180,133, 105. MS (EI): m/z = 436 [M]+
(C25H24O5S), 400, 330, 264, 235, 206, 181, 180, 175, 165, 158, 154,
145, 139, 115, 105, 91, 77.
(2S,3S)-2-(4-Nitrophenylcarbonyloxymethyl)-2-[(2S,3S)-2-(4-nitro-
phenylcarbonyloxymethyl)-3-phenyloxiran-2-yl]-3-phenyloxirane
(5a): Ti(OiPr)4 (86 mg, 0.3 mmol) and molecular sieves (3 Å, 0.5 g)
were added to a cooled solution (–30 °C) of -(+)-diethyl tartrate
(87 mg, 0.42 mmol) in dry CH2Cl2 (20 mL), the mixture was stirred
at this temperature for 20 min, and a solution of tert-butyl hydro-
peroxide in decane (5.5 , 1.1 mL, 6 mmol) was added. The mix-
ture was stirred for a further 40 min and 4 (0.4 g, 1.5 mmol) in
CH2Cl2 (30 mL) was added. The reaction flask was kept in a freezer
at –27 °C for 2 d, P(OMe)3 (0.55 mL) was then added dropwise by
syringe at –30 °C over a 30 min period, and the mixture was stirred
for 40 min. Subsequently, Et3N (0.72 g, 7.1 mmol) and p-nitroben-
zoyl chloride (1.12 g, 6 mmol) were added and the reaction mixture
was stored in a freezer for another 2 d. The mixture was then al-
lowed to warm to room temp., and stirred at this temperature for
6 h, the molecular sieves were filtered off, and the solution was
washed with an aqueous solution of tartaric acid, satd. aq.
NaHCO3 solution and brine and dried (Na2SO4), and the solvents
were evaporated. The product was purified by chromatography on
silica gel (Merck 60, CH2Cl2 as eluent) to give compound 5a
[610 mg, 68% yield;, Ͼ97% ee, determined by HPLC, Whelk(R,R),
n-hexane/ethanol 8:2, 0.8 mLmin–1]. Alternative purification: after
the workup procedure the crude mixture was filtered through silica
gel (a short column) and crystallized from CH3CN (63% yield).
(2S,3S)-2-Methyl-2-[(2S,3S)-2-methyl-3-phenyloxiran-2-yl]-3-phen-
yloxirane (7). Method A: LiAlH4 (0.078 g, 2.06 mmol) was added
at r.t. to a solution of 6 (0.9 g, 2.06 mmol) in dry THF (5 mL) and
the mixture was stirred for 14 h. Another portion of LiAlH4
(0.030 g, 0.79 mmol) was added and stirring was continued for the
next 30 min. Excess LiAlH4 was quenched by the addition of H2O
and EtOAc (15 mL), the inorganic residue was filtered off, and
chromatography on silica (n-hexane/ethyl acetate 3:1) gave 7
(235 mg, 43% yield).
1
M.p. 187 °C. [α]2D5 = –11.4 (c = 5, CHCl3). H NMR (CDCl3): δ =
3.87 (m, 2 H), 4.62 (s, 1 H), 4.67 (s, 1 H), 4.90–5.35 (brm, 2 H),
6.60–7.00 (brm, 4 H), 7.07–7.27 (m, 6 H), 8.29 (s, 8 H) ppm. 13C
NMR (CDCl3): δ = 61.6, 62.3, 66.6, 124.1, 126.3, 128.5, 128.8,
131.4, 133.3, 135.3, 151.2, 164.7 ppm. DEPT 13C NMR (CDCl3):
δ = 61.6 (CH), 66.6 (CH2) and 124.1, 126.3, 128.5, 128.8, 131.4
(arom. CH) ppm. MS(EI): m/z = 596 [M]+ (C32H24N2O10), 490,
429, 384, 340, 323, 310, 256, 218, 180, 150, 105, 104, 92, 77, 76.
Method B: LiAlH4 (0.054 g, 1.4 mmol) was added to a solution of
5b (0.42 g, 0.7 mmol) in dry THF (10 mL) and the mixture was
stirred near its boiling point for approximately 18 h (TLC monitor-
ing). Excess LiAlH4 was decomposed by the addition of H2O and
EtOAc (10 mL), the inorganic residue was filtered off, and
chromatography on silica (n-hexane/ethyl acetate 3:1) gave 7
(100 mg, 54 % yield, Ͼ99 % ee, determined by HPLC, Chiralcel
OD-H, Daicel, n-hexane/ethanol 99.5/0.5, 1.0 mL min–1) and 8
(16 mg, 8% yield). An analytical sample of 7 could be obtained by
sublimation (90 °C, 0.3 mbar) or by crystallization from n-hexane.
(2S,3S)-2-(4-Methylphenylsulfonyloxymethyl)-2-[(2S,3S)-2-(4-meth-
ylphenylsulfonyloxymethyl)-3-phenyloxiran-2-yl]-3-phenyloxirane
(5b): Ti(OiPr)4 (54 mg, 0.19 mmol) and molecular sieves (3 Å,
0.25 g) were added to a cooled solution (–30 °C) of -(+)-diethyl
tartrate (55 mg, 0.27 mmol) in dry CH2Cl2 (15 mL). The mixture
was stirred at this temperature for 20 min and a solution of tert-
butyl hydroperoxide in decane (5.5 , 0.7 mL, 3.8 mmol) was
added. The mixture was stirred for a further 40 min, 4 (0.25 g,
0.94 mmol) in CH2Cl2 (15 mL) was added, and the reaction flask
was kept in a freezer at –27 °C for 2 d. P(OMe)3 (0.35 mL) was
then added dropwise by syringe at –30 °C over a period of 30 min
and the mixture was stirred for 40 min. Subsequently, Et3N
(0.65 mL, 4.7 mmol) and p-toluenesulfonyl chloride (0.71 g,
3.73 mmol) were added and the reaction mixture was stored in a
freezer for another 2 d. The mixture was then allowed to warm to
room temp. and stirred at this temperature for 6 h, the molecular
sieves were filtered off, and the solution was washed with an aq.
solution of tartaric acid, sat. aq. NaHCO3 solution and brine and
dried (Na2SO4), and the solvents were evaporated. The product was
purified by chromatography on silica gel (n-hexane/ethyl acetate
3:2) to give compound 5b as an oil (650 mg, 88% yield, Ͼ99% ee,
determined by HPLC, Chiralcel OD-H, Daicel, n-hexane/ethanol
9:1, 1.0 mLmin–1). [α]2D5 = 7.54 (c = 14, CHCl3). 1H NMR (CDCl3):
δ = 2.62 (s, 3 H), 3.96 (s, 1 H), 4.28–4.34 (m, 2 H), 6.87–7.05 (brs,
1
m.p. 103–104 °C. [α]2D5 = 38.2 (c = 3, CHCl3). H NMR (CDCl3):
δ = 1.43 (s, 3 H), 3.57 (s, 1 H), 7.03–7.15 (brm, 2 H), 7.16–7.25
(m, 3 H) ppm. 13C NMR (CDCl3): δ = 21.6 (CH3), 63.8 (s, C), 64.4
(CH), 126.8, 127.7, 128.4 (all s, arom. CH), 135.7 (s, arom. C) ppm.
MS (EI): m/z = 266 [M]+ (C18H18O2), 248, 181, 180, 179, 178, 165,
160, 159, 145, 117, 197, 106, 105, 91, 89, 79, 77, 51.
(2R,3R)-2,3-Dimethyl-1,4-diphenylbutane-2,3-diol (8): LiAlH4
(0.134 g, 3.53 mmol) was added at room temp. to a solution of 5b
(2.14 g, 3.53 mmol) in dry THF (15 mL) and the mixture was
stirred near its boiling point for 24 h. Another portion of LiAlH4
(0.11 g, 2.9 mmol) was added and the mixture was stirred near its
boiling point for another 24 h (TLC monitoring). Excess LiAlH4
was decomposed by the addition of H2O and ether (15 mL) and
the inorganic residue was filtered off. Chromatography on silica
(n-hexane/ethyl acetate 4:1) gave 8 (438 mg, 46% yield, Ͼ99% ee,
determined by HPLC, Chiralcel OD-H, Daicel, n-hexane/ethanol
1
9:1, 1.0 mLmin–1). M.p. 75 °C. [α]2D5 = –56.5 (c = 10, ethanol). H
Eur. J. Org. Chem. 2007, 758–767
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
765

A. Börner et al.
FULL PAPER
NMR (CDCl3): δ = 1.17 (s, 3 H), 2.00 (brs, 1 H), 2.72 (d, J =
(30 mg, 0.146 mmol) in dry CH2Cl2 (10 mL). The mixture was
stirred at this temperature for 20 min, a solution of tert-butyl hy-
droperoxide in decane (5.5 , 0.35 mL, 1.93 mmol) was added, the
mixture was stirred for a further 40 min, and 11 (0.41 g,
0.988 mmol) in CH2Cl2 (10 mL) was added. The reaction flask was
kept in a freezer at –27 °C for 3 d, P(OMe)3 (0.18 mL) was then
added dropwise by syringe at –30 °C over a period of 30 min, and
the mixture was stirred for 40 min. Subsequently, Et3N (0.24 g,
2.4 mmol) and p-bromobenzoyl chloride (0.44 g, 2 mmol) were
added and the reaction mixture was stored in a freezer for another
2 d, then allowed to warm to room temp. and stirred at this tem-
perature for 6 h. The molecular sieves were filtered off, the solution
was washed with an aqueous solution of tartaric acid, sat. aq.
NaHCO3 solution and brine and dried (Na2SO4), and the solvents
were evaporated. The product was purified by chromatography on
silica gel (Merck 60, CH2Cl2/n-hexane 3:1) to give compound 12
(285 mg, 63% yield). Analytical samples were obtained by crystalli-
zation from CH3CN or EtOH or a mixture of CCl4/EtOAc. M.p.
13 Hz, 1 H), 3.14 (d, J = 13 Hz, 1 H), 7.25–7.34 (m, 5 H) ppm. 13
C
NMR (CDCl3): δ = 21.8 (s, CH3), 42.5 (s, CH2), 77.1 (s, C), 126.8,
128.6, 131.4 (all s, arom. CH), 138.1 (s, arom. C). MS (CI, isobut-
ane): m/z = 291 ([M – 2H2O + isobutyl]+ (C22H27), 277, 253, 235,
179, 161, 135, 105, 91, 79. MS (EI): m/z = 179 [M – Bn]+, 161 [M –
Bn – H2O]+, 143, 135, 117,105, 91, 77, 65, 57. Elemental analysis
(%) calcd for C18H22O2: C 79.96, H 8.20; found: C 79.85, H 7.94.
(2S,3S)-2-[(Z)-1-(4-Nitrophenylcarbonyloxymethyl)-2-phenyl-1-
ethenyl]-2-[1-(4-nitrophenyl)vinyloxymethyl]-3-phenyloxirane (9):
Ti(OiPr)4 (54 mg, 0.19 mmol) and molecular sieves (3 Å, 0.25 g)
were added to a cooled (–30 °C) solution of -(+)-diethyl tartrate
(55 mg, 0.26 mmol) in dry CH2Cl2 (10 mL). The mixture was
stirred at this temperature for 20 min, a solution of tert-butyl hy-
droperoxide in decane (5.5  0.35 mL, 1.88 mmol) was added, the
mixture was stirred for a further 40 min, and 4 (0.5 g, 1.88 mmol)
in CH2Cl2 (10 mL) was added. The reaction flask was kept in a
freezer for 5 d at –27 °C, P(OMe)3 (0.18 mL) was then added drop-
wise by syringe at –30 °C over a period of 30 min, and the mixture
was stirred for 40 min. Subsequently, Et3N (0.9 g, 8.9 mmol) and
p-nitrobenzoyl chloride (1.4 g, 7.5 mmol) were added, and the reac-
tion mixture was stored in a freezer for another 2 d and was then
allowed to warm to room temp. and stirred at this temperature for
6 h. The molecular sieves were filtered off, the solution was washed
with an aq. solution of tartaric acid, sat. aq. NaHCO3 solution and
brine and dried (Na2SO4), and the solvents were evaporated. The
mixture was chromatographed on silica gel (Merck 60, CH2Cl2 as
eluent) to give 9 and 10 in a ratio of 2:1.
159–160 °C. [α]2D5 = –55.9 (c = 5, CHCl3). H NMR (CDCl3): δ =
1
4.69 (s, 1 H), 5.06 (d, J = 12.51, 1 H), 5.19–5.65 (m, 3 H), 7.16 (s,
1 H), 7.37–7.48 (m, 3 H), 7.48–7.59 (m, 3 H), 7.60–7.77 (m, 4 H),
7.00 (d, J = 8.55 Hz, 2 H), 8.22 (d, J = 8.55 Hz, 2 H), 8.51–8.68
(m, 4 H) ppm. 13C NMR (CDCl3): δ = 63.2 (s, CH), 64.8 (s, C),
66.1 (s, CH2), 68.6 (s, CH2), 123.5 (s, CH), 126.5 (s, CH), 126.6 (s,
C), 127.6 (s, CH), 128.0 (s, CH), 128.3 (s, CH), 128.5 (s, C), 128.9
(s, CH), 130.7 (s, CH), 131.2 (s, CH), 131.8 (s, CH), 133.5 (s, C),
134.5 (s, C), 135.2 (s, C), 150.5 (s, C–NO2), 164.2 [s, C(O)O–], 165.2
[s, C(O)O–] ppm.
Computational Part: All structures (7 and 7Ј) and the reference
molecules were optimized at the MP2/6-31G* level of theory. They
are characterized as energy minimum structures at MP2/6-31G*.
Both 7 and 7Ј have C2 symmetry. All calculations were performed
with the Gaussian 03 program.[16] The MP2/6-31G* total electronic
energies (au) are –844.43455 (7), –766.08322 (7Ј), –461.96321 (2,2-
dimethyl-3-phenyloxirane), –422.78794 (2-methyl-3-phenyloxirane)
and –79.49474 (ethane). The QCISD(T)/6-31G*//MP2/6-31G* sin-
gle-point energies are –766.27423 (7Ј), –422.90518 (2-methyl-3-
phenyloxirane) and –79.53459 (ethane).
Compound 9: M.p. 165 °C. 1H NMR (CDCl3): δ = 4.49 (s, 2 H),
7.31 (s, 1 H), 7.59–7.72 (m, 3 H), 7.93– 8.01 (m, 2 H), 8.26 (d, J =
9.16 Hz, 2 H), 8.51 (d, J = 9.16 Hz, 2 H) ppm. 13C NMR (CDCl3):
δ = 69.7 (s, CH2), 123.8 (s, CH), 124.2 (s, CH), 128.8 (s, CH), 129.1
(s, CH), 131.1 (s, CH), 132.1 (s, C), 134.3 (s, CH), 135.5 (s, C),
135.9 (s, C), 150.8 (s, C–NO2), 164.7 [s, C(O)O–] ppm.
1
Compound 10: H NMR (CDCl3): δ = 4.31 (s, 1 H), 4.64–5.32 (m,
4 H), 6.78 (s, 1 H), 6.98–7.49 (m, 10 H), 8.07–8.33 (m, 8 H) ppm.
13C NMR (CDCl3): δ = 63.5, 65.0, 67.0, 69.0, 124.0, 124.1, 126.3,
126.7, 126.9, 128.2, 128.4, 128.6, 128.8, 129.3, 131.2, 131.3, 131.4,
133.4, 133.7, 135.1, 151.9 (s, C–NO2), 151.1 (s, C–NO2), 164.6 [s,
C(O)O–], 164.7 [s, C(O)O–] ppm.
Acknowledgments
(E)-3-Hydroxymethyl-4-phenyl-2-[(E)-1-phenylmethylidene]-3-
butenyl 4-Nitrobenzoate (11): A solution of p-nitrobenzoyl chloride
(0.35 g, 1.88 mmol) in CH2Cl2 (5 mL) was added dropwise with
stirring over 30 min at room temp. to a solution of 4 (0.5 g,
1.88 mmol) and Et3N (0.2 g, 2 mmol) in CH2Cl2 (5 mL). The mix-
ture was stirred for 3 h at room temp., washed with water, sat. aq.
NaHCO3 solution and brine and dried (Na2SO4), and the solvents
were evaporated. Chromatography on silica gel (Merck 60, chloro-
form/ethyl acetate 2:1) provided the monoester 11 (468 mg, 60%
yield) and the corresponding diester (300 mg, 28% yield). 1H NMR
(CDCl3): δ = 1.97 (s, 1 H), 4.28 (s, 2 H), 5.05 (s, 2 H), 6.84 (s, 1
H), 6.87 (s, 1 H), 7.21–7.38 (m, 6 H), 7.51–7.62 (m, 4 H), 7.96 (d,
J = 9 Hz, 2 H), 8.20 (d, J = 9 Hz, 2 H) ppm. 13C NMR (CDCl3):
δ = 66.7 (CH2), 70.0 (CH2), 123.8, 128.1, 128.7, 128.8, 129.0, 129.1,
129.2, 131.1, 132.8, 133.6, 135.6, 136.0, 136.7, 138.2, 150.8 (C–
NO2 ), 164.9 [-C(O)O-] ppm. MS (EI): m/z = 415 [M]+
(C25H21NO5), 397, 266, 248, 230, 229, 219, 218, 217, 215, 205, 202,
167, 142, 141, 129, 128, 115, 105, 91, 77, 65.
We are grateful for the financial support provided by the Deutsche
Forschungsgemeinschaft (Graduiertenkolleg 1213). We thank Mrs.
A. Lehmann for the measurements of the UV spectra.
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766
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Eur. J. Org. Chem. 2007, 758–767

New Target for Highly Stereoselective Katsuki–Sharpless Epoxidation
FULL PAPER
[8] For a recent discussion of this type of weak interactions, see:
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[9] Typical distances between phenyl rings with parallel displaced
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6132–6141. Some distances between nonbonded aliphatic car-
bon atoms in different phenyl rings in cyclophanes are as fol-
lows: [2.2]paracyclophane 3.09 Å, [3.3]paracyclophane 3.30 Å,
[24](1,2,4,5)cyclophane 2.95 Å, [34](1,2,4,5)cyclophane 3.20 Å:
W. Sentou, T. Satou, M. Yasutake, C. Lim, Y. Sakamoto, T.
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2441): cis 240 nm; trans 258 nm.
[11] P. George, M. Trachtman, C. W. Bock, A. M. Bret, J. Chem.
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Received: August 15, 2006
Published Online: December 7, 2006
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Eur. J. Org. Chem. 2007, 758–767
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