An efficient asymmetric epoxidation method for trans-olefins mediated by a fructose-derived ketone

Full text of DOI:10.1021/ja962345g

9806
J. Am. Chem. Soc. 1996, 118, 9806-9807
An Efficient Asymmetric Epoxidation Method for
trans-Olefins Mediated by a Fructose-Derived
Ketone
Table 1. Asymmetric Epoxidation of Representative Olefins
Catalyzed by Ketone 3a
Yong Tu, Zhi-Xian Wang, and Yian Shi*
Department of Chemistry
Colorado State UniVersity
Fort Collins, Colorado 80523
ReceiVed July 9, 1996
Epoxides are very important chiral building blocks for the
1
synthesis of enantiomerically pure complex molecules. Asym-
metric epoxidation of olefins presents a powerful strategy for
the synthesis of enantiomerically enriched epoxides. Great
2
success has been achieved in the epoxidation of allylic alcohols
3
and unfuctionalized cis-olefins. However, the epoxidation of
trans-olefins bearing no allylic alcohol group with high enan-
4
tiomeric excess still remains a challenging problem. It was
desirable to explore alternative systems for a solution. Among
5
many other powerful methods for the epoxidation of olefins,
dioxiranes are remarkably versatile oxidation reagents, and their
6,7
use as epoxidation reagents has risen to particular prominence.
The reaction is rapid and requires a simple workup. An
important feature associated with dioxiranes is that they can be
generated in situ from Oxone (potassium peroxomonosulfate)
8
and a ketone, which provides opportunities for asymmetric
epoxidation when a chiral ketone is used.
a
All reactions were carried out at 0 °C (bath temperature) with
substrate (1 equiv), ketone (3 equiv), Oxone (5 equiv), and NaHCO
15.5 equiv) in CH
b and 10); the reactions were stopped after 2 h (for detail see
supporting information). The epoxides were purified by flash chro-
matography and gave satisfactory spectroscopic characterization. En-
antioselectivity was determined by H NMR shift analysis of the epoxide
products directly with Eu(hfc)
changed (95% ee) when 0.5 and 0.25 equivs of chiral ketone were used
3
However, progress in the area of dioxirane-mediated asym-
-
4
(
7
3
CN-aqueous EDTA (4 × 10 M) (∼1.5:1) (refs
metric epoxidation has been limited.9 The enantiomeric excess
(
ee) has been low (9-20%). Since dioxiranes have two reacting
b
c
sites, it is crucial to limit possible competing approaches.
Recently, some progress has been made in this regard. Yang
1
d
3
.
Enantioselectivity remained un-
reported an intriguing C2 symmetric cyclic chiral ketone for
asymmetric epoxidation.10 An 87% ee was obtained in one case,
e
except that the yields were lowered. Enantioselectivity was determined
by chiral HPLC (Chiralcel OD). After recrystallization. Enantiose-
although the ee values for most cases were low (5-50%).
Herein we wish to report our efforts in the area of asymmetric
epoxidation. We are utilizing ketones containing the following
general features: (1) the stereogenic centers are close to the
f
g
1
lectivity was determined by H NMR shift analysis of the derived acetate
with Eu(hfc)3. h The epoxide was opened (NaOMe-MeOH), and the
resulting alcohol was converted to its acetate; enantioselectivity was
1
determined by H NMR shift analysis of the resulting acetate with
Eu(hfc)
the measured optical rotations with the reported ones. The absolute
configuration was not determined.
(
1) For a review, see: Besse, P.; Veschambre, H. Tetrahedron 1994,
0, 8885-8927.
2) For a review, see: Johnson, R. A.; Sharpless, K. B. In Catalytic
Asymmetric Synthesis; Ojima, I., Ed.; VCH: New York, 1993; Chapter 4.1.
3) For leading references, see: (a) Collman, J. P.; Zhang, X.; Lee, V.
i
3
. The absolute configurations were determined by comparing
5
j
(
(
J.; Uffelman, E. S.; Brauman, J. I. Science 1993, 261, 1404-1411. (b)
Jacobsen, E. N. In Catalytic Asymmetric Synthesis; Ojima, I., Ed.; VCH:
New York, 1993; Chapter 4.2. (c) Fukuda, T.; Katsuki, T. Tetrahedron
Lett. 1996, 37, 4389-4392.
reacting center, resulting in efficient stereochemical communica-
tion between substrates and the catalyst; (2) the presence of a
fused ring and a quaternary center R to the carbonyl group
minimizes the epimerization of the stereogenic centers; (3) one
face of the catalyst is sterically blocked to limit the possible
competing approaches. Ketone 3 has these desirable structural
features, and is readily prepared from very inexpensive D-
fructose ($15/kg) by ketalization (acetone, HClO4, 0 °C, 53%)
(4) (a) Brandes, B. D.; Jacobsen, E. N. J. Org. Chem. 1994, 59, 4378-
4
1
1
380. (b) Chang, S.; Galvin, J. M.; Jacobsen, E. N. J. Am. Chem. Soc.
994, 116, 6937-6938. (c) Bousquet, C.; Gilheany, D. G. Tetrahedron Lett.
995, 36, 7739-7742 and references cited therein.
(
5) For reviews, see: (a) Rebek, J., Jr. Heterocycles 1981, 15, 517-
5
45. (b) Davis, F. A.; Chen, B. C. Chem. ReV. 1992, 92, 919-934. (c)
Reference 1.
1
1
and oxidation (PCC, rt, 93%).
(6) For reviews see: (a) Adam, W.; Curci, R.; Edwards, J. O. Acc. Chem.
Res. 1989, 22, 205-211. (b) Murray, R. W. Chem. ReV. 1989, 89, 1187-
1
8
201. (c) Curci, R.; Dinoi, A.; Rubino, M. F. Pure Appl. Chem. 1995, 67,
11-822.
(7) For leading references of recent examples of dioxirane epoxidation,
see: (a) Adam, W.; Muller, M.; Prechtl, F. J. Org. Chem. 1994, 59, 2358-
2
364. (b) Yang, D.; Wong, M. K.; Yip, Y. C. J. Org. Chem. 1995, 60,
887-3889. (c) Denmark, S. E.; Forbes, D. C.; Hays, D. S.; DePue, J. S.;
3
Wilde, R. G. J. Org. Chem. 1995, 60, 1391-1407. (d) Murray, R. W.;
Singh, M.; Williams, B. L; Moncrieff, H. M. J. Org. Chem. 1996, 61, 1830-
1
841.
(
8) For examples of in situ generation of dioxiranes, see: (a) Corey, P.
F.; Ward, F. E. J. Org. Chem. 1986, 51, 1925-1926. (b) References 7b
and c and references cited therein.
Initial studies involving ketone 3 in the epoxidation of trans-
stilbene revealed that while the yield of stilbene epoxide
increased with the reaction time, the enantiomeric excess
decreased. Upon examination, we determined that ketone 3
(9) (a) Curci, R.; Fiorentino, M.; Serio, M. R. J. Chem. Soc., Chem.
Commun. 1984, 155-156. (b) Curci, R.; D’Accolti, L.; Fiorentino, M.; Rosa,
A. Tetrahedron Lett. 1995, 36, 5831-5834. (c) Brown, D. S.; Marples, B.
A.; Smith, P.; Walton, L Tetrahedron 1995, 51, 3587.
(
10) Yang, D.; Yip, Y. C.; Tang, M. W.; Wong, M. K.; Zheng, J. H.;
(11) Mio, S.; Kumagawa, Y.; Sugai, S. Tetrahedron 1991, 47, 2133-
2144.
Cheung, K. K. J. Am. Chem. Soc. 1996, 118, 491-492.
S0002-7863(96)02345-1 CCC: $12.00 © 1996 American Chemical Society

Communications to the Editor
J. Am. Chem. Soc., Vol. 118, No. 40, 1996 9807
Figure 1. The spiro and planar transition states for the dioxirane
epoxidation of olefins.
decomposed over time under the reaction conditions.12 The
decreased ee could be attributed to the epoxidation being
catalyzed by an achiral or less enantioselective ketone resulting
from the decomposition of ketone 3. However, >95% ee could
be achieved for stilbene oxide if the reaction was terminated in
a short reaction time (2 h).
Encouraged by this result, we investigated the asymmetric
epoxidation with a variety of olefins in order to explore the
generality of this system. To maximize the enantiomeric excess,
epoxidations were carried out using an excess of ketone 3 and
a short reaction time (Table 1). The enantiomeric excesses are
generally high for a wide range of olefins, in which a variety
of functional groups are present. For example, the halide (entry
Figure 2. The spiro and planar transition states for trans-stilbene
epoxidation catalyzed by ketone 3.
Vs spiro-2) (Figure 2). In contrast, (S,S)-stilbene oxide will be
favored if the reaction proceeds Via a planar mode (planar-2 Vs
planar-1). In the present study, it is found that (R,R)-stilbene
oxide is produced predominately, which supports the spiro
transition state. All the examples with known epoxide con-
figurations in Table 1 are consistent with the spiro mode.
Therefore, the stereochemical outcome of the reactions can be
predicted with a reasonable level of confidence based on the
spiro model.
In summary, we report a highly effective and mild asymmetric
epoxidation for trans- and trisubstituted olefins using a fructose-
derived ketone as catalyst and Oxone as oxidant. Both Oxone
and the ketone catalyst are inexpensive. The enantioselectivity
is very high in most cases studied. A variety of functional
groups can be tolerated in the olefin substrates. Most signifi-
cantly, high enantioselectiVity can be achieVed for the epoxi-
dation of unfunctionalized trans-olefins. As a first step, we have
revealed a promising structural element required for the ketone
to induce the high enantioselectivity for the epoxidation. Future
efforts will be devoted to the optimization of the ketone structure
to enhance both enantioselectivity and stability of the ketone
to make this process truly catalytic.
5
) can be directly epoxidized and the resulting epoxide can be
used for further transformations. Trisubstituted olefins are also
good substrates for high selectivity. It is Very encouraging to
note that high enantiomeric excess can be obtained with trans-
7
-tetradecene (entry 11), which suggests that this epoxidation
may be general for simple unfunctionalized trans-olefins.
It is of interest to understand the possible geometry of the
transition state in dioxirane epoxidations. Two mechanistic
1
4,15,6c
extremes (planar and spiro) are presented in Figure 1.
A
spiro transition state was proposed by Baumstark, based on the
observation that cis-olefins were more reactive than the corre-
sponding trans-olefins for epoxidation using dimethyldiox-
14
irane. His proposal came from analyzing steric effects in both
transition states. Stereochemical analysis provides another
valuable way to address this issue. The results in Table 1
provide valuable information about the reaction mode of the
epoxidation by dioxiranes. If the reaction proceeds Via a spiro
mode, (R,R)-stilbene oxide is expected to be favored (spiro-1
(
12) We are currently investigating the possible decomposition pathways
Acknowledgment. This work is supported by Colorado State
University and the Camille and Henry Dreyfus New Faculty Awards
Program. We are grateful to Professor Albert I. Meyers for the use of
his chiral HPLC apparatus.
for ketone 3.
(
13) (a) Imuta, M.; Ziffer, H. J. Org. Chem. 1979, 44, 2505-2509. (b)
Witkop, B.; Foltz, C. M. J. Am. Chem. Soc. 1957, 79, 197-201. (c) Melloni,
P.; Della, T. A.; Lazzari, E.; Mazzini, G.; Meroni, M. Tetrahedron 1985,
4
1, 1393-1399. (d) desilylated and compared with entry 3. (e) Compared
with the derived chloride of entry 3. (f) Gao, Y.; Hanson, R. M.; Klunder,
Supporting Information Available: Experimental procedure for
the in situ asymmetric epoxidation reaction, the NMR spectral and
HPLC data for the determination of the enantiomeric excess of the
formed epoxides, and the characterization data of the epoxides in Table
1 (22 pages). See any current masthead page for ordering and Internet
access instructions.
J. M.; Ko, S. Y.; Masamune, H.; Sharpless, K. B. J. Am. Chem. Soc. 1987,
1
09, 5765-5780. (g) Desilylated and compared with entry 7. (h) Rossiter,
B. E.; Sharpless, K. B. J. Org. Chem. 1984, 49, 3707-3711. (i) Desilylated
and compared with entry 9.
(14) Baumstark, A. L.; McCloskey, C. J. Tetrahedron Lett. 1987, 28,
3
311-3314.
15) Bach, R. D.; Andres, J. L.; Owensby, A. L.; Schlegel, H. B.;
McDouall, J. J. W. J. Am. Chem. Soc. 1992, 114, 7207-7217.
(
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