Microencapsulated Osmium Tetraoxide. A New Recoverable and Reusable Polymer-Supported Osmium Catalysts for Dihydroxylation of Olefins

Full text of DOI:10.1021/jo981127y

6
094
J . Org. Chem. 1998, 63, 6094-6095
Micr oen ca p su la ted Osm iu m Tetr a oxid e. A
New Recover a ble a n d Reu sa ble
Ta ble 1. Effect of Solven ts a n d Cooxid a n ts
P olym er -Su p p or ted Osm iu m Ca ta lyst for
Dih yd r oxyla tion of Olefin s
solvent
cooxidant
yield (%)
Satoshi Nagayama, Masahiro Endo, and
Sh uj Kobayashi*,†,§
H2O-acetone (2/1)
H2O- BuOH (1/1)
H2O-acetone-CH3CN (1/1/1)
H2O-acetone-CH3CN (1/1/1)
H2O-acetone-CH3CN (1/1/1)
H2O-acetone-CH3CN (1/1/1)
H2O-acetone-CH3CN (1/1/1)
NMO
NMO
NMO
Me3NO
H2O2
15
20
84
57
30
18
0
t
Graduate School of Pharmaceutical Sciences, The University of
Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033, J apan, and
Department of Applied Chemistry, Faculty of Science,
Science University of Tokyo (SUT), Kagurazaka,
Shinjuku-ku, Tokyo 162-8601, J apan
t
BuOOH
K3Fe(CN)6
Ta ble 2. Dih yd r oxyla tion of Olefin s Usin g MC OsO4a
Received J une 12, 1998
Osmium tetraoxide (OsO4) is the most reliable reagent for
the dihydroxylation of olefins to give the corresponding
diols.1 The reaction proceeds in the presence of a catalytic
amount of OsO4 using a cooxidant such as metal chlorates,
hydrogen peroxide, tert-butyl hydroperoxide, potassium fer-
ricyanide, or most commonly, N-methylmorpholine N-oxide
(NMO). Although a number of processes have gained wide
acceptance in this dihydroxylation, few fruitful industrial
applications have been accomplished, probably because OsO4
is highly toxic, expensive, volatile, and cannot be recovered.
Immobilized osmium catalysts are expected to solve these
problems, and such efforts have been made, but recovery
and reuse of polymer catalysts has not been satisfactory.2,3
Recently, we have developed an unprecedented polymer-
supported Lewis acid, a microencapsulated scandium tri-
fluoromethanesulfonate (triflate) (MC Sc(OTf)3).4 This dem-
onstrates a new method for immobilizing a catalyst onto a
polymer on the basis of physical envelopment by the polymer
and on electron interactions between the π electrons of the
benzene rings of the polystyrene-based polymer and a vacant
orbital of the Lewis acid. We intended to apply this new
technology for immobilizing osmium tetraoxide. In this
paper, we describe microencapsulated osmium tetraoxide
that can be recovered and reused and that is effective in
dihydroxylation of olefins.
Preparation of microencapsulated osmium tetraoxide (MC
5
OsO4) was performed as follows: polystyrene (1.000 g) was
dissolved in cyclohexane (20 mL) at 40 °C, and to this
solution was added OsO46 (0.20 g) as a core (OsO4 was
dissolved). The mixture was stirred for 1 h at this temper-
ature and then slowly cooled to 0 °C. Coacervates (phase
†Present address: Graduate School of Pharmaceutical Sciences, The
University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033, J apan.
a
All reactions were carried out using MC OsO4 (5 mol %) and
b
(1) (a) Schr o¨ der, M. Chem. Rev. 1980, 80, 187. (b) Singh, H. S. In Organic
NMO in H2O-acetone-CN3CN (1/1/1) at rt for 6-48 h. Carried
out at 60 °C.
Synthesis by Oxidation with Metal Compounds; Mijs, W. J ., De J onge, C.
R. H. I., Eds.; Plenum: New York, 1986; Chapter 12. (c) Haines, A. H. In
Comprehensive Organic Synthesis; Trost, B. M., Fleming, I., Eds.; Perga-
mon: Oxford, 1991; p 437. (d) Lohray, B. B. Tetrahedron: Asymmetry 1992,
separation) were found to envelop the core dispersed in the
medium, and methanol (30 mL) was added to harden the
capsule walls. The mixture was stirred at room temperature
(rt) for 1 h, and the capsules were then washed with
methanol several times and dried at room temperature for
24 h. Unencapsulated OsO4 was recovered from the wash-
ings.
3
, 1317. (e) J ohnson, R. A.; Sharpless, K. B. In Catalytic Asymmetric
Synthesis; Ojima, I., Ed.; VCH: Weinheim, 1993. (f) Kolb, H. C.; Van
Nieuwenhze, M. S.; Sharpless, K. B. Chem. Rev. 1994, 94, 2483. (g) Poli,
G.; Scolastico, C. In Stereoselective Synthesis; Helmchen, G., Hoffmann, R.
W., Mulzer, J ., Schaumann, E., Eds.; Thieme: Stuttgart, 1996; p 4547.
(
2) (a) Cainelli, G.; Contento, M.; Manescalahi, F.; Plessi; L. Synthesis
989, 45. (b) Herrmann, W. A.; Kratzer, R. M.; Blumel, J .; Friedrich, H. B.;
Fischer, R. W.; Apperley, D. C.; Mink, J .; Berkesi, O. J . Mol. Catal., A 1997,
20, 197.
3) Polymer-supported chiral ligands were reported. (a) Kim, B. M.;
1
1
MC OsO4 thus prepared7,8 was first used in the dihy-
droxylation of cyclohexene, and several solvents and co-
(
Sharpless, K. B. Tetrahedron Lett. 1990, 31, 3003. (b) Lohray, B. B.; Thomas,
A.; Chittari, P.; Ahuja, J . R.; Dhal, P. K. Tetrahedron Lett. 1992, 33, 5453.
(
c) Han, H.; J anda, K. D. J . Am. Chem. Soc. 1996, 118, 7632. (d) Bolm, C.;
Gerlach, A. Angew. Chem., Int. Ed. Engl. 1997, 36, 741. A problem of these
approaches is that recover and recycle of osmium are difficult. Cf. (e) Bolm,
C.; Gerlach, A. Eur. J . Org. Chem. 1998, 21.
(7) Microcapsules have been used for coating and isolating substances
until such time as their activity is needed, and their application to medicine
and pharmacy has been extensively studied. Donbrow, M. Microcapsules
and Nanoparticles in Medicine and Pharmacy; CRC Press: Boca Raton,
1992. We first applied this technique for immobilizing a catalyst onto a
polymer.4.
(
(
(
4) Kobayashi, S.; Nagayama, S. J . Am. Chem. Soc. 1998, 120, 2985.
5) Average M ca. 280 000. Purchased from Aldrich, Co. Ltd.
6) Purchased from Soekawa Rika, Co. Ltd.
w
S0022-3263(98)01127-X CCC: $15.00 © 1998 American Chemical Society
Published on Web 08/13/1998

Communications
J . Org. Chem., Vol. 63, No. 18, 1998 6095
Ta ble 3. Recover y a n d Reu se of MC OsO4
Ta ble 4. P r elim in a r y Stu d y on th e Ra te of Con ver sion
of th e Sta r tin g Olefin
run
1
2
3
4
5
time (min)
1
10
30
60
180
yield of product (%)
84
84
83
84
83
recovery of catalyst (%) quant quant quant quant quant
yield (OsO ) (%)
yield (MC OsO4) (%)
11
79
7
78
37
78
55
81
75
4
oxidants were examined (Table 1). All the reactions were
carried out on a 10 mmol scale using MC OsO4 containing
ca. 0.12 g of OsO4 (5 mol %) in a batch system. When a
OsO4 contamination of the products occurs. Finally, a
preliminary study on the rate of conversion of the starting
olefin was performed by using OsO4 and MC OsO4 in a model
dihydroxylation of cyclohexene using NMO as a cooxidant
t
solvent such as H2O-acetone or H2O- BuOH (which is used
1
in typical OsO4-catalyzed dihydroxylations) was used, lower
(
Table 4). It was found that the reaction proceeded faster
yields were obtained. The yield was, however, dramatically
improved when acetonitrile was added to the H2O-acetone
solution. We also examined several cooxidants. While the
reaction was successfully carried out using NMO, moderate
yields were obtained using trimethylamine N-oxide, and
much lower yields were observed using hydrogen peroxide
or potassium ferricyanide.
Several examples of the MC OsO4-catalyzed dihydroxyl-
ation of olefins in the presence of NMO in H2O-acetone-
acetonitrile are summarized in Table 2. Cyclic and acyclic
exo as well as internal olefins worked well under these
conditions. Moreover, bulky olefins such as 1-methylcyclo-
hexene and 2-methyl-2-butene also reacted smoothly in the
presence of MC OsO4 to afford the corresponding diols. The
polymer catalyst was recovered quantitatively by simple
filtration and could be reused. The activity of the recovered
catalyst did not decrease even after the fifth use (Table 3).
11
using OsO4 than using MC OsO4. While an 81% yield of
the diol was obtained using OsO4 for 3 h, a 75% yield was
obtained using MC OsO4 under the same reaction conditions.
In summary, we have successfully immobilized OsO4 onto
a polymer using a microencapsulating technique. The
polymer-supported catalyst (MC OsO4) was very effective in
the dihydroxylation of olefins. MC OsO4 was readily pre-
pared could be recovered quantitatively by simple filtration,
and could be reused. It should be noted that the volatile
property of OsO4 is very much depressed by this immobiliza-
tion and that no contamination of OsO4 in the products
occurs. Further investigations to apply MC OsO4 to large-
scale syntheses as well as asymmetric syntheses are now
in progress.
Ack n ow led gm en t. S.N. thanks the J SPS fellowship
for J apanese J unior Scientists.
The experimental procedure was very simple: mix an olefin,
MC OsO4, and NMO.9 After the reaction, simple filtration
Su p p or tin g In for m a tion Ava ila ble: Experimental proce-
dures and physical data of the products (3 pages).
separated the product and the catalyst. In addition, it was
assumed that no OsO4 was released from MC OsO4 during
or after the reaction, since MC OsO4 was recovered quan-
titatively (by weight) in all cases. This was confirmed by
the qualitative analysis of OsO4 using the iodometry.10 Since
the titration is very sensitive, these results indicate that no
J O981127Y
4
(10) OsO is treated with potassium iodide and HCl, and the produced
iodine is titrated with sodium thiosulfate in the presence of starch. See the
Supporting Information.
(
11) It was found that some reactions proceeded faster using micro-
encapsulated scandium triflate (MC Sc(OTf) ) than using Sc(OTf) due to
the polymer effect.4 This would be the case in the initial step of the
dihydroxylation using MC OsO or OsO (interaction between an olefin and
MC OsO or OsO ); however, the observed slower reaction using MC OsO
instead of OsO would be ascribed to the slower oxidation step of a
3
3
,12
(
8) Although the preparative method was similar to conventional pro-
tocols for the preparation of microcapsules, it was assumed that small
capsules of MC OsO adhered to each other probably due to the small size
of the core and that OsO was located all over the polymer surface. Similar
phenomena were observed in MC Sc(OTf)
9) Details are shown in the Supporting Information.
4
4
4
4
4
4
4
4
4
.
3
.
microencapsulated osmium ester with NMO (the rate-determining step).
(12) Kobayashi, S.; Nagayama, S. Synlett 1997, 653.
(