Osmium-catalyzed dihydroxylation of alkenes by H2O2 in room temperature ionic liquid co-catalyzed by VO(acac)2 or MeReO3

Article abstract of DOI:10.1016/j.jorganchem.2005.04.033

Room temperature ionic liquid [bmim]PF₆ was used to immobilize a bimetallic catalytic system for H₂O₂-based dihydroxylation of alkenes. Osmium tetroxide was used as the substrate-selective catalyst with either VO(acac)₂ or MeReO ₃ as co-catalyst. The latter serve as an electron transfer mediator (ETM) and activates H₂O₂. For an increased efficiency N-methylmorpholine is required as an additional ETM in most cases. A range of alkenes were dihydroxylated using this robust bimetallic system and it was demonstrated that for some of the alkenes the catalytic system can be recycled and used up to five times.

Full text of DOI:10.1016/j.jorganchem.2005.04.033

Journal of Organometallic Chemistry 690 (2005) 3614–3619
www.elsevier.com/locate/jorganchem
Osmium-catalyzed dihydroxylation of alkenes by H2O2 in
room temperature ionic liquid co-catalyzed by VO(acac)2 or MeReO3
*
´
Mikael Johansson, Auri A. Linden, Jan-E. Ba¨ckvall
Department of Organic Chemistry, Arrhenius Laboratory, Stockholm University, SE-106 91 Stockholm, Sweden
Received 15 March 2005; received in revised form 21 April 2005; accepted 21 April 2005
Available online 15 June 2005
Abstract
Room temperature ionic liquid [bmim]PF6 was used to immobilize a bimetallic catalytic system for H2O2-based dihydroxylation
of alkenes. Osmium tetroxide was used as the substrate-selective catalyst with either VO(acac)2 or MeReO3 as co-catalyst. The latter
serve as an electron transfer mediator (ETM) and activates H2O2. For an increased efficiency N-methylmorpholine is required as an
additional ETM in most cases. A range of alkenes were dihydroxylated using this robust bimetallic system and it was demonstrated
that for some of the alkenes the catalytic system can be recycled and used up to five times.
Ó 2005 Elsevier B.V. All rights reserved.
Keywords: Ionic liquid; Osmium; Dihydroxylation; Hydrogen peroxide; Electron transfer
1. Introduction
line/N-methylmorpholine-N-oxide (NMM/NMO) has
been used for this purpose.
Osmium-catalyzed dihydroxylation of alkenes is a
synthetically important reaction and many oxidation
systems have been developed for this transformation
[1,2]. From an environmental point of view it is of inter-
est to use oxidants such as hydrogen peroxide or molec-
ular oxygen, which give no waste products [2–5].
In the original version of the hydrogen peroxide-
based dihydroxylation [5] an organocatalyst, a flavin,
was used as the H2O2-activating catalyst. The flavin gen-
erates a flavin hydroperoxide, which rapidly oxidizes
NMM to NMO in situ. The latter (NMO), in turn, rap-
idly oxidizes Os(VI) back to Os(VIII).
We have recently developed several methods for the
osmium-catalyzed dihydroxylation of alkenes by hyd-
rogen peroxide [5–8]. The principle of these oxidation
systems is that the hydrogen peroxide reacts with a co-
catalyst (electron transfer mediator) to give a reactive
peroxo or hydroperoxide intermediate, which efficiently
can reoxidize Os(VI) to Os(VIII), often with the aid of
an additional electron transfer mediator (ETM). The
latter ETM, if required, is a redox catalyst that lowers
the barrier for electron transfer and N-methylmorpho-
In a modified version of the H2O2-based dihydroxyla-
tion, VO(acac)2 or MeReO3 (MTO) was employed in
place of the flavin for the activation of H2O2 [6]. One
problem encountered with MTO was that it underwent
slow decomposition [9] under the reaction conditions
employed. VO(acac)2 worked better but also this co-
catalyst was less efficient than the flavin employed in
the original version.
Ionic liquids are attracting a growing interest as
solvents for organometallic reactions [10,11]. The use
of ionic liquids in osmium-catalyzed dihydroxylation
was reported by four different groups in 2002 [12], and
recently we [8] developed a H2O2-based version of the
dihydroxylation in an ionic liquid. The latter procedure
*
Corresponding author. Tel.: +4686747178; fax: +468154908.
E-mail address: jeb@organ.su.se (Jan-E. Ba¨ckvall).
0022-328X/$ - see front matter Ó 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2005.04.033

M. Johansson et al. / Journal of Organometallic Chemistry 690 (2005) 3614–3619
3615
employed a flavin as the H2O2-activating catalyst. In the
present paper, we report on a robust bimetallic catalytic
system, employing co-catalysts VO(acac)2 (1) and MTO
(2) in an ionic liquid for the efficient dihydroxylation of
alkenes by hydrogen peroxide.
as with some of the aromatic ones (Table 2, Method
A). In particular, the more substituted aliphatic olefins
were problematic. Thus, 1-octene was the only aliphatic
olefin that gave a clean reaction and a high yield using
only 5 mol% of citric acid (Table 2, entry 8).
Since the method based on citric acid gave consider-
able amounts of double bond cleavage for the aliphatic
olefins, and it is well known that this cleavage is faster at
lower pH, we replaced citric acid with tetraethyl ammo-
nium acetate (TEAA) as in the VO(acac)2-co-catalyzed
protocol. This proved to be successful and we obtained
high yields for all the aliphatic olefins (Table 2, Method
B, entries 7–10). Also the aromatic olefins worked quite
well with this method to give satisfactory to good yields,
O
V
CH3
Re
O
O
O
O
O
N
N
PF6
O
O
[bmim]PF6
1
2
2. Results and discussion
Dihydroxylation of alkenes by H2O2 was carried out
in the ionic liquid [bmim]PF6 with acetone as co-solvent
employing K2OsO4 as catalyst and either MTO or
VO(acac)2 as co-catalysts for H2O2-activation.
Table 1
Osmium-catalyzed dihydroxylation of alkenes in ionic liquid using
VO(acac)2 as co-catalysta
2.1. VO(acac)2 as co-catalyst
Entry
Olefin
Product
Yieldb
OH
All reactions were carried out at room temperature
with slow addition of hydrogen peroxide (8 h). Reac-
tion of styrene with 30% aqueous hydrogen peroxide
in [bmim]PF6/acetone employing 2 mol% of K2OsO4
and 2 mol% of VO(acac)2 together with 23 mol% of
N-methylmorpholine (NMM) afforded 81% diol after
workup (Table 1, entry 1). Also, b- and a-methylstyrene
worked well and gave the corresponding diol in 82%
and 91% yield, respectively (Table 1, entries 2 and 3).
Several different alkenes were oxidized using these reac-
tion conditions and the results are given in Table 1.
Cyclohexene and acyclic aliphatic olefins gave good to
high yields of the corresponding diols (Table 1, entries
6–10).
OH
1
81%
OH
2
3
4
82%
91%
81%
OH
OH
OH
OH
O
O
OH
5
73%
HO
HO
HO
6
7
8
91%
80%
81%
HO
OH
2.2. MTO as co-catalyst
OH
OH
The use of MTO as the H2O2-activating catalyst in
osmium-catalyzed dihydroxylations is associated with
the problem that MTO decomposes at alkaline pH by
aq. H2O2. A solution to this problem was recently pro-
vided by allowing the reaction to occur under slightly
acidic conditions [13]. We have now immobilized this
system in ionic liquid [bmim]PF6 at room temperature.
Reaction of styrene with hydrogen peroxide in
[bmim]PF6/acetone catalyzed by K2OsO4 Æ 2H2O
(2 mol%) and MTO (2 mol%) in the presence of citric
acid afforded the corresponding diol in excellent yield
(Table 2, Method A, entry 1). Although the less basic
protocol utilizing citric acid worked well for some of
the olefins we encountered problems with cleavage of
the double bond in the case of aliphatic olefins as well
HO
HO
HO
9
86%
87%
OH
10
OH
a
Experimental conditions: 7.2 mg of K2OsO4 Æ 2H2O (2 mol%),
5.3 mg of VO(acac)2 (2 mol%), 25 lL of N-methylmorpholine (NMM)
(23 mol%), and Et4N+OAcÀ (TEAA) (2 equiv.) were stirred in 0.5 mL
of [bmim]PF6, 3.8 mL of acetone and 1.2 mL of H2O were added as co-
solvents together with the olefin (1 mmol). 30% H2O2 (1.5 mmol) was
added over 8 h followed by 8 h of reaction.
b
Isolated yields.

3616
M. Johansson et al. / Journal of Organometallic Chemistry 690 (2005) 3614–3619
Table 2
Osmium-catalyzed dihydroxylation of alkenes in ionic liquid using
MTO as co-catalyst
Table 3
Osmium-catalyzed dihydroxylation of alkenes in ionic liquid using
MTO as co-catalyst without NMMa
Entry
Substrate
Product
Method Aa
Yieldc %
Method Bb
Yieldc (%)
Entry
1
Olefin
Yield of diol (%)
95
OH
74d
68
48
56
73
86
85
90
85
72
OH
1
2
3
4
5
6
7
8
9
95
86
2
3
4
5
95
88
75
74
67
OH
O
O
OH
O
OH
O
51
OH
O
O
O
OH
77
O
OH
OH
51
OH
6
OH
OH
99
a
K2OsO4 Æ 2H2O (7.2 mg, 2 mol%), MTO (5.5 mg, 2 mol%), and
TEAA (2 equiv.) were stirred in 0.5 mL of [bmim]PF6. Acetone (3 mL)
and H2O (0.2 mL) were added as co-solvents together with the olefin
(1 mmol). H2O2 (30% aq., 1.5 mmol) was added over 8 h followed by
8 h of reaction.
OH
18
OH
OH
78
HO
HO
HO
n.d.e
41
sults show that direct oxidation of OsO3 to OsO4 by
MTO works well with some substrates but for others
the presence of NMM improves the outcome of the
dihydroxylation.
HO
HO
10
a
Method A: K2OsO4 Æ 2H2O (7.2 mg, 2 mol%), MTO (5.5 mg,
2 mol%), N-methylmorpholine (NMM) (22 lL, 20 mol%) and Citric
acid (9.6 mg, 5 mol%) were stirred in 0.5 mL of [bmim]PF6. Acetone
(1 mL) and H2O (0.2 mL) were added as co-solvents together with the
olefin (1 mmol). H2O2 (30% aq., 1.5 mmol) was added over 4 h fol-
lowed by 4–16 h of reaction.
2.3. Recycling experiments
The catalytic system used here is immobilized in the
ionic liquid. To find out if there is some loss of the cat-
alysts during the extraction the recycling of the catalytic
system (catalytic soup) [8] was studied. For our initial
experiments we chose to study the dihydroxylation of al-
lyl phenyl ether, styrene, and b-methylstyrene as model
olefins. The results from five cycles using the OsO4/
NMM/VO(acac)2/H2O2 triple catalytic system show that
it is possible to recycle the catalytic system (Table 4, en-
tries 1–3). Allyl phenyl ether, styrene and b-methylsty-
rene gave good yield for all five recycling experiments.
However, the aliphatic olefins (E)-5-decene gave moder-
ate yields in our initial second recycling experiment.
Whereas the recycling of the coupled catalytic system
was successful using VO(acac)2 as co-catalyst the MTO
supported system unfortunately turned out to be less
productive. The citric acid-based method showed severe
contamination of cleaved product already in the third
run (Table 5, entry 1). Since the method utilizing TEAA
together with MTO (method B) gave high yields with the
aliphatic olefins we chose this method for the recycling
experiments for the aliphatic olefins. The yields of the
diols resulting from the linear aliphatic olefins, 1-octene
and 2-methyl-1-heptene, dropped steadily for each recy-
cling of the ionic liquid-catalyst system (Table 5, entries
b
Method B: K2OsO4 Æ 2H2O, (7.2 mg, 2 mol%), MTO (5.5 mg,
2 mol%), N-methylmorpholine (NMM) (22 lL, 20 mol%) and TEAA
(2 equiv.) were stirred in 0.5 mL of [bmim]PF6. Acetone (3 mL) and
H2O (0.2 mL) were added as co-solvents together with the olefin
(1 mmol). H2O2 (30% aq., 1.5 mmol) was added over 8 h followed by
8 h of reaction.
c
Isolated yields.
H2O2 was added over 4 h followed by an additional 16 h of stirring.
Not determined due to poor conversion.
d
e
but some of these olefins worked better with the citric
acid-assisted method (Mehtod A).
In order to investigate the significance of the direct
oxidation of OsO3 to OsO4 by MTO we run the TEAA
based method with six different olefins without any
NMM present (Table 3). According to the results,
95% yield of diol from 1-octene (Table 3, entry 1)
and 2-methyl-1-hepetene (Table 3, entry 2) was ob-
tained. Also, cyclohexene gave a good yield (88%) of
diol (Table 3, entry 3). However, E-5-decene, styrene
and b-methylstyrene gave lower yields (Table 3, entries
4–6) compared with the methods utilizing NMM as
electron transfer mediator (cf. Tables 1 and 2). The re-

M. Johansson et al. / Journal of Organometallic Chemistry 690 (2005) 3614–3619
3617
Table 4
Recycling of the bimetallic OsO4-VO(acac)2 catalytic systema
O
OsO4
H2O2
M
1 or 2
Entry
Olefin
Yield (%)b
NMM
Run 1 Run 2 Run 3 Run 4 Run 5
HO
OH
O O
M
OsO3
H2O
O
1
2
3
81
81
82
87
88
83
79
43
74
84
80
78
82
83
Scheme 1. Coupled bimetallic catalytic system for dihydroxylation of
olefins immobilized in ionic liquid.
OsO4 (2 mol%)
81
74
63
OH
(DHQD)2PHAL (6 mol%)
OH
4
n.d.c
n.d.c
n.d.c
VO(acac)2 (2 mol%)
a
H2O2 (1.5 equiv.)
TEAA (2 equiv.)
[bmim]PF6:Acetone:H2O, rt
K2OsO4 Æ 2H2O (7.2 mg, 2 mol%), VO(acac)2 (5.1 mg, 2 mol%), N-
methylmorpholine (NMM) (22 lL, 20 mol%) and TEAA (2 equiv.)
were stirred in 0.5 mL of [bmim]PF6. Acetone (3.8 mL) and H2O
(1.2 mL) were added as co-solvents together with the olefin (1 mmol).
H2O2 (30% aq., 1.5 mmol) was added over 8 h followed by 8 h of
reaction.
80% (75% ee)
Scheme 2. Asymmetric dihydroxylation using (DHQD)2PHAL in the
osmium-VO(acac)2 catalytic system.
b
Isolated yields.
Not determined.
c
reduced osmium. Hydrogen peroxide reacts with the me-
tal oxo complex to give a reactive peroxo complex. This
peroxo complex can react directly with the reduced form
of the osmium catalyst, OsO3, to regenerate OsO4. The
selectivity of this reoxidation is increased by the use of
catalytic amounts of N-methylmorpholine (NMM). In
the latter case the amine is oxidized to the corresponding
N-oxide (NMO), which efficiently transfers an oxygen
atom to osmium.
An interesting question is if the hydrogen peroxide-
based dihydroxylation in ionic liquid is compatible with
chiral ligands. In a preliminary experiment we found
that chiral ligand (DHQD)2PHAL gave an ee of 75%
in the dihydroxylation of styrene utilizing the osmium-
VO(acac)2 catalytic system (Scheme 2). In this reaction
the chiral ligand is also working as an electron transfer
mediator. Further studies are required to improve the
enantioselectivity of the H2O2-based reaction in ionic
liquid.
1–2). However, for the cyclohexane-1,2-diol the yields
remained good through 4 runs.
2.4. Mechanism of the H2O2-based dihydroxylation
The mechanism of the coupled bimetallic catalytic
system can be described as shown in Scheme 1. In this
coupled catalytic system OsO4 is the substrate-selective
catalyst that dihydroxylates the alkene to give diol and
Table 5
Recycling of the OsO4-MTO catalytic systema
Entry
Olefin
Yield (%)
Run 1 Run 2 Run 3 Run 4
1b
2
81
98
98
72
38c
76
61
70
n.d.d
59
n.d.d
n.d.d
46
3. Conclusions
3
47
Hydrogen peroxide-based osmium-catalyzed dihydr-
oxylation using two different metal complexes, VO-
(acac)2 and MTO, as co-catalysts (electron transfer
mediators) in room temperature ionic liquid [bmim]PF6
has been investigated. The two protocols of the bimetal-
lic catalytic system were tested with a variety of aro-
matic and aliphatic olefins and were found to yield the
corresponding 1,2-diols in good to excellent yields. Elec-
tron transfer from the co-catalyst to osmium is facili-
tated by the presence of catalytic amounts of NMM as
an additional electron transfer mediator. It was demon-
strated that in some cases direct electron transfer from
MTO to osmium is efficient without added NMM.
Immobilization and recycling of the catalytic system
(catalytic soup) has been demonstrated by extraction
4
84
a
Method B: K2OsO4 Æ 2H2O (7.2 mg, 2 mol%), MTO (5.5 mg,
2 mol%), N-methylmorpholine (NMM) (22 lL, 20 mol%) and TEAA
(2 equiv.) were stirred in 0.5 mL of [bmim]PF6. Acetone (3 mL) and
H2O (0.2 mL) were added as co-solvents together with the olefin
(1 mmol). H2O2 (30% aq., 1.5 mmol) was added over 8 h followed by
8 h of reaction.
b
K2OsO4 Æ 2H2O (1.8 mg, 0.5 mol%), MTO (2.5 mg, 1 mol%), of N-
methylmorpholine (NMM) (22 lL, 20 mol%) and Citric acid (0,144 g,
75 mol%) were stirred in 0.5 mL of [bmim]PF6. Acetone (3 mL) and
H2O (0.2 mL) were added as co-solvents together with the olefin
(1 mmol). H2O2 (30% aq., 1.5 mmol) was added over 4 h followed by
8 h of reaction.
c
H2O2 was added over 8 h and the reaction stirred for additional 8 h.
Not determined due to poor conversion.
d

3618
M. Johansson et al. / Journal of Organometallic Chemistry 690 (2005) 3614–3619
of the product and reuse of the catalytic system with no
or moderate loss of activity. The bimetallic catalytic sys-
tem in room temperature ionic liquid gives a simple and
reusable ‘‘catalytic soup’’ with hydrogen peroxide as the
terminal oxidant, which is environmentally friendly
since the only by-product is water.
0.02 mmol, 2 mol%), and citric acid (9.6 mg, 0.05 mmol)
were added and mixed by gentle stirring. Acetone
(1 mL) and water (0.2 mL) were introduced, followed
by N-methylmorpholine (NMM) (22 lL, 0.2 mmol,
20 mol%) and olefin (1 mmol). Aqueous hydrogen per-
oxide (170 lL, 30% solution, 1.5 equivalents) was added
over 4 h via syringe pump followed by additional 8 h
stirring after which the volatile solvents were removed
under reduced pressure. The resulting residue of
[bmim]PF6 was then extracted three times with 10 mL
portions of diethyl ether. The ether layers were com-
bined, and reduced in volume to yield the crude diol.
The crude diol was chromatographed on silica gel with
1:1 or 1:2 EtOAc/pentane to yield the purified product.
4. Experimental
4.1. General methods
1H and 13C NMR spectra were recorded on a Varian
Unity 400 (400 MHz 1H, 100 MHz 13C) or a Varian
Unity 300 (300 MHz 1H, 75 MHz 13C) spectrometer.
Chemical shifts (d) are reported in ppm, using residual
solvent as internal standard. Millipore Matrex silica
4.4. Procedure for osmium-catalyzed dihydroxylation of
olefins by H2O2 with MeReO3 (MTO) as co-catalyst
using method B (Table 2, all entries)
˚
gel (60 A pore size, 35–70 lm) was used for flash
chromatography. Potassium osmate and tetraethylam-
monium acetate (TEAA) were purchased from Aldrich.
1-Butyl-3-methyl imidazolium hexafluorophosphate
([bmim]PF6) was purchased from Acros. All olefins,
VO(acac)2 (1) and MeReO3 (2) were obtained from
commercial suppliers and used without further
purification.
Ionic liquid [bmim]PF6 (0.5 mL) was placed in a
20 mL vial with a small stir bar. K2OsO4 Æ 2H2O (7.2
mg, 0.02 mmol, 2 mol%), MeReO3 (5.5 mg, 0.02 mmol,
2 mol%), and TEAA Æ 4H2O (523 mg, 2 mmol) were
added and mixed by gentle stirring. Acetone (3 mL)
and water (0.2 mL) were introduced, followed by
N-methylmorpholine (NMM) (28 l L, 0.23 mmol, 23
mol%) and olefin (1 mmol). Aqueous hydrogen perox-
ide (170 lL, 30% solution, 1.5 equivalents) was added
over 8 h via syringe pump followed by additional 8 h
stirring after which the volatile solvents were removed
under reduced pressure. The resulting residue of
[bmim]PF6 was then extracted three times with 10 mL
portions of diethyl ether. The ether layers were
combined, and reduced in volume to yield the crude
diol. The crude diol was chromatographed on silica
gel with 1:1 or 1:2 EtOAc/pentane to yield the purified
product.
4.2. Procedure for osmium-catalyzed dihydroxylation of
olefins by H2O2 with VO(acac)2 as co-catalyst
(Table 1, all entries)
Ionic liquid [bmim]PF6 (0.5 mL) was placed in a
20 mL vial with a small stir bar. K2OsO4 Æ 2H2O
(7.2 mg, 0.02 mmol, 2 mol%), VO(acac)2 (5.1 mg,
0.02 mmol, 2 mol%), and TEAA Æ 4H2O (523 mg,
2 mmol) were added and mixed by gentle stirring. Ace-
tone (3.8 mL) and water (1.2 mL) were introduced, fol-
lowed by N-methylmorpholine (NMM) (28 lL,
0.23 mmol, 23 mol%) and olefin (1 mmol). Aqueous
hydrogen peroxide (170 lL, 30% solution, 1.5 equiva-
lents) was added over 8 h via syringe pump. The reac-
tion mixture was allowed to stir for another 8 h, and
the volatile solvents were removed under reduced pres-
sure. The residue of [bmim]PF6 was extracted three
times with 10 mL portions of diethyl ether. The ether
layers were combined, and reduced in volume to yield
the crude diol. The crude diol was chromatographed
on silica gel with 1:1 EtOAc/pentane to yield the purified
product.
4.5. Procedure for osmium-catalyzed dihydroxylation of
olefins by H2O2 with MeReO3 (MTO) as co-catalyst
without N-methylmorpholine (NNM) (Table 3, all
entries)
Same as method B but without NMM.
4.6. Recycling and reuse of ionic liquid-immobilized
catalytic system using VO(acac)2 as co-catalyst
(Table 4, runs 2–5)
4.3. Procedure for osmium-catalyzed dihydroxylation of
olefins by H2O2 with MeReO3 (MTO) as co-catalyst
using method A (Table 2, all entries)
Acetone (3.8 mL) and water (1.2 mL) were added to
the ionic liquid layer from the first reaction, followed
by 1 mmol of olefin. Aqueous hydrogen peroxide
(170 lL, 30% solution, 1.5 equivalents) was added over
8 h. After stirring for another 8 h, the volatile solvents
were removed, and the remaining ionic liquid was ex-
tracted three times with 10 mL portions of diethyl ether.
Ionic liquid [bmim]PF6 (0.5 mL) was placed in a
20 mL vial with a small stir bar. K2OsO4 Æ 2H2O
(7.2 mg, 0.02 mmol, 2 mol%), MeReO3 (5.5 mg,

M. Johansson et al. / Journal of Organometallic Chemistry 690 (2005) 3614–3619
3619
The ether layers were combined and reduced in volume,
and the resulting crude product was chromatographed
on silica gel with 1:1 EtOAc/pentane to yield purified
diol. The subsequent reaction runs 3–5 were carried
out in exactly the same manner as described here.
3-phenoxy-1,2-propanediol [17], 1-phenyl-1,2-cyclohex-
ane-diol [18], 2-methyl-1,2-heptanediol [19], 1,2-octane-
diol [20], 3,4-dihydroxy-4-phenyl-2-butanone [21], 2,3-
dihydroxy-3-phenyl ethyl propionate [22].
4.7. Recycling and reuse of ionic liquid-immobilized
catalytic system using MeReO3 (MTO) as
co-catalyst (Table 5, runs 2–5)
References
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Acetone (3 mL) and water (0.2 mL) were added to the
ionic liquid layer from the first reaction, followed by
1 mmol of olefin. Aqueous hydrogen peroxide (170 lL,
30% solution, 1.5 equivalents) was added over 8 h. After
stirring for another 8 h, the volatile solvents were re-
moved, and the remaining ionic liquid was extracted
three times with 10 mL portions of diethyl ether. The
ether layers were combined and reduced in volume,
and the resulting crude product was chromatographed
on silica gel with 1:1 or 1:2 EtOAc/pentane to yield puri-
fied diol. The subsequent reaction runs 3–4 were carried
out in exactly the same manner as described herein.
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4.8. Procedure for asymmetric dihydroxylation of styrene
by OsO4-(DHQD)2PHAL- VO(acac)2 catalytic system
(Scheme 2)
(b) S.Y. Jonsson, H. Adolfsson, J.E. Ba¨ckvall, Chem. Eur. J. 9
(2003) 2783.
[8] A. Closson, M. Johansson, J.E. Ba¨ckvall, Chem. Commun.
(2004) 1494.
[9] (a) MTO is known to decompose into catalytically inert perrh-
enate and methanol by aqueous hydrogen peroxide under alkaline
conditions [9b,9c]. The decomposition is accelerated by an
increased pH;
K2OsO4 Æ 2H2O (7.2 mg, 0.02 mmol, 2 mol%),
VO(acac)2 (5.1 mg, 0.02 mmol, 2 mol%), and TEAA Æ
4H2O (523 mg, 2 mmol) were placed in a 20 mL vial
with a small stir bar. Ionic liquid [bmim]PF6 (0.5 mL),
acetone (3.8 mL) and water (1.2 mL) were introduced
and mixed by gentle stirring, followed by
(DHQD)2PHAL (46 mg, 0.06 mmol, 6 mol%) and sty-
rene (1 mmol). Aqueous hydrogen peroxide (170 lL,
30% solution, 1.5 equivalents) was added over 8 h via
syringe pump. The reaction mixture was allowed to stir
for another 8 h, and the volatile solvents were removed
under reduced pressure. The resulting residue of
[bmim]PF6 was then extracted three times with 10 mL
portions of diethyl ether. The ether layers were com-
bined, and reduced in volume to yield the crude diol.
The crude diol was chromatographed on silica gel with
1:1 EtOAc/pentane to yield the purified product in
80% isolated yield. Analysis by HPLC [5b] showed that
the product was of 75% ee. (1R)-1-phenyl-1,2-ethanediol
(HPLC (Daicel Chiralcel OD-H column, 95:5 iso-hex-
ane/2-propanol, flow rate 0.5 mL/min): tR(ma-
jor) = 29.9 min, tR(minor) = 31.6 min).
(b) M.M. Abu-Omar, P.J. Hansen, J.H. Espenson, J. Am. Chem.
Soc. 118 (1996) 4966;
(c) H. Adolfsson, in: J.E. Ba¨ckvall (Ed.), Modern Oxidation
Methods, Wiley-VCH, Weinheim, 2004, p. 21.
[10] C.E. Song, Chem. Commun. (2004) 1033.
[11] (a) P. Wasserscheid, T. Weller (Eds.), Ionic Liquids in Synthesis,
VCH-Wiley, 2003;
(b) , For related use of ionic liquids see:C.P. Mehnert, Chem. Eur.
J. 11 (2005) 50.
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(c) C.E. Song, D. Jung, E.J. Roh, S. Lee, D.Y. Chi, Chem.
Commun. (2002) 3038–3039;
(d) R. Yanada, Y. Takemoto, Tetrahedron Lett. 43 (2002) 6849.
´
[13] A.H. Ell, A. Closson, H. Adolfsson, J.E. Ba¨ckvall, Adv. Synth.
Catal. 345 (2003) 1012.
[14] S. Nagayama, M. Endo, S. Kobayashi, J. Org. Chem. 63 (1998)
6094.
[15] W. Kroutil, M. Mischitz, K. Faber, J. Chem. Soc., Perkin Trans.
1 (1997) 3629.
[16] B.M. Choudary, N.S. Chowdari, S. Madhi, M.L. Kantam, J.
Org. Chem. 68 (2003) 1736.
´ ´
[17] G. Egri, A. Kolbert, J. Balint, E. Fogassy, L. Novak, L. Poppe,
J. Mol. Catal. B: Enzymatic 6 (2000) 583.
4.9. The NMR data of the diols were in accordance
with those previously reported
[18] B.S. King, K.B. Sharpless, Tetrahedron Lett. 35 (1994) 5611.
[19] M. Mischitz, U. Kroutil, U. Wandel, K. Faber, Tetrahedron:
Asymmetry 6 (1995) 1261.
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Organomet. Chem. 621 (2001) 70.
[21] P.J. Walsh, K.B. Sharpless, Synlett 8 (1993) 605.
1-Phenyl-1,2-ethanediol [3b], 2-phenyl-1,2-propane-
diol [3b], 5,6-decenediol [3b], cis-1,2-cyclohexanediol
[14], 2,3-octanediol [15], 1-phenyl-1,2-propanediol [16],