A novel and efficient catalytic epoxidation of olefins and monoterpenes with microencapsulated Lewis base adducts of methyltrioxorhenium

Article abstract of DOI:10.1016/j.tet.2004.11.065

The reactivity of methyltrioxorhenium in the epoxidation of olefins can be tuned by the presence of Lewis bases as ligands of the metal center. Unfortunately, a large excess of ligand is usually required to obtain high yields and selectivities mainly because of the fluxional behaviour that these compounds show in solution. We describe here the microencapsulation technique that can resolve this problem. Microencapsulated Lewis base adducts of methyltrioxorhenium with nitrogen containing ligands are highly efficient and selective catalysts for the epoxidation of several olefins and monoterpenes with hydrogen peroxide even in the case of the most sensitive substrates. These systems show the advantages of the ligand accelerated catalysis and the benefits of heterogeneous compounds. They can be easily recovered from the reaction mixture and used for more transformations.

Full text of DOI:10.1016/j.tet.2004.11.065

Tetrahedron 61 (2005) 1069–1075
A novel and efficient catalytic epoxidation of olefins
and monoterpenes with microencapsulated Lewis base adducts
of methyltrioxorhenium
a
a
c
Raffaele Saladino,a,b, Alessia Andreoni, Veronica Neri and Claudia Crestini
*
a
`
Dipartimento di Agrobiologia ed Agrochimica, Universita della Tuscia, Via S. Camillo de Lellis s.n.c. 01100 Viterbo, Italy
b
`
INFM, Universita della Tuscia, Via S. Camillo de Lellis s.n.c. 01100 Viterbo, Italy
c
`
Dipartimento di Scienze e Tecnologie Chimiche, Universita ‘Tor Vergata’, Via della Ricerca Scientifica, 00133 Rome, Italy
Received 1 October 2004; revised 4 November 2004; accepted 25 November 2004
Available online 8 December 2004
Abstract—The reactivity of methyltrioxorhenium in the epoxidation of olefins can be tuned by the presence of Lewis bases as ligands of the
metal center. Unfortunately, a large excess of ligand is usually required to obtain high yields and selectivities mainly because of the fluxional
behaviour that these compounds show in solution. We describe here the microencapsulation technique that can resolve this problem.
Microencapsulated Lewis base adducts of methyltrioxorhenium with nitrogen containing ligands are highly efficient and selective catalysts
for the epoxidation of several olefins and monoterpenes with hydrogen peroxide even in the case of the most sensitive substrates. These
systems show the advantages of the ligand accelerated catalysis and the benefits of heterogeneous compounds. They can be easily recovered
from the reaction mixture and used for more transformations.
q 2004 Elsevier Ltd. All rights reserved.
1. Introduction
stability of the ligand and the reaction temperature.16
Lewis base adducts of MTO undergo exchange of both the
metal-coordinated base ligands and the oxo ligands in
solution in the presence of water or other nucleophilic
solvents.17 For this reason a large excess of ligand is
necessary (at least fivefold excess) to obtain the maximum
turnover frequencies (TOF), epoxide yield and conversion
of substrate.15 Unfortunately, the excess of ligand can be a
synthetic limitation in the case of expensive and chiral
Lewis bases.
During the last years methyltrioxorhenium (CH3ReO3,
MTO)1 showed excellent catalytic properties in oxidation
of olefins,2 alcohols,3 arenes,4 carbonylmetal derivatives,5
phosphorous and sulphur compounds,6 olefin metathesis,7
aldehyde olefination,8 Bayer–Villiger rearrangement9 and
hydrocarbon C–H oxygen atom insertions.10 The epoxida-
tion of olefins with hydrogen peroxide (H2O2) received
special attention. The mayor drawback of this trasformation
is the ring-opening of the newly formed oxiranyl moiety
with concomitant formation of diols. This side-reaction is
mainly due to the acidity of the catalyst system.11 Lewis
base adducts of MTO with nitrogen containing ligands, such
as pyridine,12 pyridine derivatives,13 pyrazole14 and others,
decrease the formation of diols, especially in the case of
sensitive substrates, and increase the catalytic efficiency.
MTO reacts with monodentate and bidentate ligands to give
trigonal bipyramidal and distorted octahedral adducts,
respectively.15 The activity of these complexes in several
oxy-functionalizations was found to be dependent on
different experimental parameters, such as the redox
It was quickly detected that MTO can form adducts with
ligands immobilized on inorganic and organic host.18,19 In
these systems the active rhenium species is localized in a
specific microenvironment whose properties can differ from
that of the bulk of the solution. Recently, we reported the
use of poly(4-vinylpyridine)/MTO compounds as efficient
catalysts for the epoxidation of olefins,19 monoterpenes,20
phenol and anisole derivatives,21 flavonoids,22 pyrroli-
dines23 and hydrocarbon derivatives.24 Alternative
strategies to further improve heterogeneous MTO-catalyzed
epoxidations can involve the immobilization of previously
synthesized Lewis base adducts of MTO on polystyrene by
use of the microencapsulation technique.25 In principle, the
reactivity and selectivity of MTO in these compounds can
be tuned by the chemical–physical properties of the ligand
and of the support showing the advantages of the ligand
Keywords: Olefins; Terpenes; Methyltrioxorhenium; Oxidation; Hydrogen
peroxide.
* Corresponding author. Tel.: C39 0761 357284; fax: C39 0761 357242;
e-mail: saladino@unitus.it
0040–4020/$ - see front matter q 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2004.11.065

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R. Saladino et al. / Tetrahedron 61 (2005) 1069–1075
Figure 1. Preparation of microencapsulated Lewis base adduct of MTO mI, mII and mIII, and of their parent compounds I, II and III.
accelerated catalysis and the environmental benefits of
heterogeneous systems. We report here the preparation and
applicability of novel microencapsuled Lewis base adducts
of MTO with monodentate and bidentate, aromatic and
aliphatic nitrogen containing ligands, for the epoxidation of
olefins and monoterpene derivatives, including acid-
sensitive substrates. Environment friendly H2O2 was used
as primary oxidant. Noterworthy, microencapsulated Lewis
base adducts of MTO were more reactive than their
homogeneous parent compounds even in the absence of
the excess of ligand. They were also stable catalytic systems
for several oxidations.
compounds mI–mIII were dried and used without any
further purification (Fig. 1, equation B). In each case
adducts mI–mIII were completely bound to the polystyrene
as confirmed by spectroscopic analysis of the residue
obtained after evaporation of the organic layer. Figure 2
shows a scanning electron microscopy (SEM) photograph of
the surface of particles of catalyst mIII. Particles are
characterized by a regular spherical shape of 50 mm.
Fragments are probably formed by a mechanical damage
of particles during the preparation of the sample.
2. Results
Lewis base adducts of MTO I–III with the monodentate
ligand 4-methoxyaniline (a) and the bidentate aromatic and
aliphatic ligands, 2-methyl aminopyridine (b) and racemic
trans-1,2-diaminocyclohexane (c), respectively, were pre-
pared as model compounds following a synthetic procedure
previously reported in the literature.26,27 In order to obtain
these adducts, MTO 1 and the appropriate Lewis base were
mixed in toluene, the reaction mixture was concentrated and
cooled to K35 8C, and the yellow precipitates isolated by
filtration (Fig. 1, equation A). Microencapsulated Lewis
base adducts of MTO mI–mIII were then obtained by
encapsulation of freshly prepared adducts I–III on poly-
styrene (2% cross-linked with divinylbenzene).19b
Figure 2. Scanning electron microscopy (SEM) photograph of the surface
of particles of catalyst mIII.
Briefly, to a suspension of polystyrene (600 mg) in
tetrahydrofuran was added to the appropriate adduct I–III
(0.3 mmol). After 1 h, hexane was added to harden the
capsule walls, the solvent was removed by filtration and
Epoxidations with catalysts mI–mIII and H2O2 (35% aq
solution) were first investigated using reactive olefins,
cyclooctene 2 and cyclohexene 3, and moderately active

R. Saladino et al. / Tetrahedron 61 (2005) 1069–1075
Table 1. Epoxidations of olefins with microencapsulated Lewis base adduct of MTO
1071
Entry
Substrate
Catalysta
Reaction time (h)
Conversion (%)
Epoxide yield (%)
Diol yield (%)
1
2
3
4
5
6
7
8
Cyclooctene
Cyclooctene
Cyclooctene
Cyclooctene
Cyclooctene
Cyclooctene
Cyclooctene
Cyclohexene
Cyclohexene
Cyclohexene
Cyclohexene
Cyclohexene
Cyclohexene
Cyclohexene
Styrene
1
I
0.5
3.0
3.0
2.5
2.5
0.5
0.5
1.0
2.5
2.5
2.5
2.5
1.0
1.0
6.0
8.0
8.0
9.5
5.0
1.5
1.5
94
85
98
88
O98
90
O98
O98
89
95
80
O98
87
O98
65
58
63
54
60
65
70
O98
O98
O98
O98
55
18
10
12
0
0
0
mI
II
mII
III
mIII
1
I
mI
II
mII
III
mIII
1
I
mI
II
0
45
21
14
0
0
0
9
62
70
10
11
12
13
14
15
16
17
18
19
20
21
O98
O98
O98
O98
80
73
75
95
95
0
20
21
15
0
0
0
Styrene
Styrene
Styrene
Styrene
Styrene
Styrene
MII
III
MIII
62
86
O98
O98
O98
0
All the reactions were performed in CH2Cl2/MeCN (5.0 mL, 1:1 v/v) at room temperature, with H2O2 (35% aq solution), using a value of the catalyst loading
factor of 1.0.
a Catalyst: MTO 1, MTO/4-methoxyaniline I, microencapsulated MTO/4-methoxyaniline mI, MTO/2-aminomethylpyridine II, microencapsulated MTO/2-
aminomethylpyridine II, MTO/trans-1,2-diaminocyclohexane III, microencapsulated MTO/2-aminomethylpyridine mIII.
1:1 ratio.13b It is worth noting that the highest reactivity and
selectivity were obtained with bidentate Lewis base adducts
of MTO, mII and mIII, in which cases a quantitative
conversion of substrate and yield of cycloalkene oxides 5
and 7 were obtained (Table 1, entries 5, 7, 12 and 14).
Catalysts mII and mIII were more reactive than their parent
compounds II and III (see for e.g., entry 5 vs 4 and entry 7
vs 6), mIII being the most reactive catalyst (Table 1, entries
6 and 14). Microencapsulated adducts mII and mIII were
more efficient than II and III also during the synthesis of the
sensitive styrene oxide 9 (see for e.g., Table 1, entries 19
and 21 vs entries 18 and 20, respectively). Under similar
experimental conditions, MTO 1 and catalysts I and mI
showed a lowest selectivity affording appreciable amounts
of diol 10 (Table 1, entries 15–17).
In a test for checking the leaching of catalysts, the oxidation
of 2 with mIII was stopped at ca. 50% conversion. After
centrifugation the colourless solution lost the catalytic
activity. Even if Lewis base adducts of MTO usually show a
pronounced water sensitivity, catalysts mII and mIII were
stable enough to perform at least five recycling experiments
in the oxidation of 2 with similar conversion and selectivity
(Table 2). In the fifth recycling step a very slight decrease in
activity occurred with catalyst mII.
Scheme 1.
styrene 4, as representative model substrates. All the
reactions were performed in CH2Cl2/CH3CN (5 mL, 1:1
v/v) at room temperature using 1% in weigth of active
species and a value of the loading factor of 1.0 (the loading
factor is defined as mmol of active species for gram of
support). Reactions with MTO 1 and compounds I–III were
also performed as references. In the absence of catalyst, less
than 5% conversion of substrates took place under otherwise
identical conditions. The oxidation results are summarized
in Table 1 and Scheme 1.
On the basis of these data it is reasonable to suggest that the
higher activity and selectivity of Lewis base adducts mII
and mIII with respect to their homogeneous parent
compounds II and III can be due to the microencapsulation
process. Usually, Lewis base ligands of MTO undergo
exchange reactions in the presence of water (even in the
case of more stabilizing bidendate ligands) by hydroxide
nucleophilic substitution followed by fast decomposition of
the complex with formation of methane and perrhenate.15
Probably, the low-polarity of the microenvironment inside
the polystyrene capsules stabilizes the fluxional behaviour
of the MTO adducts inducing beneficial effects on the
The oxidation of olefins 2 and 3 with MTO gave the
cycloalkene oxides 5 and 7 as the main products and diols 6
and 8 as side products (Table 1, entries 1 and 8). Lewis base
adducts of MTO with monodentate ligand, I and mI, behave
in a similar way and appreciable amounts of diols 6 and 8
were again observed in the reaction mixtures (Table 1,
entries 2, 3 and 9, 10). Accordingly, Ku¨hn and co-workers
described the poor yield of cycloalkene oxides during the
oxidation of olefins with Lewis base adducts of MTO in a

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R. Saladino et al. / Tetrahedron 61 (2005) 1069–1075
Table 2. Stability of microencapsulated Lewis base adducts of MTO in the oxidation of 2a
Catalystb
Conversion (%)
Run. no. 1
Run. no. 2
Run. no. 3
Run. no. 4
Run. no. 5
mII
MIII
97 (O98)a
98 (O98)
98(O98)
95 (O98)
96 (O98)
97 (O98)
95 (O98)
98 (O98)
91 (O98)
96 (O98)
All the reactions were performed in CH2Cl2/MeCN (5.0 mL, 1:1 v/v) at room temperature, with H2O2 (35% aq solution), using a value of the catalyst loading
factor of 1.0.
a Cycloalkene oxide yields are given in parentheses.
b Catalyst: MTO 1, MTO/4-methoxyaniline I, microencapsulated MTO/4-methoxyaniline mI, MTO/2-aminomethylpyridine II, microencapsulated MTO/2-
aminomethylpyridine II, MTO/trans-1,2-diaminocyclohexane III, microencapsulated MTO/2-aminomethylpyridine mIII.
Table 3. Epoxidations of monoterpenes with microencapsulated Lewis base adduct of MTO
Entry
Substrate
Catalysta
Time (h)
Temp (8C)
Conversion
(%)
Epoxide yield
(%)
Diol yield (%)
1
2
3
4
5
6
7
8
1S(C)3-Carene
1S(C)3-Carene
1S(C)3-Carene
1S(C)3-Carene
1S(C)3-Carene
1S(C)3-Carene
1S(C)3-Carene
R(C)Limonene
R(C)Limonene
R(C)Limonene
R(C)Limonene
R(C)Limonene
R(C)Limonene
R(C)Limonene
1R(C)-a-Pinene
1R(C)-a-Pinene
1R(C)-a-Pinene
1R(C)-a-Pinene
1R(C)-a-Pinene
1R(C)-a-Pinene
1R(C)-a-Pinene
1
II
II
mII
mII
III
mIII
1
2.5
4.0
2.5
1.5
1.5
0.5
0.5
1.5
2.0
2.0
2.0
2.0
1.0
2.5
1.0
1.5
1.5
1.5
2.0
1.0
1.0
25
25
K10
25
K10
K10
K10
25
25
K10
25
K10
K10
K10
25
25
K10
25
K10
K10
K10
O98
88
87
87
89
O98
O98
70
80
98
81
98
95
96
O98
85
O98
95
94
20
49
75
58
78
44
7
29
3
91
O98
O98
5
25
85
55
98
98
98
9
16
O98
30
90
0
0
63
52
0
43
0
9
II
II
10
11
12
13
14
15
16
17
18
19
20
21
mII
mII
III
mIII
1
II
II
mII
mII
III
mIII
0
0
75
70
0
55
0
O98
O98
O98
O98
0
0
All the reactions were performed in CH2Cl2/MeCN (5.0 mL, 1:1 v/v), with H2O2 (35% aq solution), using a value of the catalyst loading factor of 1.0.
a Catalyst: MTO 1, MTO/4-methoxyaniline I, microencapsulated MTO/4-methoxyaniline mI, MTO/2-aminomethylpyridine II, microencapsulated MTO/2-
aminomethylpyridine II, MTO/trans-1,2-diaminocyclohexane III, microencapsulated MTO/2-aminomethylpyridine mIII.
catalyst properties. This hypothesis is in accord with data
previously reported in the literature on the exchange
phenomena for MTO adducts in solution, in which case an
higher stability was observed in low polarity and non
donating media with respect to polar donor solvents.15
Under these experimental conditions microencapsulated
Lewis base adducts mII and mIII are more reactive and
selective than that with monodentate ligand, compound mI,
probably because of the known higher stability of the
complexes between MTO and bidentate ligands.
II at room temperature gave the trans-3,4-epoxycarene 14
and the diol 15 in ca. 1:1 ratio (Table 3, entry 2). This
reaction pattern was similar to that obtained with MTO
The attention was next addressed to the epoxidation of
different representative monoterpene derivatives, 1(S)-(C)-
3-carene 11, R-(C)-limonene 12 and 1R-(C)-a-pinene 13
to evaluate the generality of this procedure. In the
transformation of monoterpenes to perfumes, detergents,
flavours and biologically active substances, the oxidative
functionalization often starts with a selective epoxidation.
The reactions were performed with the most reactive
catalysts mII and mIII, and in the presence of MTO and
their parent compounds II and III as references as
previously described. In the absence of catalyst, less than
5% conversion of substrates took place under otherwise
identical conditions. The oxidation results are summarized
in Table 3 and Scheme 2. The oxidation of 11 with catalyst
Scheme 2.

R. Saladino et al. / Tetrahedron 61 (2005) 1069–1075
1073
alone, in which case the diol 15 becomes the major product
(Table 3, entry 1). A higher selectivity was obtained when
the oxidation of 11 with catalyst II was performed at
K10 8C. In this latter case the epoxide 14 was recovered in
75% yield beside to a small amount of diol 15 (Table 3,
entry 3). Again, better results were obtained after the
microencapsulation process. Thus, the epoxide 14 became
the major reaction product in the oxidation of 11 with
catalyst mII already at room temperature (Table 3, entry 4),
while 89% conversion of substrate and 91% yield of 14 were
obtained working at K10 8C (Table 3, entry 5). The
oxidation of 11 performed both with catalysts III and
mIII at K10 8C gave quantitative conversion and yield of
epoxide 14 (Table 3, entries 6 and 7).
active species is entrapped inside the capsules of a stable
polymeric support by non-covalent interactions. Under
these conditions the metal peroxide acts in a specific
microenvironment characterized by chemical–physical
properties different from that existing in the bulk of the
reaction mixture. In this paper we report for the first time
that Lewis base adducts of MTO retain their catalytic
properties after the microencapsulation with low costing
and readily available polystyrene. These novel hetero-
geneous catalysts were found to be more reactive and
selective than their homogeneous parent compounds in the
epoxidation of different olefins and monoterpene deriva-
tives. It is worth noting that a large excess of ligand was not
necessary to obtain high conversion and yield of epoxide. It
is reasonable to suggest that the microenvironment inside
the polystyrene capsules shows a beneficial effect on the
reactivity of these catalysts probably by increasing their
stability with respect to the bulk of the solution. A
significant effect of the polymeric support on the reactivity
and selectivity of MTO was previously observed during the
oxidation of phenolic derivatives. In this latter case, a
poly(4-vinylpyridine)-mediated molecular recognition
process based on hydrogen-bonding interactions between
the pyridinyl moiety and the phenolic group was found to be
operative.21 In accord with the order of stability reported for
the Lewis base adducts of MTO in solution, microencapsu-
lated complexes of MTO with bidentate ligands, compounds
mII–mIII, were more reactive than that with monodentate
ligand mI. Among the bidentate ligands, aliphatic com-
pounds appear to be more efficient than aromatic
compounds. Catalysts mII–mIII quantitatively convert
olefins to cycloalkene oxides at room temperature using
environmental friendly H2O2 as oxidant, while a low
reaction temperature (K10 8C) was necessary to obtain
similar results in the oxidation of monoterpenes. All
microencapsulated catalysts were stable systems for at
least five recycling experiments. Values of the loading
factor higher than 1.0 did not give appreciable increase in
the conversion of substrates.
Similar results were obtained in the oxidation of R-(C)-
limonene 12. Thus, the reactions performed with MTO and
II at 25 8C showed a low selectivity toward the epoxide 16,
the diol 17 being the main reaction product (Table 3, entries
8 and 9). Moreover, a quantitative conversion and 85% yield
of 16 were obtained with II at K10 8C (Table 3, entry 10).
After the microencapsulation process II showed the highest
selectivity. Accordingly, the oxidation of 12 with mII
afforded 55 and 98% yield of 16 at 25 and K10 8C,
respectively (Table 3, entries 11 and 12). The oxidation of
12 performed both with catalysts III and mIII at K10 8C
gave quantitative conversion and yield of epoxide (Table 3,
entries 13 and 14). It is worthy of note that highly sensitive
terpenic epoxides, such as a-pinene oxide, can be obtained
in excellent yield using microencapsulated Lewis base
adducts of MTO mII and mIII. Treatment of 1R-(C)-a-
pinene 13 with mII and mIII at K10 8C afforded the
a-pinene oxide 18 in quantitative conversion and yield
(Table 3, entries 15 and 16). Under these experimental
conditions pinanediol or products of oxiranyl ring
rearrangement (campholenic aldehyde, isopinocamphone)
were not identified in the reaction mixture. Again catalyst II
increased its reactivity and selectivity after the micro-
encapsulation process (see for e.g., Table 3 entry 18 vs entry
16 and entry 19 vs entry 17). Irrespective of the
experimental conditions, compounds III and mIII were
the best catalytic systems (Table 3, entries 20 and 21).
4. Experimental
All commercial products were of the highest grade available
and were used as such. Hydrogen peroxide was a 35% aq
solution (Aldrich). NMR spectra were recorder on a Bruker
(200 MHz). Gas chromatography and gas chromatography–
mass spectroscopy (GC–MS) of the reaction products were
performed using a SPB column (25 m!0.30 mm and
0.25 mm film thickness) and isothermal temperature profile
of 80 8C for the first 2 min, followed by a 10 8C/min
temperature gradient to 200 8C for 10 min. The injector
temperature was 200 8C. Chromatography grade helium was
used as the carrier gas. In GC calculations, all peaks
amounting to at least 0.3% of the total products were taken
into account. When necessary, chromatographic purification
were performed on columns packed with silica gel, 230–400
mesh, for flash technique. Mass spectra were recorded with
an electron beam of 70 eV.
3. Conclusions
The possibility to tune the reactivity and selectivity of MTO
in the oxidation of the carbon–carbon double bond is a
relevant tool to further generalize the use of this compound
in synthetic transformations including industrial appli-
cations. This result can be obtained performing the
oxidations in the presence of Lewis bases which act as
buffers of the reaction medium and as ligands for the metal
atom. To date, a large excess of Lewis base is necessary to
obtain high conversion of substrate and yield of product
mainly because of the low stability of the adducts of MTO
under the usual experimental conditions and the easy
oxidation of the ligands when they are free in solution.
Moreover, these catalytic systems cannot be recovered from
the reaction mixture at the end of the oxidation increasing
the cost of the process and the toxicity of wastes. In
principle, the microencapsulation technique can resolve
these problems. During the microencapsulation process the
4.1. Starting materials
Methyltrioxorhenium, hydrogen peroxide, olefins 2–4 and

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R. Saladino et al. / Tetrahedron 61 (2005) 1069–1075
monoterpene derivatives 11–13 were obtained from a
commercial source (Aldrich).
after the MnO2 addition), the suspension was filtered and the
filtrate dried over Na2SO4. After the evaporation of the
solvent, the crude product was analysed by gas chromato-
graphy–mass spectroscopy and when necessary purified by
flash-chromatography.
4.2. Synthesis of Lewis base adduct of MTO, compounds
I–III.
Lewis base adducts of MTO I–III containing the mono-
dentate ligand 4-methoxyaniline and the bidentate aromatic
and aliphatic ligands 2-methyl aminopyridine and trans-1,2-
diaminocyclohexane, respectively, were prepared as model
compounds following a synthetic procedure previously
reported in the literature.27 As a general procedure 1.0 mmol
of the appropriate monodentate ligand or 0.5 mmol of
bidentate ligands were added to 1.0 mmol of MTO in
toluene (10 mL) at room temperature. A yellow precipitate
was immediately formed. The reaction mixture was
concentrated, cooled to K35 8C and the precipitate isolated
by filtration.
4.4.2. Epoxidation with MTO and microencapsulated
Lewis base adducts of MTO mI–mIII. To the suspension
of the appropriate catalyst mI–mIII (1.0% in weight of
MTO adduct, loading factor 1.0) in 5.0 mL of CH3CN/
CH2Cl2 (ratio 1/1 v/v) at 25 8C or K10 8C (see Tables 1 and
3) was added the substrate (1.0 mmol) to be oxidised and
H2O2 (1.5 mmol, 35% aq solution). At the end of the
reaction the catalyst was recovered by filtration and washed
with CH2Cl2. MnO2 (2.0 mg) was added to degrade the
excess of primary oxidant, the suspension was again filtered
and the filtrate dried over Na2SO4. After the evaporation of
the solvent, the crude product was analysed by gas
chromatography–mass spectroscopy and when necessary
purified by flash-chromatography. Identity of products was
confirmed by 200 MHz 1H and 13C NMR and mass-
spectroscopy (EI) analyses. Spectra were compared with
those of authentic compounds. Listed data are available for
cycloalkene oxides and styrene oxide,19b a-pinene oxide,28
3-carene oxide29 and 1,2-limonene oxide.30
4.2.1. [4-(Methoxyaniline)]methyltrioxorhenium (VII)
1
(I). IR [KBr]: n (ReZO) cmK1: 909, 934, 962. H NMR
(CDCl3) d ppm: 2.56 (s, 3H), 3.39 (br. s, 2H), 3.73 (s, 3H),
6.63 (d, JZ9.16 Hz, 2H), 6.73, 6.63 (d, JZ8.13 Hz, 2H).
C8H12NO4Re calcd: C 25.80, H 3.25, N 3.76; Found C
25.93, H 3.15, N 3.74.
4.4.3. a-3,4-Epoxycarene 14. Oil, bp 182–184 8C [lit.31, bp
182 8C], dH [CDCl3, 200 MHz] 0.45 (1H, ddd, JZ2.2, 8.9,
9.1 Hz, H-1 eq), 0.53 (1H, ddd, JZ2.3, 8.9, 9.1 Hz, H-6 eq),
0.73 (3H, s, H-8), 1.01 (3H, s, H-9), 1.26 (3H, s, H-10), 1.49
(1H, dd, JZ2.2, 16.2 Hz, H-2 eq), 1.64 (1H, dt, JZ2.3,
16.4 Hz, H-5 eq), 2.15 (1H, dd, JZ9.1, 16.2 Hz, H-2 ax),
2.30 (1H, ddd, JZ1.9, 8.9, 16.4 Hz, H-5 ax), 2.85 (1H, t,
JZ1.9 Hz, H-4). dC [CDCl3, 200 MHz] 13.8 (C-1), 14.6
(C-8), 15.9 (C-6), 16.0 (C-7), 19.1 (C-5), 23.1 (C-10), 23.3
(C-2), 26.7 (C-9), 56.1 (C-3), 58.3 (C-4). MS (EI) m/z 152
(MC, 2), 137 (42), 109 (62), 91 (24), 81 (45), 67 (82), 43
(100), 39 (56).
4.2.2. [2-(Aminomethyl)pyridine]methyltrioxorhenium
(II). IR [KBr]: n (ReZO) cmK1: 908, 935. 1H NMR
(CD3CN) d ppm: 2.12 (s, 3H), 3.53 (br. s, 2H), 5.04 (d, JZ
22.0 Hz, 1H), 6.09 (d, JZ22.0 Hz, 1H), 8.19 (m, 1H), 8.30
(m, 1H), 8.83 (m, 1H), 9.23 (m, 1H). C7H11N2O3Re calcd: C
25.53, H 3.10, N 7.84; Found C 25.41, H 3.08, N 7.78.
4.3. Synthesis of microencapsulated Lewis base adduct of
MTO, compounds I–III
Microencapsualted Lewis base adduct of MTO, compounds
mI–mIII, were prepared following a modified procedure
previously reported for the synthesis of polystyrene/MTO
catalyst.19b In summary, to a suspension of 600 mg of
polystirene in 4 mL of tetrahydrofuran (THF) was added
0.3 mmol of the appropriate adduct I–III, and the mixture
was stirred for 1 h using a magnetic stirrer. Coocervates
were found to envelop the solid core dispersed in the
medium and 5.0 mL of hexane were added to harden the
capsule walls. The solvent was removed by filtration, and
the solid residue was washed with ethyl acetate and finally
dried under high vacuum. In each case, MTO had
completely become bound to the polymer. This result was
confirmed by spectroscopic analysis of the residue obtained
after evaporation of the organic layers. The catalysts were
used without any further purification.
4.4.4. a-Pinene oxide 16. Oil, bp 102–104 8C /50 mm
[lit.32, bp 102–103 8C/50 mmHg], dH [CDCl3, 200 MHz]
0.91 (3H, s, CH3), 1.30 (3H, s, CH3), 1.32 (3H, s, CH3), 1.59
(1H, m, CH), 1.72 (1H, m, CH), 1.90–2.05 (4H, m, CH2),
3.08 (1H, m, CH). dC [CDCl3, 200 MHz] 60.23 (s, C-1),
56.7 (d, C-2), 44.9 (d, C-6), 40.4 (s, C-10), 39.6 (d, C-4),
27.64 (t, C-5), 26.72 (q, C-9), 25.87 (t, C-3), 22.41 (q, C-8),
20.18 (q, C-7). MS (EI) m/z 152 (MC).
4.4.5. Limonene oxide 19. Oil, bp 113–114 8C /50 mm
[lit.33, bp 113–114 8C/50 mmHg], dH [CDCl3, 200 MHz]
4.65 (2H, m, CH2), 3.10 (1H, m, CH), 2.97 (1H, m, CH),
2.20–1.40 (6H, 3xm, CH2), 1.55 (3H, s, CH3), 1.20 (3H, s,
CH3). dC [CDCl3, 200 MHz] 20.19 (q, C-7), 22.05 (q, C-8),
25.81 (t, C-3), 28.53 (t, C-5), 30.66 (t, C-6), 40.68 (d, C-4),
57.35 (s, C-1), 59.24 (d, C-2), 109.0 (d, C-8), 148.78 (s,
C-7). MS (EI) m/z 152 (MC).
4.4. Epoxidation. General procedure
4.4.1. Epoxidation with MTO and Lewis base adducts of
MTO I–III. To the suspension of the appropriate catalyst (1
or I–III, 1.0% in weight) in 5.0 mL of CH3CN/CH2Cl2
(ratio 1/1 v/v) at 25 8C or K10 8C (see Tables 1 and 3) was
added the substrate (1.0 mmol) to be oxidised and H2O2
(1.5 mmol, 35% water solution). At the end of the reaction
MnO2 (2.0 mg) was added to degrade the excess of primary
oxidant (the reaction mixture was found to be unchanged
Acknowledgements
MIUR (PRIN COFIN 2003) is acknowledged for financial
support.

R. Saladino et al. / Tetrahedron 61 (2005) 1069–1075
1075
16. See for example: Takas, J.; Kiprof, P.; Riede, J.; Herrmann,
W. A. Organometallics 1990, 9, 782–787.
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32. Beil. 5, 152. The product was identical to an authentic
commercial sample (Aldrich, Co.).
33. Beil. 17, 44. The product was identical to an authentic
commercial sample (Aldrich, Co.).