Selective epoxidation of monoterpenes with H2O2 and polymer-supported methylrheniumtrioxide systems

Article abstract of DOI:10.1016/S0040-4020(03)01145-1

A convenient and efficient synthesis of monoterpene epoxides by application of heterogeneous poly(4-vinylpyridine)/methyl rhenium trioxide (PVP/MTO) and polystyrene/methyl rhenium trioxide (PS/MTO) systems is described. Even highly sensitive terpenic epoxides were obtained in excellent yield. Environment friendly, easily available, and low cost H₂O₂ was used as oxidant. Catalysts were stable systems for at least five recycling experiments.

Full text of DOI:10.1016/S0040-4020(03)01145-1

Tetrahedron 59 (2003) 7403–7408
Selective epoxidation of monoterpenes with H2O2 and
polymer-supported methylrheniumtrioxide systems
a
a
a
Raffaele Saladino,a,b Veronica Neri, Anna Rita Pelliccia and Enrico Mincione
,
*
a
`
Dipartimento di Agrobiologia ed Agrochimica, Universita della Tuscia, Via S. Camillo de Lellis s.n.c., 01100 Viterbo, Italy
`
INFM, Universita della Tuscia, Via S. Camillo de Lellis s.n.c., 01100 Viterbo, Italy
b
Received 17 February 2003; revised 23 June 2003; accepted 17 July 2003
Abstract—A convenient and efficient synthesis of monoterpene epoxides by application of heterogeneous poly(4-vinylpyridine)/methyl
rhenium trioxide (PVP/MTO) and polystyrene/methyl rhenium trioxide (PS/MTO) systems is described. Even highly sensitive terpenic
epoxides were obtained in excellent yield. Environment friendly, easily available, and low cost H2O2 was used as oxidant. Catalysts were
stable systems for at least five recycling experiments.
q 2003 Elsevier Ltd. All rights reserved.
Terpenes are the basis for many of perfumes, detergents,
flavours, agrochemicals, and therapeutically active sub-
stances.1 In terpene chemistry the oxidative functionaliza-
tion often starts with a selective epoxidation. The most
commonly employed stoichiometric oxidants for this
synthesis are organic peroxy acids that produce wastes
and are not selective for the preparation of acid-sensitive
epoxides.2 To avoid these problems, catalytic systems
including tungsten compounds,3 titanium-silica and alumina
supported catalysts,4 peroxotungstophosphate (PCWP),5
molybdenum, vanadium, and manganese complexes,6 and
metalloporphyrins,7 have been used with varying degrees of
success as well as limitations due to side reactions. Thus,
there is a great interest in developing more efficient
catalysts, mainly heterogeneous systems, for the selective
synthesis of terpenic epoxides. In the last years methyl
rhenium trioxide (CH3ReO3, MTO)8 has been shown to
possess interesting catalytic properties in oxidation reac-
tions with hydrogen peroxide (H2O2) as oxygen atom
donor.9 The epoxidation of alkenes has been extensively
studied.10 The active catalytic forms are a monoperoxo
reactivity failed, probably because of the decomposition of
the catalyst.13 Recently, with the aim to develop clean
oxidation processes, we described the preparation and
characterization of novel heterogeneous rhenium com-
pounds of general formula (polymer)f /(MTO)g (the f/g
quotient express the ratio by weight of the two components)
by heterogenation of MTO on poly(4-vinylpyridine) and
polystyrene,14 applying an extension of the ‘mediator’
concept,15 and of the microencapsulation technique,16
respectively. All the new MTO compounds were charac-
terized by FT-IR, scanning electron microscopy (SEM), and
wide-angle X-ray diffraction (WAXS).14 Apart from silica
supported MTO complexes,17 and a NaY zeolite/MTO
supercage system,18 no further data is available in the
literature about heterogeneous MTO catalysts. Polymer/
MTO catalysts are efficient and selective systems for the
epoxidation of simple olefins,14 and for the oxidation of
substituted phenol and anisole derivatives to ortho- and
para-benzoquinones.19 We report here on the applicability
of different polymer/MTO systems, poly(4-vinylpyridine)
2% and 25% cross-linked (with divinylbenzene)/MTO
(PVP-2%/MTO 1 and PVP-25%/MTO 2, respectively),
poly(4-vinylpyridine-N-oxide) 2% cross-linked/MTO
(PVPN-2%/MTO 3) and microencapsulated polystyrene
2% cross-linked/MTO (PS-2%/MTO 4), to the H2O2
selective epoxidation of monoterpenes, including acid-
sensitive ones. The structure of poly(4-vinylpyridine)/
MTO and polystyrene/MTO catalysts 1–4 is represented
in the schematic drawing in Figure 1.
metal [MeRe(O)2(O2)] and
a
bisperoxo metal
[MeRe(O)(O2)2] complex and/or their adducts with solvent
molecules.10h In this context, epoxidation of monoterpenes
with MTO was described in homogeneous phase using urea/
hydrogen peroxide adduct (UHP) as anhydrous oxygen
atom donor,11 or an excess of pyridine as Lewis base
mediator of the oxidation.12 MTO epoxidation of mono-
terpenes in fluorinated solvents, that usually increase the
Epoxidation with H2O2 were investigated using geraniol,
nerol, S-(þ)-carene, R-(þ)-limonene and 1 (R)-a-pinene, as
representative model substrates. As a general procedure, the
terpene (1 mmol) to be oxidized and H2O2 (1.2 mmol, 35%
water solution) were added to a suspension of the catalyst
Keywords: terpenic epoxides; epoxidation; a-pinene oxide.
*
Corresponding author. Address: Dipartimento di Agrobiologia ed
`
Agrochimica, Universita della Tuscia, Via S. Camillo de Lellis s.n.c.,
01100 Viterbo, Italy. Tel.: þ39-761-357284; fax: þ39-761-357242;
e-mail: saladino@unitus.it
0040–4020/$ - see front matter q 2003 Elsevier Ltd. All rights reserved.
doi:10.1016/S0040-4020(03)01145-1

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R. Saladino et al. / Tetrahedron 59 (2003) 7403–7408
Figure 1. Structures of polymer supported MTO catalysts.
(loading factor 1.0) in CH2Cl2/CH3CN (5 mL, 1:1 v/v), and
the mixture was stirred at room temperature. In the tests for
the recyclability of catalysts 1–4, the solid was separated by
filtration, washed with CH3CN, dried and then reused in
another reaction as described above. The oxidation results
are summarized in Table 1 and Schemes 1 and 2. In the
absence of the catalyst, less than 5% conversion of
substrates took place under otherwise identical conditions.
Previously performed terpene epoxidation with MTO in
homogeneous phase11,12 were used as references (Table 1,
entries 1, 6, 11, 16, 17, and 22). The oxidation of
monoterpenes geraniol 5, and nerol 6, afforded 6,7-
epoxides, 5a and 6a as main products, in which the non-
allylic double bonds were selectively oxidized. Only low
amounts of 2,3-epoxides 5b–6b, and diepoxides 5c–6c,
were recovered in the reaction mixture (Table 1, entries 2–5
and 7–10; Scheme 1). The regioselectivity demonstrated in
the oxidation of 5 and 6, is consistent with the results of
MTO in homogeneous phase, in which case double bonds
with the highest HOMO coefficients are oxidized (Table 1,
entries 1 and 6).20 Products of nucleophilic ring opening of
the oxiranyl ring or acidic rearrangement of geraniol and
nerol epoxides21 were not recovered under our experimental
conditions. Treatment of 5 with 1 afforded 5a as the main
product in 90% conversion and 77% yield (Table 1, entry 2).
In a similar way, the oxidation performed with catalysts 2–4
Table 1. Polymer-supported MTO catalysed epoxidation of monoterpenes 5–9
Entry
Catalysta
Reaction time (h)
Substrate
Conversion(%)
Products(Yield)b
1
2
3
4
5
6
7
8
MTO/pyridinec
1
2
3
1.0
1.0
1.0
1.5
1.0
0.5
1.0
1.5
1.5
1.0
1.0
3.5
2.5
2.5
3.0
1.0
1.0
2.0
0.5
1.0
1.5
1.0
1.5
1.5
5
5
5
5
5
6
6
6
6
6
7
7
7
7
7
8
8
8
8
8
8
9
9
9
92
90
90
92
96
89
90
.98
95
.98
.98
68
.98
75
.98
–
–
76
81
70
.98
96
75
79
5a(66), 5b(6), 5c(11)
5a(77), 5b(8), 5c(5)
5a(74), 5b(7), 5c(7)
5a(79), 5b(5), 5c(3)
5a(82), 5b(3), 5c(6)
6a(62), 6b(6), 6c(13)
6a(87), 6b(6), 6c(1)
6a(83), 6b(4), 6c(4)
6a(88), 6b(3), 6c(2)
6a(81), 6b(6), 6c(3)
7a(75)
7a(85)
7a(96)
7a(84)
7a(91)
8a(6)
8a(90)
8a(95)
8a(88)
4
MTO/pyridinec
1
2
3
4
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
MTO/pyridined
1
2
3
4
MTOc
MTO/pyridinec
1
2
3
4
8a(98)
8a(.98)
9a(79), diepoxide(13)
9a(83)
9a(89)
MTO/pyridinec,e
1
2
All the reaction were performed in CH2Cl2/CH3CN (5 mL, 1:1 v/v) at room temperature, with H2O2 (35% aqueous solution), using a value of the catalyst
loading factor of 1.0.
a
Catalyst: PVP-2%/MTO 1, PVP-25%/MTO 2, PVPN-2%/MTO 3, PS-2%/MTO 4.
Refers to isolated materials.
b
c
Epoxide yields in the reaction of monoterpenes with H2O2 (35% aqueous solution) in THF or CH2Cl2 at room temperature catalyzed by MTO and
MTO/pyridine; Ref. 12.
Reaction performed under the experimental conditions described in Ref. 12.
(1,2):(8,9) epoxide¼98:2; cis (1,2): trans (1,2) epoxide¼1.3:1.0.
d
e

R. Saladino et al. / Tetrahedron 59 (2003) 7403–7408
7405
Scheme 1.
gave 5a in 90–96% conversions, and 75–82% yields,
respectively (Table 1, entries 3–5).
with microencapsulated catalyst 4, in the fifth recycling step
the conversion was appreciably reduced, probably because
of a partial decomposition of MTO.14 Active methyl-
(oxo)bis(h2-peroxo)rhenium(VII)/ligand intermediates
have been prepared and characterized in homogeneous
phase.10h,23 In our case, catalytic activity was again
observed when poly(4-vinylpyridine) and poly(4-vinyl-
pyridine-N-oxide) were added to a solution where the
rhenium peroxo species was already formed. This result
indicates that the bisperoxo metal [MeRe(O)(O2)2] complex
is stable in the presence of selected organic supports.
Under similar experimental conditions at least the same
extent of conversions of 6 and yields of 6a were achieved,
with 1 and 4 being the most selective catalysts (Scheme 1,
Table 1, entries 7–10). All polymer-supported MTO
systems showed a high regiospecificity in the oxidation of
6. In a test for checking the leaching of catalysts, the
oxidation of 5 with catalyst 1 was stopped at ca. 50%
conversion.22 After centrifugation the colourless solution
lost the catalytic activity. Table 2 shows that poly(4-
vinylpyridine)/MTO catalysts are stable enough to perform
al least five recycling experiments with similar conversion
and selectivity. Even if only a very slight decrease in
activity occurs during the first four recycling experiments
The oxidation of S-(þ)-carene 7 with catalyst 1 gave the
trans-3,4-epoxycarene 7a as the only recovered product in
68% conversion and 85% yield (Scheme 2, Table 1, entry
12). The oxidation was selective and no traces of cis-3,4-
epoxycarene or the corresponding diols were recovered in
the reaction mixture. Better results were obtained with
catalysts 2 and 4 (Table 1, entries 13 and 15), while 3
showed reactivity similar to 1 (Table 1, entry 14). It is
noteworthy that in the oxidation of 7, catalysts 1–4 were
more selective than MTO (Table 1, entry 11). These results
are in accord with the higher selectivity of polymer-
supported /MTO systems with respect to MTO in the
oxidation of cardanol derivatives, in part explained on the
Table 2. Stability of polymer-supported MTO catalysts in the oxidation of 5
Catalysta
Conversion (%)b
Run. no. 1 Run. no. 2 Run. no. 3 Run. no. 4 Run. no. 5
1
2
3
4
90 (77)c
90 (74)
92 (79)
96 (82)
89 (78)
90 (74)
91 (79)
96 (82)
91 (77)
89 (72)
93 (78)
95 (80)
90 (76)
88 (71)
90 (77)
91 (79)
91 (77)
90 (73)
92 (77)
81 (75)
The reaction were performed in CH2Cl2:CH3CN 1:1 (v/v) (5 mL) at 20%
with H2O2 (35% aqueous solution) using a value of the catalysts loading
factor of 1.0.
a
Catalyst: PVP-2%/MTO 1, PVP-25%/MTO 2, PVPN-2%/MTO 3,
PS-2%/MTO 4.
Values of 5a yields are given in parentheses and are normalized to 100%
of conversion.
The reaction were performed in CH2Cl2:CH3CN 1:1 (v/v) (5 mL) at 20%
with H2O2 (35% aqueous solution) using a value of the catalysts loading
factor of 1.0.
b
c
Scheme 2.

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R. Saladino et al. / Tetrahedron 59 (2003) 7403–7408
basis of supramolecular interactions between substrates and
the heterogeneous catalyst.19 Highly sensitive terpenic
epoxides, such as a-pinene oxide, can be obtained in
excellent yield using polymer supported MTO catalysts.
Thus, the oxidation of 1(R)-a-pinene 8 with 1 afforded
a-pinene oxide 8a in 76% conversion and 95% yield as the
only recovered product (Scheme 2, Table 1, entry 18). When
the reaction was performed with 2 and 3, epoxide 8a was
again obtained as the only recovered product in 81 and 70%
conversion, and 88 and 98% yields, respectively (Table 1,
entries 19 and 20). In this case, microencapsulated 4 was the
best catalytic system affording 8a in quantitative conversion
and yield (Table 1, entry 21). Products of oxiranyl ring-
opening (pinanediol) or oxiranyl ring rearrangement
(campholenic aldehyde, isopinocamphone) were not
recovered in the reaction mixture.
packed with silica gel, 230–400 mesh, for flash technique.
Mass spectra were recorded with an electron beam of
70 eV.
1.1. Starting materials
Poly(4-vinylpyridine)/MTO and polystyrene/MTO catalysts
were prepared as previously reported.14 In summary, to a
suspension of 600 mg of the appropriate resin in 4 mL of
ethanol (tetrahydrofuran in the case of polystyrene) was
added 77 mg (0.3 mmol) of MTO, 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. The suspension was stirred for 1 h at this
temperature and then slowly cooled to 08C. 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
catalyst was used without any further purification. Terpene
derivatives 5–9 were obtained from a commercial source
(Aldrich).
A higher selectivity of heterogeneous MTO compounds
with respect to MTO was further observed in the oxidation
of R-(þ)-limonene 9 with 1 (Scheme 2). The trans-1,2-
epoxide 9a was obtained as the only recovered product in
75% conversion and 83% yield (Table 1, entry 23). Similar
results were obtained in the oxidation of 9 with 2 (Table 1,
entry 24). On the other hand, almost equal amount of cis-
and trans-limonene oxides were recovered in the epoxida-
tion with homogeneous MTO (Table 1, entry 22).12,21 In
conclusions, poly(4-vinylpyridine)/MTO and polystirene/
MTO systems are efficient and selective catalysts for the
conversion of monoterpenes to the corresponding epoxides,
using environment friendly, easily available, and low cost
H2O2 as the oxygen atom donor. All catalysts were stable
systems for at least fives recycling experiments and values
of the loading factor of the catalyst higher than 1.0 did not
give an appreciable increase in the conversion of substrates.
Irrespective of the catalyst used, the oxidation of allylic
monoterpenes 5 and 6 proceeds selectively at the more
electron-rich 6,7-double bond in accord with the electro-
philic character of the oxidant. To the best of our knowledge
this is the first example described in the literature of
heterogeneous catalysts with a peroxy acids like regio-
selectivity in the epoxidation of allylic monoterpenes.4–6 In
the oxidation of cyclic monoterpenes 7 and 9 polymer-
supported MTO catalysts showed, in some cases, a higher
reactivity and facial selectivity than their homogenous
counterpart.
1.2. Synthesis of terpene epoxides. General procedure
To the suspension of 146 mg of the appropriate catalyst
(loading factor 1.0) in 5.0 mL of CH3CN/CH2Cl2 (ratio 1:1
v/v) at 258C were added the terpene (1 mmol) to be oxidised
and H2O2 (1.2 mmol, 35% water solution). The suspension
was filtered and the recovered catalyst washed with ethyl
acetate. After drying under high vacuum, the catalyst was
used for further reaction to evaluate its stability. The solvent
was 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 epoxide 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
a-pinene oxide,23 epoxygeraniols,7 epoxynerols,7 3-carene
oxide,25 and 1,2-limonene oxide.24,25
1.2.1. 6,7-Epoxygeraniol 5a. Oil, bp 243–2448C [lit.,26 bp
2438C], dH [CDCl3, 200 MHz] 1.24–1.35 and 1.73–1.80
(2H, 2£m, H-5), 1.31 and 1.35 (6H, 2£s, H-8,9), 1.73 (3H, s,
H-10), 2.06–2.34 (2H, m, H-4), 2.73 (1H, s broad, H-6),
4.23 (2H, s broad, H-1), 5.49 (1H, s broad, H-2). dC [CDCl3,
200 MHz] 16.2 (C-10), 18.7, 24.8 and 27.1 (C-5, 8, 9), 36.3
(C-4), 58.6 (C-1), 59.4 (C-7), 64.1 (C-6), 124.6 (C-2), 138.8
(C-3). MS (EI) m/z 170 (Mþ, 1), 97 (22), 81 (75), 71 (52), 59
(95), 41 (100).
1. Experimental
All commercial products were of the highest grade available
and were used as such. Hydrogen peroxide was a 35%
aqueous solution (Aldrich). NMR spectra were recorder on a
Bruker (200 MHz). Gas chromatography and gas chroma-
tography-mass spectroscopy (GC-MS) of the reaction
1.2.2. 2,3-Epoxygeraniol 5b. Oil, bp 238–2418C [lit.,27 bp
2388C], dH [CDCl3, 200 MHz] 1.30 (3H, s, H-10), 1.28–
1.32 and 1.42–1.52 (2H, 2£m, H-5), 1.61 (3H, s, H-8), 1.68
(3H, d, J¼1.2 Hz, H-9), 2.04–2.12 (2H, m, H-4), 2.98 (1H,
m, H-2), 3.66 (1H, m, H-1), 3.82 (1H, m, H-1), 5.08 (1H, m,
H-6). dC [CDCl3, 200 MHz] 16.6 (C-10), 17.5, 23.6 and
25.6 (C-5, 8, 9), 38.4 (C-4), 61.2 (C-3), 61.3 (C-1), 63.1
(C-2), 123.2 (C-6), 132.0 (C-7). MS (EI) m/z 170 (Mþ, 1),
95 (22), 82 (34), 67 (61), 55 (33), 41 (100).
products were performed using
a
SPB column
(25 m£0.30 mm and 0.25 mm film thickness) and iso-
thermal temperature profile of 808C for the first 2 min,
followed by a 108C/min temperature gradient to 2008C for
10 min. The injector temperature was 2008C. Chromato-
graphy 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

R. Saladino et al. / Tetrahedron 59 (2003) 7403–7408
7407
1.2.3. 2,3,6,7-Diepoxygeraniol 5c. Oil, bp 258–2618C, dH
[CDCl3, 200 MHz] 1.25–1.34 (9H, 3£s, H-8, 9, 10), 1.21–
1.33 and 1.53–1.90 (4H, m, H-4,5), 2.75 (1H, s broad, H-6),
3.01 (1H, s broad, H-2), 3.73–3.82 (2H, m, H-1). dC
[CDCl3, 200 MHz] 16.5 (C-10), 18.6, 24.6, 29.7 (C-5, 8, 9),
35.65 (C-4), 60.7, 62.5, 63.5, 64.3, 64.6 (C-1,2,3,6,7). MS
(EI) m/z 186 (Mþ, 1), 111 (15), 84 (47), 71 (37), 59 (30), 53
(100).
[lit.,30 bp 113–1148C/50 mm], dH [CDCl3, 200 MHz] 4.65
(2H, m, CH2), 3.10 (1H, m, CH), 2.97 (1H, m, CH), 2.20–
1.40 (6H, 3£m, 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 (Mþ).
1.2.4. 6,7-Epoxynerol 6a. Oil, bp 243–2458C [lit.,26 bp
2438C], dH [CDCl3, 200 MHz] 1.31 (3H, s, H-8), 1.28 (3H,
s, H-9), 1.52–1.81 (2H, m, H-5), 1.78 (3H, s broad, H-10),
2.18–2.34 (2H, m, H-4), 2.74 (1H, dd, J¼5.1, 7.7 Hz, H-6),
4.07–4.21 (2H, m, H-1), 5.52 (1H, t, J¼7.2 Hz, H-2). dC
[CDCl3, 200 MHz] 18.8 and 24.8 (C-8,9), 23.3 (C-10), 26.9
(C-5), 28.4 (C-4), 58.8 (C-1), 58.9 (C-7), 63.8 (C-6), 125.2
(C-2), 138.9 (C-3). MS (EI) m/z 170 (Mþ, 3), 153 (34), 143
(66), 125 (41), 110 (63), 81 (89), 71 (93), 59 (100).
References
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ddd, J¼7.2, 9.7, 13.8 Hz, H-5), 1.62–1.75 (1H, m, H-5),
1.62 (3H, s, H-8), 1.69 (3H, s, H-9), 1.99–2.19 (2H, m,
H-4), 2.97 (1H, dd, J¼4.3, 6.9 Hz, H-2), 3.66 (1H, dd,
J¼6.9, 12.1 Hz, H-1), 3.82 (1H, dd, J¼4.3, 12.1 Hz, H-1),
5.10 (1H, tq, J¼1.3, 7.2 Hz, H-6). dC [CDCl3, 200 MHz]
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58.8 (C-1), 58.9 (C-7), 63.8 (C-6), 125.2 (C-2), 138.9 (C-3).
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[CDCl3, 200 MHz] 1.30–1.37 (9H, 3£s, H-8,9,10), 1.54–
1.87 (4H, m, H-4,5), 2.74–2.81 (1H, m, H-6), 2.98–3.05
(1H, m, H-2), 3.76 (2H, m, H-1). dC [CDCl3, 200 MHz]
18.6, 22, 23.1 and 28.9 (C-5-8-9-10), 29.4 (C-4), 59.3, 60.5
and 61 (C-1, 3, 7), 63.6 and 64 (C-2,6). MS (EI) m/z 186
(Mþ, 1), 173 (4), 167 (8), 149 (12), 143 (54), 125 (40), 111
(59), 97 (55), 85 (93), 71 (96), 59 (100).
´
Simo˜es, M. M. Q.; Silva, A. M. S.; Tome, A. C.; Cavaleiro,
J. A. S.; Tagliatesta, P.; Crestini, C. J. Mol. Catal. A: Chem.
2001, 172, 33–42.
8. Beattie, I. R.; Jones, P. J. Inorg. Chem. 1979, 18, 2318.
9. (a) Herrmann, W. A.; Fischer, R. W.; Marz, D. W. Chem. Rev.
1997, 97, 3197–3246. (b) Kuhn, F. E.; Santos, A. M.;
Goncalves, I. S.; Ro˜mao, C. C.; Lopes, A. D. Appl. Org. Chem.
2001, 15, 43–50.
10. See for example: (a) Al-Ajlouni, A. M.; Espenson, J. H. J. Org.
Chem. 1996, 61, 3969–3976. (b) Gisdakis, P.; Antonczak, S.;
1.2.7. a-3,4-Epoxycarene 7a. Oil, bp 182–1848C [lit.,28 bp
1828C], dH [CDCl3, 200 MHz] 0.45 (1H, ddd, J¼2.2, 8.9,
9.1 Hz, H-1 eq), 0.53 (1H, ddd, J¼2.3, 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, J¼2.2, 16.2 Hz, H-2 eq), 1.64 (1H, dt, J¼2.3,
16.4 Hz, H-5 eq), 2.15 (1H, dd, J¼9.1, 16.2 Hz, H-2 ax),
2.30 (1H, ddd, J¼1.9, 8.9, 16.4 Hz, H-5 ax), 2.85 (1H, t,
J¼1.9 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
(Mþ, 2), 137 (42), 109 (62), 91 (24), 81 (45), 67 (82), 43
(100), 39 (56).
¨
¨
Kostlmeier, S.; Herrmann, W. A.; Rosch, N. Angew. Chem.,
Int. Ed. Engl. 1998, 37, 2211. (c) Adam, W.; Mitchell, C. M.
Angew. Chem., Int. Ed. Engl. 1996, 35, 533–535. (d) Saladino,
R.; Carlucci, P.; Danti, M. C.; Crestini, C.; Mincione, E.
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Fischer, R. W.; Rauch, M. U.; Scherer, W. J. Mol. Catal. 1994,
`
86, 243–266. (f) Coperet, C.; Adolfsson, H.; Sharpless, K. B.
J. Chem. Soc., Chem. Commun. 1997, 1915. (g) Ferreira, P.;
Xue, W.-M.-; Bencze, E.; Herdtweck, E.; Ku¨hn, F. E. Inorg.
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R. W.; Scherer, W.; Rauch, M. U. Angew. Chem., Int. Ed.
Engl. 1993, 32, 1157–1160. For recent computational studies
on MTO epoxidation see: (i) Gisdakis, P.; Yudanov, I. V.;
1.2.8. a-Pinene oxide 8a. Oil, bp 102–1048C /50 mm
[lit.,29 bp 102–1038C/50 mm], 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 (Mþ).
¨
Rosch, N. Inorg. Chem. 2001, 40, 3755–3765. (j) Di Valentin,
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C.; Gandolfi, R.; Gisdakis, P.; Rosch, N. J. Am. Chem. Soc.
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´ ´
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2002, 43, 1001–1003.

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1
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commercially sample (Aldrich, Co.).