Dimethyl carbonate: an environmentally friendly solvent for hydrogen peroxide (H2O2)/methyltrioxorhenium (CH3ReO3, MTO) catalytic oxidations

Article abstract of DOI:10.1016/j.tet.2007.04.039

Environmentally friendly oxidations of various organic compounds with the hydrogen peroxide (H₂O₂)/methyltrioxorhenium (CH₃ReO₃, MTO) catalytic system have been described in dimethyl carbonate (DMC), a cheap commercially available and benign chemical having interesting solvating properties, low toxicity and high biodegradability. Oxidations proceeded with good conversions and in good yields. Spectrophotometric analysis demonstrated that the [CH₃ReO(O-O)₂] complex was formed in DMC and that it was stable for several days at room temperature.

Full text of DOI:10.1016/j.tet.2007.04.039

Tetrahedron 63 (2007) 6895–6900
Dimethyl carbonate: an environmentally friendly solvent
for hydrogen peroxide (H O )/methyltrioxorhenium
2
2
(CH ReO , MTO) catalytic oxidations
3 3
a,b,*
a,b a,b
Enrico Mincione, Maurizio Barontini, Fernanda Crisante,
a,b
Roberta Bernini,
c
Giancarlo Fabrizi and Augusto Gambacorta
d
a
Dipartimento di Agrobiologia e Agrochimica, Universit aꢀ degli Studi della Tuscia, Via S. Camillo De Lellis snc, 01100 Viterbo, Italy
Unit aꢀ di Ricerca VT2, Consorzio Interuniversitario La Chimica per l’Ambiente, Via della Libert aꢀ 5/12, 30175 Marghera (VE), Italy
b
c
Dipartimento di Studi di Chimica e Tecnologia delle Sostanze Biologicamente Attive, Universit aꢀ degli Studi di Roma La Sapienza,
P.le A. Moro 5, 00185 Roma, Italy
d
Dipartimento di Ingegneria Meccanica e Industriale, Universit aꢀ Roma Tre, Via della Vasca Navale 79, I-00146 Roma, Italy
Received 12 January 2007; revised 24 March 2007; accepted 12 April 2007
Available online 19 April 2007
Abstract—Environmentally friendly oxidations of various organic compounds with the hydrogen peroxide (H O )/methyltrioxorhenium
2
2
(
3 3
CH ReO , MTO) catalytic system have been described in dimethyl carbonate (DMC), a cheap commercially available and benign chemical
having interesting solvating properties, low toxicity and high biodegradability. Oxidations proceeded with good conversions and in good
yields. Spectrophotometric analysis demonstrated that the [CH ReO(O–O) ] complex was formed in DMC and that it was stable for several
days at room temperature.
3
2
Ó 2007 Elsevier Ltd. All rights reserved.
1
. Introduction
Moreover, diluted aqueous solutions of hydrogen peroxide
are stable and they can be easily handled and stored. Cata-
lysts known to activate hydrogen peroxide include: iron
Oxidations of organic compounds are very useful reactions
in the fine-chemicals industry. Stoichiometric oxidants such
as chromium(VI) salts, ceric ammonium nitrate (CAN),
nitric acid, thallium (III) nitrate, hypervalent iodine(III),
dipotassium nitrosodisulfonate (Fremy’s salt), potassium
permanganate, silver(I) oxide/nitric acid and m-chloroper-
benzoic acid have been widely employed in the past.
However, these systems have drawbacks due to their toxic-
ity, high reaction temperature and use of acidic or basic
3
4
and manganese porphyrins, phthalocyanines, iron amide
complexes, TAML, selenoxides, polyoxometallates,
5
6
7
8
9
titanium silicalite, tungsten, molybdenum and vanadium
complexes and Sn-zeolite beta.
1
0
11
During the last decade, a large number of scientific papers
have been published about the use of an organometallic rhe-
nium compound, methyltrioxorhenium (CH ReO , MTO) 1,
3
12
3
1
conditions.
as efficient activator for hydrogen peroxide. At room tem-
ꢀ
14
and soluble in many organic solvents and in ionic liquids.
perature, it is a colourless solid, thermally stable to 300 C
1
3
In recent years, increasingly stringent environmental re-
quirements have led to a great interest in the application of
sustainable and green oxidations. Convenient and environ-
mentally friendly oxygen atom donors such as molecular
oxygen and hydrogen peroxide have attracted considerable
attention. In particular, the role of hydrogen peroxide in or-
ganic synthesis has grown steadily over the years. The use
of this oxidant is particularly attractive, both for its high
oxygen content and the formation of water as a byproduct.
1
5
MTO was first synthesized in a small scale (milligrams)
but successively more efficient synthetic procedures have
1
6
been reported. Recently, a new large-scale (until 1200 g)
and economically advantageous synthesis of MTO has been
described.
2
17
The mechanism of MTO-catalyzed oxidations is based on
the formation of two peroxo complexes of stoichiometry
[CH ReO (O–O)] 2 and [CH ReO(O–O) ] 3 (Scheme 1).
3 2 3 2
Experiments with the isolated complex 3 have shown that
it is the active species in oxidation catalysis. In contrast, the
complex 2 has never been isolated and exists only in equili-
Keywords: Dimethyl carbonate; Green oxidations; Hydrogen peroxide
(H O )/methyltrioxorhenium (CH ReO , MTO).
2 2 3 3
*
Corresponding author. Tel.: +39 761 357452; fax: +39 761 357242;
e-mail: berninir@unitus.it
1
8
brium with MTO and 3.
0
040–4020/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2007.04.039

6896
R. Bernini et al. / Tetrahedron 63 (2007) 6895–6900
3
0
O
O
O
oxidations has been performed in DMC, as a reaction
medium, in organic synthesis. In this paper we investigated
the applicability of the hydrogen peroxide/methyltrioxorhe-
nium catalytic system using DMC as solvent for the oxida-
tion of a wide range of organic compounds.
O
O
H2O2
O
O
O
H2O2
O
O
O
O
Re
CH3
1
Re
Re
H3C
CH
3
2
3
Scheme 1. The hydrogen peroxide/methyltrioxorhenium catalytic system.
2
. Results and discussion
The hydrogen peroxide/methyltrioxorhenium catalytic sys-
tem has been widely used in a variety of synthetic transfor-
1
2
Before investigating the oxidation reactions, the formation
and the stability of the diperoxo complex [CH ReO(O–
O) ] 3 in DMC have been evaluated. We performed these
mations. Our research group has performed oxidative
modifications of natural organic compounds to obtain bio-
active compounds. Recently, we have investigated these
3
1
9
2
2
0–22
studies by conventional UV–vis spectroscopy. On treatment
of MTO in DMC with an excess of hydrogen peroxide (35%
water solution), a yellow solution was obtained. As in other
reactions in alternative solvents such as ionic liquids.
Continuing our research with the aim to lower the environ-
mental impact of these oxidations, we turned our attention
to dimethyl carbonate (DMC), a chemical produced through
3
1
14
organic solvents and in ionic liquids, the maximum of
ꢁ1
ꢁ1
2
3
absorbance at l¼360 nm (3¼1186 M cm ) can be attrib-
uted to the diperoxo complex 3 (Fig. 1). Spectrophotometric
determinations of absorbance at this fixed wavelength con-
firmed that the complex 3 is stable for several days at
room temperature. Probably, the DMC, a highly oxygenated
compound, has the ability to complex and to stabilize the
methyltrioxorhenium catalyst.
a green catalytic process by Enichem (Italy). Its low toxic-
ity, the absence of irritating or mutagenic effects associated
with it and its high biodegradability qualify DMC as an
2
4
environmentally friendly chemical (Table 1).
2
5
As extensively reported by Tundo et al., in organic synthe-
sis, DMC is a well known reagent used as benign substitute
for hazardous and toxic reagents such as dimethyl sulfate,
methyl iodide and phosgene. In fact, in the presence of a nu-
cleophile and in basic conditions, DMC exhibits a versatile
and tunable chemical reactivity, depending on the experi-
After verifying the stability of the diperoxo complex, we in-
vestigated the oxidation reactions of different model organic
compounds using the H O /CH ReO catalytic system in
2
2
3
3
DMC as solvent. Experimental conditions and results of
the reactions are shown in Table 2. All substrates are soluble
in DMC. When the oxidations were carried out under iden-
tical conditions but omitting the catalyst, products were
formed only in traces (<5%).
mental conditions. In particular, at the reflux temperature
ꢀ
(
90 C), it can react as a methoxycarbonylating agent; at
ꢀ
agent. Both reactions generate methanol as byproduct that
ꢀ
T>120 C (usually T¼160 C) it acts as a methylating re-
2
6
can be recycled for the same production of DMC, avoiding
the formation of unwanted inorganic salts and the related
disposal problems.
MTO has been successfully described as an efficient olefin
epoxidation catalyst. Its reactivity in this oxidation depends
on several factors such as the polarity of the solvent and the
presence of an appropriate amount of heterocyclic base
In biocatalysis, a chemoenzymatic epoxidation of alkenes
A
2
7
with DMC and hydrogen peroxide has been reported.
3
2
33
34
(
pyridine, 3-cyanopyridine, pyrazole ). We epoxidized
monoperoxy carbonic acid methyl ester was generated in
situ under neutral conditions by lipase-catalyzed perhydro-
lysis of dimethyl carbonate with hydrogen peroxide. Blank
experiments without enzyme gave no measurable amount
of this species. Furthermore, DMC has found many indus-
trial applications in the field of natural leather coating, metal
cleaning, degreasing in textiles and tanning and polymer
styrene in DMC as an example (Table 2, entry 1). The alkene
was added to a solution of urea hydrogen peroxide adduct
(UHP)/methyltrioxorhenium in DMC at room temperature.
After 16 h, styrene oxide was obtained in quantitative con-
version and yield. No heterocyclic bases were needed to in-
crease the selectivity of the oxidation and to modulate the
activity of the catalyst. The conversion and yield were
similar to the oxidation performed in an ionic liquid solu-
2
8
coating. In the pharmaceutical industry, it is used as an
extraction solvent replacing toluene.
3
5
tion but a lower amount of the catalyst was used with
DMC as solvent.
To the best of our knowledge, only palladium-catalyzed
cyclocarbonylation reactions and ruthenium tetraoxide
2
9
1
0
.2
.6
0
2
3
Table 1. Toxicological and ecotoxicological properties of DMC
Property
Value
Oral acute toxicity (rats)
Acute toxicity per contact (cavy)
Acute toxicity per inhalation (rats)
Mutagenic properties
LD50 13.8 g/kg
LD50>2.5 g/kg
LC50 140 mg/L (4 h)
None
None
>90% (28 days)
NOEC 1000 mg/L
Irritating properties (rabbits, eyes, skin)
Biodegradability
Acute toxicity (fish)
a
2
8
0
3
50
420
Acute toxicity on aerobic bacteria
of wastewaters
EC50>1000 mg/L
wavelength (nm)
Figure 1. UV–vis spectrum of MTO 1 (- - - -) and of diperoxo complex 3
(—) in DMC. Conditions: 0.93 mM MTO, 42 mM H , room temperature.
a
NOEC¼concentration, which does not produce any effect.
2 2
O

R. Bernini et al. / Tetrahedron 63 (2007) 6895–6900
6897
Table 2. Catalytic oxidations with hydrogen peroxide (H
2
O
2
)/methyltrioxorhenium (CH
3
ReO ) in DMC as solvent
3
a
a
Entry
Starting material
Experimental conditions
Conv. (%)
Products (yield %)
1
2
3
4
5
Styrene
UHP (2 equiv), MTO (0.5%), rt, 16 h
>98
>98
>98
>98
>98
Styrene oxide (>98)
ꢀ
2,3-Dimethylnaphthalene
3,5-Dimethylphenol
Diphenylmethanol
Diphenyl sulfide
H
H
H
H
2
O
2
O
2
O
2
O
2
2
2
2
(10 equiv), MTO (5%), 60 C, 20 h
ꢀ
2,3-Dimethyl-1,4-naphthoquinone (>98)
2,6-Dimethyl-1,4-benzoquinone (80)
Benzophenone (60)
Diphenyl sulfoxide (90)
Diphenyl sulfone (10)
Hydroquinone (75)
p-Benzoquinone (25)
4-Oxohomoadamantan-5-one (>98)
(3 equiv), MTO (2%), 60 C, 7 h
(2 equiv), MTO (5%), rt, 4.5 h
ꢀ
(1 equiv), MTO (1%), 50 C, 3 h
ꢀ
6
p-Hydroxybenzaldehyde
H
H
2
O
O
2
2
(2 equiv), MTO (2%), 50 C, 2.5 h
>98
>98
ꢀ
7
Adamantanone
2
(2 equiv), MTO (2%), 60 C, 3.5 h
a
GC–MS conversions and yields.
The oxidation of arenes with hydrogen peroxide/methyl-
trioxorhenium was generally performed in glacial acetic
(35% water solution) and a low amount of MTO (Table 2,
entry 5). The diphenyl sulfone was obtained in low yield
(10%).
3
6
37
acid or acetic acid/acetic anhydride, with concentrated
85%) hydrogen peroxide and at elevated temperatures. In
(
a neutral solvent such as DMC, 2,3-dimethylnaphthalene
was quantitatively converted into the corresponding 2,3-
dimethyl-1,4-naphthoquinone after 20 h with MTO and an
excess of hydrogen peroxide 35% water solution (Table 2,
entry 2).
Oxidative synthesis of phenols from o,p-hydroxy or
o,p-methoxybenzaldehydes has been performed in tradi-
tional solvents and in ionic liquids solution. p-Hydroxy-
benzaldehyde in DMC was converted into the corresponding
hydroquinone (yield: 75%) and p-benzoquinone (yield:
4
1
21
25%). Oxidation proceeded in a short reaction time (2.5 h)
and with a low amount of catalyst (Table 2, entry 6).
3
8
Acetic acid and concentrated hydrogen peroxide was also
required to oxidize phenols, by the homogeneous hydrogen
peroxide/methyltrioxorhenium catalytic system, to the cor-
responding p-benzoquinones. In DMC as solvent, the oxida-
tion of 3,5-dimethylphenol gave in high conversion (>98%)
and good yield (80%) the corresponding 2,6-dimethyl-1,4-
benzoquinone with 3 equiv of hydrogen peroxide and
MTO (Table 2, entry 3). Conversion and yield are increased
MTO catalyzes the Bayer–Villiger reaction of cyclic ketones
to the corresponding lactones.
2
0,42
In DMC, 2-adamanta-
none was quantitatively oxidized to the 4-oxohomoadaman-
tan-5-one with MTO and a low amount of hydrogen peroxide
35% water solution (Table 2, entry 7). Reaction times are
2
0
shorter than in an ionic liquid solution.
3
9
compared to acidic conditions.
After these general investigations about the efficiency of
the hydrogen peroxide/methyltrioxorhenium catalytic sys-
tem in DMC, we specifically focused our attention on the
oxidation of alkylated phenol and methoxybenzene deriva-
tives to obtain the corresponding p-benzoquinones. In fact,
we recently showed that these compounds exhibit interesting
antifungal activities against the growth of soil fungi such as
Trichoderma koningii, Paecilomyces, Aspergillus flavus,
Penicillium roseopurpureum, Geomyces pannorum var. pan-
norum, Fusarium sp. and Pestalotia sp. In particular, we
proved that some of them are more potent inhibitors against
Fusarium sp. than ketoconazole, a commercially available
The oxygen atom insertion into the C–H bond of hydrocar-
bon derivatives catalyzed by the homogeneous hydrogen
peroxide/methyltrioxorhenium catalytic system proceeded
in ethanol or in t-butanol. Generally, long reaction times
were needed (24–72 h). We observed that in DMC the cata-
lytic conversion of diphenylmethanol, as a substrate model,
to benzophenone proceeded at room temperature with only
3
9
2 equiv of hydrogen peroxide, a low percent of MTO and
a short reaction time (4.5 h, Table 2, entry 4).
The oxidation of sulfides to sulfoxides by hydrogen
peroxide under methyltrioxorhenium catalysis was per-
formed with concentrated hydrogen peroxide (85% water
2
2
antifungal agent. Experimental results are reported in
Table 3. All starting phenol and methoxybenzene derivatives
are soluble in DMC and were converted to the corresponding
p-benzoquinones in 4–24 h. Conversions and yields are
4
0
solution) in about 24 h. Diphenyl sulfide was oxidized in
DMC to the corresponding sulfoxide in 90% yield after
only 3 h, with 1 equiv of diluted hydrogen peroxide solution
3
4
higher than in acetic acid and similar to those obtained
Table 3. Catalytic oxidations of phenols and methoxytoluenes with hydrogen peroxide (H
2
O
2 3 3
)/methyltrioxorhenium (CH ReO ) in DMC as solvent
a
a
Entry
Starting material
Experimental conditions
Conv. (%)
Products (yield %)
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
1
2
3
4
5
6
7
8
9
2,3,5-Trimethylphenol
2,3,6-Trimethylphenol
2-t-Butyl-5-methylphenol
2-t-Butyl-6-methylphenol
2,6-Diisopropylphenol
2,6-Di-t-butylphenol
1-Naphtol
3,4-Dimethoxytoluene
3,5-Dimethoxytoluene
3,4,5-Trimethoxytoluene
H
H
H
H
H
H
H
H
H
H
2
2
2
2
2
2
2
2
2
2
O
2
O
2
O
2
O
2
O
2
O
2
O
2
O
2
O
2
O
2
(4 equiv), MTO (2%), 60 C, 7 h
(4 equiv), MTO (2%), 60 C, 7 h
>98
>98
>98
>98
>98
95
>98
>98
>98
>98
2,3,5-Trimethyl-1,4-benzoquinone (95)
2,3,5-Trimethyl-1,4-benzoquinone (>98)
2-t-Butyl-5-methyl-1,4-benzoquinone (>98)
2-t-Butyl-6-methyl-1,4-benzoquinone (95)
2,6-Diisopropyl-1,4-benzoquinone (95)
2,6-Di-t-butyl-1,4-benzoquinone (95)
1,4-Naphtoquinone (90)
2-Methoxy-5-methyl-1,4-benzoquinone (80)
2-Methoxy-6-methyl-1,4-benzoquinone (75)
2-Methoxy-6-methyl-1,4-benzoquinone (>98)
(8 equiv), MTO (2%), 60 C, 7 h
(6 equiv), MTO (2%), 60 C, 4 h
(8 equiv), MTO (2%), 60 C, 24 h
(8 equiv), MTO (2%), 60 C, 24 h
(6 equiv), MTO (2%), 60 C, 6 h
ꢀ
(10 equiv), MTO (4%), 60 C, 6 h
ꢀ
(10 equiv), MTO (4%), 60 C, 6 h
ꢀ
10
(10 equiv), MTO (4%), 60 C, 4 h
a
GC–MS conversions and yields.

6898
R. Bernini et al. / Tetrahedron 63 (2007) 6895–6900
by us in an ionic liquid solution; however, in DMC a lower
amount of the catalyst is needed (2–4%).
w/w) in DMC (2 mL) and the mixture was stirred at the
appropriate temperature (see Tables 2 and 3). Oxidations
were monitored by TLC and GC–MS analysis. Depending
on the substrate, for a quantitative conversion, successive
additions of hydrogen peroxide/methyltrioxorhenium were
2
2
3. Conclusions
performed. At the end of the reaction, MnO was added to
2
DMC, a highly oxygenated compound having good solvent
properties, low toxicity and ecotoxicity, can be used as
an environmentally friendly reaction medium for methyl-
trioxorhenium-catalyzed oxidations of a wide range of sub-
strates. Methyltrioxorhenium and the diperoxo complex
the solution to degrade the excess of hydrogen peroxide
and the reaction mixture was vigorously stirred for 15 min.
After filtration, methanol was added to the solution and the
azeotropic mixture (methanol:DMC¼3:1 v/v) boiling at
ꢀ
43
64 C was evaporated under vacuum.
The reaction
[
CH ReO(O–O) ] 3 are soluble in DMC and this species is
3
products were extracted with ethyl acetate (3ꢂ20 mL) and
the organic layers were dried over anhydrous sodium sulfate.
The crude product was purified by preparative TLC or by
flash chromatography on silica gel using dichloromethane/
methanol or ethyl acetate/hexane mixtures as eluents. All
2
stable for days at room temperature. Oxidations proceed with
high conversions and yields. Products are obtained after
shorter reaction times than in traditional solvents and similar
to those observed in ionic liquids. Using DMC as solvent,
often a lower amount of catalyst is needed than with tradi-
tional solvents or ionic liquids.
1
the products were identified by comparison of their H
1
3
NMR, C NMR and GC–MS spectra with those of authentic
compounds. Styrene oxide, benzophenone, diphenyl sulf-
oxide, diphenyl sulfone, hydroquinone, p-benzoquinone,
1,4-naphthoquinone and 2-methoxy-5-methyl-1,4-benzo-
quinone are commercially available compounds (Sigma,
Aldrich, Fluka); samples of 2,3-dimethyl-1,4-napththoqui-
none, 2,6-dimethyl-1,4-benzoquinone, 4-oxohomoadaman-
tan-5-one and the other benzoquinones reported in Table 3
were prepared according to previously published proce-
4. Experimental
All commercial products were of the highest grade available
and were used as such. Urea hydrogen peroxide and
hydrogen peroxide 35% water solution are commercially
available (Aldrich). NMR spectra were recorded on a Bruker
2
0,22
(
200 MHz) spectrometer and are reported in d values. Gas
dures.
calculated by GC–MS analysis.
Conversions and yields of the oxidations were
chromatography–mass spectra (GC–MS) were recorded us-
ing a GC-17A Shimadzu gas chromatograph equipped with
an electron beam of 70 eV, a SPB column (25 mꢂ0.30 mm
and 0.25 mm film thickness) and a FID as detector. The
injector temperature was 280 C. An isothermal temperature
profile of 60 C for 5 min, followed by a 10 C/min temper-
4.2.1. 2,3-Dimethyl-1,4-naphthoquinone. Yield: >98%.
Yellow oil. [Found: C, 77.6; H, 17.1; O, 5.3. C H O re-
1
0 14 2
ꢀ
quired C, 77.4; H, 17.2; O, 5.4%]. d (200 MHz, CDCl )
H 3
2.11 (6H, s, CH ), 7.60–7.65 (2H, CH ), 7.97–8.02 (2H,
3 ar
ꢀ
ꢀ
ꢀ
ature gradient to 250 C for 5 min were used. Chromato-
CH ). d (200 MHz, CDCl ) 13.5, 127.0, 133.0, 134.2,
ar C 3
+
44
graphy grade helium was used as the carrier gas. Thin
layer chromatography was carried out using Merck platen
Kieselgel 60 F254. Flash chromatography was performed
using Merck silica gel 60 (230–400 mesh).
144.2, 185.6; m/z 186 (M ).
4.2.2. 2,6-Dimethyl-1,4-benzoquinone. Yield: 80%. White
ꢀ
4
5
ꢀ
solid; mp 72–74 C (lit. 71–73 C).
4
.1. Spectrophotometric analysis
4.2.3. 4-Oxohomoadamantan-5-one. Yield: >98%. Col-
ourless oil. [Found: C, 72.5; H, 8.4; O, 19.1. C H O
0 14 2
1
Spectrophotometric analyses were performed with a Cary-4
Varian spectrometer at 25 C. Quartz cuvettes (4 mL) with
1
required C, 72.3; H, 8.5; O, 19.2%]. d (200 MHz, CDCl )
H 3
ꢀ
.0 cm optical path length were used. A solution of hydrogen
1.60–2.08 (12H, s, 5ꢂCH and 2ꢂCH), 3.04 (1H, m,
2
–(CH ) CHCO), 4.46 (1H, m, –(CH ) CHO–); d (200 MHz,
2 2
2
2
C
peroxide/methyltrioxorhenium was prepared as reported:
methyltrioxorhenium (2.78 mg, 0.011 mmol) was solubi-
lized in DMC (12 mL), and then hydrogen peroxide 35%
water solution (43.8 mL, 0.5 mmol) was added. The forma-
tion of the diperoxorhenium complex 3 was monitored by
measuring the absorbance changes of this solution in the
range l¼280–420 nm and by observing the formation of a
maximum of absorbance at l¼360 nm. The stability of the
diperoxorhenium complex was measured by monitoring the
decline in absorbance at this wavelength for seven days at
room temperature.
CDCl ) 25.7, 30.8, 33.6, 35.6, 41.1, 73.4, 179.5; m/z
3
166 (M ).
+
4.2.4. 2,3,5-Trimethyl-1,4-benzoquinone. Yield: 95%. Yel-
ꢀ
2
2
46
ꢀ
low solid; mp 27–29 C (lit. 29 C).
4.2.5. 2-tert-Butyl-5-methyl-1,4-benzoquinone. Yield:
2
2
>98%. Yellow oil. [Found: C, 74.5; H, 7.7, O, 17.8.
C H O required C, 74.1; H, 7.9; O, 18.0%]; dH
(200 MHz, CDCl ) 1.19 (9H, s, C(CH ) , 1.96 (3H, d, J
1
1 14 2
3
3 3
1.5 Hz, CH ), 6.46 (1H, q, J 1.5 Hz, CH]CCH ), 6.52
3
3
(1H, s, CH]CC(CH ) ); d (200 MHz, CDCl ) 14.9, 29.1,
131.5, 135.9, 144.1, 156.0, 187.8, 188.9; m/z 178 (M ).
3 3 C 3
+
4
.2. General procedure for the oxidation of organic
compounds with hydrogen peroxide/methyltrioxo-
rhenium in dimethyl carbonate
4.2.6. 2-tert-Butyl-6-methyl-1,4-benzoquinone. Yield:
95%. Yellow oil. [Found: C, 74.5; H, 7.6; O, 17.9.
C H O required C, 74.8; H, 7.4; O, 17.8%]; dH
2
2
In a typical experiment, hydrogen peroxide (2.0 equiv, 35%
water solution) and the substrate (1.0 mmol) to be oxidized
were added to a solution of the methyltrioxorhenium (1.0%
1
1 14 2
(200 MHz, CDCl ) 1.10 (9H, s, C(CH ) ), 1.91 (3H,
3 3
3
d, J 1.3 Hz, CH ), 6.41 (2H, m, CH]CCH and
3
3

R. Bernini et al. / Tetrahedron 63 (2007) 6895–6900
6899
CH]CC(CH ) ); d (200 MHz, CDCl ) 16.1, 28.7, 131.3,
3
(c) Teporal-Sanchez, T.; Ruiz-Garcia, R. Inorg. Chim. Acta
2004, 357, 2713–2720.
. Collins, T. J. Acc. Chem. Res. 2002, 35, 782–790.
3
C
3
+
1
31.9, 147.6, 156.2, 187.6, 188.6; m/z 178 (M ).
6
4
low oil.
.2.7. 2,6-Diisopropyl-1,4-benzoquinone. Yield: 95%. Yel-
[Found: C, 75.2; H, 8.0; O, 16.8. C H O re-
12 16 2
7. Goodman, M. A.; Detty, M. R. Organometallics 2004, 23,
3016–3020.
2
2,47
quired C, 75.0; H, 8.4; O, 16.6%]; d (200 MHz, CDCl )
H
8. (a) Yadollahi, B. Chem. Lett. 2003, 32, 1066–1067; (b)
Kholdeeva, O. A.; Trubitsina, T. A.; Maksimov, G. M.;
Golovin, A. V.; Maksimovskaya, R. I. Inorg. Chem. 2005, 44,
1635–1642; (c) Vazylyev, M.; Sloboda-Rozner, D.; Haimov,
A.; Maayan, G.; Neumann, R. Top. Catal. 2005, 34, 93–99;
(d) Sloboda-Rozner, V.; Neumann, R. Green Chem. 2006, 8,
679–681.
3
1
CH(CH ) ), 6.47 (2H, s, CH]CCH(CH ) ); d (200 MHz,
.14 (12H, d, 2CH(CH ) , 3.08 (2H, hept, J 6.8 Hz,
3 2
3
2
3 2
C
+
CDCl ) 21.1, 27.0, 129.8, 155.3, 186.8, 188.6; m/z 192 (M ).
3
4
Orange solid; mp 66–68 C (lit. 65–68 C).
.2.8. 2,6-Di-tert-butyl-1,4-benzoquinone. Yield: 95%.
ꢀ
2
2
48
ꢀ
9
. (a) Notari, B. Catal. Today 1993, 18, 163–172; (b) Corma, A.
Fine Chemicals through Heterogeneous Catalysis; Sheldon,
R. A., Van Bekkum, H., Eds.; Wiley-VCH: Weinheim, 2000;
pp 80–91.
4
1
.2.9. 1,4-Naphthoquinone (13). Yellow solid; mp 118–
ꢀ
49
ꢀ
21 C (lit. 119–120 C).
4
.2.10. 2-Methoxy-6-methyl-1,4-benzoquinone. Yield:
10. Jost, C.; Wahl, G.; Kleinhenz, D.; Sundermeyer, J. Peroxide
Chemistry; Adam, W., Ed.; Wiley-VCH: Weinheim, 2000;
pp 341–364.
2
2,,50
>
C H O required C, 63.2; H, 5.3; O, 31.5%]; dH
98%. Yellow oil.
[Found: C, 63.8; H, 5.0; O, 31.2.
8
8 3
(
s, OCH ), 5.83 (1H, s, CH]COCH ), 6.48 (1H, q, J
200 MHz, CDCl ) 2.00 (3H, d, J 1.6 Hz, CH ), 3.77 (3H,
11. (a) Corma, A.; Nemeth, L. T.; Renz, M.; Valencia, S. Nature
2001, 412, 423–425; (b) Nemeth, L.; Moscoso, J.; Erdman,
N.; Bare, S. R.; Oroskar, A.; Kelly, S. D.; Corma, A.;
Valencia, S.; Renz, M. Stud. Surf. Sci. Catal. 2004, 154C,
3
3
3
3
1
.6 Hz, CH]CCH ); dC (200 MHz, CDCl ) 15.0, 56.3,
3 3
+
1
07.2, 133.8, 142.1, 158.0, 181.0, 186.2; m/z 152 (M ).
2
626–2631.
1
2. Herrmann, W. A. Applied Homogeneous Catalysis with
Organometallic Compounds; Cornils, B., Herrmann, W. A.,
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Acknowledgements
We are grateful to Dr. Anna Maria Timperio and Prof. Lello
Zolla for their helpfulness in the spectrophotometric deter-
minations and to Prof. Elisabetta Fasella for her helpful
observations.
13. Herrmann, W. A.; Kuhn, F. E. Acc. Chem. Res. 1997, 30,
169–180.
14. Owens, G. S.; Abu-Omar, G. S. J. Mol. Catal. A: Chem. 2002,
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1
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