C-H arylation of benzoquinone in water through aniline activation: Synergistic effect of graphite-supported copper oxide nanoparticles

Article abstract of DOI:10.1021/jo4004426

A homemade CuONPs/Gr catalyst was found to be efficient for the C-H arylation of benzoquinone. This methodology represents the first example of a Meerwein arylation catalyzed by a heterogeneous catalyst.

Full text of DOI:10.1021/jo4004426

Note
pubs.acs.org/joc
C−H Arylation of Benzoquinone in Water through Aniline Activation:
Synergistic Effect of Graphite-Supported Copper Oxide
Nanoparticles
Aurelien Honraedt,† Francois Le Callonnec,† Erwan Le Grognec,† Vincent Fernandez,‡
̧
́
and Franco̧
is-Xavier Felpin*,†
†UFR Sciences et Techniques, Universite
Cedex 3, France
́
de Nantes, UMR CNRS 6230, CEISAM, 2 rue de la Houssinier
̀
e, BP 92208, 44322 Nantes
‡UFR Sciences et Techniques, Universite
Cedex 3, France
́
de Nantes, UMR CNRS 6502, IMN, 2 rue de la Houssiniere, BP 32229, 44322 Nantes
̀
S
* Supporting Information
ABSTRACT: A homemade CuONPs/Gr catalyst was found to be efficient for the C−H
arylation of benzoquinone. This methodology represents the first example of a Meerwein
arylation catalyzed by a heterogeneous catalyst.
Scheme 1. C−H Arylation of Benzoquinone with
he arylation of α,β-unsaturated compounds is usually
1
Aryldiazonium Chlorides
Texecuted through a palladium-catalyzed Heck reaction.
This reaction is now a part of the arsenal in the tool box of
every synthetic chemist and has found industrial develop-
ments.2 Although almost every kind of olefin is compatible with
the Heck process, benzoquinone-type partners are still reluctant
to react under Heck protocols. This failure has been ascribed to
the unusual electronic properties of benzoquinone and their
ability to coordinate with palladium. In order to overcome this
issue, a prehalogenation of benzoquinone is required to allow
the arylation via a Suzuki or Stille reaction.3 On the other hand,
the direct C−H arylation of benzoquinones has been recently
successfully reported by the group of Baran through the
homolytic cleavage of boronic acids.4 Actually, the addition of
aryl radicals to benzoquinone is a well-known process, mostly
performed by homolytic decomposition of aryl diazonium
chlorides.5 This transformation is usually carried out in a two-
steps one-pot procedure starting with the preparation of
diazonium chlorides in HCl solution followed by the addition
of the latter into an aqueous solution of benzoquinone 1 in the
presence of a base (2−10 equiv) as buffer (Scheme 1).
above 0 °C. In order to address these issues, we recently
reported the direct C−H arylation of benzoquinone with
anilines under neutral conditions without any acid or base.6
Although the procedure was particularly well suited for nitro-
based sensitive substrates, an excess of benzoquinone (2 equiv)
was required in order to reach synthetically acceptable yields.
The separation of unreacted benzoquinone from the coupling
product was sometimes rather difficult, and a more efficient
procedure was still required for further developments. In this
paper, we report our studies in this field that addressed the
issues discussed above. Of particular importance, we discovered
the beneficial synergistic effect of graphite-supported copper
nanoparticles on the reaction efficiency.
Although rather effective, this approach suffers from several
drawbacks: (1) the preparation of the aryl diazonium chloride
requires a large excess of HCl, (2) as a consequence, an excess
of a base is required for the neutralization of the strongly acidic
solution containing the diazonium, and (3) most aryl
diazonium chlorides are very unstable and sometimes explosive
We started a careful optimization study with the arylation of
benzoquinone 1 with 4-bromoaniline 2 (Table 1). In order to
Received: March 3, 2013
© XXXX American Chemical Society
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Note
(entries 11 and 12). Lowering of the copper loading to 0.5 mol
% resulted in a rapid decrease of the reaction yield (<65%).
With these interesting preliminary results in hand, we explored
the opportunity to develop a heterogeneous version of this
process by impregnating carbon material with copper nano-
particles. To the best of our knowledge, the use of a metal-
based heterogeneous catalyst has never been described for the
Meerwein arylation.
Table 1. Optimization Studies with a Homogeneous Metal
Source
b
entry
additive
loading (mol %)
yield (%)
We recently reported that palladium nanoparticles (NPs)
could be efficiently prepared from a methanolic solution of
palladium acetate under an atmosphere of H2 (1 atm) at room
temperature and heterogenized in the presence of carbon
material.8 Following this efficient strategy, we exposed a
methanolic solution of Cu(OAc)2·H2O to an atmosphere of
H2, in the presence of graphite as support, furnishing CuNPs/
Gr catalyst with ∼5 wt % of metal loading on the support as
determined by ICP analysis. Interestingly, the use of other
sources of Cu(II) such as CuO and CuCl2 led to a much lower
loading on the support, likely due to their poor solubility in
MeOH. High-resolution transmission electron microscopy
(HRTEM) analysis of 5% CuNPs/Gr showed a homogeneous
distribution of copper nanoparticles onto the support (Figure
1). This is a remarkable result considering the simplicity of the
c
1
30
2
52
79
54
25
55
67
70
80
83
85
82
3
hydroquinone
FeSO4·7H2O
TiCl3
10
100
100
100
100
100
100
100
100
1
4
5
6
CuCl
7
Cu2O
8
CuSO4·5H2O
CuCl2
9
10
11
12
CuO
Cu(OAc)2·H2O
Cu(OAc)2.H2O
a
Reaction conditions: aniline (1 mmol), MeSO3H (1 mmol), t-
BuONO (1.5 mmol), benzoquinone (0.9 mmol), and additive (see
table entries) were stirred at 40 °C for 24 h. Isolated yields after flash
b
c
chromatography on silica gel. MeSO3H was omitted.
improve the purification process complicated by the presence
of unreacted benzoquinone 1 in the crude mixture, we worked
with a slight excess of aniline 2. The use of MeSO3H (1 equiv)
that promotes the formation of the corresponding diazonium
salt increases the yield (52% vs 30% for entry 2 vs 1) but still at
an unacceptable level. In our previous work,6 we proposed that
in the absence of metal and external reducing agent, the
homolytic decomposition of the diazonium function was
initiated by trace of hydroquinone contained in the commercial
samples of benzoquinone. Although we initially failed to prove
Figure 1. HRTEM picture of 5% CuNPs/Gr catalyst at different
magnifications.
1
the presence of hydroquinone by H NMR, we pursued this
hypothesis to elucidate the mechanism operating. A careful
HPLC analysis showed that commercial samples as well as
freshly recrystallized batches of benzoquinone roughly contain
0.5−1% of hydroquinone. In order to prove the role of
hydroquinone in mediating the diazonium reduction, we
carried out the reaction with 10 mol % of hydroquinone.
Although the yield was spectacularly improved (79%), the
isolation of the expected compound 3 was complicated by the
presence of inseparable tarry material. To avoid the presence of
oligomers, we reasoned that a reducing metal could significantly
help the homolytic decomposition of the diazonium function to
generate an aryl radical, and thereby could work in a synergistic
fashion with traces of hydroquinone contained in commercial
samples of benzoquinone.
In this way, we evaluated Fe-, Ti-, and Cu-based aryl radical
promoters. Surprisingly, FeSO4·7H2O did not impact the
reaction outcome, and TiCl3 was even detrimental for the
arylation, although they have been both successfully employed
for the Meerwein arylation.7 By contrast, copper complexes
were all active for the studied transformation. As a general
comment, copper(I) complexes were usually less active than
copper(II)-based promoters. Among the various sources of
copper(II) complexes, Cu(OAc)2·H2O displayed the highest
yields (entries 8−12). More interestingly, the activity of
Cu(OAc)2·H2O remains high when used as catalyst with a
loading as low as 1 mol % without any trace of tarry material
preparation procedure. The TEM picture at low magnification
(Figure 1a) shows that CuNPs are uniformly dispersed on the
sheets of graphite and without formation of aggregate. A
selected enlargement (Figure 1b) shows spherical CuNPs with
a crystallite size <5 nm, although a high local concentration of
NPs. A closest analysis of the crystallite size distribution
calculated on 128 NPs revealed an average diameter of 3.1 nm,
with 83% of NPs being in the range 2−4 nm (see Figure S1,
Supporting Information).
The composition of copper species at the surface of graphite
was investigated by X-ray photoelectron spectroscopy (XPS)
analysis.9 The binding energy of the Cu 2p3/2 peak at 934.0 eV
and the satellite shakeup detected near 938−946 eV are
characteristic of Cu2+ species (see Figure S2, Supporting
Information). The absence of Cu 2p peaks associated to
metallic Cu and Cu+ at lower binding energy (932.5 eV)
indicates that copper species are only present as Cu2+. This
result indicates that the catalyst mainly consists of graphite-
supported copper oxide NPs. It was assumed that Cu(II) was
reduced by H2/MeOH to Cu(0) which rapidly oxidized to
CuO during the catalyst treatment. The absence of ester peaks
by XPS excluded any residual Cu(OAc)2·H2O impregnated
onto the surface of graphite. We determined the CuO NPs size
(t)10 considering the inelastic meam free path of Cu2p λ1, Cu3p
λ2 in the CuO layer as 1.2 and 2.4 nm respectively11 and the
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Note
average surface powder angle relative to the analyzer as 45° (see
formula S1, Supporting Information). The average diameter (t)
of NPs was estimated to be 3.1 0.8 nm and is consistent with
the estimation realized from HRTEM pictures.
Table 3. Scope of the Reaction
We next investigated the catalytic activity of these freshly
prepared heterogeneous catalysts (Table 2).
Table 2. Optimization Studies with Heterogeneous Copper
Catalysts
b
entry
catalyst
loading (mol %)
yield (%)
1
2
3
4
5
5% Cu/Gr
5% Cu/Gr
5% Cu/Gr
5
2.5
1
82
82
69
34
46
c
3% Cu/C
10
graphite
a
Reaction conditions: aniline (1 mmol), MeSO3H (1 mmol), t-
BuONO (1.5 mmol), benzoquinone (0.9 mmol), and heterogeneous
copper catalyst (see table entries) were stirred at 40 °C for 24 h.
b
c
Isolated yields after flash chromatography on silica gel. Commer-
cially available from Aldrich.
We discovered that graphite-supported CuO NPs also
display the synergistic effect, comparable to that observed
with a homogeneous molecular complex, with, however, a
slightly higher loading. Indeed, with loading lower than 2.5 mol
% Cu, a significant decreased yield was obtained (entry 2 vs. 3).
Interestingly, our homemade catalyst was much more active
than the commercial 3% Cu/C catalyst that displayed a
detrimental effect on the reaction outcome (entry 5). The
result from the background reaction, carried out in the presence
of copper-free graphite, showed that the spectacular yield
enhancement could not be attributed to the support (entry 5 vs
entry 2, Table 1). This result represents the first example of a
Meerwein arylation carried out in the presence of a
heterogeneous catalyst. From a larger perspective, examples
of organic reactions involving free-radical species and working
with a heterogeneous catalyst are extremely rare and essentially
limited to polymerization processes.12 With an optimized
procedure in hand, we next explored the scope of this
synthetically useful transformation (Table 3). The reaction
conditions are compatible with a variety of substituents
including halogens (3a−g), cyanide (3h), ketone (3i), nitro
(3j,k), ester (3l−m), and methoxy (3n). The conditions used
in this transformation do not affect radical-reactive substituents
such as halogens including iodine atom, and no trace of
hydrolysis of the ester function has been observed. It is also
noteworthy that the mild conditions developed for this process
allow the handling of an acid-sensitive free alkyne (compound
3o). These results suggest that further functionalization using
palladium- (cross-coupling reactions) and copper-catalyzed
reactions (click chemistry) as well as standard synthetic
chemistry could be envisaged for inducing molecular complex-
ity. The synergistic effect of copper is exemplified in several
examples (compounds 3a, 3b, 3d, and 3l) and enhances the
yields of the 3-arylbenzoquinones up to 40%. Meerwein
arylation carried out with CuCl2 is frequently contaminated
with unwanted Sandmeyer-type byproducts by chlorine
a
Reaction conditions: aniline (1 mmol), MeSO3H (1 mmol), t-
BuONO (1.5 mmol), benzoquinone (0.9 mmol), and CuONPs/Gr
(2.5 mol %) were stirred at 40 °C for 24 h. Yields in parentheses: the
CuONPs/Gr catalyst was omitted. CaCO3 was used as additive.
b
c
trapping, thereby decreasing the expected product yields.
With our 5% CuONPs/Gr catalyst, these side products cannot
be formed, and the crudes are usually very clean, mainly
containing the expected product and the remaining starting
material. From an environmental point of view, the process
only requires reagents with low toxicity and generates t-BuOH,
H2O, and N2 as byproducts.
The easy catalyst recovery by a single filtration is a salient
advantage of heterogeneous catalysis, allowing the metal
reprocessing and even sometimes the catalyst recycling.
Accordingly, we evaluated the robustness of our CuONPs/Gr
catalyst on a few catalytic cycles for the synthesis of 3a. We
determined that the catalytic activity was essentially conserved
after the first reuse (80%), and even after the fifth cycle only a
negligible decrease of the yield was observed (76%). The true
nature of the catalysis (i.e., heterogeneous vs homogeneous) is
still unknown at this time, and we are currently working at its
elucidation. However, ICP-MS analysis of the crude reaction
mixture after a simple filtration only showed marginal leaching.
Indeed, only 3.3% and 0.02% of soluble copper species (based
on the initial amount introduced) remained in solution after the
first and second run, respectively. This methodology can be
easily extended to the C−H arylation of naphthoquinones
providing a few modifications (Scheme 2). For instance,
because the naphthoquinone 4 is mostly insoluble in water, the
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2-(3-Bromophenyl)-1,4-benzoquinone (3c). The crude product
was purified by flash chromatography on silica gel to give the product
as an orange solid (169.7 mg, 72%): Rf = 0.29 (petroleum ether/DCM
60/40); mp 134−139 °C (lit.4 mp 138−144 °C); 1H NMR (400
MHz, CDCl3) δ 7.63 (app t, 1H, J = 1.5 Hz), 7.59 (app dt, 1H, J = 7.8,
1.5 Hz), 7.40 (app dt, 1H, J = 7.8, 1.5 Hz), 7.32 (app t, 1H, J = 7.8
Hz), 6.89−6.82 (m, 3H); 13C NMR (100 MHz, CDCl3) δ 187.3,
186.2, 144.7, 137.1, 136.5, 134.7, 133.3, 133.2, 132.2, 130.2, 128.0,
122.7; IR ν 3073, 3060, 2958, 1683, 1652, 1593, 1555 cm−1; HRMS
(MALDI) calcd for C12H9BrO2 [M + 2H]+ 263.9780, found
263.9789.2
Scheme 2. C−H Arylation of Naphthoquionone 4
use of DMSO as cosolvent proved to be required. Moreover,
the sensitivity of 4 toward acidic conditions prompted us to use
CaCO3 as buffer.
2-(4-Chlorophenyl)-1,4-benzoquinone (3d). The crude prod-
uct was purified by flash chromatography on silica gel to give the
product as an orange solid (171.9 mg, 87%): Rf = 0.18 (petroleum
4
1
In summary, we have described the beneficial synergistic
effect of graphite-supported copper(II) oxide nanoparticles
with hydroquinone for the radical C−H arylation of
benzoquinone with in situ activated anilines. This work
represents the first Meerwein arylation under heterogeneous
catalysis. The mild and experimentally simple conditions
developed allow the coupling of benzoquinone with variously
substituted anilines. The robustness of the CuONPs/Gr
catalyst was demonstrated over five recycling experiments.
ether/DCM 60/40); mp 127−129 °C (lit. mp 129.5 °C); H NMR
(400 MHz, DMSO-d6,) δ 7.55 (d, 2H, J = 8.9 Hz), 7.52 (d, 2H, J = 8.9
Hz), 6.99−6.90 (m, 3H); 13C NMR (100 MHz, DMSO-d6) δ 187.6,
186.2, 144.0, 137.3, 136.1, 134.7, 132.4, 131.6, 131.2 (2C), 128.3
(2C); IR ν 3068, 1648, 1595, 1490 cm−1; HRMS (ESI) calcd for
C12H8ClO2 [M + H]+ 219.0213, found 219.0219.
2-(4-Iodophenyl)-1,4-benzoquinone (3e). The crude product
was purified by flash chromatography on silica gel to give the product
as an orange solid (173.2 mg, 62%): Rf = 0.21 (petroleum ether/DCM
50/50); mp 137−141 °C (lit.4 mp 130−135 °C); 1H NMR (400
MHz, CDCl3) δ 7.78 (d, 2H, J = 8.6 Hz), 7.21 (d, 2H, J = 8.6 Hz),
6.88−6.81 (m, 3H,); 13C NMR (100 MHz, CDCl3) δ 187.4, 186.3,
145.1, 137.9 (2C), 137.1, 136.5, 132.8, 132.2, 130.9 (2C), 97.1; IR ν
3246, 3060, 2922, 1642, 1595, 1579 cm−1; HRMS (MALDI) calcd for
C12H9IO2 [M + 2H]+ 311.9642, found 311.9646.2
2-(3-Trifluoromethylphenyl)-1,4-benzoquinone (3f). The
crude product was purified by flash chromatography on silica gel to
give the product as a brown solid (179.4 mg, 79%): Rf = 0.24
(petroleum ether/DCM 60/40); mp 60−63 °C (lit.14 mp 60−61 °C);
1H NMR (400 MHz, DMSO-d6) δ 7.87 (s, 1H), 7.84−7.82 (m, 2H),
7.70 (app t, 1H, J = 7.8 Hz), 7.07 (d, 1H, J = 2.5 Hz), 7.02−6.93 (m,
2H); 13C NMR (100 MHz, DMSO-d6) δ 187.6, 186.1, 143.9, 137.3,
136.1, 133.8, 133.3, 133.1, 129.3, 129.0 (q, J = 31.0 Hz), 126.1, 126.0,
124.0 (q, J = 271.0 Hz); 19F NMR (376 MHz, DMSO-d6) δ −61.13;
IR ν 3052, 1659, 1609, 1586 cm−1; HRMS (ESI) calcd for C13H8F3O2
[M + H]+ 253.0482, found 253.0482.
2-(4-Trifluoromethylphenyl)-1,4-benzoquinone (3g). The
crude product was purified by flash chromatography on silica gel to
give the product as a pale brown solid (174.2 mg, 77%): Rf = 0.30
(petroleum ether/DCM 50/50); mp 104−113 °C (lit.4 mp 105−108
°C); 1H NMR (400 MHz, DMSO-d6,) δ 7.82 (d, 2H, J = 8.1 Hz), 7.73
(d, 2H, J = 8.1 Hz), 7.04 (d, 1H, J = 2.5 Hz), 7.02−6.94 (m, 2H); 13C
NMR (100 MHz, DMSO-d6) δ 187.5, 186.0, 144.0, 137.3 (2C), 137.0,
136.2, 133.4, 130.2 (2C), 129.4 (q, J = 31.0 Hz), 124.9 (q, J = 3.7 Hz),
124.0 (q, J = 270.0 Hz); 19F NMR (376 MHz, DMSO-d6,) δ −61.33;
IR ν 3074, 1649, 1597 cm−1; HRMS (ESI) calcd for C13H8F3O2 [M +
H]+ 253.0482, found 253.0483.
EXPERIMENTAL SECTION
■
Preparation of the CuONPs/Gr Catalyst. Distilled methanol (60
mL) at 25 °C was degassed with H2 during 5 min. Copper(II) acetate
monohydrate (0.4 g, 2 mmol) was added, and the resulting mixture
was stirred until complete dissolution. Graphite (0.5 g) was then
added, and the mixture was diluted with distilled methanol (5 mL) and
degassed with H2 during 5 min. The mixture was then refluxed
overnight under H2 atmosphere (1 atm). The solid phase was
separated by filtration and washed with distilled methanol (3 × 5 mL),
deionized water (3 × 5 mL), and acetone (3 × 5 mL). The filtrate was
then dried under vacuum overnight to give a black solid. The ICPMS
analysis showed a Cu/graphite catalyst at 4.5−5% w/w.
General Procedure for the C−H Arylation of Benzoquinone.
To a mixture of aniline and MeSO3H (65 μL, 1.0 mmol) in H2O (5
mL) at 25 °C was added t-BuONO (180 μL, 1.5 mmol). The reaction
mixture was stirred for 5 min and diluted with H2O (5 mL).
Benzoquinone (97.3 mg, 0.9 mmol) and the 5% CuONPs/Gr catalyst
(2.5% mol) were added successively. The temperature was warmed to
40 °C, and the mixture was stirred for 24 h. The mixture was cooled to
5 °C, and the precipitate was collected by filtration. The solid was
washed with ethyl acetate (50 mL). The recovered organic layer was
dried on Na2SO4, filtered and evaporated to dryness. The crude was
purified by flash chromatography on silica gel to give the pure product.
The same procedure was considered using a homogeneous catalyst for
the optimization studies reported in Table 1.
2-(4-Bromophenyl)-1,4-benzoquinone (3a). The crude prod-
uct was purified by flash chromatography on silica gel to give the
product as a pale orange solid (193.9 mg, 82%): Rf = 0.30 (petroleum
2-(4-Cyanophenyl)-1,4-benzoquinone (3h). The crude product
was purified by flash chromatography on silica gel to give the product
as an orange solid (134.4 mg, 71%): Rf = 0.28 (petroleum ether/DCM
ether/DCM 50/50); mp 113−115 °C (lit.6 mp 114−115 °C); H
1
NMR (400 MHz, CDCl3,) δ 7.57 (d, 2H, J = 8.7 Hz), 7.35 (d, 2H, J =
8.7 Hz), 6.88−6.81 (m, 3H); 13C NMR (100 MHz, CDCl3) δ 187.4,
186.3, 144.9, 137.1, 136.5, 132.8, 132.0 (2C), 131.6, 130.9 (2C),
125.0; IR ν 3050, 2925, 1649, 1592, 1488 cm−1; HRMS (MALDI)
calcd for C12H9BrO2 [M + 2H]+ 263.9780, found 263.9778.13
2-(2-Bromophenyl)-1,4-benzoquinone (3b). The crude prod-
uct was purified by flash chromatography on silica gel to give the
product as a brown-orange solid (165.5 mg, 70%): Rf = 0.25
(petroleum ether/DCM 50/50); mp 96−97 °C (lit.5b mp 98−100
10/90); mp 210−211 °C (lit.5e mp 210−211 °C); H NMR (400
1
MHz, DMSO-d6,) δ 7.93 (d, 2H, J = 8.6 Hz), 7.71 (d, 2H, J = 8.6 Hz),
7.05 (d, 1H J = 2.5 Hz), 7.02−6.92 (m, 2H); 13C NMR (100 MHz,
DMSO-d6) δ 187.5, 185.8, 143.8, 137.5, 137.3, 136.2, 133.5, 132.0
(2C), 130.3 (2C), 118.4, 112.1; IR ν 3092, 3063, 3047, 2238, 1661,
1590 cm−1; HRMS (ESI) calcd for C13H8NO2 [M + H]+ 210.0560,
found 210.0559.
2-(4-Benzoylphenyl)-1,4-benzoquinone (3i). The crude prod-
uct was purified by flash chromatography on silica gel to give the
product as an orange solid (182.1 mg, 70%): Rf = 0.33 (DCM); mp
108−116 °C; 1H NMR (400 MHz, DMSO-d6) δ 7.81−7.75 (m, 3H),
7.72−7.68 (m, 3H), 7.63−7.55 (m, 3H), 7.05 (d, 1H, J = 2.5 Hz),
7.00−6.94 (m, 2H); 13C NMR (100 MHz, DMSO-d6): δ 195.3, 187.6,
186.2, 144.3, 137.7, 137.3, 136.8, 136.7, 136.1, 133.1, 132.8, 129.6
(2C), 129.5 (2C), 129.3 (2C), 128.6 (2C); IR ν 3061, 1652, 1589
1
°C); H NMR (400 MHz, CDCl3) δ 7.65 (dd, 1H, J = 7.8, 1.2 Hz),
7.38 (app dt, 1H, J = 7.8, 7.5, 1.2 Hz), 7.30 (app dt, 1H, J = 7.8, 7.5,
1.8 Hz), 7.20 (dd, 1H, J = 7.5 Hz, 1.8 Hz), 6.91−6.84 (m, 2H), 6.76
(d, 1H, J = 2.3 Hz); 13C NMR (100 MHz, CDCl3) δ 187.4, 185.2,
147.8, 137.0, 136.6, 134.9, 134.7, 133.1, 131.0, 130.7, 127.5, 122.8; IR
ν 3062, 1659, 1601 cm−1; HRMS (MALDI) calcd for C12H9BrO2 [M
+ 2H]+ 263.9780, found 263.9778.2
D
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Note
cm−1; HRMS (ESI) calcd for C19H13O3 [M + H]+ 289.0859, found
289.0858.
and the mixture was stirred 24 h. The mixture was filtered on Buchner.
The liquid part was extracted three times with Et2O and the solid part
was washed with DCM. The recovered organic layer was dried on
Na2SO4, filtered, and evaporated to dryness. The crude was purified by
flash chromatography on silica gel (5% EtOAc−petroleum ether) to
give the pure product as an orange solid (198 mg, 71%): Rf = 0.31
(petroleum ether/DCM 50/50); mp 165−166 °C (lit.15 mp 164−166
2-(2-Methoxy-4-nitrophenyl)-1,4-benzoquinone (3j). The
crude product was purified by flash chromatography on silica gel to
give the product as an orange solid (191.8 mg, 82%): Rf = 0.19
(petroleum ether/ethyl acetate 80/20); mp 151−153 °C (lit.6 mp
1
156−157 °C); H NMR (400 MHz, CDCl3) δ 7.89 (dd, 1H, J = 8.3,
1
°C); H NMR (400 MHz, CDCl3) δ 8.14−8.19 (m, 1H), 8.09−8.13
2.1 Hz), 7.79 (d, 1H, J = 2.1 Hz), 7.32 (d, 1H, J = 8.3 Hz), 6.90−6.82
(m, 3H), 3.88 (s, 3H); 13C NMR (100 MHz, CDCl3) δ 187.1, 184.8,
157.8, 149.9, 144.0, 137.1, 136.5, 135.2, 131.1, 129.0, 115.8, 106.6,
56.7; IR ν 3123, 3084, 2988, 2956, 2853, 1734, 1591, cm−1; HRMS
(ESI) calcd for C13H10NO5 [M + H]+ 260.0554, found 260.0563.
2-(3-Nitrophenyl)-1,4-benzoquinone (3k). The crude product
was purified by flash chromatography on silica gel to give the product
as a beige solid (127.1 mg, 62%): Rf = 0.26 (petroleum ether/DCM
(m, 1H), 7.75−7.80 (m, 2H), 7.60 (dt, 2H, J = 2.4, 8.7 Hz), 7.60 (dt,
2H, J = 2.4, 8.7 Hz), 7.06 (s, 1H), 6.99−6.91 (m, 3H), 4.32 (s, 1H);
13C NMR (100 MHz, CDCl3) δ 185.2, 184.4, 147.3, 135.5, 134.3,
134.3, 132.7, 132.6, 132.4, 132.1, 131.3, 127.4, 126.4, 125.1; IR ν 3093,
3033, 1670, 1658, 1599, 1583 cm−1; MS (CI) m/z 312 (79Br), 314
(81Br).
30/70); mp 102−104 °C (lit.5a mp 105−107 °C); H NMR (400
1
ASSOCIATED CONTENT
■
MHz, DMSO-d6) δ 8.37 (app t, 1H, J = 2.0 Hz), 8.31 (ddd, 1H, J =
8.2, 2.4, 1.0 Hz), 7.97 (app dt, 1H, J = 8.0, 1.2 Hz), 7.76 (app t, 1H, J =
8.0 Hz), 7.12 (d, 1H, J = 2.5 Hz), 7.04−6.96 (m, 2H); 13C NMR (100
MHz, DMSO-d6) δ 187.5, 185.9, 147.5, 143.2, 137.3, 136.2, 135.8,
134.3, 133.4, 129.8, 124.3, 124.1; IR ν 3083, 1661, 1530 cm−1; HRMS
(ESI) calcd for C12H8NO4 [M + H]+ 230.0459, found 230.0458.
2-(4-Methoxycarbonylphenyl)-1,4-benzoquinone (3l). The
crude product was purified by flash chromatography on silica gel, to
give the product as an unstable orange solid (170.5 mg, 78%): Rf =
0.24 (petroleum ether/ethyl acetate 80/20); mp 144−150 °C (lit.4 mp
S
* Supporting Information
Figures S1 and S2, formula S1, XPS details, and H, 19F, and
1
13C NMR spectra. This material is available free of charge via
the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
■
Corresponding Author
*Fax: (+33) 251 125 40. E-mail: fx.felpin@univ-nantes.fr.
1
145−152 °C); H NMR (400 MHz, CDCl3) δ 8.07 (d, 2H, J = 8.4
Notes
Hz), 7.53 (d, 2H, J = 8.4 Hz), 6.88−6.84 (m, 3H), 3.92 (s, 3H); 13C
NMR (100 MHz, CDCl3) δ 187.3, 186.2, 166.5, 145.1, 137.1, 137.0,
136.5, 133.5, 131.5, 129.7 (2C), 129.4 (2C), 52.4; IR ν 3049, 2959,
1729, 1654, 1590 cm−1; HRMS (ESI) calcd for C14H11O4 [M + H]+
243.0663, found 243.0661.
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We gratefully acknowledge the “Universite
“Centre National de la Recherche Scientifique (CNRS)”, and
́
de Nantes”, the
2-(2-Methoxycarbonylphenyl)-1,4-benzoquinone (3m). The
crude product was purified by flash chromatography on silica gel to
give the product as an orange solid (121.9 mg, 56%): Rf = 0.19
(petroleum ether/DCM 10/90); mp 103−105 °C (lit.5b mp 107−109
the “Reg
“Recrutement sur poste strateg
́
ion Pays de la Loire” in the framework of a
ique” for the financial support
́
1
to this project and O. Brugier and C. Douchet (Universite
Montpellier) for ICPMS analyses. F.-X.F. is member of the
“Institut Universitaire de France (IUF)”. The mixture was
filtered on Buchner. The liquid part was extracted three times
with Et2O and the solid part was washed with DCM.
́
°C); H NMR (400 MHz, CDCl3) δ 8.07 (ddd, 1H, J = 7.7, 1.4, 0.4
Hz), 7.61 (app td, 1H, J = 7.7 Hz, J = 7.7 Hz, J = 1.4 Hz), 7.52 (app td,
1H, J = 7.7 Hz, J = 7.7 Hz, J = 1.4 Hz), 7.27 (ddd, 1H, J = 7.7, 1.4 Hz,
0.4 Hz), 6.88−6.79 (m, 2H), 6.68 (d, 1H, J = 2.2 Hz), 3.79 (s, 3H);
13C NMR (100 MHz, CDCl3) δ 187.6, 185.9, 166.8, 150.2, 137.0,
136.8, 135.1, 132.9, 131.0, 130.5, 130.2, 130.1, 129.9, 52.5; IR ν 3064,
3039, 3004, 2953, 2838, 1709, 1655, 1597, 1487 cm−1; HRMS (ESI)
calcd for C14H9O4 [M − H]− 241.0506, found 241.0510.
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■
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1
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1
ether/DCM 50/50); mp 117−123 °C; H NMR (400 MHz, DMSO-
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E
dx.doi.org/10.1021/jo4004426 | J. Org. Chem. XXXX, XXX, XXX−XXX

The Journal of Organic Chemistry
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