Microwave-assisted efficient synthesis of 1,2-diaryldiketones: a novel oxidation reaction of diarylalkynes with DMSO promoted by FeBr3

Article abstract of DOI:10.1016/j.tet.2006.05.072

This paper reports the oxidation of functionalized diarylalkynes with DMSO in the presence of the environmentally friendly FeBr₃ catalyst. This non-toxic procedure is general and has been applied successfully under microwave irradiation leading rapidly to benzil derivatives in good yields.

Full text of DOI:10.1016/j.tet.2006.05.072

Tetrahedron 62 (2006) 7667–7673
Microwave-assisted efficient synthesis of 1,2-diaryldiketones:
a novel oxidation reaction of diarylalkynes with DMSO
promoted by FeBr3
*
Anne Giraud, Olivier Provot, Jean-Franc¸ois Peyrat, Mouad Alami and Jean-Daniel Brion
*
^
´
´
Laboratoire de Chimie Therapeutique, BioCIS-CNRS (UMR 8076), Universite Paris-Sud,
´
Faculte de Pharmacie, rue J.B. Clement, 92296 Chatenay-Malabry Cedex, France
´
^
Received 19 April 2006; accepted 29 May 2006
Available online 22 June 2006
Abstract—This paper reports the oxidation of functionalized diarylalkynes with DMSO in the presence of the environmentally friendly FeBr3
catalyst. This non-toxic procedure is general and has been applied successfully under microwave irradiation leading rapidly to benzil deriv-
atives in good yields.
Ó 2006 Elsevier Ltd. All rights reserved.
1. Introduction
described by a Russian team.15 While this transformation
is a suitable method, its success was influenced by the elec-
tronic nature of the aryl substituents.16 A recent work con-
cerning the oxidation of alkynes into a-diketones with
DMSO and CH3SO3H/HCO2H/HBr17 prompted us to report
the results of our study. With respect to the environmental
concerns, there is a strong demand for a clean, safe and
highly efficient catalytic methodology for the conversion
of arylalkynes to benzil derivatives.
Benzil derivatives are an important class of compounds,
which have been reported for their application as inhibitors
of the acid corrosion of mild steel,1 as photosensitive agents
in photocurable coatings,2 and also as natural compounds.3
Moreover, benzil substrates constitute useful intermediates
in organic synthesis as precursors of various heterocyclic
compounds such as, for example, imidazoles4 or quinoxa-
lines.5 Conventionally, benzil derivativesare obtainedbyoxi-
dation of benzoins6 or hydrobenzoins.7 However, the access
to functionalized benzoins is not easy and their oxidation
very often required the use of toxic and/or expensive reagents
(e.g., thallium nitrate,6d ammonium chlorochromate–
alumina,6e RuO46g and N-hydroxyphthalimide–Co(acac)3).7c
Besides other methodologies,8,6g by far the most important
procedure for the preparation of benzils is the oxidation of
diarylalkynes, which are easily prepared by Sonogashira–
Linstrumelle coupling. Thus, a large number of oxidizing
systems have been utilized including Co(OAc)2/
Mn(OAc)2/NaBr,9 ZnCr2O7$3H2O,10 SO3–dioxane com-
2. Results and discussion
As a part of our programme aimed at the development of
new, soft and selective oxidizing methodologies,18 we
have investigated the oxidation of various internal aryl-
alkynes 1 with DMSO in the presence of catalytic amounts
of friendly transition-metal salts. Herein, we report a simple
and convenient procedure for the synthesis of a range of
functionalized benzil derivatives promoted by the non-toxic
and cheap FeBr3.
plex,11 H5IO6 and CH3ReO3/H2O2.13 However, these
12
reagents have several drawbacks in terms of toxicity, diffi-
cult reaction conditions, long reaction times and/or low
yields. DMSO as an oxidant in the presence of an excess
of NBS14 has been successfully reported to transform di-
phenylacetylene into benzil. Similarly, an attractive protocol
using DMSO as oxidant in the presence of PdCl2 has been
At the outset of this work, we began our approach by screen-
ing a variety of catalysts using diarylalkyne 1a as a model
substrate in DMSO.
The results described in Table 1 showed clearly that transi-
tion-metal catalysts promoted the oxidation of 1a while no
reaction occurred without catalyst (entry 1). Whereas all
studied metal salts (bromides or chlorides) were effective
in a surprising way, MnCl2 (two attempts) did not catalyze
the oxidation reaction (entry 8) and starting alkyne 1a was
recovered unchanged. Examination of Table 1 indicates
that transition-metal salt bromide catalysts were superiors
Keywords: Benzils; DMSO; Iron bromide; Alkynes; Microwave irradiation.
* Corresponding authors. Tel.: +33 14683 5847; fax: +33 14683 5828
(O.P.); tel.: +33 14683 5887; fax: +33 14683 5828 (M.A.); e-mail
addresses: olivier.provot@cep.u-psud.fr; mouad.alami@cep.u-psud.fr
0040–4020/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2006.05.072

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A. Giraud et al. / Tetrahedron 62 (2006) 7667–7673
Table 1. Oxidation of diarylalkyne 1a to benzil 2a
In our current work to develop rapid and efficient methods
for oxidation reactions, we thought to speed up the synthesis
MeO
of various benzils using microwave-assisted irradiation.18d
O
DMSO, 140 °C
MeO
catalyst 10 mol%
O
Our first efforts were focused on the optimization of the
reaction temperature. When the reaction of 1a is carried
out at 140 ꢀC (as base line control to evaluate the micro-
waves contribution) for 20 min, one notes that 20% of the
starting product 1a was transformed into its corresponding
benzil 2a, while only traces of 2a (<5%, indicated by GC)
were obtained by conventional thermal conditions. By
increasing gradually the reaction temperature, we were
pleased to observe that, using microwave irradiation at
200 ꢀC, diarylalkyne 1a was totally transformed into 2a in
only 20 min and with a satisfactory yield (75%).19 It should
be noted that under convention thermal heating (200 ꢀC,
20 min, sealed tube) the reaction occurred smoothly and
50% of the starting material was recovered unchanged.
InBr3 (10 mol %) and MnBr2 (10 mol %) were also tested,
but longer reaction times, by comparison with FeBr3, were
required to oxidize 1a completely (75%, 40 min and 68%,
45 min, respectively).
1a
2a
Entry
Catalyst
Time (h)
Yielda (%)
1
2
3
4
5
6
7
8
—
CuCl
CuBr
InCl3
InBr3
NiCl2
NiBr2
MnCl2
MnBr2
Fe(acac)3
FeCl3
FeBr3c
FeBr3
72
72
72
16
14
40
24
36
14
40
36
10
10
0
65
66
65
70
72
76
0b
9
75b
68
73
80
78
10
11
12
13
a
Isolated yield.
Two reproducible attempts.
1 equiv of FeBr3 was used.
b
c
Next, we investigated the oxidizing species. When using
stoichiometric amounts or slight excess (5 equiv) of
DMSO, no traces of 2a were detected even after a prolon-
gated reaction time (48 h). A similar result was obtained
when DMSO was replaced by sulfolane (tetramethylene
sulfone); the oxidation reaction failed and starting alkyne
1a was recovered unchanged. We are presently examining
alternatives to DMSO for the oxygen transfer step.
to the corresponding chlorides in terms of increasing yields
and reducing reaction times. In all studied cases, no traces of
arylalkyne 1a were found at the end of the reaction and then
purifications were easy. Of the transition-metal salts exam-
ined, FeBr3 was the most efficient catalyst delivering benzil
2a in high yield (10 h, 80%, entry 12) whereas, under the
same conditions FeCl3 and Fe(acac)3 gave similar yields
but with longer reaction times (entries 10 and 11). With
CuBr, InBr3, NiBr2 and MnBr2, the oxidation reaction was
also successful but with lower yields and longer reaction
times (entries 3, 5, 7 and 9). Finally, increasing the amount
of the iron bromide catalyst was not efficient to observe nei-
ther a reduced reaction time nor a better yield (entry 13).
To demonstrate the scope of the reaction, a series of acetyl-
enic substrates 1a–o were synthesized by Sonogashira–
Linstrumelle coupling20 and subjected to oxidation by the
DMSO–FeBr3 couple under microwave irradiation. The
results of this study are summarized in Table 2.
Table 2. Oxidation of diarylalkynes 1 to benzyl derivatives 2 under microwave irradiation
O
FeBr3 10 mol%
Ar1
Ar1
Ar2
Ar2
DMSOa, 200 °C
O
MW
2
1
Entry
1
Alkynes
1
Benzils
2
Time (min)
20
Yieldb (%)
O
1a
2a
75c
OMe
OMe
O
O
2
3
1b
1c
2b
2c
40
70
75
O
MeO
MeO
O
9
O
OMe
OMe
(continued)

A. Giraud et al. / Tetrahedron 62 (2006) 7667–7673
7669
Table 2. (continued)
Entry
Alkynes
1
Benzils
2
Time (min)
25
Yieldb (%)
64
OMe
OMe
OMe
OMe
OMe
O
OMe
OMe
OMe
OMe
OMe
4
1d
2d
O
O
O
MeO
MeO
5
1e
2e
30
65
OMe
OMe
O
6
1f
1g
1h
1i
2f
2g
2h
2i
11
20
9
61
73
75
72
72
Me
Me
O
O
7
O
O
8
Cl
Br
Cl
Br
O
O
9
9
O
O
10
1j
2j
15
NO2
NO2
O
O
11
12
1k
1l
2k
2l
21
16
46
43
CN
CN
O
O
O
NC
NC
O
13
14
1m
1n
2m
2m
120
0
OH
OH
OH
O
O
O
9
51
OAc
O
15
1o
2o
8
59
OPiv
OPiv
O
a
During this study, we did not observe a notable degradation of the DMSO21 under microwave irradiation.
Isolated yield. All compounds exhibited satisfactory spectral properties and microanalyses.
No oxidation was observed when reactions were conducted without FeBr3 in DMSO at 200 ꢀC under MWI.
b
c

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A. Giraud et al. / Tetrahedron 62 (2006) 7667–7673
Arylalkynes substituted with an electron-donating group
(Me, OMe) have been transformed into benzil derivatives
in good yields (from 61% to 76%) and with reduced reaction
times (<1 h). It should be noted that the position of the sub-
stituent (o, m, p) on the aromatic ring had no influence on the
oxidation yield, although the meta benzil 2c was obtained in
a shorter reaction time (compare entry 3 with entries 1 and 2).
We were also pleased to observe that halogenated substituted
arylalkynes 1h and 1i afforded the expected benzils with re-
duced times and good yields (<10 min, 72–75%, entries 8
and 9). Moreover, the presence of an electron-withdrawing
group on the aryl ring such as NO2 did not affect the yield
as well as the reaction time of the oxidizing process and pro-
vides benzil 2j in 72% yield (entry 10). However, by using
arylalkynes 1k and 1l substituted with an ortho or a para
cyano group, respectively, the desired corresponding benzil
derivatives 2k and 2l were obtained in moderate yields
although totally disappearance of starting material was
observed. It seems that under these conditions, the cyano
group interferes with the outcome of the present reaction
(non-identified hydrolyzed by-products were observed in
the crude reaction mixture). One can note that the phenolic
arylalkyne 1m did not give its corresponding benzil 2m,
even after a prolongated reaction time under MW irradiation.
However, when the hydroxy substituent of 1m was protected
as an acetate (1n), we observed the formation of 2m, after
oxidation of the triple bond followed by cleavage of the ace-
toxyestergroup. A similar result (oxidation and cleavage) has
been obtained with conventional heating (70%, 7 h). On the
contrary, pivaloyl substituted ester 1o was successfully trans-
formed into its corresponding benzil 2o, but without removal
of the bulky protecting group (entry 15). It is important to
note that this new oxidation process with FeBr3–DMSO is
not sensitive to the electronic nature of the acetylenic sub-
strates, unlike some others methodologies.11
occurred slowly (stirring for 72 h at 140 ꢀC, starting alkyne
1a (10%) was still recovered). In the plausible proposed
mechanism (Scheme 1) concerning the oxidation of aryl-
alkynes 1, the Fe(III), acting as a Lewis acid, may activate
the triple bond to generate I and allowed successive addi-
tions of DMSO. After a first addition, a vinyl iron species
II (or its cationic equivalent) would be formed and then trap-
ped by a second molecule of DMSO. The species III formed
would evolve to afford the desired benzyl 2 together with
Me2S and regenerated the catalyst.
In order to activate better the alkyne function, the Lewis
acidity of the Fe(III) catalyst should be increased. For that
purpose, an additional experiment was achieved by introduc-
ing 30 mol % of trifluoromethanesulfonic acid (TfOH) to the
reaction mixture (1a, 10 mol % of FeBr3, DMSO). We were
pleased to observe that under classical thermal conditions
(140 ꢀC), the oxidation proceeded in only 1 h and with
a good yield (71%). In order to determine the positive influ-
ence of TfOH associated with FeBr3, we performed the
oxidation without FeBr3, as control. Total disappearance of
1a was observed but after 10 h of reaction. It is reasonable
to think that the catalytic species formed Fe(OTf)3,22 which
is a stronger Lewis acid than FeBr3, activates considerably
the triple bond. Other attempts were achieved with various
iodine salts in the place of TfOH but unfortunately failed
to give 2a in shorter reaction times. This latest oxidation
reaction involving the synergetic couple TfOH and FeBr3
is currently under investigation in our laboratory.
4. Conclusion
In conclusion, we have developed a simple and efficient pro-
cess for oxidation of arylalkynes using DMSO and catalytic
FeBr3. The use of friendly non-toxic catalytic FeBr3, short
reaction times, high to excellent yields, low cost and easy
preparation are the obvious advantages of the present
method. Under classical thermal conditions, we have dem-
onstrated that the tandem FeBr3–DMSO can be used to
prepare benzil derivatives in reasonable reaction times and
satisfactory yields. The microwave-assisted procedure
allows for the rapid synthesis of various benzils, 20 min
compared to 10 h by conventional methods. The experimen-
tal microwaves experiments described in this paper are well
established and controlled and can be safely and beneficially
reproduced.
3. Mechanistic consideration
At first, an experiment was performed in which the DMSO
solution was degassed. Without O2, oxidation of 1a was still
observed with comparable yields and reaction times, imply-
ing that DMSO constitutes the oxidizing species. When 1a
was heated in DMSO without any catalysts, the oxidation
Ar2
O
Ar1
O
FeBr3
Ar1
Ar2
2
1
Me2S
5. Experimental
5.1. Materials
Me
Me
S
Br
Ar1
Ar2
Ar1
O
O
All glasswares were oven-dried at 140 ꢀC and all reactions
were conducted under an argon atmosphere. Tetrahydro-
furan (THF) was distilled from sodium–benzophenone
ketyl. Triethylamine (TEA) was distilled from potassium
hydroxide under argon prior to use.
Ar2
FeBr2
FeBr3
III
I
Me2S
Me
Me
Me
Ar2
S
O
S O
Br
S O
5.2. Instrumentation
Me
Me
Me
Ar1
FeBr2
All microwave experiments were performed using an Emrys
Optimizer in 2–5 mL Pyrex reaction vessels. Each contained
a Teflon stir bar and Teflon coated reaction vessel cap.
II
Scheme 1. Proposed pathway for the oxidation of arylalkynes 1.

A. Giraud et al. / Tetrahedron 62 (2006) 7667–7673
7671
The compounds were all identified by usual physical
methods, i.e., 1H NMR, 13C NMR, IR and elemental analy-
sis. 1H and 13C NMR spectra were measured in CDCl3 with
solution, dried and concentrated. The crude mixture was
then purified by column chromatography on silica gel.
1
a Bruker AC 200 or Bruker ARX 400. H NMR chemical
5.4.1. 1-(4-Methoxyphenyl)-2-phenyl-ethane-1,2-dione
2a. Yield: 75%; mp: 65 ꢀC; TLC: Rf 0.40 (cyclohexane/
EtOAc, 80/20, SiO2). Anal. Calcd for C15H12O3: C, 74.99;
shifts are reported in parts per million from an internal stan-
dard TMS or of residual chloroform (7.27 ppm). The follow-
ing abbreviations are used: m (multiplet), s (singlet),
d (doublet), t (triplet), dd (doublet of doublet), tt (triplet of
triplet). 13C NMR chemical shifts are reported in parts per
million from the central peak of deuteriochloroform
(77.14). IR spectra were measured on a Bruker Vector 22
spectrophotometer (neat, cmꢁ1). Elemental analyses were
performed with a Perkin–Elmer 240 analyzer. Mass spectra
were obtained with a LCT Micromass spectrometer. Anal-
ytical TLC were performed on Merck precoated silica gel
60F plates. Merck silica gel 60 (230–400 mesh) was used
for column chromatography. Melting points (mp) were re-
H, 5.03%. Found: C, 74.81; H, 5.21. IR (neat) nmax/cmꢁ1
:
2938, 2842, 1666, 1649, 1594, 1569, 1509, 1450, 1422,
1320, 1303, 1268, 1214, 1182, 1162, 1110, 1020, 973,
931, 877, 841, 818, 803. 1H NMR for 2a (CDCl3,
200 MHz, 298 K): d, ppm 7.98–7.92 (m, 4H), 7.69–7.66
(m, 1H), 7.52–7.44 (m, 2H), 6.96 (d, 2H, J¼9 Hz), 3.87 (s,
3H). 13C NMR for 2a (CDCl3, 50 MHz, 298 K): d, ppm
194.7 (CO), 193.0 (CO), 164.9 (C), 134.6 (CH), 133.7 (C),
132.2 (2CH), 129.7 (2CH), 128.8 (2CH), 125.9 (C), 114.2
(2CH), 55.5 (CH3). m/z MS (ES+) 263.1 (M+Na+).
€
corded on a Buchi B-450 apparatus and were uncorrected.
5.4.2. 1-(2-Methoxyphenyl)-2-phenyl-ethane-1,2-dione
2b. Yield: 70%; TLC: Rf 0.63 (cyclohexane/EtOAc, 85/15,
SiO2). Anal. Calcd for C15H12O3: C, 74.99; H, 5.03%.
Found: C, 74.58; H, 4.95. IR (neat) nmax/cmꢁ1: 2945,
1676, 1654, 1596, 1580, 1483, 1466, 1450, 1435, 1306,
5.3. General procedure for the preparation of aryl-
alkynes from aryl halides
1
All arylalkynes except 1o were known compounds and have
been prepared according to the following procedure.
1271, 1246, 1202, 1162, 1114, 1017, 875. H NMR for 2b
(CDCl3, 400 MHz, 298 K): d, ppm 8.06 (d, 1H, J¼8.0 Hz),
7.95 (d, 2H, J¼8.0 Hz), 7.64–7.60 (m, 2H), 7.56 (t, 2H,
J¼8.0 Hz), 7.16 (t, 1H, J¼8.0 Hz), 6.97 (t, 1H, J¼8.0 Hz),
3.59 (s, 3H). 13C NMR for 2b (CDCl3, 100 MHz, 298 K):
d, ppm 194.6 (CO), 193.5 (CO), 160.4 (C), 136.4 (CH),
133.7 (CH), 133.0 (C), 130.6 (CH), 129.3 (2CH), 128.7
(2CH), 124.0 (CH), 121.6 (CH), 112.4 (CH), 55.6 (CH3).
m/z MS (ES+) 263.0 (M+Na+).
5.3.1. 2,2-Diethyl-propionic acid-4-phenylethynyl-phenyl
ester 1o. To a mixture of 2,2 dimethyl-propionic acid-4-
iodo-phenyl ester (303 mg; 1 mmol), PdCl2(PPh3)2
(35.1 mg; 0.05 mmol), CuI (19.1 mg; 0.1 mmol) and TEA
(404.8 mg; 4.0 mmol) in THF (10 mL), a solution of phenyl-
acetylene (132.6 mg; 1.2 mmol) was added dropwise under
an argon atmosphere. The mixture was stirred at room tem-
perature for overnight. Then Et2O (20 mL) was added to the
crude and the mixture was filtered over a short pad of Celite.
The organic layer was washed twice with brine (5 mL), sepa-
rated, dried over MgSO4, filtered and concentrated. Result-
ing residue was further purified by flash chromatography.
5.4.3. 1-(3-Methoxyphenyl)-2-phenyl-ethane-1,2-dione
2c. Yield: 75%; TLC: Rf 0.54 (cyclohexane/EtOAc, 80/20,
SiO2). Anal. Calcd for C15H12O3: C, 74.99; H, 5.03%.
Found: C, 74.88; H, 4.99. IR (neat) nmax/cmꢁ1: 3074,
3010, 2838, 1658, 1592, 1484, 1467, 1453, 1429, 1337,
1321, 1298, 1259, 1203, 1174, 1157, 1079, 1033, 994,
932, 903, 874, 832, 803. 1H NMR for 2c (CDCl3,
200 MHz, 298 K): d, ppm 7.87 (d, 1H, J¼7.0 Hz), 7.58–
7.49 (m, 1H), 7.40–7.22 (m, 5H), 7.13 (s, 1H), 7.10–7.04
(m, 1H), 3.74 (s, 3H). 13C NMR for 2c (CDCl3, 50 MHz,
298 K): d, ppm 194.4 (2CO), 160.0 (C), 134.8 (CH), 134.2
(C), 133.0 (C), 130.0 (CH), 129.8 (2CH), 128.9 (2CH),
123.1 (CH), 121.8 (CH), 112.9 (CH), 55.4 (CH3).
Yield: 95%; mp: 92 ꢀC; TLC: Rf 0.61 (cyclohexane/EtOAc,
90/10, SiO2). Anal. Calcd for C19H18O2: C, 81.99; H,
6.52%. Found: C, 81.87; H, 6.47. IR (neat) nmax/cmꢁ1
:
2971, 1743, 1593, 1506, 1479, 1445, 1396, 1369, 1275,
1235, 1197, 1160, 1140, 1115, 1033, 1013, 954, 919, 897,
859, 842, 801. H NMR for 1o (CDCl3, 200 MHz, 298 K):
1
d, ppm 7.62–7.51 (m, 4H), 7.36–7.33 (m, 3H), 7.06 (d, 2H,
J¼8.7 Hz), 1.37 (s, 9H). 13C NMR for 1o (CDCl3, 50 MHz,
298 K): d, ppm 176.7 (CO), 151.0 (C), 132.7 (2CH), 131.6
(2CH), 128.3 (2CH), 128.3 (CH), 123.2 (C), 121.6 (2CH),
120.7 (C), 89.3 (C), 88.6 (C), 39.1 (C), 27.1 (3CH3).
5.4.4. 1-Phenyl-2-(3,4,5-trimethoxyphenyl)-ethane-1,2-
dione 2d. Yield: 64%; mp: 102 ꢀC; TLC: Rf 0.48 (cyclohex-
ane/EtOAc, 70/30, SiO2). Anal. Calcd for C17H16O5: C,
67.99; H, 5.37%. Found: C, 67.91; H, 5.30. IR (neat) nmax
/
5.4. General procedure for the preparation of benzils
2a–o from alkynes under microwave irradiation
cmꢁ1: 2932, 2834, 1664, 1581, 1504, 1460, 1450, 1413,
1343, 1317, 1283, 1233, 1180, 1157, 1129, 1076, 993,
947, 859, 819. H NMR for 2d (CDCl3, 200 MHz, 298 K):
1
To an Emrys Optimizer 2–5 mL Pyrex reaction vessel were
added alkyne (0.5 mmol), FeBr3 (15 mg; 0.05 mmol), in
DMSO (2.5 mL). The reaction vessel was then placed in
the Emrys Optimizer and exposed to microwave irradiation
according to the following specifications: temperature:
200 ꢀC, time (see Table 2), fixed hold time: on, sample
absorption: high, pre-stirring: 60 s. After cooling to room
temperature, H2O (3 mL) was added to the crude and the
mixture was extracted with EtOAc (3ꢂ2 mL). Organic
layers were then washed with an aqueous saturated NH4Cl
d, ppm 7.95 (d, 2H, J¼7.4 Hz), 7.66 (t, 1H, J¼7.4 Hz),
7.49 (t, 2H, J¼7.4 Hz), 7.11 (s, 2H), 3.93 (s, 3H), 3.85 (s,
6H). 13C NMR for 2d (CDCl3, 50 MHz, 298 K): d, ppm
194.2 (CO), 193.2 (CO), 153.4 (2C), 144.2 (C), 134.7
(CH), 133.1 (C), 129.8 (2CH), 128.9 (2CH), 127.9 (C),
107.2 (2CH), 60.9 (CH3), 56.3 (2CH3). m/z MS (ES+)
323.1 (M+Na+).
5.4.5. 1-(4-Methoxyphenyl)-2-(3,4,5-trimethoxyphenyl)-
ethane-1,2-dione 2e. Yield: 65%; mp: 140 ꢀC; TLC: Rf

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A. Giraud et al. / Tetrahedron 62 (2006) 7667–7673
0.37 (cyclohexane/EtOAc, 80/20, SiO2). Anal. Calcd for
C18H18O6: C, 65.45; H, 5.49%. Found: C, 65.46; H, 5.59.
IR (neat) nmax/cmꢁ1: 2982, 1651, 1598, 1571, 1502, 1448,
1427, 1412, 1342, 1273, 1245, 1180, 1155, 1125, 1017,
50/50, SiO2). Anal. Calcd for C14H9NO4: C, 65.88; H, 3.55;
N, 5.49%. Found: C, 65.81; H, 3.54; N, 5.48. IR (neat) nmax
/
cmꢁ1: 1660, 1594, 1523, 1450, 1344, 1200, 1170, 1110, 883,
859, 839. 1H NMR for 2j (CDCl3, 200 MHz, 298 K): d, ppm
8.36 (d, 2H, J¼8.7 Hz), 8.17 (d, 2H, J¼8.7 Hz), 7.99 (dd,
2H, J¼7.9, 1.0 Hz), 7.71 (tt, 1H, J¼7.9, 1.0 Hz), 7.55 (t,
2H, J¼7.9 Hz). 13C NMR for 2j (CDCl3, 50 MHz, 298 K):
d, ppm 192.8 (CO), 192.0 (CO), 151.1 (C), 137.3 (C),
135.4 (CH), 132.4 (C), 130.9 (2CH), 130.0 (2CH), 129.2
(2CH), 129.0 (2CH).
1
998, 948, 854. H NMR for 2e (CDCl3, 200 MHz, 298 K):
d, ppm 7.95 (d, 2H, J¼9.0 Hz), 7.23 (s, 2H), 6.98 (d, 2H,
J¼9.0 Hz), 3.94 (s, 3H), 3.89 (s, 3H), 3.88 (s, 6H). 13C
NMR for 2e (CDCl3, 50 MHz, 298 K): d, ppm 193.5 (CO),
192.8 (CO), 164.9 (C), 153.2 (2C), 144.1 (C), 132.3
(2CH), 128.1 (C), 126.1 (C), 114.3 (2CH), 107.2 (2CH),
60.9 (CH3), 56.3 (2CH3), 55.5 (CH3). m/z MS (ES+) 353.1
(M+Na+).
5.4.11. 1-(4-Cyanophenyl)-2-phenyl-ethane-1,2-dione 2k.
Yield: 46%; mp: 111.5 ꢀC; TLC: Rf 0.42 (cyclohexane/
EtOAc, 90/10, SiO2). Anal. Calcd for C15H9NO2: C,
76.59; H, 3.86; N, 5.95%. Found: C, 76.38; H, 3.61; N,
5.85. IR (neat) nmax/cmꢁ1: 3072, 2226, 1679, 1658, 1593,
1579, 1450, 1405, 1321, 1297, 1206, 1171, 1116, 999,
5.4.6. 1-Phenyl-2-p-tolyl-ethane-1,2-dione 2f. Yield: 61%;
mp: 96 ꢀC; TLC: Rf 0.51 (cyclohexane/EtOAc, 90/10, SiO2).
Anal. Calcd for C14H10O2: C, 79.98; H, 4.79%. Found: C,
79.92; H, 4.81. IR (neat) nmax/cmꢁ1: 1665, 1591, 1578,
1449, 1325, 1209, 1173, 998, 874. 1H NMR for 2f (CDCl3,
200 MHz, 298 K): d, ppm 7.97 (d, 4H, J¼8.0 Hz), 7.67
(m, 2H), 7.52 (d, 4H, J¼8.0 Hz). 13C NMR for 2f (CDCl3,
50 MHz, 298 K): d, ppm 194.0 (2CO), 134.7 (2CH), 132.9
(2CH), 129.8 (4CH), 128.9 (4CH). m/z MS (ES+) 233.0
(M+Na+).
1
971, 879, 843, 800. H NMR for 2k (CDCl3, 200 MHz,
298 K): d, ppm 8.08 (d, 2H, J¼8.0 Hz), 7.96 (d, 2H,
J¼8.6 Hz), 7.80 (d, 2H, J¼8.6 Hz), 7.69 (t, 1H,
J¼8.0 Hz), 7.53 (t, 2H, J¼8.0 Hz). 13C NMR for 2k
(CDCl3, 50 MHz, 298 K): d, ppm 193.0 (CO), 192.4 (CO),
135.9 (C), 135.3 (CH), 132.7 (C), 132.5 (2CH), 130.2
(2CH), 130.0 (2CH), 129.2 (2CH), 117.9 (C), 117.5 (C).
5.4.7. 1,2-Diphenyl-ethane-1,2-dione (benzil) 2g. Yield:
73%; TLC: Rf 0.27 (cyclohexane/EtOAc, 90/10, SiO2).
Anal. Calcd for C15H12O2: C, 80.34; H, 5.39%. Found: C,
80.26; H, 5.31. IR (neat) nmax/cmꢁ1: 1667, 1603, 1572,
1475, 1449, 1410, 1324, 1287, 1208, 1173, 1120, 1019,
5.4.12. 2-(2-Oxo-2-phenylacetyl)-benzonitrile 2l. Yield:
43%; mp: 67.5 ꢀC; TLC: Rf 0.36 (cyclohexane/EtOAc, 70/
30, SiO2). Anal. Calcd for C15H9NO2: C, 76.59; H, 3.86;
N, 5.95%. Found: C, 76.47; H, 3.79; N, 5.92. IR (neat)
nmax/cmꢁ1: 3067, 2926, 2227, 1668, 1592, 1570, 1489,
1451, 1367, 1318, 1212, 1180, 1124, 1017, 951, 888, 869.
1H NMR for 2l (CDCl3, 400 MHz, 298 K): d, ppm 8.05 (d,
2H, J¼8.4 Hz), 7.96–7.92 (m, 2H), 7.82–7.71 (m, 3H),
7.58 (t, 2H, J¼8.4 Hz). 13C NMR for 2l (CDCl3, 50 MHz,
298 K): d, ppm 192.1 (CO), 191.2 (CO), 135.6 (CH),
135.3 (CH), 135.1 (C), 134.0 (CH), 132.7 (CH), 132.4 (C),
132.3 (CH), 130.1 (2CH), 129.1 (2CH), 117.0 (C), 117.9
(CN), 112.0 (C).
1
879, 828. H NMR for 2g (CDCl3, 200 MHz, 298 K): d,
ppm 7.96 (d, 2H, J¼7.3 Hz), 7.86 (d, 2H, J¼8.0 Hz), 7.64
(t, 1H, J¼7.3 Hz), 7.49 (t, 2H, J¼7.3 Hz), 7.30 (d, 2H,
J¼8.0 Hz), 2.42 (s, 3H). 13C NMR for 2g (CDCl3,
50 MHz, 298 K): d, ppm 194.7 (CO), 194.2 (CO), 146.1
(C), 134.7 (CH), 133.1 (C), 130.6 (C), 129.9 (2CH), 129.8
(2CH), 129.7 (2CH), 128.9 (2CH), 21.8 (CH3).
5.4.8. 1-(4-Chlorophenyl)-2-phenyl-ethane-1,2-dione 2h.
Yield: 75%; mp: 77 ꢀC; TLC: Rf 0.35 (cyclohexane/EtOAc,
70/30, SiO2). Anal. Calcd for C14H9ClO2: C, 68.72; H,
5.4.13. 1-(4-Hydroxyphenyl)-2-phenyl-ethane-1,2-dione
2m. Yield: 51%; mp: 125 ꢀC; TLC: Rf 0.50 (cyclohexane/
EtOAc, 70/30, SiO2). Anal. Calcd for C14H10O3: C, 74.33;
3.71%. Found: C, 69.01; H, 3.75. IR (neat) nmax/cmꢁ1
:
1663, 1584, 1487, 1450, 1402, 1321, 1208, 1172, 1113,
1093, 1013, 873, 833. H NMR for 2h (CDCl3, 200 MHz,
1
H, 4.46%. Found: C, 74.18; H, 4.32. IR (neat) nmax/cmꢁ1
:
298 K): d, ppm 7.98–7.90 (m, 3H), 7.70–7.63 (m, 2H),
7.55–7.40 (m, 4H). 13C NMR for 2h (CDCl3, 50 MHz,
298 K): d, ppm 193.8 (CO), 193.0 (CO), 141.5 (C), 135.0
(CH), 132.8 (C), 131.4 (C), 131.2 (2CH), 129.9 (2CH),
129.4 (2CH), 129.0 (2CH).
3385, 1672, 1648, 1595, 1562, 1515, 1449, 1302,
1204, 1157, 1047, 998, 878, 845. 1H NMR for 2m
(CDCl3, 400 MHz, 298 K): d, ppm 7.88 (d, 2H, J¼7.3 Hz),
7.80 (d, 2H, J¼8.6 Hz), 7.57 (t, 1H, J¼7.3 Hz), 7.42 (t, 2H,
J¼7.3 Hz), 6.82 (d, 2H, J¼8.6 Hz), 6.80–6.10 (m, 1H). 13C
NMR for 2m (CDCl3, 50 MHz, 298 K): d, ppm 195.4
(CO), 193.6 (CO), 162.5 (C), 135.0 (CH), 133.0 (C), 132.7
(2CH), 129.9 (2CH), 129.0 (2CH), 125.6 (C), 116.1 (2CH).
5.4.9. 1-(4-Bromophenyl)-2-phenyl-ethane-1,2-dione 2i.
Yield: 72%; mp: 87 ꢀC; TLC: Rf 0.61 (cyclohexane/EtOAc,
94/6, SiO2). Anal. Calcd for C14H9BrO2: C, 58.16; H,
3.14%. Found: C, 58.02; H, 3.03. IR (neat) nmax/cmꢁ1: 1662,
1578, 1483, 1450, 1398, 1321, 1204, 1172, 1113, 1069,
5.4.14. 2,2-Dimethyl-propionic acid-4-(2-oxo-2-phenyl-
acetyl)-phenyl ester 2o. Yield: 59%; mp: 87 ꢀC; TLC: Rf
0.47 (cyclohexane/EtOAc, 90/10, SiO2). Anal. Calcd for
C19H18O4: C, 73.53; H, 5.85%. Found: C, 73.41; H, 5.79.
IR (neat) nmax/cmꢁ1: 2978, 1742, 1662, 1594, 1505, 1479,
1454, 1400, 1366, 1326, 1296, 1280, 1231, 1207, 1174,
1157, 1116, 1032, 1012, 997, 974, 904, 873, 804. 1H NMR
for 2o (CDCl3, 400 MHz, 298 K): d, ppm 8.05–7.94 (m,
4H), 7.65 (tt, 1H, J¼7.7, 1.4 Hz), 7.54–7.46 (m, 2H),
7.26–7.16 (m, 2H). 13C NMR for 2o (CDCl3, 50 MHz,
298 K): d, ppm 194.2 (CO), 193.2 (CO), 176.2 (OCO), 156.3
1
1024, 1009, 870, 829. H NMR for 2i (CDCl3, 200 MHz,
298 K): d, ppm 7.96 (d, 2H, J¼7.4 Hz), 7.84 (d, 2H,
J¼8.6 Hz), 7.68–7.64 (m, 3H), 7.52 (t, 2H, J¼7.4 Hz). 13C
NMR for 2i (CDCl3, 50 MHz, 298 K): d, ppm 193.8 (CO),
193.2 (CO), 135.0 (CH), 132.8 (C), 132.4 (2CH), 131.8 (C),
131.2 (2CH), 130.4 (C), 129.9 (2CH), 129.0 (2CH).
5.4.10. 1-(4-Nitrophenyl)-2-phenyl-ethane-1,2-dione 2j.
Yield: 72%; mp: 141 ꢀC; TLC: Rf 0.27 (cyclohexane/EtOAc,

A. Giraud et al. / Tetrahedron 62 (2006) 7667–7673
7673
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(C), 134.9 (CH), 132.9 (C), 131.5 (2CH), 130.3 (C), 129.9
(2CH), 129.0 (2CH), 122.2 (2CH), 93.2 (C), 27.0 (3CH3).
8. (a) Antoniotti, S.; Dun˜ach, E. Eur. J. Org. Chem. 2004, 3459;
(b) Clayton, M. D.; Marcinow, Z.; Rabineau, P. W.
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Acknowledgements
The CNRS is gratefully acknowledged for support of this re-
search and the MNSER for a doctoral fellowship to A.G. The
authors wish also to thank Pr. T. Besson for fruitful discus-
sions concerning the use of DMSO under MW irradiations.
10. Firouzabadi, H.; Sardarian, A. R.; Moosavipour, H.; Afshari,
G. M. Synthesis 1986, 285.
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