Glycerol as a recyclable solvent for copper-catalyzed cross-coupling reactions of diaryl diselenides with aryl boronic acids

Article abstract of DOI:10.1039/c2gc16427b

We describe herein the use of glycerol as the solvent in the copper-catalyzed cross-coupling reaction of diaryl diselenides with arylboronic acids using CuI and DMSO as additive. This cross-coupling reaction was performed with diaryl diselenides and arylboronic acids bearing electron-withdrawing and electron-donating groups, affording the corresponding diaryl selenides in good to excellent yields. The glycerol-CuI mixture can be directly reused for further cross-coupling reactions.

Full text of DOI:10.1039/c2gc16427b

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PAPER
Glycerol as a recyclable solvent for copper-catalyzed cross-coupling reactions
of diaryl diselenides with aryl boronic acids†
Vanessa G. Ricordi, Camilo S. Freitas, Gelson Perin, Eder J. Lenardão, Raquel G. Jacob,*
Lucielli Savegnago and Diego Alves*
Received 10th November 2011, Accepted 13th January 2012
DOI: 10.1039/c2gc16427b
We describe herein the use of glycerol as the solvent in the copper-catalyzed cross-coupling reaction of
diaryl diselenides with arylboronic acids using CuI and DMSO as additive. This cross-coupling reaction
was performed with diaryl diselenides and arylboronic acids bearing electron-withdrawing and electron-
donating groups, affording the corresponding diaryl selenides in good to excellent yields. The glycerol–
CuI mixture can be directly reused for further cross-coupling reactions.
More examples concerning the role of the solvent in these
reactions have been described. In studies using DMSO, it was
Introduction
The versatility and applicability of organoselenium compounds
in organic chemistry is widely described in a great number of
reviews1 and books.2 Organoselenium compounds are attractive
molecules because of their use as ionic liquids3 and in asym-
metric catalysis,1b–d their fluorescent properties4 and because of
their interesting biological activities.5 Diaryl selenides are cer-
tainly the organoselenium compounds most studied and a large
number of methodologies have been reported to prepare these
compounds.2 In some cases, the described methodologies need
long reaction times, harsh reaction conditions, stoichiometric or
greater amount of metallic reagents and sometimes the products
are only generated in moderate yields.2
To overcome these limitations, much attention has recently
been focused to develop catalytic systems to reduce the environ-
mental impact of these methodologies. Thus, metal-catalyzed
reactions of diaryl diselenides with aryl halides or aryl boronic
acids has become a versatile tool for the synthesis of symmetrical
or unsymmetrical diaryl selenides.6 A great number of studies
have focused on the use of copper, palladium, iron, indium,
rhodium, ruthenium and nickel-based catalytic systems for this
purpose.6 Most of these systems involve a homogeneous process
and specific ligands, which in some cases may increase the cost
and limit the scope of any applications.6 Recently, diaryl sele-
nides were synthesized by a copper catalyzed process through
CAr–Se bond formation under mild reaction conditions from aryl
iodides or bromides and diphenyl diselenide.7 In that work, the
solvent CH3CN acts as ligand for copper(I) iodide and no exter-
nal ligand was required.
observed that this molecule not only acts as solvent, but also as
the oxidant of the active metal species in the catalytic cycle.8
Furthermore, developing greener catalytic systems that are econ-
omical, free of external ligands and that would produce the desir-
able diarylselenides in high yields, are still highly sought after.
In this context, the development of green methodologies from
renewable resources has gained much interest recently because
of the extensive use of solvents in chemical industries, and of
the predicted disappearance of fossil oil.9 The desirable charac-
teristics for a green solvent include low flammability, high avail-
ability, biodegradability and ideally can be obtained from
renewable sources.10 With the increase in biodiesel production
world-wide, the market saturation of glycerol, a side product of
biodiesel production, is inevitable.11 The use of glycerol12 and
their eutetics13 as a sustainable solvents for green chemistry was
recently studied. Heck and Suzuki cross-couplings, ring closing
metathesis of diolefins, multicomponent reactions, asymmetrical
reduction and cycloisomerization of (Z)-enynols into furans, are
some examples of the use of glycerol as solvent in organic reac-
tions.12 Recently, glycerol has proved an efficient solvent in the
cross-coupling reaction of diaryl diselenides with (Z)- or (E)-
vinyl bromides catalyzed by CuI. In this study, the glycerol/cata-
lyst mixture was directly reused for further cross-coupling
reactions.14
Results and discussion
In this sense and due to our interest in green protocols correlated
to the organochalcogen chemistry,15 we describe here the use of
glycerol as solvent in the copper-catalyzed cross-coupling reac-
tion of diaryl diselenides with arylboronic acids by CuI as cata-
lyst and using DMSO as additive (Scheme 1).
We initially focused our attention on the optimization of the
reaction conditions for the synthesis of 4-methoxyphenyl-phenyl
selenide 3a starting from diphenyl diselenide 1a and 4-
Laboratório de Síntese Orgânica Limpa, LASOL, Universidade Federal
de Pelotas, UFPel, P.O. Box 354, 96010-900 Pelotas, RS, Brazil.
E-mail: diego.alves@ufpel.edu.br, raquel.jacob@ufpel.edu.br;
Tel: +55 (53) 3275-7533
†Electronic supplementary information (ESI) available: See DOI:
10.1039/c2gc16427b
1030 | Green Chem., 2012, 14, 1030–1034
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Scheme 1 General scheme of the reaction.
Table 1 Reaction conditions optimization using arylboronic acid 2aa
Yield of 3ab (%)
Fig. 1 Reuse of catalytic system glycerol–CuI.
Entry
Copper salt (mol%)
Additive (1 eq.)
dimethylsulfide under the reaction conditions.8 In our exper-
iment, dimethyl sulfide could be observed in small amounts in
gas chromatography analysis.
A great decrease in the yield of product 3a was observed
when the reaction was performed using 10 mol% of DMSO
(Table 1, entry 6). When the reactions were carried out using
other copper salts, such as, CuCl, CuCl2 and Cu(OAc)2 or using
reduced amounts of CuI (3 and 1 mol%), product 3a was
obtained in lower yields compared to reactions using 5 mol% of
CuI (Table 1, entries 12–17 vs. 3).
In an optimized reaction, diphenyl diselenide 1a (0.25 mmol),
4-methoxyphenyl boronic acid 2a (0.5 mmol), CuI (5 mol%)
and DMSO (0.5 mmol) were dissolved in glycerol (0.5 mL).
The heterogeneous reaction mixture was stirred for 30 hours at
110 °C under atmospheric air affording 4-methoxyphenyl-phenyl
selenide 3a in 90% yield.
1
2
3
CuO NPs (5%)
CuI (5%)
CuI (5%)
CuO NPs (5%)
CuI (5%)
CuI (5%)
CuI (5%)
CuI (5%)
CuI (5%)
CuI (5%)
—
—
30
32
90
78
91
10
31
29
32
27
23
54
47
51
92
69
55
DMSO
DMSO
DMSO
DMSO
DMF
CH3CN
H2O
4
5c
6d
7
8
9
10
11
12
13
14
15
16
17
Mg
Zn
CuI (5%)
CuCl (5%)
CuCl2 (5%)
Cu(OAc)2 (5%)
CuI (10%)
CuI (3%)
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
CuI (1%)
a Reactions are performed in the presence of compounds 1a (0.25 mmol)
and 2a (0.5 mmol) in glycerol (0.5 mL), at 110 °C for 30 h in open
atmosphere. b Yields are given for isolated product. c Reaction using
0.75 mmol of 2a. d Reaction using 10 mol% of DMSO.
After reaction optimization, a study regarding the recovering
and reusing of glycerol was performed. Subsequent to the for-
mation of product 3a, the reaction mixture was diluted and
extracted with a mixture of hexane/ethyl acetate 95 : 5 (3 ×
3 mL). The upper phase was dried and the solvent evaporated.
The inferior, glycerol phase, was dried under vacuum and
directly reused. However, only traces of compound 3a were
obtained. In view of this result, we performed two different
studies. Initially, after the first reaction, we added CuI (5 mol%)
on the recovered glycerol phase and performed the reuse. This
protocol was not efficient and product 3a was not formed. In a
further study, after the first reaction, we added DMSO
(0.5 mmol) on the recovered glycerol phase and to our satisfac-
tion the desired product 3a was obtained in 88%. After these
experiments, we proceeded the reuse study adding new DMSO
portions (0.5 mmol) in all runs, according Fig. 1. It was
observed that a good level of efficiency was maintained even
after being reused three times. Diaryl selenide 3a was obtained
in 90%, 88%, 88% and 86% yields after successive cycles. After
four runs, the efficiency of glycerol was decreased and the yield
of compound 3a was 71%.
methoxyphenylboronic acid 2a in glycerol (Table 1). Experimen-
tal procedures recently published to accomplish these cross-
coupling reactions needed the use of copper salts at temperatures
over 100 °C.8a,16 For this reason, we started studying the reaction
of substrates 1a and 2a in the presence of CuO nanoparticles
(CuO NPs) (5 mol%) using glycerol as solvent at 110 °C in open
atmosphere. Under this condition, the desired product 3a was
obtained in only 30% after 30 hours (Table 1, entry 1). A similar
result was obtained when we change the copper reagent CuO
NPs to CuI (Table 1, entry 2).
Aiming to improve the yield of product 3a, a mixture of
diphenyl diselenide 1a, arylboronic acid 2a in glycerol was
reacted in open atmosphere for 30 hours, applying different
copper salts and additives. To our satisfaction, product 3a was
obtained in 90% using 5 mol% of CuI using 1.0 eq. of DMSO
(Table 1, entry 3). We observed that the use of stoichiometric
DMSO as additive was important for the reaction success. Sub-
strates 1a and 2a were reacted in glycerol using a range of addi-
tives, such as, DMSO, DMF, CH3CN, H2O, Mg and Zn, and the
corresponding product 3a was obtained in best yields in the reac-
tions using DMSO (Table 1, entries 3 vs. 7–11). Recent studies
show that the DMSO acts as oxidant of the activity metal species
in these cross-coupling reactions and might be reduced into
After that, the scope of our methodology was evaluated by
reacting other arylboronic acids 2b–k with diphenyl diselenide
1a (Table 2). The results shown in Table 2 reveal that the reac-
tion worked well with a range of substituted arylboronic acids,
affording good yields of the products. The reactions are not
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Table 2 Synthesis of diarylselenides 3a–q using glycerol as solventa
[ref.]
Entry
1
Ar
Ar1
Product
Isolated Yield (%)
90
1a
2a
3a16a
2
85
1a
1a
2b
2c
3b16a
3
4
90
83
3c16a
1a
1a
1a
2d
2e
2f
3d16a
3e16a
3f16a
5
6
7
90
87
86
1a
1a
2g
2h
3g16a
8
9
86
82
3h16a
1a
1a
2i
2j
3i17
10
11
77
73
3j18
1a
1b
1c
2k
2a
2a
3k19
12
13
82
80
3l20
3m16a
1032 | Green Chem., 2012, 14, 1030–1034
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Table 2 (Contd.)
[ref.]
Entry
14
Ar
Ar1
Product
Isolated Yield (%)
80
1d
1e
2a
2a
3n16a
15
16
89
79
3o16a
1f
2a
2a
3p21
17
76
1g
3q15f
a Reactions are performed in the presence of diaryl diselenide (0.25 mmol), arylboronic acid (0.5 mmol), CuI (5 mol%), DMSO (0.5 mmol), glycerol
(0.5 mL), at 110 °C for 30 hours in open atmosphere.
sensitive to the electronic effect of the aromatic ring in the aryl-
boronic acid. According the results, arylboronic acids containing
electron-donating (OMe, Me), electron-withdrawing (Cl, Br) and
electron-neutral group at the aromatic ring gave good yields of
desired diaryl selenides (Table 2, entries 1–9). Differentiation in
the reactivity between bromine and boron atoms of boronic acid
can be seen by coupling of boronic acids 2h and 2i with diphe-
Scheme 2 Reaction with diphenyl ditelluride and diphenyl disulfide.
nyl diselenide 1a. In these cases, only the coupling products 3h
and 3i were obtained in 86% and 82% yield respectively,
without by-products (Table 2, entries 8–9). In our methodology,
the bromine substituent was not affected. A slight decrease in the
Conclusions
In conclusion, glycerol has proved to be an efficient solvent for
the synthesis of diaryl selenides by cross-coupling reactions of
diaryl diselenides with aryl boronic acids using a catalytic
amount of CuI and DMSO as additive, under open atmosphere
at 110 °C. This cross-coupling reaction affords the corresponding
products in good to excellent yields and a range of diaryl disele-
nides and arylboronic acids were coupled. In addition, catalytic
system glycerol–CuI can be easily recovered and utilized for
further cross-coupling reactions, specially appropriated to green
chemistry concept. Studies toward the mechanism insight and
the role of DMSO in this reaction are in progress in our
laboratory.
yield was observed using 3-trifluoromethyl group attached in the
aromatic ring at boronic acid partner (Table 2, entry 10). Reac-
tion performed with 2-naphthylboronic acid 2k furnished the
respective product 3k in satisfactory yield (Table 2, entry 11).
Later, the possibility of performing these reactions with other
diaryl diselenides 1b–g was also investigated. A range of diaryl
diselenides containing electron-donating and electron-withdraw-
ing groups at the aromatic ring were efficiently coupled with 4-
methoxyphenylboronic acid 2a, affording the respective diaryl-
selenides 3l–p in good yields (Table 2, entries 12–16). We
observed that steric effects had little influence on the coupling
reaction and dimesityl diselenide gave the desired product 3q in
76% yield (Table 2, entry 17).
In addition, under the optimized reaction conditions, the possi-
bility of performing the reaction with other diphenyl dichalco-
genides was also investigated. Thus, 4-methoxyphenylboronic
acid 2a was efficiently coupled with diphenyl ditelluride, afford-
ing the respective diaryltelluride 4 in excellent yield. However,
when the arylboronic acid 2a reacted with diphenyl disulfide,
low yield of diarylsufide 5 was obtained (Scheme 2).
Experimental
General
The reactions were monitored by TLC carried out on Merck
silica gel (60 F254) by using UV light as visualizant agent and
5% vanillin in 10% H2SO4 and heat as developing agents. NMR
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spectra were recorded with Bruker DPX 200 and DPX 400 (200
and 400 MHz) instrument using CDCl3 as solvent and calibrated
using tetramethylsilane as internal standard. Chemical shifts are
reported in δ ppm relative to (CH3)4Si for 1H and CDCl3 for 13
C
NMR. Coupling constants (J) are reported in Hertz. Mass spectra
(MS) were measured on a Shimadzu GCMS-QP2010 mass
spectrometer.
General procedure for the cross-coupling using glycerol
To
a round-bottomed flask containing organic diselenide
(0.25 mmol), aryl boronic acid (0.5 mmol), CuI (0.025 mmol;
0.0048g), was added glycerol (0.5 mL) and DMSO (0.5 mmol).
The reaction mixture was allowed to stir at 110 °C for 30 hours.
After this time, the solution was cooled to room temperature,
diluted with ethyl acetate (20 mL), and washed with water (3 ×
20 mL). The organic phase was separated, dried over MgSO4,
and concentrated under vacuum. The obtained products were
purified by flash chromatography on silica gel using hexane or a
mixture of ethyl acetate/hexane as the eluent. The spectral data
of obtained compounds are in agreement with those described in
literature.
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Recycling of glycerol
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The aforementioned procedure was used with diphenyl disele-
nide 1a (0.25 mmol), 4-methoxyphenylboronic acid 2a
(0.5 mmol), CuI (0.025 mmol; 0.0048 g), DMSO (0.5 mmol)
and glycerol (0.5 mL). After the reaction was complete, the reac-
tion mixture was washed with a mixture of hexane/ethyl acetate
(95 : 5) (3 × 3 mL) and the upper organic phases were separated
from glycerol. The product was isolated according procedure
above. The resulting glycerol phase was dried under vacuum and
reused for further reactions without previous purification.
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Acknowledgements
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The authors are grateful to FAPERGS (PRONEX 10/0005-1, 10/
0027-4 and PqG 11/1045-8), CAPES, FINEP and CNPq for the
financial support.
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1034 | Green Chem., 2012, 14, 1030–1034
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