CuO nanoparticles: an efficient and recyclable catalyst for cross-coupling reactions of organic diselenides with aryl boronic acids

Article abstract of DOI:10.1016/j.tetlet.2009.09.052

We present here an efficient and ligand-free cross-coupling reaction of organic diselenides with aryl boronic acids using a catalytic amount of CuO nanoparticles in DMSO at 100 °C under air atmosphere. This is a general cross-coupling reaction and was performed with organic diselenides and aryl boronic acids bearing electron-withdrawing and electron-donating groups affording the corresponding selenides in good to excellent yields. The CuO nanoparticles can be easily recovered and utilized for further catalytic reactions.

Full text of DOI:10.1016/j.tetlet.2009.09.052

Tetrahedron Letters 50 (2009) 6635–6638
Contents lists available at ScienceDirect
Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
CuO nanoparticles: an efficient and recyclable catalyst for cross-coupling
reactions of organic diselenides with aryl boronic acids
Diego Alves a, , Cayane G. Santos , Márcio W. Paixão , Letiére C. Soares , Diego de Souza ,
a
d
b
b
*
Oscar E. D. Rodrigues , Antônio L. Braga c
Centro Universitário Franciscano–UNIFRA–Rua dos Andradas, 1614, Centro. CEP 97010-032, Santa Maria, RS, Brazil
Universidade Federal de Santa Maria–Departamento de Química, CEP 97105-900, Camobi, Santa Maria, RS, Brazil
Universidade Federal de Santa Catarina–UFSC–Departamento de Química, CEP 88040-900, Florianópolis, SC, Brazil
b,
*
a
b
c
d
Universidade Federal de São Carlos–Departamento de Química, CEP 13565905, São Carlos, SP, Brazil
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 30 July 2009
Revised 8 September 2009
Accepted 9 September 2009
Available online 13 September 2009
We present here an efficient and ligand-free cross-coupling reaction of organic diselenides with aryl
boronic acids using a catalytic amount of CuO nanoparticles in DMSO at 100 °C under air atmosphere.
This is a general cross-coupling reaction and was performed with organic diselenides and aryl boronic
acids bearing electron-withdrawing and electron-donating groups affording the corresponding selenides
in good to excellent yields. The CuO nanoparticles can be easily recovered and utilized for further
catalytic reactions.
Ó 2009 Elsevier Ltd. All rights reserved.
Organoselenium compounds have become attractive synthetic
targets because of their chemo-, regio-, and stereoselective reac-
tions, are used in asymmetric catalysis and as drug candidates.
Metal nanoparticles catalysis offers high catalytic efficiency due
to their larger surface area and low-coordinated sites, which max-
imizes the reaction rates and minimizes consumption of the
1
2
3
1
0
Many classes of organoselenium compounds have been prepared
and studied to date, among them aryl- and vinyl selenides are cer-
catalyst. Additionally, the copper nanoparticle-catalyzed reac-
tions provide the advantages of high atom efficiency, simplified
isolation of product, and easy recovery and recyclability of the
4
tainly the most applied compounds in organic synthesis.
7
,11
A large number of methodologies have been reported to prepare
these compounds; however, the reaction often needs long time,
harsh reaction conditions, and sometimes generates the products
catalysts.
To the best of our knowledge, no copper nanoparticle-catalyzed
coupling reactions of organic diselenides with arylboronic acids
have been described to form organic selenides. Our continuing
interest in the C–Y (Y = Se, Te) bond formation under copper catal-
5
in moderate yields. In recent years, a copper-catalyzed reaction
of diaryl diselenides with aryl halides or aryl boronic acids has be-
come a versatile tool for the synthesis of symmetrical or unsym-
metrical diaryl selenides.6 Generally these copper-catalyzed
reactions involve particularly specific ligands, which may increase
the cost and limit the scope of applications. Furthermore, Rao and
co-workers described an efficient and ligand-free cross-coupling
reaction of aryl halides and diaryl diselenides using a catalytic
1
2
ysis prompted us to explore in detail a general procedure to
obtain organic selenides by copper oxide nanoparticles (CuO
NPs)-catalyzed coupling reactions of diselenides with aryl boronic
acids (Scheme 1).
Our initial studies have focused on the development of an opti-
mum set of reaction conditions. In this approach, diphenyl disele-
nide 1a and 4-methoxyphenyl boronic acid 2a were used as model
substrates. Thus, a mixture of diselenide 1a, boronic acid 2a, and
CuO NPs as a catalyst was reacted under air atmosphere for 24 h,
applying different solvents, amount of substrates, or catalyst, and
the results are summarized in Table 1.
7
amount of CuO nanoparticles (CuO NPs) as a recyclable catalyst.
The application of metal nanoparticles for organic reactions has
8
attracted immense attention in recent years. Since the turn of the
millennium, interest in metal nanoparticles catalysis has consider-
ably increased because this class of catalysts appears as one of the
most promising solutions toward efficient reactions under mild
and environmentally benign conditions in the context of Green
9
Chemistry.
CuO NPs (3%)
R
Se Se
a-l
R
+ ArB(OH)2
R
Se Ar
DMSO
o
1
2a-k
100 C, 24 h
3a-v
air
75-98%
R = Aryl and Alkyl
*
Corresponding authors.
E-mail address: dsalves@gmail.com (D. Alves).
Scheme 1.
0
040-4039/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2009.09.052

6
636
D. Alves et al. / Tetrahedron Letters 50 (2009) 6635–6638
Table 1
Table 2
Optimization of reaction conditions
Coupling products using diphenyl diselenide 1a and aryl boronic acids 2a–k
CuO NPs
solvent, 100 o
4 h, air
CuO NPs (3%)
C
Se Se
Se
3a
OMe
Se Se
+ ArB(OH)
2
Se Ar
2
DMSO
1a
2a-k
00 oC, 24 h
air
3a-k
1
1a
MeO
B(OH)2
2
a
Entry
1
R2B(OH)
2
Product yieldb (%)
Entry
CuO NPsa
Boronic acid
2a (equiv)
Solvent
Yield 3ab (%)
(mol %)
MeO
B(OH)2
Se
OMe
1
2
3
4
5
6
7
8
9
1
5
5
5
3
1
3
3
3
3
3
1.0
1.0
1.2
1.5
1.5
1.5
1.5
1.5
1.5
1.5
1.5
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO/H
1,4-Dioxane
DMF
3
CH CN
76
80
85
98
97
84
78
65
86
—
2
a
3a (97%)
B(OH)2
Se
2
3
2
O
2
b
3b (93%)
1
1
0c
1
Toluene
—
B(OH)
2
Se
a
Ò
CuO nanopowder was purchased from Aldrich , with an average of 30–40 nm
2
c
3c (90%)
as shown in technical information.
b
Yields are given for isolated products.
Reaction was performed at 80 °C.
c
B(OH)2
Se
4
We observed that this cross-coupling reaction required the use
of an excess of organoboron reagent (1.5 equiv) (Table 1; entry 4).
In this way, the use of 1.0 or 1.2 equiv of boronic acid afforded low-
er yields than the use of 1.5 equiv (Table 1; entries 1–3 vs 4). The
use of catalyst in an amount of 5 mol % yielded 98% of compound
2d
3d (94%)
Cl
B(OH)2
Se
Cl
5
6
2
e
3e (96%)
3
5
a and fortunately, when the catalyst loading was reduced from
mol % to 3 mol %, excellent yield of product 3a was obtained (Ta-
Cl
Cl
ble 1; entry 5). Finally, we observed that the influence of the sol-
vent was important for the coupling success. When 1,4 dioxane,
B(OH)2
Se
2
DMF, and a mixture of DMSO/H O were used, the desired product
was obtained in moderate to good yields (Table 1; entries 7–9),
while no cross-coupling was observed with other solvents such
2f
3f (94%)
3
as toluene and CH CN (Table 1; entries 10 and 11).
Careful analysis of the optimized reactions revealed that the
optimum conditions for this coupling reaction were found to be
the use of CuO NPs (3 mol %) as a catalytic system, diphenyl disel-
enide 1a (0.25 mmol), and 4-methoxyphenyl boronic acid 2a
Br
B(OH)2
Se
Br
7
8
2g
h
3g (97%)
F3C
CF
3
(
1.5 equiv), utilizing DMSO as a solvent. The heterogeneous reac-
tion mixture was stirred for 24 h at 100 °C under air atmosphere
B(OH)2
Se
affording the desired diaryl selenide 3a in 97% yield.13
2
3h (94%)
In order to demonstrate the efficiency of this protocol, we ex-
plored the generality of our methodology by reacting other aryl
boronic acids 2b–k with diphenyl diselenide 1a (Table 2). The re-
sults reported in Table 2 show that the reaction worked well for
a variety of aryl boronic acids. A closer inspection of the results re-
vealed that the reaction is not sensitive to electronic effects of the
substituents attached to the aromatic ring. Aryl boronic acids bear-
ing both electron-donating (Table 2; entries 1–3) and electron-
withdrawing groups (Table 2; entries 5–10) gave excellent yields
of the desired products. Differentiation in the reactivity between
bromine and boron atoms of boronic acid can be seen by coupling
of 4-bromophenyl boronic acid 2g with diphenyl diselenide 1a. In
this case, only the coupling product 3g was obtained in 97% yield,
without by-products (Table 2; entry 7). In our case, the bromine
substituent was not affected. A decrease in the yield of cross-cou-
pling was obtained when we used a hindered boronic acid 2k, fur-
nishing the corresponding products in 78% yield (Table 2; entry
O N
2
NO2
9
B(OH)2
Se
2
i
3i (98%)
O
O
10
B(OH)
2
Se
2j
3j (95%)
B(OH)
2
Se
11
1
1).
In an attempt to broaden the scope of our methodology, the
2k
3k (78%)
possibility of performing the reaction with other organic disele-
nides was also investigated (Table 3). 4-Methoxyphenyl boronic
acid 2a was coupled efficiently with a variety of organic disele-
a
Reactions performed in the presence of 1a (0.25 mmol), aryl boronic acid
(1.5 equiv), and 3 mol % of CuO NPs and DMSO (0.5 mL).
b
Yields are given for isolated products.

D. Alves et al. / Tetrahedron Letters 50 (2009) 6635–6638
6637
Table 3
Table 4
Recycling of CuO NPs
a
Coupling products using compounds 1b–l and 4-methoxyphenyl boronic acid 2a
CuO NPs (3%)
CuO NPs
DMSO, 100 o
C
R
Se Se R + MeO
b-k
B(OH)
2
R
Se
OMe
Se Se
Se
3a
OMe
DMSO
100 oC, 24 h
air
24 h, air
1
2a
3l-u
1
a
MeO
B(OH)
2
Product yieldb (%)
2a
Entry
1
R–Se–Se–R
Run
1a
Catalyst recovery (%)
Yield 3ac (%)
MeO
Se
2
MeO
Se
l (84%)
OMe
95
92
88
85
97
92
89
83
b
2
b
3
3
1
b
b
4
a
Reaction performed in the presence of 1a (0.5 mmol), aryl boronic acid
Se
Se
OMe
(
1.5 equiv), 3 mol % of CuO NPs, and DMSO (1 mL).
2
3
2
b
Recovered catalyst used.
Yields are given for isolated products.
1
c
3m (87%)
c
nides 1b–k. The results revealed that the reaction is sensitive to
the electronic effect of an aromatic ring attached to the diaryl
diselenide. For example, diaryl diselenides bearing electron-donat-
ing groups gave lower yields than the diselenides bearing electron-
withdrawing groups (Table 3; entries 1–3 vs 4–6).
We have found that steric effects had a little influence on the
coupling reaction, and diselenides containing mesityl and naphthyl
groups gave lower yields of the desired products (Table 3; entries 7
and 8). Notably, when dibenzyl diselenide 1j and dibutyl diselenide
Se
Se
OMe
2
1
d
3n (85%)
Cl
Se
Cl
Se
OMe
2
4
5
6
3
o (95%)
1
e
Cl
Cl
1
k were used, the corresponding products 3t and 3u were obtained
in excellent and good yields, respectively (Table 3; entries 9 and
0). Diphenyl ditelluride 1l was also efficiently coupled in these
conditions and diaryl telluride 3v was formed in excellent yield
Se
Se
OMe
2
1
1
f
3p (93%)
(
Table 3; entry 11).
To check the recyclability of the catalyst, it was separated from
F
3
C
F3C
Se
Se
OMe
the reaction mixture. After completion of the C–Se cross-coupling,
the reaction mixture was treated with water and ethyl acetate. The
catalyst was recovered from the aqueous solution by centrifuga-
tion, dried under vacuum, and reused for further catalytic reac-
tions. The catalyst maintained its good level of activity even
after being recycled four times as shown in Table 4.
In conclusion, we have explored in detail efficient and ligand-
free cross-coupling reactions of organic diselenides with aryl boro-
nic acids using a catalytic amount of CuO nanoparticles in DMSO at
2
1
g
3q (95%)
1
4
Se
Se
OMe
7
8
2
1
h
3r (79%)
1
00 °C under air atmosphere. This cross-coupling reaction is gen-
Se
Se
OMe
eral and affords the corresponding products in good to excellent
yields. The catalyst can be easily recovered and utilized for further
catalytic reactions. Studies toward the mechanism insight of this
reaction and the combination of others reaction partners are in
progress in our laboratory.
2
1
i
3s (82%)
Se
Se
OMe
Acknowledgments
2
9
We are grateful to UNIFRA, CAPES, FAPERGS (ARD-2009) and
CNPq (INCT—NANOMATERIAIS DE CARBONO—D.A. and INCT—
NANOBIOSIMES—O.E.D.R.) for the financial support. CAPES is also
acknowledged for the fellowship (C.G.S.).
1
j
3t (91%)
Se
Se
OMe
2
1
0
1
1
k
References and notes
3
u (75%)
1
.
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1
l
3v (94%)
a
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2
methoxyphenyl boronic acid 2a (1.5 equiv), and 3 mol % of CuO NPs and DMSO
0.5 mL).
(
b
Yields are given for isolated products.

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13. General procedure for the cross-coupling reaction: To a round-bottomed flask
containing organic diselenide (0.25 mmol), aryl boronic acid (1.5 equiv), and
CuO NPs (3 mol %) was added DMSO (0.5 mL). The reaction mixture was
allowed to stir at 100 °C for 24 h. After this time, the solution was cooled to
room temperature, diluted with ethyl acetate (20 mL), and washed with water
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4
, and
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.
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3
, 400 MHz): d 7.50 (d, J = 8.4 Hz,
2H), 7.33–7.31 (m, 2H), 7.21–7.16 (m, 3H), 6.84 (d, J = 8.4 Hz, 2H), 3.79 (s, 3H).
13
7
8
.
.
C NMR (CDCl
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3
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(0.5 mmol), aryl boronic acid (1.5 equiv), CuO, and NPs (3 mol %) was added
DMSO (1.0 mL). The reaction mixture was allowed to stir at 100 °C for 24 h.
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ethyl acetate/water (2.0 mL) was added and CuO NPs were removed by
centrifugation. After each cycle, the catalyst was recovered by simple
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cycle.
1
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.
1