An efficient synthesis of alkynyl selenides and tellurides from terminal acetylenes and diorganyl diselenides or ditellurides catalyzed by recyclable copper oxide nanopowder

Article abstract of DOI:10.1016/j.tet.2012.08.086

Herein, we report an efficient method for the synthesis of alkynyl selenides and tellurides from terminal alkynes and diorganyl diselenides or ditellurides using CuO nanopowder as a recyclable catalyst. This new methodology furnished the desired products in good to excellent yields. Furthermore, the catalyst was easily recovered and reused for further catalytic reactions without loss of activity.

Full text of DOI:10.1016/j.tet.2012.08.086

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Tetrahedron 68 (2012) 10426e10430
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Tetrahedron
journal homepage: www.elsevier.com/locate/tet
An efficient synthesis of alkynyl selenides and tellurides from terminal acetylenes
and diorganyl diselenides or ditellurides catalyzed by recyclable copper oxide
nanopowder
Marcelo Godoi a, Eduardo W. Ricardo a, Tiago E. Frizon a, Manuela S. T. Rocha a, Devender Singh b,
c
a,
*
ꢀ
~
Marcio W. Paixao , Antonio Luiz Braga
a
ꢀ
Universidade Federal de Santa Catarina, Florianopolis 88040-900, Brazil
b Leibniz Institute of Plant Biochemistry, Halle, Germany
c
~
~
Universidade Federal de Sao Carlos, Sao Carlos 13565-905, Brazil
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 22 June 2012
Received in revised form 24 August 2012
Accepted 27 August 2012
Available online 1 September 2012
Herein, we report an efficient method for the synthesis of alkynyl selenides and tellurides from terminal
alkynes and diorganyl diselenides or ditellurides using CuO nanopowder as a recyclable catalyst. This
new methodology furnished the desired products in good to excellent yields. Furthermore, the catalyst
was easily recovered and reused for further catalytic reactions without loss of activity.
Ó 2012 Elsevier Ltd. All rights reserved.
Keywords:
Selenium
Alkynyl selenides
Nano catalysis
Alkynyl tellurides
Copper oxide nanopowder
1. Introduction
several transformations due to their unique structural and elec-
tronic diversity.10 For instance, these types of compounds have
Transition metal-catalyzed coupling reactions have emerged as
a powerful tool for the synthesis of several organic molecules with
high efficiency and under mild conditions.1 Furthermore, catalytic
transformations have become the most applicable method for
carbonecarbon and carboneheteroatom bond formation.2
In this context, nanomaterials with high surface areas and re-
active morphologies have been widely studied as versatile catalysts
in organic process.3 Generally, heterogenous catalysts have pro-
vided genuine advances in relation to traditional or homogenous
ones.4 In particular, the CuO nanopowder has shown great advan-
tages, such as simplified isolation of the product, easy recyclability,
and recovery of the catalyst.5 Moreover, CuO nanoparticles have
been successfully applied as a catalyst for the synthesis of several
organoselenium compounds,6 which are attractive synthetic target
molecules in biologic-chemistry,7 as well as chemo- and regio-
selective transformations.8,9
been used as precursors in hydrohalogenation,11 hydro-
sulfonation,12 hydroboration,13 and hydrostannylation14 reactions.
Similarly, alkynyl selenides have also been used for the preparation
of selenol esters,15 which are important acyl transferring agents
and useful for the synthesis of new molecular materials, such as
liquid crystals.16 More recently, acetylenes selenides have been
employed as a powerful building block in supramolecular chem-
istry17 as well as for the synthesis of several heterocycles via cy-
clization reactions.18
The most common protocols reported for the synthesis of
alkynyl selenides involves: (i) the use of acetylene with organo-
metallics reagents followed by reaction with diorganyl diselenides
or organoselenyl halides19; (ii) selenodecarboxylation of either
arylpropiolic or cinnamic acid promoted by iodosobenzene diac-
etate20; and (iii) the reaction of alkynyl bromides with nucleophilic
species of selenium generated from different metals.21
On the other hand, alkynyl selenides are emerging as an in-
teresting class of compounds, having a variety of applications in
However, most of the procedures mentioned above have their
respective drawbacks, such as moisture sensitivity of some organ-
ometallic reagents, harsh conditions, and difficulties associated
with handling some selenium compounds, besides the use of ex-
cess amounts of alkynes or toxic metals.
* Corresponding author. Tel./fax: þ55 48 3721 6427; e-mail address: bra-
ga.antonio@ufsc.br (A.L. Braga).
0040-4020/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tet.2012.08.086

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M. Godoi et al. / Tetrahedron 68 (2012) 10426e10430
10427
Nonetheless, the preparation of alkynyl selenides through
a metal-catalyzed reaction has not been widely explored, and in
this context studies on the catalytic fashion are scarce.22 Therefore,
the development of new methodologies for the preparation of
these types of organoselenium compounds under mild reaction
conditions, employing efficient and recyclable catalysts, remains
highly desirable.
Despite the well-known effectiveness of CuO nanopowder in the
organoselenium field, the use of this nanomaterial as a catalyst for
the synthesis of alkynyl selenides has not yet been reported. Thus,
in keeping with our ongoing interest in catalytic transformations,23
an efficient method for the synthesis of alkynyl selenides using CuO
nanopowder as a recyclable catalyst is described herein (Scheme 1).
reaction system (Table 2). Firstly, a screening of the time revealed
that 14 h was the best choice, furnishing the desired product in 80%
yield (compare entries 1e3). After establishing the best reaction
time, we evaluated the effect of temperature on the reaction and on
raising the temperature from 80 to 120 ꢀC, no change in the yield
was observed (entry 4). However, when the reaction was per-
formed at 25 ꢀC, the desired product was obtained in only 38% yield
(entry 5). The effect of the base was also evaluated (entries 6e9). On
using Cs2CO3 and Na2CO3, a slight decrease in the yield value was
observed (entries 6 and 7). However, when a strong base (KOH) was
used, the yield of the reaction decreased considerably (entry 8).
Furthermore, in the absence of base only trace levels of the desired
product were obtained (entry 9).
Table 2
CuO nanopowder
Optimization of the reaction conditionsa
R1
Se R2
R1
H
+
R2SeSeR2
DMSO/ K2CO3
Air
Scheme 1. Synthesis of alkynyl selenides catalyzed by CuO nanopowder.
2. Results and discussion
Entry
Base
Solvent
Time (h)
T (ꢀC)
Yieldb (%)
1
2
3
4
5
6
7
8
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
Na2CO3
Cs2CO3
KOH
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMF
7
14
28
14
14
14
14
14
14
14
14
14
20
80
80
80
120
25
80
80
80
80
80
80
80
66
51
80
70
80
38
65
57
32
Traces
69
51
54
d
In order to establish the best conditions for our protocol, we
screened several parameters of the reaction using phenyl acetylene
and diphenyl diselenide as model substrates. The effect of the nano
CuO (II) loading was first investigated and some details are pro-
vided in Table 1.
9
d
Table 1
Optimization of the reaction conditionsa
10
11
12
13
K2CO3
K2CO3
K2CO3
K2CO3
CH3CN
DMSO/H20
THFc
a
Conditions: phenyl acetylene (0.5 mmol), diphenyl diselenide (0.25 mmol), base
(0.5 mmol), and CuO nanopowder (0.05 mmol, 10 mol %), solvent.
Entry
CuO nano (mol %)
Yield 3a (%)b
Yield 4a (%)b
b
Yields for isolated products.
The reaction was carried out under reflux.
1
2
3
4
5
6
7
1
2
5
10
20
d
d
32
45
63
80
80
20
46
48
37
16
11
10
60
39c
c
Finally, to further optimize the protocol, we evaluated the in-
fluence of different solvents on the reaction (entries 10e13). We
observed that the solvent has a substantial influence on this cross-
coupling reaction. When DMF, acetonitrile, and the DMSO/H2O
mixture were used the desired product was obtained in moderate
to good yields (entries 10e12). However, on using THF as the sol-
vent the alkynyl selenide 3a was not obtained even after 20 h (entry
13).
a
Conditions: phenyl acetylene (0.5 mmol), diphenyl diselenide (0.25 mmol),
K2CO3 (0.5 mmol), CuO nanopowder, DMSO.
b
Yields for isolated products.
An excess of 0.25 mmol of diphenyl diselenide was used in the reaction.
c
Carrying out the reaction using 1 mol % of catalyst, furnished the
desired product in only 32% yield (entry 1). However, on increasing
the amount of CuO nanoparticles to 2 mol % and 5 mol %, chemical
yields of the desired alkynyl selenide were enhanced to 45% and
63%, respectively (entries 2 and 3). When 10 mol % of the catalyst
was used the alkynyl selenide was obtained with 80% yield (entry
4). Interestingly, no significant change in the yield values of prod-
ucts could be observed when the catalyst loading was increased to
20 mol % (entry 5).
We also observed the formation of vinylic selenide, probably
due catalytic diorganyl diselenide addition to terminal alkyne.24
Moreover, when the reaction was carried out in absence of
catalyst, the desired product 3a was obtained in very poor yield and
the by-product was increased to 60% (entry 6). By using similar
reaction conditions, but with an excess of diphenyl diselenide, the
product 3a and the by-product were achieved with reasonable
yields (entry 7). Nonetheless, the production of the by-product 4a
was attenuated by the presence of catalyst as can be seen in Table 1.
Keeping our attention only for the synthesis of alkynyl selenide
3a, we investigated the influence of several parameters on the
Having identified the best conditions, the scope of the reaction
was investigated, as shown in Table 3. At first, a wide variety of
diorganyl diselenides were reacted with phenyl acetylene in order
to evaluate the electronic and steric effects (entries 1e5). Electronic
effects did not have a notable influence on this reaction. For in-
stance, when diselenides containing either withdrawing or do-
nating groups attached at the para position of the aromatic ring
were used, no significant changes in the yield value were observed
(entries 2e3). However, steric effects have been shown to adversely
affect the reaction and on using o-methylphenyl diselenide the
desired product was obtained in lower yield (entry 4). We were also
able to prepare alkynyl selenide starting from aliphatic diselenide.
When dibutyl diselenide was used under the same reaction con-
ditions, the corresponding product 3e was obtained in 79% yield
(entry 5).
In the reaction system we also investigated the combination of
a range of different acetylenes with diphenyl diselenide (entries
6e10). When terminal acetylene with an electron donating group
in the para position of the aromatic ring was used, the yield of the
reaction was enhanced, furnishing the desired product 3f with 90%

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M. Godoi et al. / Tetrahedron 68 (2012) 10426e10430
Table 3
Synthesis of several alkynyl selenidesa
Entry
1
R1
R2
Product
Yield
80
Ph
Ph
3a
3b
3c
Scheme 2. Synthesis of alkynyl tellurides.
2
3
4
p-MeOPh
p-ClPh
76
75
63
We also realized a deep study regarding the activity of the
catalyst in the reaction (Fig. 1). Thus, the CuO nanoparticles were
recovered from the reaction media and reused for further catalytic
reactions. It was noted that the catalyst maintained its activity even
after the fourth cycle, affording the desired product in very good
yield as shown in the Fig. 1.
o-MePh
3d
5
6
7
n-C4H9
79
90
91
3e
3f
p-MePh
Ph
o-MeOPh
3g
3h
8
9
n-C6H13
70
60
3i
3j
Fig. 1. Recyclability of the CuO nanoparticles.
10
HOCH2
55
In addition, TEM analysis of the CuO nanopowder was per-
formed before and after four reaction runs (Fig. 2). These experi-
mental results suggest that the reaction involves a heterogenous
process, as previously reported in the literature.5a
a
Conditions: terminal acetylene (0.5 mmol), diorganyl diselenide (0.25 mmol),
K2CO3 (0.5 mmol), and CuO nanopowder (0.05 mmol, 10 mol %), DMSO.
On the basis of previous reports,28,29 a plausible reaction path-
way for the synthesis of alkynyl selenides is illustrated in Scheme 3.
We assumed that the terminal alkyne reacts with the catalyst,
forming the [alkenyleCu] cluster 6, which reacts with diorganyl
diselenide leading to 7. Subsequently, 7 undergoes a reductive
elimination, affording the desired alkynyl selenide and the species
8. Finally, in the presence of base, the copper catalyst is regenerated
in the reaction medium, completing the cycle.
yield (entry 6). Noteworthy, when the methoxy group was at-
tached in the ortho position, the corresponding product was ob-
tained with 91% yield (entry 7). It is well known that aryl
acetylenes are more reactive than aliphatic ones and are also much
more easily deprotonated.25 Nonetheless, applying the same
methodology, we also prepared an alkynyl selenide starting from
aliphatic alkyne and the desired product was obtained in very good
yield (entry 8).
Furthermore, we attempt to synthesize alkynyl selenides bear-
ing interesting functionalities. To our delight, when alkynyl acety-
lenes containing either morpholine or alcohol groups were used,
the corresponding products were delivered in satisfactory yields
(entries 9 and 10).
It is well recognized that alkynyl tellurides are particularly
valuable synthetic intermediates for efficient application in several
transformations.26,27 Thus, using the same methodology, we also
attempted the synthesis of different alkynyl tellurides. Gratifyingly,
the corresponding products were obtained with high yields as
shown in Scheme 2.
3. Conclusion
In summary, we have successfully developed an efficient and
easy-to-perform methodology to obtain alkynyl selenides from
acetylenes and diorganyl diselenides, using CuO nanopowder as
a recyclable catalyst. Applying this new approach the correspond-
ing products were obtained in good to excellent yields. These mild
reaction conditions do not affect alcohols, amines, and other
functional groups. The catalyst was highly efficient in this coupling
reaction and it was easily recovered and reused upto four cycles
without loss of activity. Moreover, this procedure was extended to

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M. Godoi et al. / Tetrahedron 68 (2012) 10426e10430
10429
Fig. 2. TEM images of CuO nanopowder. (a) Fresh CuO nanopowder (b) CuO nanopowder after fourth run.
water, and the aqueous layer was extracted with ethyl acetate. The
organic phase was dried over MgSO4, filtered, and the volatiles
were completely removed under vacuum to give the crude product.
Purification by flash chromatography with a mixture of hexane/
ethyl acetate (99:1) afforded the desired alkynyl telluride.
R
H
1
H
R
6
BH
B-
[O]
4.3. Recyclability of the catalyst
R1Se
R1Se)2
R
After completion of the synthesis, the reaction mixture was
cooled to room temperature and a 1:1 mixture of ethyl acetate and
water (3 mL) was added, the CuO nanopowder was then recovered
by centrifugation at 3500 rpm for 30 min and dried under vacuum.
The recovered catalyst was reused directly for the next run.
H
H
R1Se
8
SeR1
R1Se
7
= CuO
4.4. Phenyl(phenylethynyl)selane21 (3a)
R
Se R1
1H NMR (200 MHz, CDCl3): 7.65e7.55 (m, 2H); 7.45e7.54 (m,
2H); 7.32e7.17 (m, 6H) ppm 13C NMR (100 MHz, CDCl3): 131.7;
129.5; 128.9; 128.3; 127.1; 123.1; 102.9; 69.2 ppm.
3
Scheme 3. Plausible reaction pathway.
4.5. (4-Methoxyphenyl)(phenylethynyl)selane22 (3b)
the synthesis of alkynyl tellurides and the desired products were
also achieved in very good yields.
1H NMR (200 MHz, CDCl3): 7.53 (d, 2H, J¼8.9 Hz); 7.50e7.41 (m,
2H); 7.34e7.27 (m, 3H); 6.88 (d, 2H, J¼8.9 Hz); 3.79 (s, 3H) ppm 13C
NMR (100 MHz, CDCl3): 159.4; 131.8; 131.7; 128.4; 128.3; 123.3;
118.3; 115.3; 101.5; 70.4; 55.4 ppm.
4. Experimental section
4.1. General procedure for the synthesis of alkynyl selenides
4.6. (4-Chlorophenyl)(phenylethynyl)selane21 (3c)
Terminal acetylene (0.5 mmol) and CuO nanopowder
(0.05 mmol, 10 mol %) were placed into a round-bottom flask, fol-
lowed by diorganyl diselenide (0.25 mmol) and undried DMSO. The
reaction was stirred at 80 ꢀC in an oil bath for 14 h. After this time
the reaction was cooled to room temperature, quenched with wa-
ter, and the aqueous layer was extracted with ethyl acetate. The
organic phase was dried over MgSO4, filtered, and the volatiles
were completely removed under vacuum to give the crude residue.
Purification by flash chromatography with a mixture of hexane/
ethyl acetate (99:1) afforded the desired alkynyl selenide.
1H NMR (200 MHz, CDCl3): 7.85e7.76 (m, 1H); 7.55e7.47 (m,
2H); 7.37e7.30 (m, 3H); 7.23e7.15 (m, 3H); 2.37 (s, 3H) ppm 13C
NMR (50 MHz, CDCl3): 136.5; 131.7; 130.22; 129.5; 129.3; 128.5;
128.3; 127.1; 123.2; 103.0; 69.1; 20.9 ppm.
4.7. (Phenylethynyl)(o-tolyl)selane10a (3d)
1H NMR (200 MHz, CDCl3): 7.65e7.55 (m, 2H); 7.45e7.54 (m,
2H); 7.32e7.17 (m, 6H) ppm 13C NMR (100 MHz, CDCl3): 131.7;
129.5; 128.9; 128.3; 127.1; 123.1; 102.9; 69.2 ppm.
4.2. General procedure for the synthesis of alkynyl tellurides
4.8. Butyl(phenylethynyl)selane21 (3e)
Terminal acetylene (0.5 mmol) and CuO nanopowder
(0.05 mmol, 10 mol %) were placed into a round-bottom flask, fol-
lowed by diorganyl ditelluride (0.25 mmol) and undried DMSO. The
reaction was stirred at 80 ꢀC in an oil bath for 14 h. After this time
the reaction was cooled to room temperature, quenched with
1H NMR (200 MHz, CDCl3): 7.44e7.38 (m, 2H); 7.33e7.27 (m,
3H); 2.88 (t, 2H, J¼6 Hz); 1.93e1.78 (m, 2H); 1.57e1.43 (m, 2H); 0.96
(t, 3H, J¼14.67 Hz) ppm 13C NMR (100 MHz, CDCl3): 131.4; 128.2;
128.0; 123.7; 99.3; 70.5; 32.2; 29.3; 22.5; 13.5 ppm.