Copper-catalyzed stereoselective synthesis of vinyl selenides under ligand-free conditions

Article abstract of DOI:10.1246/cl.2010.212

A mild and efficient protocol for the stereoselective synthesis of vinyl selenides catalyzed by CuO nanoparticles as recyclable catalyst under ligand-free conditions is reported. This methodology results in the synthesis of a variety of vinyl selenides in excellent yields with retention of stereochemistry.

Full text of DOI:10.1246/cl.2010.212

doi:10.1246/cl.2010.212
212
Published on the web January 30, 2010
Copper-catalyzed Stereoselective Synthesis of Vinyl Selenides under Ligand-free Conditions
Vutukuri Prakash Reddy, Akkilagunta Vijay Kumar, and Kakulapati Rama Rao*
Organic Chemistry Divison-I, Indian Institute of Chemical Technology, Hyderabad-500 607, India
(Received November 6, 2009; CL-090983; E-mail: ramaraok@iict.res.in)
I
SePh
A mild and efficient protocol for the stereoselective
synthesis of vinyl selenides catalyzed by CuO nanoparticles
as recyclable catalyst under ligand-free conditions is reported.
This methodology results in the synthesis of a variety of vinyl
selenides in excellent yields with retention of stereochemistry.
1.5 mol% CuO
(PhSe)2
DMSO(2.0 mL)
KOH (1.5 equiv)
1.0 mmol 0.5 mmol
80 °C
Scheme 1. CuO nanoparticles-catalyzed synthesis of vinyl
selenides.
Organoselenium compounds have received considerable
attention due to their wide utility in organic synthesis and
various biological activities especially anticancer, and anti-
oxidant properties.1 Amongst the organoselenium compounds,
vinyl selenides have acequired high significance as intermedi-
ates in the preparation of carbonyl compounds and in the
synthesis of stereoselectively functionalized alkenes.2 This led
to the development of various processes for vinyl selenides.
Though traditional methods such as the Wittig olefination,2c
selenide ion displacement of vinyl halides3 etc.4 are generally
satisfactory, stereoselective outcome has always been a limi-
tation. To overcome this limitation various approaches have
been developed.5,6 Recently Bao and co-workers developed a
protocol for the synthesis of vinyl selenides by using copper
iodide as a catalyst in the presence of zinc metal in ionic liquid
and L-proline as a ligand for 24 h.3d Ranu and co-workers
reported the nano-copper-catalyzed synthesis of vinyl selenides
in the presence of zinc metal as additive in water.7
However, most of these metal-catalyzed reactions
involve expensive and moisture-sensitive catalysts/reagents
with ligands/additives at higher temperatures causing major
problems in purification of the product and separation of
the metal catalyst. These problems are of environmental and
economic concern in large scale synthesis. Thus, it is desirable
to develop an inexpensive, environmentally benign, and re-
cyclable catalytic system for an efficient access to such highly
useful vinyl selenides under ligand-free conditions and if
possible at temperatures lower than 100 °C.
Recently, heterogeneous catalysts have become attractive
both from economic and industrial points of view as compared
to homogeneous catalysts. In general, nanoscale heterogeneous
catalysts offer higher surface area responsible for higher
catalytic activity.8 Furthermore, heterogeneous catalysts have
also the advantage of high atom efficiency, easy product
purification, and reusability of the catalyst.
Encouraged by the intense research activity in the field of
selenium chemistry and in continuation of our interest in copper-
catalyzed coupling of arylhalides with diselenide,9 we report
herein the CuO nanoparticles-catalyzed synthesis of vinyl
selenides under ligand-free conditions (Scheme 1). However,
to the best of our knowledge, this is the first example of the
synthesis of vinyl selenides in the absence of any ligand or co-
metal catalyst.
Table 1. Cross coupling of diphenyl diselenide with trans-¢-
iodostyrenea
Entry
Base
Solvent
Yieldb/%
1
2
3
4
5
6
8
9
10
11
12
13
K3PO4
KOH
KOH
KOH
KOH
Cs2CO3
K3PO4
K3PO4
KOH
KOH
none
DMSO
DMF
trace
79
DMSO
DMSO
DMSO
PhMe
DMF
PhMe
PhMe
Water
10c
81d
97
trace
trace
0
0
0
DMSO
DMSO
17
25e
KOH
aReaction conditions: trans-¢-iodostyrene (1.0 mmol), diphen-
yl diselenide (0.5 mmol), CuO (1.5 mol %), base (1.5 equiv),
b
c
d
solvent (2.0 mL), 80 °C, 4 h. Isolated yield. At rt. At 50 °C.
eAbsence of catalyst.
conditions including bases, solvents, catalysts, and temperature.
Among the bases examined, KOH (Table 1, Entry 5) was found
to be the best for coupling providing the highest yield. Other
bases, such as Cs2CO3 and K3PO4 (Table 1, Entries 1 and 6)
gave trace yields. The influence of solvents on the reaction was
also investigated. DMSO as a solvent gave the best yield of the
product in comparison with other solvents (Table 1, Entry 5).
The reaction temperature was investigated by using
1.5 mol % of CuO as the catalyst and 1.5 equiv of KOH as the
base in DMSO. The yield of the target product was greatly
improved as the reaction temperature was increased, and higher
yields were provided at 80 °C (Table 1, Entry 5). The coupling
efficiency was evidently decreased in the absence of base
(Table 1, Entry 12), and only a trace amount of the product was
observed without addition of the catalyst (Table 1, Entry 13).
Several metal oxides were also tested (compare Table 2), and
CuO was observed to be the most effective catalyst (Table 2,
Entry 6).10
We have also made a study of the cross coupling with
various nucleophiles under these conditions (Table 3). In
general, selenols are avoided because of their instability in air
and/or moisture and foul-smelling nature. N-(Phenylseleno)-
The coupling reaction of trans-¢-iodostyrenes with diphen-
yl diselenide was used as a model reaction to optimize reaction
Chem. Lett. 2010, 39, 212-214
© 2010 The Chemical Society of Japan
www.csj.jp/journals/chem-lett/

213
Table 2. Effect of different catalysts for the synthesis of vinyl
selenidesa
Table 4. Nano CuO-catalyzed cross coupling of various trans-
¢-halostyrene and cis-¢-halostyrene with diphenyl diselenidea
Yieldb/%
Entry
Catalyst
Yieldb/%
Entry
Halides
Product
1
2
3
4
5
6
7
8
nano-ZnO
nano-Bi2O3
nano-In2O3
nano-Sb2O3
nano-Co3O4
nano-CuO
nano-Fe2O3
nano-NiO
31
29
35
24
26
98
33
46
X
Se
1
2
3
4
5
X = I
Br
Cl
X = I
Br
98
61
0
96
45
X
Se
X
I
Se
6
7
X = I
Br
95
41
MeO
MeO
MeO
MeO
Se
Se
aReaction conditions: trans-¢-iodostyrene (1.0 mmol), diphen-
yl diselenide (0.5 mmol), catalyst (1.5 mol %), KOH (1.5
equiv), DMSO (2.0 mL) at 80 °C. Isolated yield.
8
89
MeO
MeO
OMe
OMe
b
I
9
92
90
93
Table 3. Effect of different nucleophiles for the synthesis of
vinyl selenidesa
F3C
Cl
F3C
Cl
I
Se
Se
Se
10
11
Yieldsc/%
Nucleophiles
Entry
I
SeH
1
2
79
Br
F
Br
F
I
(PhSe)2
98b
12
13
93
90
O
I
Se
3
95
N Se
F
F
O
aReaction conditions: nucleophiles (1.0 mmol), CuO
(1.5 mol %), KOH (1.5 equiv), DMSO (2.0 mL) at 80 °C.
Br
I
Se
14
15
56
81
O
c
bDiphenyl diselenide (0.5 mmol). Isolated yield.
O
O
Se
O
phthalimide was more expensive compared to diphenyl disele-
nide. Among these nucleophiles, diphenyl diselenide appeared
to be the best choice for cross coupling.
aReaction conditions: trans-¢-iodostyrene or cis-¢-halostyrene
(1.0 mmol), diphenyl diselenide (0.5 mmol), CuO (1.5 mol %),
KOH (1.5 equiv), DMSO (2.0 mL) at 80 °C. Isolated yield.
b
To explore the scope of this novel transformation, we first
examined the cross coupling of diphenyl diselenide with
different trans-¢-iodostyrenes (Table 4).11 In general, all reac-
tions were very clean, and the vinyl selenides were obtained
in high yields under the optimized conditions. This protocol
efficiently coupled trans-¢-iodostyrene having electron-rich,
electron-neutral, and electron-poor functionalities with diphenyl
diselenide (Table 4, Entries 1, 4, 6, and 8-13). Encouraged
by these results, we tested the coupling of several trans-¢-
bromostyrenes with diphenyl diselenide under the same con-
ditions. The reaction of trans-¢-bromostyrenes with diphenyl
diselenide proceeded smoothly to afford the desired product in
reasonable yield (Table 4, Entry 2). However, low yields were
observed in the coupling of substituted trans-¢-bromostyrene
and cis-¢-bromostyrene (Table 4, Entries 5, 7, and 14).
Furthermore, the stereochemistry of the vinyl selenides was
retained in all the cases. This protocol was also applied for the
cross coupling of ¢-alkoxycarbonyl-substituted vinyl iodide
with diphenyl diselenide and the corresponding vinyl selenide
was obtained in excellent yield (Table 4, Entry 15).
Table 5. Recycling of CuO nanoparticles
1.5 mol% CuO
SePh
I
DMSO(2.0 mL)
KOH (1.5 equiv)
80 °C
Ph
(PhSe)2
Ph
1.0 mmol 0.5 mmol
Catalyst
recovery/%
Recycles
Yield/%
1
2
3
4
98
95
91
91
96
93
90
90
water (2.0 mL) was added and CuO was removed by centrifu-
gation. After each cycle, the catalyst was recovered by simple
centrifugation, washed with deionized water followed by
acetone and then dried in vacuo. The recovered CuO was used
directly in the next cycle (Table 5). TEM images of the catalyst
indicated no change before and after the reaction, which
confirms the heterogeneous nature of the catalyst (Figures 1a
and 1b). This indicates that the catalysis may be occurring on the
surface of CuO nanoparticles.12
In addition, the recyclability of the catalyst was checked
using the coupling of trans-¢-iodostyrene with vinyl selenide as
the model reaction. After the reaction was complete, the reaction
mixture was allowed to cool, and a 1:1 mixture of ethyl acetate/
Chem. Lett. 2010, 39, 212-214
© 2010 The Chemical Society of Japan
www.csj.jp/journals/chem-lett/

214
VPR thanks CSIR and AVK, KS thank UGC, New Delhi, for
the award of fellowships.
(a)
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7
8
Figure 1. TEM images of the catalyst (a) before and (b) after
the reaction.
R
9
V. P. Reddy, A. V. Kumar, K. Swapna, K. R. Rao, Org. Lett.
2009, 11, 951.
SePh
X
R
10 All catalysts including CuO nanoparticles were purchased
from Sigma Aldrich.
R
R
11 To a stirred solution of diphenyl diselenide (0.5 mmol) and
trans-¢-iodostyrene (1.0 mmol) in DMSO (2.0 mL) was
added CuO nanoparticles (1.5 mol %) followed by KOH (1.5
equiv) and stirred at 80 degrees for 4 h. The progress of the
reaction was monitored by TLC. After the reaction was
complete, the reaction mixture was allowed to cool, and a
1:1 mixture of ethyl acetate/water (2.0 mL) was added and
CuO was removed by centrifugation. The organic layer was
washed and separated, the aqueous layer was further washed
with another 10-mL portion of ethyl acetate, and the
combined organic extracts were dried with anhydrous
Na2SO4. The solvent and volatiles were completely removed
under vacuum to give the crude product, which was
subjected to column chromatographic separation to give
analytically pure product (98%) as yellow oil.
=CuO
X
Se
Ph
KOH
DMSO
(Ph-Se)2
Ph Se K
KX
Scheme 2. A plausible mechanism for the CuO nanoparticle-
catalyzed cross coupling of vinyl halides and diphenyl
diselenide in the presence of DMSO and KOH.
A plausible mechanism for the CuO nanoparticle-catalyzed
cross coupling of vinyl halides and diphenyl diselenide is
illustrated in Scheme 2.13
In conclusion, CuO acts as an active, moisture stable,
inexpensive, and nontoxic catalyst for the stereoselective syn-
thesis of vinyl selenides under ligand-free conditions in
excellent yields. This method precludes the use of external
ligands and provides, in most cases, the desired vinyl selenides
in high yields. The catalyst was simply recovered and reused
without significant loss of catalytic activity.
12 S. Jammi, S. Sakthivel, L. Rout, T. Mukherjee, S. Mandal, R.
Mitra, P. Saha, T. Punniyamurthy, J. Org. Chem. 2009, 74,
1971.
13 In this reaction, DMSO may be acting as a reducing agent
required in the reaction by producing dimsyl ion in the
presence of KOH. Ref: D. H. Hunter, D. J. Cram, J. Am.
Chem. Soc. 1966, 88, 5765.
Chem. Lett. 2010, 39, 212-214
© 2010 The Chemical Society of Japan
www.csj.jp/journals/chem-lett/