A highly regioselective bisselenation of allenes with diphenyl diselenide catalyzed by tetrakis(triphenylphosphine)palladium(0)

Article abstract of DOI:10.1016/j.tetlet.2005.03.168

Tetrakis(triphenylphosphine)palladium(0) acts as an effective catalyst for highly regioselective bisselenation of allenes with diphenyl diselenide.

Full text of DOI:10.1016/j.tetlet.2005.03.168

Tetrahedron
Letters
Tetrahedron Letters 46 (2005) 3649–3652
A highly regioselective bisselenation of allenes with diphenyl
diselenide catalyzed by tetrakis(triphenylphosphine)palladium(0)
a
Ikuyo Kamiya, Etsuyo Nishinaka and Akiya Ogawa
a
b,
*
a
Department of Chemistry, Faculty of Science, Nara Women’s University, Kitauoyanishi-machi, Nara 630-8506, Japan
b
Department of Applied Chemistry, Faculty of Engineering, Osaka Prefecture University, 1-1 Gakuen-cho,
Sakai, Osaka 599-8531, Japan
Received 2 February 2005; revised 19 March 2005; accepted 23 March 2005
Available online 9 April 2005
Abstract—Tetrakis(triphenylphosphine)palladium(0) acts as an effective catalyst for highly regioselective bisselenation of allenes
with diphenyl diselenide.
Ó 2005 Elsevier Ltd. All rights reserved.
Very recently, the transition-metal-catalyzed reactions
of organosulfur compounds have been growing, and
highly selective transformations of organosulfur com-
pounds have been developed by using transition metal
activated carbon–carbon double bond compounds un-
dergo the palladium-catalyzed bisselenation successfully
(Eq. 2).
1
SePh
catalysts. In contrast, examples of transition-metal-cata-
lyzed reactions of organoselenium compounds are still
R
cat. Pd(PPh3)4
ð2Þ
+
(PhSe)2
R
SePh
•
2
rare, because organoselenium compounds bind transi-
Table 1 summarizes the results of the palladium-cata-
lyzed bisselenation of cyclohexylallene (1a) in various
solvents. Although benzene is the best solvent for the
palladium-catalyzed bisselenation of alkynes, the bissel-
enation of 1a in benzene was sluggish (entry 1). Ethereal
solvent like THF and halogenated solvent like 1,2-
dichloroethane were ineffective for the desired bisselen-
ation (entries 2 and 3). Polar solvents, especially aceto-
nitrile, worked as an excellent solvent, providing the
corresponding bisselenation product in high to excellent
yields (entries 4 and 5). In this bisselenation, the molar
tion metal catalysts much more strongly compared
with organosulfur compounds, and make the catalytic
reactions ineffective. In 1991, we have found that the
palladium-catalyzed addition of diphenyl diselenide to
alkynes gives the corresponding vicinal diselenoalkenes
3
in good yields (Eq. 1). However, only alkynes can be
employed as substrates for this bisselenation.
cat. Pd(PPh3)4
benzene, 80 ˚C
R
+
(PhSe)2
SePh
ð1Þ
R
PhSe
ratio of 1a and (PhSe) is important: the use of slightly
2
excess amounts of 1a led to the formation of 2a in high
yield (entries 5–7).
On the other hand, a number of transition-metal-
catalyzed addition reactions of compounds bearing a
heteroatom–heteroatom linkage to allenes have been
4
investigated hitherto. Contrary to this, the correspond-
Table 2 summarizes the results of the bisselenation using
some other catalysts. In contrast to the zero-valent pal-
ladium complex (entry 1), divalent palladium complexes
such as PdCl (PPh ) and Pd(OAc) exhibited lower cat-
ing addition reactions of group 16 heteroatom com-
pounds to allenes have never been reported to the best
of our knowledge. In order to develop the bisselenation
of carbon–carbon double bonds, much effort has been
devoted and finally we have disclosed that allenes as
2
3 2
2
alytic activity toward the bisselenation of 1a (entries 2
and 3). Recently, we have found the combination of
Pd(OAc) and pyridine leads to the highly regioselective
2
5
hydroselenation of alkynes with benzeneselenol. How-
ever, the Pd(OAc) –pyridine system was ineffective
Keywords: Bisselenation; Allenes; Diphenyl diselenide; Tetrakis-
(triphenylphosphine)palladium(0).
2
*
Corresponding author. Tel./fax: +81 72 254 9290; e-mail: ogawa@
chem.osakafu-u.ac.jp
for this bisselenation of 1a (entry 4). The attempted bis-
selenation using WilkinsonÕs catalyst resulted in the
0
040-4039/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2005.03.168

3650
I. Kamiya et al. / Tetrahedron Letters 46 (2005) 3649–3652
Table 1. Influence of solvents on palladium-catalyzed bisselenation
Table 3. Palladium-catalyzed bisselenation of allenes with (PhSe)
2
cHex
cHex
R
R
SePh
SePh
cat. Pd(PPh3)4
SePh
SePh
cat. Pd(PPh3)4
+
(PhSe)2
+
(PhSe)2
•
solvent, reflux, 12 h
CH CN
3
1a
2a
a
Yield (%) [E/Z]
Entry Substrate
Product
nHex
a
Yield (%)
Entry
Solvent
Temp. (°C)
[E/Z]
nHex
b
72
SePh
SePh
1
[49/51]
1
2
3
4
5
Benzene
THF
ClCH CH
80
69
14
[36/64]
[44/56]
[69/31]
[31/69]
[93/7]
•
9
36
1b
2b
2
2
Cl
83
Pyridine
115
82
70
cHex
cHex
tBu
SePh
SePh
CH
CH
CH
3
3
3
CN
CN
CN
96 (96)
65
61
b
6
c
82
82
[75/25]
[75/25]
2
3
•
96
[93/7]
7
1a
2a
Reaction conditions: Pd(PPh
3
)
4
(5 mol %), 1a (0.6 mmol), solvent
tBu
Ph
Ph
SePh
SePh
(0.5 mL), (PhSe)
a 1
H NMR (isolated) yield.
Allene 1a (0.5 mmol).
2
(0.5 mmol), 12 h.
•
No reaction
b
1c
2c
c
Allene 1a (0.5 mmol), (PhSe)
2
(0.6 mmol).
Ph
Ph
SePh
SePh
c
Table 2. Transition-metal-catalyzed bisselenation of cyclohexylallene
•
4
5
67
[41/59]
[49/51]
cHex
cHex
1d
2d
catalyst
SePh
SePh
+
(PhSe)2
solvent, reflux, 12 h
1
a
2a
SePh
SePh
b
67
a
•
Entry
Catalyst
Solvent
Temp.
(
Yield
(%)
[E/Z]
°C)
1e
2e
1
2
3
4
5
Pd(PPh
3
)
PdCl (PPh
4
CH
CH
CH
3
3
3
CN
CN
CN
82
82
82
96
36
20
[93/7]
[53/47]
[60/40]
PhSe
9
2
3
)
2
SePh
Pd(OAc)
Pd(OAc)
2
•
2
Pyridine
CH CN
115
82
Trace
A complex
mixture
6
9
81
[100/0]
RhCl(PPh
3
)
3
3
1
f
2f
6
7
Pt(PPh
3
)
4
CH
CH
3
CN
CN
82
82
37
No reaction
[41/59]
No catalyst
3
3 4 3
Reaction conditions: Pd(PPh ) (5 mol %), allene (0.6 mmol), CH CN
(
0.5 mL), (PhSe)
Isolated yield.
2
(0.5 mmol), 82 °C, 12 h.
Reaction conditions: catalyst (5 mol %), 1a (0.6 mmol), solvent
0.5 mL), (PhSe) (0.5 mmol), 12 h.
a 1
H NMR yield.
a
(
2
b 1
H NMR yield.
(PhSe)C@CHSePh was obtained in 7% yield as
byproduct.
c
Ph(CH
2
)
2
a
formation of a complex mixture (entry 5), whereas plat-
inum(0) catalyst indicated moderate catalytic activity
toward the desired bisselenation of 1a (entry 6). In the
absence of the catalyst, no reaction took place at all
under identical conditions (entry 7). This fact clearly
indicates that the present bisselenation of 1a proceeds
as a catalytic reaction of palladium(0).
successfully (entries 1 and 2), whereas no reaction was
observed with tertiary alkyl substituted allene (1c), most
probably due to the bulkiness of the tertiary butyl group
of 1c (entry 3). Similar conditions could be employed
with benzyl and phenyl substituted allenes (1d and 1e)
(entries 4 and 5). In the case of benzylallene (1d), small
Table 3 summarizes the results of the Pd(PPh ) -
3
amounts of the double bond isomerized byproduct was
obtained exceptionally (see footnote c). Internal allene
(1f) also underwent the desired bisselenation efficiently
(entry 6).
4
catalyzed bisselenation of several allenes with (PhSe)2.
The representative procedure is as follows: to a
mixture of cyclohexylallene (0.6 mmol) and Pd(PPh3)4
(
diselenide (0.5 mmol) under N atmosphere. The result-
0.025 mmol) in CH CN (0.5 mL) was added diphenyl
3
The stereoselectivity and applicable substrates are simi-
lar to those observed in the previously reported photo-
initiated bisselenation of allenes with (PhSe) by a
2
ing mixture was stirred magnetically for 12 h with heat-
ing at 82 °C. After the reaction was complete, the
reaction mixture was filtered through Celite, followed
by washing with diethyl ether. The combined filtrate
was concentrated under the reduced pressure, and the
purification of the product was performed upon pre-
parative TLC on silica gel using hexane/AcOEt = 100:0
2
7
radical mechanism. However, this transition-metal-
catalyzed bisselenation involves the formation of organo-
palladium intermediate, which can be utilized for
further useful transformations such as carbonylation
with carbon monoxide (vide post).
6
,7
to 96:4 as an eluent.
Scheme 1 shows two possible reaction pathways, which
includes the following: (1) (PhSe) adds oxidatively to
the low-valent palladium(0) complex, that is, Pd(PPh3)2,
Primary and secondary alkyl substituted allenes (1b and
a) underwent regioselective bisselenation with (PhSe)2
2
1

I. Kamiya et al. / Tetrahedron Letters 46 (2005) 3649–3652
3651
PdL4
–2L
2L
R
SePh
SePh
R
SePh
SePh
PdL2
R
SePh
R
SePh
PdSePh
R
PdSePh
SePh
(
PhSe)2
C
B
PhSePd
D
R
R
•
•
Pd(SePh)2
A
2
Scheme 1. Possible pathways for bisselenation of allenes with (PhSe) .
to generate an active catalyst (A); (2) allene coordinates
to the palladium species (A) and then selenopalladation
of allene takes place at the terminal carbon–carbon dou-
ble bonds to form either vinylpalladium intermediate (B)
or r-allylpalladium intermediate (C); (3) reductive elimi-
nation of the bisselenation product with regeneration of
the catalyst.
In summary, we have developed the highly selective pal-
ladium-catalyzed bisselenation of allenes with diphenyl
diselenide. The transition-metal-catalyzed reaction of
allenes with (PhSe) under the pressure of CO is now
2
under investigation in detail.
References and notes
In this scheme, if C is in equilibrium with p-allylpalla-
dium intermediate (D), D may generate r-allylpalladium
intermediate (E) to provide the corresponding regioiso-
meric bisselenation product (Eq. 3). However, no forma-
tion of the bisselenation product at the inner carbon–
carbon double bond of allene suggests that this bissele-
nation of allenes does not involve the formation of
1
. For reviews concerning transition-metal-catalyzed reactions
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Oshima, K., Eds.; Wiley-VCH: Weinheim, 2004; Vol. 2,
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Chem. Rev. 2004, 104, 3079–3159; (c) Ogawa, A. In
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8
allylpalladium species such as C, D, and E.
R
SePh
R
SePh
D
ð3Þ
PhSePd
PhSe
E
To clarify the reaction pathway, the present bisselena-
tion of 1a was conducted under similar reaction condi-
tions in the presence of carbon monoxide (30 atm). The
resulting reaction mixture involves the formation of a
carbonylating product (3, 37%) along with the bisselena-
tion product (2a, 4%). However, the product (4) derived
from the carbonylation at the terminal carbon of 1a was
not obtained at all.
4
02.
2
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9
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1
example: 2f: [E-isomer] H NMR (400 MHz, CDCl
3
) d
2
1.09–1.23 (m, 1H), 1.37–1.69 (m, 7H), 1.81–1.93 (m, 1H),
1.97–2.08 (m, 2H), 2.20–2.27 (m, 1H), 4.51–4.61 (br m, 1H),
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3
3
(m, 4H); C NMR (100 MHz, CDCl ) d 25.09, 26.00,
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128.85, 129.09, 130.46, 130.49, 134.01, 134.46 (@C–SePh),
135.64 (CH@); IR (KBr) 3050–3000, 2925, 2853, 1580,
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ꢀ1
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9
8
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2
H24Se : C, 58.10; H, 5.53. Found: C,
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8. Alternative pathway is as follows: the reductive elimination
of the bisselenation product from r-allylpalladium inter-
mediate (C) is very fast, not generating p-allylpalladium
intermediate (D).
4