The first example of palladium-catalyzed intermolecular allylaryloxylation of an internal alkyne by allyl aryl ethers

Article abstract of DOI:10.1016/j.tetlet.2011.08.065

The allylaryloxylation of an internal alkyne by allyl aryl ethers was realized by Pd(dba)₂/P(OPh)₃ catalyst system to afford cis adducts in moderate yields.

Full text of DOI:10.1016/j.tetlet.2011.08.065

Tetrahedron Letters 52 (2011) 5501–5503
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The first example of palladium-catalyzed intermolecular allylaryloxylation
of an internal alkyne by allyl aryl ethers
⇑
Hitoshi Kuniyasu , Kazunobu Takekawa, Atsushi Sanagawa, Takashi Wakasa, Takanori Iwasaki,
⇑
Nobuaki Kambe
Department of Applied Chemistry, Graduate School of Engineering, Osaka University, Suita, Osaka 565-0871, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
The allylaryloxylation of an internal alkyne by allyl aryl ethers was realized by Pd(dba)2/P(OPh)3 catalyst
system to afford cis adducts in moderate yields.
Received 16 July 2011
Revised 4 August 2011
Accepted 11 August 2011
Available online 18 August 2011
Ó 2011 Elsevier Ltd. All rights reserved.
Keywords:
Allyl aryl ether
Carboaryloxylation
Internal alkyne
Palladium catalyst
The simultaneous addition of carbon and oxygen functional
groups across the carbon–carbon triple bonds is very useful trans-
formation to prepare compound with a vinyl ether framework by a
single step. Some transition-metal catalyzed intramolecular addi-
tions based on this strategy have been reported (Scheme 1a).1 Fur-
thermore, nickel catalyzed intermolecular CAO bond additions to
alkynes accompanied by elimination of carbon monoxide and iso-
cyanate have recently been developed.2 However, to the best of our
knowledge, intramolecular direct addition of CAO bond to alkyne
has not been documented (Scheme 1b).3
On the other hand, we have reported a series of palladium and
platinum catalyzed decarbonylative and CO-retained inter- and
intramolecular carbothiolation and carboselenation of alkynes.4–6
Herein reported is the first example of intramolecular direct
addition of CAO bond to an alkyne. Because we have reported that
ethyl phenylpropiolate (1a) exhibited high reactivity toward the
insertion into the SAPt bond of trans-Pt(Cl)(SAr)(PPh3)2 as well as
the Pt-catalyzed decarbonylative carbothiolation,5f the reaction of
1a with allyl phenyl ether (2a) was examined (Table 1). Although
Pd(PPh3)4 showed the catalytic activity, the yield of the anticipated
product 3a was very low (entry 1).
unsatisfactory (Entries 3–9). Platinum dichloride (PtCl2), which is
known to be an efficient catalyst for the intramolecular carboalk-
oxylation,1a,c did not catalyze the formation of 3a (entry 10). While
the reaction with Pd(dba)2/dppe as a catalyst afforded the antici-
pated 3a in 36% yield (entry 11), the use of dppe with the combi-
nation of other transition-metal complexes such as Rh(PPh3)3Cl,
[Rh(cod)2Cl]2, and Ru(PPh3)3Cl2 have failed (Entries 12–14). Nei-
ther N,P nor N,N bidentate ligand showed catalytic activity (Entries
15 and 16). Although Pd(dba)2/P(OEt)3 was not active (entry 17),
Pd(dba)2/P(OAr)3 catalyzed the reactions to afford the desired 3a
(Entries 18–24). When 2 equiv of 1a for 2a was employed, the yield
of 3a was improved (entry 18 vs entry 19). Among examined, the
combination of Pd(dba)2/P(OPh)3 with 2 equiv of 1a gave the best
yield to furnish 3a in 52% isolated yield as a thermodynamically
stable oil (entry 20).
The structure of 3 was unambiguously determined by HSQC,
HMBC, and 2D-NOESY spectroscopies using 3b (vide infra) as a rep-
resentative compound. As for the by-products of the reaction,
C
C
cat. M
Contrary to the case of the aryl thiolation and acyl thiolation of
alkynes by thioesters,5b,m Pt(PPh3)4 did not exhibit the catalytic
activity (entry 2). Other phosphine ligands such as P(C6H4CF3-p),
PCy3, P(2-furyl)3, dppm, dppp, dppf, and dppBz with the combina-
tion of Pd(dba)2 did catalyze the reactions, but the yields were
(a)
(b)
and/or
O
O
O C
cat. M
+
C
O
C
O
⇑
Corresponding authors.
E-mail address: kuni@chem.eng.osaka-u.ac.jp (H. Kuniyasu).
Scheme 1. Transition-metal catalyzed intra- and intermolecular addition of CAO
bond to alkynes.
0040-4039/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2011.08.065

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H. Kuniyasu et al. / Tetrahedron Letters 52 (2011) 5501–5503
Table 1
compound 4, the adduct of PhOH to 1a as well as 5 or 6, in which two
molecules of1a are incorporated, were indicatedby1HNMR andmass
spectroscopies together with a small amount of isomer of 3 (Scheme
2). The reaction of methyl phenylpropiolate (1b) with 2a afforded the
corresponding adduct in a moderate yield (entry 25). The reaction is
quite sensitive to substituents in Ar of EtOC(O)CCAr (1). Unfortu-
nately, introductions of electron-donating, electron-withdrawing,
and o-hydroxyl groups totally suppressed the reactions (Scheme 3,
1c–1f). The alkyne1g with C(O)OCH2Cl3 group, which isa goodsubsti-
tuent for PtCl2 catalyzed intramolecular trans addition of CAO bond,
did not promote the present transformation.1a The substitution of
Ph by 2-thienyl group (1h), C(O)OEt by 3-pyridyl (1i), and C(O)OEt
by C(O)Me (1j) also hampered the reactions.
The results of the additions of 2 with different substituents to
1a were summarized in Table 2. It turned out that no clear rela-
tionship between electronic effect and yield of 3 was observed:
The corresponding 3 were produced in a range of 16–60% yields.
On the other hand, no reaction took place by the treatment of
CH2@C(Ph)CH2OPh (2j) with 1a.
Screening of transition-metal catalysts for the addition of 2a to 1aa
EtO
O
O
cat. M/L
toluene
OPh
Ph
+
Ph
OPh
EtO
1a
2a
3a
Entry
M
L
3a (%)b
1
2
3
4
5
6
7
8
Pd(PPh3)4
Pt(PPh3)4
Pd(dba)2
Pd(dba)2
Pd(dba)2
Pd(dba)2
Pd(dba)2
Pd(dba)2
Pd(dba)2
PtCl2
None
None
4
0
1
25
3
9
10
7
9
0
P(C6H4CF3-p)3
PCy3
P(2-furyl)3
dppm
dppp
dppf
dppBz
None
9
10
11
12
13
14
Pd(dba)2
Rh(PPh3)3Cl
dppe
dppe
36
0
0
The possible reaction mechanisms for the present Pd-catalyzed
allylaryloxylation of 1a by 2 are shown in Scheme 4.
[Rh(cod)2Cl]2
Ru(PPh3)3Cl2
dppe
dppe
0
The reaction can be triggered by the oxidative addition of 2 to
Pd(0) complex to afford p
-allyl palladium 7.7 Then regio- and ster-
15
Pd(dba)2
0
0
eoselective cis insertion of 2 into either OAPd bond or CAPd bond
can furnish 8 or 9. Then CAC or CAO bond-forming reductive elim-
ination from the Pd(II) complex can conclude one catalytic cycle.
To get information about the reaction mechanism, the reaction
of 1a with ally phenyl carbonate (C3H5OC(O)OPh, 10) was exam-
ined (Eq. (1)).
After 4 h under toluene reflux, the decarbonylated 2a was pro-
duced in 85% yield together with 2% of 3a. One possible explanation
of this fact is that even when the p-allyl Pd-complex such as 7 was
generated via oxidative addition of 10 to Pd(0) and the subsequent
eliminationofCO2, 1aishardlyincorporated intothepalladiumcom-
plex and the equilibrium between 2/Pd(0) and 7 strongly leans to the
former side. For the insertion of 1a into the groups 16 and 10 element
bond, we have already reported that the cis insertion of 1a into the
N
PPh2
N
16
Pd(dba)2
N
17
18
Pd(dba)2
Pd(dba)2
Pd(dba)2
Pd(dba)2
Pd(dba)2
Pd(dba)2
Pd(dba)2
Pd(dba)2
Pd(dba)2
P(OEt)3
0
29
52
P(OC6H4OMe-p)3
P(OC6H4OMe-p)3
P(OPh)3
P(OC6H4Me-p)3
P(OC6H4Cl-p)3
P(OC6H3OMe-p)3
P(OC6H4OCF3-p)3
P(OPh)3
19c
20c
21c
22c
23c
24c
25e
60 (52)d
52
58
25
20
63
a
Unless otherwise noted, 1a (1.2 mmol), 2a (1.0 mmol), M (5 mol %), L (12 mol %
for monodentate, and 6 mol % for bidentate ligand) was treated under toluene
reflux for 24 h.
SAPt bond of trans-Pt(Cl)(SAr)(PPh3)2 (11) with Pt at the
a-carbon
of CO2Et and SArat
a
-carbon ofPhgroup (Eq. (2)).5f It shouldbenoted
b
NMR yield.
2 mmol of 1a.
Isolated yield.
2 mmol of methyl phenylpropiolate (1b) in stead of 1a.
c
that the Pt-OEt distance (3.0 Å) of the resultant vinyl platinum 12
was within the sum of the van der Waals radii (3.2 Å), implying that
the interaction between Pt and O atoms plays a crucial role in achiev-
ing regioselective cis insertion of 1a into the SAPt bond of 11.
d
e
Pd(dba)2/P(OPh)3
O
OPh
1a
2a
+
3a
+
EtO
O
EtO
EtO
O
ð1Þ
ð2Þ
EtO
H
O
4 h
O
+
85%
2%
Ph
Ph
Ph
Ph
OPh
10
OPh
OEt
OPh
Ph
O
SAr
O
EtO
Ph
O
6
O
Ph3P
Pt PPh3
Cl
Ph
Ph3P
4
5
EtO
Pt
SAr
Cl
PPh3
12
Scheme 2. Structures of possible by-products.
11
1a
O
O
O
O
OMe
CF3
Cl
EtO
EtO
EtO
EtO
Cl
HO
1c
1g
1d
1h
1e
1f
O
O
S
O
Ph
Ph
Cl3CCH2O
EtO
N
Me
1j
1i
Scheme 3. Inert allynes toward the addition of 2a.

H. Kuniyasu et al. / Tetrahedron Letters 52 (2011) 5501–5503
5503
Table 2
and the following CAC bond-forming reductive elimination of 3
as the most probable pathway. Although the room to improve
the reactivity and selectivity still remain unsolved, we believe that
the potential of direct addition of CAO bond to unsaturated bond is
presented by this study.
Palladium-catalyzed addition of 2 to 1aa
EtO
O
O
Pd(dba)2/P(OPh)3
toluene
OAr
Ph
+
Ph
OAr
EtO
Acknowledgments
1a
2
3
A partial support of this work through Grant-in-Aid for Scien-
tific Research, Ministry of Education and Science. Thanks are due
to the Instrumental Analysis Center, Faculty of Engineering, Osaka
University, for assistance in obtaining HSQC, HMBC, and 2D-NOESY
spectra with a Varian Unity-INOVA600 with VnmrJ Version 2.2 and
mass spectra with a JEOL JMS-DX303 instrument.
Entry
Ar
Ph
C6H4Me-p
2
3
yield (%)b
b
1
2
3
4
5
6
7
8
9
2a
2b
2c
2d
2e
2f
2g
2h
2i
3a
3b
3c
3d
3e
3f
3g
3h
3i
60 (52)
31
18
40
46
44
16
41
49
C6H4OMe-p
C6H4NO2-p
C6H4CF3-p
C6H4CN-p
C6H4C(O)Me-p
C6H4Cl-o
References and notes
C6H4Ph-p
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b
Isolated yield.
PdL2
2
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3
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L = P(OPh)3
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O
O
EtO
Ph
EtO
Ph
Pd
OAr
PdL2
OAr
Pd
L
OAr
8
9
7
1a
Scheme 4. Possible reaction mechanisms.
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T.; Kuniyasu, H.; Kambe, N. J. Am. Chem. Soc. 2008, 130, 10504; (c) Toyofuku, M.;
Fijiwara, S.; Shin-ike, T.; Kuniyasu, H.; Kambe, N. J. Am. Chem. Soc. 2005, 127,
9706.
On the basis of above discussion, we propose the mechanism
involving the formation of 7, regio- and stereoselective cis inser-
tion of 1a into the OAPd bond of 7 to produce vinyl palladium 8,
7. Urata, H.; Suzuki, H.; Moro-oka, Y.; Ikawa, T. J. Organomet. Chem. 1989, 364, 235.