Palladium-catalyzed hydrophenoxycarbonylation of internal alkynes by phenol and CO: The use of Zn for the formation of active catalyst

Article abstract of DOI:10.1016/j.tetlet.2010.10.017

The palladium-catalyzed hydrophenoxycarbonylation of internal alkynes by phenol and carbon monoxide was successfully realized by Pd(OAc)₂/dppp catalyst system in the co-presence of Zn dust.

Full text of DOI:10.1016/j.tetlet.2010.10.017

Tetrahedron Letters 51 (2010) 6818–6821
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Tetrahedron Letters
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Palladium-catalyzed hydrophenoxycarbonylation of internal alkynes by
phenol and CO: the use of Zn for the formation of active catalyst
⇑
⇑
Hitoshi Kuniyasu , Takahiro Yoshizawa, 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 palladium-catalyzed hydrophenoxycarbonylation of internal alkynes by phenol and carbon monox-
ide was successfully realized by Pd(OAc)2/dppp catalyst system in the co-presence of Zn dust.
Ó 2010 Elsevier Ltd. All rights reserved.
Received 6 September 2010
Revised 30 September 2010
Accepted 5 October 2010
Available online 13 October 2010
Keywords:
Carbon monoxide
Internal alkyne
Phenol
Reppe carbonylation
Zn powder
cat. Ni
Nu
The transition metal-catalyzed addition reactions of nucleo-
philes and carbon monoxide to alkynes, widely known as Reppe
carbonylation (Scheme 1), have been well-studied for a long
period.1–3
CO
Nu = RO, RNH, RS
Nu-H
+
+
O
Scheme 1. Reppe carbonylation.
For the syntheses of
a,b-unsaturated esters according to this
protocol, alcohols have been employed in most cases. However,
the reactions with phenols, which can serve as very powerful strat-
reported that the addition of acid is quite effective to promote
the reaction. Thus, the effect of acids such as AcOH (10 mol %)3d
and TsOH3d,3e (5 mol %) was next tested; however, the yields of
3a were not improved in the reactions with 2 (entries 10 and
11). To anticipate the increase of yield of 3a, some reactions were
next tested with Pd(II)/dppp as catalysts. As a result, Pd(OAc)2/
dppp showed higher activity to form 3a in 18% yield (entry 16),
while no reaction took place with PdCl2, PdCl2(MeCN)2,
[PdCl(C3H5)2]2, and Pd(acac)2 (entries 12–15). It was found that
the production of 3a was significantly promoted by the addition
of Zn as a reducing reagent: 3a was produced in 44% yield in the
co-presence of 10 mol % of Zn (entry 17). The increase of the
amount of Zn improved the yield of 3a (entries 18–21). Gratify-
ingly, 3a was produced quantitatively with 1.5 equiv of Zn (entry
21), while decreasing the amount of dppe resulted in the low yield
of 3a. Two equivalent of 1a was required due to the formation of
egy for the syntheses of
a,b-unsaturated arylesters have been
hardly developed. For instance, Miura and co-workers have re-
ported Pd-catalyzed addition of phenols and CO to terminal al-
kynes, which is the only example of Reppe carbonylation using
phenols.4 Furthermore, to the best of our knowledge, no example
of Reppe carbonylation of internal alkynes by phenol is docu-
mented. Herein we wish to report the first example of carbonyla-
tive addition of phenol and carbon monoxide to internal alkynes.
First, the effects of ligand (0.05 mmol) under the reaction of 4-
octyne (1a, 1.0 mmol) with PhOH (2, 0.5 mmol) and CO (1 atm) in
the presence of Pd(dba)2 (0.05 mmol) were examined in toluene
(0.5 mL) at 100 °C for 24 h (Table 1). No reaction took place when
monodentate ligands such as PPh3, PCy3, and P(t-Bu)3 were em-
ployed (entries 1–3). Treatment with bidentate phosphine exhib-
ited catalytic activity to afford the desired
a,b-unsaturated
undetermined by-products. Although the additions of Mg and Mn
3a,3b
phenyl ester 3a, albeit quite in low yields (entries 4–9). Among
examined, the use of dppp resulted in the best yield (5% of 3a, en-
try 6). In the case of Reppe carbonylation with alcohols, it was
were somewhat effective for the formation of 3a, SnCl2
and
Fe rather suppressed the reaction (entries 22–25). Only 11% of 3a
was produced when DBA (10 mol %) was added to Pd(OAc)2/
dppp/Zn reaction system, demonstrating that the coordination of
DBA to palladium complex significantly suppressed the reaction
(compare entry 26 with entry 21).
⇑
Corresponding authors. Tel.: +81 66879 7389; fax: +81 6 6879 7390.
E-mail address: kuni@chem.eng.osaka-u.ac.jp (H. Kuniyasu).
0040-4039/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2010.10.017

H. Kuniyasu et al. / Tetrahedron Letters 51 (2010) 6818–6821
6819
Table 1
The results of reactions of some alkynes 1 with 2 and CO under
the optimized conditions are summarized in Table 2. Unlike the
case of reaction by Pd(PPh3)4-catalyzed carbonylation of terminal
alkyne by phenols,4 the reaction using aliphatic terminal alkyne
1b produced only 22% of 3b and 4% of 3b0 along with complicated
by-products (entry 1). On the other hand, the treatment with
diphenyl acetylene (1c) produced the corresponding adduct 3c in
91% yield (entry 2). The X-ray crystallographic analyses of 3c and
3d demonstrated that the PhOC(O) group and H attached in a cis-
fashion and, in the case of 3d, PhOC(O) group was bound at the
Palladium-catalyzed hydrophenoxycarbonylation of 4-ocyne (1a)a
Pr
cat. Pd (5mol%)
Pr
OPh
Pr
Pr
PhOH CO
+
+
PR3/additive
O
1a
2
3a
b
Entry
Pd
PR3
Additiveb
3a(%)c
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26e
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
Pd(dba)2
Pd(dba)2
PdCl2
PdCl2(MeCN)2
[PdCl(C3H5)2]2
Pd(acac)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
PPh3 (10)
PCy3 (10)
P(t-Bu)3 (10)
dppm (5)
dppe (5)
dppp (5)
dppb (5)
dppf (5)
Xantphos (5)
dppp (5)
dppp (5)
dppp (5)
dppp (5)
dppp (5)
dppp (5)
dppp (5)
dppp (5)
dppp (5)
dppp (5)
dppp (5)
dppp (5)
dppp (5)
dppp (5)
dppp (5)
dppp (5)
dppp (5)
—
—
—
—
—
—
—
—
0
0
0
1
3
5
2
4
1
3
5
0
0
0
0
a-carbon of Ph group, showing that Pd-catalyzed regio- and stere-
oselective hydrophenoxycarbonylation took place successfully (
Figs. 1 and 2).5–7
The additions to 1e and 1f also were accomplished regio- and
stereoselectively to furnish the corresponding adducts 3e and 3f
in 84% and 59% yields, respectively (entries 4 and 5). The reactions
with trimethylsilyl substituted internal alkyne 1g and 1h afforded
3g and 3h with PhOC(O) group substituted at b-carbon of TMS
group (entries 6 and 7). The reaction with 1-phenyl-1-propyne
(1i) produced a mixture of regioisomer 3i (63%) and 3i0 (35%)
(entry 8). In stark contrast to these internal alkynes, no reactions
occurred with TMSCCC(O)OEt (1j), TMSCCTMS (1k), and PhCCCH2
OMe (1l) (not shown).
Although a number of hydroalkoxycarbonylation have been re-
ported,2,3 attempted reactions using primary, secondary, and ter-
tiary alcohols instead of phenol were all ineffective under the
present reaction conditions.
A proposed reaction mechanism for the Pd-catalyzed hydro-
phenoxycarbonylation of internal alkynes (1) by phenol (2) and
CO is shown in Scheme 2. The reduction of Pd(OAc)2 by Zn in the
presence of DPPP would trigger the reaction to give highly active
Pd(0)-complex.8,9 The following oxidative addition of H–O bond
of 2 to the Pd(0)-complex would yield phenoxy palladium 5.10
Then the insertion of CO into O–Pd bond of 5 would form phenoxy-
carbonyl complex 6.11 The insertion of 1 either into the resultant
—
AcOH (10)
TsOH (5)
—
—
—
—
—
18
44
82
92
Zn (10)
Zn (20)
Zn (50)
Zn (100)
Zn (150)
Mg (150)
Mn (100)
SnCl2
Fe (150)
Zn (150)
92
99 (94)d
65
29
0
0
11
a
Unless otherwise noted, 1a (1.0 mmol), 2 (0.5 mmol), and CO (1 atm) was
treated in toluene (0.5 mL) at 100 °C for 24 h.
b
mol % is shown in parentheses.
GLC yield.
Isolated yield.
DBA (10 mol %) was added.
c
d
e
Table 2
Palladium-catalyzed hydrophenoxycarbonylation of 1 with 2aa
R2
cat. Pd(OAc)2
dppp/Zn
R1
OPh
R2
CO
+
R1
2
+
1
O
3
Entry
1
1
Product 3
Yieldb
n-C6H13
n-C6H13
n-C6H13
OPh
OPh
O
26%c (22/4)
1b
O
3b'
3b
Ph
Ph
Ph
Ph
OPh
2
91%
54%
O
1c
3c
Ph
Ph
OPh
OPh
N
N
3
4
1d
O
3d
Ph
O
O
Ph
EtO
EtO
84%
O
1e
3e
(continued on next page)

6820
H. Kuniyasu et al. / Tetrahedron Letters 51 (2010) 6818–6821
Table 2 (continued)
Entry
1
Product 3
Yieldb
59%
O
O
OPh
EtO
EtO
5
O
3f
1f
Me3Si
Ph
Ph
Me3Si
Me3Si
OPh
OPh
6
7
53%
1g
O
O
3g
3h
Me3Si
44%
1h
Ph
Ph
Ph
OPh
OPh
8
98% (64/36)
O
3i'
1i
O
3i
a
Conditions: 1 (1.0 mmol), 2 (0.5 mmol), CO (1 atm), Pd(OAc)2 (0.05 mmol) DPPE (0.05 mmol), Zn (0.75 mmol), and toluene (0.5 mL) at 100 °C for 24 h.
Isolated yield.
GLC yield. A complicated mixture was also produced.
b
c
Figure 1. ORTEP diagram of 3c.
Figure 2. ORTEP diagram of 3d.
Pd(OAc)2
dppp, Zn
2
3
P
P
Pd
4
O
R2
R1
P
P
OPh
P
P
P
Pd
R2
R1
Pd
OPh
Pd
OPh
H
H
O
P
5
7
8
P
P
Pd
OPh
H
O
CO
6
1
Scheme 2. A possible reaction mechanism.

H. Kuniyasu et al. / Tetrahedron Letters 51 (2010) 6818–6821
6821
H–Pd bond of 6 or into the C–Pd bond of 6 would follow to form
References and notes
either 7 or 8. Finally, C–C or C–H bond-forming reductive elimina-
tion of 3 would occur to regenerate Pd(0) complex.
1. (a) Reppe, V. W. Liebigs Ann. 1953, 582, 1; (b) Reppe, V. W.; Kröper, H. Liebigs
Ann. 1953, 582, 38.
2. For a review: Kiss, G. Chem. Rev. 2001, 101, 3435.
The present phenoxycarbonylation prototype was also applied
to the intermolecular cyclization reaction (Eq. 1). When the solu-
tion of 2-phenylethynyl-1-phenol (9) in the presence of
Pd(OAc)2/dppp/Zn was carried out under 5 atm of CO, the antici-
pated benzofuranone derivative 10 was produced in 72% yield
(Eq. 1).12,13
3. For selected examples: (a) Knifton, J. F. J. Mol. Catal. 1977, 2, 293; (b) Tsuji, Y.;
Kondo, T.; Watanabe, Y. J. Mol. Catal. 1987, 40, 295; (c) Drent, E.; Arnoldy, P.;
Budzelaar, P. H. M. J. Organomet. Chem. 1993, 455, 247; (d) Drent, E.; Arnoldy,
P.; Budzelaar, P. H. M. J. Organomet. Chem. 1994, 475, 57; (e) Kushino, Y.; Itoh,
K.; Miura, M.; Nomura, M. J. Mol. Catal. 1994, 89, 151; (f) Inoue, S.; Yokota, K.;
Tatamidani, H.; Fukumoto, Y.; Chatani, N. Org. Lett. 2006, 12, 2519.
4. Itoh, K.; Miura, M.; Nomura, M. Tetrahedron Lett. 1992, 33, 5369.
5. Crystal data for 3c: Space group P21/n (#14) with a = 14.6545(3) Å,
Pd(OAc)2 (5 mol%)
dppp (5 mol%)
Zn (0.75 mmol)
Ph
b = 5.8047(1) Å, c = 19.1876(3) Å, b = 97.8266(8)°, Z = 4,
q
= 1.234 g/cm3,
Ph
R = 0.186, and Rw = 0.151.
6. Crystal data for 3d: Space group P21/n (#14) with a = 12.0800(2) Å,
+
CO
b = 5.9938(1) Å, c = 22.8585(5) Å, b = 110.5010(8)°, Z = 4,
q
= 1.291 g/cm3,
O
ð1Þ
toluene (2.5 mL)
OH
O
R = 0.155, and Rw = 0.149.
5 atm
°
100 C, 24 h
7. For the determination of regio- and stereochemistry of other 3, see the
Supplementary data for more details.
0.5 mmol
10
72%
9
8. The 31P NMR spectrum of the reaction of Pd(OAc)2 with DPPP in the presence of
Zn in toluene-d8 suggested the quantitative formation of Pd(dppp)2 (a) Portnoy,
M.; Milstein, D. Organometallics 1993, 12, 1655; (b) Mason, M. R.; Verkade, J. G.
Organometallics 1992, 11, 2212.
In summary, this study substantiated that some internal al-
kynes exhibited high catalytic activity as substrates of Reppe car-
9. (a) Amatore, C.; Jutand, A.; Thuilliez, A. Organometallics 2001, 20, 3249; (b)
Doherty, S.; Robins, E. G.; Nieuwenhuyzen, M.; Champkin, P. A.; Clegg, W.
Organometallics 2002, 21, 4147.
10. For the oxidative addition of PhOH to Pd(PCy3)2, see: (a) Bugno, C. D.; Pasquali,
M.; Leoni, P.; Sabatino, P.; Braga, D. Inorg. Chem. 1989, 28, 1390; (b) Braga, D.;
Sabatino, P. J. Organomet. Chem. 1987, 334, C46.
11. (a) Scrivanti, A.; Beghetto, V.; Campagna, E.; Zanato, M.; Matteoli, U.
Organometallics 1998, 17, 630; (b) Murray, T. F.; Norton, J. R. J. Am. Chem. Soc.
1979, 101, 4107.
bonylation by phenol and CO to provide
a,b-unsaturated
arylesters, which are of great importance as synthetic intermedi-
ates. The reaction can be achieved by using Pd(OAc)2/dppp and ex-
cess amount of Zn. The scope and limitations as well as
mechanistic details of the present transformation are under
investigation.
12. The reductive and carbonylative cyclization of 9 by Rh-catalyst under much
more harsh conditions (100 atm of CO at 175 °C) has been reported, see:
Yoneda, E.; Sugioka, T.; Hirano, K.; Zhang, S.; Takahashi, S. J. Chem. Soc., Perkin
Trans. 1 1998, 477.
13. When the reaction was performed in the presence of 1 atm of CO, 5-end
cyclization without incorporating CO took place as a side reaction.
Acknowledgment
Thanks are due to the Instrumental Analysis Center, Faculty of
Engineering, Osaka University, for assistance in obtaining mass
spectra with a JEOL JMS-DX303 instrument.