Palladium/phosphite or phosphate catalyzed oxidative coupling of arylboronic acids with alkynes to produce 1,4-diaryl-1,3-butadienes

Article abstract of DOI:10.1002/adsc.200700533

The intermolecular oxidative coupling of arylboronic acids with internal alkynes efficiently proceeds in a 2:2 manner in the presence of palladium acetate, a triaryl phosphite or phosphate, and silver carbonate as catalyst, ligand, and oxidant, respectively, to produce the corresponding 1,4-diaryl-1,3-butadiene derivatives.

Full text of DOI:10.1002/adsc.200700533

FULL PAPERS
DOI: 10.1002/adsc.200700533
Palladium/Phosphite or Phosphate Catalyzed Oxidative
Coupling of Arylboronic Acids with Alkynes to Produce
1,4-Diaryl-1,3-butadienes
Hakaru Horiguchi,a Hayato Tsurugi,a Tetsuya Satoh,a,* and Masahiro Miuraa,*
a
Department of Applied Chemistry, Faculty of Engineering, Osaka University, Suita, Osaka 565-0871, Japan
Fax : (+81)-6-6879-7362; e-mail: satoh@chem.eng.osaka-u.ac.jpmiura@chem.eng.osaka-u.ac.jp
Received: November 10, 2007; Published online: February 8, 2008
Supporting information for this article is available on the WWW under http://asc.wiley-vch.de/home/.
Abstract: The intermolecular oxidative coupling of spectively, to produce the corresponding 1,4-diaryl-
arylboronic acids with internal alkynes efficiently 1,3-butadiene derivatives.
proceeds in a 2:2 manner in the presence of palladi-
À
um acetate, a triaryl phosphite or phosphate, and Keywords: arylation; C C coupling; dienes; multi-
silver carbonate as catalyst, ligand, and oxidant, re- component reactions; palladium; phosphite ligands
Introduction
boronic acids with diarylacetylenes to form 2:2 cou-
pling products, 1,4-diaryl-1,3-butadienes (path b).[6] In
The transition-metal-catalyzed arylation of internal al- this coupling, the silver salt acts as an oxidant.[7,8] The
kynes by halogenated or metalated aromatic reagents reaction appears to be synthetically useful as a simple
through carbometalation is a powerful tool for con- and straightforward route to multiarylated butadienes.
structing p-conjugated molecules.[1] Some of these re- Although the reaction with dialkylacetylenes takes
actions are carried out with addition of various termi- place to give 1,2,3,4-tetraalkyl-1,4-diarylbutadienes
nators including organometallic reagents,[2] alkenes,[3] having good solubilities, the product yields are moder-
and terminal alkynes[4] to give rise to three-compo- ate to low due to the facile deactivation of the palla-
nent coupling products. In other cases, the reactions dium catalyst under the oxidative conditions.[6,7b]
involve cyclometalation in the terminal step to yield
cyclic compounds.
In the course of our study of the catalytic processes
involving carbometalation of alkynes,[3a–b,5,6,9] we ob-
As an example for the latter case, we have reported served a notable ligand effect in the 2:2 coupling of
an effective protocol for the palladium-catalyzed 1:2 arylboronic acids with dialkylacetylenes in that it can
coupling of aryl iodides with diphenylacetylene as proceed selectively and efficiently under palladium
well as acetylenedicarboxylates in the presence of a catalysis by employing a triaryl phosphite to give the
silver salt as a base to afford the corresponding naph- corresponding highly substituted 1,3-butadienes. In
thalenes (path a in Scheme 1).[5] The Pd/Ag catalytic addition, it has also been found that the 2:2 coupling
system has also been applied to the reaction of aryl- of arylboronic acids with diarylacetylenes is consider-
ably enhanced by addition of a triaryl phosphate
rather than the phosphite.
Results and Discussion
When phenylboronic acid (1a) (2 mmol) was reacted
with 4-octyne (2a) (4 mmol) in the presence of
A
N
alyst and an oxidant, respectively, in DMF/H2O (9:1)
at 1208C for 3 h, 4,7-diphenyl-5,6-dipropyl-4,6-deca-
diene (3a) was formed in 45% yield along with a
trace amount of direct homo-coupling product, bi-
Scheme 1. Coupling of aryl iodides and boronic acids with
alkynes.
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Table 1. Reaction of phenylboronic acid (1a) with 4-octyne
(2a).[a]
ed (entry 10). Finally, 3a was obtained in 85% yield,
when the reaction was conducted using tris(4-methyl-
phenyl) phosphite as a ligand (entry 11). This yield is
almost twice as high as that in our previous report.[6]
It is possible that the phosphite ligands are oxidized
to the corresponding phosphates under the oxidative
conditions with the silver salt. While the phosphates
showed substantial effects (entries 12 and 13), they
were less effective than tris(4-methylphenyl) phos-
phite. Under the conditions using Cu(OAc)2·H2O as
G
an oxidant combined with K2CO3 in place of the
silver salt, the reaction was sluggish (entry 14). The
NMR spectra of 3a isolated in entry 11 indicated that
it has the (4Z,6Z) configuration, as previously report-
ed,[6] without contamination by any other geometrical
isomers.
Table 2 summarizes the results for the reactions of
various arylboronic acids 1a–e with dialkylacetylenes
Table 2. Reaction of arylboronic acids 1a–e with dialkylace-
tylenes 2a–d.[a]
[a]
Reaction conditions: [1a]:[2a]:[Pd
G
N
2:4:0.05:2 (in mmol), in DMF/H2O (9:1, 5 mL) under N2
at 1408C.
[b]
GC yield based on the amount of 1a (entries 1–9) or 2a
(entries 10–13) used. Value in parentheses indicates yield
after purification.
At 1208C.
In DMF (5 mL).
[c]
[d]
[e]
[f]
1a (4 mmol) and 2a (2 mmol) were used.
Cu
A
in place of Ag2CO3.
phenyl (4a) (Table 1, entry 1). Thus, the reaction stop-
ped at a moderate conversion, which may be attribut-
ed to catalyst deactivation. The result is comparable
to those observed previously in 1,4-dioxane/H2O and
1-propanol.[6] At a higher temperature of 1408C, the
initial reaction rate was enhanced, but the yield of 3a
was not improved (entry 2). In pure DMF, the yield
of by-product 4a increased (entry 3). For elongating
catalyst lifetime, a number of monodentate ligands
(0.1 mmol) were added in the reaction medium (en-
tries 4–8). Among them, triphenyl phosphite was
found to improve the yield of 3a up to 55% (entry 8).
[a]
Reaction conditions: [1]:[2]:[Pd
4:2:0.05:0.05:2 (in mmol), in DMF/H2O (9:1, 5 mL) at
1408C under N2.
A=(PhO)3P, B =[(4-MeC6H4)O]3P.
GC yield based on the amount of 1 (entries 7 and 8) or 2
(entries 1–6, 9 and 10) used. Value in parentheses indi-
cates yield after purification.
A
G
[b]
[c]
[d]
[e]
[f]
1 (2 mmol) and 2 (4 mmol) were used.
(4Z,6Z):
ACHTREUNG
(4Z,6Z):
A
ACHTREUNG
Decreasing the amount of the phosphite to 0.05 mmol 2a–d in the presence of Pd(OAc)2/phosphite. In the
C
somewhat increased the yield (entry 9). Under the reaction of 1a with dialkylacetylenes 2b–d, the cata-
conditions using an excess amount of 1a (4 mmol) lyst system with (PhO)3P ligand (ligand A) unexpect-
with 2a (2 mmol), the yield of 3a was enhanced to edly gave similar or slightly better results compared
67%, while the amount of 4a also increased as expect- with those using [(4-MeC6H4)O]3P (ligand B)
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Palladium/Phosphite or Phosphate Catalyzed Oxidative Coupling of Arylboronic Acids
FULL PAPERS
(Table 2, entries 1–6). In these reactions, the corre- phate (0.1 or 0.05 mmol) (entries 3 and 4). Among
sponding dienes 3b–d were obtained in 55–84% yields some phosphates examined (entries 3–6), tris(4-meth-
as single major cross-coupling products. In the reac- ylphenyl) phosphate gave the best yield of 91%
tions of electron-poor boronic acids 1b and 1c, better (entry 5). The use of diphenyl phosphate increased
results were obtained under conditions using excess the yield of biphenyl 4a, but it was less effective for
alkyne 2a. Thus, the reactions of 1b and 1c (2 mmol) the cross-coupling (entry 7).
with 2a (4 mmol) gave dienes 3e and 3f in 72 and
71% yields, respectively (entries 7 and 8). Electron-
In the presence of the catalyst system of Pd-
(OAc)2/[(4-MeC6H4)O]3P=O, the reaction of (4-meth-
A
ACHTREUNG
rich boronic acids 1d and 1e also underwent the cou- ylphenyl)boronic acid (1d) with bis(4-methylphenyl)a-
pling with 2a to afford dienes 3g and 3h in 71 and cetylene (5b) also proceeded smoothly to form
63% yields (entries 9 and 10). The NMR spectra of 1,1,2,3,4,4-hexakis(4-methylphenyl)-1,3-butadiene (6b)
the products indicated that they contained minor in 81% isolated yield (Scheme 2). This is significantly
amounts of their geometrical isomer(s) [3g: (4Z,6Z):- higher than that obtained previously in the absence of
A
3h:
(4Z,6Z):
G
N
ACHTREUNG
5a (2 mmol) in the presence of Pd(OAc)2 (0.05 mmol)
A
and Ag2CO3 (2 mmol) in 1-propanol/H2O (9:1) at
1208C for 1 h, 1,1,2,3,4,4-hexaphenyl-1,3-butadiene
(6a) was produced in 74% yield (Table 3, entry 1).
Table 3. Reaction of phenylboronic acid (1a) with diphenyl-
A
Scheme 2. Reaction of (4-methylphenyl)boronic acid (1d)
with di(4-methylphenyl)acetylene (5b). Reaction conditions:
[1d]:[5b]:[Pd
A
G
N
1.5:1:0.025:0.025:1 (in mmol), in 1-propanol/H2O (9:1,
2.5 mL) under N2 at 1208C for 0.5 h.[a] GC yield. Value in
parentheses indicates yield after purification.
(4-Methoxyphenyl)boronic acid (1e) reacted with
bis(4-methoxyphenyl)acetylene (5c) to afford a cy-
clized product 7 in 60% yield (Scheme 3). This may
be formed via the 2:2 coupling, subsequent electrocy-
clic rearrangement[10] of the resulting butadiene, and
[1,5] hydrogen shift.
On the other hand, treatment of (4-chlorophenyl)-
boronic acid (1b) with bis(4-chlorophenyl)acetylene
(5d), even under the conditions using the silver oxi-
dant gave a 2:1 coupling product, 1,1,2,2-tetrakis(4-
[a]
Reaction conditions: [1a]:[5a]:[Pd
G
N
3:2:0.05:2 (in mmol), in 1-propanol/H2O (9:1, 5 mL) chlorophenyl)ethane (8), albeit with a low yield
under N2 at 1208C.
(Scheme 4). In this case, formation of the expected
butadiene could not be detected.
A plausible mechanism for the reaction of arylbor-
onic acids 1 with alkynes 2 or 5 is illustrated in
Scheme 5, which is similar to that proposed previous-
ly.[6] The formation of an arylpalladium intermediate
[b]
[c]
GC yield based on the amount of 5a used. Value in pa-
rentheses indicates yield after purification.
At 808C.
Addition of triphenyl phosphite (0.1 mmol) showed Y via transmetalation between a Pd(II) species (L=
no apparent effect (entry 2). However, the yield of 6a ligand or solvent) and 1 followed by insertion of two
was improved to 84% by addition of triphenyl phos- alkyne molecules forms a dienylpalladium intermedi-
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Hakaru Horiguchi et al.
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cy.[12] While the exact role of the added phosphites
and phosphates is not clear at the present stage, they
may support unstable Pd(0) or regenerated Pd(II)
species to prolong the catalyst’s lifetime.[13–15]
Conclusions
We have shown effective protocols for the palladium-
catalyzed oxidative coupling of arylboronic acids with
internal alkynes using a triaryl phosphite or phos-
phate as the ligand to selectively give the correspond-
ing 2:2 coupling products, 1,4-diaryl-1,3-butadienes.
These reactions provide a straightforward route to
arylated butadienes, which are of interest for their
photo- and electrochemical and biological proper-
ties.[16]
Scheme 3. Reaction of (4-methoxyphenyl)boronic acid (1e)
with di(4-methoxyphenyl)acetylene (5c). Reaction condi-
tions: [1e]:[5c]:[Pd
A
G
N
=1.5:1:0.025:0.025:1 (in mmol), in 1-propanol/H2O (9:1,
[a]
2.5 mL) under N2 at 1208C for 0.5 h. Isolated yield.
Experimental Section
ate Z. The successive second transmetalation and re-
ductive elimination give 1,4-diarylated 1.3-diene 3 or
6.[11] The L2Pd(0) species generated in the last step
may be reoxidized by the silver salt to close the cata-
lytic cycle. During palladium-catalyzed oxidation re-
actions, in general, the last reoxidation is considered
to be the crucial step to determine catalyst efficien-
General Remarks
1H and 13C NMR spectra were recorded at 400 and
100 MHz, or 270 MHz and 68 MHz, respectively, for CDCl3
solutions. MS data were obtained by EI. GC analysis was
carried out using a silicon OV-17 column (i. d. 2.6 mm”
1.5 m) or a CBP-1 capillary column (i. d. 0.5 mm”25 m).
GC-MS analysis was carried out using a CBP-1 capillary
Scheme 4. Reaction of (4-chlorophenyl)boronic acid (1b) with di(4-chlorophenyl)acetylene (5d). Reaction conditions:
[1b]:[5d]:[Pd(OAc)2]:[{(4-MeC6H4)O}3P=O]:[Ag2CO3]=1.5:1:0.025:0.025:1 (in mmol), in 1-propanol/H2O (9:1, 2.5 mL) under
N2 at 1208C for 0.5 h. GC yield. Value in parentheses indicates yield after purification.
A
N
ACHTREUNG
[a]
Scheme 5. A plausible mechanism for the coupling of arylboronic acids with alkynes.
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Palladium/Phosphite or Phosphate Catalyzed Oxidative Coupling of Arylboronic Acids
FULL PAPERS
column (i. d. 0.25 mm”25 m). The structures of all products
1579; b) C. Zhou, R. C. Larock, J. Org. Chem. 2005, 70,
3765.
1
were unambiguously determined by H and 13C NMR with
the aid of NOE, COSY, HMQC, and HMBC experiments.
Diarylacetylenes 5b–d were prepared according to pub-
lished procedures.[17] Other starting materials were commer-
cially available. Characterization data of all the products are
reported in the Supporting Information.
[3] a) K. Shibata, T. Satoh, M. Miura, Org. Lett. 2005, 7,
1781; b) K. Shibata, T. Satoh, M. Miura, Adv. Synth.
Catal. 2007, 349, 2317; c) T. Kurahashi, H. Shinokubo,
A. Osuka, Angew. Chem. 2006, 118, 6484; Angew.
Chem. Int. Ed. 2006, 45, 6336; d) M. L. Kantam, P. Sri-
nivas, K. B. Shiva Kumar, R. Trivedi, Cat. Commun.
2007, 8, 991.
The following experimental procedure may be regarded
as typical in methodology and scale.
[4] a) M. Pal, K. Parasuraman, V. Subramanian, R. Dakar-
apu, K. R. Yeleswarapu, Tetrahedron Lett. 2004, 45,
2305; b) L. R. Pottier, J.-F. Peyrat, M. Alami, J.-D.
Brion, Synlett 2004, 1503; c) M. Shi, L.-P. Liu, J. Tang,
Org. Lett. 2005, 7, 3085.
Pd-Catalyzed Reaction of Phenylboronic Acid (1a)
with 4-Octyne (2a) (entry 11 in Table 1)
A mixture of phenylboronic acid (1a) (4 mmol, 488 mg), 4-
octyne (2a) (2 mmol, 220 mg), Pd(OAc)2 (0.05 mmol,
G
[5] S. Kawasaki, T. Satoh, M. Miura, M. Nomura, J. Org.
11 mg), [(4-MeC6H4)O]3P (0.05 mmol, 18 mg), Ag2CO3
(2 mmol, 551 mg), and 1-methylnaphthalene (ca. 60 mg) as
internal standard was stirred in DMF/H2O (5 mL, 9:1)
under nitrogen at 1408C. After 3 h, the reaction mixture was
cooled to room temperature, Et2O (100 mL) and water
(100 mL) were added, and insoluble materials were removed
by filtration through filter paper. Then the organic layer was
washed by water (100 mL, three times) and dried over
sodium sulfate. GC and GC-MS analyses confirmed the for-
mation of (4Z,6Z)-4,7-diphenyl-5,6-dipropyl-4,6-decadiene
(3a) (0.85 mmol, 85%) and biphenyl (4a) (0.52 mmol). The
product 3a (279 mg, 75%) was isolated by column chroma-
tography on silica gel using hexane as eluant and subsequent
Kugelrohr distillation to remove hydrocarbon impurities
such as the internal standard.
Chem. 2003, 68, 6836.
[6] T. Satoh, S. Ogino, M. Miura, M. Nomura, Angew.
Chem. 2004, 116, 5173; Angew. Chem. Int. Ed. 2004, 43,
5063.
[7] It has been reported that using O2 as an oxidant gave
2:1 coupling products: a) C. Zhou, R. C. Larock, Org.
Lett. 2005, 7, 259; b) C. Zhou, R. C. Larock, J. Org.
Chem. 2006, 71, 3184; the 2:1 coupling products were
also obtained in Pd-catalyzed and -promoted arylation
of alkynes with aryltin and arylmagnesium reagents;
ArSn: c) H. Oda, M. Morishita, K. Fugami, H. Sano,
M. Kosugi, Chem. Lett. 1996, 811; d) K. Fugami, S. Ha-
giwara, H. Oda, M. Kosugi, Synlett 1998, 477; ArMg:
e) C. Broquet, H. Riviere, J. Organomet. Chem. 1982,
226, 1; in contrast to the reactions with arylmetal re-
agents, the use of the corresponding methylmetal re-
agents results in 2:2 coupling to give 1,4-dimethyl-1,3-
butadienes.[4c,e].
Compound 3a: mp 83–858C (lit.[6] mp 888C); 1H NMR
(270 MHz, CDCl3): d=0.77 (t, J=6.9 Hz, 6H), 0.82 (t, J=
6.9 Hz, 6H), 1.13–1.22 (m, 4H), 1.24–1.44 (m, 4H), 1.56–
1.67 (m, 2H), 2.00–2.12 (m, 2H), 2.17–2.29 (m, 4H), 7.06–
7.20 (m, 10H); 13C NMR (68 MHz, CDCl3): d=14.2, 14.9,
21.5, 22.8, 36.1, 36.5, 125.5, 127.2, 128.6, 136.6, 139.1, 143.8;
MS: m/z=374 (M+).
[8] After the publication of our preliminary communica-
tion, Zhou and Larock reported the 2:2 coupling of
boronic acids with dialkylacetylenes under O2 with
moderate efficiencies, while only the 2:1 coupling
occurs with diarylacetylenes.[4b].
[9] a) K. Kokubo, K. Matsumasa, M. Miura, M. Nomura, J.
Org. Chem. 1996, 61, 6941; b) S. Pivsa-Art, T. Satoh, M.
Miura, M. Nomura, Chem. Lett. 1997, 823; c) T. Yasu-
kawa, T. Satoh, M. Miura, M. Nomura, J. Am. Chem.
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Satoh, M. Miura, M. Nomura, J. Org. Chem. 2004, 69,
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Miura, Org. Lett. 2007, 9, 1407; g) K. Ueura, T. Satoh,
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[10] For example, see: M. Irie, Chem. Rev. 2000, 100, 1685.
[11] Although the reason why only two molecules of the al-
kynes are selectively incorporated into the products is
not definitive at the present stage, it may be attributed
to stabilization of the dienylpalladium intermediate (Z
in Scheme 5) by chelation: see, X. Zeng, Q. Hu, M.
Qian, E.-I. Negishi, J. Am. Chem. Soc. 2003, 125,
13636.
Acknowledgements
This work was partly supported by a Grant-in-Aid from the
Ministry of Education, Culture, Sports, Science and Technol-
ogy, Japan.
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