Nickel-catalyzed decarboxylative polymerization of 6-alkynylisatoic anhydride

Article abstract of DOI:10.1246/cl.2011.1240

A new methodology for preparation of polyquinolone was developed. Iterative nickel-catalyzed reaction of 6-alkynylisatoic anhydride monomer affords polyquinolone via decarboxylative cycloaddition without formation of residual by-product. It was demonstrat

Full text of DOI:10.1246/cl.2011.1240

doi:10.1246/cl.2011.1240
1240
Published on the web October 8, 2011
Nickel-catalyzed Decarboxylative Polymerization of 6-Alkynylisatoic Anhydride
Kenichiro Nakai, Takahiro Shiba, Yasufumi Yoshino, Takuya Kurahashi,* and Seijiro Matsubara*
Department of Material Chemistry, Graduate School of Engineering, Kyoto University, Kyoto 615-8510
(Received July 4, 2011; CL-110562; E-mail: tkuraha@orgrxn.mbox.media.kyoto-u.ac.jp)
A new methodology for preparation of polyquinolone was
Scheme 2. The Cu-catalyzed reaction of 3 with 4-dodecylaniline
(4) gave the coupling product 5 in 90% yield. Iodination of 5
with iodine and hydrogen peroxide afforded 6 in 86% yield,
which was then reacted with ethyl chloroformate to give isatoic
anhydride 7 in 60% yield. The palladium-catalyzed Sonogashira
coupling reaction of 7 with trimethylsilylacetylene 8 furnished
1, an alkynylisatoic anhydride monomer, in 64% yield. It is
worth mentioning that the whole procedure to prepare monomer
1 from 3 did not require silica gel chromatography to purify
the reaction products after each step. The purifications of the
reaction products were done by recrystallization.
The decarboxylative polymerization of alkynylisatoic an-
hydride monomer 1 proceeded in toluene (80 °C, 12 h) and
furnished polyquinolone 2 in 65% yield with [Ni(cod)2]/PMe3
catalyst. Among phosphine ligands examined, PCy3 gave the
best yield of polyquinolone 2. Thus, the polymerization of 1
with [Ni(cod)2]/PCy3 in toluene at elevated reaction temperature
(100 °C) and prolonged reaction time (24 h) gave the desired
polymer 3 in 92% yield (Scheme 3). In other reaction solvents,
such as 1,4-dioxane and THF, yields were even lower. The
reaction of 1 with palladium or rhodium catalyst (e.g.,
[Pd(PPh3)4] and [RhCl(cod)]2) did not afford any polymer or
oligomer even with prolonged reaction time. MALDI-TOF MS
was used to determine the structures of the polyquinolone 2.
It was observed that the spectrum has a peak repeat of
developed. Iterative nickel-catalyzed reaction of 6-alkynylisatoic
anhydride monomer affords polyquinolone via decarboxylative
cycloaddition without formation of residual by-product. It was
demonstrated for the first time that decarboxylative cycloaddition
can be an elementary process of chain growth polymerization for
preparation of polyheterocycles with high regioregularity.
Since conjugated polymers are potentially important mate-
rials for applications such as semiconducting, conducting, and
light-emitting materials, synthesis of polymers with a sp2-sp2
bond formation along the polymer chains has been an interesting
research subject.1 Although there are a large number of methods
for synthesis of such polymers, the development of new
methodologies, which would allow for unprecedented types of
conjugated polymers, remains an important research topic.
Recently, we demonstrated nickel-catalyzed decarboxylative
cycloaddition of alkynes with isatoic anhydrides to give
quinolone.2-4 Our success in synthesis of a quinolone from the
readily available isatoic anhydride and alkynes with decarbox-
ylative cycloadditions prompted us to investigate new polymer-
ization reactions, which would allow us to prepare an unprece-
dented type of polyheterocycle, polyquinolone 2, from 6-
alkynylisatoic anhydride 1 (Scheme 1). The process enables
the straightforward synthesis of polyheterocycles without for-
mation of residual by-product such as metal halides, which
are usually produced when the polymer is synthesized with
transition-metal-catalyzed polycondensation using dihalo-
organic compounds and may contaminate the resulting poly-
mer.5 Herein, we report our results of nickel-catalyzed decar-
boxylative cycloaddition to provide polyquinolone 2 from 6-
alkynylisatoic anhydride 1.
O
O
NH2
Cu(OAc)2 (3 mol %)
K2CO3 (1 equiv)
I2 (0.7 equiv)
H2O2 (0.7 equiv)
OH
OH
NH
+
DMF, refulx, 3 h
AcOH, 50 °C, 4 h
Cl
10
3
4
10
5 90% yield
Me3Si
H
Alkynylisatoic anhydride monomer 1 was prepared from
2-chlorobenzoic acid (3) according to the route shown in
O
O
N
[PdCl2(PPh3)2] (5 mol %)
CuI (5 mol %)
I
I
OH
O
NH
O
ClCOOEt, reflux, 24 h
Iterative Decarboxylative Cycloaddition
NEt3, 60 °C, 12 h
R1
O
transition metal catalyst
O
10
10
6 86% yield
7 60% yield
– n CO2
N
O
R2
1
O
R1
Me3Si
O
O
N
Iterative Coupling Reaction
O
N
O
R2
n
2
X
R1
transition metal catalyst
– n MtlX
N
X
10
R2
Mtl; Zn, Mg, Cu, etc.
monomer 1 64% yield
Scheme 1. Synthesis of polyquinolone 2.
Scheme 2. Synthesis of alkynylisatoic anhydride 1.
Chem. Lett. 2011, 40, 1240-1241
© 2011 The Chemical Society of Japan
www.csj.jp/journals/chem-lett/

1241
O
N
SiMe3
Me3Si
O
N
O
[Ni(cod)2] (5 mol %)
PCy3 (10 mol %)
([Catalyst] = 1.0 10–2
6
3
SiMe3
O
)
O
N 2
toluene (1.5 mL)
100 °C, 24 h
– n CO2
O
N
2' 94% yield
[Ni(cod)2] (5 mol %)
PCy3 (10 mol %)
O
single isomer
10
10
+
Me3Si
O
toluene (0.2 M)
100 °C, 24 h
n
1.0 equiv
O
1 (0.3 mmol, [M]0 = 2.0 10–1
)
2 92% yield
8
1'
Scheme 3. Synthesis of polyquinolone 2 from monomer 1 with
nickel-catalyzed decarboxylative cycloaddition.
N
SiMe3
not observed
Scheme 4. Regioselective reaction of 1¤ with 8 (ref. 3).
This work was supported by Grants-in-Aid from MEXT,
Japan. T.K. also acknowledges support from the Asahi Glass
Foundation, and Kansai Research Foundation.
References and Notes
1
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Figure 1. MALDI-TOF mass spectra of polyquinolone 2.
¦m/z = 459, which corresponds to the molecular weight of the
quinolone unit (Figure 1). This result clearly shows that the
polymerization consisted of iterative decarboxylative cyclo-
addition of alkynylisatoic anhydride monomer 1.
2
The molecular weight of the polymer 2 as well as the
distribution of molecular weights was determined by gel
permeation chromatography (GPC). The distribution of molecu-
lar weights was determined with polystyrene standards. It was
found that the molecular weight (Mn) of polyquinolone 2 was
5.1 © 104 and the distribution of molecular weights (Mw/Mn) was
calculated to be 4.92. Even though the molecular weight (Mn) and
distribution of molecular weights (Mw/Mn) of polyquinolone
2 were not drastically affected by the reaction conditions of
the polymerization (e.g., initial concentration of monomer and
monomer/catalyst ratio), lower molecular weight (Mn = 2.1 ©
104) was observed when the polymerization was carried out in
benzene in place of toluene presumably due to rapid precipitation
of insoluble oligomer during the chain growth reaction.
Considering that the reaction of isatoic anhydride 1¤ with
phenyl(trimethylsilyl)acetylene (8) under the same reaction con-
ditions afforded correspondingly substituted quinolone 2¤ in
94% isolated yield with complete regioselectivity (Scheme 4),3
we assumed that the polymerization of alkynylisatoic anhydride
monomer 1 afforded polyquinolone 2, which consisted of
quinolone subunits connected with carbon-carbon bond between
C-2 and C-6, regioselectively (Scheme 3). Indeed, only a single
peak assigned to a trimethylsilyl group was observed by
1H NMR measurement of polyquinolone 2; the polymerization
proceeded with high regioregularity.
3
4
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5
In summary, a new methodology for preparation of poly-
quinolone was developed. We demonstrated for the first time
that nickel-catalyzed decarboxylative cycloaddition can be an
elementary process of chain growth polymerization for prepa-
ration of polyheterocycles with high regioregularity.6
6
Supporting Information is available electronically on the CSJ-
Journal Web site, http://www.csj.jp/journals/chem-lett/index.html.
Chem. Lett. 2011, 40, 1240-1241
© 2011 The Chemical Society of Japan
www.csj.jp/journals/chem-lett/