Palladium-catalyzed arylation of methylene-bridged polyarenes: Synthesis and structures of 9-arylfluorene derivatives

Article abstract of DOI:10.1002/adsc.201100931

In the presence of a catalytic system comprised of palladium(II) acetate and tricyclohexylphosphine, the reaction of fluorene with haloarenes generated 9-arylfluorenes in good to excellent yields. The scope and limitations of the coupling reaction were investigated. This synthetic protocol is more efficient than conventional methods. A wide range of functional groups, including alkyl, alkoxy, ester, and nitrile, can tolerate the reaction conditions herein. Sterically congested haloarenes also gave satisfactory results. Furthermore, this synthetic method is utilized to prepare 9,9-diarylfluorenes and tetraarylindenofluorene. Depending on the reaction conditions, the arylation of bowl-shaped sumanene gave monoarylated sumanene either as the sole product or with another diaryl-substituted product. Copyright

Full text of DOI:10.1002/adsc.201100931

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DOI: 10.1002/adsc.201100931
Palladium-Catalyzed Arylation of Methylene-Bridged Polyarenes:
Synthesis and Structures of 9-Arylfluorene Derivatives
Jheng-Jhih Chen,a Satoru Onogi,b Ya-Chu Hsieh,a Chien-Chi Hsiao,a
Shuhei Higashibayashi,b,c Hidehiro Sakurai,b,c and Yao-Ting Wua,*
a
Department of Chemistry, National Cheng Kung University, No. 1 Ta-Hsueh Rd., 70101 Tainan, Taiwan
Fax : (+886)-6-274-0552; e-mail: ytwuchem@mail.ncku.edu.tw
School of Physical Sciences, The Graduate School of Advanced Studies, Myodaiji, Okazaki 444-8787, Japan
Research Center for Molecular Scale Nanoscience, Institute for Molecular Science, Myodaiji, Okazaki 444-8787, Japan
b
c
Received: December 2, 2011; Revised: February 2, 2012; Published online: May 15, 2012
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/adsc.201100931.
Abstract: In the presence of a catalytic system com- results. Furthermore, this synthetic method is utilized
prised of palladium(II) acetate and tricyclohexyl- to prepare 9,9-diarylfluorenes and tetraarylindeno-
phosphine, the reaction of fluorene with haloarenes fluorene. Depending on the reaction conditions, the
generated 9-arylfluorenes in good to excellent yields. arylation of bowl-shaped sumanene gave monoary-
The scope and limitations of the coupling reaction lated sumanene either as the sole product or with an-
were investigated. This synthetic protocol is more ef- other diaryl-substituted product.
ficient than conventional methods. A wide range of
functional groups, including alkyl, alkoxy, ester, and
nitrile, can tolerate the reaction conditions herein. Keywords: arylation; fluorenes; indenofluorenes;
Sterically congested haloarenes also gave satisfactory palladium; polyarenes; sumanene
Introduction
preparations of 9-arylfluorenes 1 and 9,9-diarylfluor-
enes are important, and conventional methods for
Fluorene is the simplest methylene-bridged arene and synthesizing 1 are summarized in Scheme 1. The reac-
it is an important building block for various organic
materials, including those used in optoelectronics,[1]
semiconductors,[2] and solar cells.[3] Unlike benzenoids,
fluorene and other methylene-bridged polyarenes are
classified as non-alternant aromatic hydrocarbons be-
cause their additional methylene carbons cannot pres-
ent aromaticity associated with the Kekulꢀ struc-
ture.[4] Moreover, the methylene protons exhibit high
acidity,[5] which allows fluorene to be easily converted
to 9,9-dialkylfluorenes. Molecules of this type are
more stable and soluble than the parent compound.
However, for use in optoelectronics, 9,9-diarylfluor-
enes are superior to 9,9-dialkylfluorenes because the
alkyl pendant group of the latter can be photochemi-
cally or electrooxidatively cleaved,[6] resulting in poor
color purity. The high strength of the bond between
the pendant aryl groups and the C-9 carbon of fluor-
ACHTUNGTRENNUNGene in 9,9-diarylfluorenes gives them excellent mor-
phological and thermal stability.[7] In addition to their
use in organic materials, 9-arylfluorenes are useful
precursors for the formation of chiral ligands,[8] which
are used in polymer catalysts.[8d] Accordingly, efficient Scheme 1. Synthetic methods for preparing 9-arylfluorenes.
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FULL PAPERS
tion of 9-fluorenone with aryllithium or aryl-Grignard are formed by the reaction of 2-biphenylcarbaldehyde
reagents yields the corresponding carbinols, which are with aryllithium or aryl-Grignard reagents. Of these
subsequently transformed into 1 by treatment with re- synthetic methods, routes A and F are the most exten-
ductants, such as Et2O·BF3/Et3SiH system (route A).[9] sively used, but functional group tolerance is a major
Additionally, 1 can be formed from 9-bromofluorene limitation. Routes B–E have not been comprehensive-
through many reaction mechanisms (routes B–D). Or- ly investigated (with only one example of each reac-
ganostannoxane-supported palladium nanoparticles tion), and their scope and limitations are unclear.
efficiently catalyze the Suzuki reaction of 9-bromo- Therefore, the direct preparation of 9-arylfluorenes
fluorene with phenylboronic acid (route B).[10] In the by the metal-catalyzed coupling reaction of fluorene
presence of p-toluenesulfonic acid, 9-bromofluorene with haloarenes has great potential.[16] The synthetic
in toluene is transformed into a regioisomeric mixture method proposed herein should not only mitigate the
of 9-(2-tolyl)fluorene and 9-(4-tolyl)fluorene (route drawbacks of routes A–F, but also efficiently reduce
C), with the latter as the major product. In this reac- the number of reaction steps. In our earlier study of
tion, the fluorenyl cation is believed to be the key in- the synthesis of fluorene by the palladium-catalyzed
termediate.[11] The zinc-mediated radical reaction of cyclization of 2-bromo-2’-methylbiphenyl (2a), 9-(2-
9-bromofluorene with anthracene in CS2 yields 9-(9- biphenyl)fluorene (1a) was obtained as a by-product
anthryl)fluorene (route D).[12] Alternatively, the for- in low yield (Scheme 1).[17a] Compound 1a should be
mation of the central five-membered ring can be obtained by the cross-coupling reaction of fluorene
adopted as the key step in the synthesis of 1.[13] For with 2a.[18] Accordingly, this investigation concerns
example, using a catalytic system consisting of phenyl the arylation of fluorene and methylene-bridged poly-
methyl sulfoxide (PMSO) and the oxidized Keggin- arenes.
type polyoxomolybdate [PMo12O40]3À in dichloroben-
zene (DCB), triphenylmethane furnishes 9-phenyl-
fluorene via the triphenylmethane cation (route E).[14] Results and Discussion
Alternatively, Friedel–Crafts cyclizations of biaryl al-
cohols or acetates catalyzed by a Brønsted or Lewis The reaction conditions for synthesizing 9-(2-tolyl)-
acid, such as HCl/HOAc, polyphosphoric acid or fluorene (1b) from fluorene and 2-bromotoluene (2b)
BF3·Et2O, can also furnish 1 (route F).[15] As in route were systematically studied (Table 1). The palladium
A, the biphenyl derivatives that are used in route F catalyst, base, and solvent all have crucial roles. The
Table 1. Optimization of reaction conditions for the preparation of 1b.[a]
Entry
Catalyst (mol%)
PdCl2A(PCy3)2 (5)
Ligand (mol%)
Base
Solvent
Fluorene:1b[b]
Isolated yield [%]
1
2
3
4
5
6
7
8
G
–
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
K2CO3
Na2CO3
KOAc
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
DMAc
DMAc
DMAc
DMAc
NMP
NMP
NMP
NMP
1,4-dioxane
DMF
DMAc
DMAc
DMAc
DMAc
DMAc
9:91
–
Pd(OAc)2 (5)
Pd(OAc)2 (2)
Pd(OAc)2 (1)
Pd(OAc)2 (5)
Pd(OAc)2 (5)
Pd(OAc)2 (5)
Pd(OAc)2 (5)
Pd(OAc)2 (5)
Pd(OAc)2 (5)
Pd(OAc)2 (5)
Pd(OAc)2 (5)
Pd(OAc)2 (5)
Pd(OAc)2 (5)
Pd(OAc)2 (5)
R
PCy3·HBF4 (10)
PCy3·HBF4 (4)
PCy3·HBF4 (2)
PCy3·HBF4 (10)
PCy3·HBF4 (10)
PCy3·HBF4 (10)
PCy3·HBF4 (10)
PCy3·HBF4 (10)
PCy3·HBF4 (10)
0:100
0:100
0:100
34:66
85:5
100:0
100:0
6:94
0:100
66:34
73:27
14:86
70:30
20:80
94
95
90
55
–
–
–
87
95
–
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
N
N
T
9
T
N
N
R
E
T
A
10
11
12
13
14
15
PN
PPh3 (10)
dppm (5)
dppe (5)
–
–
–
–
IPr·HCl (10)
[a]
The reaction was performed with fluorene (0.50 mmol), 2 (0.60 mmol) and base (0.75 mmol) in a thick-walled sealed
tube at 1308C for 12 h.
Determination by GC MS.
[b]
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Palladium-Catalyzed Arylation of Methylene-Bridged Polyarenes
Table 2. Preparation of 9-arylfluorenes.[a]
Entry
Ar–X
Ratio (fluorene/2)
Temp. [8C]
Product
Isolated yield [%]
1
2
3
4
5
6
7
8
2-CH3-C6H4Br (2b)
C6H5Cl (2c)
C6H5Br (2d)
1/1.2
1/1.2
1/1.2
1/1.2
1.3/1
1/1.2
1/1.5
1/1.2
1/1.2
1/1.2
1/1.2
1/1.2
1.2/1
1.2/1
1/1.2
1/1.2
1/1.2
130
130
130
130
110
130
130
110
110
130
110
130
130
130
130
130
130
1b
1c
1c
1e
1f
1g
1h
1i
1i
1j
1j
1k
1l
95[b]
95
95
2-Ph-C6H4Br (2e)
75c
79[c]
0
2-CO2CH3-C6H4Cl (2f)
4-CHO-C6H4Br (2g)
4-CO2CH3-C6H4Br (2h)
4-Ac-C6H4Br (2i)
4-Ac-C6H4Br (2i)
4-CF3-C6H4Br (2j)
75
57
9
85[d]
51
10
11
12
13
14
15
16
17
4-CF3-C6H4Br (2j)
82
70
4-CN-C6H4Br (2k)
4-OCH3-C6H4Br (2l)
4-OCH3-C6H4Br (2l)
2,6-(CH3)2-C6H3Br (2m)
9-bromophenanthrene (2n)
1-bromo-2-methylnaphthalene (2o)
0
1l
95[e]
94
1m
1n
1o
83[f]
84 g]
[a]
The reaction was conducted with fluorene and 2 (0.50 mmol) in a thick-walled sealed tube.
[b]
[c]
[d]
[e]
[f]
1
The ratio (syn/anti=63/37) was determined by H NMR.
1
The rotamers of 1e and 1f cannot be easily distinguished by H NMR. For details, see: ref.[26]
The reaction was conducted with Cs2CO3 (3.0 equiv.).
The reaction was conducted with ligand L1.
The ratio (syn/anti=57/43) was determined by H NMR.
1
[g]
1
The ratio (syn/anti=60/40) was determined based on the H NMR spectrum of the crude product. Both syn-1o and anti-
1o were obtained in their pure forms.
combination of Pd
ACHTUNGTRENNUNG
drastically outperform PdCl CTHGNUTRENNUNG
ic systems that are shown in Table 1. The fluorenyl 1-bromo-2-methylnaphthalene (2o) furnished the cor-
anion is the key intermediate in this reaction. The use responding products in good yields (entries 4, 15 and
of Cs2CO3 was preferred over the use of Na2CO3, 17 in Table 2).
K2CO3 or KOAc due to its greater basicity (entries 3
The electronic properties of haloarenes strongly in-
and 6–8 in Table 1). Unlike other solvents, such as N- fluence the reaction efficiency. The reaction with elec-
methylpyrrolidinone (NMP) and 1,4-dioxane, dime- tron-deficient arenes, such as methyl 2-chloroben-
thylacetamide (DMAc) and DMF yielded excellent zoate (2f), 4-bromoacetophenone (2i), and 4-bromo-
results (entries 2, 5, 9 and 10 in Table 1). Under the 1-(trifluoromethyl)benzene (2j), must be conducted at
optimal conditions herein, the desired 1b was ob- a lower temperature (1108C) to inhibit the formation
tained in 95% yield (entry 3 in Table 1).
of the biphenyl by-product by self-dimerization (en-
The reactivity of haloarenes 2 was tested under the tries 5, 8–11 in Table 2). Due to the presence of acidic
optimal conditions and on most occasions, the desired protons, excess base is required to form 4-(9-fluoren-
products 1 were obtained in good to excellent yields
ACHTUNGTRENyNGNU l)acetophenone (1i) efficiently (entries 8 and 9 in
(Table 2). This procedure is compatible with many Table 2). Unlike in other examples, 4-bromoanisole
functional groups, such as alkyl, alkoxy, ester, nitrile, (2l) did not yield the coupling product 1l under the
and others. 4-Bromobenzaldehyde (2g) cannot be regular conditions in Table 2, but the yield of the
used in this reaction because the aldol condensation is latter compound was dramatically improved when
much faster than the coupling reaction, according to ligand PCy3 was replaced by L1 (entries 13 and 14 in
GC-MS analysis (entry 6 in Table 2). Chlorobenzene Table 2). It is noteworthy that the protocol herein for
(2c) and bromobenzene (2d) produced 9-phenylfluor- synthesizing alkyl 2-(9-fluorenyl)benzoates is simpler
ene (1c) in the same yield (entries 2 and 3 in Table 2). to implement than the coupling reaction of 2-(trime-
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Scheme 2. Formation mechanism and stereochemistry of 1.
thylsilyl)phenyl triflate with alkyl fluorene-9-carboxyl-
ate.[19]
With compounds 1 in hand, the stereochemistry of
9-(2-substituted phenyl)fluorene derivatives such as
1b, 1e, 1f, 1n and 1o was investigated because their
bulky aryl substituents inhibit their rotation.[20] For
example, the rotation barriers of 1b and 1n, measured
in tetrachloroethene, were determined to be 14.3 and
29.8 kcalmolÀ1, respectively.[21] These high values
allow their rotamers to be observed. The stereochem-
istry of 1 was initially analyzed by considering the
mechanism of formation proposed in Scheme 2. The
reaction of arylpalladium 4 with fluorenyl anion fol-
Figure 1. The molecular structure of syn-1o (left) and anti-1o
(right). The aryl hydrogen atoms are omitted for clarity.
1
The H NMR signals of the protons in one methyl
lowed by rearrangement yields complex cis-5, whose group in 1m and the methyl protons in anti-1b and
steric repulsion is low when the substituent R is locat- anti-1o exhibit high-field shifts.[28] For example, the
ed far from the fluorenyl backbone. Then, the reduc- chemical shifts of the methyl protons in syn-1o and
tive elimination of cis-5 yields anti-1 (with the sub- anti-1o are approximately 2.88 and 1.35 ppm, respec-
stituent R anti to the fluorene 9-H). The anti/syn iso- tively, but a proton in a normal benzylic methyl group
merization has been extensively examined.[22] De- resonates at around 2.3 ppm. This finding is caused by
pending on the bulkiness of the substituent R, anti- the ring current because the methyl hydrogen is locat-
1 may directly convert into syn-1, which is thermody- ed over the fluorene ring with substantial shielding.
namically more stable. Under basic conditions, 9-aryl- Fortunately, the syn- and anti-rotamers of 1o can be
fluorenyl anion 6 is also responsible for anti/syn iso- separated and analyzed by X-ray crystallography
merization through inversion of the 9-position[23] or (Figure 1).[25] The distance between the methyl carbon
rotation of the aryl substituent.[22a] As expected, syn- and the fluorenyl plane in anti-1o is estimated to be
1 was obtained as the major rotamer in several of the 2.93 ꢂ. The crystallographic data recorded herein are
cases in Table 2. However, the observed products 1e useful for a theoretical study of the correlation be-
and 1f were first believed to be a single rotamer, tween the ring current effect and the distance be-
based on their NMR spectra. Other similar deriva- tween a proton and the aromatic plane.[29]
tives, such as alkyl 1-(9-fluorenyl)-naphthalene-2-car-
The synthetic method herein was also adopted to
boxylates,[8c] ethyl 2-(9-fluorenyl)benzoates[19] and 1,4- prepare 9,9-diarylfluorenes 7 (Table 3). Both electron-
di(9-fluorenyl)-2,5-diphenylbenzene,[24] prepared by rich and electron-deficient haloarenes gave the corre-
different synthetic routes have the same stereochem- sponding products in good yields. 9,9-DiACTHUNRTGNE(GNU 3-anisyl)-
istry. Indeed, X-ray crystallographic analysis revealed fluorene (7p) was efficiently generated in a reaction
that 1e is the single syn-rotamer.[25] Unlike the X-ray with the ligand dppe in dioxane for a longer reaction
crystallographic study, the chemical shift of the fluo- time. It is noteworthy that a recently developed pro-
renyl 9-H in the 1H NMR spectrum is not always tocol enabled the conversion of 7p into spirobifluor-
a suitable indicator for identifying the configuration ene 8 in good yield (Scheme 3).[30]
of rotamers, because its value is strongly influenced
An attempt was made to synthesize 10 by the reac-
by the substituents and/or is almost identical for both tion of fluorene with excess 5,6-dichloroacenaphthene
rotamers in some cases. For example, an attempt was (9) (entry 4 in Table 3). Perhaps because of the steric
made to observe and identify syn- and anti-conform- effect, the reaction gave only 5-(9-fluorenyl)acenaph-
ers of 1e and 1f based on variable-temperature NMR thene, which was formed through the mono-coupling
experiments. However, their rotamers, according to reaction and subsequent dechlorination. The reaction
the chemical shift of 9-H, cannot be easily distinguish- of 6,12-dihydroindeno
ACHTUNGTRNE[NUNG 1,2-b]fluorene (11) with excess
ed at either low or high temperature.[26,27]
4-bromo-4-n-butylbenzene (1q) furnished 6,6,12,12-
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Palladium-Catalyzed Arylation of Methylene-Bridged Polyarenes
Table 3. Multiarylations methylene-bridged arenes.[a]
Entry
Ar–X (equiv.)
C6H5Cl (2.4)
4-CF3-C6H4Br (3.0) I (4/8 mol%)
3-OMe-C6H4Br (2.5) II (5/10 mol%)
Conditions (amount) Solvent Time [days] Product (isolated yield [%])
1
2
3
I (4/8 mol%)
DMAc 0.5
dioxane 0.5
7c (75)
7j (85)
7p (81)
dioxane
3
1
4
4
I (6/12 mol%)
DMF
10 (0)[b]
5
4-n-Bu-C6H4Br (6.0) II (15/15 mol%)
dioxane
12 (58)[c]
[a]
The reaction was conducted with fluorene or 11 (0.50 mmol), haloarene and Cs2CO3 (3 equiv.) in a thick-walled sealed
tube at 1308C. Conditions I: Pd(OAc)2/PCy3·HBF4. Conditions II: Pd(OAc)2/dppe.
An inseparable mixture of two rotamers of 5-(9-fluorenyl)acenaphthene was isolated (72%, syn/anti=55/45).
G
ACHTUNGTRENNUNG
[b]
[c]
Cs2CO3 (8 equiv.) was used.
densation through the anion generated at the benzylic
positions have been reported,[33–35] the arylation has
not been developed yet. Since aryl-substituted suma-
nenes provide the possibility for expansion of the
backbone of sumanene (15),[36] our developed Pd-cat-
alyzed arylation was applied to the coupling reaction
between sumanene (15) and bromoxylene 2m
(Scheme 4). The desired xylylsumanene 16 was suc-
Scheme 3. Formation of spirobifluorene 8.
cessfully obtained in 48% yield by employing the op-
timized conditions for the arylfluorene [Pd(OAc)2
tetraaryl-6,12-dihydroindenoACHTUNGTERG[NNUN 1,2-b]fluorene 12 in 58% (5 mol%), PCy3·HBF4 (10 mol%), Cs2CO3 (1.5 equiv.)
ACHTUNGTRENNUNG
yield as the sole product (entry 5 in Table 3). In this in DMAc at 1308C]. After screening the bases, a com-
reaction, the use of dppe and dioxane reduced the bination of K2CO3 (5.0 equiv.) and 18-crown-6
amount of triaryl-substituted by-product. Unfortu- (5.0 equiv.) was found to give the dixylylsumanene 17
nately, isotruxene (13) and truxene (14) were not as in 28% yield and 16 in 37% yield. Interestingly, the
reactive as indenofluorene 11 in multiarylation reac- 1H NMR of 16 shows two kinds of conformers of 16
tions.[31] The reaction did not give the corresponding in a 5:1 ratio. The conformers derive from the bowl-
hexaaryl-substituted arenes, but rather a mixture of to-bowl inversion of the sumanene skeleton, where
complex products. Isotruxene (13) was easily pre- the xylyl group is directed to the endo-orientation or
pared by palladium-catalyzed cyclization of 1,2,4- exo-orientation to the bowl structure (Figure 2). The
tris(2-chlorophenyl)-3,5,6-trimethylbenzene (see Sup- 1H NMR of 17 also shows one major set of signals ac-
porting Information).
companying minor signals. In this case, the configura-
tions of two xylyl groups of 17 could be endo-endo,
exo-exo, and endo-exo. While the endo-endo and exo-
exo correspond to the interconvertible conformers
through bowl-to-bowl inversion, the endo-exo confor-
mer is a stereoisomer of the other two. The assign-
ment of configurations of xylyl groups in 16 and 17
and more detailed investigations of their dynamics
are now under investigation.
Sumanene (15) is an elementary subunit of buck-
minsterfullerene.[32] Its curvature[33] and bowl-to-bowl
inversion barrier (ca. 20 kcalmolÀ1)[34] have been de-
termined. Although the silylation, alkylation, and con-
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Scheme 4. Synthesis of xylylsumanenes.
General Procedure for Preparation of 9,9-Diaryl-
fluorenes (GP2)
A mixture of fluorene (0.50 mmol), haloarene (1.20 mmol),
PdACHTNURGTENUNG(OAc)2 (4.48 mg, 20.0 mmol), PCy3·HBF4 (14.7 mg,
40.0 mmol), Cs2CO3 (529 mg, 1.50 mmol) and DMAc
(3.0 mL) in a thick-walled Pyrex tube was purged with nitro-
gen for 5 min. The sealed tube was kept in an oil bath at
1308C for 12 h. After cooling to room temperature, the solu-
tion was extracted with EA (3ꢃ15 mL) and washed with
water. The organic phase was dried over MgSO4 and fil-
tered. The solvents of the filtrate were removed under re-
duced pressure. The residue was subjected to chromatogra-
phy on silica gel. A crystal can be obtained by crystallization
from CH2Cl2/CH3OH.
Figure 2. The bowl-to-bowl inversion of the sumanene skele-
ton.
Conclusions
Procedure for the Arylation of Sumanene (15)
A mixture of sumanene 15 (20.0 mg, 0.0757 mmol), 2,6-di-
methyl-1-bromobenzene (11 mL, 0.091 mmol), PdACHTUNGTRENNUNG(OAc)2
This work has developed a simple and efficient proce-
dure for the mono- and multiarylations of methylene-
bridged arenes. Applications of our protocol to the
construction of extended p-bowls and organic materi-
als, as well as studies of their physical properties are
currently underway.
(0.8 mg, 3.8 mmol), PCy3·HBF4 (2.8 mg, 7.6 mmol), K2CO3
(78.5 mg, 0.379 mmol), 18-crown-6 (100.0 mg, 0.379 mmol)
and DMAc (379 mL) in a thick-walled Pyrex tube was
purged with nitrogen. The sealed tube was kept in an oil
bath at 1308C for 12 h. After cooling to room temperature,
1M HCl solution (1 mL) was added and the solution was ex-
tracted with hexane/toluene (1:1, 3ꢃ5 mL) and washed with
water. The organic phase was dried over Na2SO4 and fil-
tered. The solvents of the filtrate are removed under re-
duced pressure. Purification by PTLC (n-hexane/dichloro-
methane=7:3) then GPC gave 19 (yield: 10.3 mg, 37%) as
a colorless solid, 20 (yield: 10.0 mg, 28%) as a colorless
solid and recovered 15 (yield: 6.6 mg, 13%).
Experimental Section
General Procedure for Synthesis of 9-Arylfluorenes
(GP1)
A mixture of fluorene (0.50 mmol), haloarene (0.63 mmol),
PdACHTUNGTRENNUNG(OAc)2 (2.25 mg, 10.0 mmol), PCy3·HBF4 (8.50 mg,
20.0 mmol), Cs2CO3 (247 mg, 0.75 mmol) and DMAc
(2.5 mL) in a thick-walled Pyrex tube was purged with nitro-
gen for 5 min. The sealed tube was kept in an oil bath at
1308C for 12 h. After cooling to room temperature, the solu-
tion was extracted with Et2O or EA (2ꢃ10 mL) and washed
with water. The organic phase was dried over MgSO4 and
filtered. The solvents of the filtrate were removed under re-
duced pressure. The residue was subjected to chromatogra-
phy on silica gel. A crystal can be obtained by crystallization
from CH2Cl2/CH3OH.
Acknowledgements
This work was supported by the National Science Council of
Taiwan (NSC 98-2113M-006-002-MY3) and JSPS Asian
CORE Program. We also thank Prof. S.-L. Wang and Ms. P.-
L. Chen (National Tsing Hua University, Taiwan) for the X-
ray structure analyses.
1556
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ꢁ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Synth. Catal. 2012, 354, 1551 – 1558

Palladium-Catalyzed Arylation of Methylene-Bridged Polyarenes
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19.8482(13) ꢂ,
a=77.784(2),
b=76.864(2)
g=
72.071(2)8, V=1673.19(18) ꢂ3. syn-1o: C24H18, mono-
clinic crystals of space group P121/c1, Z=4, unit cell di-
mensions:
14.5229(17) ꢂ,
a=7.6904(10),
a=g=90,
b=5.7749(7),
b=91.622(7)8,
c=
V=
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data of syn-1e (CCDC 854257), syn-1o (CCDC 854255)
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1558
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Adv. Synth. Catal. 2012, 354, 1551 – 1558