An extremely simple dibenzopentalene synthesis from 2-bromo-1- ethynylbenzenes using nickel(O) complexes: Construction of its derivatives with various functionalities

Article abstract of DOI:10.1002/chem.200802471

An extremely simple dibenzopentalene synthesis from readily available 2-bromo-1-ethynylbenzenes using a nickel(O) complex is described. Although the yields are moderate, the formation of three C-C bonds in a single process and the high availability of the

Full text of DOI:10.1002/chem.200802471

FULL PAPER
DOI: 10.1002/chem.200802471
An Extremely Simple Dibenzopentalene Synthesis from 2-Bromo-1-
ethynylbenzenes Using Nickel(0) Complexes: Construction of Its Derivatives
with Various Functionalities
Takeshi Kawase,*[a, b] Akihito Konishi,[a] Yasukazu Hirao,[a] Kouzou Matsumoto,[a]
Hiroyuki Kurata,[a] and Takashi Kubo*[a]
Abstract: An extremely simple diben-
zopentalene synthesis from readily
available 2-bromo-1-ethynylbenzenes
using a nickel(0) complex is described.
Although the yields are moderate, the
ture was confirmed by X-ray crystallo-
graphic analysis. The high stability of
this complex should play a key role in
this reaction. The reaction is applicable
to the preparation of dibenzopenta-
lenes bearing various functional
groups. Their electronic properties are
consistent with theoretical calculations.
The cyclic voltammograms of these
compounds reveal highly amphoteric
redox properties. In particular, the
electron-donating property of a tetra-
methoxy derivative is greater than that
of oligothiophenes and dibenzodithio-
phenes and almost comparable to that
of pentacene.
ꢀ
formation of three C C bonds in a
single process and the high availability
of the starting materials are important
advantages of this reaction. The corre-
sponding aryl–nickel(II) complex as an
important intermediate was isolated as
relatively stable crystals, and the struc-
Keywords: alkynes · aromatic com-
pounds · electrochemistry · organo-
metallic compounds
chemistry
· theoretical
Introduction
fore, dibenzopentalenes with appropriate functionalities
would be promising for application as functional dyes with
highly amphoteric redox properties. Since the first synthesis
of dibenzopentalenes by Brand in 1912,[3a] various dibenzo-
pentalenes bearing functional groups at positions 5 and 10
have been prepared.[3] The derivatives functionalized at the
aromatic rings are rarely prepared probably because of the
limitation of the known synthetic methods. From the view-
point of materials science, the potential of the p-system has
not been well explored.
Dibenzopentalene 1 is a fairly
stable compound with a planar
structure, despite possessing a
4np-electron periphery.[1] The
antiaromatic character provides
corresponding stable dianion
and dication species.[2] There-
In 1999, Youngs and co-workers reported the formation
of dibenzopentalene derivative 2 from 2-iodo-1-ethynylben-
zene 3 under the usual conditions for Sonogashira coupling
(Scheme 1).[4] This reaction, however, seems to be an excep-
tional case because the reaction of 2-iodo-1-ethynylbenzenes
[a] Prof. Dr. T. Kawase, A. Konishi, Dr. Y. Hirao, Dr. K. Matsumoto,
Prof. Dr. H. Kurata, Prof. Dr. T. Kubo
Department of Chemistry, Graduate School of Science
Osaka University, Toyonaka
Osaka 560–0043 (Japan)
Fax : (+81)6-6850-5384
E-mail: kawase@eng.u-hyogo.ac.jp
kubo@chem.sci.osaka-u.ac.jp
[b] Prof. Dr. T. Kawase
Present address: Department of Materials Science and Chemistry
Graduate School of Engineering
University of Hyogo, 2167 Shosha
Himeji, Hyogo, 671–2280 (Japan)
Fax : (+81)79-267-4889
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.200802471.
Scheme 1. Youngs’ dibenzopentalene synthesis. TBDS=tert-butyldime-
thylsilyl.
Chem. Eur. J. 2009, 15, 2653 – 2661
ꢀ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
2653

commonly afforded phenyleneethynylene macrocycles.[5]
The dibenzopentalene synthesis starting from 2-halo-1-ethy-
nylbenzenes is quite attractive from the viewpoint of syn-
thetic chemistry because of the high availability of the start-
ꢀ
ing materials and the formation of three C C bonds in one
process. It has been known that nickel(0) complexes effec-
tively catalyze the Ullman-type coupling of aryl halides.[6]
On the other hand, we found a nickel(0)-mediated reaction
that yields dibenzopentalenes from 2-bromo-1-ethynylben-
zenes in place of the corresponding biaryls. Although the
yields were not so high, the reaction is applicable to the
preparation of dibenzopentalenes bearing various functional
groups. Herein, we discuss the preparation and the proper-
ties of the newly obtained di-
Scheme 2. A nickel(0)-mediated reaction of 4. Regents and conditions:
1) [NiCl2A(PPh3)2] (0.2 equiv), Zn (1.5 equiv), Et4NI (1.0 equiv), THF
(0.04m), 508C, 24 h; 2) [NiCl2A(PPh3)2] (0.2 equiv), Zn (1.5 equiv), THF
(0.04m), 508C, 24 h. TMS=trimethylsilyl.
CTHUNGTRENNUNG
CTHUNGTRENNUNG
benzopentalene derivatives.
Results and Discussion
The treatment of 2-bromo-4-
methyl-1-(2-trimethylsilylethy-
nyl)benzene (4) with a Ni0 com-
plex, generated from the reduc-
tion of [NiCl2ACHTUNGTRENNUNG(PPh3)2] with zinc
dust in THF in the presence of
Et4NI,[6c] furnished the corre-
sponding biaryl 5 in 30% yield.
Surprisingly, the reaction was
carried out in the absence of
Et4NI to produce 6 in approxi-
mately 20% with high reprodu-
cibility (Scheme 2). The struc-
ture of 6 was estimated from
spectral data and finally con-
firmed by X-ray crystallograph-
ic analysis (Figure 1, left).[7] We
investigated the reaction under
various conditions, and the re-
sults are summarized in Table 1.
It has been known that the
presence of an excess amount
of PPh3 or Iꢀ ions effectively
promotes biaryl coupling.[6] In-
versely, the presence of these
ꢀ
Figure 1. ORTEP drawings of 6 (left) and 8 (right) (50% probability). Selected bond lengths [ꢁ] for 6: C1 C2
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
1.364(2), C2 C3 1.503(2), C3 C4 1.425(2), C4 C5 1.383(2), C5 C6 1.404(2), C6 C7 1.385(3), C7 C8 1.409(2),
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
C8 C3 1.383(2), C1 C1* 1.471(3), C4 C1* 1.471(2); 8: Br Ni 2.372(1), Ni P1 2.218(3), Ni P2 2.219(3), Ni C
1.875(7).
Table 1. Reaction of 4 with [NiCl2ACHTNUGTRNEUNG(PPh3)2] under various conditions.
Entry
Conditions
Yield [%]
equiv
solvent
t [h]
T [8C]
additive
4
5
6
of 4
1[a]
0.2
0.05
0.05
0.2
0.2
1.3
0.2
0.2
0.5
1.0
1.0
1.0
1.0
THF (0.04m)
THF (0.04m)
DMF (0.04m)
THF (0.04m)
THF (0.04m)
THF (0.04m)
THF (0.04m)
THF (0.04m)
toluene (0.2m)
toluene (0.2m)
toluene (0.2m)
24
24
24
24
48
100
24
24
24
24
24
50
50
50
50
50
50
50
50
110
110
110
80
Et4NI (1.0 equiv)
PPh3 (0.4 equiv)
PPh3 (0.4 equiv)
none
none
none
none
none
none
none
20
70
75
53
37
27
11
6
–
–
–
–
30
14
–
–
–
–
trace
48
–
–
–
–
2[b]
3[b]
4[a]
21
24
22
15
21
27
35
39
41
20
5[a]
6[a]
7[a,c]
8[a,d]
9[a]
10[a]
–
–
–
–
additives hampered the forma- 11[a]
COD (1.0 equiv)
none
none
12[a]
toluene/DME (4:1, 0.2m)
DME (0.2m)
24
24
tion of 6 (Table 1, entries 1–3).
Convincingly, the reaction using
2-iodo-4-methyl-1-(2- trimethyl-
silylethynyl)benzene (7) de-
ceased the yield of 6 (Table 1,
entry 6) because iodide ions
13[a]
80
–
[a] 1.5 equivalents of Zn were added. [b] 1.0 equivalents of Zn were added. [c] Iodide 7 was employed.
[d] [NiCl2A(dppp)] was employed.
CTHUNGTRENNUNG
were formed during the reaction. When 0.2 equivalents of
the nickel complex ([NiCl2A(PPh3)2] or [NiCl2A(dppp)]; dppp=
l,3-bis(diphenylphosphine)propane) were employed, a con-
siderable amount of 4 was recovered (Table 1, entries 3 and
7). A prolonged reaction time and an increase in the nickel
complex resulted in decreased recovery, but the yield of 6
did not increase (Table 1, entries 4 and 5). Actually, 6 is rel-
atively labile under the reaction conditions. Upon two days
of exposure to the reaction conditions, only 36% of 6 was
recovered, as a considerable amount of 6 changed into in-
soluble material. Although the mechanistic details have not
been clarified yet, the Ni0 complex generated under these
G
CHTUNGTRENNUNG
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Chem. Eur. J. 2009, 15, 2653 – 2661

Nickel-Catalyzed Synthesis of Dibenzopentalenes
FULL PAPER
under conditions may have led both to the formation and
decomposition of dibenzopentalene. The fact that yields of 6
do not exceed approximately 20% show the counterbalance
between both processes.
ployed, 6 was obtained in 35–39% yield (Table 1, entries 10
and 11). The presence of a small amount of 1,2-dimethoxy-
ethane (DME; toluene/DME=4:1) accelerated the reaction
rate, and the yield of 6 went up to 41% yield (Table 1, entry
12). However, the reaction in DME alone decreased the
yield to 20% (Table 1, entry 13). The reactions carried out
in low-polarity solvent systems provided better yields. These
conditions would hamper the decomposition of 6.
The reactions using [Ni
were examined to investigate the reaction mechanism be-
cause [Ni
(PPh3)2] as an active Ni0 reagent forms cleanly
under mild conditions. A solution of 4, [Ni(cod)2], and PPh3
ACHTUNGERTN(NUNG cod)2] (cod=1,5-cyclooctadiene)
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
in a 1:1:2 stoichiometry in THF was heated at 508C to
afford an aryl–nickel(II) complex 8 (21% yield) together
with 3 (16% yield; Scheme 3). Complex 8 can be purified
A simple radical coupling mechanism cannot be adopted
because the oxidative coupling of 2-lithio-4-methyl-1-(2-tri-
methylsilylethynyl)benzene, generated from 4 using CuCl2,
afforded 5 in high yield. The thermal reaction of 8 led to 6
ꢀ
through the formation of three C C bonds involving a dime-
ꢀ
rization reaction. The insertion reaction of the C Ni bond
to alkyne is known in several nickel-mediated reactions.[9]
Although plausible reaction mechanisms cannot be conclud-
ed at this stage, the high thermal stability of 8 presumably
plays a key role in this reaction. Further mechanistic studies
will be reported in due course.
2-Bromoarylacetylenes 9–16 with various functionalities
were prepared (Scheme 5) and subjected to this reaction
under the conditions of entry 12 in Table 1 to give dibenzo-
pentalenes 17–22 in acceptable yields (Scheme 6). Unfortu-
Scheme 3. Preparation and thermal reaction of aryl–nickel(II) complex 8.
by column chromatography on silica gel and was obtained
as air-stable pale yellow crystals. The structure was estab-
lished by X-ray crystallographic studies (Figure 1, right).[7]
The oxidative addition of [NiACHTNUGTRNEUNG(PPh3)2] to 4 produced 8. This
type of aryl–nickel(II) complex has been known as an inter-
mediate of nickel-mediated homo-coupling reactions, and
ordinarily as a thermally labile and air-sensitive compound.
However, some derivatives bearing bulky ligands are stable
enough to be isolable.[8] The molecular structure of 8 reveals
ꢀ
that the C Ni bond is effectively submerged by a bulky tri-
methylsilyethynyl group and two triphenylphosphine ligands.
On the other hand, complex 8 is relatively thermally labile;
furthermore, heating a solution of 8 in toluene to over 808C
led to 6 being obtained in high yield (Scheme 3). The forma-
tion of 6 obviously indicates that 8 is an important inter-
mediate of the dibenzopentalene synthesis. According to the
results, the highest yield was obtained (i.e., 46%) when a so-
lution of 4 in toluene (0.2m) was heated at 1108C in the
presence of [NiACHTUNGTRENNUNG(cod)2], PPh3, and zinc dust in a 1:2:1 stoichi-
ometry (Scheme 4). Dilute conditions (0.04m) or the ab-
sence of zinc dust resulted in a drastic decrease in the yield
of 6.
Scheme 4. Synthesis of dibenzopentalene 6 using [NiACHTNUTRGNEUNG(cod)2].
Scheme 5. Synthesis of ortho-haloethynylbenzenes. Reagents and condi-
ꢁ
tions: i) [PdCl
(PPh3)2], CuI, Et3N/THF (1:1), TMS-C C-H, RT, 12 h;
Given these results, we investigated the conditions using
[NiCl2A(PPh3)2] as a reagent for convenience. When one
equivalent of the complex and toluene as a solvent were em-
ii) nBuLi, THF, ꢀ708C; iii) CuCl2; iv) I2; v) K2CO3, MeOH, RT, 12 h;
CHTUNGTRENNUNG
vi) [PdCl2ACHTUNGRTNEUNG(PPh3)2], CuI, Et3N/THF (1:1), ArI, RT, 12 h; vii) LDA, THF,
ꢀ708C, then ClCOOEt. LDA=lithium diisopropylamide.
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2655

T. Kubo et al.
nately, the reaction of bromophenylacetylenes 15 or 16 af-
forded complex mixtures. However, taking into account that
ꢀ
three C C bonds form in one reaction, the yields are not so
poor.
Figure 2. Absorption spectra of 6 and 17–19 (left) and 20–22 (right) in
CH2Cl2.
Scheme 6. Synthesis of dibenzopentalenes bearing various functionalities.
Consistent with the reported molecular structures of di-
benzopentalenes,[3g] 6 also has large and small bond alterna-
tions in the five- and six-membered rings, respectively. Al-
though the large bond alternation greatly suppresses the an-
tiaromatic character of the pentalene moieties, the geometry
of the benzene rings might be affected by the 8p-electron
ꢀ
system. The large bond length of the C3 C4 bond would re-
flect a propensity to dislike unfavorable effects from the
4np-cyclic conjugation of the pentalene moiety, whereas the
aromatic character of the benzene rings appears to be ade-
quately operative according to the small bond alternation of
the other bonds in the benzene rings. The nucleus-independ-
ent chemical shift (NICS) calculation[10] supports this consid-
eration. The NICS(1) values of unsubstituted dibenzopenta-
lene calculated at the GIAO-RB3LYP/6–31G**//RB3LYP/
6–31G** level were +5.88 and ꢀ6.23 for the five- and six-
membered rings, respectively. The pentalene moiety possess-
es much less paratropicity than pentalene itself (+18.42),
whereas the benzene rings retain almost more than half of
diatropicity of benzene itself (ꢀ11.31).
Figure 3. The molecular orbitals of unsubstituted dibenzopentalene calcu-
lated with the RB3LYP/6–31G** method. Energy diagram (eV) of diben-
zopentalene derivatives
6 and 17–19 evaluated by the TD-DFT
(RB3LYP/6–31G**) calculation.
Table 2. Absorption wavelengths and oscillator strengths of dibenzopen-
talene evaluated by the TD-DFT (RB3LYP/6–31G**) calculation.
Compd
Absorption [nm]
Assignments (%)
(oscillator strength)
6
544 (0.00)
393 (0.18)
HOMO!LUMO (45)
HOMOꢀ1!LUMO (36)
HOMO!LUMOꢀ1 (8)
HOMO!LUMO (45)
HOMOꢀ1!LUMO (37)
HOMO!LUMOꢀ1 (7)
HOMO!LUMO (45)
HOMOꢀ1!LUMO (40)
HOMO!LUMOꢀ1 (3)
HOMO!LUMO (45)
HOMOꢀ1!LUMO (36)
HOMOꢀ1!LUMO (8)
17
18
19
538 (0.00)
394 (0.19)
The electronic spectra of the dibenzopentalenes exhibit
three characteristic absorption bands: the longest, but rela-
tively weak, absorption band (450–700 nm); the second lon-
gest absorption band (350–450 nm); the third longest, and
most intense, absorption band (250–350 nm; Figure 2). Ac-
cording to calculations at the TD-DFT(RB3LYP/6–31G**)
level of theory (Figure 3 and Table 2),[11] the longest absorp-
tion bands (S0!S1 bands) are attributable to HOMO!
LUMO transitions, which are symmetry forbidden and typi-
cal of 4np-electron systems. Actually, the observed longest
absorption bands are relatively weak (loge=2.5ꢂ3.0). The
second and third longest absorption bands are also assigna-
ble to the HOMOꢀ1!LUMO and HOMO!LUMO+1
transitions, respectively. The 2,3,7,8-tetramethoxy derivative
18 shows a considerably large bathochromic shift in the
HOMO!LUMO transition, though others exhibit quite
similar absorption curves. The anomaly in the absorption
bands of 18 is completely supported by the time-dependent
696 (0.00)
433 (0.13)
539 (0.00)
409 (0.17)
density functional theory (TD-DFT) calculations. The DFT
results suggest that the small HOMO–LUMO gap of 18 rel-
ative to 6, 17, and 19 would stem from a large positive shift
in energy of the HOMO, which is consistent with electro-
chemical results (see below). On the other hand, substitu-
tion of aryl groups at positions 5 and 10 causes bathochro-
mic shifts of approximately Dl=50 nm in the first and
second absorption bands of 20–22. Substitution at the para
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Chem. Eur. J. 2009, 15, 2653 – 2661

Nickel-Catalyzed Synthesis of Dibenzopentalenes
FULL PAPER
position of the aryl groups provides relatively small varia-
tions (Figure 2, right).
Conclusion
The redox properties of the dibenzopentalenes were ex-
amined by cyclic voltammetry (the redox potentials are
summarized in Table 3). These dibenzopentalenes basically
A nickel(0)-mediated reaction of 2-bromoethynylbenzene
derivatives afforded dibenzopentalene derivatives. Although
ꢀ
the yields are low to moderate, the formation of three C C
bonds in a single process and the high availability of the
starting materials are highly advantageous for this reaction.
This process could be widely applicable to bromoalkynes
with various functionalities and p flames, such as polycyclic
and heteroaromatic compounds, to produce a variety of
novel p-conjugated systems with pentalene skeletons. The
electronic properties of the functionalized dibenzopenta-
lenes are consistent with theoretical calculations and the di-
benzopentalenes have highly amphoteric redox properties.
Particularly, the tetramethoxy derivative possesses consider-
ably strong electron-donating properties that are almost
comparable to those of pentacene. Further studies are now
in progress.
Table 3. Redox potentials of 6 and 17–22 in DMF.[a]
ox
ox
red
red
Compound
E
[V]
E
[V]
E
[V]
E
[V]
2,1/2
2,1/2
1,1/2
1,1/2
6
17
18
19
20
21
22
1.06[b]
1.16[b]
0.72[b]
0.87[b]
0.97[b]
0.35
ꢀ1.60
ꢀ1.53
ꢀ1.63
ꢀ1.23
ꢀ1.62
ꢀ1.66
ꢀ1.38
ꢀ2.17[b]
ꢀ2.17[b]
ꢀ2.21[b]
ꢀ1.85[b]
ꢀ2.18[b]
ꢀ2.24[b]
ꢀ1.74
[c]
[c]
–
–
0.98[b]
1.13[b]
1.05[b]
0.87[b]
0.81[b]
0.94[b]
[a] V versus Ag/Ag+ in 0.1m nBu4NClO4/DMF; scan rate: 100 mVsꢀ1
+258C; Fc/Fc+ =+0.05 V. [b] Half-wave potentials. [c] Not detected.
;
possess four-stage redox properties as expected and the
redox potentials vary with the electronic properties of the
substituents. In particular, the cyclic voltammogram of 18
exhibits reversible first oxidation (oxE1) and pseudoreversi-
ble second oxidation waves (Figure 4). The oxidation poten-
Experimental Section
General: All the reactions dealing with air- or moisture-sensitive com-
pounds were carried out in a dry reaction vessel under a positive pressure
of nitrogen. Air- and moisture-sensitive liquids and solutions were trans-
ferred by syringe. Analytical thin-layer chromatography was performed
using glass plates precoated with Merck art. 7730 Kieselgel 60 GF-254.
The TLC plates were visualized by exposure to UV light. Solutions in or-
ganic solvents were concentrated by rotary evaporation at approximately
15 Torr using a diaphragm pump. Column chromatography was per-
formed on Merck Kiesel gel 60 and Merck art. 1097 aluminum oxide 90
(Aktivitatss fufe II-III).
All the reagents were purchased from Tokyo Kasei Co., Nakarai Tesc.,
Wako Co., and other commercial suppliers and were used as supplied,
unless otherwise stated. Solutions of butyllithium in hexane were pur-
chased from Mitsuwa Pure Chemicals, Inc. Anhydrous diethyl ether and
toluene were purchased from Kanto Chemical Co. and dried as necessary
by using standard procedures. THF and DME were purchased from
Wako Chemical Co. and distilled from sodium/benzophenone at 760 Torr
in a nitrogen atmosphere before used. Trimethylsilylacetylene was pur-
chased from Shin-Etsu Chemical Co., Ltd. Compounds 9[15] and 16,[16] 3-
bromo-4-iodotoluene,[17] 4-bromo-5-iodo-1,2-dimethoxybenzene,[18] and
methyl 3-bromo-4-iodobenzoate[19] were prepared according to previously
reported procedures.
Figure 4. Cycic voltammograms of 18 (left) in CH2Cl2 and 22 (right) in
DMF at 258C.
Melting points were recorded on a Yanaco MP 500D apparatus and un-
corrected. FAB and EI mass spectra were measured on a JEOL JMS-SX
102 instrument and Shimadzu GCMS-QP5050 A. H NMR spectra (tetra-
tials for 18 indicate a high electron-donating property and
the oxE1 value is higher than for oligothiophenes[12] and di-
benzodithiophenes[13] and almost comparable to pentacene
(Eox =0.22 V, Ered =ꢀ1.87 V, ferrocene/ferrocenium (Fc/Fc+)
=0 V in C6H4Cl2).[14] Combined with the relatively long-
wavelength absorption, the HOMO of 18 was elevated to a
considerably higher energy level. On the other hand, me-
thoxycarbonyl derivatives 19 and 22 possess higher electron
affinities than the others. In particular, 22 shows two readily
reversible reduction waves, thus indicating the formation of
a stable dianion species. Because the dibenzopentalene dia-
nion has the highest electron density at positions 5 and 10,[2]
methoxycarbonylphenyl groups at these positions effectively
stabilize the formed dianion. These redox properties are
almost comparable to those of perfluoropentacene (Eox =
0.79 V, Ered =ꢀ1.13 V, Fc/Fc+ =0 V in C6H4Cl2).[14b]
1
methylsilane (TMS) as an internal standard (d=0 ppm)) and 13C NMR
spectra (CDCl3; as an internal standard (d=77.0 ppm)) were recorded on
JEOL lambda-500, JEOL JNM-GSX-400, and JEOL EX-270 apparatus.
The chemical shifts are given in ppm. IR spectra were recorded on a
JASCO FT-IR-460 K2 spectrometer. Electronic (UV/Vis) spectra were
recorded on a Jasco V-570 spectrophotometer.
2-Bromo-4-methyl-1-(2-trimethylsilylethynyl)benzene (4): A solution of
2-bromo-1-iodo-4-methylbenzene (15.4 g, 51.9 mmol), [PdCl2ACHTUNGTRENNUNG(PPh3)2]
(0.666 g, 0.95 mmol), and copper(I) iodide (0.119 g, 0.62 mmol) in trie-
thylamine (100 mL), THF (100 mL), and trimethylsilylacetylene (12 mL,
84.3 mmol) was stirred for 12 h under N2. The reaction mixture was dilut-
ed with n-hexane (50 mL), washed with hydrochloric acid (6 molLꢀ1),
water, and brine. The organic layer was dried over anhydrous Na2SO4.
The filtrate was evaporated, and the residue was purified by distillation
(102.0–104.08C, 1.5 mmHg) to give 4 as a yellow oil (7.98 g, 58%).
B.p. 102.0?104.08C; 1H NMR (270 MHz, CDCl3, 258C): d=0.27 (s, 9H),
2.32 (br s, 3H), 7.04 (m, 1H), 7.34 (d, J=7.7 Hz, 1H), 7.40 ppm (m, 1H);
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T. Kubo et al.
13C NMR (68 MHz, CDCl3, 258C): d=0.41, 21.63, 99.11, 103.75, 122.77,
126.04, 128.31, 133.39, 133.80, 140.70 ppm; IR (neat): n˜ =2960 (m), 2922
(w), 2898 (w), 2163 (m), 1602 (w), 1485 (m), 1447 (w), 1391 (w), 1251
(m), 1227 (m), 1045 (m), 877 (m), 843 (bm), 820 (m), 776 (w), 760 (m),
700 (w), 675 (w), 633 (w), 562 cmꢀ1 (w); MS (EI, 70 eV): m/z (rel. intensi-
ty): 268 ([M+2]+, 23), 266 ([M]+, 21), 253 (65), 251 (66), 149 (100); ele-
mental analysis (%) calcd for C12H15BrSi: C 53.93, H 5.66, Br 29.90, Si
10.51; found: C 53.97, H 5.76.
1H NMR (270 MHz, CDCl3, 258C): d=0.28 (s, 9H), 7.52 (d, J=8.1 Hz,
1H), 7.88 (dd, J=1.9, 8.1 Hz, 1H), 8.22 ppm (d, J=1.6 Hz, 1H);
13C NMR (100 MHz, CDCl3, 258C): d=ꢀ0.22, 52.45, 102.28, 103.24,
125.55, 127.74, 129.27, 129.51, 130.78, 133.23, 165.13 ppm; IR (neat): n˜ =
3069 (w), 2956 (s), 2899 (w), 2844 (w), 2163 (m), 2068 (w), 1944 (w), 1730
(s), 1597 (s), 1548 (w), 1489 (w), 1436 (m), 1385 (m), 1287 (s), 1251 (s),
1111 (s), 1044 (m), 972 (w), 871 (s), 845 (s), 803 cmꢀ1 (w); MS (EI,
70 eV): m/z (rel. intensity): 312 ([M+2]+, 23), 310 ([M]+, 23), 297 (100),
295 (99); HRMS (EI): m/z calcd for C13H15BrO2Si: 310.0025; found:
310.0001.
2-Iodo-4-methyl-1-(2-trimethylsilylethynyl)benzene
(7):
nBuLi
(1.6 molLꢀ1, 3.8 mL, 6.1 mmol) was added to a solution of 4 (1.35 g,
5.04 mmol) in THF (30 mL) at ꢀ708C under N2. The reaction mixture
was stirred at this temperature for 15 min and then I2 (2.20 g, 8.68 mmol)
was added. The reaction mixture was allowed to warm to ambient tem-
perature and diluted with n-hexane (50 mL). The solution was washed
with saturated aqueous NaS2O3, water, and brine. The organic layer was
dried over anhydrous Na2SO4. The filtrate was evaporated, and the resi-
due was purified by distillation (ca. 1208C, 1.5 mmHg) to give 7 as a col-
orless oil (1.21 g, 76%). 1H NMR (270 MHz, CDCl3, 258C): d=0.28 (s,
9H), 2.29 (brs, 3H), 7.08 (brd, J=8.1 Hz, 1H), 7.34 (d, J=8.1 Hz, 1H),
7.6 ppm (s, 1H); 13C NMR (68 MHz, CDCl3, 258C): d=ꢀ0.15, 20.89,
97.79, 101.16, 106.66, 126.70, 128.61, 132.36, 139.21, 140.07 ppm; IR
(neat): n˜ =3056 (w), 3028 (w), 2959 (m), 2920 (w), 2898 (w), 2161 (m),
1906 (w), 1595 (w), 1549 (w), 1477 (m), 1446 (w), 1408 (w), 1387 (w),
1332 (w), 1251 (m), 1225 (w), 1140 (w), 1038 (m), 995 (w), 872 (s), 844
(s), 820 (m), 760 (m), 700 cmꢀ1 (w); MS (EI, 70 eV): m/z (rel. intensity):
314 ([M]+, 34), 299 (73), 149 (95), 105 (100); elemental analysis (%)
calcd for C12H15ISi: C 45.87, H 4.81, I 40.38, Si 8.94; found: C 46.21, H
4.74.
2-Bromo-1-ethynyl-4-methylbenzene (15): K2CO3 (16.1 g) was added to a
solution of 2-bromo-4-methyl-1-(2-trimethylethynyl)benzene (4) in THF
(20 mL) and methanol (80 mL) under N2. The suspension was stirred for
12 h at ambient temperature and quenched with water (100 mL). The re-
action mixture was extracted with n-hexane (2ꢂ100 mL). The combined
organic layers were washed with water and brine and dried over anhy-
drous Na2SO4. The filtrate was evaporated and the residue was purified
by column chromatography on silica gel (40 g). From a hexane fraction,
15 was obtained as a pale-yellow oil (2.51 g, 75%). 1H NMR (270 MHz,
CDCl3, 258C): d=2.33 (s, 3H), 3.31 (s, 1H), 7.06 (d, J=7.8 Hz, 1H), 7.40
(d, J=7.9 Hz, 1H), 7.42 ppm (s, 1H); 13C NMR (68 MHz, CDCl3, 258C):
d=21.09, 80.94, 82.01, 121.23, 125.28, 127.91, 132.95, 133.75, 140.66 ppm;
IR (neat): n˜ =3293 (s), 3030 (w), 2921 (w), 2864 (w), 2110 (w), 1908 (w),
1602 (m), 1484 (s), 1043 (m), 862 (m), 820 (s) 710 (w), 677 cmꢀ1 (m); MS
(EI, 70 eV): m/z (rel. intensity): 196 ([M+2]+, 64), 194 ([M]+, 65), 115
(100); elemental analysis (%) calcd for C9H7Br: C 53.42, H 3.62, Br
40.96; found: C 55.69, H 3.70.
Ethyl 3-(2-bromo-4-methylphenyl)propiolate (16):
A solution of 2-
2-Bromo-1-(2-trimethylsilylethynyl)benzene (9): A solution of 2-bromo-
1-iodobenzene (5.32 g, 18.8 mmol), [PdCl2ACHTNUTRGNE(UNG PPh3)2] (0.256 g, 0.36 mmol),
bromo-1-ethynyl-4-methylbenzene 15 (0.789 g, 4.78 mmol) in THF
(5 mL) was added to a solution of LDA, which was generated from diiso-
propylamine (1.25 mL) and nBuLi (1.6m, 5.5 mL, 8.8 mmol) in THF
(10 mL), at ꢀ708C under N2. The reaction mixture was stirred at this
temperature for 20 min and then ethyl chloroformate (1.6 mL,
16.7 mmol) was added. The mixture was allowed to warm to ambient
temperature, quenched with aqueous ammonium chloride, and extracted
with n-hexane/ethyl acetate. The organic layer was washed with water
and brine and dried over anhydrous Na2SO4. The filtrate was evaporated
and the residue was purified by column chromatography on silica gel
(10 g, toluene/n-hexane=3:1) to give 16 as a pale-yellow oil (0.766 g,
60%). 1H NMR (270 MHz, CDCl3, 258C): d=1.35 (t, J=7.3 Hz, 3H),
2.35 (s, 3H), 4.30 (q, J=7.0 Hz, 2H), 7.08–7.12 (m, 1H), 7.44–7.45 (m,
1H), 7.47 ppm (d, J=7.8 Hz, 1H); 13C NMR (68 MHz, CDCl3, 258C):
d=14.10, 21.28, 62.08, 84.01, 84.30, 119.38, 126.37, 128.13, 133.38, 134.57,
142.69, 153.89 ppm; IR (neat): n˜ =2982 (w), 2212 (w), 1422 (m), 1709 (s),
1601 (w), 1488 (w), 1446 (w), 1390 (w), 1366 (w), 1297 (m), 1259 (m),
1194 (m), 1142 (w), 1095 (w), 1050 (w), 1021 cmꢀ1 (w); MS (EI, 70 eV):
m/z (rel. intensity): 268 ([M+2]+, 29), 266 ([M]+, 30), 223 (71), 221 (78),
copper(I) iodide (0.037 g, 0.19 mmol), triethylamine (100 mL), and trime-
thylsilylacetylene (3.2 mL, 22.4 mmol) was stirred for 12 h under N2. The
reaction mixture was diluted with n-hexane (50 mL) and washed with hy-
drochloric acid (6 molLꢀ1), water, and brine. The organic layer was dried
over anhydrous Na2SO4. The filtrate was evaporated, and the residue was
purified by distillation (ꢂ1008C, 1.5 mmHg) to give 9 as a yellow oil
(2.86 g, 60%). 1H NMR (270 MHz, CDCl3, 258C): d=0.28 (s, 9H), 7.15
(m, J=7.6, 1.9 Hz, 1H), 7.23 (m, J=7.6, 1.4 Hz, 1H), 7.49 (m, J=7.6,
1.6 Hz, 1H), 7.57 ppm (m, J=7.8, 1.4 Hz, 1H).
1-Bromo-3,4-dimethoxy-5-(2-trimethylsilylethynyl)benzene (10): A solu-
tion of 1-bromo-2-iodo-4,5-dimethoxybenzene (2.17 g, 6.32 mmol),
[PdCl2ACHTUNGTRENNUNG(PPh3)2] (0.094 g, 0.13 mmol), copper(I) iodide (0.044 g,
0.26 mmol), triethylamine (15 mL), and trimethylsilylacetylene (2.2 mL,
15.4 mmol) was stirred at 508C for 12 h under N2. The reaction mixture
was diluted with n-hexane/ethyl acetate (2:1, 50 mL) and washed with hy-
drochloric acid (6 molLꢀ), water, and brine. The organic layer was dried
over anhydrous Na2SO4. The filtrate was evaporated and the residue was
purified by distillation (140?1608C, 1.5 mmHg) to give 10 as a yellow
solid (1.17 g, 59%). M.p. 88.9–89.38C; 1H NMR (270 MHz, CDCl3,
258C): d=0.27 (s, 9H), 3.86 (s, 3H), 3.87 (s, 3H), 6.96 (s, 1H), 7.01 ppm
(s, 1H); 13C NMR (68 MHz, CDCl3, 258C): d=ꢀ0.08, 56.09, 56.16, 97.63,
103.81, 115.09, 115.41, 117.06, 117.16, 147.96, 149.97 ppm; IR (neat): n˜ =
3004 (w), 2960 (w), 2898 (w), 2844 (w), 2156 (m), 1599 (m), 1564 (w),
1508 (s), 1482 (w), 1442 (m), 1383 (w), 1332 (w), 1265 (s), 1248 (s), 1218
(s), 1200 (m), 1171 (m), 1047 (w), 1030 (w), 974 (m), 953 (w), 864 (s), 842
(s), 802 (m), 762 (m), 706 cmꢀ1 (w); MS (EI, 70 eV): m/z (rel. intensity):
314 ([M+2]+, 85), 312 ([M]+, 83), 299 (97), 297 (100); elemental analysis
(%) calcd for C13H17BrO2Si: C 49.84, H 5.47, Br 25.51, O 10.21, Si 8.97;
found: C 50.21, H 5.44.
196 (93), 194 (100); HRMS
267.0015; found: 267.0000.
(ESI): m/z calcd for C12H12O2Br [M+H]+:
ACHTUNGTRENNUNG
1-(2-Bromo-4-methylphenyl)-2-(4-methylphenyl)ethyne (12): A solution
of 15 (0.68 g, 3.48 mmol), para-iodotoluene (0.70 g, 3.21 mmol), [PdCl2-
AHCTUNTGREG(NUNN PPh3)2] (0.062 g, 0.09 mmol), copper(I) iodide (0.025 g, 0.13 mmol), and
triethylamine (30 mL) was stirred for 12 h at ambient temperature under
N2. The reaction mixture was diluted with n-hexane (50 mL); washed
with hydrochloric acid (6 molmLꢀ1), water, and brine; and dried over an-
hydrous Na2SO4. The filtrate was evaporated and the residue was purified
by distillation under reduced pressure (220–2508C, 2 mmHg) to give 12
as a colorless solid (0.78 g, 85%). M.p. 81.5–82.28C; 1H NMR (270 MHz,
CDCl3, 258C): d=2.34 (s, 3H), 2.37 (s, 3H), 7.08 (m, 1H), 7.16 (d, J=
8.6 Hz, 1H), 7.17 (m, 1H), 7.42 (2H, AA’XX’), 7.46 ppm (2H, AA’XX’);
13C NMR (68 MHz, CDCl3, 258C): d=21.10, 21.52, 87.53, 93.37, 120.08,
122.57, 125.32, 127.93, 129.11, 131.52, 132.82, 132.95, 138.61, 139.79 ppm;
IR (KBr): n˜ =3025 (w), 2916 (w), 2215 (w), 1909 (w), 1597 (w), 1557 (w),
1511 (s), 1480 (m), 1260 (w), 1208 (w), 1179 (w), 1105 (w), 1040 (m),
1018 (w), 957 (w), 945 (w), 876 (w), 817 (s), 762 (w), 708 cmꢀ1 (w); MS
(EI, 70 eV): m/z (rel. intensity): 286 ([M+2]+, 93), 284 ([M]+, 100), 205
(38), 189 (48); elemental analysis (%) calcd for C16H13Br: C 67.39, H
4.59, Br 28.02; found: C 67.09, H 4.55.
Methyl 3-bromo-4-[(trimethylsilyl)ethynyl]benzoate (11): A solution of
methyl 3-bromo-4-iodobenzoate (8.59 g, 25.2 mmol), [PdCl2ACTHNUTRGEN(UNG PPh3)2]
(0.72 g, 1.02 mmol), copper(I) iodide (0.103 g, 0.54 mmol), triethylamine
(100 mL), and trimethylsilylacetylene (11 mL, 77.3 mmol) was stirred at
508C for 12 h under N2. The reaction mixture was diluted with n-hexane/
ethyl acetate (2:1, 50 mL) and washed with hydrochloric acid (6 molLꢀ1),
water, and brine. The organic layer was dried over anhydrous Na2SO4.
The filtrate was evaporated, and the residue was purified by distillation
(130–1408C, 1.5 mmHg) to give 11 as
a yellow oil (2.33 g, 30%).
2658
www.chemeurj.org
ꢀ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2009, 15, 2653 – 2661

Nickel-Catalyzed Synthesis of Dibenzopentalenes
FULL PAPER
1-(2-Bromo-4-methylphenyl)-2-(4-methoxyphenyl)ethyne (13): A solution
of 15 (0.78 g, 4.14 mmol), para-iodoanisole (0.85 g, 3.62 mmol), [PdCl2-
ACHTUNGTRENNUNG(PPh3)2] (0.058 g, 0.083 mmol), and copper(I) iodide (0.014 g,
(decomp); 1H NMR (270 MHz, CDCl3, 258C): d=0.45 (s, 9H), 1.76 (s,
3H), 5.96 (d, J=7.7 Hz, 1H), 6.15 (d, J=7.7 Hz, 1H), 6.70 (s, 1H), 7.31–
7.68 ppm (m, 30H); UV/Vis (CH2Cl2): lmax (loge)=420 (2.98), 316 (4.15),
286 (4.43), 259 (4.66), 232 nm (4.92); IR (KBr): n˜ =3902 (w), 3802 (w),
3725 (w), 3650 (w), 3052 (w), 2958 (w), 2141 (m), 1653 (w) 1482 (m),
1435 (s), 1251 (m), 1095 (s), 1029 (w), 870 (s), 840 (s), 755 (m), 692 (s),
634 (w), 522 cmꢀ1 (s); MS (EI, 70 eV): m/z (rel. intensity): 374 (8), 262
(100), 183 (77); MS (ESI) m/z: 849.2000, 587.1183, 410.9997.
The preparation of dibenzopentalene 6 from NiII complex (8): A solution
of 8 (0.015 g, 0.018 mmol) in toulene (6 mL) was heated with dryer at
808C for a few minutes. The solution changed from pale yellow to
yellow–orange. The crude product was subjected to column chromatogra-
phy on silica gel to give 6 (0.0033 g, 83%).
0.074 mmol) in triethylamine (20 mL) and THF (10 mL) was stirred for
12 h at ambient temperature under N2. The reaction mixture was diluted
with n-hexane/ethyl acetate (50 mL); washed with hydrochloric acid (6
molmLꢀ1), water, and brine; and dried over anhydrous Na2SO4. The fil-
trate was evaporated, and the residue was purified by distillation under
reduced pressure (220–2508C, 2 mmHg) to give 13 as a pale yellow solid
(1.04 g, 95%). M.p. 79.4–79.88C; 1H NMR (270 MHz, CDCl3, 258C): d=
2.34 (s, 3H), 3.83 (s, 3H), 6.88 (2H, AA’XX’), 7.08 (m, 1H), 7.41 (d, J=
8.1 Hz, 1H), 7.43 (m, 1H), 7.50 ppm (2H, AA’XX’); 13C NMR (68 MHz,
CDCl3, 258C): d=21.09, 55.31, 86.93, 93.24, 114.02, 115.27, 122.68,
125.21, 127.93, 132.70, 132.92, 133.10, 139.62, 159.83 ppm; IR (KBr): n˜ =
2960 (w), 2932 (w), 2835 (w), 2218 (m), 1604 (s), 1512 (s), 1289 (m), 1248
(s), 1173 (m), 1149 (m), 1107 (w), 1025 (s), 955(w), 878 (w), 837 (s), 813
(s), 760 cmꢀ1 (w); MS (EI, 70 eV): m/z (rel. intensity): 302 ([M+2]+, 98),
300 ([M]+, 100); elemental analysis (%) calcd for C16H13BrO: C 63.81, H
4.35, Br 26.53, O 5.31; found: C 63.92, H 4.32.
General procedure for the preparation of dibenzopentalenes: A suspen-
sion of 2-bromo-1-ethynylbenzenes (4 and 9–14; 1 mmol), Zn powder
(1.5 mmol, 0.098 g), and [NiCl2ACHTNUTRGNE(UNG PPh3)2] (1.0 mmol, 0.654 g) in toluene
(4 mL) and DME (1 mL) was heated at 808C for 24 h under N2. The
dark red reaction mixture was subjected to column chromatography on
alumina with hexane and or hexane/CH2Cl2 as the eluent to remove in-
soluble materials. The crude product was purified by column chromatog-
raphy on silica gel.
1-(2-Bromo-4-methylphenyl)-2-(4-methoxycarbonylphenyl)ethyne (14): A
solution of 15 (0.78 g, 4.00 mmol), methyl para-iodobenzoate (1.16 g,
4.41 mmol), [PdCl2ACHTUNGTRENNUNG(PPh3)2] (0.068 g, 0.096 mmol), and copper(I) iodide
2,7-Dimethyl-5,10-ditrimethylsilylindenoACTHNUTRGNEU[GN 2,1-a]indene (6): The reaction
(0.011 g, 0.057 mmol) in triethylamine (20 mL) and THF (10 mL) was
stirred for 12 h at ambient temperature under N2. The reaction mixture
was diluted with n-hexane/ethyl acetate (50 mL); washed with hydrochlo-
ric acid (2 molmLꢀ1), water, and brine; and dried over anhydrous
Na2SO4. The filtrate was evaporated, and the residue was purified by dis-
tillation under reduced pressure (220–2508C, 2 mmHg) to give 14 as a
colorless solid (0.75 g, 57%). M.p. 107.2–107.98C; 1H NMR (270 MHz,
CDCl3, 258C): d=2.36 (s, 3H), 3.93 (s, 3H), 7.11 (m, 1H), 7.45 (d, J=
8.1 Hz, 1H), 7.46 (m, 1H), 7.62 (2H, AA’XX’), 8.02 ppm (2H, AA’XX’);
13C NMR (68 MHz, CDCl3, 258C): d=21.17, 52.20, 91.01, 92.26, 121.84,
125.54, 127.82, 128.03, 129.49, 129.65, 131.49, 133.07, 140.63, 166.51 ppm;
IR (KBr): n˜ =3065 (w), 2950 (w), 2360 (w), 2218 (w), 1721 (s, C=O), 1599
(m), 1558 (w), 1513 (w), 1483 (w), 1458 (w), 1435 (m), 1405 (m), 1308
(m), 1281 (s), 1176 (m), 1108 (m), 1043 (w), 1015 (w), 960 (w), 892 cmꢀ1
(w); MS (EI, 70 eV): m/z (rel. intensity): 330 ([M+2]+, 99), 328 ([M]+,
100), 287 (44), 285 (45), 259 (14), 257 (14); elemental analysis (%) calcd
for C17H13BrO2: C 62.03, H 3.98, Br 24.27, O 9.72; found: C 62.17, H
3.97.
was carried out using 4 (0.267 g, 1.00 mmol) to give 6 as red–brown nee-
dles after recrystallization from n-hexane (0.077 g, 41%). M.p. 209.6–
210.08C; 1H NMR (270 MHz, CDCl3, 258C): d=0.38 (s, 18H), 2.19 (s,
6H), 6.61 (m, 2H), 6.84 (m, 1H), 7.03 ppm (d, J=7.6 Hz, 2H); 13C NMR
(68 MHz, CDCl3, 258C): d=0.24, 21.52, 123.33, 125.46, 126.43, 132.98,
137.80, 140.11, 155.69, 158.83 ppm; UV/Vis lmax (loge)=442 (3.96), 417
(4.01), 397 (3.79), 299 (4.75), 292 (4.72), 236 nm (4.33); IR (KBr): n˜ =
3675 (w), 3649 (w), 3628 (w), 3567 (w), 3067 (w), 2959 (m), 2908 (w),
2361 (w) 1869 (w), 1595 (w), 1438 (m), 1250 (m), 1240 (m), 1159 (w), 866
(m), 843 (s), 809 (s), 755 (m), 74 cmꢀ1 (w); MS (EI, 70 eV): m/z (rel. in-
tensity): 374 ([M]+, 100), 359 (23), 343 (17), 301 (48); elemental analysis
(%) calcd for C24H30Si2: C 76.94 H 8.07, Si 14.99; found: C 77.12, H 8.10.
5,10-Bis(trimethylsilyl)indenoACTHUNRTGNEUNG[2,1-a]indene (17): The reaction was carried
out using 9 (0.253 g, 1.00 mmol) to give 17 as red–brown needles (0.053 g,
31%). Red–brown prisms were obtained from recrystallization from
hexane/EtOH. M.p. 145.8–146.28C; 1H NMR (400 MHz, CDCl3, 258C):
d=0.43 (s, 18H), 6.82–6.85 (m, 4H), 7.03–7.05 (m, 2H), 7.15–7.17 ppm
(m, 2H); 13C NMR (100 MHz, CDCl3, 258C): d=0.35, 123.51, 124.33,
126.37, 127.88, 135.77, 141.56, 155.06, 158.32 ppm; UV/Vis lmax (loge)=
441.0 (3.98), 416 (4.02), 398 (3.81), 286 (4.68), 232 nm (4.31); IR (KBr):
n˜ =3084 (w), 2967 (w), 1422 (w), 1331 (w), 1262 (w), 1247 (m), 1100 (w),
967 (m), 843 (s), 741 cmꢀ1 (s); MS (EI, 70 eV): m/z (rel. intensity): 346
([M]+, 100); elemental analysis (%) calcd for C22H26Si2: C 76.23, H 7.56,
Si 16.21; found: C 75.92, H 7.43.
2,2’-Bis(2-trimethylsilylethynyl)-5,5’-dimethylbiphenyl (5): A solution of
n-butyllithium in hexane (1.6m, 0.75 mL, 1.2 mmol) was added by syringe
to a solution of 4 (0.268 g, 1.00 mmol) in THF (15 mL) at ꢀ708C under
N2. The reaction mixture was stirred at this temperature for 45 min and
then CuBr2 (0.38 g, 1.7 mmol) was added. The reaction mixture was al-
lowed to warm to ambient temperature. The mixture was passed over a
column of alumina with hexane as the eluent to remove insoluble copper
salts. The crude product was purified by column chromatography on
silica gel (40 g, hexane) to give 5 as a pale yellow oil (0.095 g, 51%). B.p.
2,3,7,8-Tetramethoxy-5,10-bis(trimethylsilyl)indeno
G
(18):
The reaction was carried out using 10 (0.316 g, 1.00 mmol) to give 18 as
green–yellow leaflets (0.030 g, 13%). Green–yellow leaflets were ob-
tained after recrystallization from n-hexane/CH2Cl2. M.p. 215.7–216.58C;
1H NMR (270 MHz, CDCl3, 258C): d=0.40 (s, 18H), 3.79 (s, 6H), 3.80 (s,
6H), 6.56 (s, 2H), 6.70 ppm (s, 2H); 13C NMR (100 MHz, CDCl3, 258C):
d=0.26, 56.15, 56.23, 108.99, 109.67, 129.33, 139.56, 147.18, 148.19,
148.69, 158.32 ppm; UV/Vis lmax (loge)=571 (2.40), 442 (3.66), 319
(4.86), 239 nm (4.25); IR (KBr): n˜ =2939 (w), 2899 (w), 1586 (m), 1462
(s), 1436 (s), 1404 (w), 1286 (s), 1245 (m), 1219 (m), 1162 (w), 1122 (w),
1020 (m), 875 (m), 855 (s), 745 cmꢀ1 (m); MS (EI, 70 eV): m/z (rel. inten-
sity): 466 ([M]+, 100); elemental analysis (%) calcd for C26H34O4Si2: C
66.91, H 7.34, O 13.71, Si 12.04; found: C 66.74, H 7.07.
1
110.0?115.08C; H NMR (270 MHz, CDCl3, 258C): d=0.05 (s, 18H), 2.36
(s, 6H), 7.08 (m, 2H), 7.25 (m, 2H), 7.43 ppm (d, J=7.9 Hz, 2H);
13C NMR (68 MHz, CDCl3, 258C): d=ꢀ0.25, 21.39, 96.23, 104.92, 119.46,
127.75, 130.98, 132.21, 137.59, 143.30 ppm; IR (neat): n˜ =33025 (w), 2959
(w), 2923 (w), 2898 (w), 2157 (m), 1604 (w), 1473 (w), 1408 (w), 1250
(m), 1217 (w), 1135 (w), 1043 (w), 864 (m), 842 (m), 819 (m), 759 (w),
699 (w), 634 cmꢀ1 (w); MS (EI, 70 eV): m/z (rel. intensity): 374 ([M]+,
100]; elemental analysis (%) calcd for C24H30Si2: C 76.94, H 8.07, Br
14.99; found: C 76.70, H 8.09.
trans-[Bromo(5-methyl-2-trimethylsilylethynylphenyl)bis(triphenylphos-
phine)nickel(II)] (8): A suspension of 4 (0.269 g, 1 mmol), [NiACTHNUTRGEN(UNG cod)2]
Dimethyl
5,10-bis(trimethylsilyl)indenoACTHNGUTRENNU[G 2,1-a]indene-2,7-dicarboxylate
(0.277 g, 1.0 mmol), and PPh3 (0.524 g, 2.0 mmol) in THF (15 mL) was
heated at 508C for 24 h under argon. The dark-red reaction mixture was
passed over a column chromatography on alumina using hexane/CH2Cl2
as the eluent to remove insoluble materials. The crude products were
subjected to column chromatography on silica gel to give 4 (0.036 g,
13%) and 6 (0.036 g, 16%) from hexane elutions and 8 as a yellow solid
from a CH2Cl2 elution (0.187 g, 21%). Pure 8 was obtained as yellowish
plates after recrystallization from hexane/CH2Cl2. 8: M.p. 179.7–180.18C
(19): The reaction was carried out using 14 (0.321 g, 1.03 mmol) and zinc
powder (1.6 mmol, 0.104 g) with toluene (5 mL) as a solvent to give 13 as
red–brown prisms (0.058 g, 24%). Red–brown prisms were obtained after
recrystallization from n-hexane/CH2Cl2. M.p. 264.3–265.28C; 1H NMR
(270 MHz, CDCl3, 258C): d=0.46 (s, 18H), 3.89 (s, 6H), 7.25 (d, J=
8.0 Hz, 2H), 7.60 (dd, J=8.0, 1.4 Hz, 2H), 7.74 ppm (d, J=1.4 Hz, 2H);
13C NMR (100 MHz, CDCl3, 258C): d=0.26, 52.10, 123.02, 125.28, 129.06,
129.52, 140.11, 144.70, 154.74, 157.62, 166.70 ppm; UV/Vis lmax (loge)=
Chem. Eur. J. 2009, 15, 2653 – 2661
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T. Kubo et al.
449 (3.88), 423 (3.86), 310 (4.63), 304 (4.63), 228 nm (4.30); IR (KBr): n˜ =
2951 (w), 1712 (s), 1543 (w), 1431 (m), 1340 (m), 1295 (s), 1256 (s), 1199
(m), 1102 (m), 846 (s), 759 (s), 628 cmꢀ1 (w); MS (EI, 70 eV): m/z (rel. in-
tensity): 462 ([M]+, 100), 447 (33), 431 (8), 389 (37); elemental analysis
(%) calcd for C26H30O4Si2: C 67.49, H 6.54, O 13.83, Si 12.14; found: C
67.39, H 6.44.
Mitchell, J. Org. Chem. 1963, 28, 1861; d) W. Frank, R. Gompper,
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119, 1526; Angew. Chem. Int. Ed. 2007, 46, 1504; h) G. Babu, A.
Orita, J. Otera, Chem. Lett. 2008, 37, 1296.
2,7-Dimethyl-5,10-di-para-tolylindenoACHTNUGTRNEUNG[2,1-a]indene (20): The reaction
[4] M. Chakraborty, C. A. Tessier, W. J. Youngs, J. Org. Chem. 1999, 64,
2947.
was carried out using 12 (0.286 g, 1.00 mmol) to give 20 as red–brown
leaflets (0.032 g, 16%). Red–brown leaflets were obtained after recrystal-
lization from CH2Cl2/n-hexane. M.p. 285.7–286.68C; 1H NMR (270 MHz,
CDCl3, 258C): d=2.18 (s, 6H), 2.45 (s, 6H), 6.62 (m, 2H), 6.82 (s, 2H),
7.08 (d, J=7.6 Hz, 2H), 7.31 (4H, AA’XX’), 7.55 ppm (4H, AA’XX’);
13C NMR (68 MHz, CDCl3, 258C): d=21.49, 21.51, 121.59, 123.37, 127.35,
128.47, 129.31, 131.26, 132.50, 137.51, 138.51, 139.41, 143.19, 150.16 ppm;
UV/Vis lmax (loge)=452 (4.23), 429 (4.23), 406 (4.02), 325 (4.30), 294
(4.57), 267 nm (4.61); IR (KBr): n˜ =1596 (w), 1508 (m), 1440 (s), 1295
(w), 1169 (w), 838 (w), 813 (s), 736 (w), 536 cmꢀ1 (m); MS (EI, 70 eV):
m/z (rel. intensity): 410 ([M]+, 100), 205 (18); elemental analysis (%)
calcd for C32H26: C 93.62 H 6.38; found: C 93.30, H 6.41
[5] a) J. D. Kinder, C. A. Tessier, W. J. Youngs, Synlett 1993, 149; b) M.
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1359.
5,10-Bis(4-methoxyphenyl)-2,7-dimethylindenoACTHNUTRGNEUG[N 2,1-a]indene (21): The re-
action was carried out using 13 (0.301 g, 1.00 mmol) to give 21 as red–
brown needles (0.029 g, 13%). Red–brown needles were obtained after
recrystallization from CH2Cl2/n-hexane. M.p. 254.8–255.78C; 1H NMR
(270 MHz, CDCl3, 258C): d=2.19 (s, 6H), 3.89 (s, 6H), 6.63 (m, 2H),
6.83 (m, 2H), 7.04 (4H, AA’XX’), 7.09 (d, J=7.3 Hz, 2H), 7.60 ppm
(4H, AA’XX’); 13C NMR (100 MHz, CDCl3, 258C): d=21.58, 55.35,
114.00, 121.34, 123.21, 126.51, 127.24, 129.87, 132.49, 137.25, 138.79,
142.63, 149.99, 159.71 ppm; UV/Vis lmax (loge)=457 (4.28), 436 (4.28),
339 (4.17), 293 (4.63), 273 nm (4.58); IR (KBr): n˜ =3006 (w), 2952 (w),
2833 (w), 1601 (m), 1567 (w), 1508 (s), 1459 (w), 1449 (m), 1312 (w),
1300 (m), 1249 (s), 1168 (m), 1109 (w), 1033 (m), 846 (w), 805 (w),
790 cmꢀ1 (w); MS (EI, 70 eV): m/z (rel. intensity): 442 ([M]+, 100), 427
(13), 221 (28); elemental analysis (%) calcd for C32H26O2: C 86.85 H
5.92, O 7.23; found: C 86.58, H 5.86.
[7] a) Crystal data of 6: C48H60Si4, Mr =749.34, 0.30ꢂ0.20ꢂ0.20 mm3,
crystal system=monoclinic, a=7.282(3), b=15.076(6), c=
10.496(4) ꢁ, b=109.695(4)8, V=1084.8(7) ꢁ3, space group P21/n
(no. 14), Z=1,
0.041, wR2(all data)=0.118, S=1.92, reflections/parameters=2052/
mACTHNGUTERNNUG , T=150 K, R1ACHTNUGRTENNUGN
(MoKa)=1.68 cmꢀ1 (F2>2s(F2))=
AHCTUNGTRENNUNG
178. b) Crystal data of 8: C48H45BrNiP2Si, Mr =850.52, 0.20ꢂ0.10ꢂ
0.10 mm3, crystal system=monoclinic, a=41.777(3), b=10.7641(8),
c=21.290(2) ꢁ, b=115.760(2)8, V=8622(1) ꢁ3, space group C2/c
(no. 15), Z=8, m
0.095, wR2(all data)=0.247, S=1.00, reflections/parameters=4559/
(MoKa)=15.13 cmꢀ1, T=296 K, R1(F2>2s(F2))=
ACHUTGTNRENNUG CAHTUNGTRENNUGN
AHCTUNGTRENNUNG
478. CCDC-702714 (6) and CCDC-702715 (8) contain the supple-
mentary crystallographic data for this paper. These data can be ob-
tained free of charge from The Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/data_request/cif
5,10-Bis(4-methoxycarbonylphenyl)-2,7-dimethylindenoACTHNUTRGENUGN[2,1-a]indene
(22): The reaction was carried out using 14 (0.326 g, 1.00 mmol) to give
22 as red–brown needles (0.031 g, 13%), which were obtained after re-
crystallization from CH2Cl2/n-hexane. M.p. 296.3–297.08C; 1H NMR
(270 MHz, CDCl3, 258C): d=2.19 (s, 6H), 3.97 (s, 6H), 6.63 (d, J=
7.6 Hz, 2H), 6.77 (s, 2H), 7.02 (d, J=7.4 Hz, 2H), 7.71 (4H, AA’XX’),
8.19 ppm (4H, AA’XX’); 13C NMR (100 MHz, CDCl3, 258C): d=21.60,
52.26, 121.84, 123.37, 127.76, 128.41, 129.90, 130.09, 131.74, 138.31, 138.61,
138.86, 144.42, 149.65, 166.57 ppm; UV/Vis lmax (loge)=455 (4.23), 434
(4.25), 317 (4.59), 276 (4.85), 230 nm (4.49); IR (KBr): n˜ =2952 (w), 1717
(s), 1599 (m), 1559 (w), 1434 (m), 1405 (w), 1285 (s), 1180 (w), 1113 (m),
1017 (w), 967 (w), 870 (w), 805 (w), 780 (w), 741 cmꢀ1 (w); MS (EI,
70 eV): m/z (rel. intensity): 498 ([M]+, 100), 363 (7), 249 (8); elemental
analysis (%) calcd for C34H26O4: C 81.91 H 5.26, O 12.84; found: C 81.75,
H 5.26.
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Acknowledgements
This work was supported by a Grant-in-Aid for Exploratory Research
from the Ministry of Education, Culture, Sports, Science and Technology
(Japan) (no. 16350073).
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Nickel-Catalyzed Synthesis of Dibenzopentalenes
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Received: November 26, 2008
Published online: February 2, 2009
Chem. Eur. J. 2009, 15, 2653 – 2661
ꢀ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
2661