Palladium-Catalyzed Reaction of Haloarenes with Diarylethynes: Synthesis, Structural Analysis, and Properties of Methylene-Bridged Arenes

Article abstract of DOI:10.1021/acs.joc.5b02111

Fluorenes and methylene-bridged polyarenes were easily and efficiently synthesized from haloarenes (or aryl triflates) and diarylethynes by a one-pot, two-step procedure. This protocol involves the palladium-catalyzed cycloisomerization and a subsequent base-mediated retro-aldol condensation. A major advantage is that the starting materials need not have ortho functional groups to complete the annulation. The backbone of the designed products was enlarged using dihaloarenes, highly π-conjugated haloarenes, or diarylalkynes. The mechanism of the formation of benzo[a]fluorene was investigated. The bowl-shaped structure of methylene-bridged indenocorannulene was verified by X-ray crystallography. The photophysical and electrochemical properties of the products thus prepared were investigated.

Full text of DOI:10.1021/acs.joc.5b02111

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pubs.acs.org/joc
Palladium-Catalyzed Reaction of Haloarenes with Diarylethynes:
Synthesis, Structural Analysis, and Properties of Methylene-Bridged
Arenes
Che-Wei Lee, En-Chih Liu, and Yao-Ting Wu*
Department of Chemistry, National Cheng Kung University, No. 1 Ta-Hsueh Road, 70101 Tainan, Taiwan
S
* Supporting Information
ABSTRACT: Fluorenes and methylene-bridged polyarenes
were easily and efficiently synthesized from haloarenes (or aryl
triflates) and diarylethynes by a one-pot, two-step procedure.
This protocol involves the palladium-catalyzed cycloisomeriza-
tion and a subsequent base-mediated retro-aldol condensation.
A major advantage is that the starting materials need not have ortho functional groups to complete the annulation. The backbone
of the designed products was enlarged using dihaloarenes, highly π-conjugated haloarenes, or diarylalkynes. The mechanism of
the formation of benzo[a]fluorene was investigated. The bowl-shaped structure of methylene-bridged indenocorannulene was
verified by X-ray crystallography. The photophysical and electrochemical properties of the products thus prepared were
investigated.
Crafts reaction, metal-catalyzed C−H bond activation,6 or
INTRODUCTION
■
carbene insertion.7 2-Halo-2′-methylbiphenyl is converted to
fluorene through the palladium-catalyzed benzylic C−H bond
activation and subsequent C−C bond formation (method I).8
The intermediate 2-methyl-2′-palladabiphenyl in this reaction
can also be formed by the cascade coupling of 1,2-
dihalobenzenes with 2-tolylboronic acid9a or 2,6-dimethylphe-
nylmagnesium bromide.9b Biphenyl triazene under acidic
conditions (method II)10a or (2-biphenyl)methanol in the
presence of nanostructured MoO3 (method IV)10b forms
fluorene, and the latter should be upon intramolecular Friedel−
Crafts arylation. The preparation of fluorene from 1-benzyl-2-
halobenzene (method III),11 2-(chloromethyl)biphenyl,12a or
2-phenylbenzyl trifluoroacetate12b (method V) involves the
palladium-catalyzed activation of the aryl C−H bond. The
rhodium-catalyzed cyclization of 2,2-diphenylethanoic acid
involves 2-fold aryl C−H bond cleavages and subsequent
decarboxylation to produce fluorene (method VI).13 2-
Cycloheptatrienyl biphenyl and 2-biphenyl N-tosylhydrazone
(method VII) furnish fluorene via gold carbene14a and free
carbene,14b respectively. Although some of the synthetic
methods in Scheme 1 are very effective, their starting materials
must have an ortho functional group for cyclization or
formation of a suitable intermediate. The exception is 2,2-
diphenylacetic acid (method VI), but the corresponding
precursors for substituted fluorenes have to be prepared by
the arylation of phenylacetates.13 Our recent investigations
demonstrated that an MBA is directly generated from a
haloarene and a diarylacetylene, and no ortho functional groups
in both starting materials are required (method VIII). Despite
the advantages of such a reaction and the importance of MBAs,
Fluorene, the simplest methylene-bridged arene (MBA), is an
important compound with many interesting physical properties,
which enable it and its derivatives to be (potentially) applied in
organic materials, including those used in optoelectronics,
organic field-effect transistors (OFETs), solar cells, and other
devices.1 Unlike benzonoids, the methylene carbon in an MBA
undergoes a wide range of chemical reactions, modifying its
physical properties. For example, fluorene can be converted to
9,9-diarylfluorene,2a which is used in optoelectronic devices to
maintain high color purity owing to its excellent morphological
and thermal stabilities.2b A fully conjugated hydrocarbon based
on an MBA, such as indenofluorenes or tetracyclopentate-
traphenylene (TCT), may exhibit biradical (or tetraradical)
properties (Chart 1).3 The five-membered ring in an MBA may
increase its curvature to form a buckybowl, which is a fragment
of buckminsterfullerene or the end-cap of a carbon nanotube.4
Fluorene is generally prepared from biphenyl derivatives.5
Scheme 1 presents synthetic methods that involve the Friedel−
Chart 1
Received: September 9, 2015
© XXXX American Chemical Society
A
DOI: 10.1021/acs.joc.5b02111
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Featured Article
Scheme 1. Preparations of Fluorene
Table 1. Optimization of Reaction Conditions for the Preparation of 11-(Phenylmethylene)benzo[a]fluorene (5a)
a
entry
catalyst
solvent
base (equiv)
additive (equiv)
conversion (%)
ratio of 2/3a/4a/5a/6/7
b
1
Pd(OAc)2 + PPh3
Pd(OAc)2 + DPPM
PdCl2(dppf)
DMF
NaOAc (2)
CsOPiv (2)
DBU (3)
n-Bu4NCl (1)
77
100
100
100
0
0:0:24:61:0:15
5:0:40:50:0:5
0:37:63:0:0:0
22:0:55:23:0:0
b
2
DMF
3
dioxane
dioxane
dioxane
dioxane
dioxane
dioxane
dioxane
dioxane
dioxane
dioxane
dioxane
anisole
DMF
CsOPiv (1.1)
CsOPiv (1.1)
CsOPiv (1.1)
CsOPiv (1.1)
CsOPiv (1.1)
CsOPiv (1.1)
CsOPiv (1.1)
CsOPiv (1.1)
4
PdCl2(dppf)
Cs2CO3 (3)
iPr2NH (3)
pyridine (3)
piperidine (3)
DABCO (3)
DBN (3)
5
PdCl2(dppf)
6
PdCl2(dppf)
57
28:0:21:51:0:0
22:0:27:18:34:0
0:0:1:0:0:98
7
PdCl2(dppf)
100
90
8
PdCl2(dppf)
9
PdCl2(dppf)
44
5:0:95:0:0:0
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
PdCl2(PPh3)2
DBU (3)
100
25
0:50:50:0:0:0
24:0:76:0:0:0
6:0:22:72:0:0
23:0:20:0:0:57
0:34:66:0:0:0
0:27:73:0:0:0
0:25:75:0:0:0
0:34:66:0:0:0
0:40:60:0:0:0
0:51:49:0:0:0
0:48:42:10:0:0
0:20:60:20:0:0
0:44:54:0:2:0
9:0:11:75:0:0
2:0:13:85:0:0
0:0:1:0:0:98
PdCl2(PPh3)2
DBU (0.5)
DBU (0.5)
PdCl2(PPh3)2
CsOPiv (1.1)
CsOPiv (1.5)
CsOPiv (1.1)
CsOPiv (1.1)
CsOPiv (1.1)
CsOPiv (1.1)
CsOPiv (1.1)
CsOPiv (1.1)
CsOPiv (1.1)
CsOPiv (1.1)
CsOPiv (1.1)
CsOPiv (1.1)
CsOPiv (2)
100
100
100
100
100
100
100
100
100
100
100
96
PdCl2(PPh3)2
PdCl2(PPh3)2
DBU (3)
DBU (3)
DBU (3)
DBU (3)
DBU (3)
DBU (3)
DBU (3)
DBU (3)
DBU (3)
DBU (0.5)
DBU (0.5)
PdCl2(PPh3)2
PdCl2(PPh3)2
NMP
PdCl2(PPh3)2
DMAc
p-xylene
dioxane
dioxane
dioxane
dioxane
dioxane
dioxane
dioxane
dioxane
dioxane
PdCl2(PPh3)2
Pd(OAc)2 + DPPE
Pd(OAc)2 + DPPM
Pd(OAc)2 + CyJohnPhos
Pd(OAc)2 + P(o-tol)3
Pd(OAc)2 + DPPE
Pd(OAc)2 + DPPE
Pd(OAc)2 + DPPE
Pd(OAc)2 + DPPE
PdCl2 + DPPE
100
40
CsOPiv (1.5)
CsOPiv (2)
c
26
DBU (0.5)
DBU (0.5)
100
100
0:0:12:88:0:0
0:0:9:91:0:0
c,d
27
CsOPiv (2)
a
A mixture of 1-bromonaphthalene (0.25 mmol), alkyne 1a (1.1 equiv), palladium catalyst (5 mol %), ligand (10 mol % for PPh3, CyJohnPhos, or
P(o-tol)3; 5 mol % for DPPE or DPPM), base, and solvent (1.5 mL) in a sealed tube was heated for 24 h. The conversion of 1-bromonaphthalene
and the ratio of the compounds was determined by GC MS. Ligands DPPF = 1,1′-bis(diphenylphosphino)ferrocene, DPPE = 1,2-
b
bis(diphenylphosphino)ethane, DPPM = 1,1-bis(diphenylphosphino)methane, CyJohnPhos = (2-biphenyl)dicyclohexylphosphine. The reaction
c
was conducted according to the Larock’s protocol at 100 °C. For details, see refs 15a and 19. The reaction was performed in dioxane (6 mL).
d
Under the optimal conditions, an inseparable mixture of 4a and 5a (ratio 9:91) was obtained with a combined yield of 90%. A large-scale synthesis
(5.0 mmol) gave a total yield of 85% (4a:5a = 9:91).
B
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Table 2. Optimization of Reaction Conditions for the Preparation of Benzo[a]fluorene (3a) from 11-
(Phenylmethylene)benzo[a]fluorene (5a)
a
entry
base (equiv)
solvent (mL)
temp (°C)
time (h)
additive
conversion (%)
ratio of 3a/8a
yield (%)
1
KOH (10)
NaOH (10)
LiOH (10)
DBU (10)
KOH (10)
t-BuOK (10)
t-BuOK (10)
t-BuOK (10)
B1
dioxane (3)
dioxane (3)
dioxane (3)
dioxane (3)
dioxane (3)
dioxane (3)
dioxane (3)
dioxane (3)
dioxane (3)
p-xylene (3)
NMP (3)
150
150
150
150
150
150
150
150
150
150
150
150
150
110
24
24
24
24
24
6
34
40
100:0
100:0
2
A1
A1
A1
A1
A2
A2
A2
A2
A2
A2
A2
A3
A3
3
0
4
10
100:0
68:32
67:33
65:35
70:30
75:25
70:30
100:0
68:32
88:12
100:0
5
100
100
100
100
100
100
100
100
100
100
6
7
12
24
24
24
24
24
24
12
8
55
68
9
10
11
12
13
14
B1
B1
16
64
B1
quinoline (3)
dioxane (6)
dioxane (6)
B1
B1
88
a
The reaction was conducted with a mixture of 4a and 5a (ratio 9:91, 0.25 mmol) in a sealed tube. The ratio of the compounds was determined by
GC−MS. The recovery of 4a was neglected. Additive A1 = (n-Bu)4NBr (0.5 equiv); A2 = 18-crown-6 (0.5 equiv); A3 = 18-crown-6 (0.5 equiv) +
N2H4 (3 equiv). Base B1 = t-BuOK (5 equiv) + KOH (5 equiv).
Scheme 2. Proposed Reaction Mechanism for the Formation of 3a from 5a
this work develops a simple and efficient protocol for
synthesizing various MBAs.
formed in a significant amount (entries 1 and 2, Table 1). More
importantly, the efficient generation of a methylene group by
the cleavage of an exocyclic alkenyl substituent has not yet been
reported.16
RESULTS AND DISCUSSION
■
The palladium-catalyzed reaction of 1-bromonaphthalene
with diphenylethyne (1a) was systematically examined, and the
palladium catalyst, ligand, base, and additive were all critical to
affect formations of compounds 2−7. In the preparation of 5a,
a system of DPPE and PdCl2 or Pd(OAc)2 was found to
outperform other catalysts PdCl2(dppf), PdCl2(PPh3)2, and
catalytic combinations that are listed in Table 1. DBU appeared
to be superior to other bases such as Cs2CO3, i-Pr2NH,
pyridine, piperidine, DBN, and DABCO; it inhibited the
reductive debromination of 1-bromonaphthalene and promoted
the selective generation of 4a (entries 3−9, Table 1). The
reaction was conducted with DMF, NMP, DMAc, p-xylene,
anisole, or 1,4-dioxane as a solvent, and the last was observed to
lower the amount of 4a formed (entries 14−18, Table 1). The
absence of the additive cesium pivalate (CsOPiv) greatly
reduced the conversion of 1-bromonaphthalene (entry 11,
Table 1). A mixture of CsOPiv and DBU with a suitable ratio
under dilute conditions strongly improved the formation of 5a
The palladium-catalyzed annulation of 1-bromonaphthalene
with diphenylethyne (1a) yielded a mixture of naphthalene (2),
benzo[a]fluorene (3a), 4,5-diphenylacephenanthrylene (4a),
11-(phenylmethylene)benzo[a]fluorene (5a), 1-naphthyl-1,2-
diphenylethene (6) and phenanthrene 7 (Table 1). The best
result was that benzo[a]fluorene (3a) and 1,2-diphenylace-
naphthrylene (4a) were obtained in almost equal amounts,
based on GC−MS analysis (entries 10 and 19, Table 1). Owing
to the low chemoselectivity between 3a and 4a, the one-pot
procedure was modified to a two-step protocol. The desired
product 3a was assumed to be generated from the key
intermediate 5a by the base-mediated cleavage of the exocyclic
alkenyl moiety. This assumption faces several challenges.
Although Larock’s method, which is adopted to synthesize 9-
(alkylidene)fluorene by the palladium-catalyzed cycloisomeriza-
tion of an iodobenzene derivative with an arylalkyne,15 provides
useful information concerning the mechanism of formation of
5a, it could not be utilized herein because the byproduct 4a was
C
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Table 3. One-Pot Synthesis of Methylene-Bridged Arenes through the Palladium-Catalyzed Reaction of Haloarenes with
Diarylethynes and the Subsequent Retro-Aldol Condensation
D
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Table 3. continued
a
Method A: (step 1) PdCl2 (5 mol %), DPPE (5 mol %), bromoarene (0.25 mmol), alkyne (1.1 equiv), DBU (0.5 equiv), CsOPiv (2 equiv), and
dioxane (6 mL) in a sealed tube was heated for 24 h; (step 2) a mixture of KOH (5 equiv), t-BuOK (5 equiv), N2H4·H2O (3 equiv), and 18-crown-6
(0.5 equiv) was heated for 12 h. For the synthesis of a bis(methlyene)-bridged arene from a dibromoarene, the reaction was conducted with 3 equiv
of alkyne and 2-fold reagents and catalysts in the same amount of solvent. Method B: similar to method A, but the first step was conducted with a
catalytic system that was composed of PdCl2(PCy3)2 (10 mol %), P(t-Bu)3·HBF4 (20 mol %), DBU (2 equiv), and CsOPiv (2 equiv) at 150 °C.
Method C: similar to method A, but the palladium-catalyzed cycloisomerization was conducted with a mixture of Pd(OAc)2 (5 mol %), DPPE (5
b
mol %), bromoarene (0.25 mmol), alkyne (1.2 equiv), CsOPiv (2 equiv), DBU (1 equiv), and dioxane (3 mL) at 130 °C. The reaction was
performed with 5.0 mmol of 1-bromonaphthalene. For details, see the Experimental Section.
(entries 26 and 27, Table 1). The use of less CsOPiv or the
absence of DBU reduced the reaction efficiency, but an excess
of the latter enhanced the amount of byproduct 4a. Under the
optimal conditions, an inseparable mixture of 4a and 5a (ratio
9:91) was obtained with a combined yield of 90%. A large-scale
synthesis (5.0 mmol) in a flask under reflux gave a yield of 85%
(entry 27, Table 1). Unlike diphenylethyne (1a), other phenyl-
substituted alkynes, such as 1-phenyl-1-propyne and 1-cyclo-
propyl-2-phenylethyne, yielded unsatisfactory results because
they mostly underwent benzannulation with 1-bromonaph-
thalene to form phenanthrene derivatives.
halobenzenes, sterically congested 2-bromotoluene furnished
1-methylfluorene (13a) in a lower yield (57%) with the
recovery of 20% of the starting material (entry 20, Table 3).
The regioselectivity of this protocol strongly depends on the
aryl halides and the diarylacetylenes. For example, reactions of
2-bromonaphthalenes and 2-bromoanthracene with diary-
lethynes, such as diphenylethyne (1a), bis(3,5-
dimethylphenyl)ethyne (1h), di(4-chlorophenyl)ethyne (1j),
and di(1-naphthyl)ethyne (1k), yielded corresponding prod-
ucts 9a−h, 10j,k, and 19a as the sole regioisomers (entries 12−
16 and 28, Table 3). In contrast, the combinations 2-
bromofluorene/1a, bromobenzene/di(2-naphthyl)ethyne (1l),
and 1-bromonaphthalene/di(3-tolyl)ethyne (1g) each gener-
ated two regioisomers (entries 9, 23, and 26, Table 3), with the
best result obtained in the first case (66% yield, 17b:17b′ =
80:20).
The reaction conditions utilized herein are suitable for not
only bromoarenes but also iodoarenes and aryl triflates, with
comparable reactivities (entries 4 and 13, Table 3). The use of
iodobenzene in the synthesis of fluorene gave a higher yield
than bromobenzene (entry 18, Table 3). When the catalytic
system that comprised PdCl2 and DPPE was replaced with
PdCl2(PCy3)2 and P(t-Bu)3·HBF4 (method B), 1-chloronaph-
thalene also gave 3a, but with an unsatisfactory yield (55%,
entry 2, Table 3).
The use of potassium hydroxide and hydrazine for alkene
cleavage should cause a compatibility issue with carbonyl
derivatives. The reaction of 4-bromobenzaldehyde with 1a was
examined. Indeed, the aldehyde group could not tolerate the
reaction conditions herein, but this problem was solved by
replacing 4-bromobenzaldehyde with 2-(4-bromophenyl)-1,3-
dioxolane (entry 21, Table 3).
The reactivity of dibromoarenes and solubility of each
product in common organic solvents both critically affect the
reaction efficiencies of the 2-fold annulations. Among these
dibromoarenes, 3,6-dibromophenanthrene gave the best result
with a yield of 88% (entry 33, Table 3) because of its high
reactivity and ease of purification (see the Experimental
Section). The products that were obtained from 1,4- and 1,3-
dibromobenzenes and 2,6-dibromonaphthalene were regiose-
lectively acquired in 50−63% yields (entries 29−32, Table 3).
Notably, derivatives of 6,12-dihydroindeno[1,2-b]fluorene
(20a) have been suggested to be suitable candidates for
OFETs and OLEDs (organic light-emitting diodes).18
The cleavage of the exocyclic alkenyl moiety in 5a was
intensively investigated using hydroxyl anions or tert-butoxide
in dioxane (Table 2). Potassium hydroxide provided better
results than the corresponding sodium and lithium salts (entries
2, 3, and 5, Table 2). Although t-BuOK is generally regarded as
a non-nucleophilic base, its ability to generate hydroxyl anion
from water under nonanhydrous conditions should not be
ignored (entries 6−8, Table 2). It was observed that more 3a
was formed when a mixed base KOH/t-BuOK was employed
instead of t-BuOK alone (entries 8 and 9, Table 2). The phase-
transfer catalysts N(n-Bu)4Br and 18-crown-6 increased the
reaction efficiency (entries 1, 5, and 9, Table 2). In addition to
the desired product 3a, 11-benzylbenzo[a]fluorene (8a) was
observed as a serious byproduct. This unfavorable outcome was
improved upon by the addition of hydrazine (entries 9 and 13,
Table 2), whose role in this reaction is described in Scheme 2.
Under the optimal conditions, 3a was obtained with a yield of
88% (entry 14, Table 2). Since both the Pd-catalyzed
cycloisomerization and the based-mediated alkene cleavage
were performed in dioxane, an attempt was made to conduct
this synthetic approach as a one-pot, two-step procedure; in
doing so, 3a was afforded with yields of 80% and 70% on scales
of 0.25 and 5.0 mmol, respectively (entry 1, Table 3, method
A). This one-pot, two-step protocol can be easily implemented:
the reagents for the second step are just added to a flask or
Pyrex tube that contains the reaction mixture formed in the first
step. When the unacidified crude product was directly exposed
to ambient air and stirred at room temperature for 4 h,
benzo[a]fluoren-11-one was obtained with a yield of 70%
(based on 0.25 mmol of 1-bromonaphthalene). Notably, these
protocols developed herein are much more efficient than
conventional methods,17 which require many synthetic steps
from commercially available starting materials.
The reactivity of alkynes 1 in annulation was examined using
1-bromonaphthalene, and products 3 were obtained with
moderate to excellent yields (entries 1−11, Table 3). Reactions
with π-extended haloarenes or diarylalkynes also efficiently
generated desired products. Fluorene and its derivatives 11−14
were obtained with higher yields (entries 17−21, Table 3)
when the reactions were performed with Pd(OAc)2 and more
DBU (1.0 equiv) (method C). In contrast to other
The formation of 5a through 1,4-palladium migration can be
easily formulated on the basis of the literature,15a,19 but the
generation of 3a from 5a was unknown. In order to gain insight
into the mechanism of cleavage of the exocyclic alkenyl moiety,
the reaction products were analyzed. In the absence of
hydrazine, significant amounts of benzoic acid and a reduced
product, 11-benzylbenzo[a]fluorene (8a), were obtained.
When 3i was prepared under the optimal conditions (method
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A, Table 3), a mixture of 3,4,5-trimethoxybenzaldehyde and
3,4,5-trimethoxytoluene was observed, and the aldehyde was
identified by direct comparison with the authentic sample using
GC−MS. On the basis of the outcomes of the above
experiments, Scheme 2 presents a putative reaction mechanism
for the formation of 3a from 5a. The reaction is initiated by the
nucleophilic attack of a hydroxide ion at an alkenyl carbon in
5a, followed by proton transfer to yield the adduct 24, which
fragments into a mixture of benzaldehyde and 3a upon
protonation. The base-mediated cleavage of the exocyclic
alkenyl moiety can be treated as the retro-aldol condensation.
Benzaldehyde enhanced the formation of the reduction product
8a by a redox process similar to the Cannizzaro reaction, which
involves the base-mediated disproportionation of benzaldehyde
to yield a mixture of benzyl alcohol and potassium
benzoate.16b,20 Hydroxide attacks the carbonyl moiety in
benzaldehyde to yield phenylmethanediol anion 25, from
which a hydride is transferred to 5a to generate 8a upon
protonation. Adding hydrazine to consume benzaldehyde
suppresses the latter undesired process.21
two 15h bowls in a column was determined to be 3.85 Å. All of
the bowl stacks are aligned in one direction, forming polar
crystals, consistent with the polar space group Pna21. Owing to
its uniform packing order, 15h may have potential applications
as an organic material with high electron mobility, piezo-
electricity, or pyroelectricity.27 Notably, 1,2,5,6-tetrabromocor-
annulene and 15h have the same space group and very similar
structural features.28
The photophysical properties of selected compounds in
CH2Cl2 (10 μM) at room temperature were investigated herein
(Table 4 and Supporting Information) and found to be strongly
Table 4. Physical Properties of Methylene-Bridged
Polyarenes
a
entry
compd
λabs (nm)
λem (nm)
354, 366
Ered (V)
1
2
3
4
5
6
7
8
9
3a
344
−2.66
−2.64
−2.62, −2.92
−2.14, −2.64
−2.76
9a
340
353, 361, 379
371, 381
10k
15h
16a
17b
18a
22h
23a
340, 360
364, 415
352, 372
335
453
440, 466
X-ray-quality crystals of 15h were obtained by the slow
evaporation of MeOH into the solution in CH2Cl2.22
Compound 15h is a bowl-shaped molecule in a sterically
congested environment. The distance of the nonbonded
contact between the two carbon atoms shown in Figure 1
415, 430
381, 403
349, 367
329, 346
439
−2.24, −2.79
−2.86
−2.77
370, 390, 412
382, 393, 404, 458
a
Photophysical properties were measured at a concentration ca. 10 μM
in CH2Cl2, and absorption bands over 330 nm are listed. Redox
properties were investigated with compounds (concentration ca. 10
mM) in background electrolyte solution of 0.1 M (n-Bu)4NBF4
(tetrabutylammonium tetrafluoroborate) in DMSO with the scan
rate of 0.1 V/s and potentials vs the Fc/Fc+ couple.
influenced by the aromatic π system in the backbone. In
contrast to benzo[a]fluorene (3a), its benzoannulated deriva-
tive, 13H-indeno[2,1-a]anthracene (18a), exhibits significantly
red-shifted absorption and emission bands (entries 1 and 7,
Table 4), whereas the two “regioisomers” benzo[a]fluorene
(3a) and benzo[b]fluorene (9a) display very similar photo-
physical properties (entries 1 and 2, Table 4). Notably,
indenocoranuulene 15h and 13H-indeno[1,2-b]fluoranthene
(16a) exhibit an absorption and an emission band, respectively,
at the longest wavelength of any of the compounds that are
presented in Table 4. Compound 17b was observed to have the
largest Stokes shift (80 nm; entry 6 in Table 4).
The redox properties of selected MBAs were elucidated by
cyclic voltammetry and are presented in Table 4 and the
Supporting Information. The oxidation waves of all compounds
were not observed in this electrochemical window (from +0.45
to −3.25 V vs Fc/Fc+). Reduction signals (Ered) of most
compounds can be detected, but all are irreversible, indicating
the low thermodynamic stability of these anionic species. This
phenomenon is very similar to the electrochemical properties of
fluorene and its derivatives.29 The reduction of fluorene first
yields a fluorenyl radical anion, which then forms a stable
fluorenyl anion and 0.5 equiv of the hydrogen molecule
through the cleavage of the C−H bond and dimerization of the
hydrogen atoms on the electrode surface. The reduction
potential(s) of the investigated compounds is sensitive to the
aromatic π system in the backbone. Indenocoranuulene 15h
displays the lowest reduction potential (−2.14 V) among
compounds listed in Table 4. The first reduction potential for
3a (−2.66 V) is higher than that of its benzoannulated
derivative 18a (−2.24 V) (entries 1 and 7, Table 4). As
Figure 1. (a) Crystallographic structure and the POAV pyramidaliza-
tion angles (degrees) of buckybowl 15h. (b) Crystal packing along the
c axis. Only carbon atoms are shown for clarity.
was determined to be 3.23 Å, which is shorter than the sum of
their van der Waals radii (3.70 Å).23 This bay-region clash leads
the methyl carbon atom to be out-of-plane distorted from the
m-xylyl ring by 0.22 Å. This steric interaction does not strongly
affect the bowl curvature. The structure of 15h is slightly more
curved than that of corannulene, as determined by comparing
their bowl depths and the maximum POAV (π-orbital axis
vector) pyramidalization angles24 of the corannulene fragments
(0.90 vs 0.87 Å25 and 9.0 vs 8.2°). Their comparable curvatures
also reflect their similar bowl-to-bowl inversion barriers of
around 11 kcal/mol.26 A significant difference between
corannulene and 15h is in their molecular packings. The
aggregation of the former is highly disordered, whereas the
latter forms bowl-in-bowl stacks. The shortest distance between
F
DOI: 10.1021/acs.joc.5b02111
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Featured Article
dibromoarene (entries 29−33, Table 3), the reaction was conducted
with 3 equiv of alkyne and 2-fold reagents and catalysts in the same
amount of solvent.
Method B (Entry 2, Table 3). Similar to method A, but the step
for the cycloisomerization was conducted with 1-chloronaphthalene
(40.7 mg, 0.25 mmol), diphenylethyne (53.5 mg, 0.30 mmol),
PdCl2(PCy3)2 (18.5 mg, 25.0 μmol, 10 mol %), PtBu3·HBF4 (14.5 mg,
50.0 μmol, 20 mol %), DBU (76 mg, 0.50 mmol), CsOPiv (117 mg,
0.5 mmol), and dioxane (6 mL) at 150 °C for 24 h.
Method C (Entries 17−21, Table 3). Similar to method A, but
the step for the cycloisomerization was conducted with haloarene
(0.25 mmol), alkyne (0.30 mmol), Pd(OAc)2 (2.8 mg, 12.5 μmol, 5
mol %), DPPE (5.0 mg, 12.5 μmol, 5 mol %), DBU (38.1 mg, 0.25
mmol), CsOPiv (117 mg, 0.5 mmol), and dioxane (3 mL).
11H-Benzo[a]fluorene (3a). White solid [43.2 mg (80%) from 1-
bromonaphthalene; 29.7 mg, (55%) from 1-chloronaphthalene]. The
1H NMR spectrum is identical to that reported in the literature.13
Procedure for large-scale preparation: A mixture of 1-bromonaphthalene
(1.04 g, 5.00 mmol), 1a (1.16 g, 6.50 mmol), PdCl2 (44.3 mg, 0.25
μmol, 5 mol %), DPPE (99.6 mg, 0.25 μmol, 5 mol %), DBU (380 mg,
2.50 mmol), CsOPiv (2.34 g, 10.0 mmol), and dioxane (120 mL) in a
three-neck flask equipped with a reflux condenser was refluxed under
nitrogen for 24 h (bath temperature 140 °C). After the mixture was
cooled to room temperature, KOH (1.40 g, 25.0 mmol), t-BuOK (2.81
g, 25.0 mmol), and N2H4·H2O (751 mg, 15.0 mmol) were added, and
the reaction mixture was refluxed under nitrogen for 12 h (bath
temperature 110 °C). The flask was cooled to room temperature and
then immersed into an ice bath. Hydrochloric acid (2 N, 50 mL) was
slowly added, and the aqueous phase was extracted with CH2Cl2 (2 ×
30 mL). The combined extracts were dried over MgSO4, and the
solvent of the filtrate was removed under reduced pressure. The
residue was subjected to chromatography on silica gel, eluting with
hexane to give 3a (0.76 g, 70%) as a white solid.
expected, benzo[a]fluorene (3a) and benzo[b]fluorene (9a)
have similar reduction potentials (−2.66 vs −2.64 V; entries 1
and 2, Table 4). A mono(methylene)-bridged arene exhibits a
lower reduction potential than a bis(methylene)-bridged arene.
This conclusion is supported by the two facts described as
follows: The reduction potentials for bis(methylene)-bridged
arenes 22h and 23a were determined to be −2.86 and −2.77 V,
respectively, and they are the first and second highest values in
Table 4 (entries 8 and 9). The redox properties of 17b cannot
be determined, revealing that its reduction potential is higher
than that of fluorene (−3.11 V). Unlike 6,12-dihydroindeno-
[1,2-b]fluorene (20a) reported in the literature,30 the second
reduction potentials for bis(methylene)-bridged arenes such as
17b, 22h, and 23a were not observed.
CONCLUSIONS
■
Fluorenes and higher π-conjugated MBAs have been easily and
efficiently synthesized by a one-pot, two-step procedure from
haloarenes and diarylethynes by the palladium-catalyzed
cycloisomerization and a subsequent base-mediated retro-
aldol condensation. A major advantage of this protocol is that
the starting materials need not have ortho functional groups to
complete the annulation. The extension of this simple synthetic
approach to the preparation of more extended derivatives and
investigations of their properties are in progress.
EXPERIMENTAL SECTION
General Methods. H NMR spectra were recorded on 300, 400,
■
1
and 500 MHz spectrometers. 13C NMR spectra were recorded on 75,
100, and 125 MHz NMR spectrometers. MS and HRMS were
obtained on a double-focusing sector mass spectrometer (ionization
mode: EI or FAB). Melting points were measured by a hot-stage
melting point apparatus and are uncorrected. The authentic sample of
3,4,5-trimethoxybenzaldehyde was purchased from a commercial
supplier. 1-Phenyl-1-propyne,31 1-cyclopropyl-2-phenylethyne,32 and
diarylethynes,33 including 1,2-di(4-tolyl)ethyne (1b), 1,2-di(4-n-butyl-
phenyl)ethyne (1c), 1,2-di(4-tert-butylphenyl)ethyne (1d), 1,2-di(4-
anisyl)ethyne (1e), 1,2-di(4-fluorophenyl)ethyne (1f), 1,2-di(3-tolyl)-
ethyne (1g), 1,2-bis(3,5-dimethylphenyl)ethyne (1h), 1,2-bis(3,4,5-
trimethoxyphenyl)ethyne (1i), 1,2-di(4-chlorophenyl)ethyne (1j), 1,2-
di(1-naphthyl)ethyne (1k), and 1,2-di(2-naphthyl)ethyne (1l), were
prepared according or similar to the literature procedures. Haloarenes
such as 3-bromofluoranthene,34 bromocorannulene,35 1-bromoanthra-
cene,36 2-bromoanthracene,37 2,7-dibromonaphthalene,38 1,5-dibro-
monaphthalene,39 3,6-dibromophenanthrene,40 2-naphthyl trifluoro-
methanesulfonate,41 and 2-(4-bromophenyl)-1,3-dioxolane42 were
synthesized according to the literature procedures.
8-Methyl-11H-benzo[a]fluorene (3b). White solid [46.2 mg
(80%) from 1-bromonaphthalene; 40.8 mg (71%) from 1-iodonaph-
thalene], mp 181.4−182.1 °C. 1H NMR (300 MHz, CDCl3, ppm): δ =
3
2.49 (s, 3H), 4.15 (s, 2H), 7.15 (d, J = 7.7 Hz, 1H), 7.43−7.57 (m,
3H), 7.66 (s, 1H), 7.86 (d, 3J = 9.1 Hz, 1H), 7.91 (d, 3J = 8.5 Hz, 2H),
3
8.02 (d, J = 8.3 Hz, 1H). 13C{1H} NMR (75 MHz, CDCl3, plus
DEPT, ppm): δ = 21.6 (CH3), 35.2 (CH2), 118.7 (CH), 120.3 (CH),
124.1 (CH), 124.6 (CH), 125.2 (CH), 126.4 (CH), 127.2 (CH),
127.7 (CH), 128.9 (CH), 130.8 (Cquat), 132.8 (Cquat), 136.4 (Cquat),
139.0 (Cquat), 140.2 (Cquat), 140.4 (Cquat), 142.8 (Cquat). EI MS (70
eV), m/z: 230 (100) [M+], 215 (69) [M+ − CH3]. HRMS (EI): calcd
for C18H14 230.1096, found 230.1097.
8-(n-Butyl)-11H-benzo[a]fluorene (3c). White solid [44.2 mg
(65%)], mp 127.8−128.2 °C. 1H NMR (300 MHz, CDCl3, ppm): δ =
0.97 (t, 3J = 7.5 Hz, 3H), 1.43 (sex, 3J = 7.5 Hz, 2H), 1.70 (quin, 3J =
3
7.5 Hz, 2H), 2.75 (t, 3J = 7.5 Hz, 2H), 4.15 (br s, 2H), 7.15 (dd, J =
4
3
4
7.6, J = 1.4 Hz, 1H), 7.46 (td, J = 7.6, J = 1.4 Hz, 1H), 7.51−7.54
(m, 2H), 7.66 (s, 1H), 7.87 (d, 3J = 8.4 Hz, 1H), 7.91 (d, 3J = 7.4 Hz,
1H), 7.92 (d, J = 8.4 Hz, 1H), 8.01 (d, J = 8.3 Hz, 1H). 13C{1H}
NMR (75 MHz, CDCl3, plus DEPT, ppm): δ = 14.0 (CH3), 22.5
(CH2), 34.1 (CH2), 35.3 (CH2), 35.8 (CH2), 118.7 (CH), 119.6
(CH), 124.1 (CH), 124.6 (CH), 125.2 (CH), 126.4 (CH), 126.7
(CH), 127.7 (CH), 128.9 (CH), 130.8 (Cquat), 132.8 (Cquat), 139.1
(Cquat), 140.2 (Cquat), 140.6 (Cquat), 141.6 (Cquat), 142.7 (Cquat). EI MS
(70 eV), m/z: 272 (65) [M+], 229 (77), 228 (72), 215 (100) [M+ −
C4H9]. HRMS (EI): calcd for C21H20 272.1565, found 272.1573.
8-tert-Butyl-11H-benzo[a]fluorene (3d). White solid [47.6 mg
(70%)], mp 157.9−158.3 °C. 1H NMR (300 MHz, CDCl3, ppm): δ =
3
3
General procedures for the Pd-catalyzed annulation of a haloarene
with an alkyne:
Method A (Entries 1−16 and 22−28, Table 3). A mixture of
haloarene (or aryl triflate, 0.25 mmol), alkyne (0.28 mmol), PdCl2 (2.2
mg, 12.5 μmol, 5 mol %), DPPE (5.0 mg, 12.5 μmol, 5 mol %), DBU
(19.0 mg, 0.125 mmol), CsOPiv (118 mg, 0.50 mmol), and dioxane (6
mL) in a thick-walled Pyrex tube was purged with nitrogen for 5 min.
The sealed tube was kept in an oil bath at 130 °C for 24 h. After being
cooled to room temperature, the reaction mixture was treated with
KOH (70.1 mg, 1.25 mmol), t-BuOK (140 mg, 1.25 mmol), 18-
crown-6 (33.0 mg, 0.125 mmol), and N2H4·H2O (37.5 mg, 0.75
mmol) and purged with nitrogen for 5 min. The sealed tube was
placed again in an oil bath at 110 °C for 12 h. The tube was cooled to
room temperature and then immersed in an ice bath. Hydrochloric
acid (2 N, 2.5 mL) was slowly added, and the aqueous phase was
extracted with CH2Cl2 (2 × 15 mL). The combined extracts were
dried over MgSO4, and the solvent of the filtrate was removed under
reduced pressure. The residue was subjected to chromatography on
silica gel. For the synthesis of a bis(methlyene)-bridged arene from a
3
4
1.44 [s, 9H, C(CH3)3], 4.15 (s, 2H), 7.39 (dd, J = 7.9, J = 1.8 Hz,
1H), 7.47 (td, 3J = 7.5, 4J = 1.8 Hz, 1H), 7.54 (td, 3J = 8.0, 4J = 1.5 Hz,
1H), 7.57 (d, 3J = 8.0 Hz, 1H), 7.87 (d, 3J = 8.6 Hz, 1H), 7.88 (d, 4J =
1.5 Hz, 1H), 7.91 (d, 3J = 8.6 Hz, 1H), 7.95 (d, 3J = 8.4 Hz, 1H), 8.02
3
(d, J = 8.1 Hz, 1H). 13C{1H} NMR (75 MHz, CDCl3, plus DEPT,
ppm): δ = 31.7 [C(CH3)3], 34.9 [C(CH3)3], 35.2 (CH2), 116.5 (CH),
118.7 (CH), 123.7 (CH), 124.1 (CH), 124.4 (CH), 125.2 (CH),
126.4 (CH), 127.7 (CH), 128.9 (CH), 130.8 (Cquat), 132.8 (Cquat),
139.2 (Cquat), 140.2 (Cquat), 140.5 (Cquat), 142.5 (Cquat), 150.0 (Cquat).
G
DOI: 10.1021/acs.joc.5b02111
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The Journal of Organic Chemistry
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EI MS (70 eV), m/z: 272 (100) [M+], 257 (53), 215 (66) [M+ −
C4H9]. HRMS (EI): calcd for C21H20 272.1565, found 272.1569.
8-Methoxy-11H-benzo[a]fluorene (3e). White solid [40.6 mg
(66%)], mp 152.8−153.3 °C. 1H NMR (300 MHz, CDCl3, ppm): δ =
3.93 (s, 3H), 4.12 (s, 2H), 6.89 (dd, 3J = 8.2, 4J = 2.3 Hz, 1H), 7.37 (d,
4J = 2.3 Hz, 1H), 7.44 (d, 3J = 7.4 Hz, 1H), 7.51 (d, 3J = 8.0 Hz, 1H),
7.54 (t, 3J = 7.5 Hz, 1H), 7.88 (s, 2H), 7.91 (d, 3J = 8.1 Hz, 1H), 8.01
202 (56). HRMS (EI): calcd for C18H13ClO 280.0655, found
280.0656.
9-Methoxy-13H-dibenzo[a,h]fluorene (10k). Pale yellow solid
1
[51.8 mg (70%)], mp 276.3−277.1 °C. H NMR (300 MHz, CDCl3,
3
4
ppm): δ = 3.97 (s, 3H), 4.32 (s, 2H), 7.14 (dd, J = 8.9, J = 2.5 Hz,
4
3
4
1H), 7.28 (d, J = 2.5 Hz, 1H), 7.49 (td, J = 7.5, J = 1.2 Hz, 1H),
7.57 (td, 3J = 7.5, 4J = 1.2 Hz, 1H), 7.78 (d, 3J = 8.9 Hz, 1H), 7.91 (d,
3J = 8.0 Hz, 1H), 7.94 (d, 3J = 7.0 Hz, 1H), 7.95 (s, 1H), 8.02 (d, 3J =
3
(d, J = 8.0 Hz, 1H). 13C{1H} NMR (75 MHz, CDCl3, plus DEPT,
8.4 Hz, 1H), 8.03 (d, J = 8.3 Hz, 1H), 8.14 (s, 1H). 13C{1H} NMR
3
ppm): δ = 34.9 (CH2), 55.6 (CH3), 105.0 (CH), 112.5 (CH), 118.6
(CH), 124.1 (CH), 125.4 (CH × 2), 126.5 (CH), 127.7 (CH), 128.9
(CH), 130.7 (Cquat), 132.9 (Cquat), 135.4 (Cquat), 138.8 (Cquat), 141.0
(Cquat), 143.9 (Cquat), 159.3 (Cquat). EI MS (70 eV), m/z: 246 (100)
[M+], 202 (46). HRMS (EI): calcd for C18H14O 246.1045, found
246.1051.
(75 MHz, CDCl3, plus DEPT, ppm): δ = 34.9 (CH2), 55.3 (CH3),
106.3 (CH), 116.5 (CH), 117.9 (CH), 119.1 (CH), 123.2 (CH),
124.3 (CH), 125.7 (CH), 126.6 (CH), 128.0 (CH), 128.4 (Cquat),
128.9 (CH), 129.2 (CH), 130.8 (Cquat), 133.3 (Cquat), 134.2 (Cquat),
138.4 (Cquat), 139.0 (Cquat), 140.8 (Cquat), 141.9 (Cquat), 157.4 (Cquat).
EI MS (70 eV), m/z: 296 (100) [M+]. HRMS (EI): calcd for C22H16O
296.1201, found 296.1205.
8-Fluoro-11H-benzo[a]fluorene (3f). White solid [34.5 mg
1
(59%)], mp 149.8−150.5 °C. H NMR (300 MHz, CDCl3, ppm): δ
3
3
4
Fluorene (11a). White solid [30.0 mg (72%) from 1-
= 4.15 (s, 2H), 7.01 (ddd, J = 9.3, J = 8.2, J = 2.4 Hz, 1H), 7.45−
7.58 (m, 4H), 7.85 (d, 3J = 8.5 Hz, 1H), 7.89 (d, 3J = 8.8 Hz, 1H), 7.92
1
bromobenzene; 37.4 mg (90%) from 1-iodobenzene]. The H NMR
spectrum is identical to that reported in the literature.44
3
3
(d, J = 8.8 Hz, 1H), 8.01 (d, J = 8.4 Hz, 1H). 13C{1H} NMR (75
2
11H-Benzo[b]fluorene (9a) and 7H-Benzo[c]fluorene (11l′).
MHz, CDCl3, plus DEPT, ppm): 35.1 (CH2), 106.8 (d, JC,F = 23.0
Hz, CH), 113.0 (d, JC,F = 23.0 Hz, CH), 118.7 (CH), 124.1 (CH),
125.68 (d, JC,F = 8.3 Hz, CH), 125.69 (CH), 126.7 (CH), 128.0
1
2
White solid [32.4 mg (60%), ratio 70:30]. The H NMR spectrum of
11l′ is identical to that reported in the literature.8
3
1
3-Methylfluorene (12a). White solid [34.2 mg (76%)]. The H
(CH), 129.0 (CH), 130.6 (Cquat), 133.0 (Cquat), 138.2 (Cquat), 138.5
NMR spectrum is identical to that reported in the literature.13
(Cquat), 141.2 (Cquat), 144.5 (d, 3JC,F = 9.1 Hz, Cquat), 162.7 (d, 1JC,F
=
1
1-Methylfluorene (13a). White solid [25.7 mg (57%)]. The H
243.1 Hz, Cquat). EI MS (70 eV), m/z: 234 (100) [M+]. HRMS (EI):
calcd for C17H11F 234.0845, found 234.0837.
NMR spectrum is identical to that reported in the literature.10a
Fluorene-3-carbalaldehyde (14a). The title compound was
prepared similar to method C, but the acidified solution was stirred at
room temperature for 1 h (monitored by GC−MS). 14a. Pale yellow
9-Methyl-11H-benzo[a]fluorene (3g) and 7-Methyl-11H-
benzo[a]fluorene (3g′). White solid [35.1 mg (61%), ratio 72:28].
1
The H NMR spectrum of 3g′ is identical to that reported in the
1
literature.8
solid [35.4 mg (73%)], mp 248.2−248.8 °C. H NMR (300 MHz,
3
4
CDCl3, ppm): δ = 4.00 (s, 2H), 7.36 (td, J = 7.6, J = 1.5 Hz, 1H),
7,9-Dimethyl-11H-benzo[a]fluorene (3h). White solid [53.1 mg
3
3
3
1
7.42 (t, J = 7.6 Hz, 1H), 7.58 (d, J = 7.4 Hz, 1H), 7.70 (d, J = 7.7
Hz, 1H), 7.84 (dd, 3J = 7.7, 4J = 1.5 Hz, 1H), 7.88 (d, 3J = 7.0 Hz, 1H),
8.29 (s, 1H), 10.11 (s, 1H). 13C{1H} NMR (75 MHz, CDCl3, plus
DEPT, ppm): δ = 37.3 (CH2), 120.41 (CH), 120.44 (CH), 125.2
(CH), 125.5 (CH), 127.2 (CH), 127.7 (CH), 129.1 (CH), 135.7
(Cquat), 140.4 (Cquat), 142.8 (Cquat), 143.1 (Cquat), 150.2 (Cquat), 192.4
(CHO). FAB MS, m/z: 194 (31) [M+], 165 (100) [M+ − CHO].
HRMS (FAB): calcd for C14H10O 194.0732, found 194.0739.
(87%)]. The H NMR spectrum is identical to that reported in the
literature.43
7,8,9-Trimethoxy-11H-benzo[a]fluorene (3i). White solid [46.7
mg (61%)], mp 142.7−143.2 °C. 1H NMR (300 MHz, CDCl3, ppm):
δ = 3.96 (s, 6H), 4.10 (s, 3H), 4.13 (s, 2H), 7.00 (s, 1H), 7.43 (t, 3J =
7.4 Hz, 1H), 7.52 (t, 3J = 7.4 Hz, 1H), 7.85 (d, 3J = 8.6 Hz, 1H), 7.89
3
3
3
(d, J = 8.4 Hz, 1H), 7.96 (d, J = 8.3 Hz, 1H), 8.19 (d, J = 8.5 Hz,
1H). 13C{1H} NMR (75 MHz, CDCl3, plus DEPT, ppm): δ = 36.2
(CH2), 56.4 (CH3), 61.0 (CH3), 61.2 (CH3), 104.8 (CH), 121.3
(CH), 123.8 (CH), 124.8 (CH), 126.2 (CH), 127.7 (CH), 128.3
(Cquat), 128.8 (CH), 130.3 (Cquat), 132.0 (Cquat), 138.4 (Cquat), 138.6
(Cquat), 139.5 (Cquat), 141.4 (Cquat), 149.1 (Cquat), 153.0 (Cquat). EI MS
(70 eV), m/z: 306 (100) [M+]. HRMS (EI): calcd for C20H18O3
306.1256, found 306.1250.
2,4-Dimethyl-13H-indeno[1,2-a]coranuulene (15h). Yellow
crystals [57.6 mg (63%)], mp 197.3−197.9 °C. 1H NMR (300
MHz, CDCl3, ppm): δ = 2.47 (s, 3H, CH3), 3.16 (s, 3H, CH3), 4.24
3
(s, 2H, CH2), 7.19 (s, 1H), 7.34 (s, 1H), 7.81 (d, J = 8.8 Hz, 1H),
7.82 (s, 2H), 7.83 (s, 2H), 7.87 (d, 3J = 8.8 Hz, 1H), 7.94 (d, 3J = 8.7
Hz, 1H), 8.25 (d, 3J = 8.9 Hz, 1H). 13C{1H} NMR (75 MHz, CDCl3,
plus DEPT, ppm): δ = 21.2 (CH3), 23.5 (CH3), 35.7 (CH2), 123.1
(CH), 125.0 (CH), 126.4 (CH), 126.79 (CH), 126.83 (CH), 126.9
(CH), 127.1 (CH), 127.6 (CH), 127.8 (CH), 128.2 (Cquat), 128.6
(Cquat), 130.1 (Cquat), 130.5 (Cquat), 130.9 (CH), 131.0 (Cquat), 131.7
(Cquat), 135.0 (Cquat), 135.77 (Cquat), 135.83 (Cquat), 135.9 (2 × Cquat),
136.1 (Cquat), 139.1 (Cquat), 140.7 (Cquat), 142.1 (Cquat), 145.0 (Cquat).
EI MS (70 eV), m/z: 366 (100) [M+], 351 (65) [M+ − CH3]. HRMS
(EI): calcd for C29H18 366.1409, found 366.1411.
11H-Benzo[b]fluorene (9a). White solid [45.9 mg (85%)]. The
1H NMR spectrum is identical to that reported in the literature.8
2,4-Dimethyl-11H-benzo[b]fluorene (9h). White solid [50.1 mg
(82%)], mp 107.2−107.9 °C. 1H NMR (300 MHz, CDCl3, ppm): δ =
2.42 (s, 3H), 2.81 (s, 3H), 4.05 (s, 2H), 7.03 (s, 1H), 7.25 (s, 1H),
7.44−7.47 (m, 2H), 7.83−7.86 (m, 1H), 7.92−7.95 (m, 1H), 7.93 (s,
1H), 8.25 (s, 1H). 13C{1H} NMR (75 MHz, CDCl3, plus DEPT,
ppm): δ = 21.2 (CH3), 21.4 (CH3), 36.4 (CH2), 120.8 (CH), 122.9
(CH), 123.3 (CH), 125.2 (CH × 2), 127.5 (CH), 128.4 (CH), 130.1
(CH), 132.2 (Cquat), 133.1 (Cquat), 133.7 (Cquat), 136.7 (Cquat), 137.2
(Cquat), 141.5 (Cquat), 141.7 (Cquat), 144.5 (Cquat). EI MS (70 eV), m/
z: 244 (100) [M+], 229 (85) [M+ − CH3]. HRMS (EI): calcd for
C19H16 244.1252, found 244.1250.
13H-Indeno[1,2-b]fluoranthene (16a). Pale yellow solid [42.1
mg (58%)], mp 162.1−162.9 °C. 1H NMR (300 MHz, CDCl3, ppm):
3
δ = 4.23 (s, 2H), 7.33−7.40 (m, 3H), 7.47 (t, J = 7.5 Hz, 1H), 7.64
3
3
(d, J = 7.1 Hz, 1H), 7.67 (d, J = 7.1 Hz, 1H), 7.88−7.98 (m, 5H),
8.30 (s, 1H). 13C{1H} NMR (75 MHz, CDCl3, plus DEPT, ppm): δ =
35.2 (CH2), 113.1 (CH), 119.4 (CH), 119.6 (CH), 121.3 (CH), 121.5
(CH), 123.6 (CH), 125.0 (CH), 126.4 (CH), 126.8 (CH), 127.3
(CH), 127.6 (CH), 128.3 (CH), 132.5 (Cquat), 136.8 (Cquat), 137.5
(Cquat), 139.5 (Cquat), 139.8 (Cquat), 140.5 (Cquat), 141.4 (Cquat), 142.6
(Cquat), 143.4 (Cquat). One Cquat cannot be observed due to signals
overlap. EI MS (70 eV), m/z: 290 (100) [M+]. HRMS (EI): calcd for
C23H14 290.1096, found 290.1098.
3-Chloro-7-methoxy-11H-benzo[b]fluorene (10j). White solid
1
[59.6 mg (85%)], mp 165.6−166.2 °C. H NMR (400 MHz, CDCl3,
3
4
ppm): δ = 3.96 (s, 3H), 4.00 (s, 2H), 7.15 (dd, J = 8.9, J = 2.4 Hz,
4
3
4
1H), 7.24 (d, J = 2.4 Hz, 1H), 7.30 (dd, J = 7.8, J = 1.8 Hz, 1H),
3
3
4
7.46 (d, J = 7.8 Hz, 1H), 7.75 (d, J = 8.9 Hz, 1H), 7.85 (d, J = 1.8
Hz, 1H), 7.87 (s, 1H), 8.07 (s, 1H). 13C{1H} NMR (100 MHz,
CDCl3, plus DEPT, ppm): δ = 35.8 (CH2), 55.3 (CH3), 106.2 (CH),
117.2 (CH), 118.6 (CH), 120.7 (CH), 123.4 (CH), 126.2 (CH),
127.3 (CH), 128.9 (Cquat), 129.2 (CH), 133.0 (Cquat), 134.1 (Cquat),
139.0 (Cquat), 139.8 (Cquat), 142.2 (Cquat), 143.0 (Cquat), 157.5 (Cquat).
EI MS (70 eV), m/z: 282/280 (22/64) [M+], 245 (100) [M+ − Cl],
3-Methyl-10,12-dihydroindeno[2,1-b]fluorene (17b). The
pure form of 17b was obtained by crystallization of a mixture of
17b and 17b′ [44.2 mg (66%), ratio 80:20] from CH2Cl2/MeOH.
1
17b. White solid, mp 202.3−203.1 °C. H NMR (300 MHz, CDCl3,
ppm): δ = 2.49 (s, 3H), 3.91 (s, 2H), 3.95 (s, 2H), 7.13 (dd, 3J = 7.5,
H
DOI: 10.1021/acs.joc.5b02111
J. Org. Chem. XXXX, XXX, XXX−XXX

The Journal of Organic Chemistry
Featured Article
3
4J = 1.1 Hz, 1H), 7.31 (t, 3J = 7.4 Hz, 1H), 7.41 (td, J = 7.4, 4J = 1.1
Synthesis of Benzo[a]fluoren-11-one. Similar to method A, but
the crude product of benzo[a]fluorene was exposed to ambient air and
stirred at room temperature for 4 h (monitored by TLC) before
treatment with hydrochloric acid at 0 °C. The title compound was
purified by chromatography on silica gel, eluting with hexane/CH2Cl2
(10:1), and obtained with a yield of 70% (40.2 mg, based on 0.25
mmol of 1-bromonaphthalene) as orange solid. The 1H NMR
spectrum is identical to that reported in the literature.17g
Hz, 1H), 7.44 (d, 3J = 7.7 Hz, 1H), 7.56 (d, 3J = 7.5 Hz, 1H), 7.68 (s,
1H), 7.71 (s, 1H), 7.88 (d, J = 7.6 Hz, 1H), 8.16 (s, 1H). 13C{1H}
3
NMR (75 MHz, CDCl3, plus DEPT, ppm): δ = 21.6 (CH3), 36.4
(CH2), 36.8 (CH2), 110.9 (CH), 119.7 (CH), 120.3 (CH), 121.7
(CH), 124.7 (CH), 125.0 (CH), 126.4 (CH), 126.7 (CH), 127.4
(CH), 136.4 (Cquat), 140.56 (Cquat), 140.59 (Cquat), 140.7 (Cquat),
141.87 (Cquat), 141.93 (Cquat), 142.4 (Cquat), 143.0 (Cquat), 143.5
(Cquat). EI MS (70 eV), m/z: 268 (100) [M+], 253 (57) [M+ − CH3].
HRMS (EI): calcd for C21H16 268.1252, found 268.1251.
ASSOCIATED CONTENT
■
13H-Indeno[2,1-a]anthracene (18a). Yellow solid [36.6 mg
(55%)], mp 248.7−249.5 °C. 1H NMR (300 MHz, CDCl3, ppm): δ =
S
* Supporting Information
4.30 (s, 2H), 7.35 (td, 3J = 7.4, J = 1.1 Hz, 1H), 7.43 (t, J = 7.5 Hz,
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.joc.5b02111.
4
3
3
3
1H), 7.46−7.52 (m, 2H), 7.67 (d, J = 7.5 Hz, 1H), 7.84 (d, J = 7.5
Hz, 1H), 7.92 (d, 3J = 8.7 Hz, 1H), 8.00−8.09 (m, 3H), 8.49 (s, 1H),
8.55 (s, 1H). 13C{1H} NMR (75 MHz, CDCl3, plus DEPT, ppm): δ =
36.0 (CH2), 118.9 (CH), 119.5 (CH), 122.1 (CH), 124.8 (CH), 125.2
(CH), 125.7 (CH), 126.2 (CH), 126.8 (CH), 127.6 (CH), 128.4 (CH
× 2), 129.3 (Cquat), 131.4 (Cquat × 2), 132.1 (Cquat), 138.3 (Cquat),
139.6 (Cquat), 142.9 (Cquat), 143.4 (Cquat). One CH cannot be
observed due to signals overlap. EI MS (70 eV), m/z: 266 (100) [M+].
HRMS (EI): calcd for C21H14 266.1096, found 266.1095.
NMR spectral data of all methylene-bridged arenes,
photoabsorption and fluorescence spectra, cyclic voltam-
mograms, and X-ray crystallographic analysis of 15h
(PDF)
crystallographic data of 15h (CIF)
13H-Indeno[1,2-b]anthracene (19a). Pale yellow solid [50.6 mg
(76%)], mp 232.4−233.1 °C. 1H NMR (300 MHz, CDCl3, ppm): δ =
4.16 (s, 2H), 7.37 (td, 3J = 7.4, 4J = 1.5 Hz, 1H), 7.40−7.48 (m, 3H),
AUTHOR INFORMATION
■
Corresponding Author
*Fax: +886-6-2740552. E-mail: ytwuchem@mail.ncku.edu.tw.
3
7.58 (d, J = 7.5 Hz, 1H), 7.97−8.03 (m, 3H), 8.09 (s, 1H), 8.35 (s,
1H), 8.42 (s, 1H), 8.51 (s, 1H). 13C{1H} NMR (75 MHz, CDCl3, plus
DEPT, ppm): δ = 36.3 (CH2), 117.5 (CH), 120.9 (CH), 123.1 (CH),
125.08 (CH), 125.11 (CH), 125.4 (CH), 125.8 (CH), 126.3 (CH),
Notes
The authors declare no competing financial interest.
127.1 (CH), 127.97 (CH), 128.03 (CH), 128.1 (CH), 131.5 (Cquat
×
ACKNOWLEDGMENTS
2), 131.6 (Cquat), 140.5 (Cquat), 140.9 (Cquat × 2), 143.9 (Cquat). One
Cquat cannot be observed due to signals overlap. EI MS (70 eV), m/z:
266 (100) [M+]. HRMS (EI): calcd for C21H14 266.1096, found:
266.1097.
6,12-Dihydroindeno[1,2-b]fluorene (20a). White solid [31.8
mg (50%)]. The 1H NMR spectrum is identical to that reported in the
literature.8
■
This work was supported by the Ministry of Science and
Technology of Taiwan (101-2628-M-006-002-MY3). We thank
Prof. Sue-Lein Wang and Ms. Pei-Lin Chen (National Tsing
Hua University, Taiwan) for the X-ray structure analyses. We
are indebted to Professor Jay Siegel (University of Zurich) for a
gift of corannulene.
3,9-Dimethyl-6,12-dihydroindeno[1,2-b]fluorene (20b).
1
White solid [44.5 mg (63%)]. The H NMR spectrum is identical
to that reported in the literature.9a
REFERENCES
■
10,12-Dihydroindeno[2,1-b]fluorene (21a). White solid [36.3
mg (57%)]. The 1H NMR spectrum is identical to that reported in the
literature.8
(1) For recent reviews, see: (a) Polyfluorenes. In Advances in Poymer
Science; Scherf, U., Neher, D., Eds.; Springer: Berlin, 2008; Vol. 212.
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M.; Lanzani, G. In Semiconducting Polymers, 2nd ed.; Hadziioannou, G.,
Malliaras, G. G., Eds.; Wiley-VCH: Weinheim, 2007; p 205.
2,4,7,9-Tetramethyl-11,14-dihydrofluoreno[2,3-b]fluorene
(22h). White solid [49.6 mg (55%)], mp >300 °C dec. 1H NMR (300
MHz, CDCl3, ppm): δ = 2.43 (s, 6H), 2.85 (s, 6H), 4.06 (s, 4H), 7.03
(s, 2H), 7.25 (s, 2H), 7.92 (s, 2H), 8.35 (s, 2H). 13C{1H} NMR (75
MHz, CDCl3, plus DEPT, ppm): δ = 21.3 (CH3), 21.4 (CH3), 36.4
(CH2), 121.4 (CH), 122.6 (CH), 123.3 (CH), 130.1 (CH), 131.0
(Cquat), 132.8 (Cquat), 133.5 (Cquat), 136.8 (Cquat), 136.9 (Cquat), 141.0
(Cquat), 141.3 (Cquat), 144.5 (Cquat). EI MS (70 eV), m/z: 360 (100)
[M+], 345 (35) [M+ − CH3]. HRMS (EI): calcd for C28H24 360.1878,
found 360.1872.
(c) Beaupre,
22, E6.
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13,16-Dihydrodiindeno[1,2-b:2′,1′-h]phenanthrene (23a).
The title compound was prepared according to method A, but it
was purified using a different method due to its low solubility in
common organic solvents. The reaction mixture at 0 °C was treated
with hydrochloric acid (2 N, 10 mL), and the collected precipitates
were washed with water (5 mL) and methanol (5 mL). The off-white
solid was loaded onto the top of a 2 cm thick layer of silica gel. Elution
with hexane/CH2Cl2 (10:1) gave 23a (78.1 mg, 88%) as a pale yellow
1
solid, mp >295 °C dec. H NMR (300 MHz, CDCl3, ppm): δ = 4.18
(s, 4H), 7.37 (t, 3J = 7.1 Hz, 2H), 7.45 (t, 3J = 7.1 Hz, 2H), 7.62 (d, 3J
3
= 7.1 Hz, 2H), 7.85 (s, 2H), 7.97 (d, J = 7.1 Hz, 2H), 8.26 (s, 2H),
8.89 (s, 2H). 13C{1H} NMR (75 MHz, CDCl3, plus DEPT, ppm): δ =
37.0 (CH2), 118.7 (CH), 118.9 (CH), 120.5 (CH), 125.2 (CH), 126.9
(CH), 127.0 (CH), 127.3 (CH), 129.8 (Cquat), 131.5 (Cquat), 140.6
(Cquat), 141.3 (Cquat), 141.9 (Cquat), 143.8 (Cquat). EI MS (70 eV), m/
z: 354 (100) [M+]. HRMS (EI): calcd for C28H18 354.1409, found
354.1410.
I
DOI: 10.1021/acs.joc.5b02111
J. Org. Chem. XXXX, XXX, XXX−XXX

The Journal of Organic Chemistry
Featured Article
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