Synthesis of Dibenzo[h,rst]pentaphenes and Dibenzo[fg,qr]pentacenes by the Chemoselective C-O Arylation of Dimethoxyanthraquinones

Article abstract of DOI:10.1021/acs.orglett.7b01666

A convenient method for the syntheses of dibenzo[h,rst]pentaphenes and dibenzo[fg,qr]pentacenes via the ruthenium-catalyzed chemoselective C-O arylation of 1,4- and 1,5-dimethoxyanthraquinones is described. Dimethoxyanthraquinones reacted selectively with

Full text of DOI:10.1021/acs.orglett.7b01666

Letter
pubs.acs.org/OrgLett
Synthesis of Dibenzo[h,rst]pentaphenes and
Dibenzo[fg,qr]pentacenes by the Chemoselective C−O Arylation of
Dimethoxyanthraquinones
Yusuke Suzuki,† Kohei Yamada,† Kentaro Watanabe,† Takuya Kochi,† Yutaka Ie,‡,§ Yoshio Aso,‡
and Fumitoshi Kakiuchi*,†,§
†Department of Chemistry, Faculty of Science and Technology, Keio University, 3-14-1 Hiyoshi, Kohoku-ku, Yokohama, Kanagawa
223-8522, Japan
‡The Institute of Science and Industrial Research (ISIR) Osaka University, 8-1, Mihogaoka, Ibaraki, Osaka 567-0047, Japan
§JST, ACT-C, 4-1-8 Honcho, Kawaguchi, Saitama 332-0012, Japan
S
* Supporting Information
ABSTRACT: A convenient method for the syntheses of dibenzo-
[h,rst]pentaphenes and dibenzo[fg,qr]pentacenes via the ruthenium-
catalyzed chemoselective C−O arylation of 1,4- and 1,5-dimethoxy-
anthraquinones is described. Dimethoxyanthraquinones reacted
selectively with arylboronates at the ortho C−O bonds to give
diarylation products. An efficient two-step procedure consisting of a
Corey−Chaykofsky reaction and subsequent dehydrative aromatiza-
tion afforded derivatives of dibenzo[h,rst]pentaphenes and dibenzo-
[fg,qr]pentacenes. Hole-transporting characteristics were observed
for a device with a bottom-contact configuration that was fabricated from one of these polycyclic aromatic hydrocarbons.
onsiderable interest has developed regarding the use of
Cpolycyclic aromatic hydrocarbons (PAHs) as organic
semiconductors because these compounds have unique proper-
tiesaselectronicandopticalmaterials, includingbeinglightweight
and highly flexible.1 A variety of PAHs have been synthesized for
this purpose, and their properties have been investigated. The
classes of PAHs that have been extensively studied include those
containing linearly fused aromatic rings2 such as acenes and
phenacenes and those possessing two-dimensionally extended π-
systems3−6 such as perylenes, pyrenes, and coronenes. Further
expansion of the π-systems by the synthesis of benzo-fused
versions of PAH cores has also been explored.2,3
[fg,qr]pentacenes 214 as our target molecules, because the
synthesis and electronic properties for these compounds have
received limited attention. The projected synthetic routes are
shown in Scheme 1. The chemoselective C−O arylation of 1,4-
Scheme 1. Projected Synthetic Routes of PAHs 1 and 2
Wehavebeenstudyingcatalytic arylations ofunreactive C−H,7
C−O,8 and C−N9 bonds in aromatic ketones with arylboronates
and have applied these reactions to the concise synthesis of
substituted linearly fused PAHs such as anthracenes, pentacenes,
dibenzoanthracenes, and picenes.10 Anthraquinone was used as a
template for the syntheses of highly substituted acenes, and C−
H/C−O functionalization at all four ortho positions of the
carbonyl groups was the key step.10a,c Catalytic C−O
functionalization11 has also been applied to the syntheses of
PAH derivatives by other groups such as Campana et al.12
̃
We envisioned that if the chemoselective arylation of ortho C−
OMe bonds in preference to C−H bonds could be achieved for
anthraquinone derivatives, the use of an anthraquinone derivative
possessing methoxy groups at appropriate positions as substrates
would allow us to prepare anthracene derivatives with π-systems
expanded toward the desired directions. To pursue this
possibility, we chose dibenzo[h,rst]pentaphenes 113 and dibenzo-
Received: June 2, 2017
© XXXX American Chemical Society
A
DOI: 10.1021/acs.orglett.7b01666
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
dimethoxyanthraquinone (3) with arylboronate 4 using
RuH2(CO)(PPh3)3 (5) as a catalyst would be expected to give
1,4-diarylanthraquinone 6, which could then be converted into 1
in a short sequence taking advantage of the presence of carbonyl
groups. Similarly, 1,5-dimethoxyanthraquinone (7) could be
transformed into 2. While 1 can be seen as a benzo-fused version
of pentaphene or pyrene, 2 may be regarded as a benzo-fused
pentacene or a perylene derivative.
dehydrative aromatization successfully gave the desired PAH
derivative 1. The reaction of 6a with trimethylsulfonium iodide
and sodium hydride at room temperature for 1 h gave the
corresponding diepoxide 9a.15 The screening of various Lewis
acidcatalystsshowedthatInCl316 waseffectiveforthedehydrative
aromatization of 9a to give 3,12-dimethyldibenzo[h,rst]-
pentaphene 1a (38% yield from 6a) (eq 2). After examining the
We report herein the convenient syntheses of PAHs 1 and 2
using the Ru-catalyzed chemoselective C−O arylation of
dimethoxyanthracenes with arylboronates. An efficient two-step
procedureforconvertingthediarylatedanthraquinonesto1and2
was also established.
The C−O arylation of 1,4-dimethoxyanthraquinone (3) was
first examined. The reaction of 3 with 2.5 equiv of 4-
methylphenylboronate 4a in the presence of 10 mol % of catalyst
5 in refluxing toluene for 10 h proceeded chemoselectively and
afforded 1,4-diarylanthraquinone 6a in 75% isolated yield (Table
1, entry 1). The reaction proceeds smoothly with arylboronates
reaction conditions, 1a was obtained in 40% yield from 6a by
using DMSO/THF as a solvent at 50 °C for the epoxide
formation and conducting the dehydrative aromatization without
purifying epoxide 9a by silica gel column chromatography, which
could have caused the partial degradation of 9a (Table 2, entry 1).
Table 1. Ruthenium-Catalyzed Chemoselective C−O
a
Arylation of 1,4-Dimethoxyanthraquinone (3)
Table 2. Two-Step Conversion of 1,4-Diarylanthraquinones 6
a
to Dibenzo[h,rst]pentaphenes 1
entry
4
R
6
yield (%)
1
2
3
4
5
6
7
4a
4b
4c
4d
4e
4f
Me
6a
6b
6c
6d
6e
6f
75
85
78
72
89
74
85
n-C6H13
n-C12H25
i-Pr
entry
6
R
1
yield of 1 (%, from 6)
1
2
6a
6b
6c
6d
6e
6f
Me
1a
1b
1c
1d
1e
1f
40
60
12
42
47
17
48
n-C6H13
n-C12H25
i-Pr
i-Bu
b
3
O(n-C6H13)
O(n-C12H25)
4
5
4g
6g
i-Bu
a
c
Reaction conditions: 3 (1 equiv), 4 (2.5 equiv), 5 (10 mol %),
toluene (5 mL per 1 mmol of 3), 120 °C, 10 h.
6
O(n-C6H13)
O(n-C12H25)
7
6g
1g
a
Reaction conditions: 6 (0.3 mmol), Me3SI (3 mmol), NaH (4.5
bearing various para substituents such as 4-n-hexyl- (4b), 4-n-
dodecyl- (4c), 4-iso-propyl- (4d), 4-iso-butyl- (4e), 4-n-hexyloxy-
(4f), and 4-n-dodecyloxy (4g) groups to give the corresponding
1,4-diarylanthraquinones 6b-g in 72−89% yields (entries 2−7).
TheC−Oarylation of3alsoproceeds with2-thienylboronates 4h
and 4i, and the corresponding dithienylanthraquinones 6h and 6i
were obtained in 54% and 55% yields, respectively, when 20 mol
% of catalyst 5 was used (eq 1).
mmol), DMSO (6 mL), THF (6 mL), 50 °C, 1 h, then InCl3 (0.036
b
mmol), 1,2-dichloroethane (DCE) (7.5 mL), reflux, 12 h. The
c
Corey−Chaykovsky reaction was performed at rt. The Corey−
Chaykovsky reaction was performed for 30 min.
This protocol was then applied to various 1,4-diarylanthra-
quinones, and the corresponding dibenzo[h,rst]pentaphenes
1b−g were produced in 12−60% isolated yields from 6b−g
(Table 2, entries 2−7).17
The synthesis of thiophene-containing dibenzo[h,rst]-
pentaphene analogs was examined using similar transformations.
In this case, the use of InCl3 as a catalyst for the dehydrative
aromatization was not successful, and SnCl2 was found to be a
superiorcatalyst. Thetwo-stepprotocol from6husingSnCl2 gave
a 13% yield of 1h (eq 3). Similarly, n-hexyl derivative 1i was
obtained in 6% yield from 6i. The thiophene-containing
dibenzo[h,rst]pentaphene core found in 1h and 1i without
further π-extension has not been reported.
The conversion of 1,4-diarylanthraquinone 6 to PAH
derivative 1 was then examined. A survey of various methods
revealed that the use of Corey−Chaykovsky reaction and
The three-step synthetic strategy for 1 was then applied to the
preparation of dibenzo[fg,qr]pentacene derivatives 2 using 1,5-
dimethoxyanthraquinone (7) as a substrate (Table 3). The C−O
B
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Letter
Table 3. Synthesis of Dibenzo[fg,qr]pentacenes 2 from 1,5-
a
Diarylanthraquinones 7
Figure 1. Crystal structure of 1b. (a) Top view. (b) Side view. The n-
hexyl groups are omitted for clarity.
Figure 2. Crystal structure of 2b. (a) The ORTEP drawing at a 50%
probability. H atoms are omitted for clarity. (b) Top view. (c) Side view.
In (b) and (c), the n-hexyl groups are omitted for clarity.
entry
1
4
Lewis acid
temp (°C)
8, yield (%)
2, yield (%)
4a
4b
4f
InCl3
InCl3
InCl3
SnCl2
reflux
reflux
reflux
60
8a, 64
8b, 68
8f, 80
8i, 50
2a, 55
2b, 38
2f, 48
2i, 19
b
2
3
c
4
4i
a
Reaction conditions (7 to 8): 7 (1 equiv), 4 (2.5 equiv), 5 (10 mol
%), toluene (5 mL per 1 mmol of 7), 120 °C, 10 h. Reaction
conditions (8 to 2): 8 (0.3 mmol), Me3SI (3 mmol), NaH (4.5 mmol),
DMSO (6 mL), THF (6 mL), 50 °C, 1 h, then a Lewis acid (0.036
b
mmol), 1,2-dichloroethane (DCE) (7.5 mL), reflux, 12 h. The
c
Corey−Chaykovsky reaction was performed at rt. The C−O arylation
was performed for 20 h using 20 mol % of 5.
arylation of 7 with arylboronates 4a,b,f,i provided the
corresponding 1,5-diarylated anthraquinones 8a,b,f,i in 50−
68% yields. Thesubsequent Corey−Chaykovsky reaction toform
diepoxides 10a,b,f,i, followed byLewisacid catalyzeddehydrative
aromatization gave the desired dibenzo[fg,qr]pentacene deriva-
tives 2a,b,f and the thiophene-containing analog 2i in 19−55%
yields.
The crystal structures of dibenzo[h,rst]pentaphene 1b and
dibenzo[fg,qr]pentacene 2b were obtained by X-ray diffraction
analysis. In the crystal of 1b, all of the molecules are aligned in
parallel and partially π-stacked in a columnar manner, while each
molecule points in the opposite direction from the two
neighboring molecules in the column (Figure 1). The interplanar
distances of the molecules in a column are 3.43 and 3.52 Å. In
contrast, dibenzo[fg,qr]pentacene 2b adopts a herringbone
structure in which the tilt angle is 75.1° (Figure 2). The
interplanar distances of 2b (3.32 and 3.30 Å) were slightly shorter
than those of 1b.
Disubstituted dibenzo[h,rst]pentaphenes (1) are predicted to
exhibit good OFET properties.14 Theoretical calculations by the
DFT method at the B3LYP/6-31G(d,p) level suggest that the
highest occupied molecular orbital (HOMO) of 1a is delocalized
over the molecular surface (Figure 3a) and the HOMO level of 1a
Figure 3. (a) HOMO surface of 1a. (b) Transfer characteristics of OFET
based on 1b at a drain voltage of −100 V. (c) (a) XRD data and (d) AFM
image of 1b film on HMDS-modified SiO2.
was estimated to be −5.07 eV, which is a suitable level to serve as
an active material for p-type OFETs. We chose 1b, instead of 1a,
for examining the OFET properties due to their solubility in
chlorobenzene. On the basis of the packing diagram in Figure 1,
the intermolecular transfer integral for 1b between HOMOs of π-
stacked moleculeswas estimated tobe77meVusingPW91/TZP,
as implemented in the Amsterdam Density Functional (ADF)
program. This result suggests that 1b has hole-transport
characteristics along the π-stacked direction. The OFET
performance of 1b was evaluated by employing the bottom-gate
bottom-contact configuration. The active layer was prepared on
C
DOI: 10.1021/acs.orglett.7b01666
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Letter
hexamethyldisilazane (HMDS)-modified SiO2/Si substrates by
spin-coating from a 1.0 wt % chlorobenzene solution. This
compound showed typical p-type characteristics, and the hole
mobility was found to be 1.4 × 10−3 cm2 V−1 s−1 with an on/off
current ratio of 106 and a threshold voltage of −15 V. Its transfer
characteristics are shown in Figure 3b. The structural order of 1b
in the film state was investigated by X-ray diffraction (XRD)
measurements. As shown in Figure 3c, this film displayed a clear
diffraction peak, indicating that 1b forms a crystalline structure in
thinfilms. Thepeakat2θ=3.7°correspondstoad-spacingof23.9
Å, which is almost equal to the molecular length along the long
axis (25.9 Å). This indicates that 1b is aligned in an edge-on
orientation on the SiO2 substrate. This is favorable for carrier
transport in OFETs. On the other hand, the atomic force
microscopy (AFM) image of 1b film showed the presence of large
crystalline grains that were several micrometers in size and
observable grain boundaries, resulting in moderate hole mobility.
In conclusion, we report a convenient synthetic method for
preparing dibenzo[h,rst]pentaphenes (1), dibenzo[fg,qr]penta-
cenes (2), and their thiophene-containing analogs by the
ruthenium-catalyzed coupling of 1,4- (3) and 1,5-dimethoxy-
anthraquinone (7) with aryl- and thienylboronates. The cross-
coupling proceeded selectively at the C−O bonds in the
anthraquinones to give the corresponding 1,4- and 1,5-diarylated
anthraquinones. Transformations of the carbonyl groups in the
diarylated anthraquinones to epoxides by the Corey−Chaykov-
sky reaction, followed by a Lewis acid catalyzed dehydrative
aromatization, resulted in the production of 1 and 2. Compound
1b, when fabricated on OFET devices with a bottom-contact
configuration, exhibited hole-transporting characteristics.
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ASSOCIATED CONTENT
■
S
* Supporting Information
TheSupportingInformationisavailablefreeofchargeontheACS
Publications website at DOI: 10.1021/acs.orglett.7b01666.
Full experimental details, characterization data of all new
compounds, and X-ray crystallographic data for 1b and 2b
(PDF)
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6098. (b) Koreeda, T.; Kochi, T.; Kakiuchi, F. Organometallics 2013, 32,
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Crystallographic data for 1b and 2b (CIF)
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: kakiuchi@chem.keio.ac.jp.
ORCID
(12) Mar
Sotorrios, L.; Marcos, M. L.; Choquesillo-Lazarte, D.; Biel, B.; Crovetto,
L.; Gomez-Bengoa, E.; Gonzalez, M. T.; Martin, R.; Cuerva, J. M.;
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Campana, A. G. Chem. Sci. 2017, 8, 1068.
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Fumitoshi Kakiuchi: 0000-0003-2605-4675
Notes
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The authors declare no competing financial interest.
(14) For compounds 2:Fujiyama, T.; Totani, Y.; Nakatsuka, M. (Mitsui
Chemicals, Inc., Japan). Jpn. Kokai Tokkyo Koho,JP2006303524A 2006.
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Nishinaga, S.; Nishihara, Y. Tetrahedron Lett. 2014, 55, 4002.
(17) Some of the yields of 1 were low mainly due to the difficulty in
removing some uncharacterized minor impurities.
ACKNOWLEDGMENTS
■
This work was supported in part by JSPS KAKENHI Grant
Numbers JP15H05839 in Middle Molecular Strategy, and
CREST and ACT-C (Grant Number JPMJCR12Y8) from the
Japan Science and Technology Agency (JST), Japan. T.K. is also
grateful for support by JSPS KAKENHI Grant Number
16H01040 (Precisely Designed Catalysts with Customized
Scaffolding). Dedicated to Professor Teruaki Mukaiyama in
celebration of his 90th birthday (Sotsuju).
D
DOI: 10.1021/acs.orglett.7b01666
Org. Lett. XXXX, XXX, XXX−XXX