Borylation on benzo[1,2- b:4,5- b ′]- and naphtho[1,2- b:5,6- b ′]dichalcogenophenes: Different chalcogene atom effects on borylation reaction depending on fused ring structure

Article abstract of DOI:10.1021/ol302521d

The direct borylation reactions of two types of α-silyl-protected acenedichalcogenophenes, i.e., benzo[1,2-b:4,5-b′]- and naphtho[1,2-b:5,6-b′]dichalcogenophenes, were examined, and it was observed that the reaction efficiency largely depends on the fused

Full text of DOI:10.1021/ol302521d

ORGANIC
LETTERS
Borylation on Benzo[1,2‑b:4,5‑b0]- and
Naphtho[1,2‑b:5,6‑b0]dichalcogeno-
phenes: Different Chalcogene Atom
Effects on Borylation Reaction Depending
on Fused Ring Structure
2012
Vol. 14, No. 21
5448–5451
Masahiro Nakano,†,§ Shoji Shinamura,†,§ Ryusuke Sugimoto,† Itaru Osaka,†
Eigo Miyazaki,† and Kazuo Takimiya*,†,‡
Department of Applied Chemistry, Graduate School of Engineering,
Hiroshima University, Higashi-Hiroshima 739-8527, Japan, and Emergent Molecular
Function Research Team, RIKEN Advanced Science Institute, Wako,
Saitama 351-0198, Japan
ktakimi@hiroshima-u.ac.jp
Received September 12, 2012
ABSTRACT
The direct borylation reactions of two types of R-silyl-protected acenedichalcogenophenes, i.e., benzo[1,2-b:4,5-b0]- and naphtho[1,2-b:5,6-
b0]dichalcogenophenes, were examined, and it was observed that the reaction efficiency largely depends on the fused ring structure and
chalcogenophene ring.
Direct borylation of aromatic compounds catalyzed by
Ir complexes in the presence of bis(pinacolato)diboron,
first reported by Ishiyama and co-workers,1 is a useful
reaction for the synthesis of arylboronic acid pinacol
esters,1 vital reagents for the SuzukiꢀMiyaura cross-coupling
reaction.2 Acenes such as naphthalene,3 anthracene,4
and tetracene5 can be directly borylated by the reaction
to give a regioisomeric mixture of syn- (2,7-isomer for
naphthalene and anthracene, 2,9-isomer for tetracene)
and anti-diborylated acenes (2,6-isomer for naphthalene
and anthracene, 2,8-isomer for tetracene). These bory-
lated acenes, after separation into each isomer, are useful
intermediates for the synthesis of π-extended macro-
cycles4 and organic semiconductors applicable to organic
field-effect transistors (OFETs).5
† Hiroshima University.
‡ RIKEN Advanced Science Institute.
§ These authors contributed equally.
(1) (a) Ishiyama, T.; Takagi, J.; Ishida, K.; Miyaura, N.; Anastasi,
N. R.; Hartwig, J. F. J. Am. Chem. Soc. 2002, 124, 390–391. (b)
Ishiyama, T.; Nobuta, Y.; Hartwig, J. F.; Miyaura, N. Chem. Commun.
2003, 2924–2925.
(2) Miyaura, N.; Suzuki, A. Chem. Rev. 1995, 95, 2457–2483.
(3) Coventry, D. N.; Batsanov, A. S.; Goeta, A. E.; Howard, J. A. K.;
Marder, T. B.; Perutz, R. N. Chem. Commun. 2005, 2172–2174.
(4) Ozawa, R.; Yoza, K.; Kobayashi, K. Chem. Lett. 2011, 40,
941–943.
We have recently found that the direct borylation can
take place selectively at the naphthalene core part on
(5) Kimoto, T.; Tanaka, K.; Sakai, Y.; Ohno, A.; Yoza, K.; Kobayashi,
K. Org. Lett. 2009, 11, 3658–3661.
r
10.1021/ol302521d
Published on Web 10/17/2012
2012 American Chemical Society

R-protected naphtho[1,2-b:5,6-b0]dithiophene (NDT3)6ꢀ8
and demonstrated that the resulting core-borylated NDT3
(1) is a versatile intermediate (Figure 1), which allows us to
synthesize new NDT3-based building blocks with various
substituents, including 5,10-dibromo, dichloro, dicyano,
dialkyl, dihydroxy, dialkoxy, and diester derivatives as well
as isomeric NDT3-based polymers with different main
chain structures.9 In addition, we have also found that
the same methodology consisting of the R-protection and
the coreborylation reactions isapplicabletootherisomeric
naphthodithiophenes (NDTs),9 but the efficiency of the
borylation reaction fairly depends on the fused ring struc-
ture of NDTs. Although angular-shaped NDT4 readily
afforded the corresponding borylated compound in an
excellent yield, linear-shaped NDT1 required a long reac-
tion time and excess reagent and catalyst to effect the
borylation reaction. Even under such intensified reaction
conditions, desired 5,10-diborylated NDT1 was isolated in
42% yield with a monoborylated one (57% isolated yield).
reactions on other acenedichalcogenophenes10 for the
following reasons. First, as demonstrated by the usefulness
of 1, analogous orthogonally functionalized acenedichal-
cogenophenes should be useful and can contribute to the
development of new opto/electronic materials.10 Second,
chalcogenophenes such as furan and selenophene can
give different structural perturbation on the borylation
reaction from that of thiophene, which will give the
scope of direct borylation on acenedichalcogenophenes.
We here report on the borylation chemistry of two
acenedichalcogenophene series, i.e., naphtho[1,2-b:5,6-b0]-
dichalcogenophenes6a,11 and benzo[1,2-b:4,5-b0]dichalcogeno-
phenes (Figure 2).12,13
Figure 2. Molecular structures of acenedichalcogenophenes.
Scheme 1 shows the synthesis of 5,10-bis(4,4,5,5-tetra-
methyl-1,3,2-dioxaborolan-2-yl)-2,7-bis(triisopropylsilyl)-
naphtho[1,2-b;5,6-b0]difuran (4) and -diselenophene (5).
As in the case of NDT3 with basically the same molecular
geometry, both the initial introduction of TIPS groups and
the following direct borylation under typical reaction
conductions,1 (substrate: 1 mmol, bis(pinacolato)diboron:
2 mmol, [Ir(OMe)(COD)]2: 5 μmol, dtbpy: 10 μmol, 80 °C
for 10 h in dry cyclohexane) were straightforward in giving
the corresponding R-TIPS-protected and core borylated
naphthodichalcogenophenes in good yields.
Figure 1. Molecular structures of four isomeric naphthodithio-
phenes7 and orthogonally functionalized NDT3 (1).
With these results on the borylation chemistry on the
isomeric NDTs, we were interested in similar borylation
(6) (a) Shinamura, S.; Miyazaki, E.; Takimiya, K. J. Org. Chem.
2010, 75, 1228–1234. (b) Shinamura, S.; Osaka, I.; Miyazaki, E.; Nakao,
A.; Yamagishi, M.; Takeya, J.; Takimiya, K. J. Am. Chem. Soc. 2011,
133, 5024–5035. (c) Osaka, I.; Abe, T.; Shinamura, S.; Takimiya, K.
J. Am. Chem. Soc. 2011, 133, 6852–6860. (d) Osaka, I.; Abe, T.;
Shimawaki, M.; Koganezawa, T.; Takimiya, K. ACS Macro Lett.
2012, 1, 437–440.
Scheme 1. Synthesis of Borylated NDF3 (4) and NDS3 (5)
(7) The present numbering of NDT isomers, i.e., NDT1 for naphtho-
[2,3-b:6,7-b0]dithiophene, NDT2 for naphtho[2,3-b:7,6-b0]dithiophene,
NDT3 for naphtho[1,2-b:5,6-b0]dithiophene, and NDT4 for naphtho-
[2,1-b:6,5-b0]dithiophene, is just for convenience without any scientific
significance, which follows our recent publications (ref 6b, 6c). The same
numbering for naphthodifuran (NDF) and naphthodiselenophene
(NDS) isomers are used in this communication, although not all the
isomers are discussed.
(8) Recently effective synthesis of NDT1 and NDT3 derivatives and
their application to the synthesis of oligomers and polymers were
reported. See: (a) Loser, S.; Bruns, C. J.; Miyauchi, H.; Ortiz, R. P.;
Facchetti, A.; Stupp, S. I.; Marks, T. J. J. Am. Chem. Soc. 2011, 133,
8142–8145. (b) Loser, S.; Miyauchi, H.; Hennek, J. W.; Smith, J.;
Huang, C.; Facchetti, A.; Marks, T. J. Chem. Commun. 2012, 48,
8511–8513. (c) Sanjaykumar, S. R.; Badgujar, S.; Song, C. E.; Shin,
W. S.; Moon, S.-J.; Kang, I.-N.; Lee, J.; Cho, S.; Lee, S. K.; Lee, J.-C.
Macromolecules 2012, 45, 6938–6945.
(9) Shinamura, S.; Sugimoto, R.; Yanai, N.; Takemura, N.; Kashiki,
T.; Osaka, I.; Miyazaki, E.; Takimiya, K. Org. Lett. 2012, 14, 4718–
4721.
(10) (a) Anthony, J. E. Chem. Rev. 2006, 106, 5028–5048. (b) Anthony,
J. E. Angew. Chem., Int. Ed. 2008,47, 452–483. (c) Takimiya, K.; Shinamura,
S.; Osaka, I.; Miyazaki, E. Adv. Mater. 2011, 23, 4347–4370.
(11) (a) Dingankar, P. R.; Gore, T. S.; Gogte, V. N. Indan J. Chem.
1971, 9, 24–30. (b) Nakano, M.; Shinamura, S.; Houchin, Y.; Osaka, I.;
Miyazaki, E.; Takimiya, K. Chem. Commun. 2012, 48, 5671–5673.
Org. Lett., Vol. 14, No. 21, 2012
5449

We then examined direct borylation on the benzene core
of the benzo[1,2-b:4,5-b0]dichalcogenophenes (BDF, BDT,
and BDS). Note that the direct borylation on anthracene,
an isoelectronic hydrocarbon of the present benzodichal-
cogenophenes, selectively occurs at the 2-, 6-/7-positions
and completely no borylation takes place at the peri-
positions.12 Depicted in Scheme 2 is the synthesis of 4,8-
diborylated derivatives of benzodichalcogenophenes. Dif-
ferent from the former angular-shaped naphthodithiophene
cases, the borylation was not only just less effective than the
former cases, requiring a long reaction time (∼2 days) to
obtain the diborylated compound, but also largely affected
by the chalcogen atoms, though the initial introduction of
TIPS groups, regardless of the chalcogen atoms in the
molecular framework, can be done easily.
the boron atom and the adjacent oxygen (for 9, 2.99 A),
sulfur (for 10, 3.30 A), or selenium (for 11, 3.36 A) in the
benzodichalcogenophene cores are shorter than the sum of
van der Waals radii (for BꢀO, 3.07 A, BꢀS: 3.45 A, for
BꢀSe: 3.55 A).13 Among these reaction sites, the ones on
the BDS core are most sterically hindered, being consistent
with the poor reactivity in the borylation reaction (Figure
S1). Although the large selenophene rings in BDS tend to
reduce the reactivity, it should be emphasized that the
present results are distinct from the case of anthracene, in
which the borylation does not take place at the peri-
positions. Again, this difference can be explained by steric
effects; the steric relaxation caused by the chalcogen-
ophene rings without a hydrogen atom on one side should
play a critical role in allowing the borylation reaction on
the central benzene ring in benzodichalcogenophenes.
Although all these orthogonally functionalized acenedi-
chalcogenophenes (4, 5, 9ꢀ11) have not been exploited
fully yet,9 the boryl functionality should be a useful handle
for the synthesis of interesting molecules, via not only the
Suzuki Miyaura coupling2 but also the corresponding
dibromo derivatives, which are readily converted from
the diboryl compounds. As an example for such conver-
sions, the synthesis of 4,8-dibromo-BDF (12), -BDT (13),
and -BDS (14) were demonstrated (Scheme 3).9,15,16 Re-
cent fruitful results on the BDT building blocks functio-
nalized with alkyl, alkyloxy, or aromatic substituents at
4,8-positionsin the application tosemiconducting polymer
for OPVs17 make 9ꢀ14 potential intermediates for further
material development. In fact, not just the BDT-based
polymers, the related BDF-18 or BDS-based polymers19
have been recently examined as donor materials for OPV
devices. Compared to the BDT building blocks, such BDF
and BDS building blocks functionalized at the 4,8-posi-
tions are less accessible by using the conventional synthetic
methods, and thus the present intermediates (9, 11, 12, and
14) would accelerate the development of furan- and sele-
nophene-based materials.
Scheme 2. Synthesis of Borylated BDF (9), BDT (10), and
BDS (11)
These results suggest that steric effects caused by the
adjacent chalcogenophene ring in the linear-shaped ben-
zodichalcogenophenes change the reactivity of borylation.
In fact, single crystal X-ray analyses of 9, 10, and 11
indicate that the borylated sites, 4- and 8-positions, are
fairly crowded, though at a glance they seem to have room
enough to accommodate the pinacolatoboryl groups
(Figure 3); nonbonded intramolecular distances between
In summary, we have studied the direct borylation
reaction of two series of acenedichalcogenophenes and
found that the reaction is fairly affected not only by the
molecular shape of the ring system but also by the chalco-
gene atoms in the case of the linear-shaped benzodichal-
cogenophenes. The reactivity elucidated here can be
Figure 3. Molecular structures of 9, 10, and 11 elucidated by single crystal X-ray analysis.
5450
Org. Lett., Vol. 14, No. 21, 2012

Acknowledgment. This work was partially supported
by a Grant-in-Aid for Scientific Research from the
Ministry of Education, Culture, Sports, Science and
Technology, Japan (No. 23245041), Promoting R & D
program from Japan Science and Technology Agency
(JST) of Japan, and Founding Program for World-
Leading R&D on Science and Technology (FIRST),
Japan. HRMSs were carried out at the Natural Science
Center for Basic Research and Development (N-BARD),
Hiroshima University. One of the authors (S.S.) is
grateful for the research fellowship for young scientists
from JSPS.
Scheme 3. Conversion of 9ꢀ11 to Corresponding Bromide
(12ꢀ14)
Supporting Information Available. Experimental de-
tails, spectroscopic data, and crystallographic informa-
tion files (CIF) for 9ꢀ11. This material is available free of
charge via the Internet at http://pubs.acs.org.
generally understood by the steric bulk around the boryla-
tion sites. We also demonstrated that these orthogonally
functionalized compounds are readily converted into the
corresponding dibromo compounds, which can also be a
useful intermediate for further elaborated materials applicable
to organic semiconductors. We thus hope that further materi-
al developments based on acenedichalcogenophenes will be
accelerated in the near future by using these intermediates.20
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The authors declare no competing financial interest.
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