Fluoride-Ion-Catalyzed Synthesis of Ladder-type Conjugated Benzobisbenzofurans via Intramolecular Nucleophilic Aromatic Substitution Reaction under Metal-free and Mild Conditions

Substitution Reaction under Metal-free and Mild Conditions

Letter

Fluoride-Ion-Catalyzed Synthesis of Ladder-type Conjugated

Benzobisbenzofurans via Intramolecular Nucleophilic Aromatic

Katsutoshi Sekino, Naoki Shida, Ryosuke Shiki, Natsuki Takigawa, Hiroki Nishiyama, Ikuyoshi Tomita,

and Shinsuke Inagi*

Cite This: https://dx.doi.org/10.1021/acs.orglett.0c00531

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sı Supporting Information

ABSTRACT: The ﬂuoride-ion-catalyzed synthesis of benzobis-

benzofuran derivatives is described. Fluorine-containing aryl silyl

ethers were reacted with 5 mol % of Bu NF to give desired

compounds in high yield under mild conditions. Syn-selective

cyclization reaction was discovered for a particular compound as a

kinetic product. Computational analysis revealed that the ﬂuorine

substituents in the anti-type benzobisbenzofurans aﬀect the order

of the molecular orbitals.

onjugated ladder polymers are of signiﬁcant interest for

their application in organic electronics due to their

outstanding thermal and chemical stability and eﬃcient charge

molecules is the shortest motif of the ladder-type conjugated

polybenzofurans.

Several approaches to construct dibenzofuran skeletons have

carrier mobility, arising from their planar structure in the main

been reported (Figure 2 ). Intramolecular C −C coupling

chain. Many conjugated ladder polymers have been

synthesized via a postpolymerization cyclization reaction called

ladderization. Heteroatoms are often incorporated into the

conjugated backbones due to the expectation for high

performances and the synthetic requirements. Signiﬁcant

eﬀorts have been devoted to sulfur- and nitrogen-incorporated

conjugated ladder polymers, whereas oxygen-incorporated

systems, such as ladder-type polybenzofurans (Figure 1), are

Figure 1. Structures of ladder-type polybenzofurans.

much less studied, presumably due to the lack of ladderization

strategy. Still, the oxygen-incorporated conjugated ladder

polymers attract a high level of interest based on the studies

of the small molecular analogous compounds.

In this Letter, we propose a ﬂuoride-ion-catalyzed

Figure 2. Concept of this work.

Received: February 10, 2020

nucleophilic aromatic substitution reaction (S Ar) for

ladderization, envisioning its future use in the postpolymeriza-

tion ladderization. Benzobisbenzofurans, which have two

dibenzofuran units with one shared benzene ring (i.e., n = 1

in Figure 1), are chosen as a model motif because this class of

XXXX American Chemical Society

Org. Lett. XXXX, XXX, XXX−XXX

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Letter

Table 1. Fluoride-Ion-Catalyzed Formation of Benzobisbenzofuran Derivatives 2a−e

entry

substrate

solvent

temperature (°C)

time (h)

product

yield (%)

DMF

NMP

DMF

NMP

110

200

100

200

quant.

Substrates (1a, 1d−f: 95 μmol, 1b: 64 μmol, 1c: 19 μmol) were reacted in solvents in the presence of Bu NF (5 mol %) under an Ar atmosphere.

DMF: N,N-dimethylformamide, NMP: N-methylpyrrolidone. Isolated yields.

concomitant with C −H activation from diaryl ethers is

group. MOM protection yielded 82% of the product.

Subsequently, the bromo group was replaced with boronic

acid pinacol ester, followed by deprotection of the MOM

group with hydrochloric acid, and then protected again with a

tert-butyldimethylsilyl (TBS) group, giving a total yield of 22%

for three steps. By performing Suzuki−Miyaura coupling with

bromopentaﬂuorobenzene, precursors 1a−c were obtained in

63−87% yield. 1d−f were synthesized from 2-hydroxyphe-

nylboronic acid pinacol ester in two steps (Scheme S2). 2-

Hydroxyphenylboronic acid pinacol ester was protected by the

TBS group to give the products in 90% yield. Then, 1d−f were

obtained in 82−94% yield by Suzuki−Miyaura coupling with

1,4-dibromotetraﬂuorobenzene.

widely reported with the aid of transition-metal catalysts such

as Pd, Rh, and Ag. Another approach is an intramolecular

O-arylation of 2-arylphenol based on the intramolecular

etheriﬁcation via C−H activation in the presence of Pd and

Cu catalysts. The third approach is the S Ar reaction. S Ar is

useful to introduce various functional groups by reacting with

nucleophiles without the use of any transition-metal catalysts.

Nakano et al. reported the intramolecular S Ar reaction of 2-

o-ﬂuoroaryl)phenol derivatives in the presence of inorganic

bases under high-temperature conditions.

Our strategy is a one-step approach to construct a

dibenzofuran motif from ﬂuorine-containing aryl silyl ethers

by using a catalytic amount of external ﬂuoride ions (Figure 2).

(

Precursors 1a−f were reacted with 5 mol % Bu NF at an

Such a ﬂuoride-ion-catalyzed S Ar reaction is recently gaining

elevated temperature under an argon atmosphere. Desired

ring-fused compounds 2a−e were obtained in >80% yield

(Table 1). The reaction with 1a, which has ﬁve ﬂuorine atoms,

completed in 2 h at 80 °C, whereas 1b bearing four ﬂuorine

atoms required 2 h under 110 °C, and 1c reacted completely in

4 h at 200 °C. This result was attributed to the decreasing

electron density of the aromatic ring as the number of ﬂuorines

increases, and the phenoxide ion is more likely to attack the

aromatic ring. 1d−f reacted to give the cyclized product at 90,

100, and 200 °C, respectively. It is noteworthy that the

temperature for the reaction of 1e is much lower (100 °C for 3

h) than that of 2-(o-ﬂuoroaryl)phenol derivative in the

presence of K CO (165 °C for 18 h), where analogous

renewed attention in organic and polymer synthesis due to

the transition-metal-free nature of the reaction. The reaction

proceeds under mild conditions due to the energetic advantage

of strong Si−F bond formation. A silyl ether precursor is

employed for the reaction instead of phenol derivatives, and

thus the solubility of the precursor in common organic solvents

is improved, especially in comparison with the corresponding

phenol derivatives. Besides that, only volatile trialkylsilyl-

ﬂuoride is generated as a byproduct, and thus contamination of

the end product by residual metals is avoided. Such impurities

can be problematic, especially in the production of the

polymeric materials.

The synthetic procedures for precursors 1a −c and 1d−f are

described in the Supporting Information. 1a−c were

synthesized from 2,5-dibromohydroquinone in ﬁve steps

products are obtained (Figure S1). This result indicates that

our strategy can oﬀer mild conditions for the S Ar-based

construction of the benzofuran motif.

Scheme S1). Because the borylation reaction did not proceed

Cyclization with 1d was anticipated to give two isomers, syn-

isomer 2d and anti-isomer 2d′. However, the reaction with 1d

completed in 3 h under 90 °C to give one isomer exclusively.

with silyl-protected 2,5-dibromohydroquinone under any

conditions attempted, we employed a route to protect 2,5-

dibromohydroquinone ﬁrst with a methoxymethyl (MOM)

The C{H} NMR spectrum of the isolated product showed a

Org. Lett. XXXX, XXX, XXX−XXX

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Letter

double doublet peak at 141 ppm with coupling constants of

47.5 and 15.8 Hz, indicating one-bond and two-bond

couplings with ﬂuorine atoms, respectively. These data

strongly suggest the formation of syn-isomer 2d. Single-crystal

X-ray structure analysis was also performed for the product to

conﬁrm the formation of 2d (Figure S2 ). 2d showed a planar

structure with a herringbone packing. The minimum face-to-

face distance was 3.35 Å, whereas that of nonﬂuorinated

analogue 2e was 3.49 Å (Figure S3 ). This result suggests a

stronger π−π interaction in 2d than 2e, presumably due to the

intermolecular interaction of the donor unit and the acceptor

unit in the crystalline structure of 2d. Multiple hydrogen

bonds between F−H and O−H were also conﬁrmed in the

crystal structure of 2d. These interactions are also reﬂected in

the melting point of this molecule. The melting point of 2d

was 280 °C, whereas the melting point of 2e was 185 °C. All of

these results suggest the signiﬁcant eﬀect of the introduction of

ﬂuorine atoms in the conjugated backbone.

The reaction conditions required for 1e and 1f were

surprisingly diﬀerent, although the number of ﬂuorine atoms in

the central aromatic rings was equally two. The reaction with

Figure 3. Plausible reaction mechanism.

aromatic ring to form a Meisenheimer complex, followed by

the elimination of the ﬂuoride ion. Because the ﬂuoride ion is

regenerated upon the reaction, this reaction proceeds with a

catalytic amount of ﬂuoride ions (Figure 3).

UV−vis absorption and ﬂuorescence (FL) measurements

and cyclic voltammetry (CV) measurements were performed

for product 2a−e. The absorption and FL spectra showed

mirror images, suggesting the structural rigidity of these

molecules (Figure 4 and Table S2). The largest absorption

peaks of 2a−c appeared at 312, 311, and 329 nm, respectively,

indicating that the introduction of ﬂuorine atoms causes the

^b ^l ^u ^e ^s ^h ⁱ ^f ^t ^o ^f ^λ max in anti-type molecules. Absorption spectra of

1e, where two ﬂuorine atoms locate at the ortho position,

smoothly proceeded at 100 °C to give syn-product 2e. On the

contrary, the reaction of 1f, where two ﬂuorine atoms locate at

the para position to give anti-product 2c, required 200 °C for

the completion. The diﬀerence in the reaction conditions

observed here seems to stem from the comparable reason for

the exclusive production of syn-product 2d from 1d.

To gain more insight into the selectivity of the reaction of

d, computational simulations were performed with density

functional theory (DFT). Calculations were performed at the

B3LYP or ωB97XD level of theory. Optimizations and single-

point calculations were performed on 2d and 2d′ as well as the

one-sided fused products of 1d. The corresponding Meisen-

heimer intermediates and transition states were also success-

fully simulated. The rate-determining step in common S Ar

reactions is the nucleophilic attack, whereas the elimination

step is much faster. Therefore, the transition states for the

elimination step are not discussed. The energy diagrams of

these products are shown in Figures S4 −S6. There was only a

slight diﬀerence in the energies of the end products 2d and 2d′

(

<0.20 kcal/mol). The charge density of the carbon atom

connected to the ﬂuorine atom in the one-sided cyclized

product was found to be aﬀected by the geometry, although

the charge di ﬀ erences between C_p_a_r_aand C_o_r_t_h_owere quite small

in any case (Figures S4 and S5 ). Thus the exclusive production

of syn-type 2d is not attributed to these factors. The transition

state to give syn-type was 1.1 to 1.5 kcal/mol more stable than

that of anti-type (Figures S6 and S7 ). This trend was also

conﬁrmed when a single-point calculation was performed with

the B3LYP-D3 level of theory using the 6-311G+(2df,2p) basis

set including the solvent eﬀect (Figure S8 ). From these

calculations, it was concluded that 2d was obtained as a kinetic

product. This result also explains the reason for the milder

reaction condition required for 1e than that for 1f, where the

kinetic barrier for 1e was probably smaller than that for 1f. The

cyclization of 1d at a high temperature (200 °C) in NMP

solely a ﬀ orded 2d due to the irreversibility of the reaction

Scheme S3 ).

The plausible mechanism of this reaction is shown in Figure

. First, the ﬂuoride ion derived from Bu NF deprotects the

Figure 4. Absorption (solid line) and FL (dashed line) spectra of 2a−

e. Black arrows indicate the excitation wavelength for the FL

measurement.

silyl ether to generate a phenoxide ion. The phenoxide ion

causes an intramolecular nucleophilic attack on the ﬂuorinated

Org. Lett. XXXX, XXX, XXX−XXX

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Letter

Figure 5. Orbital energy levels around the frontier orbital of 2a−e, dibenzo[a,h]anthracene, and picene simulated at the B3LYP/6-31G(d) level

theory. MOs of the HOMO−1, HOMO, and LUMO are described (iso value = 0.02).

a−c showed characteristic peaks in the 340−350 nm region.

blue-shifted compared with the experimental data, TD-DFT

well simulated each transition observed in the experimental

spectra. The TD-DFT simulation revealed that transitions at

the lowest energy region arise from the signiﬁcant contribution

of highlighted occupied orbitals (see Figure 5) to the LUMO

Similar transitions have also been reported for the anti-type

benzobisbenzothiophenes. ^F^o^r^s^yⁿ^-^t^y^p^e^m^o^l^e^c^u^l^e^s^,^λmax of

d,e was 316 and 317 nm, respectively. Because the Stokes

shifts for 2c−e were small, FL spectra were collected under the

excitation at 314, 300, and 303 nm for 2c−e, respectively,

instead of exciting with the wavelength of the largest

absorption. The normalized FL spectra were identical under

diﬀerent excitation wavelengths (Figure S9). Anti-type

compounds 2a−c showed higher internal quantum eﬃciency

(

Table S4).

In conclusion, we have successfully synthesized various

benzobisbenzofuran derivatives by using an intramolecular

S_NAr reaction with ﬂuoride ions as a catalyst under mild

conditions. This system has features such as a high yield, no

use of a transition-metal catalyst, and high solubility of the

precursor derived from the silyl group, which are ideal for the

postpolymerization ladderization to address the variety of

ladder-type conjugated polymers.

(ϕ = 0.57 to 0.64) compared with syn-type 2d,e (ϕ = 0.25 to

.44) (Table S2 ). This is probably because the anti-type

molecules show less self-absorption than syn molecules. The

electrochemical properties were evaluated by CV measurement

The Supporting Information is available free of charge at

Figure S12 ). All compounds 2a−e showed irreversible redox

behavior in 0.1 M Bu NPF /CH Cl .

To better understand the electronic structure of 2a−e,

molecular orbitals (MOs) of these compounds were simulated

with DFT calculation at the B3LYP/6-31G(d) level of theory.

Isoelectronic compounds, dibenzo[a,h]anthracene and picene,

were also simulated for comparison. Previously, it was reported

that the HOMOs of benzo[2,1-b:3,4-b′]dithiophene deriva-

tives corresponded to that of picene, whereas its oxygen

analogue showed a diﬀerent shape in the HOMO, suggesting

that the elements incorporated at the bridging position

signiﬁcantly aﬀect its MOs. Among the compounds prepared

in this study, we found that the HOMO of anti-product 2a,c or

syn-product 2d,e resembled the HOMO−1 of dibenzo[a,h]-

anthracene or picene, respectively. Accordingly, the HOMO−1

of 2a,c and 2d,e corresponds to the HOMOs of dibenzo-

ASSOCIATED CONTENT

■

sı Supporting Information

https://pubs.acs.org/doi/10.1021/acs.orglett.0c00531.

General experimental procedure, material information,

reaction conditions, and spectroscopic data (PDF)

Accession Codes

CCDC 1974979 contains the supplementary crystallographic

data for this paper. These data can be obtained free of charge

via www.ccdc.cam.ac.uk/data_request/cif , or by emailing

data_request@ccdc.cam.ac.uk , or by contacting The Cam-

bridge Crystallographic Data Centre, 12 Union Road,

Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

[

a,h]anthracene and picene, respectively (Figure 5, high-

lighted). On the contrary, 2b showed exceptional order in

MOs. The HOMO of 2b corresponds to those of dibenzo-

[

a,h]anthracene, whereas the HOMO−1 showed the shape of

the HOMO−1 of dibenzo[a,h]anthracene. This result suggests

that the substituents in the aromatic ring can alter the MOs in

this type of molecule. This tendency was also conﬁrmed when

the simulation was performed with the B3LYP-D3/def2TZVP

level of theory (Figure S13).

AUTHOR INFORMATION

■

Corresponding Author

Shinsuke Inagi − Department of Chemical Science and

Engineering, School of Materials and Chemical Technology,

Tokyo Institute of Technology, Yokohama 226-8502, Japan;

PRESTO, Japan Science and Technology Agency (JST),

Saitama 332-0012, Japan; orcid.org/0000-0002-9867-

1210 ; Email: inagi@cap.mac.titech.ac.jp

TD-DFT analysis was performed for anti-type molecules

a−c at the B3LYP/6-311G+(2df,2p) level of theory. 2a −c

showed two transitions in the 300−350 nm region (Figures

S14 −16, Table S4). Although the simulated transitions were

Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters

Authors

ault, B.; Lee, D.; Huestis, M. P.; Stuart, D. R.; Fagnou, K.

Letter

(5) (a) Lieg

Intramolecular Pd(II)-Catalyzed Oxidative Biaryl Synthesis under Air:

Katsutoshi Sekino − Department of Chemical Science and

Engineering, School of Materials and Chemical Technology,

Tokyo Institute of Technology, Yokohama 226-8502, Japan

Naoki Shida − Department of Chemical Science and

Engineering, School of Materials and Chemical Technology,

Tokyo Institute of Technology, Yokohama 226-8502, Japan

Ryosuke Shiki − Department of Chemical Science and

Engineering, School of Materials and Chemical Technology,

Tokyo Institute of Technology, Yokohama 226-8502, Japan

Natsuki Takigawa − Department of Chemical Science and

Engineering, School of Materials and Chemical Technology,

Tokyo Institute of Technology, Yokohama 226-8502, Japan

Hiroki Nishiyama − Department of Chemical Science and

Engineering, School of Materials and Chemical Technology,

Tokyo Institute of Technology, Yokohama 226-8502, Japan

Ikuyoshi Tomita − Department of Chemical Science and

Engineering, School of Materials and Chemical Technology,

Tokyo Institute of Technology, Yokohama 226-8502, Japan;

orcid.org/0000-0003-3995-5528

Reaction Development and Scope. J. Org. Chem. 2008 , 73 , 5022 −

5028. (b) Du, Z.; Zhou, J.; Si, C.; Ma, W. Synthesis of Dibenzofurans

by Palladium-Catalysed Tandem Denitrification/C-H Activation.

Synlett 2011 , 2011 , 3023 −3025. (c) Nervig, C. S.; Waller, P. J.;

Kalyani, D. Palladium-Catalyzed Intramolecular C-H Arylation of

Arenes Using Tosylates and Mesylates as Electrophiles. Org. Lett.

2012 , 14 , 4838 −4841. (d) Ferguson, D. M.; Rudolph, S. R.; Kalyani,

D. Palladium-Catalyzed Intra-and Intermolecular C-H Arylation

Using Mesylates: Synthetic Scope and Mechanistic Studies. ACS

Catal. 2014 , 4 , 2395 −2401. (e) Panda, N.; Mattan, I.; Nayak, D. K.

Synthesis of Dibenzofurans via C-H Activation of o -Iodo Diaryl

Ethers. J. Org. Chem. 2015, 80, 6590−6597.

6) Maetani, S.; Fukuyama, T.; Ryu, I. Rhodium-Catalyzed

Decarbonylative C-H Arylation of 2-Aryloxybenzoic Acids Leading

to Dibenzofuran-derivatives. Org. Lett. 2013, 15, 2754−2757.

(7) Lockner, J. W.; Dixon, D. D.; Risgaard, R.; Baran, P. S. Practical

Radical Cyclizations with Arylboronic Acids and Trifluoroborates.

Org. Lett. 2011, 13, 5628−5631.

(8) (a) Kawaguchi, K.; Nakano, K.; Nozaki, K. Synthesis of Ladder-

Type π -Conjugated Heteroacenes via Palladium-Catalyzed Double N-

Arylation and Intramolecular O -Arylation. J. Org. Chem. 2007 , 72 ,

Complete contact information is available at:

https://pubs.acs.org/10.1021/acs.orglett.0c00531

5119 −5128. (b) Wei, Y.; Yoshikai, N. Oxidative Cyclization of 2-

Arylphenols to Dibenzofurans under Pd(II)/Peroxybenzoate Catal-

ysis. Org. Lett. 2011, 13, 5504−5507. (c) Xiao, B.; Gong, T. J.; Liu, Z.

J.; Liu, J. H.; Luo, D. F.; Xu, J.; Liu, L. Synthesis of Dibenzofurans via

Palladium-Catalyzed Phenol-Directed C-H Activation/C-O Cycliza-

tion. J. Am. Chem. Soc. 2011, 133, 9250−9253.

Notes

The authors declare no competing ﬁnancial interest.

9) (a) Zhao, J.; Wang, Y.; He, Y.; Liu, L.; Zhu, Q. Cu-Catalyzed

ACKNOWLEDGMENTS

Oxidative C(sp )-H Cycloetherification of o -Arylphenols for the

Preparation of Dibenzofurans. Org. Lett. 2012 , 14 , 1078 −1081.

b) Liu, J.; Fitzgerald, A. E.; Mani, N. S. Facile Assembly of Fused

■

This study was supported by a Support for Tokyo Tech

Advanced Researchers (STAR) grant funded by the Tokyo

Institute of Technology Fund (Tokyo Tech Fund). We thank

Dr. Yoshihisa Sei at the Suzukakedai Materials Analysis

Division, Technical Department, Tokyo Institute of Technol-

ogy for single-crystal X-ray analysis.

Benzo[4,5]Furo Heterocycles. J. Org. Chem. 2008 , 73 , 2951 −2954.

10) Truong, M. A.; Nakano, K. Syntheses of Dibenzo[d,d ′]Benzo-

[

2,1-b :3,4-b ′]]Difuran-derivatives and Their Application to Organic

Field-Effect Transistors. Beilstein J. Org. Chem. 2016 , 12 , 805 −812.

(11) Liu, C.; Zang, X.; Yu, B.; Yu, X.; Xu, Q. Microwave-Promoted

TBAF-Catalyzed S Ar Reaction of Aryl Fluorides and ArSTMS: An

Efficient Synthesis of Unsymmetrical Diaryl Thioethers. Synlett 2011,

REFERENCES

■

12) (a) Wang, Y.; Watson, M. D. Transition-metal-free Synthesis of

143−1148.

Alternating Thiophene-Perfluoroarene Copolymers. J. Am. Chem. Soc.

Conjugated Ladder Polymers. Chem. Sci. 2017 , 8 , 2503 −2521.

1) (a) Lee, J.; Kalin, A. J.; Yuan, T.; Al-Hashimi, M.; Fang, L. Fully

b) Zhu, C.; Kalin, A. J.; Fang, L. Covalent and Noncovalent

Approaches to Rigid Coplanar π -Conjugated Molecules and Macro-

molecules. Acc. Chem. Res. 2019, 52, 1089−1100.

2) (a) Takagi, K.; Kato, R.; Yamamoto, S.; Masu, H. Amide-bridged

006 , 128 , 2536 −2537. (b) Dutta, T.; Woody, K. B.; Watson, M. D.

Transition-metal-free Synthesis of Poly(phenylene Ethynylene)s with

Alternating Aryl-Perfluoroaryl Units. J. Am. Chem. Soc. 2008 , 130 ,

52 −453. (c) Sanji, T.; Iyoda, T. Transition-metal-free Controlled

ladder poly(p -phenylene): synthesis by direct arylation and π -stacked

assembly. Polym. Chem. 2015 , 6 , 6792 −6795. (b) Daigle, M.; Morin,

J.-F. Helical Conjugated Ladder Polymers: Tuning the Conformation

and Properties through Edge Design. Macromolecules 2017, 50, 9257−

Polymerization of 2-Perfluoroaryl-5-trimethylsilylthiophenes. J. Am.

Chem. Soc. 2014, 136, 10238−10241.

13) Chertkov, V. A.; Sergeyev, N. M. Proton-Coupled 13 _C _N _M _R

264. (c) Hollingsworth, W. R.; Lee, J.; Fang, L.; Ayzner, A. L.

Spectra of Fluorobenzene. J. Magn. Reson. 1976, 21, 159−163.

14) Karlsson, B.; Pilotti, A.-M.; Soderholm, A.-C. Quinone

Exciton Relaxation in Highly Rigid Conjugated Polymers: Correlating

Radiative Dynamics with Structural Heterogeneity and Wavefunction

Delocalization. ACS Energy Lett. 2017, 2, 2096−2102. (d) Yin, Y.;

Zhang, S.; Chen, D.; Guo, F.; Yu, G.; Zhao, L.; Zhang, Y. Synthesis of

an Indacenodithiophene-based Fully Conjugated Ladder Polymer and

its Optical and Electronic Properties. Polym. Chem. 2018 , 9 , 2227 −

231. (e) Trilling, F.; Auslander, M.-K.; Scherf, U. Ladder-Type

Polymers and Ladder-Type Polyelectrolytes with On-chain Dibenz-

a,h ]anthracene Chromophores. Macromolecules 2019, 52, 3115−

122.

3) (a) Mei, J.; Diao, Y.; Appleton, A. L.; Fang, L.; Bao, Z. Integrated

Materials Design of Organic Semiconductors for Field-Effect

Transistors. J. Am. Chem. Soc. 2013 , 135 , 6724 −6746. (b) Anthony,

J. E. Functionalized Acenes and Heteroacenes for Organic Electronics.

Chem. Rev. 2006, 106, 5028−5048.

4) Tsuji, H.; Nakamura, E. Design and Functions of Semi-

conducting Fused Polycyclic Furans for Optoelectronic Applications.

Oligomerization. V. Structure of Benzo[1,2-b :6,5-b ]Bis[1]Benzofuran,

C H O . Acta Crystallogr., Sect. C: Cryst. Struct. Commun. 1983, 39,

(

275−1277.

15) Thalladi, V. R.; Weiss, H.-C.; Blaser, D.; Boese, R.; Nangia, A.;

Desiraju, G. R. C-H ···F Interactions in the Crystal Structures of Some

Fluorobenzenes. J. Am. Chem. Soc. 1998, 120, 8702−8710.

(16) Senger, N. A.; Bo, B.; Cheng, Q.; Keeffe, J. R.; Gronert, S.; Wu,

W. The Element Effect Revisited: Factors Determining Leaving

Group Ability in Activated Nucleophilic Aromatic Substitution

Reactions. J. Org. Chem. 2012, 77, 9535−9540.

[

18) Truong, M. A.; Nakano, K. Syntheses and Properties of Ladder-

(17) Wang, Y.; Parkin, S. R.; Gierschner, J.; Watson, M. D. Highly

Fluorinated Benzobisbenzothiophenes. Org. Lett. 2008, 10, 3307−

310.

Type π -Conjugated Compounds Containing a Benzo[2,1-b :3,4-

b ′]Dithiophene Skeleton. Bull. Chem. Soc. Jpn. 2016, 89, 1034−1040.

Acc. Chem. Res. 2017, 50, 396−406.