One-Pot Regiodirected Annulations for the Rapid Synthesis of ?-Extended Oligomers

Andrea Nitti, Peshawa Osw, Giuseppe Calcagno, Chiara Botta, Samuel I. Etkind, Gabriele Bianchi,

Letter

One-Pot Regiodirected Annulations for the Rapid Synthesis of

π ‑Extended Oligomers

∇

Riccardo Po, Timothy M. Swager, and Dario Pasini *

Cite This: https://dx.doi.org/10.1021/acs.orglett.0c01043

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sı Supporting Information

ABSTRACT: We demonstrate the broad applicability of the

annulation protocol combining, in one pot, a direct arylation and

cross aldol condensation for the straightforward synthesis at gram-

scale of π-extended thiophene-based scaﬀolds. The regiospeciﬁc

direct arylation drives the subsequent cross-aldol condensation

proceed under the same basic conditions, and the overall protocol

has broad applicability in the synthesis of extended aromatics

wherein the thiophene ring is annulated with furans, pyridines,

indoles, benzothiophenes, and benzofurans. These scaﬀolds can be

further elaborated into π-extended, highly ﬂuorescent oligomers

with a central deﬁcient benzothiadiazole unit with up to nine

aromatic rings through coupling reactions.

he discovery of novel π-conjugated molecules is of

foremost importance for the continued development of

organic semiconductors for applications in solid-state devices.

Although conjugated polymers are the current choice for solid

state organic devices as a consequence of their ﬁlm forming

and mechanical properties, the use of oligomers has been

pushed forward recently. Conjugated oligomers can share

some of the electronic properties of conjugated polymers, and

additionally present advantages over polymers, including their

well-deﬁned structure, easier puriﬁcation procedures, and lack

of chemical defects. Chemical modularity in the structures of

such oligomeric architectures allows the ﬁne-tuning of

Figure 1. E factors obtained with previous multistep literature

syntheses (black) and with our work (blue).

b′]dithiophene 2 that has a nearly 2 orders of magnitude lower

E factor when compared to previously reported multistep

absorbance, emission, and HOMO/LUMO levels.

Despite their enormous potential, large-scale applications of

π-extended organic materials are generally hampered by the

excessive costs of production, which do not yet take into

account established sustainability indexes like the E factor (kg

of organic waste/kg of product). E factor values for organic

syntheses.

In this contribution, we report the extension of scope of the

DHA-cross aldol annulation protocol to produce a library of

thiophene-annulated π-molecules. The synthetic protocol is

regiodirected and allows the study of regioisomers with

diﬀerent conjugation patterns. We were able to further

elaborate the annulated products into π-extended oligomers

of up to nine aromatic rings by incorporating benzo[c][1,2,5]-

thiadiazole (BT) units that have considerable utility in organic

semiconductors are often in the excess of 10 , in some cases

largely surpassing those for organic small molecules which are

active components of pharmaceutical formulations. Our group

has recently introduced a one-pot cascade methodology,

comprising direct arylation (DHA) and cross-aldol con-

photovoltaics, solar concentrators, OLED, and OFET.

densations as the sequence of two alkaline-mediated reactions

in a single process. The DHA step occurs regiospeciﬁcally on

the 2-position of 3-thiopheneacetic acid and facilitates the

subsequent cross aldol step, which completes the formation of

an aromatic annulated ring system. This methodology is an

Received: March 22, 2020

attractive route to annulation of π-extended thiophene-based

systems (Figure 1). For example, we developed a one-step

syntheses of naphtho[1,2-b]thiophene 1 and benzo[1,2-b:6,5-

XXXX American Chemical Society

Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters

Letter

In this library, the starting o-bromo aromatic aldehyde was

systematically varied, whereas the other key synthon for

annulation, 3-thiopheneacetic acid, was kept constant. The

structures of the newly synthesized compounds, together with

the isolated yields, are reported in Table 1. Several aldehydes

were used that incorporate electron-rich (thiophene, pyrrole,

indole, furan residues) and electron-deﬁcient (pyridine)

residues. o-Bromo aromatic aldehydes 3a−e and 3i were

commercially available, aldehyde 3f was prepared though

benzylic bromination and oxidation of the commercially

available 2-bromo-3-methylbenzothiophene, and aldehydes

Table 1. Reaction sScheme for DHA-Cross-Aldol

Condensation between o-Bromoaldehydes Used as Starting

Materials and 3-Thiopheneacetic Acid

g and 3h were prepared from commercially available 2-

coumaranone and indolin-2-one through a Vilsmeier−Hack

reaction. Conditions and full characterization details are

reported in the Supporting Information.

All of the reactions detailed in Table 1 were performed using

the same reaction conditions. The reactions were quenched

with concentrated HCl and ﬁltration gave pure carboxylic acid

products, whereas the methyl esters are easily obtained by

addition of MeI at room temperature in a one-pot procedure.

Only ﬁltration through a short silica gel pad was required to

isolate pure ester products. Excellent isolated yields were

obtained for ester and free acids in almost all entries.

Slightly lower yields were obtained with benzothiophene and

benzofuran derivatives (entries 5−7). In the case of the indole-

containing aldehyde 3h, the isolated yield of annulated

products was comparable to the previous entries (42%), but

decarboxylation occurred so that both products 15 and 16

were isolated and characterized. Both products, in the same

ratio, were obtained when reaction times were prolonged to 4

days, other conditions being equal. In the case of entry 9, the

synthesis of pyridine-thiophene mixed compound 17 using

commercially available 2-bromonicotinaldehyde 3i failed when

the reaction was carried out for 12 h, but the desired product

could be obtained in moderate yields (33%) when the reaction

was carried out for substantially longer reaction times (7 days).

This could be the result of the coordinating ability of the

nitrogen containing heterocyclic system toward the catalyst.

Our protocols are noteworthy for their eﬃciency and

regiodirected outcome. Speciﬁcally, it is possible to achieve the

rapid and high yielding synthesis of benzodithiophene (BDT)

scaﬀolds with both thiophenes on the same side (“linear”,

compound 6) or with an inverted thiophene structures (“bent”,

not previously reported in the literature, compound 8), merely

by changing the position of the bromine and aldehyde

functionalities on the starting substrates. The same complete

regiospeciﬁcity could be observed by using benzothiophene

derivatives 3e and 3f. The complete regiodirection of the

reaction is guaranteed by the previously described mecha-

nism, wherein the DHA step occurs ﬁrst and directs the

subsequent cross aldol reaction step to aﬀord the desired

product. In fact, cross-aldol byproducts occurring without

annulation were not observed in the H NMR of any of the

crude reaction mixtures reported in Table 1. The lack of

polymeric byproducts that might be expected from Pd-

calalyzed DHA homocoupling of the bromoaryls is further

proof of the high selectivity and eﬃciency of the intermolecular

DHA. The possibility to obtain both acid or ester derivatives in

one-pot procedures aﬀords a wide range of interesting

postfunctionalization scenarios.

The substitution patterns of aromatic rings generates

signiﬁcant diﬀerent conjugation pathways, and consequently

diverse physical properties. In fact, “linear” and “bent”

Yield (in parentheses) calculated after puriﬁcation by acidiﬁcation or

ﬂash chromatography. Reaction conditions: o-bromoaldehyde (1

equiv), 3-thiopheneacetic acid (1 equiv), Pd(OAc) (0,01 equiv),

PPh (0,1 equiv), K CO (3 equiv) in dry DMF (5 mL) at 110 °C for

2 h. Data taken from ref 6a. Reaction carried out for 1 week.

Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters

the H NMR spectra (Figure 2 ) of 6 and 8 revealed little

Letter

annulations produce conjugated structures, such as 6 and 8, in

which quinoidal resonance forms are much more or much less

likely to describe the molecule, respectively. These resonance

considerations are strong predictors of the electronic nature of

semiconducting polymers. Inspection of the chemical shifts in

cores to create Donor−BT−Donor (D−BT−D) architectures

(Scheme 1).

In order to improve solubility, long alkyl chains were

installed on the π-scaﬀolds of 12 and 13. Following the DHA-

cross-aldol one-pot alkylation protocol, ester derivatives 18 and

20, bearing C₂₀branched alkyl chains, were obtained in good

yields (46% and 51%, respectively). Synthons 18 and 20 were

initially screened for DHA reactivity using commercially

available BT derivative 22, obtaining 24 (46%) and 26

(

41%) after puriﬁcation by ﬂash chromatography. Side

products 28 and 29, the result of homocoupling, often

observed in DHA reactions, were isolated in minor yields (4%

and 2% respectively), and no starting material was recovered.

The extension of the DHA protocol for the synthesis of

compounds 25 and 27 using ﬂuorinated BT 23 with

compounds 18 and 20 did not lead to the formation of the

desired products. To overcome the synthetic diﬃculties

observed using the DHA protocol, we evaluated the synthesis

of compound 25 and 27 using a Stille protocol. Compounds

9 and 21 were obtained in good yields by stannylation of

_F_i_g_u_r_e₂_._S_t_a_c_k_e_d1H NMR spectra (CDCl , 400 MHz) of the

compounds 18 and 20 after lithiation by LDA and quenching

with tributyltin chloride. Compounds 25 and 27 were thus

obtained by Stille reactions in 75% and 80% yields,

respectively, after ﬂash chromatography.

aromatic region for compounds 6 (blue), 8 (green), and 10 (red).

The photophysical properties of dyes 24−27 in CHCl

diﬀerences. The diﬀerences in the H NMR are more strongly

chloroform are summarized in Table 2. The UV−vis spectra

of all compounds show a low energy band between 460 and

480 nm likely arising from π−π* transitions.

dependent on the nature of ﬁve-membered rings (thiophene or

furan, see 8 vs 10) as demonstrated by the large shift of several

proton signals. Unfortunately, a comparison between “linear”

and “bent” annulation products was not feasible for the furan

heterocycles because 2-bromofuran-3-carbaldehyde is an

unknown compound and all synthetic procedures attempted

failed to give this product. Compounds 6 and 8 show very

Table 2. Basic Properties in Solution (CHCl ) of

Compounds 24−27

compd

λ_a_b_s(nm)

ε (cm⁻mol⁻¹·L) λ_e_m(nm) QY (%) τ (ns)

314, 478

303, 480

312, 467

301, 466

1.64 × 10⁴

3.58 × 10⁴

1.65 × 10⁴

3.79 × 10⁴

590

588

569

567

4.0

4.1

2.6

3.2

similar π−π* transition energies, as indicated by the λ of

max

their UV/vis spectra with nearly superimposable emission

spectra. UV−vis and emission spectra for all compounds

synthesized are shown in the SI.

We have investigated the extension of our synthetic

protocols to generate larger π-systems. “Linear” and “bent”

benzodithiophene derivatives 12 and 13, respectively, as a

result of their high planarity and π-conjugation, were identiﬁed

as good candidates for the rapid construction of oligomers

incorporating electron-withdrawing BT units as the central

All oligomers exhibit intense broad emission bands centered

between 570 and 590 nm typical of conjugated oligomers with

substantial degrees of conformational freedom. All oligomers

are highly ﬂuorescent, with quantum yields between 0.81−0.95

and large Stokes shifts (over 100 nm). PL and UV−vis spectra

Scheme 1. Synthesis of Donor−BT−Donor Oligomers 24−27, and Structure of Side Products 28 and 29

DHA protocol: Pd(OAc) , PPh , PivOH, K CO , dry DMF, 120°C, 24 h. Stille protocol: Pd(PPh ) , dry toluene, reﬂux, 24 h.

3 4

Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters

estimated by cyclic voltammetry (Figure 3 ), displayed a

Letter

of “linear” and “bent” benzodithiophene-containing oligomeric

couples 24−26 and 25−27, respectively, show that the two

regioisomeric scaﬀolds have similar electron-donating ability

toward the BT core. Comparison of the UV−vis spectra of 24

with 25 and 26 with 27 reveal signiﬁcant red shifts of 10 nm

upon ﬂuorination. The bathochromic shifts by the introduction

of ﬂuorine in the BT backbone are in agreement with previous

FAIR data including the primary NMR FID ﬁles for

compounds 9, 10, 17, 18, 19, 20, 21, 24 , 25, 26 ( H and

C NMR) and 8, 11, 14, 15, 16, 27 (ZIP)

AUTHOR INFORMATION

Corresponding Author

■

observations. HOMO−LUMO levels of the oligomers, as

Dario Pasini − Department of Chemistry and INSTM Research

Unit, University of Pavia, 27100 Pavia, Italy; orcid.org/

000-0002-8273-3798 ; Email: dario.pasini@unipv.it

Authors

Andrea Nitti − Department of Chemistry and INSTM Research

Unit, University of Pavia, 27100 Pavia, Italy; orcid.org/

000-0002-7232-5707

Peshawa Osw − Department of Chemistry, University of Pavia,

7100 Pavia, Italy; Department of Chemistry, College of

Science, Salahaddin University, 44001 Erbil, Kurdistan, Iraq

Giuseppe Calcagno − Department of Chemistry, University of

Pavia, 27100 Pavia, Italy

Chiara Botta − Istituto per lo Studio delle Macromolecole

(

ISMAC), CNR, 20133 Milano, Italy

Samuel I. Etkind − Department of Chemistry, Massachusetts

Institute of Technology, Cambridge, Massachusetts 02139,

United States; orcid.org/0000-0002-9596-4616

Gabriele Bianchi − Research Center for Renewable Energies and

Environment, Istituto Donegani, 28100 Novara, Italy;

orcid.org/0000-0002-7448-7363

Riccardo Po − Research Center for Renewable Energies and

Environment, Istituto Donegani, 28100 Novara, Italy;

orcid.org/0000-0002-8374-195X

Figure 3. CV-derived energy level diagrams for 24−27.

detectable lowering of the HOMO level in the “bent” vs

“linear” derivative with the BT core (24 vs 26). To understand

the role of the HOMO−LUMO structures in regard to the

intended D−BT−D structures, density functional theory

Complete contact information is available at:

DFT) calculations were undertaken for oligomers 24−27

Timothy M. Swager − Department of Chemistry, Massachusetts

Institute of Technology, Cambridge, Massachusetts 02139,

United States

see Supporting Information). As expected, the HOMO is

delocalized primarily over the Donor unit, while the LUMO

resides primarily on the BT unit.

https://pubs.acs.org/10.1021/acs.orglett.0c01043

In conclusion, we have demonstrated that the DHA-cross

aldol reaction is an eﬃcient methodology for the annulation of

several heteroaryl building blocks. Our one-pot method

provides diﬀerent typologies of polycyclic extended π-systems,

with up to four fused rings containing alternating thiophene

rings with several heterocyclic systems. Four novel D−BT−D

highly emissive oligomers were synthesized, which as a

consequence of their high quantum yields and large Stokes

shifts are promising candidate for applications as luminescent

Author Contributions

^∇A.N. and P.O. contributed equally to this work.

Notes

The authors declare no competing ﬁnancial interest.

ACKNOWLEDGMENTS

■

solar concentrators. The regiodirected methodology can be

We gratefully acknowledge funding by MIUR (PRIN 2017

BOOSTER Prot. 2017YXX8AZ), Eni S.p.A., and the

University of Pavia (postdoctoral fellowship to A.N., funding

to D.P. for visiting professorship at MIT Progetto Pavia−

Boston 2019).

susceptible of various interesting modiﬁcations, developing

chromophores with substantially diﬀerent shapes for applica-

tions as organic electronic materials. Given the importance of

generating diﬀerent molecular isomers for the tailoring of

electronic and magnetic properties properties, and for the

construction of chiral helical chromophores, the presented

chemistry is a valuable new method for organic materials

community.

REFERENCES

■

1) (a) Li, H.; Shi, W.; Song, J.; Jang, H.-J.; Dailey, J.; Yu, J.; Katz, H.

E. Chemical and Biomolecule Sensing with Organic Field-Effect

Transistors. Chem. Rev. 2019 , 119 , 3 −35. (b) Torsi, L.; Magliulo, M.;

Manoli, K.; Palazzo, G. Organic field-effect transistor sensors: a

tutorial review. Chem. Soc. Rev. 2013 , 42 , 8612 −8628. (c) Usta, H.;

Facchetti, A.; Marks, T. J. n-Channel Semiconductor Materials Design

for Organic Complementary Circuits. Acc. Chem. Res. 2011 , 44 (7),

ASSOCIATED CONTENT

sı Supporting Information

■

The Supporting Information is available free of charge at

https://pubs.acs.org/doi/10.1021/acs.orglett.0c01043.

01 −510. (d) Chatterjee, T.; Wong, K. T. Perspective on Host

Full experimental details and synthetic routes of

elaborated precursors and new compounds; ﬁgures

about UV−vis and photoluminescence spectroscopy;

Materials for Thermally Activated Delayed Fluorescence Organic

Light Emitting Diodes. Adv. Opt. Mater. 2019, 7, 1800565. (e) Yang,

Z. Y.; Mao, Z.; Xie, Z. L.; Zhang, Y.; Liu, S. W.; Zhao, J.; Xu, J.; Chi,

Z.; Aldred, M. P. Recent advances in organic thermally activated

delayed fluorescence materials. Chem. Soc. Rev. 2017, 46, 915−1016.

copies of H, C NMR, ESI-MS, and GC−MS spectra

for new compounds (PDF)

Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters

Letter

f) Miao, J.; Zhang, F. Recent Progress on Photomultiplication Type

Organic Photodetectors. Laser Photonics Rev. 2018 , 13 , 1800204.

g) Ahmadi, M.; Wu, T.; Hu, B. A Review on Organic −Inorganic

(6) For selected references on annulative reactions for applications

in materials science, see: (a) Yu, J.; Yan, H.; Zhu, C. Synthesis of

Multiply Substituted Polycyclic Aromatic Hydrocarbons by Iridium-

Catalyzed Annulation of Ring-Fused Benzocyclobutenol with Alkyne

through C −C Bond Cleavage. Angew. Chem., Int. Ed. 2016, 55, 1143−

1146. (b) Koga, Y.; Kaneda, T.; Saito, Y.; Murakami, K.; Itami, K.

Synthesis of partially and fully fused polyaromatics by annulative

chlorophenylene dimerization. Science 2018 , 359 , 435 −439. (c) VanV-

eller, B.; Robinson, D.; Swager, T. M. Triptycene Diols: A Strategy for

Planar π -Systems Demonstrated by the Catalytic Conversion of a PPE

into a PPV. Angew. Chem., Int. Ed. 2012, 51, 1182−1186.

Halide Perovskite Photodetectors: Device Engineering and Funda-

mental Physics. Adv. Mater. 2017, 29, 1605242. (h) Zhang, G.; Zhao,

J.; Chow, P. C. Y.; Jiang, K.; Zhang, J.; Zhu, Z.; Zhang, J.; Huang, F.;

Yan, H. Nonfullerene Acceptor Molecules for Bulk Heterojunction

Organic Solar Cells. Chem. Rev. 2018, 118, 3447−3507. (i) Lu, L.;

Zheng, T.; Wu, Q.; Schneider, A. M.; Zhao, D.; Yu, L. Recent

Advances in Bulk Heterojunction Polymer Solar Cells. Chem. Rev.

015 , 115 , 12666 −12731. (j) Heeger, A. J. 25th anniversary article:

Bulk heterojunction solar cells: understanding the mechanism of

operation. Adv. Mater. 2014 , 26 , 10 −28. (k) McQuade, D. T.; Pullen,

A. E.; Swager, T. M. Conjugated polymer-based chemical sensors.

Chem. Rev. 2000 , 100 , 2537 −2574. (l) Cinar, M. E.; Ozturk, T.

Thienothiophenes, Dithienothiophenes, and Thienoacenes: Synthe-

ses, Oligomers, Polymers, and Properties. Chem. Rev. 2015 , 115 ,

(7) (a) Nitti, A.; Bianchi, G.; Po, R.; Swager, T. M.; Pasini, D.

Domino Direct Arylation and Cross-Aldol for Rapid Construction of

Extended Polycyclic π -Scaffolds. J. Am. Chem. Soc. 2017, 139, 8788−

8791. (b) Bianchi, G.; Nitti, A.; Pasini, D. Anthradithiophene

derivatives, process for the preparation thereof and polymers that

contain them. WO2019/175367A1. (c) Nitti, A.; Signorile, M.;

Boiocchi, M.; Bianchi, G.; Po, R.; Pasini, D. Conjugated Thiophene-

Fused Isatin Dyes through Intramolecular Direct Arylation. J. Org.

Chem. 2016, 81, 11035−11042.

036 −3140. (m) Beaujuge, P. M.; Reynolds, J. R. Color control in π -

conjugated organic polymers for use in electrochromic devices. Chem.

Rev. 2010, 110, 268−320.

(

(8) Selected examples of D−BT−D oligomers: (a) Nitti, A.; Osw,

2) (a) Grimsdale, A. C.; Chan, K. L.; Martin, R. E.; Jokisz, P. G.;

P.; Abdullah, M. N.; Galbiati, A.; Pasini, D. Scalable Synthesis of

Naphthothiophene-based D-π -D Extended Oligomers through

Cascade Direct Arylation Processes. Synlett 2018, 29, 2577−2581.

Holmes, A. B. Synthesis of Light-Emitting Conjugated Polymers for

Applications in Electroluminescent Devices. Chem. Rev. 2009, 109,

897−1091. (b) Root, S. E.; Savagatrup, S.; Printz, A. D.; Rodriquez,

(

b) Yao, S.; Kim, B.; Yue, X.; Colon Gomez, M. Y.; Bondar, M. V.;

D.; Lipomi, D. J. Mechanical Properties of Organic Semiconductors

for Stretchable, Highly Flexible, and Mechanically Robust Electronics.

Chem. Rev. 2017, 117, 6467 −6499.

Belfield, K. D. Synthesis of Near-Infrared Fluorescent Two-Photon-

Absorbing Fluorenyl Benzothiadiazole and Benzoselenadiazole

Derivatives. ACS Omega 2016, 1, 1149−1156. (c) Ellinger, S.;

Graham, K. R.; Shi, P.; Farley, R. T.; Steckler, T. T.; Brookins, R. N.;

Taranekar, P.; Mei, J.; Padilha, L. A.; Ensley, T. R.; Hu, H.; Webster,

S.; Hagan, D. J.; Van Stryland, E. W.; Schanze, K. S.; Reynolds, J. R.

Donor −Acceptor −Donor-based π -Conjugated Oligomers for Non-

linear Optics and Near-IR Emission. Chem. Mater. 2011, 23, 3805−

(3) (a) Lin, Y.; Zhan, X. Oligomer Molecules for Efficient Organic

Photovoltaics. Acc. Chem. Res. 2016, 49, 175−183. (b) Coughlin, J. E.;

Henson, Z. B.; Welch, G. C.; Bazan, G. C. Design and Synthesis of

Molecular Donors for Solution-Processed High-Efficiency Organic

Solar Cells. Acc. Chem. Res. 2014 , 47 , 257 −270. (c) Lin, Y.; Li, Y.;

Zhan, X. Small molecule semiconductors for high-efficiency organic

photovoltaics. Chem. Soc. Rev. 2012 , 41 , 4245 −4272.

817.

9) For selected examples of regiodirected reactions, see:

a) Mendez-Andino, J.; Paquette, L. A. Convergent Regiodirected

Assembly of 2,3-Disubstituted Furans. Org. Lett. 2000, 2 , 4095 −4097.

b) Anis ’kov, A. A.; Sazonov, A. A.; Klochkova, I. N. Regiodirected

(

(4) (a) Sheldon, R. A. The E Factor: Fifteen years on. Green Chem.

Pellegrino, A. All That Glisters Is Not Gold ”: An Analysis of the

007, 9, 1273 −1283. (b) Po, R.; Bianchi, G.; Carbonera, C.;

Synthetic Complexity of Efficient Polymer Donors for Polymer Solar

Cells. Macromolecules 2015, 48, 453−461. (c) Po, R.; Bernardi, A.;

Calabrese, A.; Carbonera, C.; Corso, G.; Pellegrino, A. From lab to

fab: how must the polymer solar cell materials design change? − an

industrial perspective. Energy Environ. Sci. 2014 , 7 , 925 −943.

synthesis of hydroazolic compounds with the use of thiosemicarba-

zide. Mendeleev Commun. 2009, 19, 52−53.

(10) Jung, J. W.; Liu, F.; Russell, T. P.; Jo, W. H. Fluorination on BT

consistent: Medium Bandgap Conjugated Polymer for High Perform-

ance Polymer Solar Cells Exceeding 9% Power Conversion Efficiency.

Adv. Mater. 2015, 27, 7462−7468.

(d) Nitti, A.; Po, R.; Bianchi, G.; Pasini, D. Direct Arylation

Strategies in the Synthesis of π -Extended Monomers for Organic

Polymeric Solar Cells. Molecules 2017, 22, 21−31.

(

11) (a) Barker, J. E.; Dressler, J. J.; Car

denas Valdivia, A.; Kishi, R.;

ez-García, C. J.;

Strand, E. T.; Zakharov, L. N.; MacMillan, S. N.; Gom

(5) For selected references on direct arylations for the synthesis of

Nakano, M.; Casado, J.; Haley, M. M. Molecule Isomerism Modulates

the Diradical Properties of Stable Singlet Diradicaloids. J. Am. Chem.

Soc. 2020, 142, 1548−1555. (b) Wang, P.; Lin, S.; Lin, Z.; Peeks, M.

D.; Van Voorhis, T.; Swager, T. M. A Semiconducting Conjugated

Radical Polymer: Ambipolar Redox Activity and Faraday Effect. J. Am.

Chem. Soc. 2018, 140, 10881 −10889.

conjugated oligomers and polymers for applications in materials

science, see: (a) Gobalasingham, N. S.; Thompson, B. C. Direct

arylation polymerization: A guide to optimal conditions for effective

conjugated polymers. Prog. Polym. Sci. 2018, 83, 135−201.

(b) Matsidik, R.; Komber, H.; Luzio, A.; Caironi, M.; Sommer, M.

Defect-free naphthalene diimide bithiophene copolymers with

controlled molar mass and high performance via direct arylation

polycondensation. J. Am. Chem. Soc. 2015 , 137 , 6705 −6711. (c) Bura,

T.; Morin, P.-O.; Leclerc, M. En route to defect-free polythiophene

derivatives by direct heteroarylation polymerization. Macromolecules

(12) Shen, Y.; Chen, C.-F. Helicenes: Synthesis and Applications.

Chem. Rev. 2012, 112, 1463−1535.

015, 48, 5614−5620. (d) Okamoto, J.; Zhang, J.; Housekeeper, J. B.;

Marder, S. R.; Luscombe, C. K. C −H arylation reaction: atom

efficient and greener syntheses of π -conjugated small molecules and

macromolecules for organic electronic materials. Macromolecules

013, 46, 8059−8078. (e) Sanzone, A.; Cimo, S.; Mattiello, S.;

Ruffo, R.; Facchinetti, I.; Bonacchini, G. E.; Caironi, M.; Sassi, M.;

Sommer, M.; Beverina, L. Preparation of Naphthalene Dianhydride

Bithiophene Copolymers by Direct Arylation Polycondensation and

the Latent Pigment Approach. ChemPlusChem 2019, 84, 1346−1352.

(f) Nitti, A.; Debattista, F.; Abbondanza, L.; Bianchi, G.; Po, R.;

Pasini, D. Donor −acceptor conjugated copolymers incorporating

tetrafluorobenzene as the π -electron deficient unit ’. J. Polym. Sci., Part

A: Polym. Chem. 2017, 55, 1601−1610.