Construction of Heteroacenes with Fused Thiophene and Pyrrole Rings via the Fischer Indolization Reaction

A general approach to construct selenopheno[3,2-b]indole-cored molecules using Fischer indolization

A wide series of various selenopheno[3,2-b]indole-based compounds, including 2-aryl-substituted selenopheno[3,2-b]indoles as well as derivatives of benzo[4,5]selenopheno[3,2-b]indole, pyrido[3',2':4,5]selenopheno[3,2-b]indole, pyrazino[2',3':4,5]selenopheno[3,2-b]indole and chromeno[3',4':4,5]selenopheno[3,2-b]indol-6-one, were prepared from the appropriate 3-aminoselenophen-2-carboxylates via a one-pot two-step procedure based on the Fischer indole synthesis. The present synthetic strategy includes the conversion of 3-aminoselenophen-2-carboxylates into 2-unsubstituted 3-aminoselenophenes, their C-2 protonation to form selenophen-3(2H)-iminium cations, and the reaction of these iminium intermediates with arylhydrazines to obtain arylhydrazones of selenophen-3(2H)-ones followed by their Fischer indolization affording selenopheno[3,2-b]indole molecules.

Thieno[3,2-b]indole–benzo[b]thieno[2,3-d]thiophen-3(2H)-one-based D–π–A molecules as electron transport materials for perovskite solar cells

New small molecule D–π–A compounds, bearing thieno[3,2-b]indole and benzo[b]thieno[2,3-d]thiophen-3(2H)-one scaffolds, were prepared, characterized and utilized as electron transport materials in perovskite solar cells.

Novel benzo[b]thieno[2,3-d]thiophene derivatives with an additional alkyl-thiophene core: synthesis, characterization, and p-type thin film transistor performance

Newly synthesized benzo[b]thieno[2,3-d]thiophene derivatives were employed as active layers of organic field effect transistors, and these transistors showed decent electrical performance.

An Approach to the Construction of Benzofuran-thieno[3,2-b]indole-Cored N,O,S-Heteroacenes Using Fischer Indolization

A series of 6H-benzofuro[2',3':4,5]thieno[3,2-b]indoles were readily synthesized from methyl 3-aminothieno[3,2-b]benzofuran-2-carboxylates using a one-pot procedure with Fischer indolization as the key step. At the same time, 3-aminothieno[3,2-b]benzofuran-2-carboxylates were prepared from 3-chlorobenzofuran-2-carbaldehydes in three steps, including replacement of the Cl atom at the C-3 position of these starting substrates onto the -SCH2CO2Me moiety, conversion of the CHO group at the C-2 position into the CN group, followed by base-promoted cyclization of the formed carbonitrile. The present route was elaborated by us because we failed to obtain directly the desired 3-aminothiophene-2-carboxylate by reaction of 3-chlorobenzofuran-2-carbonitrile with methyl thioglycolate in the presence of various bases. In turn, 3-chlorobenzofuran-2-carbaldehydes were prepared from benzofuran-3(2H)-ones following the Vilsmeier-Haack-Arnold reaction.

An Effective Route to Dithieno[3,2-b:2′,3′-d]thiophene-Based Hexaheteroacenes

A series of 12H-[1]benzo[4′′,5′′]thieno[2′′,3′′:4′,5′]thieno[2′,3′:4,5]thieno[3,2-b]indoles were efficiently prepared in three steps starting from available benzo[b]thieno[2,3-d]thiophen-3(2H)-ones. These fused ketones were treated with the Vilsmeier reagent and hydroxylamine hydrochloride to give the corresponding 3-chlorobenzo[b]thieno[2,3-d]thiophene-2-carbonitriles, which then reacted with methyl sulfanylacetate to form methyl 3-aminobenzo[4′,5′]thieno[2′,3′:4,5]thieno[3,2-b]thiophene-2-carboxylates, in accordance with the Fiesselmann thiophene synthesis protocol. Finally, the desired N,S-heterohexacenes were obtained by conversion of these fused 3-aminothiophene-2-carboxylates into the corresponding 3-aminothiophene intermediates, which acted as synthetic equivalents of thiophen-3(2H)-ones, followed by their acid-promoted reaction with arylhydrazines, in accordance with the Fischer indolization procedure.

Elemental-Sulfur-Incorporated Cyclizations of Pyrrolidines Leading to Thienopyrroles

We report, herein, the synthesis of thieno[3,2-b]pyrroles from the direct oxidative [4 + 1] cyclization of 2-alkynyl pyrrolidines with elemental sulfur. This transformation likely originates from electrophilic attack at the β-position of pyrrolidine followed by an intramolecular thienannulation to deliver the desired product. Mechanistic investigation suggests that the present reaction involves the formation of dihydrothieno[3,2-b]pyrrole as an intermediate.

Construction of 2,3-disubstituted benzo[b]thieno[2,3-d]thiophenes and benzo[4,5]selenopheno[3,2-b]thiophenes using the Fiesselmann thiophene synthesis

A series of 3-(hetero)aryl-substituted benzo[b]thieno[2,3-d]thiophenes, bearing various electron withdrawing groups at C-2 position of their scaffolds, were obtained using a convenient approach based on the Fiesselmann thiophene synthesis. To realize this strategy, the Friedel-Crafts acylation of (hetero)arenes with easily accessible 3-chlorobenzo[b]thiophene-2-carbonyl chlorides was initially performed to afford 3-chloro-2-(hetero)aroylbenzo[b]thiophenes. The latter ketones were treated either with methyl thioglycolate in the presence of DBU and calcium oxide powder or successively with sodium sulfide, an alkylating agent, containing methylene active component, and also DBU and calcium oxide, to form the desired benzo[b]thieno[2,3-d]thiophene derivatives. In addition, similar benzo[4,5]selenopheno[3,2-b]thiophene derivatives were prepared in the same manner using 3-bromobenzo[b]selenophen-2-yl substrates. The obtained functional derivatives of both benzo[b]thieno[2,3-d]thiophene and benzo[4,5]selenopheno[3,2-b]thiophene are of interest for further elaboration of organic semiconductor materials.

Benzo[b]selenophene/thieno[3,2-b]indole-Based N,S,Se-Heteroacenes for Hole-Transporting Layers

Two series of new N,S,Se-heteroacenes, namely, 6H-benzo[4',5']selenopheno[2',3':4,5]thieno[3,2-b]indoles and 12H-benzo[4″,5″]selenopheno[2″,3″:4',5']thieno[2',3'4,5]thieno[3,2-b]indoles, were successfully obtained using an effective strategy based on Fiesselmann thiophene and Fischer indole synthesis. The new molecules exhibit a large optical band gap (2.82 eV < E _g ^opt < 3.23 eV) and their highest occupied molecular orbital (HOMO) energy formed by the plane π-core ranges between -5.2 and -5.6 eV, with the narrower optical band gap and lower HOMO level corresponding to selenated heteroacenes. In thin solid films of the heteroacenes, hole mobility measured using the conventional CELIV technique ranges between 10^-5 and 10^-4 cm²·V^-1·s^-1. All these make the proposed condensed-ring compounds a promising platform for the development of hole-transporting materials applicable in organic electronics.

Synthesis of aryl-substituted thieno[3,2-b]thiophene derivatives and their use for N,S-heterotetracene construction

Fiesselmann thiophene synthesis was applied for the convenient construction of thieno[3,2-b]thiophene derivatives. Thus, new 5- or 6-aryl-3-hydroxythieno[3,2-b]thiophene-2-carboxylates were obtained by condensation of 5- or 4-aryl-3-chlorothiophene-2-carboxylates, respectively, with methyl thioglycolate in the presence of potassium tert-butoxide. The saponification of the resulting esters, with decarboxylation of the intermediating acids, gave the corresponding thieno[3,2-b]thiophen-3(2H)-ones. The latter ketones were used to synthesize new N,S-heterotetracenes, namely 9H-thieno[2',3':4,5]thieno[3,2-b]indoles by their treatment with arylhydrazines in accordance with the Fischer indolization reaction.

Fe(iii)-Catalyzed synthesis of pyrrolo[3,2-b]pyrroles: formation of new dyes and photophysical studies

A new method for the synthesis of 1,2,4,5-tetrarylpyrrolo[3,2-b]pyrroles has been developed employing iron(iii) perchlorate as a catalyst.

Synthesis of furo[3,2-b:4,5-b']diindoles and their optical and electrochemical properties

An efficient two-step palladium catalyzed synthesis of furo[3,2-b:4,5-b']diindoles, a hitherto unknown symmetrical heterocyclic core structure, was developed. The synthesis is based on a regioselective Suzuki-Miyaura cross coupling reaction of tetrabromofuran and subsequent double N-arylation. Selected compounds were studied with regard to their optical and electrochemical properties. The compounds show fluorescence with high quantum yields and non-reversible oxidation events. The compounds possess similar HOMO-LUMO band gaps compared to their sulfur and nitrogen analogs. Variation of the substituents hardly affects the HOMO-LUMO gap, but allows for some fine-tuning of the electron affinity and ionization potential as well as quantum yields. The compounds prepared represent interesting candidates for the development of organic electronic materials.

A new convenient synthetic route towards 2-(hetero)aryl-substituted thieno[3,2-b]indoles using Fischer indolization

A number of 2-(hetero)aryl-substituted thieno[3,2-b]indoles have been successfully prepared using an efficient transition-metal-free strategy, involving the Fiesselmann synthesis of methyl 5-(hetero)aryl-3-hydroxythiophene-2-carboxylates from 2-bromo-3-(hetero)arylacrylates and methyl thioglycolate, and the transformation of the synthesized 3-hydroxyesters into the corresponding thiophen-3(2H)-ones, followed by their treatment with arylhydrazines to directly form the targeted structures via Fischer indolization. At the same time, structural variety of the obtained thieno[3,2-b]indoles has been achieved due to a wide range of available starting materials, including both 2-bromo-3-(hetero)arylacrylates and arylhydrazines. In addition, two π-extended molecules, namely 1,4-bis(4H-thieno[3,2-b]indol-2-yl)benzene and 2,5-bis(4H-thieno[3,2-b]indol-2-yl)thiophene, have been synthesized in line with the current approach towards 2-(hetero)arylated thieno[3,2-b]indoles.

Dibenzothienopyrrolo[3,2-b]pyrrole: The Missing Member of the Thienoacene Family

Dibenzothienopyrrolo[3,2-b]pyrrole and the corresponding bis(S,S-dioxide) were synthesized by using a concise synthetic strategy. Despite the presence of six fused aromatic rings, π-expanded pyrrolo[3,2-b]pyrroles of this type absorb and emit at relatively short wavelengths, which reflects inefficient π conjugation due to the angular arrangement of the aromatic rings. They exhibit interesting and complex electrochemical behavior, which highlights their potential in organic electronics. Both heteroacenes undergo two-stage oxidation while retaining the independence of each 1-phenyl-1H-[1]benzothieno[3,2-b]pyrrole, which was proved by in situ electron spin resonance measurements. Interestingly, electrochemically generated dicationdiradicals are not only distributed over the pyrrolo[3,2-b]pyrrole scaffold, but also over the phenyl substituents located on nitrogen atoms.

Synthesis of Thieno[3,2-b]indoles via Halogen Dance and Ligand-Controlled One-Pot Sequential Coupling Reaction

A two-pot synthesis of thieno[3,2-b]indole from 2,5-dibromothiophene is described. A halogen dance of 2,5-dibromothiophene was performed with LDA, and subsequent Negishi coupling was performed with 2-iodoaniline derivatives to provide the corresponding coupling products. The resulting two bromo groups have different reactivities, which were utilized for the one-pot Suzuki-Miyaura coupling/intramolecular Buchwald-Hartwig amination to produce thieno[3,2-b]indole via an assisted tandem catalysis that involved in situ ligand exchange.