One-pot approach to construct benzo[4,5]thieno[3,2-b]indoles, pyrido[3′,2’:4,5]thieno[3,2-b]indoles and pyrazino[2′,3’:4,5]thieno[3,2-b]indoles based on the Fischer indole synthesis

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.

Synthesis of New Fused 4H-Thieno[3,2-b]pyrrole Derivatives via Decomposition of Methyl 4-Azido-5-arylthiophene-2-carboxylates

This article is focused on the development of practical approaches to the synthesis of 4-azido-5-arylthiophene-2-carboxylates and 4-amino-5-arylthiophene-2-carboxylates using the Fiesselmann reaction. The photochemical and thermal (including microwave-assisted) decomposition of 4-azido-5-arylthiophene-2-carboxylates have been studied in order to synthesize fused 4H-thieno[3,2-b]pyrrole derivatives. The proposed approaches allow to obtain functionally substituted heteroacenes, which are of interest as building blocks for organic semiconductors.

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.