Palladium-catalyzed amination and cyclization to heteroannellated indoles and carbazoles

New ortho-bromodiarylamines in the benzo[b]thiophene series were prepared by palladium-catalyzed amination, either in the benzene or in the thiophene ring. These were submitted to palladium-catalyzed cyclization, under different required conditions, to give several differently substituted thieno[3,2-c] or [2,3-b]carbazoles and indolo[3,2-b]benzo[b]thiophenes. This constitutes a novel synthetic route to both tetracyclic systems.     

Multibromo-N-alkylcarbazoles: synthesis, characterization, and their benzo[b]thiophene derivatives

We present an efficient method for the selective bromination of N-alkylcarbazoles using N-bromosuccinimide (NBS) in THF. Four brominated N-alkylcarbazoles including 3-bromo-, 3,6-dibromo-, 1,3,6-tribromo- and 1,3,6,8-tetrabromo-carbazoles were prepared and identified by ¹H NMR spectroscopy. Subsequent cross-coupling of these carbazoles with benzo[b]thien-2-ylboronic acid gave the corresponding benzo[b]thien-2-yl functionalized carbazoles in good yields.     

Acid-catalyzed condensation of 2,2′-diamino-1,1′-biaryls for the synthesis of benzo[c]carbazoles

2,2′-Diamino-1,1′-biaryls were found to undergo ring-closure condensation reaction to afford benzo[c]carbazoles in good to excellent yield. Coupled with the synthesis of 2,2′-biaryldiamines from diaryl hydrazides via [3,3]-sigmatropic rearrangement, it constitutes a new efficient synthetic method for benzo[c]carbazoles and related compounds.     

Facile synthesis of regio-isomeric naphthofurans and benzodifurans

Naphtho[1,2-b]furans 1a-f, naphtho[2,1-b]furans 2a-f, benzo[1,2-b:5,4-b′]difurans 3a-b, benzo[1,2-b:4,5-b′]difurans 4a-b, and benzo[1,2-b:4,3-b′]difurans 5a-b were synthesized by base-catalyzed cyclization reaction of the corresponding o-alkoxybenzoylarene derivatives. The o-alkoxybenzoylarenes were obtained from the etherification reaction of the o-hydroxybenzoylarenes, which were prepared either by the reaction of methoxyarenes with benzoyl chloride in the presence of aluminum chloride or by photo-Fries rearrangement of aryl benzoates.     

Tandem Synthesis of Benzo[b]carbazoles and Their Photoluminescent Properties

5 H‐Benzo[b]carbazoles were prepared through a tandem reaction between 2‐ethynyl‐N‐triphenylphosphoranylidene anilines and α‐diazoketones through ketenimine intermediates in moderate‐to‐good yields. By using this approach, benzo[b]benzo[5,6]indolo[3,2‐h]carbazoles, fluoreno[9,1‐ab]carbazoles, and fluoreno[9,1‐ab]fluoreno[1′,9′:5,6,7]indolo[3,2‐h]carbazoles were constructed in one pot. Moreover, the resulting products emitted light within the range 410–521 nm, with quantum yields of up to 62 %.     

A concise synthesis of novel naphtho[a]carbazoles and benzo[c]carbazoles

Starting from simple indole precursors the synthesis of naphtho[a]carbazoles and benzo[c]carbazoles is described. Key steps include the use of the Suzuki-Miyaura reaction to afford 2- or 3-aryl substituted indoles, as well as a potassium t-butoxide and light assisted aromatic ring-forming reaction.     

Synthesis,photophysical and electrochemical properties of novel 6,12-di(thiophen-2-yl) substituted indolo[3,2-b]carbazoles

Novel 5,11-dialkyl-6,12-di(thiophen-2-yl) substituted 5,11-dihydroindolo[3,2-b]carbazoles have been obtained and plausible ways for their further modifications via the Friedel–Crafts reaction are presented. The formylation of these indolo[3,2-b]carbazoles with dichloromethyl alkyl esters catalysed by Lewis acids leads to the formation of the corresponding 2,8-diformyl derivatives. Applicability of this formylation method for modification of indolo[3,2-b]carbazoles bearing electron-rich aromatic substituents at C-6 and C-12 has also been demonstrated. The Knoevenagel condensation of 2,8-dialdehydes with active methylene nitriles has been studied. The measurements of optical and redox properties for a number of new indolo[3,2-b]carbazoles have been performed.     

Photochromism of diarylethene derivatives bearing a benzo[b]silole unit

Photochromic benzo[b]silole derivatives, 1-(1,1-dimethyl-2-phenylbenzo[b]silol-3-yl)-2-(2-phenylbenzo[b]thien-3-yl)perfluorocyclopentene and 1-(1,1-dimethyl-2-phenylbenzo[b]silol-3-yl)-2-(2-phenyl-1-benzofuran-3-yl)perfluorocyclopentene, were synthesized and their photochromic performance was examined in solution.     

Synthesis and rotational barriers of atropisomers of 1,2-bis[5-(11H-benzo[b]fluorenyl)]benzenes and related compounds

Several 1,2-bis[5-(11H-benzo[b]fluorenyl)]benzenes and related compounds were synthesized via a cascade reaction sequence of the corresponding benzannulated enyne-allene precursors. The X-ray structures showed that the two benzo[b]fluorenyl moieties attached via the C5 carbons to the adjacent carbon atoms of the central benzene ring are oriented essentially perpendicular to the central benzene ring. The rates of rotation around the carbon-carbon single bonds attaching the benzo[b]fluorenyl moieties to the central benzene ring are relatively slow, allowing several anti and syn atropisomers to be separated at ambient temperature.     

Synthesis of benzimidazo[2,1-b]benzothiazole derivatives through sequential Cu-catalyzed domino coupling and Pd-catalyzed Suzuki reaction

A variety of benzo[d]benzo[4,5]imidazo[2,1-b]thiazoles were efficiently and conveniently synthesized from the Cu-catalyzed domino coupling of o-dihaloarenes with 2-mercaptobenzimidazoles. The reaction is also applicable to a series of multi-functional substrates, affording the halo-containing products with excellent selectivity. The brominated products can further react with arylboronic acids under Pd catalysis to furnish the aryl-substituted benzimidazo[2,1-b]benzothiazole derivatives.     

Heck-like coupling and Pictet-Spengler reaction for the synthesis of benzothieno[3,2-c]quinolines

A series of 6-arylbenzothieno[3,2-c]quinolines were synthesised in three steps from benzo[b]thiophene. After a selective Heck-type coupling of benzo[b]thiophene with different o-nitroaryl bromides to obtain 2-(o-nitroaryl)benzo[b]thiophenes, corresponding 2-(benzo[b]thiophen-2-yl)anilines were involved in a Pictet-Spengler reaction to form the quinoline cycle.     

Synthesis of 1,3-disubstituted benzo[c]thiophene analogs containing benzo[b]thiophene/benzo[b]pyrrole

The synthesis of 1,3-disubstituted benzo[c]thiophene analogs incorporating benzo[b]thiophene/benzo[b]pyrrole units is described.     

Microwave-assisted synthesis of novel N-(4-phenylthiazol-2-yl)-benzo[d]thiazole-, thiazolo[4,5-b]pyridine-, thiazolo[5,4-b]pyridine- and benzo[d]oxazole-2-carboximidamides inspired by marine topsentines and nortopsentines

We report the synthesis of novel N-(4-phenylthiazol-2-yl)-substituted benzo[d]thiazole-, thiazolo[4,5-b]pyridine-, thiazolo[5,4-b]pyridine- and benzo[d]oxazole-2-carboximidamides, which were inspired by marine topsentines and nortopsentines. Condensation of 4,5-dichloro-1,2,3-dithiazolium chloride (Appel salt) with various ortho-halogenated anilines, aminopyridines and aminophenols gave the corresponding aryliminodithiazoles in good to excellent yields. Copper(I)-mediated or nucleophilic-assisted cyclization of aryliminodithiazoles furnished cyano-functionalized benzo[d]thiazoles, thiazolo[4,5-b]- and thiazolo[5,4-b]-pyridines and benzo[d]oxazoles. The latter were condensed with substituted 4-phenylthiazol-2-amines to furnish twenty seven new polyaromatic carboximidamides in moderate to good yields.     

Synthesis and characterization of benzo[c]thiophene analogs incorporating benzo[b]thiophene/1-hexylindole/benzo[b]furan

Synthesis of 1,3-disubstituted benzo[c]thiophene analogs incorporating heterocycles such as benzo[b]thiophene/1-hexylindole/benzo[b]furan and thiophene units is described. Optical and electrochemical studies of the benzo[c]thiophene analogs are also reported.     

An unexpected route toward the synthesis of spiro-benzo[b]acridine-furan derivatives

A facile and straightforward procedure for the synthesis of spiro-benzo[b]acridine-6,2′-furan derivatives via the reaction between benzo[b]acridine-6,11-dione, electron-deficient acetylenic compounds, and an isocyanide is described. The benzo[b]acridine-6,11-dione is obtained from the reaction between 2-(aminomethyl)aniline and 2-hydroxynaphthalene-1,4-dione via an unexpected reaction pathway. The products are synthesized in medium to high yields and no complicated purification is required.     

Synthesis, photophysical and electrochemical properties and theoretical studies on three novel indolo[3,2-b]carbazole derivatives containing benzothiazole units

Three novel indolo[3,2-b]carbazoles derivatives were successfully synthesized by condensation reaction and structurally characterized by elemental analysis, mass spectrometry and proton nuclear magnetic resonance spectroscopy methods, which belong to donor-π-acceptor systems comprising an indolo[3,2-b]carbazole group as an electron donor and two benzothiazole rings as electron acceptors. The thermal, electrochemical and photophysical properties of the compounds were characterized by thermogravimetric analysis combined with electrochemistry, UV-vis absorption spectroscopy and fluorescence spectroscopy. On the other hand, the geometries, molecular orbitals, charge-injection and transport properties were determined by quantum chemical calculations. The results show that the compounds synthesized exhibit good thermal stability and high fluorescence quantum yields, indicating the potential application as optoelectronic materials.     

Synthesis of new benzo[b]thieno fused ring systems via transition metal-mediated cyclisations

The compact synthesis of a new ring fused benzo[b]thieno derivative with an embedded nine-membered ring system via ring closing metathesis methodology is described. The preparation of the novel 11H-benzo[b]thieno[2,3-c]pyrrolo[2,3-a]indol-11-one via palladium-mediated oxidative cyclisation of benzo[b]thien-2-oyl indole derivatives is also reported.     

Application of directed metalation in synthesis. Part 8: Interesting example of chemoselectivity in the synthesis of thioaurones and hydroxy ketones and a novel anionic ortho-Fries rearrangement used as a tool in the synthesis of thienopyranones and thiafluorenones

Chemoselective synthesis of thioaurones or 3-hydroxy benzo[b]thiophen-2-aryl ketones, 1-hydroxy naphtho[2,1-b]thiophen-2-aryl ketones and chalcones from N,N-diethyl-ortho-methyl sulfanyl aryl amides were described. (Benzo[b]thiophen-2-yl) alkylates and (naphtho[2,1-b]thiophen-2-yl) alkylates undergo a novel anionic ortho-Fries rearrangement leading to (3-hydroxy benzo[b]thiophen-2-yl) and (1-hydroxy naphtho[2,1-b]thiophen-2-yl) alkyl ketones. The hydroxy ketones were used as intermediates in the synthesis of wide range of benzothienopyranones and thiafluorenones.     

Bis benzothiophene Schiff bases: synthesis and in silico-guided biological activity studies

Since benzo [ b ] thiophene scaffold is one of the privileged structures in drug discovery as this core exhibitsactivities for different biological problems, in this study bis (benzo[ b ]thiophene-2-yl) alkyl methanimine derivatives (1-9) were synthesized by reacting benzo[ b ]thiophene-2-carbaldehyde with diamines. All newly compounds were characterized by IR, ¹H NMR and ¹³C NMR spectroscopic methods. Synthesized compounds were investigated using binary QSARbased models on therapeutic activity prediction of synthesized compounds and they showed high predicted activities in following diseases: bacterial, angina, allergy, depression and obesity. Thus, they were then tested for their antimicrobial and antileishmanial activities as a result of this theoretical study. Compound 1(N, N’- (propane-1,3-diyl) bis (1-(benzo [ b ] thiophene-2-yl)) methanimine) was found the most active compound in both diseases. Thus, its molecular docking studies were also carried out.     

Synthesis of solid state fluorescent quino[2,3-b]carbazoles via copper(II) triflate-catalyzed heteroannulation: application to detection of TNT

New analogues of solid state fluorescent quino[2,3-b]carbazoles have been synthesized from heteroannulation of quinoline alkynylaldehyde and indole. Their preliminary photophysical properties are studied and application as chemosensory material for detection of trinitrotoluene is explored.