Novel synthesis of benzo[b]carbazoles

A new method was adopted for the synthesis of benzo[b]carbazoles by Claisen condensation followed by Fischer indole cyclization. Newly synthesized benzo[b]carbazoles were treated with ethanol amine in the presence of polyphosphoric acid which leads to the formation of pyrazino carbazoles. All the synthesized compounds were characterized by all spectral means.     

Indium-catalyzed annulation of 2-aryl- and 2-heteroarylindoles with propargyl ethers: concise synthesis and photophysical properties of diverse aryl- and heteroaryl-annulated[a]carbazoles

Treatment of 2-aryl- and 2-heteroarylindoles with propargyl ethers in the presence of a catalytic amount of indium nonafluorobutanesulfonate [In(ONf)(3)] gave aryl- and heteroaryl-annulated[a]carbazoles in good yields. The synthetically attractive feature is reflected by its applicability to a wide range of 2-aryl- and 2-heteroarylindoles. In the annulation reaction, propargyl ethers act as C3 sources (HC[triple bond]C-CH(2)OR). Among these, two carbon atoms are incorporated into the product as members of a newly constructed aromatic ring and the remaining carbon atom forms a methyl group on the aromatic ring, where the methyl group is always located next to the C3 position of the indole nucleus. The methyl group can be easily removed through SeO(2) oxidation followed by decarbonylation with RhCl(CO)(PPh(3))(2)-Ph(2)P(CH(2))(3)PPh(2) as a catalyst. The new annulation strategy is applicable also to symmetrical dimers such as bithiophene and bifuran derivatives. Mechanistic studies suggest that the first step is addition reaction initiated by regioselective nucleophilic attack of the C3 of 2-aryl- and 2-heteroarylindoles to the internal carbon atom of the C[triple bond]C bond in propargyl ethers. The next stage is ring-closing S(N)2 process kicking out the alkoxy group and then aromatization via a 1,3-hydrogen shift is the final step. The two carbon-carbon bond-forming reactions achieved in one-pot contribute largely to the reduction in the number of steps for the synthesis of aryl- and heteroaryl-annulated[a]carbazoles. Furthermore, utilization of the Fischer indole synthesis for efficient supply of the substrates, 2-aryl- and 2-heteroarylindoles, is another important factor shortening the overall process. The development of the annulation with a wide substrate scope provided a unique opportunity to evaluate photophysical properties of a series of aryl- and heteroaryl-annulated[a]carbazoles. Almost all the compounds evaluated in this study were found to emit purple to green light in the visible region. Some interesting structure-property correlations are also described.     

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.     

Stereoselective synthesis of 3-alkylideneoxindoles via palladium-catalyzed domino reactions

We have developed efficient catalytic methods for the stereoselective and diversity synthesis of various (E)-, (Z)-, and disubstituted 3-alkylideneoxindoles and 3-alkylidenebenzofuran-2-ones via palladium-catalyzed Heck/Suzuki-Miyaura, Heck/Heck, and Heck/carbonylation/Suzuki-Miyaura domino reactions.     

Efficient synthesis of 5H-cyclopenta[c]quinoline derivatives via palladium-catalyzed domino reactions of o-alkynylhalobenzene with amine

A novel and efficient route for the synthesis of 5H-cyclopenta[c]quinoline derivatives via a palladium-catalyzed domino reaction of o-alkynylhalobenzene with amine is described. The starting materials are easily available, and the reaction proceeds smoothly with high efficiency, which shows broad scope with good functional group tolerance.     

One-pot synthesis of benzo[c]carbazoles by photochemical annulation of 2-chloroindole-3-carbaldehydes

A novel and efficient procedure for the synthesis of benzo[c]carbazoles has been achieved in moderate to high yields by the one-pot photochemical annulations of 2-chloroindole-3-carbaldehydes by styrenes via photodechlorination-initiated coupling of 2-chloroindole-3-carbaldehydes with styrenes, electrocyclic reactions and deformylative aromatization in the presence of pyridine.     

Base-mediated cyclization reaction of 2-alkynylphenylphosphine oxides: synthesis and photophysical properties of benzo[b]phosphole oxides

The base-mediated intramolecular cyclization reaction of 2-alkynylphenylphosphine oxides affords benzo[ b]phosphole oxides, which show intense blue-green fluorescence. Benzo[ b]phospholes are also prepared by the reduction of benzo[ b]phosphole oxides.     

Iodine-mediated cascade cyclization of enediynes to iodinated benzo[a]carbazoles

Treatment of N,N-dimethyl 2-[2-(2-ethynylphenyl)ethynyl]anilines (1) with 1.2 equiv of iodine in CH(2)Cl(2) gave benzo[a]carbazoles (2) in good yields. Mechanistic studies showed this reaction must go through the haloindole (3) followed by iodonium ion catalyzed atom-transfer cyclization reaction to give the benzo[a]carbazoles.     

A facile synthesis of indolo[3,2,1-jk]carbazoles via palladium-catalyzed intramolecular cyclization

A new efficient synthesis of indolo[3,2,1-jk]carbazoles by the palladium-catalyzed cyclization of N-(2-bromoaryl)carbazoles is described. The reaction involves intramolecular C-C bond formation, coupled with the cleavage of a C-X bond and a C-H bond on carbazole ring. Substitutions on N-aryl core with either electron-donating or electron-withdrawing groups are introduced, and different reaction factors for cyclization are evaluated.     

One-pot synthesis of carbazoles by palladium-catalyzed N-arylation and oxidative coupling

One-pot N-arylation and oxidative coupling can be promoted by a common palladium catalyst in the presence of appropriate additives: palladium-catalyzed N-arylation of anilines with aryl triflates under the standard conditions followed by addition of acetic acid under oxygen or air atmosphere afforded various types of functionalized carbazoles in good to excellent yields.     

Triazole-fused indolo[2,3-a]carbazoles: synthesis,structures, and properties

The synthesis, structure, and photophysical and electrochemical properties of triazole fused indolo[2,3-a]carbazole derivatives 2 - 5 are reported. The key step involved in the synthesis of triazole fused indolo[2,3-a]carbazole derivatives is the Cadogan ring closing reaction. 2-Hexyl-5,6-dinitro-2H-benzo[d][1,2,3]triazoles having 4,7-diaryl capping were subjected to the Cadogan cyclization reaction to obtain compounds 2-5 . In contrast to thiadiazole-fused indolo[2,3-a]carbazole 1 , bromination of triazole-fused indolo[2,3-a]carbazole 4 afforded only meta-dibrominated product with respect to the nitrogen of fused pyrrole rings on treatment with both N-bromosuccinimide (NBS) and elemental bromine. These compounds showed positive solvatochromism in their emission spectra. Incorporation of electron-donating substituent in the indole moiety resulted in the elevation of the highest occupied molecular orbital (HOMO) level. Density functional theory (DFT) calculations were performed to support the experimental findings.     

Intramolecular [4+2] cycloaddition reactions of indolylalkylpyridazines: synthesis of annulated carbazoles

Mono- and bicyclic 1,2-diazines tethered to indole dienophiles by alkylene chains were found to undergo thermally induced intramolecular Diels-Alder reactions with inverse electron demand, affording tetra- and pentacyclic condensed carbazoles.     

New domino approach for the synthesis of 2,3-disubstituted benzo[b]furans via copper-catalyzed multi-component coupling reactions followed by cyclization

An efficient domino process for the construction of 2,3-disubstituted benzo[b]furans has been developed via copper-catalyzed three-component coupling reactions of salicylaldehydes, amines, and alkynes followed by base-assisted O-annulation reaction.     

Organic semiconducting materials from sulfur-hetero benzo[k]fluoranthene derivatives: synthesis, photophysical properties, and thin film transistor fabrication

A new family of air-stable sulfur-hetero oligoarenes based on the benzo[k]fluoranthene unit has been facilely developed as the active materials for thin film organic field-effect transistors. The Diels-Alder reaction between cyclopentadienone 1 and 2,2'-(ethyne-1,2-diyl)bisthiophene followed by decarbonylation afforded fluoranthene derivative 2. After bromination and subsequent substitution through Suzuki coupling reaction, the FeCl3-oxidative cyclization produced sulfur-hetero benzo[k]fluoranthene derivatives 8-12. In dilute chloroform solution, the absorption and emission behaviors of 2 and 4-7 showed characteristic features of the fluoranthene units, while their emission lambda(max) red-shifted with an increase of the effective conjugation length. The steady state absorption and emission spectra of these newly synthesized compounds were thoroughly investigated and discussed. Thin film organic field-effect transistors (OFETs) using 8-11 as active materials were fabricated in a "top contact" configuration. Substituents at the skeleton play an important role in the film morphologies, which lead to different mobilities, while the charge mobilities of 8-11 from OFETs were improved after thermal annealing of the thin films. A carrier mobility as high as 0.083 cm(2) V(-1) s(-1) and current on/off ratio of 10(6) were achieved through vacuum-deposited film followed by the thermal annealing process from 11.     

Facile synthesis of benzo[4,5]furo[3,2-c]pyridines via palladium-catalyzed intramolecular Heck reaction

The heating of 4-chloropyridine with 2-bromophenol in either neat or DME as solvent gives rise to 2-bromophenoxy pyridines, which were treated with Pd(OAc)₂ and various ligands to afford functionalized benzo[4,5]furo[3,2-c]pyridines.     

Toluene dioxygenase-catalyzed cis-dihydroxylation of benzo[b]thiophenes and benzo[b]furans: synthesis of benzo[b]thiophene 2,3-oxide

Enzymatic cis-dihydroxylation of benzo[b]thiophene, benzo[b]furan and several methyl substituted derivatives was found to occur in both the carbocyclic and heterocyclic rings. Relative and absolute configurations and enantiopurities of the resulting dihydrodiols were determined. Hydrogenation of the alkene bond in carbocyclic cis-dihydrodiols and ring-opening epimerization/reduction reactions of heterocyclic cis/trans-dihydrodiols were also studied. The relatively stable heterocyclic dihydrodiols of benzo[b]thiophene and benzo[b]furan showed a strong preference for the trans configuration in aqueous solutions. The 2,3-dihydrodiol metabolite of benzo[b]thiophene was utilized as a precursor in the chemoenzymatic synthesis of the unstable arene oxide, benzo[b]thiophene 2,3-oxide.     

Construction of benzo[d]imidazo[2,1-b]thiazole derivatives via a simple multi-component domino cyclization

Research on Chemical Intermediates - An operationally simple and highly efficient one-pot multi-component domino cyclization for the preparation of benzo[d]imidazo[2,1-b]thiazole derivatives from...