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.     

1,3-Dipolar cycloaddition of 2- and 3-nitroindoles with azomethine ylides. A new approach to pyrrolo[3,4-b]indoles

The 1,3-dipolar cycloaddition of unstabilized azomethine ylides with 2- and 3-nitroindoles furnishes the expected hexahydropyrrolo[3,4-b]indole cycloadducts in good to excellent yields. The cycloadducts can be denitrated with Bu₃SnH/AIBN, and cycloadduct 5 was oxidized with MnO₂ to yield the known pyrrolo[3,4-b]indole 13.     

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.     

1,3-Dipolar cycloaddition of azomethine ylides generated from aziridines in supercritical carbon dioxide

The 1,3-dipolar cycloaddition of azomethine ylides with DMAD in supercritical carbon dioxide is reported. The photolysis reaction conditions were optimized with a suitable adjustment of pressure, temperature, irradiation time and co-solvent concentration leading to a more efficient reaction than in neat acetonitrile. Similar results were observed using thermal reaction conditions. Supercritical carbon dioxide with a minute co-solvent addition is shown to be a very efficient medium for promoting this type of cycloadditions.     

Direct construction of novel dispiro heterocycles through 1,3-dipolar cycloaddition of azomethine ylides

The 1,3-dipolar cycloaddition of 2-oxo-(2H)-acenaphthylen-1-ylidene-malononitrile and 2-fluoren-9-ylidene-malononitrile as dipolarophiles have been investigated for the first time with the azomethine ylides generated in situ from N-substituted isatin and sarcosine to furnish novel dispiro heterocycles. The structure and relative stereochemistry of both types of cycloadducts were confirmed by single crystal X-ray diffraction, as well as with the help of ¹H, ¹³C, and HMBC spectroscopic methods.     

Novel organic dyes containing bis-dimethylfluorenyl amino benzo[b]thiophene for highly efficient dye-sensitized solar cell

Novel organic dyes, JK-16 and JK-17 containing bis-dimethylfluorenyl amino benzo[b]thiophene are designed and synthesized. Under standard global AM 1.5 solar condition, the JK-16 sensitized cell gave a short circuit photocurrent density (J_sc) of 15.33 mA cm⁻², open circuit voltage (V_oc) of 0.74 V, and a fill factor of 0.66, corresponding to an overall conversion efficiency η of 7.43%, and the JK-17 sensitized cell gave a J_sc of 12.66 mA cm⁻², V_oc of 0.67 V, and a fill factor of 0.65, corresponding to an overall conversion efficiency η of 5.49%.     

Bromination of 3-substituted benzo[b]thiophenes: access to Raloxifen intermediate

A practical route to prepare halogeno-derivatives is described, starting from easily available 3-cyano-benzo[b]thiophene. Main efforts have been devoted to the optimization of the experimental procedures (solvent, bromination) to promote selectivity. Synthetic studies investigate the potential access to an advanced intermediate of Raloxifen.     

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.     

Microwave-assisted solvent-free intramolecular 1,3-dipolar cycloaddition reactions leading to hexahydrochromeno[4,3-b]pyrroles: scope and limitations

We report the microwave-assisted solvent-free synthesis of hexahydrochromeno[4,3-b]pyrroles. Intramolecular 1,3-dipolar cycloadditions proceed under these conditions within 15-40 min in 16-84% yields. An influence of the microwave irradiation upon various [3+2] cycloaddition reaction intermediates was studied. Additionally, a scope and limitations of these reactions including an influence of the dipolarophile geometry upon the cycloaddition selectivity and steric demands of the dipole upon its reactivity were also disclosed. These observations led us to postulate a preferable transition state of the reaction. Finally, an influence of the microwave irradiation to the isomerization of activated olefins was also described.     

Intermolecular cycloaddition of nonstabilized azomethine ylides generated from 1,3-thiazolidine-4-carboxylic acids: synthesis of 5,7a-dihydro-1H,3H-pyrrolo[1,2-c]thiazoles

The 1,3-dipolar cycloaddition of dimethyl acetylenedicarboxylate with nonstabilized azomethine ylides, generated via the decarboxylative condensation of 1,3-thiazolidine-4-carboxylic acids with aldehydes, afforded 5,7a-dihydro-1H,3H-pyrrolo[1,2-c]thiazole derivatives. 2-Substituted-1,3-thiazolidine-4-carboxylic acids led to the stereoselective formation of 5,7a-dihydro-1H,3H-pyrrolo[1,2-c]thiazoles. Quantum-chemistry calculations were carried out allowing the rationalization of the observed stereoselective formation of the anti-dipole.     

Microwave-assisted facile synthesis of [a]-annelated pyrazolopyrroloindoles via intramolecular azomethine imine 1,3-dipolar cycloaddition

The synthesis of [a]-annelated pyrazolopyrroloindoles via intramolecular 1,3-dipolar cycloaddition of in situ generated azomethine imine from N-allylated indole-2-carboxaldehyde, in regio- and stereoselective manner by using microwave irradiation is described. A one-pot strategy for the expedient synthesis of pyrazolopyrroloindoles has been developed.     

Photochromic properties of diarylethene derivatives having chryso[b]thiophene rings

Diarylethene derivatives having one or two chryso[b]thiophene ring(s) have been synthesized. In solution the derivatives underwent photochromism and the derivative with one chryso[b]thiophene ring exhibited photochromism even in the single crystalline phase. The color of the UV irradiated single crystal changed from blue to green by rotation the sample under polarized light.     

Asymmetric construction of substituted pyrrolidines via 1,3-dipolar cycloaddition of azomethine ylides and chiral acrylates derived from biomass

The first application of chiral auxiliaries synthesized from levoglucosenone (a biomass-derived anhydrosugar) in asymmetric 1,3-dipolar cycloaddition reactions of azomethine ylides is herein reported. The corresponding pyrrolidinic cores were obtained in excellent levels of regio and stereocontrol, good to excellent π-facial selectivities, and could be isolated enantiomerically pure by column chromatography. Unexpected NMR observations coupled with DFT calculations allowed the stereochemical assignment of the synthesized adducts. The stereochemical assignment performed in silico was further unambiguously validated by structural X-ray diffraction analysis.     

Synthesis of end-blocked thienyl oligomers incorporating benzo[c]thiophene

A straightforward synthesis of end-capped bithienyl, quaterthienyl and sexithienyl systems incorporating benzo[c]thiophene units is presented.     

Novel synthesis of naphtho[2,1-b]pyrano pyrrolizidines and indolizidines through intramolecular 1,3-dipolar cycloaddition reaction

A facile synthesis of a series of naphtho[2,1-b]pyrano pyrrolizidines and indolizidines was accomplished in good yields in a one-pot reaction through intramolecular 1,3-dipolar cycloaddition of azomethine ylides with Baylis-Hillman adducts as dipolarophiles. The protocol is applicable to a wide variety of photochromic and biologically active napthopyrano products. The regio and stereochemical outcome of the cycloaddition reaction was ascertained by X-ray crystallographic study of some of the products.     

A facile entry into a novel class of dispiroheterocyclic framework through 1,3-dipolarcycloaddition of azomethine ylides with 3-arylidene-4-chromanones as dipolarophiles

The cycloaddition reaction of azomethine ylides, generated through decarboxylation, with (E)-3-arylidene-4-chromanones as dipolarophiles has been investigated. A high degree of regioselectivity has been observed in the synthesis of a new class of functionalized dispiroheterocyclic compounds bearing chromanone and acenaphthenequinone framework. The structures were established by spectroscopic techniques as well as single crystal X-ray analysis.     

Highly diastereoselective 1,3-dipolar cycloaddition of nonstabilized azomethine ylides to 3-nitro-2-trihalomethyl-2H-chromenes: synthesis of 1-benzopyrano[3,4-c]pyrrolidines

Reactions of 3-nitro-2-trifluoro(trichloro)methyl-2H-chromenes, including 2-unsubstituted derivatives, with N-alkyl-α-amino acids (sarcosine, proline) and paraformaldehyde proceed diastereoselectively to give 1-benzopyrano[3,4-c]pyrrolidines in good yields as a result of a 1,3-dipolar cycloaddition of the intermediate nonstabilized azomethine ylide at the Δ³-bond of the chromene system.     

An efficient phosphine-free palladium coupling for the synthesis of new 2-arylbenzo[b]thiophenes

Straightforward and rapid access to 2-arylbenzo[b]thiophenes has been developed. It involved a catalytic coupling of 3-activated benzo[b]thiophenes with several aryl halides in the presence of a phosphine-free palladium system. In case of fragile functional groups such as aldehydes, a quaternary ammonium was used as an additive as with the other substrates, the coupling performed better and faster in the presence of a crown ether, the best one being DCH-18-C-6, with good yields and low reaction times. This method would provide a direct access to novel structures of biological interest.     

Access to 2,3-diaryl-4-nitrothiochroman S,S-dioxides from 3-nitrobenzo[b]thiophene

The base-induced cyclization of (E)-2-aryl-1-[2-(benzylsulfonyl)phenyl]-1-nitroethenes to polysubstituted thiochroman S,S-dioxides exhibits a diastereoselectivity that can be oriented towards a selected isomer by means of appropriate adjustments of the experimental conditions. The interest of such a result also rests on the promising pharmacological activity of the products, whose structure encompasses different well-acknowledged pharmacophores. A conformational ¹H NMR investigation, backed by molecular-mechanics calculations, has also been accomplished.     

1,3-Dipolar cycloaddition for selective synthesis of functionalized spiro[indoline-3,3'-pyrrolizines]

The 1,3-dipolar cycloaddition reaction of dimethyl hex-2-en-4-ynedioate with azomethine ylides derived from reaction of L-proline with various isatins in methanol selectively resulted in the formation of functionalized spiro[indoline-3,3'-pyrrolizine]acrylates as main products and spiro[indoline-3,3'-pyrrolizine]propiolates as minor products.This result indicated that the electron-deficient alkyne has higher reactivity than that of electron-deficient alkene in 1,3-dipolar cycloaddition reaction.