A Modular and Catalytic Methodology To Access 2,5-Furan-Based Phenylene/Thiophene Oligomers through a One-Pot Decarboxylative Cross-Coupling from 5-Bromofurfural

A library of 2,5-furan-based phenylene/thiophene oligomers were synthesized starting from 5-bromofurfural, a derivative of biomass-derived furfural. Varied electronic groups are coupled onto the furan motif, followed by the installation of a phenylene or thiophene central linker through a one-pot Pd-catalyzed decarboxylative cross-coupling reaction. Resulting oligomers containing the furan-phenylene-furan core possess high photoluminescent quantum yields in solution (83-98%), which are crucial for optoelectronic devices. Absorbance and photoluminescence maxima are tuned by changing peripheral functional groups and the center linker coupled onto the furan backbone.

Furan-Containing Chiral Spiro-Fused Polycyclic Aromatic Compounds: Synthesis and Photophysical Properties

Spiro-fused polycyclic aromatic compounds (PACs) have received growing interest as rigid chiral scaffolds. However, furan-containing spiro-fused PACs have been quite limited. Here, we design spiro[indeno[1,2-b][1]benzofuran-10,10′-indeno[1,2-b][1]benzothiophene] as a new family of spiro-fused PACs that contains a furan unit. The compound was successfully synthesized in enantiopure form and also transformed to its S,S-dioxide derivative and the pyrrole-containing analog via aromatic metamorphosis. The absorption and emission properties of the obtained furan-containing chiral spiro-fused PACs are apparently different from those of their thiophene analogs that have been reported, owing to the increased electron-richness of furan compared to thiophene. All of the furan-containing chiral spiro-fused PACs were found to be circularly polarized luminescent materials.

One-Pot Synthesis of Spiro-isobenzofuran Compounds via the Sequential Condensation/Oxidation Reaction of Ninhydrin with 4-Amino-1,2-naphthoquinones/2-Amino-1,4-naphthoquinones under Mild Conditions

A one-pot route for the synthesis of spiro-isobenzofuran compounds was developed via the condensation reaction of ninhydrin with 4-amino-1,2-naphthoquinones or 2-amino-1,4-naphthoquinones in acetic acid followed by the oxidative cleavage of the corresponding vicinal diols at room temperature. Various derivatives of spiro[benzo[g]indole-2,1'-isobenzofuran]-3,3',4,5(1H) tetraones and spiro[benzo[f]pyrrolo[2,3-h]quinoxaline-2,1'-isobenzofuran]-3,3'(1H)-diones were synthesized in good to high yields. Moreover, further condensation of spiro[benzo[g]indole-2,1'-isobenzofuran]-3,3',4,5(1H)-tetraones with 1,2-diamines resulted in the new spiro-isobenzofuran compounds having phenazine rings in high yields.

Structures, Lewis Acidities, Electrophilicities, and Protecting Group Abilities of Phenylfluorenylium and Tritylium Ions

The isolation, characterization, and the first X-ray structures of a fluorenylium ion and its Lewis adducts with nitrogen- and phosphorus-centered Lewis bases are reported. Kinetics of the reactions of a series of fluorenylium ions with reference π-, σ-, and n-nucleophiles of various sizes and nucleophilicities allowed the interplay between electronic and structural parameters on the electrophilicities of these planarized tertiary carbenium ions to be elucidated. Structure-reactivity correlations and extensive comparisons of their reactivities with those of di- and triarylcarbenium ions are described. Quantitative determination of the electrofugalities of fluorenylium ions revealed to which extent they are complementing tritylium ions as protecting groups and how their tuning is possible. Determination of the equilibrium constants of the Lewis adducts formation between pyridines of calibrated Lewis basicities and phenylfluorenylium and tritylium ions allowed the determination of their Lewis acidities and to showcase the potential of these carbon-centered Lewis acids in catalysis.

Palladium-catalyzed 2,5-diheteroarylation of 2,5-dibromothiophene derivatives

Conditions allowing the one pot 2,5-diheteroarylation of 2,5-dibromothiophene derivatives in the presence of palladium catalysts are reported. Using KOAc as the base, DMA as the solvent and only 0.5–2 mol % palladium catalysts, the target 2,5-diheteroarylated thiophenes were obtained in moderate to good yields and with a wide variety of heteroarenes such as thiazoles, thiophenes, furans, pyrroles, pyrazoles or isoxazoles. Moreover, sequential heteroarylation reactions allow the access to 2,5-diheteroarylated thiophenes bearing two different heteroaryl units.

Reactivity of bromofluorenes in palladium-catalysed direct arylation of heteroaromatics

The palladium-catalysed direct arylation using 2-bromofluorene or 2,7-dibromofluorene and heteroaromatics as the coupling partners proceeded using only 0.1–0.5 mol% catalyst.