Synthesis of Indole/Benzofuran-Containing Diarylmethanes through Palladium-Catalyzed Reaction of Indolylmethyl or Benzofuranylmethyl Acetates with Boronic Acids

The palladium-catalyzed synthesis of indole/benzofuran-containing diarylmethanes starting from indolylmethyl or benzofuranylmethyl acetates with boronic acids has been investigated. The success of the reaction is influenced by the choice of precatalyst: with indolylmethyl acetates the reaction works well with [Pd(η3-C3H5)Cl]2/XPhos while with benzofuranylmethyl acetates Pd2(dba)3/XPhos is more efficient. The good to high yields and the simplicity of the experimental procedure make this protocol a versatile synthetic tool for the preparation of 2- and 3-substituted indoles and 2-benzo[b]furans. The methodology can be advantageously extended to the preparation of a key precursor of Zafirlukast.

Three-Dimensional Electrochemical Oxidation of Recalcitrant Dye Using Green Iron Microparticles

This study evaluated the effect of the addition of green iron microparticles (Fe-MPs) as a three-dimensional electrode on efficiency of the electrochemical oxidation process. Polyphenols present in green tea extract act as a reducing and capping agent during green synthesis of the Fe-MPs. Scanning electron microscopy and energy-dispersive X-ray spectroscopy analysis indicates that the average size of particles is 100 µm, with about ~47 wt % of Fe in oxide form. The addition of Fe-MPs as a third electrode in the conventional electro-oxidation (EO) process converts it into a three-dimensional (3D) catalytic EO process to enhance the decolorization efficiency. Green synthesized Fe-MPs function as several microelectrodes in the process. Adsorption study indicated that only 12% of decolorization is due to adsorption on the Fe-MPs surface. Moreover, improvement in generation of hydroxyl radicals was validated by applying dimethyl sulfoxide as scavenger, and it was observed that generation of hydroxyl radicals decreased with the addition of DMSO. Results showed that decolorization efficiency increased in the 3D EO process with Fe-MPs by about 24% compared to the conventional 2D process without the Fe-MPs dosing, and initial pH as well as the Fe-MPs dose has a significant effect on decolorization efficiency during the 3D process. It is observed that reaction works better at highly acidic pH (2-4), and decolorization efficiency improved with higher doses of Fe-MPs.

N-Triflination of pyrazolones: A new method for N-S bond formation

A simple method is developed for N-triflination of pyrazolones using CF3SO2Na (Langlois reagent) and phenyliodine(III)bis(trifluoroacetate) (PIFA), which occurs quickly in 5 min. The reaction works at the imine nitrogen centre...

Preparation of Azulenes Substituted at Seven-Membered Cycle with 2- and 3-thiophenevinyl Groups

This paper comes as a continuation of our efforts to prepare vinylazulenes, moving our attention to the seven-membered azulene cycle. Several azulenic substrates were tested in order to study the possibility of preparation of poly(thiophenevinyl)azulenes, needed for the generation of dendrimeric structures. The compounds containing methyls in positions 4,6 and 8 could be condensed with 2- and 3- thiophenecarbaldehyde in tBuOK/THF yielding mono-, bis- and tris- condensed products in function of molar ratio of reagents, catalyst, solvent. The reaction works in thermodynamic control, preferring 6-position instead of 4(8)-position, which generates less stable alkenes (steric hindrance) and has a trans stereochemistry. Usually mixtures of products are obtained if more condensation position are present, even if a large aldehyde excess is used. In forcing conditions, the intermediate alcohols suffer an Oppenauer hydride transfer to the excess aldehyde, generating undesired ketones. For condensation of a methyl group situated on the five-membered cycle it must be activated by substitution with +PPh3 followed by a Wittig condensation.

Visible-light-induced addition of carboxymethanide to styrene from monochloroacetic acid

Where monochloroacetic acid is widely used as a starting material for the synthesis of relevant groups of compounds, many of these synthetic procedures are based on nucleophilic substitution of the carbon chlorine bond. Oxidative or reductive activation of monochloroacetic acid results in radical intermediates, leading to reactivity different from the traditional reactivity of this compound. Here, we investigated the possibility of applying monochloroacetic acid as a substrate for photoredox catalysis with styrene to directly produce γ-phenyl-γ-butyrolactone. Instead of using nucleophilic substitution, we cleaved the carbon chlorine bond by single-electron reduction, creating a radical species. We observed that the reaction works best in nonpolar solvents. The reaction does not go to full conversion, but selectively forms γ-phenyl-γ-butyrolactone and 4-chloro-4-phenylbutanoic acid. Over time the catalyst precipitates from solution (perhaps in a decomposed form in case of fac-[Ir(ppy)3]), which was proven by mass spectrometry and EPR spectroscopy for one of the catalysts (N,N-5,10-di(2-naphthalene)-5,10-dihydrophenazine) used in this work. The generation of HCl resulting from lactone formation could be an additional problem for organometallic photoredox catalysts used in this reaction. In an attempt to trap one of the radical intermediates with TEMPO, we observed a compound indicating the generation of a chloromethyl radical.

Gold-catalyzed cyclization of 1-(2′-azidoaryl) propynols: synthesis of polysubstituted 4-quinolones

α-Imino gold carbene intermediate is produced from 1-(2′-azidoaryl) propynols, which triggers a 1,2-carbon migration and is converted to 2,3-disubstituted 4-quinolones. The reaction works under mild conditions and tolerates various functional groups.

Synthesis of 1,4-Diketones via Titanium-Mediated Reductive Homocoupling of α-Haloketones

1,4-Diketones have been synthesized via a reductive homocoupling of α-haloketones. Addition of a Grignard reagent to titanium(IV) isopropoxide affords a low-valent titanium(III) intermediate that is believed to mediate a radical dimerization reaction. The reaction works well for a variety of aromatic α-haloketones including heteroaromatic compounds.

A titanium-based photo-Fenton bifunctional catalyst of mp-MXene/TiO2−x nanodots for dramatic enhancement of catalytic efficiency in advanced oxidation processes

A pseudo-Fenton reaction works synergistically with photocatalysis to greatly accelerate the oxidative degradation rate.

Reactions catalyzed by a binuclear copper complex: selective oxidation of alkenes to carbonyls with O2

A binuclear copper complex bearing a simple salicylate ligand catalyses the efficient cleavage of styrenes into ketones and aldehydes with O2 as the oxidant. The reaction works under an atmosphere of O2 (balloon) with 0.5 mol% of catalyst and could be performed on a gram scale, providing an alternative to ozonolysis.