Tetrabutyl ammonium bromide-mediated benzylation of phenols in water under mild condition

Synthesis of 7-hydroxydibenzopyran-6-ones via benzannulation of coumarins

We have successfully demonstrated a facile synthesis of a variety of 7-hydroxydibenzopyran-6-ones via a two-step protocol from 3-acylcoumarins having a latent Nazarov dienone functionality. Condensation of 3-acylcoumarins and ethyl cyanoacetate under basic (wet K₂CO₃) and microwave irradiation conditions followed by decarboethoxylative aromatization with Br₂ or DDQ furnished dibenzopyran-6-ones in high yields. The formation of ring C of the dibenzopyran-6-one motif critically depended on an active methylene compound and C7 substitution on coumarins. The Ar-Br or ArOTf substitution in dibenzopyran-6-ones was leveraged for the palladium-catalysed Suzuki coupling with diverse aryl boronic acids to increase the structural diversity. Reductive decyanation of C10 cyano dibenzopyran-6-ones furnished some of the isomers of urolithin A.

Oil-in-Water emulsions stabilized by alumina nanoparticles with organic electrolytes: Fate of particles

HYPOTHESIS

Oil-in-dispersion emulsions can be stabilized by like charged particles and surfactant. Surfactant adsorbs at the oil-water interface to reduce the interfacial tension and endow the interface with charge, while particles remain dispersed in the aqueous phase to provide electrostatic repulsion between droplets and particles. Can weakly surface-active organic electrolytes adsorb at the oil-water interface and behave like surfactants in stabilizing oil-in-dispersion emulsions with like charged particles?

EXPERIMENTS

Symmetrical organic electrolytes, tetraalkylammonium bromides (R₄NBr), with either no or very low interfacial activity endowing oil droplets with charge were combined with alumina nanoparticles to stabilize emulsions. The effect of R chain length (varying from methyl to butyl) on the type and stability of emulsions was investigated.

FINDINGS

Mixtures of high concentrations of short chain R₄NBr salts (R = methyl or ethyl) and alumina particles stabilise oil-in-water Pickering emulsions, whereas longer chain (R = propyl or butyl) analogues stabilize oil-in-dispersion emulsions assisted by alumina particles. Tetrapropylammonium and tetrabutylammonium cations adsorb at the oil-water interface reducing the interfacial tension and endowing the interface with charge. The stability of the oil-in-dispersion emulsions is dominated by the electrostatic repulsion between the droplets and between droplets and particles in the continuous aqueous phase.

A Green and Efficient Solvent- and Catalyst-Free Ultrasonic Dibenzylation Procedure

A greener improvement was achieved for the synthesis of diverse N,N-dibenzylated compounds from the reaction of various aromatic amines with benzyl bromide using the ultrasound irradiation in solvent- and catalyst-free conditions. The dibenzylation reactions were carried out in different solvents and solvent-free conditions under ultrasound irradiation at various temperatures. The yields were very low in all applied solvents, while in the solvent-free condition and at room temperature, the yields were excellent. Due to obtaining the high reaction yields, the catalyst was not used.

Static phase transfer catalysis for Williamson reactions: Pickering interfacial catalysis

A static PIC system with silica particles was prepared for PTC reactions and exhibited enhanced catalytic activity.

A Ligand-Enabled Palladium-Catalyzed Highly para-Selective Difluoromethylation of Aromatic Ketones

A practical and highly para-selective C-H difluoromethylation of aromatic ketones has been developed by employing tetrakis(triphenylphosphine)palladium(0) as the catalyst and triphenylphosphine as the ligand. In addition to general aromatic ketones, this transformation was compatible with bioactive compounds and well-known drugs, such as oxybenzone, ketoprofen, zaltoprofen, and propafenone. Moreover, a mechanistic study revealed that a palladium intermediate coordinated by a carbonyl group promotes highly para-selective difluoromethylation.

Photoreductive Removal of O-Benzyl Groups from Oxyarene N-Heterocycles Assisted by O-Pyridine-pyridone Tautomerism

Facile photoreductive protocols have been developed to remove benzyl O-protective groups from oxyarene N-heterocycles at positions capable for 2-/4-O-pyridine-2-/4-pyridone tautomerism. Blue light irradiation, a [Ru] or [Ir] photocatalyst, and ascorbic acid in a water-acetonitrile solution debenzylates a variety of aryl N-heterocycles cleanly and selectively. Ascorbic acid has two functions in the reaction. On the one hand, it protonates the N-heterocycles that reduces their reduction potentials notably and on the other hand it acts as a sacrificial reductant. Reduction potentials and free energy barriers calculated at the CPCM-B3LYP/6-31+G** level can predict the reactivities of the studied substrates.

Heterodiazocines: Synthesis and Photochromic Properties, Trans to Cis Switching within the Bio-optical Window

Diazocines, bridged azobenzenes, exhibit superior photophysical properties compared to parent azobenzenes such as high switching efficiencies, quantum yields, and particularly switching wavelengths in the visible range. Synthesis, however, proceeds with low yields, and derivatives are difficult to prepare. We now present two heterodiazocines which are easier to synthesize, and the general procedures should also provide facile access to derivatives. Moreover, both compounds can be switched with light in the far-red (650 nm). Accessibility and photophysical properties make them ideal candidates for applications such as photoswitchable drugs and functional materials.