Organic Reactions on Silica in Water

A one-pot three-component reaction involving 2-aminochromone in aqueous micellar medium: a green synthesis of hexahydrochromeno[2,3-b]quinolinedione

An efficient and green synthesis of hitherto unreported 11-(chromen-3-yl)-8,8-dimethyl-8,9-dihydro-6H-chromeno[2,3-b]quinoline-10,12(7H,11H)-dione has been accomplished by a three-component reaction involving 2-aminochromone, chromone-3-carbaldehyde, and 5,5-dimethyl-1,3-cyclohexanedione (dimedone) in 0.5 M aqueous SDS solution. The mechanism of the reaction has been studied by isolating the reaction intermediate. This methodology features eco-friendly reaction conditions, a simple working procedure, high atom-economy and high efficiency in product formation.

Efficient Passerini reactions in an aqueous vesicle system

The formation of α-acyloxy carboxamides from a carboxylic acid, an aldehyde and an isocyanide (Passerini reaction) was investigated in aqueous solution in the presence of different types of surfactants.

Pd complex of an NNN pincer ligand supported on γ-Fe2O3@SiO2 magnetic nanoparticles: a new catalyst for Heck, Suzuki and Sonogashira coupling reactions

Pd-BIP-γ-Fe₂O₃@SiO₂ was used successfully as an air- and moisture-stable magnetically recyclable catalyst for Heck, Suzuki and Sonogashira coupling reactions.

Organocatalysis by p-sulfonic acid calix[4]arene: a convenient and efficient route to 2,3-dihydroquinazolin-4(1H)-ones in water

An efficient and eco-friendly method is reported for the synthesis of 2,3-dihydroquinazolin-4(1H)-ones using p-sulfonic acid calix[4]arene as a recyclable organocatalyst in excellent yields in water at room temperature.

Synthesis of Passerini adducts from aldehydes and isocyanides under the auxiliary of water

An efficient protocol for the synthesis of the Passerini adducts α-acyloxycarboxamides from aldehydes, isocyanides and water in a molecular ratio of 3 : 1 : 3 was described.

A Pd complex of a NNN pincer ligand supported on γ-Fe2O3@SiO2 as the first magnetically recoverable heterogeneous catalyst for C–P bond forming reactions

A Pd complex of the NNN pincer ligand supported on γ-Fe₂O₃@SiO₂ was used as a new catalyst for a phosphonation reaction.

Versatile functionalization of carbon electrodes with a polypyridine ligand: metallation and electrocatalytic H+ and CO2 reduction

A carbon electrode is functionalized with a polypyridine ligand and subsequently metallated to catalyze the electroreduction of H⁺ and CO₂.

Enantioselective 1,2-reductions of β-trifluoromethylated-α,β-unsaturated ketones to chiral allylic alcohols over organoruthenium-functionalized mesoporous silica nanospheres

Organoruthenium-functionalized silica nanospheres display excellent catalytic activity and high enantioselectivity in the enantioselective 1,2-reductions of β-trifluoromethylated-α,β-unsaturated ketones.

Our recent progress on the intramolecular Diels-Alder reaction approach in natural products synthesis: synthetic studies of the octahydronaphthalene substructure of versipelostatins and the A/B/C-tricyclic substructure of GKK1032s

During this decade, the enantio- and stereoselective synthesis of natural products has been actively explored in the author's laboratory. In this account, the author outlines practical syntheses of the polycyclic substructures of two novel structurally formidable antibiotics, namely, the trans-fused octahydronaphthalene moiety of versipelostatins and the A/B/C-tricyclic decahydrofluorene moiety of GKK1032s. Both syntheses have been achieved with remarkable regio- and stereoselectivity via intramolecular Diels-Alder reactions using well-designed enantiomeric substrates.

Recycling nanoparticle catalysts without separation based on a pickering emulsion/organic biphasic system

A conceptually novel methodology is explored for in situ recycling of nanoparticle catalysts based on transforming a conventional organic/aqueous biphasic system into a Pickering emulsion/organic biphasic system (PEOBS). The suggested PEOBS exists as two phases, with the nanoparticle catalyst "anchored" in the Pickering emulsion phase, but is "continuous" between the organic phase and the continuous phase of the Pickering emulsion. Aqueous hydrogenations are used to evaluate the reaction performances of PEOBS, and the underlying principles of PEOBS are preliminarily elaborated. The unique properties of PEOBS lead to many intriguing findings, which are unlikely to be achieved in the reported biphasic systems. PEOBS exhibits more than a fourfold enhancement in catalysis efficiency in comparison with a conventional biphasic system. Impressively, PEOBS enables the organic product to be facilely isolated through simple decantation and the nanoparticle catalyst can be recycled in situ without the need for "separation". Its recycling effectiveness is justified by ten reaction cycles without significant catalyst loss. The simple protocol, in conjunction with the stability to simultaneously achieve high catalysis efficiency and excellent catalyst recyclability, makes PEOBS a promising methodology to develop more sustainable nanocatalysis.

Pickering-emulsion inversion strategy for separating and recycling nanoparticle catalysts

With the recent advances in nanoscience and nanotechnology, more and more nanoparticle catalysts featuring high accessibility of active sites and high surface area have been explored for their use in various chemical transformations, and their rise in popularity among the catalysis community has been unprecedented. The industrial applications of these newly discovered catalysts, however, are hampered because the existing methods for separation and recycling, such as filtration and centrifugation, are generally unsuccessful. These limitations have prompted development of new methods that facilitate separation and recycling of nanoparticle catalysts, so as to meet the burgeoning demands of green and sustainable chemistry. Recently, we have found that Pickering-emulsion inversion is an appealing strategy with which to realize in situ separation and recycling of nanoparticle catalysts and thereby to establish sustainable catalytic processes. We feel that at such an early stage, this strategy, as an alternative to conventional methods, is conceptually new for readers but that it has potential to become a popular method for green catalysis. This Concept article aims to provide a timely link between previous efforts and both current and future research on nanoparticle catalysts, and is expected to facilitate further investigation into this strategy.

Micrometer-scale mixing with Pickering emulsions: biphasic reactions without stirring

A general strategy that avoids stirring for organic/aqueous reactions involving solid catalysts is reported. The strategy involves converting a conventional biphasic system into a Pickering emulsion phase with micrometer-scale droplets ensuring good mixing. In test reactions, nitrotoluene reduction and epoxidation of allylic alcohols, the reaction efficiency is comparable to conventional stirrer-driven biphasic catalysis reaction systems. Short diffusion distances, arising from the compartmentalization of densely packed droplets, play an important role in boosting the reaction efficiency.

RhNPs/SBA-NH2: a high-performance catalyst for aqueous phase reduction of nitroarenes to aminoarenes at room temperature

A RhNPs/SBA-NH₂ catalyst with <3 nm sized nanoparticles has been synthesized and used in the chemoselective hydrogenation of nitroarenes at room temperature in aqueous medium with N₂H₄·H₂O with high TOF.

Cross-linked poly(dimethylaminoethyl acrylamide) coated magnetic nanoparticles: a high loaded, retrievable, and stable basic catalyst for the synthesis of benzopyranes in water

A high loaded basic magnetic catalyst was synthesized using a distillation–precipitation–polymerization method. The catalyst shows high activity in water for the synthesis of 4H-benzopyrans.

Tuning the wettability of mesoporous silica for enhancing the catalysis efficiency of aqueous reactions

A series of mesoporous silica-based catalysts with finely-tuned surface wettability have been synthesized. Their catalysis efficiency towards aqueous hydrogenations is highly dependent on their surface wettability and can be five times higher than that of the commercial Pd/C catalyst.

Facile construction of functionalized periodic mesoporous organosilica for Ir-catalyzed enantioselective reduction of α-cyanoacetophenones and α-nitroacetophenones

A facile construction of organoiridium-functionalized periodic mesoporous organosilica and its application in the enantioselective reduction of α-cyano and α-nitroacetophenones are studied.

Water-medium organic synthesis over active and reusable organometal catalysts with tunable nanostructures

Robust and reusable heterogeneous organometal catalysts open a new avenue to green chemical synthesis in water.