Vigorously stirred LaO suspensions for Michael additions in water.

This work demonstrates the effectiveness of vigorously stirred lanthanum oxide (LaO) suspensions in catalyzing Michael additions in water. These surfactant-free suspensions offer a counterintuitive yet highly efficient approach compared to traditional methods. Notably, the reactions are ineffective in the absence of water, suggesting a crucial role for the aqueous environment.

Small-Molecule-Based Strategy for Mitigating Deactivation of Chiral Lewis Acid Catalysis.

Chiral Lewis acid catalysts are widely used in organic synthesis due to their diverse applications. However, their high Lewis acidity makes them susceptible to deactivation by basic Lewis reagents and water. Here, we present a novel strategy for mitigating this deactivation using small molecules.

Direct Aromatic Nitrosation Using 2-Methoxyethyl Nitrite as a NO Cation Source.

This work presents an acid-free method for aromatic nitrosation using 2-methoxyethyl nitrite (MOE-ONO). While originally developed as a NO radical source in our group, we demonstrate the utility of MOE-ONO as a NO cation source for aromatic electrophilic nitrosation. This method successfully nitrosates phenols, naphthols, and other pronucleophiles, completely suppressing undesired nitration by NO radicals.

Nanoscale and chiral metal-organic frameworks for asymmetric reactions in water: bridging Lewis acid catalysis and biological systems.

Nowadays, stereoselective control over the sheer variety of chemical transformations benefits from the multipotency of chiral Lewis acids. Their use under biocompatible conditions has long posed a challenge because profuse amounts of biogenic nucleophiles readily deactivate them. To bridge the gap between chiral Lewis acid catalysis and biocompatible chemistry, the conversion of UiO(BPY)-type nanosized metal-organic frameworks (NMOFs) into chiral variants was herein exemplified.

Efficient Radical-Mediated Intermolecular α-Alkylation Reactions of Carbonyl Compounds with Nonactivated Alkenes.

Alkylation reactions are fundamental carbon-carbon bond-forming reactions in synthetic organic chemistry. Among them, intermolecular α-alkylation reactions of carbonyl compounds with alkenes are important because they are more atom-economical than the equivalent processes using alkyl halides. However, intermolecular reactions with nonactivated alkenes such as 1-hexene, which can allow the use of a wide range of valuable substrates, have been considered to be very challenging for a long time.

Development of Catalytic Enantioselective Mannich Reactions Using Esters.

Catalytic enantioselective Mannich reactions of simple nonactivated esters proceeded using a chiral potassium strong base catalyst prepared from a chiral bisoxazoline and potassium hexamethyldisilazide. Alkyl acetates, alkyl propionates, and an alkyl butyrate were employed as the simple esters, and the desired reactions proceeded smoothly to afford Mannich products in good to high yields with high enantioselectivities. One of the products was successfully employed in the asymmetric total synthesis of Maraviroc.

Water vs. Organic Solvents: Water-Controlled Divergent Reactivity of 2-Substituted Indoles.

Water is not a good solvent for most organic compounds, yet water can offer many benefits to some organic reactions, hence enriching organic chemistry. Herein, the unique divergent reactivity of 2-substituted indoles with ⋅NO sources is presented. The amount of water solvent was harnessed for a scalable, benign, and expedient synthesis of indolenine oximes, albeit with water's inability to dissolve the reactants.

Photoinduced Efficient Catalytic α-Alkylation Reactions of Active Methylene and Methine Compounds with Nonactivated Alkenes.

In catalytic α-alkylation reactions of carbonyl compounds, although S2-type substitution reactions of enolates with alkyl halides are a conventional methodology, addition reactions with alkenes are more desirable because of their atom-economical character; however, reactions with nonactivated alkenes are challenging. Here, we developed highly efficient catalytic α-alkylation reactions of active methylene and methine compounds with nonactivated alkenes such as 1-decene using an organophotocatalyst and lithium thiophenoxide as a Lewis acid/Brønsted base/hydrogen atom transfer (HAT) multifunctional catalyst under blue-light irradiation. The reaction was also performed with a higher degree of efficiency under a continuous-flow system to obtain the products in multigram scales.

Frictional properties of phase-separated agarose hydrogels in water permeation.

We studied the friction coefficient between the polymer gel network and water for thermoreversible agarose gels under various conditions of agarose concentration and gelation temperature. Since agarose gels exhibit phase separation below the gelation temperature, strongly depends on the thermal history. We found that the friction coefficient of the phase-separated agarose gel normalized by the water viscosity, /, is expressed as / = /νSD where is the frictional pore size and and are constant parameters.

Highly enantioselective hydroxymethylation of unmodified α-substituted aryl ketones in water.

Catalytic asymmetric direct-type aldol reactions of ketones with aldehydes are a perennial puzzle for organic chemists. Notwithstanding the emergence of a myriad of chiral catalysts to address the inherent reversibility of the aldol products, a general method to access acyclic α-chiral ketones from prochiral aryl ketones has remained an unmet synthetic challenge. The approach outlined herein is fundamentally different to that used in conventional catalysis, which typically commences with an α-proton abstraction by a Brønsted base.

Heterogeneous Single-Atom Zinc on Nitrogen-Doped Carbon Catalyzed Electrochemical Allylation of Imines.

Organometallic reagents are effective for carbon-carbon bond formation; however, consumption of stoichiometric amounts of metals is problematic. We developed electrochemical allylation reactions of imines catalyzed by nitrogen-doped carbon-supported single-atom zinc, which were fixed on a cathode to afford a range of homoallylic amines efficiently. The system could suppress generation of metallic waste, and the catalyst electrode showed advantages over bulk zinc in terms of activity and robustness.

Development of Metal-Free, Trifluoromethanesulfonic Acid-Immobilized Nitrogen-Doped Carbon Catalysts for Povarov Reactions.

A metal-free, heterogeneous acid catalyst, trifluoromethanesulfonic acid-immobilized nitrogen-doped carbon catalyst, was developed for Povarov reactions. This catalyst exhibited excellent catalytic activity, achieving high turnover frequency (>400 h) and good cis-selectivity of the desired 1,2,3,4-tetrahydroquinoline products. The reaction had a broad substrate scope, and the multicomponent Povarov reaction proceeded smoothly with readily accessible aldehydes and anilines.

Effect of Activation Methods of Molecular Sieves on Ketimine Synthesis.

Although the use of molecular sieves for imine synthesis is a common protocol, there have been no comprehensive studies on heat-drying methods. This can be crucial for reproducibility. It was found that molecular sieve 5A dried at 160 °C for 5 h under vacuum efficiently promoted the condensation of various ketones and amines to afford even relatively bulky ketimines.

Photocatalytic Addition Reactions of Ketene Silyl Acetals with Alkenes through Formation of α-Carbonyl Radicals.

Addition reactions of ketene silyl acetals with alkenes that do not have an electron-withdrawing group are generally difficult because the nucleophilicity of ketene silyl acetals and the electrophilicity of alkenes are not sufficient. Herein, we report photocatalytic addition reactions of ketene silyl acetals with alkenes that proceed through formation of α-carbonyl radicals. In the presence of an appropriate protic additive, the reactions proceeded smoothly under blue-light irradiation to afford the desired products in moderate to high yields.

2-Methoxyethyl Nitrite as a Reagent for Chemoselective On-Water Nitration.

An on-water approach has been developed that allows a nitration of tyrosines and phenols under mild conditions. We envisioned that the assembly of tyrosine/tyrosyl radical couples with interfacial water molecules would realize a biomimetic stacking hydrogen atom transfer (HAT) transition state to facilitate the electron-transfer process. The optimal organic nitrite, 2-methoxyethyl nitrite, resulted in rapid coupling of the tyrosyl radicals with ⋅NO at the oil-water interface to afford the nitrated phenols.

Efficient Recycling of Catalyst-Solvent Couples from Lewis Acid-Catalyzed Asymmetric Reactions in Water.

Bioinspired supramolecular architectures were used to compartmentalize highly charged aqua scandium ions into chiral hydrophobic scaffolds for Lewis acid-catalyzed asymmetric reactions. Recycling without significant loss in catalytic performance is a formidable task, especially for Lewis acid-catalyzed reactions. This is because Lewis basic impurities derived from starting materials, products, and water are highly competitive ligands for both substrate binding and metal complexation, thus poisoning the Lewis acids and leading to their leaching.

Brønsted base-catalyzed imino-ene-type allylation reactions of simple alkenes as unactivated allyl compounds.

Catalytic imino-ene-type allylation reactions of unactivated allyl compounds were achieved. In the presence of a catalytic amount of a strongly basic KOBu-LiTMP or NaOBu-LiTMP mixed system, the desired reactions proceeded smoothly at low temperature. Notably, a gaseous alkene, propylene, could also be used in this reaction system.

Nitrogen-Doped Carbon-Incarcerated Zinc Electrodes as Heterogeneous Catalysts for Electrochemical Allylation of Carbonyl Compounds.

Electrochemical allylation reactions of carbonyl compounds using cathodes prepared from nitrogen-doped carbon (NDC)-incarcerated zinc catalysts have been developed. A range of aldehydes and ketones afforded the desired allylic alcohols in high yields with <10 mol % zinc leaching, and the heterogeneous nature of the active species was suggested. Compared with bulk zinc electrodes, NDC-stabilized zinc nanoparticle species were compatible with a broader range of heteroaromatic substrates and enabled the use of an undivided cell.

Development of chiral potassium strong Brønsted base catalysts for enantioselective carbon-carbon bond-forming reactions.

Chiral alkaline metal Brønsted bases are traditional and reliable promoters in enantioselective catalysis. Here, new chiral potassium strong base catalysts were developed for enantioselective carbon-carbon bond-forming reactions of weakly acidic carbon pronucleophiles. Chiral potassium amide or alkyl potassium catalyzed enantioselective addition reactions to imines or α,β-unsaturated amides with good to high enantioselectivities.

Enantioselective hydrophosphonylation of -Boc imines using chiral guanidine-thiourea catalysts.

The enantioselective hydrophosphonylation of -Boc imines was investigated using a new family of pseudo-symmetric guanidine-thiourea catalysts, providing α-amino phosphonates in moderate to high yields with good enantioselectivity. The catalyst was heterogenized by polymerization with styrene and the resulting catalyst was applied to reactions under continuous-flow conditions.

Development of Trifluoromethanesulfonic Acid-Immobilized Nitrogen-Doped Carbon-Incarcerated Niobia Nanoparticle Catalysts for Friedel-Crafts Acylation.

Heterogeneous trifluoromethanesulfonic acid-immobilized nitrogen-doped carbon-incarcerated niobia nanoparticle catalysts (NCI-Nb-TfOH) that show excellent catalytic performance with low niobium loading (1 mol %) in Friedel-Crafts acylation have been developed. These catalysts exhibit higher activity and higher tolerance to catalytic poisons compared with the previously reported TfOH-treated NCI-Ti catalysts, leading to a broader substrate scope. The catalysts were characterized via spectroscopic and microscopic studies.

α-Alkylation of Ketones with Alkenes Enabled by Photoinduced Activation of Silyl Enol Ethers in the Presence of a Small Amount of Water.

Under blue-light irradiation conditions with a photocatalyst [1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene], silyl enol ethers reacted with alkenes in the presence of a small amount of water to afford the α-alkylation products in good to high yields. A thiol cocatalyst was found to expand the substrate scope of the reaction.

Chiral Metal Salts as Ligands for Catalytic Asymmetric Mannich Reactions with Simple Amides.

Catalytic asymmetric Mannich reactions of imines with weakly acidic simple amides were developed using a chiral potassium hexamethyldisilazide (KHMDS)-bis(oxazoline) potassium salt (K-Box) catalyst system. The desired reactions proceeded to afford the target compounds in high yields with high diastereo- and enantioselectivities. It was suggested that a K enolate interacted with K-Box to form a chiral K enolate that reacted with imines efficiently.

Asymmetric C(sp)-H functionalization of unactivated alkylarenes such as toluene enabled by chiral Brønsted base catalysts.

Benzylic functionalisation of unactivated alkylarenes remains as a significant challenge in asymmetric catalysis due to their less reactive nature. Here, we show development of catalytic asymmetric C(sp)-H functionalization of unactivated alkylarenes such as toluene with imines. The reactions proceeded smoothly under proton-transfer conditions using a chiral, strong Brønsted base catalyst system.