Mild Conditions Research Articles

In Situ Synthesis of Iron-Based Porphyrin Metal-Organic Frameworks for the Baeyer-Villiger Oxidation Using Air as an Oxidant.

Iron-based porphyrin metal-organic frameworks (PMOFs) are a new type of material with good stability, catalytic activities, and reusability, which have broad application prospects. However, the synthesis of iron-based PMOFs with different metalloporphyrin units requires a considerable amount of reagents and time. Herein, an in situ synthesis method was developed to simplify the synthetic process of iron-based PMOFs. A series of highly stable iron-based PMOFs (Msitu-PMOF-3(Fe) (M = Fe, Co, Ni, Cu, Pd)) were synthesized in one pot without the preparation of metalloporphyrin ligands in advance. This synthesis method is simpler and more efficient, saving considerable time and material costs. The resultant Msitu-PMOF-3(Fe) exhibits a high tolerance to aqueous solutions with pH ranging from 0 to 11, as well as various organic solvents. The catalytic experiments show that both Fesitu-PMOF-3(Fe) and Cositu-PMOF-3(Fe) can catalyze the Baeyer-Villiger oxidation of cyclohexanone using air as an oxidant at 35 °C. Moreover, when the mixtures of Fesitu-PMOF-3(Fe) and Cositu-PMOF-3(Fe) were employed as catalyst, they can exert a cooperative catalysis effect, resulting in a significantly enhanced catalytic activity compared to a single component. The mild reaction condition, high catalytic efficiency, and excellent selectivity endow this catalytic system with a good application prospect. This work not only provides a new approach for the synthesis of iron-based PMOFs but also offers guidance for the Baeyer-Villiger oxidation reactions using air under mild conditions.

Low-Temperature Borylation of C(sp3)-O Bonds of Alkyl Ethers by Gold-Metal Oxide Cooperative Catalysis.

Since ether moieties are often found not only in petrochemical products but also in natural organic molecules, the development of methods for manipulating C-O bonds of ethers is important for expanding the range of compound libraries synthesized from biomass resources, which should contribute to the goal of carbon neutrality. We report herein that gold nanoparticles supported on Lewis acidic metal oxides, namely α-Fe2O3, showed excellent catalytic activity for the reaction of dialkyl ethers and diborons, which enables the conversion of unactivated C(sp3)-O bonds to C(sp3)-B bonds at around room temperature. Various acyclic and cyclic ethers as well as a series of diborons participated in the heterogeneous gold-catalyzed borylation of unactivated C(sp3)-O bonds, to give a series of alkylboronates in high yields. Mechanistic studies corroborated that the present borylation of C(sp3)-O bonds of dialkyl ethers proceeded at the interface between gold nanoparticles and Lewis acidic metal oxides. Furthermore, adsorption IR measurements supported the notion that strong Lewis acid sites were generated at the boron atom of diborons adsorbed at the interface between Lewis acidic metal oxides and gold nanoparticles, which enabled us to ensure that the cooperation of gold nanoparticles and Lewis acidic metal oxides was responsible for the efficient transformation of unactivated C(sp3)-O bonds in ethers under mild conditions. This novel reaction technology which is specific to heterogeneous catalysts enables the activation of stable C(sp3)-O bonds of oxygenated chemical feedstock, which is beneficial for the sustainable synthesis of value-added organoboron compounds.

Enzymatic Upgrading of Biomass-Derived Aldoses to Rare Deoxy Ketoses Catalyzed by Transketolase Variants.

A sustainable, convenient, scalable, one-step method for the two-carbon chain elongation of cheap and biomass-derived pentoses (l-arabinose, and 2-deoxy-d-ribose) and hexose l-rhamnose was developed to produce Cn+2 deoxy ketoses (C-7 and C-8) using transketolase, an enzyme catalyzing the quasi-irreversible transfer of a ketol group from an α-keto acid to an aldehyde. Deoxygenated ketoses - commonly obtained by chemical synthesis - were afforded through a suitable combination of both nucleophile and electrophile substrates in the presence of rationally designed TK variants. Pyruvate as nucleophile with pentose l-arabinose (C-5) as electrophile gave 1-deoxy-L-gluco-heptulose (C-7), while ß-hydroxypyruvate (HPA) as nucleophile with acceptors 2-deoxy-d-ribose (C-5) and 6-deoxy-l-mannose (l-rhamnose) (C-6) led to formation of 4-deoxy-d-altro-heptulose (C-7) and 8-deoxy-l-glycero-l-galacto-octulose (C-8), respectively. These three deoxy ketoses were easily obtained with efficient TK variants under mild conditions with complete or high substrate conversions, good to excellent yields and high diastereoselectivities. This strategy offers interesting prospects to study the biological activities of these three rare and valuable deoxy ketoses on various cellular targets.

Photoredox-Catalyzed Regioselective 1,3-Alkoxypyridylation of gem-Difluorocyclopropanes.

Difluoromethylene and pyridine cores are very important structural units in medicinal chemistry. Herein, we report the development of photoredox-catalyzed ring-opening and 1,3-alkoxypyridylation of gem-difluorinated cyclopropanes using 4-cyanopyrines and alcohols, employing cyclopropane radical cations as the key intermediate. The reaction exhibits high regioselectivity under mild conditions and can also be practiced on gram-scale synthesis, telescoped reaction, and late-stage functionalization of biological molecules.

Expeditious and environmentally benign synthesis of imidazo[4,5,1-ij]quinolines via sequential Povarov reaction/reductive cyclization.

In this contribution, a novel, simple, diastereoselective and environmentally benign two-step diversity-oriented synthesis of imidazo[4,5,1-ij]quinolines is described for the first time. The synthesis of the target compounds involves a deep eutectic solvent-mediated one-pot Povarov reaction leading to the obtention of 8-nitrotetrahydroquinolines, followed by a microwave-assisted reductive cyclocondensation employing different aromatic and aliphatic aldehydes. The target compounds were obtained in up to 70% overall yield starting from commercially available o-nitroanilines, natural phenylpropanoids (trans-anethole and trans-isoeugenol) and aromatic or aliphatic aldehydes. The eutectic solvent employed in the first step was reused in four runs without observing a drastic decrease in catalytic activity, and sodium dithionite showed to be an efficient and green reducing agent for the second step. This methodology provides significant advantages in terms of synthetic and green chemistry such as mild reaction conditions, short reaction time, energy-efficiency, simple work-up procedure, low cost, scalability and utilization of renewable substrates and a reusable solvent.

Effect of Pd/Cu(Co) ratio on catalytic performance of PdCu(Co)/NC bimetallic catalysts for furfural selective hydrogenation.

PdxCuy/NC and PdxCoy/NC with different metal mass ratios of Pd to Cu (or Co) are synthesized. They (Pd : Cu (or Co) = 3 : 7) show excellent catalytic activity and high selectivity to furfuryl alcohol (FA) (or tetrahydrofurfuryl alcohol (THFA)) under quite mild conditions due to synergistic effect of Pd-Cu (Co)-NC.

Caboxylative Coupling of N‐(Arylmethyl)sulfonimides with Allyltributylstannane Catalyzed by Palladium Nanoparticles Involving Benzylic C−N Cleavage

AbstractThe palladium‐catalyzed three‐component coupling of aryl (hetero) methylsulfonamide, allyltributyltin and carbon dioxide (carboxylative Stille coupling reaction) was successfully conduced to produce β,γ‐unsaturated esters in satisfactory to good yields. The reaction was carried out under mild conditions by using in situ generated palladium nanoparticles as catalyst through the formation of π‐allylpalladium sulfonamide intermediates in the presence of tetrabutylammonium bromide (TBAB).

Molecular----Squeeze Triggers Guest Desorption from Sponge-Like Macrocycle Crystals.

Desorption in conventional porous sorbents often employ external forces including inert gas blowing, heating, vacuum treatment to trigger guest release. We here report an unprecedented molecular-squeeze triggered guest release behavior from sponge-like macrocycle crystals. The crystals function as typical sponge to include guest molecules within their microscopic voids that are adaptively formed, thus acting as adsorbents for toluene/pyridine separations. Intriguingly, vaporized ethyl acetate ( EA ) molecules trigger the guest release from the crystals without entering the pores or voids of the crystals to replace the guests. Instead, they work as external forces applied directly onto the crystals themselves, ''squeezing" the materials to close the voids through supramolecular interactions between EA and macrocycles on the crystal surface and release the guest molecules. Various experimental techniques as well as molecular dynamics simulations reveal the mechanism of the molecular-squeeze induced guest release procedure. The EA -regenerated crystals can be recycled multiple times without the loss of separation performance. Compared with conventional guest release procedure, this method is manipulated in a mild condition, showing the potential in saving cost and energy.

Electrified Dynamically Responsive Ammonia Decomposition to Hydrogen Based on Magnetic Heating of a Ru Nanocatalyst.

Storing and transporting pressurized or liquid hydrogen is expensive and hazardous. As a result, safer methods, such as chemical storage in ammonia, are becoming increasingly important. However, the instantaneous start of a conventionally heated decomposition reactor is challenging. Here we report on the electrified and dynamically responsive decomposition of ammonia as a means of releasing on-demand chemically bonded hydrogen based on the rapid magnetic heating of a well-designed Ru-based nanocomposite catalyst. Under relatively mild conditions (400 °C, 1 bar) a rapid decomposition rate of 5.33 molNH3 gRu-1 h-1 was achieved. Experimental observations under non-isothermal, dynamic conditions coupled with modelling at the level of density functional theory and micro-kinetic modeling confirmed the minute-scale response of the H2 release. The rapid response of our catalytic system would, at least in principle, enable the utilization of intermittent, renewable electricity and a tunable H2/NH3 ratio in the reactor's effluent.

Visible‐Light‐Induced C(sp2)−P Cross‐Coupling Reactions Catalyzed by Boron Carbonitride

A visible‐light‐induced protocol is developed for the construction of C(sp2)−P bonds with heterogeneous boron carbonitrides (BCN). The system features with broad scope and mild reaction conditions, providing various aryl phosphates in moderate to good yields from arenes and arylhalides. Mechanism studies verify a radical process, and C−H bond cleavage is not involved in the rate‐determined step. Furthermore, the strategy allows the late‐stage phosphonation of biologically active compounds and gram‐scale synthesis, which offers a metal‐free arene for valuable phosphorus‐containing compounds.

Nickel-Catalyzed Decarboxylative Cross-Coupling of NHPI Esters to Access 1,4-Dialkylbenzenes.

A practical nickel-catalyzed decarboxylative cross-coupling of N-hydroxyphthalimide esters with 1,4-diiodobenzene analogues has been developed. Under mild reaction conditions, a series of structurally interesting 1,4-dialkylbenzene analogues have been accessed with good functional group tolerance, which are versatile precursors for organic synthesis and a kind of important unit for bioactive molecules, polymers, and other materials. The synthetic application of this methodology was demonstrated by the synthesis of 3-6-dialkylcarbazole derivatives.

Alkali Metal Amide-Catalyzed α-Deuteration of Sulfides.

The catalytic α-deuteration of sulfides was developed under mild conditions by using alkali metal amides [KN(SiMe3)2 and CsN(SiMe3)2] as the catalyst. This approach successfully achieves a selective and efficient H/D exchange reaction of sulfides with D2 without using transition metal catalysts. A series of deuterium-labeled thioanisoles and alkyl methyl sulfides were obtained in good to high levels of deuterium incorporation.

Copper-Catalyzed Asymmetric Nucleophilic Substitutions of TsSCF3: Synthesis of Chiral SCF3-Containing Compounds.

By employing electrophilic TsSCF3 as an efficient SCF3 source, we reported Cu/SOP (chiral sulfoxide-phosphine ligand)-catalyzed enantioselective nucleophilic substitutions. Under this protocol, α-pyridyl-α-fluoro esters as latent carbon nucleophiles, compounds containing a C-SCF3 stereocenter along with azacycles and fluorine atoms, were obtained in good yields and enantioselectivities under mild conditions (up to 68% yield, 92% ee).

Regioselective Synthesis of N-Aryl Pyrazoles from Alkenyl Sulfoxonium Ylides and Aryl Diazonium Salts.

A convenient and practical method has been developed for synthesizing various N-aryl pyrazoles from vinyl sulfoxonium ylides and diazonium salts. When using 1,3-disubstituted vinyl sulfoxonium ylides, the reaction selectively yields 1,3,5-trisubstituted pyrazoles. On the other hand, employing 2,3-disubstituted vinyl sulfoxonium ylides results in the formation of 1,3,4-trisubstituted pyrazoles. The reaction proceeds through the novel aryl diazene-derived vinyl sulfoxonium ylide. Furthermore, this method efficiently produces pyrazoles from aniline derivatives in a one-pot transformation. The reaction takes place under transition metal-free, mild conditions using easily accessible starting materials, making it a practical approach for generating pyrazoles in pharmaceutical chemistry.

Stereocontrolled Synthesis of Cyclobutylamines Enabled by Lewis Acid-Catalyzed (3 + 2 + 2) Cycloaddition/Ring-Opening Strategy of Bicyclo[1.1.0]butanes with Triazinanes.

Herein, we develop a modular and efficient "cycloaddition/ring-opening" strategy of bicyclo[1.1.0]butanes (BCBs) with triazinanes to provide a series of syn-diastereoselective cyclobutylamines via 2,4-diazabicyclo[4.1.1]octanes (aza-BCOs). The reaction features simple operation, mild reaction conditions, and a broad substrate scope. Mechanistic studies suggest that the cycloaddition follows a stepwise (3 + 2 + 2) rather than (4 + 3) cycloaddition, involving an SN2 nucleophilic addition of formaldimine to Lewis acid-activated BCB species. A scale-up experiment and various synthetic transformations of the product further highlight the synthetic utility. We expect that our findings will encourage the exploration of BCB chemistry to access more synthetically challenging cyclobutane frameworks.

Improving Retinoic Acid Efficacy: Lipase-Catalyzed Synthesis of Derivatives with Antiviral Activity.

An efficient enzymatic approach was applied to the synthesis of new derivatives of retinoic acid. Nine derivatives, four of them new compounds, were obtained through lipase-catalysis with excellent yield. In order to find the optimal reaction conditions, the influence of various parameters such as enzyme source, nucleophile : substrate ratio, enzyme : substrate ratio, solvent and temperature was studied. The excellent results obtained by lipase catalysis made the procedure very efficient considering their advantages such as mild reaction conditions and low environmental impact. In addition, several synthesized compounds exhibited lower cytotoxicity than the retinoic acid in Vero cells and a remarkably higher antiviral activity against Herpes simplex virus type 1 (HSV-1) and Herpes simplex virus type 2 (HSV-2).

Rongalite as a Methylene Surrogate: Synthesis of Heterodiarylmethanes via C(sp2)-H Functionalization.

An efficient method for the synthesis of heterodiarylmethanes through the coupling of imidazo[1,2-a]pyridines and heteroarenes using indoles employing rongalite as a methylenating reagent has been developed. This regioselective C-H functionalization provides a wide range of heterodiarylmethanes of imidazo[1,2-a]pyridines and imidazo[2,1-b]thiazole. Here, rongalite plays a crucial role in generating a C1 unit in situ, which triggers the heterodiarylmethylation process. The use of inexpensive rongalite (ca. $0.03/1 g), mild reaction conditions, and gram-scale synthesis are some of the key features of this methodology.

Benzylic C(sp3)−H Phosphonylation via Dual Photo and Copper Catalysis

AbstractAlkyl phosphonates are important motifs in medicinal chemistry, yet their efficient synthesis by direct C(sp3)−H functionalization remains a challenge. Here, we report straightforward access to benzylic phosphonates by direct C(sp3)−H functionalization in a cross‐dehydrogenative‐coupling reaction between non‐specialized alkylarenes and unfunctionalized phosphites. Notably, the C−H substrates are used as the limiting reagents. The scope of benzylic C−H substrates is broad, and the mild reaction conditions allow for good functional group tolerance. Mechanistic studies indicate that the reaction proceeds via a radical pathway rather than the cationic pathway followed for specialized benzylic C−H substrates in previous methods.

Glycogen: A Novel Biopolymer Catalyst for the One-Pot Synthesis of Spirooxindoles, Spiro-Acenaphthylenes, and Spiro-2-Aminopyrans Derivatives under Mild Conditions

Background: Glycogen, a naturally occurring macromolecule, in its granular form and without any post-modification was found to be an efficient and eco-friendly bifunctional heterogeneous organocatalyst. Objective: This catalyst can be useful for the domino synthesis of various spiropyren annulated derivatives through three-component condensation of isathin, malononitrile, and diverse 1,3-dicarbonyl compounds, activated CH-acids, through Knoevenagel-Michael-annulation sequence under mild conditions. Methods: Corresponding spiro derivatives were obtained in high to excellent yields after 5-15 min stirring in 2 mL EtOH and 60°C in the presence of 0.01 g of glycogen, equimolar amounts of isatin/ acenaphthoquinone/ninhydrin, malononitrile, and 1,3-dicarbonyl compounds. Results: FTIR and 1H NMR spectroscopic showed there isn't any catalyst in the media and desired products were obtained in excellent purity. Conclusion: Avoiding any transition metal, one-pot, and multicomponent procedure catalyzed by a biopolymer, broad substrate scope, and operational simplicity are essential features of this methodology for the preparation of medicinally important compounds.

Co-N-C catalyst with single atom active sites for base-free aerobic oxidation of 5-hydroxymethylfurfural to 2,5-furandicarboxylic acid under mild conditions

The production of 2,5-furandicarboxylic acid (FDCA), a promising biodegradable alternative to fossil-based terephthalic acid (PTA), from biomass-derived 5-hydroxymethylfurfural (HMF) is of significant importance. A major challenge is to develop an effective non-precious metal catalyst system that does not require a homogeneous base. In this study, we present a noble-metal-free Co-N-C catalyst, derived from the pyrolysis of cobalt-phenanthroline complexes on a carbon support. This catalyst demonstrates exceptional performance, achieving a FDCA yield of 99.9 % and maintaining reusability for up to five catalytic cycles in the base-free oxidation of HMF to FDCA under mild conditions. Through controlled experiments and comprehensive characterizations, we propose that the active sites in the Co-N-C catalyst are Co single atoms bonded to nitrogen within graphitic sheets. This approach provides valuable insights into the exact nature of the active sites in such noble-metal-free M-N-C catalysts designed for biomass conversion