First atroposelective Chan-Lam coupling for the synthesis of C-N linked biaryls

The first atroposelective Chan-Lam coupling for the synthesis of C-N axial enantiomers is reported with good yields and ee. MnO2 additive is crucial for the success of the coupling. The longstanding problem of the lack of enantioselective synthesis to make chiral C-N linked atropisomers is solved.

Impact of multiple H/D replacements on the physicochemical properties of flurbiprofen

Although deuterium incorporation into pharmaceutical drugs is an attractive way to expand drug modalities, their physicochemical properties have not been sufficiently examined. This study focuses on examining the changes in physicochemical properties between flurbiprofen (FP) and flurbiprofen-d8 (FP-d8), which was successfully prepared by direct and multiple H/D exchange reactions at the eight aromatic C-H bonds of FP. Although the effect of deuterium incorporation was not observed between the crystal structures of FP and FP-d8, the melting point and heat of fusion of FP-d8 were lower than those of FP. Additionally, the solubility of FP-d8 increased by 2-fold compared to that of FP. Calculation of the interaction energy between FP/FP-d8 and water molecules using the multi-component density functional theory method resulted in increased solubility of FP-d8. These novel and valuable findings regarding the changes in physicochemical properties triggered by deuterium incorporation can contribute to the further development of deuterated drugs.

Multiple deuteration of triphenylphosphine and live-cell Raman imaging of deuterium-incorporated Mito-Q

All aromatic C-H bonds of triphenylphosphine (PPh3) were efficiently replaced by C-D bonds using Ru/C and Ir/C co-catalysts in 2-PrOH and D2O, an inexpensive deuterium source. Furthermore, non-radioactive and safe deuterium-incorporated Mito-Q (drug candidate) was prepared from deuterated PPh3 and used for the live-cell Raman imaging to evaluate the mitochondrial uptake.

Syntheses of 25-Adamantyl-25-alkyl-2-methylidene-1α,25-dihydroxyvitamin D3 Derivatives with Structure-Function Studies of Antagonistic and Agonistic Active Vitamin D Analogs

The active form of vitamin D₃, 1α,25-dihydroxyvitamin D₃ [1,25(OH)₂D₃], is a major regulator of calcium homeostasis through activation of the vitamin D receptor (VDR). We have previously synthesized vitamin D derivatives with large adamantane (AD) rings at position 24, 25, or 26 of the side chain to study VDR agonist and/or antagonist properties. One of them-ADTK1, with an AD ring and 23,24-triple bond-shows a high VDR affinity and cell-selective VDR activity. In this study, we synthesized novel vitamin D derivatives (ADKM1-6) with an alkyl group substituted at position 25 of ADTK1 to develop more cell-selective VDR ligands. ADKM2, ADKM4, and ADKM6 had VDR transcriptional activity comparable to 1,25(OH)₂D₃ and ADTK1, although their VDR affinities were weaker. Interestingly, ADKM2 has selective VDR activity in kidney- and skin-derived cells-a unique phenotype that differs from ADTK1. Furthermore, ADKM2, ADKM4, and ADKM6 induced osteoblast differentiation in human dedifferentiated fat cells more effectively than ADTK1. The development of vitamin D derivatives with bulky modifications such as AD at position 24, 25, or 26 of the side chain is useful for increased stability and tissue selectivity in VDR-targeting therapy.

Microwave-assisted C-C bond formation of diarylacetylenes and aromatic hydrocarbons on carbon beads under continuous-flow conditions

The synthesis of polycyclic aromatic compounds generally requires stoichiometric oxidants or homogeneous metal catalysts, however, the risk of contamination of inorganic residues can affect their properties. Here we present a microwave (MW)-assisted platinum on beaded activated carbon (Pt/CB)-catalyzed C-C bond formation of diarylacetylenes and aromatic hydrocarbons under continuous-flow conditions. Various fused aromatic compounds were continuously synthesized via dehydrogenative C(sp²)-C(sp²) and C(sp²)-C(sp³) bond formation with yields of up to 87% without the use of oxidants and bases. An activated, local reaction site on Pt/CB in the flow reaction channel reaching temperatures of more than three hundred degrees Celsius was generated in the catalyst cartridge by selective microwave absorption in CB with an absorption efficiency of > 90%. Mechanistic experiments of the transformation reaction indicated that a constant hydrogen gas supply was essential for activating Pt. This is an ideal reaction with minimal input energy and no waste production.

Oxidative Functionalization of Catechol Derivatives Substituted with Electron-Withdrawing Groups

Catechols possessing electron-withdrawing groups at the C3 position effectively underwent oxidative functionalization at the C4 position in the presence of phenyliodine(III) diacetate (PIDA) and heteroarene nucleophiles (e.g., indole, indazole, and benzotriazole) to produce the corresponding biaryl products. The PIDA-mediated oxidation of catechol derivatives afforded the ortho-benzoquinone intermediate, which subsequently underwent regioselective nucleophilic addition to the α,β-unsaturated carbonyl moiety of ortho-benzoquinone using indole, indazole, and benzotriazole to give 4-substituted catechol derivatives in a one-pot manner. Notably, the nucleophilic substitution positions of indazole and benzotriazole were perfectly controlled. Additionally, the reaction using N-methylaniline as the nucleophile afforded a tertiary amine product.

Aryl Boronic Esters Are Stable on Silica Gel and Reactive under Suzuki-Miyaura Coupling Conditions

A wide range of aryl boronic 1,1,2,2-tetraethylethylene glycol esters [ArB(Epin)s] were readily synthesized. Purifying aryl boronic esters by conventional silica gel chromatography is generally challenging; however, these introduced derivatives are easily purified on silica gel and isolated in excellent yields. We subjected the purified ArB(Epin) to Suzuki-Miyaura couplings, which provided higher yields of the desired biaryl products than those obtained using the corresponding aryl boronic acids or pinacol esters.

Highly Selective Hydrogenative Conversion of Nitriles into Tertiary, Secondary, and Primary Amines under Flow Reaction Conditions

Flow reaction methods have been developed to selectively synthesize tertiary, secondary, and primary amines depending on heterogeneous platinum-group metal species under catalytic hydrogenation conditions using nitriles as starting materials. A 10 % Pd/C-packed catalyst cartridge affords symmetrically substituted tertiary amines in good to excellent yields. A 10 % Rh/C-packed catalyst cartridge enables the divergent synthesis of secondary and primary amines, with either cyclohexane or acetic acid as a solvent, respectively. Reaction parameters, such as the metal catalyst, solvent, and reaction temperature, and continuous-flow conditions, such as flow direction and second support of the catalyst in a catalyst cartridge, are quite important for controlling the reaction between the hydrogenation of nitriles and nucleophilic attack of in situ-generated amines to imine intermediates. A wide variety of aliphatic and aromatic nitriles could be highly selectively transformed into the corresponding tertiary, secondary, and primary amines by simply changing the metal species of the catalyst or flow parameters. Furthermore, the selective continuous-flow methodologies are applied over at least 72 h to afford three different types of amines in 80-99 % yield without decrease in catalytic activities.

Platinum on Carbon-Catalysed Site-Selective H-D Exchange Reaction of Allylic Alcohols Using Alkyl Amines as a Hydrogen Source

We developed platinum on carbon-catalysed deuteration reaction of tert-allylic alcohols using deuterium oxide as a deuterium source. Amylamine was dehydrogenated by platinum on carbon to generate an appropriate amount of...

Heavy water recycling for producing deuterium compounds

Deuterium oxide (D₂O) is a special variety of water that serves as a crucial resource in a range of applications, but it is a costly and unusual resource. We therefore developed a new D₂O concentration system that combines a polymer electrolyte water electrolyzer and a catalytic combustor for recycling used D₂O. In this study, 1.6 L of used D₂O, with a concentration of 93.1%, was electrolyzed for 13.6 h to obtain 0.62 L of D₂O, with a concentration of 99.3%. In addition, the recombined water obtained by burning electrolytic gas using the catalytic combustor was also electrolyzed for 8.8 h to obtain 0.22 L of D₂O, with a concentration of 99.0%. The estimated separation factor of this electrolyzer at 25 °C was 3.6, which is very close to the equilibrium constant of the water/hydrogen isotope exchange reaction. Recycled D₂O was used as a deuterium source for the deuteration reaction of sodium octanoate, and 93.6% deuterated sodium octanoate was obtained. It is concluded that there were no impurities in the recycled D₂O that interfered with the deuteration reaction. These results can lead to the development of a cost-effective deuteration method for these materials.

Heavy water recycling for the production of deuterium compounds.

Oxidative Two-way Regiocontrolled Coupling of 3-Methoxycarbonylcatechol and Indoles to Arylindoles

3-Methoxycarbonylcathechol effectively underwent the two-way regiocontrolled coupling with indoles via an ortho-benzoquinone intermediate, resulted by phenyliodine(III) diacetate oxidation, to generate 4-adducts or 5-adducts with or without BF3•Et2O in a one-pot...

Ruthenium-on-Carbon-Catalyzed Facile Solvent-Free Oxidation of Alcohols: Efficient Progress under Solid-Solid (Liquid)-Gas Conditions

A protocol for the ruthenium-on-carbon (Ru/C)-catalyzed solvent-free oxidation of alcohols, which proceeds efficiently under solid-solid (liquid)-gas conditions, was developed. Various primary and secondary alcohols were transformed to corresponding aldehydes and ketones in moderate to excellent isolated yields by simply stirring in the presence of 10% Ru/C under air or oxygen conditions. The solvent-free oxidation reactions proceeded efficiently regardless of the solid or liquid state of the substrates and reagents and could be applied to gram-scale synthesis without loss of the reaction efficiency. Furthermore, the catalytic activity of Ru/C was maintained after five reuse cycles.

Gold-Catalyzed Tandem Oxidative Coupling Reaction between β-Ketoallenes and Electron-Rich Arenes to 2-Furylmethylarenes

A tandem oxidative coupling reaction of β-ketoallenes and arenes was developed, which leads to the formation of 2-furylmethylarenes using AuCl₃ and phenyliodine diacetate. The Au^III salt catalyzed the cyclization of β-ketoallenes to form a 2-furylmethyl gold intermediate, and the subsequent C-H functionalization of arenes proceeded smoothly. During the oxidative coupling, nucleophilic additions occurred at the center and terminal carbon atoms of the allene moiety to form C-O and C-C bonds.

Revisiting the synthesis of aryl nitriles: a pivotal role of CAN

Facilitated by the dual role of Ceric Ammonium Nitrate (CAN), herein we report a cost-effective approach for the cyanation of aryl iodides/bromides with CAN-DMF as an addition to the existing pool of combined cyanation sources. In addition to being an oxidant, CAN acts as a source of nitrogen in our protocol. The reaction is catalyzed by a readily available Cu(ii) salt and the ability of CAN to generate ammonia in the reaction medium is utilized to eliminate the additional requirement of a nitrogen source, ligand, additive or toxic reagents. The mechanistic study suggests an evolution of CN- leading to the synthesis of a variety of aryl nitriles in moderate to good yields. The proposed mechanism is supported by a series of control reactions and labeling experiments.

Copper-Catalyzed Aqueous N-O Bond Cleavage of 2-Oxa-3-Azabicyclo Compounds to Cyclic cis-1,4-Amino Alcohols

The N-O bond cleavage of 2-oxa-3-azabicyclo substrates, which are readily prepared by the hetero Diels-Alder reaction between nitroso dienophiles and cyclic 1,3-dienes, was effectively catalyzed by heterogeneous copper-on-carbon (Cu/C) under aqueous conditions to give the corresponding cyclic cis-1,4-amino alcohol derivatives. The present method was applied to the direct incorporation of the hydroxy and amino groups derived from a nitroso substrate into cyclic 1,3-dienes with cis-selectivity by the combination of the in situ formation of 2-oxa-3-azabicyclo compounds and following Cu/C-catalyzed N-O bond cleavage. The obtained cis-4-aminocyclohexenols, derived from cyclohexadiene as a cyclic 1,3-diene, could be selectively oxidized by using the ruthenium-on-carbon (Ru/C) catalyst under oxygen atmosphere to the corresponding 4-aminocyclohexenones at 50-65 °C or para-iminoquinones at 100-110 °C as useful reactive synthetic precursors.

Skeletal reorganization divergence of N-sulfonyl ynamides

Skeletal reorganization is a type of intriguing processes because of their interesting mechanism, high atom-economy and synthetic versatility. Herein, we describe an unusual, divergent skeletal reorganization of N-sulfonyl ynamides. Upon treatment with lithium diisopropylamine (LDA), N-sulfonyl ynamides undergo a skeletal reorganization to deliver thiete sulfones, while the additional use of 1,3-dimethyl-tetrahydropyrimidin-2(1H)-one (DMPU) shifts the process to furnish propargyl sulfonamides. This skeletal reorganization divergence features broad substrate scope and scalability. Mechanistically, experimental and computational studies reveal that these processes may initiate from a lithiation/4-exo-dig cyclization cascade, and the following ligand-dependent 1,3-sulfonyl migration or β-elimination would control the chemodivergence. This protocol additionally provides a facile access to a variety of privileged molecules from easily accessible ynamides.

Skeletal reorganizations are intriguing processes in chemical synthesis due to their mechanism, atom-economy and synthetic versatility. Herein, the authors describe a divergent skeletal reorganization of N-sulfonyl ynamides to thiete sulfones and propargyl sulfonamides.

Hydroquinone and benzoquinone-catalyzed aqueous Knoevenagel condensation

A Knoevenagel condensation of various aldehydes with malononitrile effectively proceeded in the presence of hydroquinone/benzoquinone mixed catalysts at room temperature in H₂O. Furthermore, γ-deuterium-labeled α,β-unsaturated nitrile derivatives were also constructed via a deuteration of an aliphatic aldehyde in D₂O using a basic resin and the subsequent Knoevenagel condensation.

Preparation of N2-Ethyl-2'-deoxyguanosine-d4 as an Internal Standard for the Electrospray Ionization-Tandem Mass Spectrometric Determination of DNA Damage by Acetaldehyde

The deuteration of N²-ethyl-2'-deoxyguanosine (Et-dG), which is a DNA adduct generated from acetaldehyde, was studied by the addition reaction of acetaldehyde-d₄ to 2'-deoxyguanosine (dG) in deuterium oxide (D₂O), with the aim to obtain an isotope internal standard for the liquid chromatography/tandem mass spectrometry (LC/MS/MS) quantitation of Et-dG. The replacement of the dG C-8 hydrogen atom by a deuteron atom took place at 50°C in D₂O and afforded a mixture of Et-dG-d₄ and Et-dG-d₅. Et-dG-d₄, which was stable in aqueous solutions, was prepared by incubating the mixture in H₂O at 60°C for 48 h. The calibration curve was obtained by multiple reaction monitoring (MRM) measurements using a hydrophilic interaction chromatography-electrospray ionization-tandem mass spectrometric (HILIC/ESI-MS/MS) system between the Et-dG concentration, ranging from 1.0 × 10^-10 to 4.0 × 10^-9 M in the sample solutions, and the relative peak areas of Et-dG (m/z: 296.1 → 180.1) to the value of Et-dG-d₄ (m/z: 300.2 → 184.2), with an internal standard showing good linearity (R² = 0.995, n = 5).

Arylation of indoles using cyclohexanones dually-catalyzed by niobic acid and palladium-on-carbons

3-Arylindoles were easily constructed from indoles and cyclohexanone derivatives using a combination of catalytic niobic acid-on-carbon (Nb₂O₅/C) and palladium-on-carbon (Pd/C) under heating conditions without any oxidants. The Lewis acidic Nb₂O₅/C promoted the nucleophilic addition of indoles to the cyclohexanones, and the subsequent dehydration and Pd/C-catalyzed dehydrogenation produced the 3-arylindoles. The additive 2,3-dimethyl-1,3-butadiene worked as a hydrogen acceptor to facilitate the dehydrogenation step.

N-Heterocyclic Carbene Catalyzed Deuteration of Aldehydes in D2O

An N-heterocyclic carbene (NHC)-catalyzed direct deuteration of aldehydes in a mixed solvent of deuterium oxide (D2O) and cyclopentyl methyl ether was established. The present deuteration is possibly initiated by the formation of a Breslow intermediate from the aldehyde and the NHC, with subsequent trapping by D2O providing the monodeuterated aldehyde.

Facile Hydrogenative Deprotection of N-Benzyl Groups Using a Mixed Catalyst of Palladium and Niobic Acid-on-Carbon

The palladium-on-carbon (Pd/C)-catalyzed hydrogenative deprotection of the N-benzyl-protecting group was effectively facilitated by the combined use of niobic acid-on-carbon (Nb₂O₅/C). Nb₂O₅/C is an acidic heterogeneous catalyst prepared from NbCl₅ and activated carbon. The catalysts were easily removed from the reaction mixture and reusable. Deprotected amines were obtained in excellent yields without an additional neutralization process. The facilitating effect of Nb₂O₅/C was also observed during the Pd/C-catalyzed hydrogenative deprotection of the N-benzyloxycarbonyl (Cbz) and O-benzyl groups.

Pd catalysts supported on dual-pore monolithic silica beads for chemoselective hydrogenation under batch and flow reaction conditions

Two different types of palladium catalysts supported on dual-pore monolithic silica beads [5% Pd/SM and 0.25% Pd/SM(sc)] for chemoselective hydrogenation were developed.

Practical and reliable synthesis of 2',3',5',5″-tetradeuterated uridine derivatives

Deuterated drugs are valuable in the fields of drug discovery and medicinal chemistry. 2',3',5',5″-tetradeuterated uridine derivatives were synthesised from 2,3,5,5'-selectively tetradeuterated ribose using Sajiki's H-D exchanged Ru/C-H2-D2O-NaOH system and silyl-Hilbert-Johnson methods. The total deuterium content of the tetradeuterated uridines was over 92% using either basic or acidic reaction conditions. These derivatives would be expected as building blocks for the synthesis of deuterium-substituted nucleic acid probes for tracking the pharmacokinetics of nucleic acid drugs.

Platinum-on-Carbon-Catalyzed Aqueous Oxidative Lactonization of Diols by Using Molecular Oxygen

A lactonization of various diols catalyzed by platinum on carbon (Pt/C) in water under an atmosphere of molecular oxygen was developed. Derivatives of 1,4- 1,5- and 1,6-diols were transformed into the corresponding five-, six-, and seven-membered lactones by the present oxidative lactonization method.

One-Pot Reaction of Carboxylic Acids, Ynol Ethers, and m-CPBA for Synthesis of α-Carbonyloxy Esters

A novel one-pot reaction of carboxylic acids, ynol ethers, and m-CPBA for the synthesis of α-carbonyloxy esters in the presence of Ag₂O is described. This process provides a direct approach to α-carbonyloxy esters with the achievement of formation of three C-O bonds. The protocol is featured with readily available starting materials and broad substrate scope. Control reactions and isotope-labeling reactions were conducted to elucidate a plausible mechanism.

Birch-Type Reduction of Arenes in 2-Propanol Catalyzed by Zero-Valent Iron and Platinum on Carbon

Catalytic arene reduction was effectively realized by heating in 2-propanol/water in the presence of Pt on carbon (Pt/C) and metallic Fe. 2-Propanol acted as a hydrogen source, obviating the need for flammable (and hence, dangerous and hard-to-handle) hydrogen gas, while metallic Fe acted as an essential co-catalyst to promote reduction. The chemical states of Pt and Fe in the reaction mixture were determined by X-ray absorption near-edge structure analysis, and the obtained results were used to suggest a plausible reaction mechanism, implying that catalytic reduction involved Pt- and Fe-mediated single-electron transfer and the dehydrogenation of 2-propanol.

Polyethyleneimine-Modified Polymer as an Efficient Palladium Scavenger and Effective Catalyst Support for a Functional Heterogeneous Palladium Catalyst

The polyethyleneimine-modified polymers, polystyrene-divinylbenzene-based (TAs) and polymethacrylate-based polymers (TAm), were used as palladium scavengers to eliminate residual palladium species after palladium on carbon-catalyzed Sonogashira-type coupling reaction. Since both TAs and TAm indicated relatively favorable elimination abilities toward residual palladium species in the reaction mixture, the affinities of TAs and TAm for palladium species were used as supports for palladium catalysts. The TAm-supported palladium catalyst (Pd/TAm) indicated better catalyst properties for the chemoselective hydrogenation compared to those of the corresponding TAs-supported palladium catalyst (Pd/TAs). Aromatic benzyl ethers; aromatic and aliphatic N-Cbzs; and aromatic carbonyl groups were smoothly hydrogenated in the presence of 1-5 mol % of Pd/TAm in MeOH or 2-PrOH. In contrast, the hydrogenation of aromatic ketones was selectively suppressed in morpholine which act as appropriate catalyst poison and solvent. Furthermore, Pd/TAm-catalyzed chemoselective hydrogenation was applicable to continuous-flow reaction.

Multicomponent Ugi Reaction of Indole- N-carboxylic Acids: Expeditious Access to Indole Carboxamide Amino Amides

A novel multicomponent Ugi-type reaction for the synthesis of indole carboxamide amino amides from aldehydes, amines, isocyanides, and indole- N-carboxylic acids, which were simply prepared from indoles and CO₂, is described. This method provides an expeditious and practical access to indole tethered peptide units, along with the achievement of remarkable structural diversity and brevity. Gram-scale reaction was conducted to demonstrate the scalability, and the products could be transformed to new indole derivatives.