Transition-Metal-Free Upscaling of 2,5-Furandicarboxylic Acid Synthesis and Investigation of the Reaction Mechanism.

An environmentally friendly oxidation system has proposed for the practical and scalable production of value-added 2,5-furandicarboxylic acid from 1 kg of 5-hydroxymethylfurfural. The system is composed of a simple base, oxygen, and a green solvent, thereby providing a sustainable and economical approach to organic synthesis. To gain insight into the mechanism of this oxidation process, NMR spectroscopic analysis and kinetic study are used for the mechanistic investigation of this environmentally friendly oxidation process.

Transition-Metal-Free Unusual Oxidative Cleavage of Homoallylic Alcohol and Its Application in the Upcycling of Terpene to Value-Added Chemicals.

A NaOtBu-O -mediated oxidative dehomologation of homoallylic alcohols into structurally different carboxylic acids through direct oxidative cleavage of either the C(sp )-C(sp ) or C(sp )-C(sp ) bond utilizing enolate chemistry was demonstrated. Furthermore, under transition-metal-free conditions, this protocol has been applied to convert terpene as biomass feedstock into value-added chemicals.

Preparation of Contiguous Bisaziridines for Regioselective Ring-Opening Reactions.

Aziridines, a class of reactive organic molecules containing a three-membered ring, are important synthons for the synthesis of a large variety of functionalized nitrogen-containing target compounds through the regiocontrolled ring-opening of C-substituted aziridines. Despite the tremendous progress in aziridine synthesis over the past decade, accessing contiguous bisaziridines efficiently remains difficult. Therefore, we were interested in synthesizing contiguous bisaziridines bearing an electronically diverse set of N-substituents beyond the single aziridine backbone for regioselective ring-opening reactions with diverse nucleophiles.

Synergistic Catalysis: Highly Enantioselective Cascade Reaction for the Synthesis of Dihydroacridines.

The first stereoselective synthesis of dihydroacridines through synergistic catalysis, achieving the final target compounds with good to excellent yields and good to excellent enantioselectivities and diastereoselectivities, is reported. The synergistic approach consists in the activation of substituted quinolines with a Lewis acid catalyst that react in a cascade fashion with activated enals in the iminium form. Mechanistic calculations support a consecutive Michael-aldol reaction, followed by dehydration.

Birch Reduction of Aromatic Compounds by Inorganic Electride [CaN]e in an Alcoholic Solvent: An Analogue of Solvated Electrons.

Birch reduction of aromatic systems by solvated electrons in alkali metal-ammonia solutions is widely recognized as a key reaction that functionalizes highly stable π-conjugated organic systems. In spite of recent advances in Birch reduction with regard to reducing agent and reaction conditions, there remains an ongoing challenge to develop a simple and efficient Birch reaction under mild conditions. Here, we demonstrate that the inorganic electride [CaN]e promotes the Birch reduction of polycyclic aromatic hydrocarbons (PAHs) and naphthalene under alcoholic solvent in the vicinity of room temperature as a solid-type analogy to solvated electrons in alkali metal ammonia solutions.

New development in the enantioselective synthesis of spiro compounds.

The enantioselective synthesis of spirocycles has long been pursued by organic chemists. Despite their unique 3D properties and presence in several natural products, the difficulty in their enantioselective synthesis makes them underrepresented in pharmaceutical libraries. Since the first pioneering reports of the enantioselective construction of spirosilanes by Tamao et al.

A metal-free and mild approach to 1,3,4-oxadiazol-2(3H)-ones via oxidative C-C bond cleavage using molecular oxygen.

A mild metal-free approach to 1,3,4-oxadiazol-2(3H)-ones via 1,3,4-oxadiazin-5(6H)-ones is described. This novel transformation, promoted by the electron-withdrawing p-substituents on the phenyl group at the α-carbonyl position, features a tandem reaction consisting of oxidative hydroxylation and C-C bond cleavage using molecular oxygen. The method utilizes KCO in CHCN without any oxidants, transition metals, or additives, enabling the tunable synthesis of 1,3,4-oxadiazin-5(6H)-ones, 1,3,4-oxadiazol-2(3H)-ones, and α-ketoamides under mild aerobic conditions.

Copper-Catalyzed Asymmetric Synthesis of Borylated cis-Disubstituted Indolines.

A copper-catalyzed, intramolecular borylative cyclization of vinyl arenes with imines is reported, which affords enantio-enriched indolines as a single diastereomer under mild conditions. A benzylcopper species is generated by Cu-Bpin addition to the alkene, which then acts as a nucleophile for intramolecular imine addition. The reaction is applicable to various vinyl arenes with an imine moiety at the ortho-position, including heterocycles, for formation of borylated indolines in good yields and ee values up to 90 %.

Preparation of Chiral Contiguous Epoxyaziridines and Their Regioselective Ring-Opening for Drug Syntheses.

Synthetically valuable chiral (aziridin-2-yl)oxirane-3-carbaldehydes bearing three consecutive functional groups including aziridine, epoxide, and aldehyde were prepared from the stereoselective epoxidation of (aziridin-2-yl)acrylaldehydes with H O using organocatalyst (2R)- or (2S)-[diphenyl(trimethylsilyloxy)methyl]pyrrolidine as organocatalyst. The regioselective ring opening of aziridines and epoxides enabled us to achieve the highly efficient asymmetric synthesis of the antibiotic edeine D fragment 3-hydroxy-4,5-diaminopenatanoic acid, an intermediate for the formal synthesis of non-proteinogenic amino acid (-)-galantinic acid, and for potent antifungal agent (+)-preussin, and the medicinally important framework 3-hydroxy-2-hydroxymethylpyrrolidine.

Asymmetric Synthesis of α-Fluoro-β-Amino-oxindoles with Tetrasubstituted C-F Stereogenic Centers via Cooperative Cation-Binding Catalysis.

Biologically relevant chiral 3,3-disubstituted oxindole products containing a β-fluoroamine unit are obtained in high yields and with excellent stereoselectivity (up to 99% ee, dr >20:1 for syn) through the organocatalytic direct Mannich reaction of 3-fluoro-oxindoles as fluoroenolate precursors and α-amidosulfones as the bench-stable precursors of sensitive imines by using a chiral oligoethylene glycol and KF as a cation-binding catalyst and base, respectively. This protocol can be easily scaled without compromising the asymmetric induction. Furthermore, this protocol was also successfully extended to generate tetrasubstituted C-Cl and C-Br stereogenic centers.

Mixed Monosilyl Acetals and Catalyst-Dependent Chemoselective Mukaiyama Aldol Reactions.

We report a direct, simple, and straightforward approach for the construction of a mixed monosilyl acetal as a new and synthetically valuable functional group by mixing an aldehyde, sodium tert-butoxide, and trimethylsilyl azide. We also demonstrate a catalyst-dependent chemoselective reaction between mixed monosilyl acetals and silyl ketene acetals through Mukaiyama aldol reactions to give different structures of O-protected β-hydroxy esters in excellent yields with high chemoselectivities. This study provided the existence of an oxonium ion intermediate and of its kinetically controlled reaction with the pre-equilibrated silyl enol ether obtained from (E)- and (Z)-isomerization.

Impact of Carboxyl Groups in Graphene Oxide on Chemoselective Alcohol Oxidation with Ultra-Low Carbocatalyst Loading.

A highly efficient and simple chemoselective aerobic oxidation of primary alcohols to either aldehydes or carboxylic acids in the presence of nitric acid was developed, utilising 5 wt% graphene oxide as a carbocatalyst under ambient reaction conditions. Carboxylic acid functional groups on graphene oxides played a vital role in carbocatalyst activity, greatly influencing both the reactivity and selectivity. We also applied this protocol to a variant of the Knoevenagel condensation for primary alcohols and malonates with a secondary amine co-catalyst via cooperative catalysis.

Chemoselective Hydrodehalogenation of Organic Halides Utilizing Two-Dimensional Anionic Electrons of Inorganic Electride [CaN]·e.

Halogenated organic compounds are important anthropogenic chemicals widely used in chemical industry, biology, and pharmacology; however, the persistence and inertness of organic halides cause human health problems and considerable environmental pollution. Thus, the elimination or replacement of halogen atoms with organic halides has been considered a central task in synthetic chemistry. In dehalogenation reactions, the consecutive single-electron transfer from reducing agents generates the radical and corresponding carbanion and thus removes the halogen atom as the leaving group.

Organocatalytic regiospecific synthesis of 1H-indene-2-carbaldehyde derivatives: suppression of cycloolefin isomerisation by employing sterically demanding catalysts.

The regiospecific synthesis of 1H-indene-2-carbaldehyde derivatives was achieved through transition-metal-free, reductive cyclisation of ortho-formyl trans-cinnamaldehydes with Hantzsch ester in the presence of an aminocatalyst. In particular, cycloolefin isomerisation of the resulting products could be inhibited efficiently by the introduction of a sterically demanding stereo-defined aminocatalyst.

Enantioselective Organocatalytic Cyclopropanation of Enals Using Benzyl Chlorides.

Herein, we describe the first enantioselective cyclopropanation of enals using benzyl chlorides as bifunctional (nucleophilic and electrophilic) reagents. The reaction is simply catalyzed by chiral secondary amines to afford the formyl cyclopropane derivatives in good yields with moderate to excellent stereoselectivities.

Metal-Free Chemoselective Oxidative Dehomologation or Direct Oxidation of Alcohols: Implication for Biomass Conversion.

A transition metal-free, chemoselective reaction was performed using the sodium tert-butoxide-oxygen (NaO(t) Bu-O2 ) system, resulting in either oxidative dehomologation or direct oxidation of alcohols. In particular, the newly developed protocol may be used to predict the major product formed, which depends on alkyl chain length of the alcohols and reaction conditions. The rational mechanism of this transformation was also demonstrated by performing an (18) O isotopic labelling experiment.

Acetaldehyde: A Small Organic Molecule with Big Impact on Organocatalytic Reactions.

Stereocontrolled formation of carbon-carbon and carbon-heteroatom bonds through asymmetric organocatalysis is a formidable challenge for modern synthetic chemistry. Among the most significant contributions to this field are the transformations involving the use of acetaldehyde or α-heteroatom-substituted acetaldehydes for constructing valuable synthons (e.g.

Two dimensional inorganic electride-promoted electron transfer efficiency in transfer hydrogenation of alkynes and alkenes.

A simple and highly efficient transfer hydrogenation of alkynes and alkenes by using a two-dimensional electride, dicalcium nitride ([CaN]·e), as an electron transfer agent is disclosed. Excellent yields in the transformation are attributed to the remarkable electron transfer efficiency in the electride-mediated reactions. It is clarified that an effective discharge of electrons from the [CaN]·e electride in alcoholic solvents is achieved by the decomposition of the electride alcoholysis and the generation of ammonia and Ca(OPr).

Chemoselective reduction and oxidation of ketones in water through control of the electron transfer pathway.

The selective synthesis of different products from the same starting materials in water, which is the most abundant solvent in nature, is a crucial issue as it maximizes the utilization of materials. Realizing such reactions for ketones is of considerable importance because numerous organic functionalities can be obtained via nucleophilic addition reactions. Herein, we report chemoselective reduction and oxidation reactions of 1,2-diketones in water, which initiates anionic electron transfer from the inorganic electride [Ca24Al28O64](4+)·4e(-), through controlling the pathway of the electrons to substrates.

Hydrotrifluoromethylation and iodotrifluoromethylation of alkenes and alkynes using an inorganic electride as a radical generator.

The trifluoromethyl (CF3) group is a staple synthon that can alter the physical and chemical properties of organic molecules. Despite recent advances in trifluoromethylation methods, the development of a general synthetic methodology for efficient and selective trifluoromethylation remains an ongoing challenge motivated by a steadily increasing demand from the pharmaceutical, agrochemical and materials science industries. In this article, we describe a simple, efficient and environmentally benign strategy for the hydrotrifluoromethylation of unactivated alkenes and alkynes through a radical-mediated reaction using an inorganic electride, [Ca2N](+) · e(-), as the electron source.

Transition-metal-free and chemoselective NaO(t)Bu-O2-mediated oxidative cleavage reactions of vic-1,2-diols to carboxylic acids and mechanistic insight into the reaction pathways.

A method for efficient oxidative cleavage of vic-1,2-diols using a NaO(t)Bu-O2 system resulted in the formation of carboxylic acids in high yields. The present protocol is an eco-friendly alternative to a conventional transition-metal-based method. This new strategy allows large-scale production with nonchromatographic purification while also suppressing competitive reaction pathway such as benzilic acid rearrangement.

The scalable pinacol coupling reaction utilizing the inorganic electride [Ca2N](+)·e(-) as an electron donor.

The scalable pinacol coupling reaction is realized utilizing the inorganic electride [Ca2N](+)·e(-) as an electron donor in organic solvents. The bond cleavages of the [Ca2N](+) layers by methanol play a vital role in transferring anionic electrons to electrophilic aldehydes, accompanying the formation of Ca(OMe)2 and ammonia.

Chemoselective and repetitive intermolecular cross-acyloin condensation reactions between a variety of aromatic and aliphatic aldehydes using a robust N-heterocyclic carbene catalyst.

We found that chemoselectivity of the crossed acyloin product is controlled by the adjustment of the aromatic aldehyde/aliphatic aldehyde ratio. Moreover, we observed the persistent catalytic activity of the homogeneous NHC catalyst in a solution due to NHC catalyst robustness.

Organocatalytic asymmetric synthesis of β(3)-amino acid derivatives.

β(3)-Amino acid derivatives are an essential resource for pharmaceutical production, medicinal chemistry, and biochemistry. In this article, recent developments in versatile organocatalysis, i.e.

N-heterocyclic carbene-catalysed intermolecular Stetter reactions of acetaldehyde.

A facile method for the intermolecular Stetter reaction of various Michael acceptors with acetaldehyde as a biomimetic acylanion source was realized using N-heterocyclic carbene catalysis. This catalytic system has also been applied to the enantioselective Stetter reaction and resulted in moderate to good enantioselectivities for the corresponding Stetter products.