Absence Of Transition Metal Catalyst Research Articles

Temperature-Controlled Divergent Synthesis of Pyrazoles and 1-Tosyl-1H-pyrazoles under Transition-Metal-Catalyst- and Oxidant-Free Conditions.

Herein, a general and practical temperature-controlled approach for the divergent synthesis of pyrazoles and 1-tosyl-1H-pyrazoles via electrophilic cyclization in the absence of transition-metal catalysts and oxidants was developed. The desired products were obtained in moderate to excellent yields from common starting materials in both ionic liquids and ethanol by simply tuning the reaction temperature. This strategy employs easily synthesized substrates, mild reaction conditions, and excellent functional-group tolerance.

Synthesis of Novel Trisubstituted Olefin-Type Probe Molecules Containing N-Heterocycles and Their Application in Detection of Malononitrile

Recently, the construction of the trisubstituted olefin-type probe molecules has elicited the attention of many researchers. However, the synthesis of the trisubstituted olefin-type probes containing two N-heterocycles simultaneously has been rarely reported. In this study, starting from the inexpensive mucobromic acid 1 and N-heterocyclic compound 2, we first utilized a simple one-step reaction to synthesize a series of trisubstituted olefin-type compounds 3 simultaneously bearing with the structure of two N-heterocyclic rings in the absence of transition metal catalysts with a yield of 62–86%. The optimal reaction conditions were systematically explored, and the structure of the obtained compounds 3 were well characterized with 1H NMR, 13C NMR, X-ray single-crystal and HR-MS. The preliminary observation showed that, in the presence of base, mucobromic acid 1 reacts as its ring-opening structure, and the successive nucleophilic substitution reaction and Michael addition reaction can generate the target product 3. Considering that the aldehyde group in the molecular structure of the trisubstituted olefin-type compounds 3 may react with malononitrile, we carried out some relevant investigations so as to realize the visual detection of malononitrile. Interestingly, among the products, compounds 3a–3c can be prepared in portable test strips through a simple process and used to achieve the naked-eye detection of malononitrile in environmental systems as designed.

Dehalogenative Arylation of Unactivated Alkyl Halides via Electroreduction.

Herein, a facile and efficient dehalogenative arylation of unactivated alkyl halides enabled by electrochemical reductive coupling is developed, affording a series of C(sp2)-C(sp3) products in moderate to good yields. This protocol proceeds in the absence of transition metal catalysts and redox mediators. The reaction features mild conditions, broad substrate scope, and high tolerance of functional groups and is demonstrated to be applicable for gram-scale synthesis and late-stage functionalization of natural products.

Valorization of beetle infected spruce to produce textile fibers and biofuels: Environmental sustainability evaluated by life cycle assessment

To achieve a viable forest-based biorefinery, both the carbohydrate and lignin parts of the raw material should be valorized. While lignin-first approaches have successfully been applied to hardwoods, where up to 50% of the lignin –close to the ‘theoretical maximum yield’– has been transformed to valuable monophenols; limited studies have targeted softwoods. Softwood lignin comprises lower amount of beta-ether bonds and this results in lower theoretical and observed yields of monophenols in reductive catalytic fractionation (RCF): below 5 wt% yield of initial biomass has been reported. In this study, we use beetle infected spruce, a softwood, as raw material. A fast fractionation was developed to give a pulp and a lignin fraction in the absence of transition metal catalysts. The carbohydrate matrix was valorized to dissolving grade pulp in 37 wt% from biomass (86% yield), and successfully spun to Lyocell fibers. The lignin fraction was dissolved in furfural –operating as green ‘solubility-enhancing-agent’– to blend lignin in inert carrier liquids to promote controlled hydrotreatment to yield biofuels in 10 wt% (60% carbon yield) from initial biomass. Life cycle assessment (LCA) of the value-chain showed improved sustainability in several footprint categories compared to cotton production. Thus, upgrading of a considered forestry waste to high value textile fibers and biofuels has been achieved: in case of lignin beyond the ‘theoretical maximum yield’. This is an important step to mitigate a future growing demand of textiles without negatively affecting irrigation or land use.

Catalyst- and Additive-Free Electrochemical CO2 Fixation into Morita–Baylis–Hillman Acetates

AbstractThe electrochemical carboxylation of Morita–Baylis–Hillman (MBH) acetates with CO2 is presented. The process proceeds in the absence of transition-metal catalysts and relies on the cathodic reduction of MBH acetates to generate nucleophilic anions that are able to trap low-pressure CO2. Valuable succinate derivatives are obtained (20 examples) in high yields (up to 90%) and with excellent functional group tolerance. A remarkable substrate-controlled (electronic nature) regioselectivity of the transformation is documented along with a mechanistic rationale based on control experiments.

Recent advances in catalytic decarboxylative transformations of carboxylic acid groups attached to a non-aromatic sp2 or sp carbon.

Chemists learn the most important transformations of the carboxylic acid functionality (COOH) from as early as the first semester of their studies. Carboxylic acids are not only safe to store and handle, but also broadly accessible with great structural diversity either from commercial sources or by means of a large variety of well-known synthesis routes. Consequently, carboxylic acids have long been recognized as a highly adaptable starting material in organic synthesis. A large body of reactions of carboxylic acids are based on catalytic decarboxylative conversions, in which the COOH group of carboxylic acids is catalytically replaced without trace by extrusion of CO2 chemo- and regioselectively. Within the last two decades, the area of catalytic decarboxylative transformations has expanded significantly by utilizing various classes of carboxylic acids as the substrate, including (hetero)aromatic acids, alkyl acids, α-keto acids, α,β-unsaturated acids and alkynoic acids. A literature survey reveals that compared to aromatic acids, the number of original research papers on decarboxylative reactions of α-keto acids, α,β-unsaturated acids and alkynoic acids has been rising every year lately, particularly within past five to six years. The prime aim of the current review is to give an overview of the decarboxylative transformations of α-keto acids, α,β-unsaturated acids and alkynoic acids that have been developed since 2017. The article focuses on the decarboxylative functionalizations that occur in the presence or absence of transition metal catalysts and/or under photoredox catalysis.

Transition-Metal-Free N-Arylation of N-Methoxysulfonamides and N,O-Protected Hydroxylamines with Trimethoxyphenyliodonium (III) Acetates

AbstractTrimethoxyphenyliodonium(III) acetate [TMP-iodonium(III) acetate] functions as an efficient arylation reagent for N,O-protected hydroxylamines, generating aniline derivatives in the absence of transition metal catalysts. Various N-methoxysulfonamides participated in the amination reaction to produce the corresponding N-methoxysulfonylanilines. This amination reaction was compatible with several protecting groups, including Troc (2,2,2-trichloroethoxycarbonyl), Cbz (benzyloxycarbonyl), Boc (tert-butoxycarbonyl), benzyl, acetyl, and silyl groups. This method uses TMP-iodonium(III) acetate and efficiently synthesizes various aniline derivatives that are versatile synthetic intermediates for functional organic molecules.

2,3]-Sigmatropic Rearrangement of Arylhydroxylamines: Rapid Access to ortho-Sulfonylated Anilines

AbstractIn the absence of transition-metal catalysts and additional oxidants, arylhydroxylamines can undergo an unconventional O-sulfinylation/[2,3]-sigmatropic rearrangement/rearomatization cascade with trifluoromethylsulfinyl chloride to rapidly and efficiently synthesize versatile ortho-sulfonylated aromatic amines. This Synpacts article describes the discovery, further study, and practical application of the rearrangement reactions in arylhydroxylamine compounds and highlights our recent advances in this area.1 Introduction2 Discovery of a New Reaction3 O-Sulfinylation of Arylhydroxylamines Followed by [2,3]-σ Rearrangement4 Conclusion

Recent Advances in Cross-Couplings of Functionalized Organozinc Reagents

AbstractCross-couplings involving organozinc reagents usually require a Pd-catalyst (Negishi cross-coupling), however, uncatalyzed cross-couplings of zinc organometallics proceed well in the absence of transition-metal catalysts with reactive electrophiles such as benzal 1,1-diacetates, benzhydryl acetates, and iminium trifluoroacetates. Organozinc compounds also undergo C–N bond formation with O-benzoylhydroxylamines or organic azides in the presence of cobalt- or iron-catalysts. Highly diastereoselective and enantioselective cross-couplings can be readily performed with room-temperature configurationally stable alkylzinc species, producing diastereoselectively and enantiomerically enriched products. Finally, highly regioselective magnesiations of functionalized arenes and heteroarenes undergo Negishi (after transmetalation with ZnCl2) or Cu-catalyzed cross-couplings.1 Introduction2 Uncatalyzed Cross-Couplings of Organozinc Reagents with Highly Electrophilic Partners3 Iron- and Cobalt-Catalyzed Aminations using Organozinc Reagents4 Stereo- and Regioselective Cross-Couplings of Organozinc Reagents5 Conclusion

Metal‐Free Doubly Decarboxylative Three‐Component Reaction: Synthesis of Propargyl Amines

AbstractArylalkynoic acids, glyoxylic acid, and amines were reacted in the absence of transition metal catalysts to produce the corresponding arylpropargyl amines via double decarboxylation. In addition to cyclic secondary amines, non‐cyclic secondary amines also reacted with various substituted arylalkynoic acids and glyoxylic acid to afford the desired products in good yields. It was revealed that the carboxylic acid functionality was important for increasing the product yield.

Sulfur-Promoted Redox Cyclization of 2,2′-Dinitrodiphenyl Disulfides and Benzylamines

AbstractThis study aims to develop green and sustainable advanced synthetic methods based on redox cyclization. Elemental sulfur is shown to promote the efficient synthesis of 2-substituted benzothiazoles from 2,2′-dinitrodiphenyl disulfides and benzylamines via redox cyclization in the absence of transition-metal catalysts and solvents. The 2-substituted benzothiazoles are obtained in good to excellent yields. This synthetic methodology is highly atom-economical and does not require any external oxidizing and/or reducing agents.

Green synthesis of graphite from CO2 without graphitization process of amorphous carbon

Environmentally benign synthesis of graphite at low temperatures is a great challenge in the absence of transition metal catalysts. Herein, we report a green and efficient approach of synthesizing graphite from carbon dioxide at ultralow temperatures in the absence of transition metal catalysts. Carbon dioxide is converted into graphite submicroflakes in the seconds timescale via reacting with lithium aluminum hydride as the mixture of carbon dioxide and lithium aluminum hydride is heated to as low as 126 °C. Gas pressure-dependent kinetic barriers for synthesizing graphite is demonstrated to be the major reason for our synthesis of graphite without the graphitization process of amorphous carbon. When serving as lithium storage materials, graphite submicroflakes exhibit excellent rate capability and cycling performance with a reversible capacity of ~320 mAh g–1 after 1500 cycles at 1.0 A g–1. This study provides an avenue to synthesize graphite from greenhouse gases at low temperatures.

Grignard-Reagent-Promoted Desulfonylation/Intramolecular Coupling for the Synthesis of 2-(1-Fluorovinyl)pyridines.

A novel process involving Grignard-reagent-promoted desulfonylation/intramolecular coupling of readily available α-fluoro-α,β-unsaturated-(2-pyridyl)sulfones was realized that provided a series of polysubstituted 2-(1-fluorovinyl)pyridines in good yields. The intrinsic coordination between pyridine and Mg(II) along with the "negative fluorine effect" of the substrates should play the key role for the smooth transformation in the absence of transition-metal catalysts.

Transition-Metal-Free Synthesis of 2-Substituted Benzothiazoles from Nitrobenzenes, Methylheteroaryl Compounds, and Elemental Sulfur, Based on Nitro-Methyl Redox-Neutral Cyclization.

Greener and more sustainable chemical processes are required to address increasing environmental pollution and depletion of natural resources. This paper aims to develop greener and more sustainable modern synthetic chemical processes using redox-neutral cyclization. Redox-neutral cyclization has been shown to promote the efficient synthesis of 2-substituted benzothiazoles from easily available nitrobenzenes, methyl-heteroaryl compounds, and elemental sulfur in the absence of transition-metal catalysts. The 2-substituted benzothiazoles were obtained in reasonable yields through the sulfuration of electron-deficient C-H bonds with elemental sulfur. This synthetic methodology also affords a high atom economy without the use of any external oxidizing and/or reducing reagents.

Triarylborane-Catalyzed Alkenylation Reactions of Aryl Esters with Diazo Compounds.

Herein we report a facile, mild reaction protocol to form carbon–carbon bonds in the absence of transition metal catalysts. We demonstrate the metal‐free alkenylation reactions of aryl esters with α‐diazoesters to give highly functionalized enyne products. Catalytic amounts of tris(pentafluorophenyl)borane (10–20 mol %) are employed to afford the C=C coupled products (31 examples) in good to excellent yields (36–87 %). DFT studies were used to elucidate the mechanism for this alkenylation reaction.

Base-promoted selective O-phosphorylation of aryl triflates with P(O)-H compounds

Compared to previous transition metal-catalyzed C-phosphorylation reactions for constructing C–P bonds, in the absence of transition metal catalysts and ligands, a direct O-phosphorylation of aryl triflates selectively occurred with P(O)-H compounds in the presence of a base via the construction of O–P bonds. This transformation proceeds under simple and mild conditions, and provides a new method for the preparation of valuable organophosphoryl compounds from readily available P(O)-H compounds and triflates.

8+3]-Cycloaddition of Tropones with Azaoxyallyl Cations.

Although azaoxyallyl cations are widely used as 1,3-dipoles for various cycloaddition reactions leading to nitrogen-containing heterocycles, their application in higher-order cycloaddition reaction remains scarce. Herein, we present the [8+3]-cycloaddition reaction of tropones with in situ generated azaoxyallyl cations allowing the one-step construction of cycloheptatriene-fused 1,4-oxazinones in moderate to good yields. This base-promoted new carbon-oxygen and carbon-nitrogen bond-forming reaction takes place under mild conditions in the absence of transition metal catalysts.

Nonafluoro- tert-butoxylation of Diaryliodonium Salts.

A highly efficient method to incorporate the nonafluoro- tert-butoxy group into various arenes is developed. This C-O cross-coupling reaction proceeds smoothly in the absence of transition-metal catalyst with good functional group tolerance and scalability. In comparison with the conventional approach, this method avoids the use of nonafluoro- tert-butyl alcohol as the reaction solvent and does not require handling of hazardous diazonium salts. A series of OC(CF3)3-containing analogues of 19F NMR-based probes targeting various biologically relevant analytes are prepared.

Synthesis of 3,5‐Diaryl‐2,6‐dicyanoanilines from Tandem Reactions of Ynones with Malononitrile

AbstractA new method for the synthesis of 3,5‐diaryl‐2,6‐dicyanoanilines from tandem reactions of ynones with malononitrile in the absence of transition metal catalysts is described. This protocol has good functional group tolerance, mild condition, high yield and simple work‐up procedure.

Nucleophilic substitution of hydrogen–the Boger reaction sequence as an approach towards 8-(pyridin-2-yl)coumarins

5,7-Dimethoxy-8-(3,6-diphenylpyridin-2-yl)coumarins were obtained from 5,7-dimethoxycoumarins and 3,6-diphenyl-1,2,4-triazines via the protocol comprising aromatic S N H substitution in the triazine ring followed by the Boger transformation of formed triazine moiety into the pyridine one. The advantages of the suggested method are simple procedures, high yields, and the absence of transition-metal catalysts.