Catalyst‐Free Hydroxytrifluoromethylation of Alkenes UsingIodotrifluoromethane

The importance of CF₃‐containing molecules in pharmaceuticals, agrochemicals and materials intrigues the intense interest in synthetic methodology of these compounds. With a purpose to enrich trifluoromethylation methodology, we carefully examined the substrate scope of hydroxytrifluoromethylation of alkenes using iodotrifluoromethane, and the reaction provided β‐trifluoromethyl alcohols in good yields under extremely mild conditions without catalysts. We found that our reaction can be applied to not only styrenes but also various aliphatic alkenes with excellent selectivity; no ketone was detected in most of our cases. Another feature of our discovery is “simple”. The reaction was carried out in air, irradiated by visible light, at room temperature and most importantly no catalyst was needed. A solution of CF₃I in DMSO was used as the facile trifluoromethylating reagent, which simplified the utilization of gaseous CF₃I. Based on ¹⁹F NMR spectroscopy, we observed a halogen bond between CF₃I and tertiary amine in this reaction. The interaction may promote single electron transfer by the visible light irradiation.     

Catalyst‐Free and Solvent‐Free Facile Hydroboration of Imines

A facile process for the catalyst‐free and solvent‐free hydroboration of aromatic as well as heteroaromatic imines is reported. This atom‐economic methodology is scalable, compatible with sterically and electronically diverse imines, displaying excellent tolerance towards various functional groups, and works efficiently at ambient temperature in most of the cases, affording secondary amines in good to excellent yield after hydrolysis.     

Co‐Catalyst‐Free Chemical Fixation of CO2 into Cyclic Carbonates by using Metal‐Organic Frameworks as Efficient Heterogeneous Catalysts

The concentration of carbon dioxide (CO₂) in the atmosphere is increasing at an alarming rate resulting in undesirable environmental issues. To mitigate this growing concentration of CO₂, selective carbon capture and storage/sequestration (CCS) are being investigated intensively. However, CCS technology is considered as an expensive and energy‐intensive process. In this context, selective carbon capture and utilization (CCU) as a C1 feedstock to synthesize value‐added chemicals and fuels is a promising step towards lowering the concentration of the atmospheric CO₂ and for the production of high‐value chemicals. Towards this direction, several strategies have been developed to convert CO₂, a Greenhouse gas (GHG) into useful chemicals by forming C?N, C?O, C?C, and C?H bonds. Among the various CO₂ functionalization processes known, the cycloaddition of CO₂ to epoxides has gained considerable interest owing to its 100% atom‐economic nature producing cyclic carbonates or polycarbonates in high yield and selectivity. Among the various classes of catalysts studied for cycloaddition of CO₂ to cyclic carbonates, porous metal‐organic frameworks (MOFs) have gained a special interest due to their modular nature facilitating the introduction of a high density of Lewis acidic (LA) and CO₂‐philic Lewis basic (LB) functionalities. However, most of the MOF‐based catalysts reported for cycloaddition of CO₂ to respective cyclic carbonates in high yields require additional co‐catalyst, say tetra‐n‐butylammonium bromide (TBAB). On the contrary, the co‐catalyst‐free conversion of CO₂ using rationally designed MOFs composed of both LA and LB sites is relatively less studied. In this review, we provide a comprehensive account of the research progress in the design of MOF based catalysts for environment‐friendly, co‐catalyst‐free fixation of CO₂ into cyclic carbonates.     

Catalyst‐Free Enantiospecific Olefination with In Situ Generated Organocerium Species

Described is the in situ formation of triorganocerium reagents and their application in catalyst‐free Zweifel olefinations. These unique cerium species were generated through novel exchange reactions of organohalides with n‐Bu₃Ce reagents. The adequate electronegativity of cerium allowed for compensating the disadvantages of both usually functional‐group‐sensitive organolithium species and less reactive organomagnesium reagents. Exchange reactions were performed on aryl and alkenyl bromides, enabling enantiospecific transformations of chiral boron pinacol esters. Finally, these new organocerium species were engaged in selective 1,2‐additions onto enolisable and sterically hindered ketones.     

Visible‐Light Promoted Catalyst‐Free Imidation of Arenes and Heteroarenes

We described herein a catalyst‐free visible‐light photolytic protocol for the imidation of arenes and heteroarenes. N‐Bromosaccharin was identified as a viable and chemoselective nitrogen radical precursor that undergoes controllable homolytic cleavage under ambient light irradiation. The reaction can be applied to a number of arenes and heteroarenes with good chemo‐ and regioselectivity. Mechanistic studies revealed that radical chain termination by electron transfer‐proton transfer (ET‐PT) is the leading productive pathway for the reaction.     

Catalyst‐Free Reductive Coupling of Aromatic and Aliphatic Nitro Compounds with Organohalides

A rare reductive coupling of nitro compounds with organohalides has been realized. The reaction is initiated by a partial reduction of the nitro group to a nitrenoid intermediate. Therefore, not only aromatic but also aliphatic nitro compounds are efficiently transformed into monoalkylated amines, with organohalides as the alkylating agent. Given the innate reactivity of the nitrenoid, a catalyst is not required, resulting in a high tolerance for aryl halide substituents in both starting materials.     

Catalyst‐Free One‐Pot Synthesis of Ketene Imines under Ultrasound Irradiation

An efficient and simple procedure for the synthesis of ketene imines via a one‐pot three‐component reaction of cyclohexyl isocyanide, diethyl acetylenedicarboxylate, and 1,4‐dihydropyridines under ultrasonic irradiation is described. The remarkable advantages are the simplicity of the experimental procedures, high yields, and short reaction times.     

Ligand‐Free Palladium‐Catalyzed Aerobic Oxidative Coupling of Carboxylic Anhydrides with Arylboronic Acids

We report a new, effective and environmentally friendly protocol for selective aerobic oxidative coupling of arylboronic acids with carboxylic anhydrides in the presence of ligand‐free palladium catalyst. The aryl benzoates are obtained in good to excellent yields.     

Visible Light‐Induced Synthesis of Biscoumarin Analogs under Catalyst‐Free Conditions

Biscoumarin analogs were synthesized by the reaction between two equivalent of 4‐hydroxycoumarin and one equivalent of aryl aldehydes induced by visible light [22 W compact fluorescent lamp (CFL) bulb]. This new method is simple, cost‐effective, and furnished excellent yields with broad substrate generality in short reaction time.     

Catalyst‐Free and Green Synthesis of Some Novel Benzamide Derivatives

In the present work, a simple, green, rapid, and catalyst‐free procedure for the synthesis of benzamide derivatives by ring opening of azlactones with diamines such as ethylene diamine and 1,3‐propylenediamine is described. The present method offers several advantages such as short reaction times, easy work‐up, and mild reaction conditions in the absence of catalyst and any toxic solvent and material. In addition, the structure obtained by X‐ray crystallography was compared with the theoretical results obtained by density functional theory using the B3LYP functional and cc‐pVDZ basis sets.     

Catalyst‐Free Formal Thioboration to Synthesize Borylated Benzothiophenes and Dihydrothiophenes

The first ring‐forming thioboration reaction of C?C π bonds is reported. This catalyst‐free method proceeds in the presence of a commercially available external electrophilic boron source (B‐chlorocatecholborane) in good to high yields. The method is scalable and tolerates a variety of functional groups that are intolerant of other major borylation methods. The resulting borylated benzothiophenes participate in a variety of in situ derivatization reactions, showcasing that these borylated intermediates do not need to be isolated prior to downstream functionalization. This methodology has been extended to the synthesis of borylated dihydrothiophenes. Mechanistic experiments suggest that the operative mechanistic pathway is through boron‐induced activation of the alkyne followed by electrophilic cyclization, as opposed to S?B σ bond formation, providing a mechanistically distinct pathway to the thioboration of C?C π bonds.     

Catalyst‐Free Deaminative Functionalizations of Primary Amines by Photoinduced Single‐Electron Transfer

The use of pyridinium‐activated primary amines as photoactive functional groups for deaminative generation of alkyl radicals under catalyst‐free conditions is described. By taking advantage of the visible light absorptivity of electron donor–acceptor complexes between Katritzky pyridinium salts and either Hantzsch ester or Et₃N, photoinduced single‐electron transfer could be initiated in the absence of a photocatalyst. This general reactivity platform has been applied to deaminative alkylation (Giese), allylation, vinylation, alkynylation, thioetherification, and hydrodeamination reactions. The mild conditions are amenable to a diverse range of primary and secondary alkyl pyridiniums and demonstrate broad functional group tolerance.     

A Catalyst‐Free Amination of Functional Organolithium Reagents by Flow Chemistry

Reported is the electrophilic amination of functional organolithium intermediates with well‐designed aminating reagents under mild reaction conditions using flow microreactors. The aminating reagents were optimized to achieve efficient C?N bond formation without using any catalyst. The electrophilic amination reactions of functionalized aryllithiums were successfully conducted under mild reaction conditions, within 1 minute, by using flow microreactors. The aminating reagent was also prepared by the flow method. Based on stopped‐flow NMR analysis, the reaction time for the preparation of the aminating reagent was quickly optimized without the necessity of work‐up. Integrated one‐flow synthesis consisting of the generation of an aryllithium, the preparation of an aminating reagent, and their combined reaction was successfully achieved to give the desired amine within 5 minutes of total reaction time.     

Ligand‐Enabled Auxiliary‐Free meta‐C−H Arylation of Phenylacetic Acids

The meta ‐C−H arylation of free phenylacetic acid was realized using 2‐carbomethoxynorbornene (NBE‐CO₂Me) as a transient mediator. Both the modified norbornene and the mono‐protected 3‐amino‐2‐hydroxypyridine type ligand are crucial for this auxiliary‐free meta ‐C−H arylation reaction. A series of phenylacetic acids, including mandelic acid and phenylglycine, react smoothly with various aryl iodides to provide the meta ‐arylated products in high yields.     

Catalyst‐Free Polyhydroboration of Dodecaborate Yields Highly Photoluminescent Ionic Polyarylated Clusters

The incorporation of polyhedral boranes into novel photoluminescent materials is an area with increasing interest. While the neutral carboranes have been widely investigated for this purpose, the dodecaborate ion has received much less attention. Herein we report a significant expansion to the scope of substitution reactions for the dodecaborate ion, whereby this cluster was observed to react directly with a wide range of arenes in a step‐wise and controlled manner. In the products of these reactions, the dodecaborate ion serves as a core upon which up to nine mono‐ or polycyclic aromatic hydrocarbon ligands are exohedrally bonded. Spectroscopic evidence suggests the presence of conjugation between the π systems of the aryl ligands and the dodecaborate core, resulting in materials which exhibit high solution‐phase photoluminescence, as well as molar absorptivities and Stokes shifts that are significantly larger than those of the free arenes from which they were derived. We propose that this broad reactivity is a valuable synthetic tool for the incorporation of polyhedral boron into novel organic structures.     

Label‐Free Detection of Transferrin Receptor by a Designed Ligand‐Protein Sensor

Advanced detection of biomarkers in biofluids plays an important role in disease diagnosis and prognosis. Current techniques with pre‐labelling suffer from high cost and complicated operation, etc. Herein, we designed a label‐free electrochemical biosensor for rapid detection of transferrin receptor with desirable linear range, sensitivity, specificity, reproducibility, and stability for practical applications.