Radical Replacement Process for Ligated Boryl Radical-Mediated Activation of Unactivated Alkyl Chlorides for C(sp3)-C(sp3) Bond Formation.

The ligated boryl radical (LBR) has emerged as a potent tool for activating alkyl halides in radical transformations through halogen-atom transfer (XAT). However, unactivated alkyl chlorides still present an open challenge for this strategy. We herein describe a new activation mode of the LBR for the activation of unactivated alkyl chlorides to construct a C(sp3)-C(sp3) bond. Mechanistic studies reveal that the success of the protocol relies on a radical replacement process between the LBR and unactivated alkyl chloride, forming an alkyl borane intermediate as the alkyl radical precursor. Aided with the additive K3PO4, the alkyl borane then undergoes one-electron oxidation, generating an alkyl radical. The incorporation of the radical replacement activation model to activate unactivated alkyl chlorides significantly enriches LBR chemistry, which has been applied to activate alkyl iodides, alkyl bromides, and activated alkyl chlorides via XAT.

Dense Monolayer Network Structures of Double Hydrophilic Hyperbranched Copolymers at the Air/Water Interface.

Influences of subphase pH and temperature on the interfacial aggregation behavior of two double hydrophilic hyperbranched copolymers of poly[oligo(ethylene glycol) methacrylate-co-(2-diisopropylamino)ethyl methacrylate] (P(OEGMA-co-DIPAEMA)) at the air/water interface are studied by the Langmuir film balance technique. Morphologies of their Langmuir-Blodgett (LB) films are characterized by atomic force microscopy (AFM). At the interface, P(OEGMA-co-DIPAEMA) copolymers tend to form a dense network structure of circular micelles composed of branching agent-connected carbon backbone cores and mixed shells of OEGMA and DIPAEMA segments (pendant groups). This network structure containing many honeycomb-like holes with diameters of 6-8 nm is identified for the first time and clearly observed in the enlarged AFM images of their LB films. Under acidic conditions, surface pressure versus molecular area isotherms of the two copolymers in the low-pressure region show larger mean molecular area than those under neutral and alkaline conditions due to the lack of impediment from DIPAEMA segments. Upon further compression, each isotherm exhibits a wide pseudo-plateau, which corresponds to OEGMA segments being pressed into the subphase. Furthermore, the isotherms under neutral and alkaline conditions exhibit the lower critical solution temperature behavior of OEGMA segments, and the critical temperature is lower when the hyperbranched copolymer contains higher OEGMA content.

Cross-Electrophile C-PIII Coupling of Chlorophosphines with Organic Halides: Photoinduced PIII and Aminoalkyl Radical Generation Enabled by Pnictogen Bonding.

Pnictogen bonding (PnB) has gained recognition as an appealing strategy for constructing novel architectures and unlocking new properties. Within the synthetic community, the development of a straightforward and much simpler protocol for cross-electrophile C-PIII coupling remains an ongoing challenge with organic halides. In this study, we present a simple strategy for photoinduced PnB-enabled cross-electrophile C-PIII couplings using readily available chlorophosphines and organic halides via merging single electron transfer (SET) and halogen atom transfer (XAT) processes. In this photomediated transformation, the PnB formed between chlorophosphines and alkyl amines facilitates the photogeneration of PIII radicals and α-aminoalkyl radicals through SET. Subsequently, the resulting α-aminoalkyl radicals activate C-X bonds via XAT, leading to the formation of carbon radicals. This methodology offers operational simplicity and compatibility with both aliphatic and aromatic chlorophosphines and organic halides.

Photocatalytic Charge-Transfer Complex Enables Hydroarylation of Alkenes for Heterocycle Synthesis.

Here, we report a photocatalytic charge-transfer complex (CTC) strategy for one electron reduction of alkenes using thiolate as a catalytic electron donor. This catalytic CTC system could engage hydroarylation of both activated and unactivated alkenes for the synthesis of various heterocycles. The reactions do not require any photocatalysts or acids and are easy to perform. Mechanistic studies revealed the formation of a CTC between catalytic thiolate and alkene.

Iron-Catalyzed Intramolecular Arene C(sp2 )-H Amidations under Mechanochemical Conditions.

In a ball mill, FeBr3 -catalyzed intramolecular amidations lead to 3,4-dihydro-2(1H)-quinolinones in good to almost quantitative yields. The reactions do not require a solvent and are easy to perform. No additional ligand is needed for the iron catalyst. Both 4-substituted aryl and ß-substituted dioxazolones provide products with high selectivity. Mechanistically, an electrophilic spirocyclization followed by C-C migration explains the formation of rearranged products.

Introduction of Lipophilic Side Chains to NH-Sulfoximines by Palladium Catalysis Under Blue Light Irradiation.

Palladium catalysis under blue (LED) light irradiation allows conversion of NH-sulfoximines into products with long lipophilic side chains attached to the S═N moiety. The three-component reactions involve both radicals and organometallic intermediates stemming from alkyl bromides and butadienes. The substrate scope is broad, and the products are formed in moderate to good yields.

Visible-Light-Mediated α-Ketoacylations of NH-Sulfoximines with gem-Difluoroalkenes.

A photochemical approach for the preparation of α-keto-N-acyl sulfoximines from NH sulfoximines and gem-difluoroalkenes has been developed. In the presence of NBS, the reactions proceed in air without the need of a photocatalyst or additional oxidant. Results of mechanistic studies suggest that the two oxygens in the products stem from water and dioxygen.

Visible Light-Promoted Synthesis of ß-Keto Sulfoximines from N-Tosyl-Protected Sulfoximidoyl Chlorides.

Under visible light, N-tosyl-protected sulfoximidoyl chlorides react with aryl alkynes to give ß-keto sulfoximines. The reaction is characterized by a high functional group tolerance and good yields. It can be improved by the presence of a ruthenium photocatalyst. Air is the source of the ketonic oxygen in the products.

Visible light-induced C-C bond cleavage in a multicomponent reaction cascade allowing acylations of sulfoximines with ketones.

Visible light induces C-C-bond cleavage reactions of ketones, which can be utilized for N-acylations of sulfoximines. No (photo)catalyst is required, and the reactions occur at ambient temperature in air. The substrate scope is broad for both ketones and sulfoximines. For converting NH-sulfoximines, the presence of NBS is essential.

Photocatalytic Synthesis of Difluoroacetoxy-containing Sulfoximines.

[Bis(difluoroacetoxy)iodo]benzene and NH-sulfoximines react to give new hypervalent iodine(III) reagents, which under photocatalysis transfer difluoroacetoxy and sulfoximidoyl groups to styrenes with high regioselectivity. The results of mechanistic investigations suggest the intermediacy of radicals and reveal the importance of the difluoroacetoxy group on the iodine reagent.

Recent Advances in the Pd-Catalyzed Coupling of Arylhydrazines and Ammonium Salts via C-N Bond Cleavage.

Both arylhydrazines and quaternary ammonium salts are readily accessible or commercially available chemicals that show versatile reactivity in Pd-catalyzed coupling reactions via C-N bond cleavage. A tremendous array of coupling reactions involving reaction partners such as organoborons, aryl silanes, alkenes, alkynes, arylation or alkylation reagents in C-H functionalization and carbonylation reactions are summarized, in which arylhydrazines or quaternary ammonium salts function as aryl or alkyl donors. This account mainly focuses on recent advances in Pd-catalyzed coupling reactions with arylhydrazines or quaternary ammonium salts via C-N bond cleavage, including mechanistic elucidations.

Synthesis of Benzothiadiazine-1-oxides by Rhodium-Catalyzed C-H Amidation/Cyclization.

A rhodium-catalyzed C-H amidation/cyclization sequence provides benzothiadiazine-1-oxides from sulfoximines and 1,4,2-dioxazol-5-ones in good yields. The reaction is characterized by a high functional group tolerance and, in contrast to most previous transformations of this type, is well-suited for S-alkyl-S-aryl-substituted sulfoximines.

Use of Hypervalent Iodine Reagents in Visible Light-Promoted α-Ketoacylations of Sulfoximines with Aryl Alkynes.

In visible light, sulfoximidoyl-containing hypervalent iodine reagents react with aryl alkynes to give N-α-ketoacylated sulfoximines in good to high yields. The process is metal- and base-free, providing the diketonic products without the use of highly oxygenated reagents such as peroxides. Results from mechanistic investigations suggest the intermediacy of radicals and reveal the importance of molecular oxygen.

Photocatalytic Fluoro Sulfoximidations of Styrenes.

Reactions of difluoroiodotoluene with NH-sulfoximines provide new hypervalent iodine(III) reagents, which photocatalytically transfer a fluoro and a sulfoximidoyl group onto styrenes with high regioselectivity. The substrate scope is broad with respect to both sulfoximines and olefins. Following an operationally simple protocol, a large library of fluorine-containing N-functionalized sulfoximines can be accessed. Results from mechanistic investigations revealed the importance of radical intermediates.

Access to (Z)-1,2-Endiamides and 1,1-Endiamides via a Base-Promoted Tandem Reaction.

An efficient base-promoted tandem reaction between vinyl 1,1-dichlorides and secondary sulfonamides with ynamide as the key intermediate is described. This method provides a facile approach to (Z)-1,2-endiamide and aryl 1,1-endiamide derivatives via the ß-hydroamidation of terminal ynamides and the α-hydroamidation of internal ynamides, respectively. This reaction proceeded through double elimination of vinyl chlorides and double addition of nucleophiles to alkynes. In addition, it features readily available starting materials, mild reaction conditions, a broad substrate scope, a wide functional group tolerance, and an operational convenience.

Transition-Metal-Free Approach to Polysubstituted Furans.

A convenient and straightforward strategy for the synthesis of 2,3-disubstituted and 2,3,5-trisubstituted furans via a base-promoted domino reaction of ß-keto compounds with vinyl dichlorides is described. This transition-metal-free approach proceeds under operationally simple reaction conditions featuring easily available starting materials, a broad substrate scope, and good functional group tolerance.

Transition-Metal-Free One-Step Synthesis of Ynamides.

A robust transition-metal-free one-step strategy for the synthesis of ynamides from sulfonamides and ( Z)-1,2-dichloroalkenes or alkynyl chlorides is presented. This method is not only effective for internal ynamides but also amenable for terminal ynamides. Various functional groups, even the vinyl moiety, are compatible, and thus, this strategy offers the opportunity for further functionalization.

Regio- and Stereo-Selective Intermolecular Hydroamidation of Ynamides: An Approach to ( Z)-Ethene-1,2-Diamides.

An efficient intermolecular trans-selective ß-hydroamidation of ynamides to furnish a series of ( Z)-ethene-1,2-diamide derivatives with excellent regio- and stereo-selectivities is described. The trans-ß-addition reactions have been illustrated for a wide range of substrates and proceeded under basic reaction conditions using readily available materials in the absence of a transition-metal catalyst. The synthetic approach to these novel ( Z)-ethene-1,2-diamide derivatives paves the way for further exploration of their synthetic application.

Palladium-Catalyzed Oxidative Cross-Coupling of Arylhydrazines and Arenethiols with Molecular Oxygen as the Sole Oxidant.

A highly efficient palladium-catalyzed oxidative cross-coupling of arylhydrazines and arenethiols with molecular oxygen as the sole oxidant to afford unsymmetrical diaryl sulfides has been developed. The only byproducts are nitrogen and water. A broad range of functional groups, even the reactive iodides, are tolerated and thus offer the opportunity for further functionalization.

A Robust One-Step Approach to Ynamides.

A robust one-step synthetic strategy for ynamide with cheap and easily available stock chemicals vinyl dichlorides and electron deficient amides as the starting material is described. In the absence of transition-metal catalyst, the reaction proceeds under mild reaction conditions in open air and thus rendering a convenient operation. This strategy is not only suitable for both terminal and internal ynamide synthesis but also amenable for large-scale preparation. Broad substrate scopes with respect to vinyl dichloride as well as electron-deficient amide were observed.