Enantioselective electroreductive alkyne-aldehyde coupling.

Electrocatalytic methods that facilitate the asymmetric reductive coupling of two π-components with complete control over regio-, stereo-, and enantioselectivity remain underexplored. Herein, we report a highly regio- and enantioselective cobaltaelectro-catalyzed alkyne-aldehyde coupling reaction, in which protons and electrons serve as the hydrogen source and reductant, respectively. Earth-abundant cobalt and air-stable (S,S)-2,3-bis(tert-butylmethylphosphino)quinoxaline (QuinoxP*) are used as the catalyst and ligand, respectively.

Electrocatalytic Hydrogenation of Olefins.

Electrochemical synthesis offers a powerful and sustainable alternative to conventional chemical manufacturing techniques. The direct and selective electrohydrogenation of olefins has enormous potential applicability; however, this reactivity has not been sufficiently demonstrated. Herein, we show that an efficient Pt-based electrocatalyst from commercially available PtCl can promote such transformations.

Asymmetric paired oxidative and reductive catalysis enables enantioselective alkylarylation of olefins with C(sp)-H bonds.

Enantioselective transformations of hydrocarbons to three-dimensional chiral molecules remain a significant challenge in synthetic chemistry. This study uses asymmetric paired oxidative and reductive catalysis to promote the enantioselective alkylarylation of olefins through the functionalization of C(sp)-H bonds in alkanes. This asymmetric photoelectrocatalytic approach enables the facile construction of a wide range of enantioenriched α-aryl carbonyls with excellent enantioselectivity (up to 96% ee) from readily accessible starting materials.

Selective C(sp)-H arylation/alkylation of alkanes enabled by paired electrocatalysis.

We report a combination of electrocatalysis and photoredox catalysis to perform selective C(sp)-H arylation/alkylation of alkanes, in which a binary catalytic system based on earth-abundant iron and nickel is applied. Reaction selectivity between two-component C(sp)-H arylation and three-component C(sp)-H alkylation is tuned by modulating the applied current and light source. Importantly, an ultra-low anodic potential (~0.

Rape straw biochar enhanced Cd immobilization in flooded paddy soil by promoting Fe and sulfur transformation.

Cd is normally associated with sulfide and Fe oxides in flooded paddy soil. The mechanisms of biochar enhanced Cd immobilization by promoting Fe transformation and sulfide formation are unclear. Rape straw biochar (RSB) pyrolyzed at 450 °C (LB) and 800 °C (HB) was added to Cd-contaminated paddy soil at 1% (LB1, HB1) and 2% (LB2, HB2) doses.

Unlocking the Nucleophilicity of Strong Alkyl C-H Bonds via Cu/Cr Catalysis.

Direct functionalization of inert C-H bonds is one of the most attractive yet challenging strategies for constructing molecules in organic chemistry. Herein, we disclose an unprecedented and Earth abundant Cu/Cr catalytic system in which unreactive alkyl C-H bonds are transformed into nucleophilic alkyl-Cr(III) species at room temperature, enabling carbonyl addition reactions with strong alkyl C-H bonds. Various aryl alkyl alcohols are furnished under mild reaction conditions even on a gram scale.

Paired Oxidative and Reductive Catalysis: Breaking the Potential Barrier of Electrochemical C(sp )-H Alkenylation.

Due to the intrinsic inertness of alkanes, strong oxidative conditions are typically required to enable their C(sp )-H functionalization. Herein, a paired electrocatalysis strategy was developed by integrating oxidative catalysis with reductive catalysis in one cell without interference, in which earth-abundant iron and nickel are employed as the anodic and cathodic catalysts, respectively. This approach lowers the previously high oxidation potential required for alkane activation, enabling electrochemical alkane functionalization at the ultra-low oxidation potential of ≈0.

Electrooxidative Activation of B-B Bond in B cat : Access to gem-Diborylalkanes via Paired Electrolysis.

This report describes the unprecedented electrooxidation of a solvent (e.g., DMF)-ligated B cat complex, whereby a solvent-stabilized boryl radical is formed via quasi-homolytic cleavage of the B-B bond in a DMF-ligated B cat radical cation.

Electrochemical Borylation of Alkyl Halides: Fast, Scalable Access to Alkyl Boronic Esters.

Herein, a fast, scalable, and transition-metal-free borylation of alkyl halides (X = I, Br, Cl) enabled by electroreduction is reported. This process provides an efficient and practical access to primary, secondary, and tertiary boronic esters at a high current. More than 70 examples, including the late-stage borylation of natural products and drug derivatives, are furnished at room temperature, thereby demonstrating the broad utility and functional-group tolerance of this protocol.

Site-selective C-H activation and regiospecific annulation using propargylic carbonates.

Herein we describe an unprecedented Ru-catalyzed site-selective and regiospecific annulation of benzoic acids with propargylic carbonates. The weakly coordinating carboxylic acid moiety outperformed other typically used directing groups in C-H activation, including ketone, nitrile, sulfonamide, amide and strongly coordinating nitrogen heterocycles. This is an important step towards the application of C-H activation reactions in complex (functional) real-world molecules.

Mn /Ag Relay Catalysis: Traceless Diazo-Assisted C(sp )-H/C(sp )-H Coupling to β-(Hetero)Aryl/Alkenyl Ketones.

An unprecedented Mn /Ag -relay-catalyzed C(sp )-H/C(sp )-H coupling of (vinyl)arenes with α-diazoketones is reported, wherein the diazo group was exploited as a traceless auxiliary for control of regioselectivity. Challenging β-(hetero)aryl/alkenyl ketones were obtained through this operationally simple approach. The cascade process merges denitrogenation, carbene rearrangement, C-H activation, and hydroarylation/hydroalkenylation.

Manganese(I)-Catalyzed C-H (2-Indolyl)methylation: Expedient Access to Diheteroarylmethanes.

An unprecedented Mn -catalyzed (2-indolyl)methylation of heteroarenes is reported. This method makes use of an aromatizing cascade strategy to install a (2-indolyl)methyl group into target molecules, thereby leading to the expedient synthesis of previously challenging and important unsymmetrical diheteroarylmethanes, in particular bis(2-indolyl)methanes. The proposed cascade process comprises the reorganization of multiple bonds with controlled regioselectivity and high atom economy and can be performed on a gram-scale.

Redox-Neutral Manganese(I)-Catalyzed C-H Activation: Traceless Directing Group Enabled Regioselective Annulation.

A strategy is reported in which traceless directing groups (TDGs) are used to promote the redox-neutral Mn -catalyzed regioselective synthesis of N-heterocycles. Alkyne coupling partners bearing a traceless directing group, which serves as both the chelator and internal oxidant, were used to control the regioselectivity of the annulation reactions. This operationally simple approach is highly effective with previously challenging unsymmetrical alkyne systems, including unbiased dialkyl alkynes, with perfect regioselectivity.

Manganese-catalyzed allylation sequential C-H and C-C/C-Het bond activation.

Manganese-catalyzed sequential C-H and C-C/C-Het bond activation to synthesize allylic alcohols, allylated arenes, functionalized cyclopentenes and skipped dienes is reported. This protocol can be readily scaled up and various coupling partners are applied in manganese catalysis for the first time. Moreover, manganese-catalyzed alkenyl C(sp)-H activation is also shown.

Manganese(I)-Catalyzed Regioselective C-H Allenylation: Direct Access to 2-Allenylindoles.

A Mn -catalyzed regioselective C-H allenylation is reported that allows a broad range of 2-allenylindoles to be synthesized regioselectively on a gram scale under simple conditions. Notably, a highly efficient chirality transfer was observed (up to 93 % ee) in this transformation. This procedure was further found to allow, for the first time, the direct preparation of ketones by Mn -catalyzed C-H activation.

Markovnikov-Selective Radical Addition of S-Nucleophiles to Terminal Alkynes through a Photoredox Process.

Direct radical additions to terminal alkynes have been widely employed in organic synthesis, providing credible access to the anti-Markovnikov products. Because of the Kharasch effect, regioselective control for the formation of Markovnikov products still remains a great challenge. Herein, we develop a transition-metal-free, visible light-mediated radical addition of S-nucleophiles to terminal alkynes, furnishing a wide array of α-substituted vinyl sulfones with exclusive Markovnikov regioselectivity.

Radical Enantioselective C(sp )-H Functionalization.

Radical style: Several breakthroughs have recently been achieved in enantioselective C(sp )-H functionalization through radical activation. These new strategies show how radical chemistry can be used to convert alkanes into functionalized chiral molecules (see scheme; HAT=hydrogen atom transfer).

Dioxygen-induced oxidative activation of a P-H bond: radical oxyphosphorylation of alkenes and alkynes toward β-oxy phosphonates.

The dioxygen-induced radical oxyphosphorylation of alkenes and alkynes is presented, wherein a P-H bond was activated by molecular oxygen. Various β-oxy phosphonates could be facilely synthesized without the assistance of any transition metals or extra organic initiators. Mechanistic studies showed that HP(O)Ph acts as a reductant to accelerate oxyphosphorylation.

Catalyst-Free Difunctionalization of Activated Alkenes in Water: Efficient Synthesis of β-Keto Sulfides and Sulfones.

Difunctionalization of activated alkenes, a powerful strategy in chemical synthesis, has been accomplished for direct synthesis of a series of β-keto sulfides and β-keto sulfones. The transformation, mediated by O2 , proceeds smoothly in water and without any catalyst. Prominent advantages of this method include mild reaction conditions, purification simplicity, and gram-scale synthesis, underlining the practical utility of this methodology.

Regio- and Stereoselective Oxysulfonylation of Allenes.

A highly regio- and stereoselective oxysulfonylation of allenes was developed that provided direct access to 2-sulfonyl allylic alcohols in good yields. By means of dioxygen activation, selective difunctionlization of allenes could be successfully achieved under mild metal-free conditions. Preliminary mechanistic investigation disclosed that this transformation probably goes through a radical process.