A Cobalt-Catalyzed Enantioconvergent Radical Negishi C(sp3)–C(sp2) Cross-Coupling with Chiral Multidentate N,N,P-Ligand

Cobalt-Catalyzed Three-Component Alkyl Arylation of Acrylates with Alkyl Iodides and Aryl Grignard Reagents

A highly regioselective cobalt-catalyzed three-component alkyl arylation of acrylates with alkyl iodides and aryl Grignard reagents has been established. The reaction efficiently provides an alternative strategy for the construction of α-aryl esters with a broad substrate scope and good yields under mild conditions. The practical applicability of this protocol is shown by the scaled-up reaction and further transformations of the products. In addition, the preliminary mechanistic explorations demonstrated that the alkyl radicals generated by the efficient cobalt catalysis are instantaneously added to the acrylates to finally afford the desired products.

Three-Component Radical Cross-Coupling: Asymmetric Vicinal Sulfonyl-Esterification of Alkenes Involving Sulfur Dioxide

A novel catalytic system for radical cross-coupling reactions based on copper and chiral Pyridyl-bis(imidazole) (PyBim) ligands is described. It overcomes the challenges of chemoselectivity and enantioselectivity, achieving a highly enantioselective vicinal sulfonyl-esterification reaction of alkenes involving sulfur dioxide. This strategy involves the use of earth-abundant metal catalyst, mild reaction conditions, a broad range of substrates (84 examples), high yields (up to 97% yield), and exceptional control over enantioselectivity. The reaction system is compatible with different types of radical precursors, including O-acylhydroxylamines, cycloketone oxime esters, aryldiazonium salts, and drug molecules. Chiral ligand PyBim is identified as particularly effective in achieving the desired high enantioselectivity. Mechanistic studies reveal that copper/PyBim system plays a vital role in C─O coupling, employing an outer-sphere model. In addition, the side arm effect of ligand is observed.

Cobalt-Catalyzed Enantioconvergent Negishi Cross-Coupling of α-Bromoketones

Cobalt-catalyzed enantioconvergent cross-coupling of α-bromoketones with aryl zinc reagents is achieved to access chiral ketones bearing α-tertiary stereogenic centers with high enantioselectivities. The more challenging and sterically hindered α-bromoketones bearing a 2-fluorophenyl group or β-secondary and tertiary alkyl chains could also be well-tolerated. Adjusting the electronic effect of chiral unsymmetric N,N,N-tridentate ligands is critical for improving the reactivity and selectivity of this transformation, which is beneficial for further studies of asymmetric 3d metal catalysis via ligand modification. The control experiments and kinetic studies illustrated that the reaction involved radical intermediates and the reductive elimination was a rate-determining step.

Metal-Catalyzed Enantioconvergent Transformations

Enantioconvergent catalysis has expanded asymmetric synthesis to new methodologies able to convert racemic compounds into a single enantiomer. This review covers recent advances in transition-metal-catalyzed transformations, such as radical-based cross-coupling of racemic alkyl electrophiles with nucleophiles or racemic alkylmetals with electrophiles and reductive cross-coupling of two electrophiles mainly under Ni/bis(oxazoline) catalysis. C-H functionalization of racemic electrophiles or nucleophiles can be performed in an enantioconvergent manner. Hydroalkylation of alkenes, allenes, and acetylenes is an alternative to cross-coupling reactions. Hydrogen autotransfer has been applied to amination of racemic alcohols and C-C bond forming reactions (Guerbet reaction). Other metal-catalyzed reactions involve addition of racemic allylic systems to carbonyl compounds, propargylation of alcohols and phenols, amination of racemic 3-bromooxindoles, allenylation of carbonyl compounds with racemic allenolates or propargyl bromides, and hydroxylation of racemic 1,3-dicarbonyl compounds.

Low-cost transition metal catalysed Negishi coupling: an update

The Negishi coupling is a significant C-C bond-forming reaction to access synthetically valuable organic compounds. In recent years, researchers have developed sustainable first-row transition metal (Fe, Co, Ni and Cu) based complexes in place of the conventional Pd catalyst for this reaction. Several such low-cost metal-based catalysts showed high efficiency and potential application in natural product synthesis. This review focuses on the recent achievements in low-cost transition metal-based Negishi coupling reactions, covering reports from 2016.

Cu-Catalyzed Site-Selective Benzylic Chlorination Enabling Net C-H Coupling with Oxidatively Sensitive Nucleophiles

Site-selective chlorination of benzylic C-H bonds is achieved using a CuICl/bis(oxazoline) catalyst with N-fluorobenzenesulfonimide as the oxidant and KCl as a chloride source. This method exhibits higher benzylic selectivity, relative to established chlorination protocols, and is compatible with diverse alkyl arenes. Sequential benzylic C-H chlorination/nucleophilic substitution affords C-O, C-S, and C-N coupling products with oxidatively sensitive coupling partners.