Iridium-Catalyzed Branch-Selective Hydroalkylation of Simple Alkenes with Malonic Amides and Malonic Esters

Ligand Enabled Iridium-Catalyzed Enantioselective Hydroalkenylation of α-Olefins and Styrenes with Acrylamides

A new type of chiral spiro diphosphite ligand has been developed. Using these ligands, iridium-catalyzed highly enantioselective hydroalkenylation of α-olefins and styrenes with acrylamides has been realized. A variety of aliphatic and aromatic alkenes were successfully coupled with acrylamides to produce γ-substituted chiral acrylamides. The reaction exhibits excellent branched selectivity and high enantioselectivity along with broad substrate scope and good functional group tolerance. DFT calculations indicate that the methyl groups in the ligand play a crucial role in controlling both regioselectivity and enantioselectivity of the reaction.

Synthesize of β-Amino Esters from Enamides via 1,8-Diazabicyclo[5.4.0]undecane-7-ene-Mediated Hydroalkylation

A 1,8-diazabicyclo[5.4.0]undecane-7-ene (DBU)-mediated hydroalkylation of enamides with malonic acid diesters/β-carbonyl esters has been established, featuring no metal involvement, mild reaction conditions, and good functional group tolerance. The protocol enables the expedited preparation of a variety of β-amino esters. Preliminary mechanistic investigations, encompassing control experiments and capture experiments of key intermediates, have substantiated the proposed DBU-mediated hydroalkylation pathway.

Nickel-Catalyzed Branched Hydroalkylation of Alkenes with Diazo Compounds

A nickel-catalyzed, branched-selective hydroalkylation of alkenes using diazo compounds has been developed. This protocol enables the functionalization of both activated and unactivated alkenes, in both directed and nondirected manners. Mono-, di-, and trisubstituted alkenes can be effectively transformed. Highly diastereoselective hydroalkylations have also been demonstrated. The method provides a novel approach for introducing an α-carbonyl moiety to alkenes, which is currently inaccessible by existing methods. Preliminary mechanistic investigations suggest a carbene-type mechanism, which is unusual for nickel catalysis.

Heteroaryl-Directed Iridium-Catalyzed Enantioselective C-H Alkenylations of Secondary Alcohols

Under iridium-catalyzed conditions, 2-aza-aryl-substituted secondary alcohols undergo C(sp3)-H addition reactions to alkynes to provide alkenylated tertiary alcohols. The processes occur with very high regio- and enantioselectivity. An analogous addition to styrene is shown to provide a prototype C(sp3)-H alkylation process. A mechanism based on directed aza-enolization of the reactant alcohol is proposed.

A directed enolization strategy enables by-product-free construction of contiguous stereocentres en route to complex amino acids

Homochiral α-amino acids are widely used in pharmaceutical design as key subunits in chiral catalyst synthesis or as building blocks in synthetic biology. Many synthetic methods have been developed to access rare or unnatural variants by controlling the installation of the α-stereocentre. By contrast, and despite their importance, α-amino acids possessing β-stereocentres are much harder to synthesize. Here we demonstrate an iridium-catalysed protocol that allows the direct upconversion of simple alkenes and glycine derivatives to give β-substituted α-amino acids with exceptional levels of regio- and stereocontrol. Our method exploits the native directing ability of a glycine-derived N-H unit to facilitate Ir-catalysed enolization of the adjacent carbonyl. The resulting stereodefined enolate cross-couples with a styrene or α-olefin to install two contiguous stereocentres. The process offers very high levels of regio- and stereocontrol and occurs with complete atom economy. In broader terms, our reaction design offers a unique directing-group-controlled strategy for the direct stereocontrolled α-alkylation of carbonyl compounds, and provides a powerful approach for the synthesis of challenging contiguous stereocentres.

Efficient Radical-Mediated Intermolecular α-Alkylation Reactions of Carbonyl Compounds with Nonactivated Alkenes

Alkylation reactions are fundamental carbon-carbon bond-forming reactions in synthetic organic chemistry. Among them, intermolecular α-alkylation reactions of carbonyl compounds with alkenes are important because they are more atom-economical than the equivalent processes using alkyl halides. However, intermolecular reactions with nonactivated alkenes such as 1-hexene, which can allow the use of a wide range of valuable substrates, have been considered to be very challenging for a long time. In this review, radical-mediated intermolecular α-alkylation reactions of carbonyl compounds with nonactivated alkenes are discussed. The examples are grouped into three types of reactions: peroxide-mediated reactions, metal-oxidant-mediated reactions, and photoactivated reactions. Photoredox-catalyzed alkylation reactions under visible-light irradiation are discussed as a particularly promising recent hot topic. This review provides brief history and new prospects on the α-alkylation process with nonactivated alkenes using α-carbonyl radical species.

Iridium-Catalyzed Enantioselective Alkene Hydroalkylation via a Heteroaryl-Directed Enolization-Decarboxylation Sequence

Upon exposure to a cationic Ir(I)-complex modified with the chiral diphosphine DuanPhos, hydroalkylations of styrenes and α-olefins with diverse heteroaryl tert-butyl acetates occur with complete branched selectivity and very high enantioselectivity. The initial adducts undergo acid promoted decarboxylation in situ to provide alkylated heteroarenes possessing defined β-stereocenters. The processes are postulated to proceed via a stereodefined chiral Ir-enolate, which arises upon heteroarene directed enolization of the heteroaryl acetate precursor. The method can be classified as an enantioselective decarboxylative C(sp3)-C(sp3) cross-coupling.

Photoinduced Efficient Catalytic α-Alkylation Reactions of Active Methylene and Methine Compounds with Nonactivated Alkenes

In catalytic α-alkylation reactions of carbonyl compounds, although SN2-type substitution reactions of enolates with alkyl halides are a conventional methodology, addition reactions with alkenes are more desirable because of their atom-economical character; however, reactions with nonactivated alkenes are challenging. Here, we developed highly efficient catalytic α-alkylation reactions of active methylene and methine compounds with nonactivated alkenes such as 1-decene using an organophotocatalyst and lithium thiophenoxide as a Lewis acid/Brønsted base/hydrogen atom transfer (HAT) multifunctional catalyst under blue-light irradiation. The reaction was also performed with a higher degree of efficiency under a continuous-flow system to obtain the products in multigram scales. The present reaction system enables highly efficient and practical α-alkylation reactions of active methylene and methine compounds to be achieved.