Convergent Synthesis of α-Branched Amines by Transition-Metal-Catalyzed C-H Bond Additions to Imines

α-Branched amines through radical coupling with 2-azaallyl anions, redox active esters and alkenes

α-Branched amines are fundamental building blocks in a variety of natural products and pharmaceuticals. Herein is reported a unique cascade reaction that enables the preparation of α-branched amines bearing aryl or alkyl groups at the β- or γ-positions. The cascade is initiated by reduction of redox active esters to alkyl radicals. The resulting alkyl radicals are trapped by styrene derivatives, leading to benzylic radicals. The persistent 2-azaallyl radicals and benzylic radicals are proposed to undergo a radical-radical coupling leading to functionalized amine products. Evidence is provided that the role of the nickel catalyst is to promote formation of the alkyl radical from the redox active ester and not promote the C-C bond formation. The synthetic method introduced herein tolerates a variety of imines and redox active esters, allowing for efficient construction of amine building blocks.

Chiral-Directing-Group-Assisted Rhodium(III)-Catalyzed Asymmetric Addition of Inert Arene C-H Bond to Aldimines with Subsequent Intramolecular Cyclization

By using a chiral directing group, an asymmetric rhodium(III)-catalyzed C-H bond addition to aldimines followed by intramolecular cyclization to form chiral isoindolinones has been achieved (up to 68 % yield, up to 93 % ee). A three-component variant that resembles Mannich reaction was also realized (41 % yield, 83 % ee). Product elaborations and preliminary mechanistic studies were described.

Multicomponent Synthesis of α-Branched Tertiary and Secondary Amines by Photocatalytic Hydrogen Atom Transfer Strategy

A multicomponent carbonyl alkylative amination reaction is described. A variety of N-arylamines, aldehydes, and hydrocarbons have been examined as reaction substrates using tetrabutylammonium decatungstate as photocatalyst, providing the corresponding α-branched tertiary and secondary amines in good to moderate yields. The reaction proceeds through the generation of alkyl radicals by a light-promoted hydrogen atom transfer process followed by free radical addition to iminium ions generated in situ.

Multicomponent Aromatic and Benzylic Mannich Reactions through C-H Bond Activation

Multicomponent Mannich reactions through C-H bond activation are described. These transformations allowed for the straightforward generation of densely substituted benzylic and homo-benzylic amines in good yields. The reaction involves a reaction between two transient species: an organometallic species, generated by transition-metal-catalyzed sp² or sp³ C-H bond activation and an in situ generated imine. The use of an acetal as an aldehyde surrogate was found essential for the reaction to proceed. The process could be successfully applied to Rh^III -catalyzed sp² C-H bond functionalization and extended to Cu^II -catalyzed sp³ C-H bond functionalization.