Chiral Bidentate Boryl Ligand Enabled Iridium-Catalyzed Asymmetric C(sp2)–H Borylation of Diarylmethylamines

Iridium-Catalyzed Regio- and Enantioselective Borylation of Unbiased Methylene C(sp3 )-H Bonds at the Position β to a Nitrogen Center

Reported herein is the pyrazole-directed iridium-catalyzed enantioselective borylation of unbiased methylene C-H bonds at the position β to a nitrogen center. The combination of a chiral bidentate boryl ligand, iridium precursor, and pyrazole directing group was responsible for the high regio- and enantioselectivity observed. The method tolerated a vast array of functional groups to afford the corresponding C(sp³ )-H functionalization products with good to excellent enantioselectivity.

Activation of the Si–B interelement bond related to catalysis

Covering the past seven years, this review comprehensively summarises the latest progress in the preparation and application of Si–B reagents, including the discussion of relevant reaction mechanisms.

C-H Borylation of Diphenylamines through Adamantane-1-carbonyl Auxiliary by BBr3

A method for ortho-C-H borylation of diphenylamines using BBr₃ as the boron source has been reported. The noncatalytic adamantane-1-carbonyl directed reaction exhibited site exclusivity and good functional group tolerance. Generally, the borylation occurred at the more electron-rich aromatic ring and the borylated products could be converted to various useful intermediates. Besides, the derived arylation and removal of auxiliary of the product could be achieved in a one-pot fashion.

Enantioselective remote C-H activation directed by a chiral cation

Chiral cations have been used extensively as organocatalysts, but their application to rendering transition metal-catalyzed processes enantioselective remains rare. This is despite the success of the analogous charge-inverted strategy in which cationic metal complexes are paired with chiral anions. We report here a strategy to render a common bipyridine ligand anionic and pair its iridium complexes with a chiral cation derived from quinine. We have applied these ion-paired complexes to long-range asymmetric induction in the desymmetrization of the geminal diaryl motif, located on a carbon or phosphorus center, by enantioselective C-H borylation. In principle, numerous common classes of ligand could likewise be amenable to this approach.

Mechanism and origins of stereo- and enantioselectivities of palladium-catalyzed hydroamination of racemic internal allenes via dynamic kinetic resolution: a computational study

DFT calculations were performed to investigate the Pd-catalyzed hydroamination of racemic internal allenes with pyrazoles.

Tertiary amine-directed and involved carbonylative cyclizations through Pd/Cu-cocatalyzed multiple C-X (X = H or N) bond cleavage

A novel Pd/Cu-cocatalyzed carbonylative cyclization by C-H activation and N-dealkylative C-N bond activation has been developed for the chemoselective construction of synthetically useful heterocycles. The N,N-dimethylamine group on o-indolyl-N,N-dimethylarylamines was found to act as both the directing group and reactive component in this C-H carbonylative cyclization reaction. Furthermore, a unique C-H oxidation/carbonylative lactonization of diarylmethylamines is firstly demonstrated under modified reaction conditions, which could be easily applicable to the one-step synthesis of multi-substituted phthalides bearing an N,O-ketal skeleton that is difficult to access by previously reported methods. Mechanistic studies implicate that Pd/Cu-cocatalyzed C-H oxidation/carbonylative lactonization is a sequential reaction system via Cu-catalyzed C(sp3)-H oxidation and Pd-catalyzed oxidative carbonylation of the C(sp2)-H bond. It was found that trace amounts of water are essential to promote the Cu-catalyzed C(sp3)-H oxidation of diarylmethylamine for the formation of the hydroxyl group, which could act as an in situ-formed directing group in the intramolecular carbonylative lactonization step.

A Computational Mechanistic Study of Pd(II)-Catalyzed Enantioselective C(sp3)-H Borylation: Roles of APAO Ligands

A computational mechanistic study has been performed on Pd(II)-catalyzed enantioselective reactions involving acetyl-protected aminomethyl oxazolines (APAO) ligands that significantly improved reactivity and selectivity in C(sp³)-H borylation. The results support a mechanism including initiation of C(sp³)-H bond activation generating a five-membered palladacycle and ligand exchange, followed by HPO₄^2--promoted transmetalation. These resulting Pd(II) complexes further undergo sequential reductive elimination by coordination of APAO ligands and protonation to afford the enantiomeric products and deliver Pd(0) complexes, which will then proceed by oxidation and deprotonation to regenerate the catalyst. The C(sp³)-H activation is found to be the rate- and enantioselectivity-determining step, in which the APAO ligand acts as the proton acceptor to form the two enantioselectivity models. The results demonstrate that the diverse APAO ligands control the enantioselectivity by differentiating the distortion and interaction between the major and minor pathways.