Metal-catalyzed enantioselective allylation, which involves the substitution of allylic metal intermediates with a diverse range of different nucleophiles or S(N)2'-type allylic substitution, leads to the formation of C-H, -C, -O, -N, -S, and other bonds with very high levels of asymmetric induction. The reaction may tolerate a broad range of functional groups and has been applied successfully to the synthesis of many natural products and new chiral compounds.

Metal-catalyzed enantioselective allylation in asymmetric synthesis.

Reactions of C−H Bonds in Water

As two coexisting and fast-growing research fields in modern synthetic chemistry, the merging of organocatalysis and C–H bond functionalization is well foreseeable, and the joint force along this line has been demonstrated to be a powerful approach in making inert C–H bond functionalization more viable, predictable, and selective. In this review, we provide a comprehensive summary of organocatalysis in inert C–H bond functionalization over the past two decades. The review is arranged by types of inert C–H bonds including alkane C–H, arene C–H, and vinyl C–H as well as those activated benzylic C–H, allylic C–H, and C–H bonds alpha to the heteroatom such as nitrogen and oxygen. In each section, the discussion is classified by the explicit organocatalytic mode involved.

Organocatalysis in Inert C–H Bond Functionalization

Kunbing Ouyang,†,‡ Wei Hao,† Wen-Xiong Zhang,*,†,§ and Zhenfeng Xi† †Beijing National Laboratory for Molecular Sciences (BNLMS), Key Laboratory of Bioorganic Chemistry and Molecular Engineering of the Ministry of Education, College of Chemistry, Peking University, Beijing 100871, China ‡Institute of Chemistry, Chinese Academy of Sciences (CAS), Beijing 100190, China State Key Laboratory of Elemento-Organic Chemistry, Nankai University, Tianjin 300071, China

Transition-Metal-Catalyzed Cleavage of C-N Single Bonds.

Metal-catalyzed asymmetric processes offer one of the most straightforward ways to introduce stereogenic centers Hence, the development of novel chiral ligands that can effectively induce asymmetry in reactions is crucial in modern organic synthesis While many established chiral ligands bind to a metal through heteroatoms, structures that coordinate to metals through carbon atoms have received little attention so far Here, we highlight the increasing number of such chiral chelating olefin ligands as well as their application in a variety of metal-catalyzed transformations

Chiral olefins as steering ligands in asymmetric catalysis.

Asymmetric synthesis of diarylmethylamines with high enantioselectivity (95−99% ee) was realized by use of a new C2-symmetric diene ligand, (1R,4R)-2,5-diphenylbicyclo[2.2.2]octa-2,5-diene (Ph-bod*), for the rhodium-catalyzed asymmetric arylation of N-tosylarylimines with arylboroxines.

C2-Symmetric Bicyclo[2.2.2]octadienes as Chiral Ligands: Their High Performance in Rhodium-Catalyzed Asymmetric Arylation of N-Tosylarylimines

Catalytic arylative cyclization of alkynals has been developed by the use of phosphine-free rhodium/diene complexes as catalysts. An asymmetric variant of this process has been successfully realized by employing a C2-symmetric chiral bicyclo[2.2.2]octadiene ligand. The rhodium/diene catalyst system is also effective for arylative cyclization of other substrates such as alkynones and enynes, achieving multiple carbon−carbon bond formations in a single step.

Catalytic Asymmetric Arylative Cyclization of Alkynals: Phosphine-Free Rhodium/Diene Complexes as Efficient Catalysts

C2-Symmetric bicyclo[2.2.2]octa-2,5-dienes containing benzyl, phenyl, and substituted phenyl groups at 2 and 5 positions were prepared enantiomerically pure by way of bicyclo[2.2.2]octane-2,5-dione as a key intermediate. These chiral diene ligands were successfully applied to rhodium-catalyzed asymmetric 1,4-addition of arylboronic acids to α,β-unsaturated ketones. High enantioselectivity (up to 99% ee) as well as high catalytic activity was observed in the addition to both cyclic and linear substrates.

Preparation of C2-symmetric bicyclo[2.2.2]octa-2,5-diene ligands and their use for rhodium-catalyzed asymmetric 1,4-addition of arylboronic acids.

Vinyl boronic esters are valuable substrates for Suzuki-Miyaura cross-coupling reactions. However, boron-substituted alkenes have drawn little attention as radical acceptors, and the radical chemistry of vinylboron ate complexes is underexplored. We show here that carbon radicals add efficiently to vinylboron ate complexes and that their adduct radical anions undergo radical-polar crossover: A 1,2-alkyl/aryl shift from boron to the α-carbon sp2 center provides secondary or tertiary alkyl boronic esters. In contrast to the Suzuki-Miyaura coupling, a transition metal is not required, and two carbon-carbon bonds are formed. The valuable boronic ester moiety remains in the product and can be used in follow-up chemistry, enlarging the chemical space of the method. The cascade uses commercial starting materials and provides access to perfluoroalkylated alcohols, γ-lactones, γ-hydroxy alkylnitriles, and compounds bearing quaternary carbon centers.

Radical-polar crossover reactions of vinylboron ate complexes

https://www.rsc.org/suppdata/CC/b9/b904624k/b904624k.pdf

Kazuhiro Okamoto

Papers

C2-Symmetric Bicyclo[2.2.2]octadienes as Chiral Ligands: Their High Performance in Rhodium-Catalyzed Asymmetric Arylation of N-Tosylarylimines

Catalytic Asymmetric Arylative Cyclization of Alkynals: Phosphine-Free Rhodium/Diene Complexes as Efficient Catalysts

Preparation of C2-symmetric bicyclo[2.2.2]octa-2,5-diene ligands and their use for rhodium-catalyzed asymmetric 1,4-addition of arylboronic acids.

Radical-polar crossover reactions of vinylboron ate complexes

Electronic and steric tuning of chiral diene ligands for rhodium-catalyzed asymmetric arylation of imines