Feng Ligand: Privileged Chiral Ligand in Asymmetric Catalysis

Abstract

Feng ligand | N,N'-Dioxide | O ligands | Asymmetric catalysis | Lewis acids Catalysts and ligands possessing the great ability to tolerate over a wide range of mechanistically unrelated reactions are remarked as "privileged", which are rather scarce but extremely meaningful in asymmetric catalysis. Feng and co-workers have developed a library of conformationally flexible, C 2-symmetric N,N'-dioxide amide compounds with original design and featured structure (named as Feng ligand now). They were initially reported as chiral organocatalysts in 2005 and have been further developed as a new class of privileged chiral ligands since 2006. Tremendous success, including versatile coordination chemistry with plenty of metal sources (main-group metals, transition metals, and rare-earth metals), a truly broad scope of asymmetric reactions (more than 50 types), diverse areas of catalysis (organocatalysis, Lewis-acid catalysis, bimetallic relay catalysis, and photocatalysis), numerous synthetic applications of bioactive compounds, has been achieved using Feng N,N'-dioxide. Besides, they demonstrate that chiral ligands with conformationally flexible property can offer excellent chiral environment as well, which challenges the conventional idea preferring rigid structures in the design of chiral ligands. Herein, we briefly introduced the discovery of Feng ligand and the millstones during the development. We also covered the successful applications of Feng ligand by other scientists as well as novel chiral ligands inspired by them. Contents 1. Introduction 969 2. Initial Discovery 970 3. Representative Applications 971 3.1. Classical asymmetric reactions 971 3.2. Novel asymmetric reactions 975 4. Studies by Other Groups 977 4.1. Reactions using Feng ligand 977 4.2. Novel chiral ligands inspired by Feng ligand 980 5. Conclusions 980

Enantioselective Formal Vinylogous N–H Insertion of Secondary Aliphatic Amines Catalyzed by a High-Spin Cobalt(II) Complex

“…The latter two were hard to separate, and the thermodynamically unstable ( Z )- C1 was isolated as the major product in most cases. In the reaction with chiral Feng N , N′ -dioxide L 3 -Tq t Bu as the ligand − and Co­(OTf) 2 as the metal precursor, ( Z )- C1 was isolated in 66% yield with 97% ee, and the combined yield of ( E )- C1 and D1 was around 20% with 90:10 ratio (entry 1). The α/γ-regioselectivity was high and the γ-insertion products dominated.…”

Catalytic asymmetric synthesis of spirocyclobutyl oxindoles and beyond via [2+2] cycloaddition and sequential transformations

“…Considering the frequent occurrence of the spirocyclobutyl oxindole skeleton in bioactive molecules, 12 h – j ,15 it is highly desirable to develop reliable access to spirocyclobutyl oxindole derivatives. 16 In continuation with our interest in chiral N , N ′-dioxide/metal Lewis acid catalysis 17 and inspired by elegant studies 5,13,14 on the N -allenamide chemistry, herein, we demonstrated that catalysts could promote the direct asymmetric [2+2] cycloaddition of ( E )-alkenyloxindoles with N -allenamides for straightforward access to optically active spirocyclobutyl oxindole derivatives ( Scheme 1b ). Moreover, further diversified transformation 18 of the internal C C bond-involved product catalyzed by a copper salt enabled the one-pot synthesis of tetradropyranoindole derivatives, which seem to be the formal [4+2] cycloaddition adducts of the terminal C C bond of N -allenamides.…”

Porous Silica Support for Immobilizing Chiral Metal Catalyst: Unravelling the Activity of Catalyst on Asymmetric Organic Transformations

“…Homogeneous asymmetric catalyst has made significant progress in the last decade, due to its facile interaction between the catalyst and the reactant which results in high activity and selectivity. The main pitfall is separation of the catalyst from the products, which often leads to loss of the catalyst [1,2] . Another drawback is leaching of the metal from the homogeneous catalysts into the products.…”