Highly Recyclable Self-Supported Chiral Catalysts for the Enantioselective α-Hydrazination of β-Ketoesters

Polymerization/depolymerization of chiral metallo-supramolecular assembly induced by redox change

We report on the polymerization/depolymerization of chiral metallo-supramolecular assembly by Cu^I /Cu^II redox change. By combining a monotopic enantiopure ligand with a ditopic ligand of opposite configuration, ML₂ -type complexes are generated with chiral self-recognition or self-discrimination depending on the oxidation state of copper. In presence of Cu^I , the formation of heterochiral complexes is favored, thus generating dinuclear species whereas Cu^II advocates for the formation of homochiral species, namely, a mixture of mononuclear species and metallo-supramolecular polymeric species. Thus, cyclic voltammetry was used to study such a chirality-induced stimulus sensitive polymerization/depolymerization process.

Further Developments and Applications of Oxazoline-Containing Ligands in Asymmetric Catalysis

The chiral oxazoline motif is present in many ligands that have been extensively applied in a series of important metal-catalyzed enantioselective reactions. This Review aims to provide a comprehensive overview of the most significant applications of oxazoline-containing ligands reported in the literature starting from 2009 until the end of 2018. The ligands are classified not by the reaction to which their metal complexes have been applied but by the nature of the denticity, chirality, and donor atoms involved. As a result, the continued development of ligand architectural design from mono(oxazolines), to bis(oxazolines), to tris(oxazolines) and tetra(oxazolines) and variations thereof can be more easily monitored by the reader. In addition, the key transition states of selected asymmetric transformations will be given to illustrate the features that give rise to high levels of asymmetric induction. As a further aid to the reader, we summarize the majority of schemes with representative examples that highlight the variation in % yields and % ees for carefully selected substrates. This Review should be of particular interest to the experts in the field but also serve as a useful starting point to new researchers in this area. It is hoped that this Review will stimulate both the development/design of new ligands and their applications in novel metal-catalyzed asymmetric transformations.

Chiral stimuli-responsive metallo-supramolecular assembly induced by CuII/CuI redox change

We investigated the selective formation of homoleptic and heteroleptic metal complexes controlled by means of the chiral molecular instruction of the ligand and the coordination geometry of the metal.

Readily Available Chiral Benzimidazoles-Derived Guanidines as Organocatalysts in the Asymmetric α-Amination of 1,3-Dicarbonyl Compounds

The synthesis and the evaluation as organocatalysts of new chiral guanidines derived from benzimidazoles in the enantioselective α-amination of 1,3-dicarbonyl compounds using di-t-butylazodicarboxylate as aminating agent is herein disclosed. The catalysts are readily synthesized through the reaction of 2-chlorobezimidazole and a chiral amine in moderate-to-good yields. Among all of them, those derived from (R)-1-phenylethan-1-amine (1) and (S)-1-(2-naphthyl)ethan-1-amine (3) turned out to be the most efficient for such asymmetric transformation, rendering good-to-high yields and moderate-to-good enantioselectivities for the amination products.

Catalytic asymmetric α-amination of β-keto esters and β-keto amides with a chiral N,N′-dioxide–copper(i) complex

The highly efficient asymmetric α-amination of β-keto esters and β-keto amides was realized by using a chiral N,N′-dioxide/Cu(i) complex. Under mild reaction conditions, a series of chiral α-amino dicarbonyl compounds were obtained in good result.

IMes-acac: hybrid combination of diaminocarbene and acetylacetonato sub-units into a new anionic ambidentate NHC ligand

The mesoionic 5-acetylimidazolium-4-olate serves as precursor for an anionic, hybrid NHC, "IMes-acac", consisting of fused diaminocarbene and acetylacetonato units, whose respective coordination abilities are evaluated by the formation of a series of representative copper(I) complexes illustrating the ambidentate character of the ligand.

Recyclable BINOL–quinine–squaramide as a highly efficient organocatalyst for α-amination of 1,3-dicarbonyl compounds and α-cyanoacetates

An efficient organocatalytic asymmetric α-amination of 1,3-dicarbonyl and α-cyanoacetates compounds towards chiral α-amino acid precursors is reported.

Polytopic bis(oxazoline)-based ligands for recoverable catalytic systems applied to the enantioselective Henry reaction

Polytopic chiral ligands based on bis(oxazoline) motifs can be efficiently used to prepare recoverable catalytic systems for Henry reactions using a release–capture strategy.

Asymmetric benzoylation and Henry reaction using reusable polytopic bis(oxazoline) ligands and copper(ii)

Multitopic bis(oxazoline)-based chiral ligands are associated with copper to generate catalysts for the asymmetric benzoylation of meso-hydrobenzoin, the kinetic resolution of rac-hydrobenzoin and the asymmetric Henry reaction.