Synthesis of planar chiral imidazo[1,5-a]pyridinium salts based on [2.2]paracyclophane for asymmetric β-borylation of enones

Chiral Biaryl N-Heterocyclic Carbene-Palladium Catalysts with Anagostic C-H···Pd Interaction for Enantioselective Desymmetric C-N Cross-Coupling

Novel chiral biaryl imidazo[1,5-a]pyridine carbene-palladium complexes (ImPy-Pd) featuring an anagostic C-H···Pd interaction and a C5-aryl substituent have been developed and successfully applied to the Pd-catalyzed enantioselective desymmetric C-N cross-coupling of malonamide derivatives, providing chiral 3,4-dihydroquinoline-2-ones with quaternary stereocenters in high yields (≤99%) and enantioselectivities (≤97:3 er). The chiral catalyst exerts stereocontrol by restricting the rotation of substituents around the metal center through anagostic interactions with sterically bulky substituents.

The concise synthesis and resolution of planar chiral [2.2]paracyclophane oxazolines by C-H activation

Planar chiral [2.2]paracyclophanes are resolved through the direct C–H arylation of enantiopure oxazolines, providing a convenient route to ligands and chiral materials. Preliminary results show that hydrolysis followed by decarboxylative phosphorylation leads to enantiopure [2.2]paracyclophane derivatives that are otherwise challenging to prepare.

Racemic bromo[2.2]paracyclophanes are directly transformed into enantiomerically pure planar chiral oxazolines in one step with simultaneous resolution of planar chirality.

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.

Recent Advances in Metal-Catalyzed Asymmetric 1,4-Conjugate Addition (ACA) of Nonorganometallic Nucleophiles

The metal-catalyzed asymmetric conjugate addition (ACA) reaction has emerged as a general and powerful approach for the construction of optically active compounds and is among the most significant and useful reactions in synthetic organic chemistry. In recent years, great progress has been made in this area with the use of various chiral metal complexes based on different chiral ligands. This review provides comprehensive and critical information on the enantioselective 1,4-conjugate addition of nonorganometallic (soft) nucleophiles and their importance in synthetic applications. The literature is covered from the last 10 years, and a number of examples from before 2007 are included as background information. The review is divided into multiple parts according to the type of nucleophile involved in the reaction (such as C-, B-, O-, N-, S-, P-, and Si-centered nucleophiles) and metal catalyst systems used.

Well-Defined Chiral Copper NHC Complex in the Asymmetric Conjugated β-Borylation and One-Pot Metathesis-Asymmetric β-Borylation Reactions

Highly stereoselective conjugate β-borylation, using a new chiral NHC-based copper catalyst, has been achieved. The chiral NHC copper complex was prepared in gram scale and showed high enantioselectivity and activity (up to 10 000 turnovers at 100 ppm of catalyst loading). This method was employed in the synthesis of a chiral β-borylated ester from simple unconjugated alkenes though an unprecedented one-pot cross metathesis-asymmetric borylation sequence.

Chirality and catalysis with aromatic N-fused heterobicyclic carbenes

The benzoannulation of the most common families of aromatic NHCs, imidazol-2-ylidenes and 1,2,4-triazol-3-ylidenes, results in heterobicyclic imidazo[1,5-a]pyridin-3-ylidenes ('s) and [1,2,4]triazolo[4,3-a]pyridin-3-ylidenes ('s), characterized by a bridged N atom. These are versatile platforms that offer multiple possibilities for the modulation of the steric and electronic properties of the carbene ligand and/or organocatalyst, and offer also diverse opportunities for the introduction of several types of chiralities. In this paper the different families of chiral and carbenes and their application in asymmetric catalysis will be discussed.

Diboron(4) Compounds: From Structural Curiosity to Synthetic Workhorse

Although known for over 90 years, only in the past two decades has the chemistry of diboron(4) compounds been extensively explored. Many interesting structural features and reaction patterns have emerged, and more importantly, these compounds now feature prominently in both metal-catalyzed and metal-free methodologies for the formation of B-C bonds and other processes.

[2.2]Paracyclophane-based N-heterocyclic carbene as efficient catalyst or as ligand for copper catalyst for asymmetric α-silylation of N-tosylaldimines

A carbene precursor plays a dual role as both an organocatalyst and as a ligand for the copper catalyst in asymmetric silylation.

The synthesis of substituted amino[2.2]paracyclophanes

Amino[2.2]paracyclophanes can be prepared by direct amination of bromo[2.2]paracyclophanes or more generally by a formylation–oxime formation–oxidation–Lossen-like rearrangement sequence.

[2.2]Paracyclophane-based carbene–copper catalyst tuned by transannular electronic effects for asymmetric boration

The catalytic performance of [2.2]paracyclophane-based carbene–copper complexes in the asymmetric boration can be controlled by the electronic tuning of carbene ligands.

A Cu(ii)-based strategy for catalytic enantioselective β-borylation of α,β-unsaturated acceptors

The unique nature and readily availability of Cu(v) species underscores the value of the Cu(v)-based catalyst over an array of well-documented Cu(i)-based catalysts.

Asymmetric boron conjugate addition to α,β-unsaturated carbonyl compounds catalyzed by CuOTf/Josiphos under non-alkaline conditions

The asymmetric boron conjugate addition onto α,β-unsaturated ketones and esters has been developed by using the CuOTf/Josiphos complex as the catalyst under non-alkaline conditions.

Synthesis and application of a dual chiral [2.2]paracyclophane-based N-heterocyclic carbene in enantioselective β-boration of acyclic enones

A N-heterocyclic carbene was used as both an organocatalyst and a ligand for transition metal catalysis in asymmetric boration.