Enantioselective Allylic C-H Bond Oxidation of Olefins Using Copper Complexes of Chiral Oxazoline Based Ligands

Photoinduced Copper-Catalyzed Enantioselective Allylic C(sp3)-H Oxidation of Acyclic 1-Aryl-2-alkyl Alkenes as Limiting Substrates

Herein, we disclose a simple copper-catalyzed method for enantioselective allylic C(sp3)-H oxidation of unsymmetrical acyclic alkenes, specifically 1-aryl-2-alkyl alkenes. The C-H substrates are used in limiting amounts, and the products are obtained with high enantioselectivity, E/Z-selectivity, and regioselectivity. The method exhibits broad functional group tolerance, and E/Z-alkene mixtures are suitable C-H substrates. The transformation is enabled by light irradiation, which sustains the enantioselective copper catalysis by photoinduced oxidant homolysis.

Chiral amido-oxazoline functionalized MCM-41: A sustainable heterogeneous catalyst for enantioselective Kharasch-Sosnovsky and Henry reactions

In this study, a series of chiral amido-oxazoline ligands was synthesized with a primary focus on immobilizing the most effective ligands on MCM-41 mesoporous material. Following several attempts, the para-nitro group of the chiral amido-oxazoline ligands was successfully reduced to amino group, enabling their immobilization on MCM-41. The resulting chiral heterogeneous amido-oxazoline ligands were characterized using various techniques, including FT-IR, XRD, TGA, SEM, TEM, EDX, and BET-BJH, confirming the successful immobilization of the amido-oxazoline ligands. A comparison of the efficiency of the homogeneous and heterogeneous amido-oxazoline-based ligands in the Kharasch-Sosnovsky and Henry reactions revealed better performance of the heterogeneous ligand. The immobilized amido-oxazoline-copper complexes exhibited remarkable catalytic activity, achieving excellent yields and enantioselectivities (up to 88 % ee) in the Kharasch-Sosnovsky reaction, and delivering excellent yields with moderate enantioselectivities in the Henry reaction. Notably, the Henry reaction proceeded with moderate diastereoselectivity, favoring the syn diastereomer, under solvent-free conditions, highlighting the sustainability of the process. The heterogeneous nature of the catalysts facilitated effortless recovery and efficient reusability.

Photocatalysis Meets Copper Catalysis: A New Opportunity for Asymmetric Multicomponent Radical Cross-Coupling Reactions

ConspectusIn recent years, radical-mediated cross-coupling reactions have emerged as a compelling strategy for achieving a rich diversity in molecular topologies under benign conditions. However, the inherent high reactivity of radicals presents considerable challenges in controlling reaction pathways and selectivity, which often results in a limited range of substrates and a constrained reaction profile. Given the capacity of visible-light photoredox catalysis to generate a wide variety of reactive radicals and radical ions in a controlled manner and the propensity of copper complexes toward radical species, we envisaged that the synergy between chiral copper catalysts and photoactive catalysts would pave the way for developing innovative strategies. This integration is poised to unlock a broad spectrum of enantioselective multicomponent radical cross-coupling reactions.In this Account, we describe our insights and recent efforts in the realm of enantioselective multicomponent radical cross-coupling reactions. These advancements have been achieved through the innovative application of dual photoredox/copper catalysis or bifunctional copper catalysis under visible light irradiation. Our work is systematically divided into two sections based on the activation modes. The first section focuses on photoinduced copper-catalyzed chiral C-C and C-O bond formation through a radical addition/nucleophilic trap sequence. Our discussion of chiral C-C bond formation is particularly concentrated on the asymmetric carbocyanation and carboarylation of vinylarenes, 1,3-enynes, and 1,3-dienes. Our findings underscore that irradiation with visible light can adeptly modulate the pace of radical generation, thus orchestrating consecutive reaction stages and ensuring the attainment of both chemo- and stereoselectivity. In the domain of chiral C-O bond formation, leveraging carboxylic acids as a nucleophilic oxygen source, we introduce a suite of esterification reactions of benzylic, allylic, and propargylic radicals. These radicals are derived from a variety of radical precursors, showcasing the versatility of our approach. The following section highlights our innovative discovery in the field of dual photoredox/copper catalysis, which enables enantioselective three-component radical transformations via the direct activation of aromatic alkenes. This methodology begins with the generation of formal distonic radical anions through the photocatalytic single-electron reduction of aromatic alkenes, thus, enabling orthogonal reactivity. Employing H2O, D2O, and CO2 as external electrophile agents, we have developed three types of radical cyanofunctionalization reactions: hydrocyanation, deuteriocyanation, and cyanocarboxylation. These reactions provide practical access to diversely functionalized chiral nitriles with high enantiomeric excess.Collectively, these synthetic methodologies highlight the immense potential inherent in the synergistic integration of photocatalysis and asymmetric copper catalysis. This Account aspires to deepen our comprehension of the advantages conferred by these catalytic systems, elucidating the crucial role of photocatalysis in facilitating enantioselective multicomponent radical cross-couplings. We anticipate that this Account will provide valuable insights and stimulate the evolution of innovative methodologies within this rapidly expanding field.

Metal-catalyzed asymmetric reactions enabled by organic peroxides

As a class of multifunctional reagents, organic peroxides play vital roles in the chemical industry, pharmaceutical synthesis and polymerization reactions. Metal-catalyzed asymmetric catalysis has emerged as one of the most straightforward and efficient strategies to construct enantioenriched molecules, and an increasing number of metal-catalyzed asymmetric reactions enabled by organic peroxides have been disclosed by researchers in recent years. Despite remarkable progress, the types of asymmetric reactions facilitated by organic peroxides remain limited and the catalysis systems need to be further broadened. To the best of our knowledge, there is still no review devoted to summarizing the reactions from this perspective. In this review, we will endeavor to highlight the advances in metal-catalyzed asymmetric reactions enabled by organic peroxides. We hope that this survey will summarize the functions of organic peroxides in catalytic reactions, improve the understanding of these compounds and inspire future developments in this area.

Chiral Pseudohomogeneous Catalyst Based on Amphiphilic Carbon Quantum Dots for the Enantioselective Kharasch-Sosnovsky Reaction

The term "chiral pseudohomogeneous catalyst (PHC)" denotes a novel concept that characterizes subnanometric particles exhibiting atomic-level chirality. The PHC based on chiral amphiphilic carbon quantum dots possesses distinctive features that combine the strengths of both homogeneous and heterogeneous catalysts, thereby heralding a significant breakthrough in the fields of asymmetric synthesis and medicinal chemistry. To the best of our knowledge, this is the first and the only reported research of a chiral PHC that demonstrates exceptional performance in controlling the enantioselectivity of the Kharasch-Sosnovsky reaction, yielding the corresponding products in high conversion (95%) with a moderate enantiomeric excess (75%). Notably, the chiral information on l-tryptophan can be effectively transferred from the outer shell of the nanosized catalyst, thereby inducing enantioselectivity in C-H activation and subsequent C-O forming events. Additionally, we have investigated the impact of various factors on the allylic oxidation reaction, including the amount, diversity, and hydrophilic/hydrophobic nature of the catalyst, as well as the influence of the solvent, Cu salts, temperature, and the type of alkene and perester, in order to comprehensively explore the reaction conditions. Furthermore, the catalyst can be readily recycled from the reaction medium, making this PHC a promising innovation that can significantly impact practical applications. In summary, this breakthrough can be aptly described as a "Golden Gate" due to its unparalleled potential to open up novel avenues for research and innovation.

Emerging Trends in Copper-Promoted Radical-Involved C-O Bond Formations

The C-O bond is ubiquitous in biologically active molecules, pharmaceutical agents, and functional materials, thereby making it an important functional group. Consequently, the development of C-O bond-forming reactions using catalytic strategies has become an increasingly important research topic in organic synthesis because more conventional methods involving strong base and acid have many limitations. In contrast to the ionic-pathway-based methods, copper-promoted radical-mediated C-O bond formation is experiencing a surge in research interest owing to a renaissance in free-radical chemistry and photoredox catalysis. This Perspective highlights and appraises state-of-the-art techniques in this burgeoning research field. The contents are organized according to the different reaction types and working models.