Applications of enantiopure 4,5-diphenyl substituted box and pybox ligands in asymmetric catalysis

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.

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

This review article discusses historical and contemporary research studies of asymmetric allylic oxidation of olefins using homogeneous and heterogeneous copper complexes of various kinds of oxazoline-based ligands, until the end of 2021. It is revealed that this strategy is a powerful method to form a new stereogenic center bearing an oxygen substituent adjacent to an unchanged C=C bond. Enantioselectivities as well as chemical yields, and also the reactivity, are strongly dependent on the type of substrate, oxidant, the copper salt and its oxidation state, ligand structure, temperature, nature of the solvent, and additives such as phenylhydrazine and porous materials.

Synthesis of 2-Arylpiperidines via Pd-Catalyzed Arylation of Aza-Achmatowicz Rearrangement Products with Arylboronic Acids

The first Pd-catalyzed arylation of aza-Achmatowicz rearrangement products with arylboronic acids is achieved, providing versatile 2-aryldihydropyridinones for facile synthesis of highly functionalized 2-arylpiperidines. Key to this arylation is the use of non-phosphine-ligand palladium precatalyst. The substrate scope is demonstrated with >26 examples, and the utility of 2-aryldihydropyridinones is illustrated by the synthesis of a small collection of 2-arylpiperidines with substituents or functional groups at any carbon (C2-C6) as well as two NK₁ receptor antagonists (+)-CP-999,94 and (+)-L-733,060.

Enantioselective functionalization of allylic C-H bonds following a strategy of functionalization and diversification

We report the enantioselective functionalization of allylic C-H bonds in terminal alkenes by a strategy involving the installation of a temporary functional group at the terminal carbon atom by C-H bond functionalization, followed by the catalytic diversification of this intermediate with a broad scope of reagents. The method consists of a one-pot sequence of palladium-catalyzed allylic C-H bond oxidation under neutral conditions to form linear allyl benzoates, followed by iridium-catalyzed allylic substitution. This overall transformation forms a variety of chiral products containing a new C-N, C-O, C-S, or C-C bond at the allylic position in good yield with a high branched-to-linear selectivity and excellent enantioselectivity (ee ≤97%). The broad scope of the overall process results from separating the oxidation and functionalization steps; by doing so, the scope of nucleophile encompasses those sensitive to direct oxidative functionalization. The high enantioselectivity of the overall process is achieved by developing an allylic oxidation that occurs without acid to form the linear isomer with high selectivity. These allylic functionalization processes are amenable to an iterative sequence leading to (1,n)-functionalized products with catalyst-controlled diastereo- and enantioselectivity. The utility of the method in the synthesis of biologically active molecules has been demonstrated.

A new approach to the synthesis of peptidomimetic renin inhibitors: palladium-catalyzed asymmetric allylation of acyclic alkyl aryl ketones

A new approach to the synthesis of Tekturna, a recently marketed drug for hypertension, takes advantage of a modified protocol of the Stoltz palladium-catalyzed asymmetric allylation with a t-BuPHOX ligand for the synthesis of allylated acyclic alkyl aryl ketones. The method led to an α-isopropyl α-allyl aryl ketone in 90% yield and 88 to 91% ee, which was used in the synthesis of an advanced intermediate toward Tekturna. A beneficial effect of protic additives, such as BHT (2,6-di-tert-butyl-p-cresol), on the time and enantioselectivity of the reaction was discovered.

Allylic alkylations catalyzed by palladium-bis(oxazoline) complexes derived from heteroarylidene malonate derivatives

A series of simple heteroarylidene malonate-type bis(oxazoline) ligands 4 and 5 were applied to the palladium-catalyzed allylic alkylation reaction, and the ligand 4a bearing a phenyl group afforded excellent enantioselectivity (up to 96% ee) for the allylic alkylation product. Other substrates were also examined, giving the allylic alkylated products in high yield but with poor ee values.

Metal-catalyzed enantioselective allylation in asymmetric synthesis

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.

Studies on enantioselective allylic oxidation of olefins using peresters catalyzed by Cu(i)-complexes of chiral pybox ligands

Enantioselective allylic oxidation of olefins with various peresters, using a catalytic amount of Cu(I)-pybox complex, can be tuned to achieve high asymmetric induction (up to 98% ee) by choosing a unique combination of a ligand and a perester at room temperature. The asymmetric induction in the reaction strongly depends on the nature of the substituents attached to the aryl ring of peresters. The presence of a gem-diphenyl group at C-5 and secondary or tertiary alkyl substituents at the chiral center (C-4) of the oxazoline rings is crucial for high enantioselectivity. A pi-pi stacking model has been proposed and discussed to explain the stereochemical outcome of the reaction.