Enantioselective Construction of Single and Vicinal All-Carbon Quaternary Stereocenters through Ion-Pair-Catalyzed 1,6-Conjugate Addition

Arylcyanomethylenequinone Oximes: An Overview of Synthesis, Chemical Transformations, and Biological Activity

Quinone methides are a class of biologically active compounds that can be used in medicine as antibacterial, antifungal, antiviral, antioxidant, and anti-inflammatory agents. In addition, quinone methides have the potential to be used as pesticides, dyes, and additives for rubber and plastics. In this paper, we discuss a subclass of quinone methides: methylenequinone oximes. Although the first representatives of the subgroup were synthesized in the distant past, they still need to be additionally studied, while their chemistry, biological properties, and perspective of practical applications require to be comprehensively summarised. Based on the analysis of the literature, it can be concluded that methylenequinone oximes exhibit a diversified profile of properties and outstanding potential as new drug candidates and reagents in organic synthesis, both of electrophilic and nucleophilic nature, worthy of wide-ranging further research.

Anion-accelerated asymmetric Nazarov cyclization: access to vicinal all-carbon quaternary stereocenters

We have developed a catalytic asymmetric Nazarov cyclization that results in the formation of two contiguous all-carbon quaternary stereocenters in high yield with excellent levels of asymmetric induction. This method requires no catalyst recognition elements in the starting materials that are simple diketoesters. Geometrically pure E or Z isomers of the starting material lead to diastereomerically pure products with high enantioselectivity because the species that undergoes cyclization is a rhodium enolate that is configurationally stable.

Construction of Vicinal All-Carbon Stereogenic Centers via Copper-Catalyzed Asymmetric Decarboxylative Propargylation: Enantio- and Diastereoselective Synthesis of Substituted Spirolactones

The formation of vicinal all-carbon quaternary stereocenters remains a formidable challenge. We report herein the synthesis of such highly congested structural dyads by copper-catalyzed decarboxylative propargylation between propargyl carbonates and indanone-based nucleophiles. The implementation of diphenylethylenediamine (DPEN)-based ligands is the key to success. A wide range of functional groups was tolerated, delivering the indanone-based spirolactones in good yields with high diastereo- and enantioselectivity. The mechanistic observations suggest the capability of the new copper complex to enable stereocontrolled addition to copper-allenylidene species.

Hydride-Abstraction-Initiated Catalytic Stereoselective Intermolecular Bond-Forming Processes

The stereoselective intermolecular bond-forming reactions through the direct manipulation of ubiquitous yet inert C(sp³)-H bonds represent an important and long-standing goal in chemistry. In particular, developing such a stereoselective bimolecular transformation involving carbocation intermediates generated via site-selective hydride abstraction or formal hydride abstraction by organic oxidants would avoid the preinstallation of directing groups and is therefore attractive. Hydride-abstraction-initiated bimolecular transformations have received considerable attention, but existing examples lack stereoselective studies. Prevalent stereoselective studies typically suffer from the narrow substrate scope of specific and highly reactive N-aryl amines and diarylmethanes together with limited synthetic utility. This Account describes our recent advances in the development and synthetic application of hydride-abstraction-initiated stereoselective intermolecular C-C and C-H bond-forming processes with significantly expanded scopes involving structurally diverse N-acyl amines and ethers together with nitriles, esters, and perfluoroalkyl moieties.We first explored hydride-abstraction-initiated stereoselective intermolecular C-C bond-forming processes. Utilizing triarylmethyl cations or oxoammonium ions as hydride abstractors, we accomplished the diastereoselective oxidative C-H functionalization of structurally diverse N-acyl amines and ethers with a range of organoboranes and C-H components, efficiently installing a series of alkyl, alkenyl, aryl, and alkynyl species into the α-position of heteroatoms with good levels of diastereocontrol. Subsequently, we developed an "acetal pool" strategy as the toolbox to regulate the stability of cationic intermediates and the compatibility of organic oxidants with a delicate asymmetric catalysis system. Utilizing this strategy, we achieved the catalytic enantioselective oxidative C-H alkenylation, arylation, alkynylation, and alkylation of diverse N-acyl heterocycles with a range of boronates and C-H components. Simultaneously, we extended this strategy to the asymmetric oxidative C-H alkylation of ethers. Notably, the method allows solvents that are used daily, such as tetrahydrofuran, tetrahydropyran, and diethyl ether, to be facilely transformed to high-value-added optically pure bioactive molecules. We further expanded the scope of this challenging area from the C(sp³)-H bond adjacent to electron-donating heteroatoms to valuable electron-withdrawing functional groups including nitriles, esters, and perfluoroalkyl moieties for the stereoselective construction of single and vicinal quaternary carbon stereocenters, respectively.We studied hydride-abstraction-initiated catalytic asymmetric intermolecular C-H bond-forming processes, known as redox deracemization. Utilizing the acetal pool strategy, we reported the first redox deracemization of cyclic benzylic ethers. Later, we disclosed an aerobic one-pot deracemization of diverse α-amino acid derivatives with excellent functional group compatibility. We further achieved the deracemization of the tertiary stereogenic center adjacent to electron-withdrawing groups including perfluoroalkyl, cyano, and ester moieties, which are otherwise difficult to construct.

Enantioselective Construction of Vicinal Quaternary-Tetrasubstituted Carbon Stereocenters by Copper-Catalyzed Decarboxylative Propargylic Substitution

Enantioselective construction of vicinal tetrasubstituted carbon stereocenters is a formidable challenge in organic synthesis. A copper-catalyzed asymmetric decarboxylative propargylic substitution with 3-amino oxindoles as trisubstituted carbon nucleophiles and propargylic cyclic carbonates as tertiary carbon electrophiles was developed. A range of 3-amino-3,3'-disubstituted oxindoles bearing vicinal quaternary-tetrasubstituted carbon stereocenters were obtained in high yields and good to excellent stereoselectivities (up to 98% yield, >20:1 dr, and 98.5:1.5 er).