Synthesis of bridged tricyclo[5.2.1.01,5]decanes via nickel-catalyzed asymmetric domino cyclization of enynones

P-Stereogenic Phosphorus Ligands in Asymmetric Catalysis

Chiral phosphorus ligands play a crucial role in asymmetric catalysis for the efficient synthesis of useful optically active compounds. They are largely categorized into two classes: backbone chirality ligands and P-stereogenic phosphorus ligands. Most of the reported ligands belong to the former class. Privileged ones such as BINAP and DuPhos are frequently employed in a wide range of catalytic asymmetric transformations. In contrast, the latter class of P-stereogenic phosphorus ligands has remained a small family for many years mainly because of their synthetic difficulty. The late 1990s saw the emergence of novel P-stereogenic phosphorus ligands with their superior enantioinduction ability in Rh-catalyzed asymmetric hydrogenation reactions. Since then, numerous P-stereogenic phosphorus ligands have been synthesized and used in catalytic asymmetric reactions. This Review summarizes P-stereogenic phosphorus ligands reported thus far, including their stereochemical and electronic properties that afford high to excellent enantioselectivities. Examples of reactions that use this class of ligands are described together with their applications in the construction of key intermediates for the synthesis of optically active natural products and therapeutic agents. The literature covered dates back to 1968 up until December 2023, centering on studies published in the late 1990s and later years.

Nickel-Catalyzed Enantioselective Reductive Arylation of Common Ketones

A nickel complex of chiral bisoxazolines catalyzed the stereoselective reductive arylation of ketones in high enantioselectivity. A range of common acyclic and cyclic ketones reacted without the aid of directing groups. Mechanistic studies using isolated complex of a chiral bis(oxazoline) (L)Ni(Ar)Br revealed that Mn reduction was not needed, while Lewis acidic titanium alkoxides were critical to ketone insertion.

Atroposelective Synthesis of C-N Vinylindole Atropisomers by Palladium-Catalyzed Asymmetric Hydroarylation of 1-Alkynylindoles

Transition-metal-catalyzed hydroarylation of unsymmetrical internal alkynes remains challenging because of the difficulty in controlling regioselectivity and stereoselectivity. Moreover, the enantioselective hydroarylation of alkynes using organoboron reagents has not been reported. Herein, we report for the first time that palladium compounds can catalyze the hydroarylation of 1-alkynylindoles with organoborons for the synthesis of chiral C-N atropisomers. A series of rarely reported vinylindole atropisomers was synthesized with excellent regio-, stereo- (Z-selectivity), and enantioselectivity under mild reaction conditions. The ready availability of organoborons and alkynes and the simplicity, high stereoselectivity, and good functional group tolerance of this catalytic system make it highly attractive.

Enantioselective Synthesis of Bicyclo[3.2.1]octadienes via Palladium-Catalyzed Intramolecular Alkene-Alkyne Coupling Reaction

Bicyclo[3.2.1]octadiene compounds and derivatives exist in a number of natural products and bioactive compounds. Nevertheless, catalytic enantioselective protocols for the synthesis of these skeletons have not been disclosed. Herein we reported a palladium-catalyzed asymmetric intramolecular alkene-alkyne coupling of alkyne-tethered cyclopentenes, affording a library of enantionenriched bicyclo[3.2.1]octadienes in excellent yields and enantioselectivities (mostly >99 % ee). Moreover, the products could undergo an unusual iodination-induced 1,2-acyl migration, forming iodinated bicyclo[3.2.1]octadienes with three vicinal stereocenters. The enone and isolated olefin motifs embedded in the products provide useful handles for downstream elaboration.

Recent Progress in Asymmetric Domino Intramolecular Cyclization/Cascade Reactions of Substituted Olefins

The domino cyclization/coupling strategy is one of the most effective methods to produce cyclized and multi-functionalized compounds from olefins, which has attracted huge attention from chemists and biochemists especially for its considerable potential of enantiocontrol. Nowadays, more and more studies are developed to achieve difunctionalization of substituted olefins through an asymmetric domino intramolecular cyclization/cascade reaction, which is still an elegant choice to accomplish several synthetic ideas such as complex natural products and drugs. This review surveys the recent advances in this field through reaction type classification. It might serve as useful knowledge desktop for the community and accelerate their research.

Nickel-Catalyzed Enantioselective Reductive Arylation and Heteroarylation of Aldimines via an Elementary 1,4-Addition

Nickel catalysts of chiral pyrox ligands promoted enantioselective reductive arylation and heteroarylation of aldimines, using directly (hetero)aryl halides and sulfonates. The catalytic arylation can also be conducted with crude aldimines generated from condensation of aldehydes and azaaryl amines. Mechanistically, density functional theory (DFT) calculations and experiments pointed to an elementary step of 1,4-addition of aryl nickel(I) complexes to N-azaaryl aldimines.

Enantioselective Nickel-Catalyzed Reductive anti-Arylative Annulation of Alkyne-Tethered Malononitriles to Construct Quaternary Stereocenters

A nickel-catalyzed reductive desymmetrizing annulation of alkyne-tethered malononitriles and (hetero)aryl iodides is reported for the access of cyclohexenones containing an α-all-carbon quaternary stereocenter. The use of a nickel catalyst derived from an electron-rich phosphinooxazoline ligand combined with iron powder as a reductant is crucial to the success of this transformation.

Asymmetric Total Synthesis of Illisimonin A

The discovery of illisimonin A in 2017 extended the structural repertoire of the Illicium sesquiterpenoids─a class of natural products known for their high oxidation levels and neurotrophic properties─with a new carbon backbone combining the strained trans-pentalene and norbornane substructures. We report an asymmetric total synthesis of (-)-illisimonin A that traces its tricyclic carbon framework back to a spirocyclic precursor, generated by a tandem-Nazarov/ene cyclization. As crucial link between the spirocyclic key intermediate and illisimonin A, a novel approach for the synthesis of tricyclo[5.2.1.0^1,5]decanes via radical cyclization was explored. This approach was applied in a two-stage strategy consisting of Ti(III)-mediated cyclization and semipinacol rearrangement to access the natural product's carbon backbone. These key steps were combined with carefully orchestrated C-H oxidations to establish the dense oxidation pattern.

Nickel-Catalyzed Arylative Cyclizations of Alkyne- and Allene-Tethered Electrophiles using Arylboron Reagents

The use of arylboron reagents in metal‐catalyzed domino addition–cyclization reactions is a well‐established strategy for the preparation of diverse, highly functionalized carbo‐ and heterocyclic products. Although rhodium‐ and palladium‐based catalysts have been commonly used for these reactions, more recent work has demonstrated nickel catalysis is also highly effective, in many cases offering unique reactivity and access to products that might otherwise not be readily available. This review gives an overview of nickel‐catalyzed arylative cyclizations of alkyne‐ and allene‐tethered electrophiles using arylboron reagents. The scope of the reactions is discussed in detail, and general mechanistic concepts underpinning the processes are described.

Desymmetrization of Cyclic 1,3-Diketones under N-Heterocyclic Carbene Organocatalysis: Access to Organofluorines with Multiple Stereogenic Centers

Symmetric 1,3-diketones with fluorine or fluorinated substituents on the prochiral carbon remain to be established. Herein, we have developed a novel prochiral fluorinated oxindanyl 1,3-diketone and successfully applied these substrates in carbene-catalyzed asymmetric desymmetrization. Accordingly, a versatile strategy for asymmetric generation of organofluorines with fluorine or fluorinated methyl groups has been developed. Multiple stereogenic centers were selectively constructed with satisfactory outcomes. Structurally diverse enantioenriched organofluorines were generated with excellent results in terms of yields, diastereoselectivities, and enantioselectivities. Notably, exchanging fluorinated methyl groups to fluorine for this prochiral 1,3-diketones leads to switchable stereoselectivity. Mechanistic aspects and origin of stereoselectivity were studied by DFT calculations. Notably, some of the prepared organofluorines demonstrated competitive antibacterial activities.

Enantioselective nickel-catalyzed anti-arylmetallative cyclizations onto acyclic electron-deficient alkenes

Enantioselective nickel-catalyzed reactions of (hetero)arylboronic acids or alkenylboronic acids with substrates containing an alkyne tethered to various acyclic electron-deficient alkenes are described.

Enantioselective Nickel-Catalyzed anti-Arylmetallative Cyclizations onto Acyclic Ketones

Domino reactions involving nickel-catalyzed additions of (hetero)arylboronic acids to alkynes, followed by cyclization of the alkenylnickel intermediates onto tethered acyclic ketones to give chiral tertiary-alcohol-containing products in high enantioselectivities, are described. The reversible E/Z isomerization of the alkenylnickel intermediates enables overall anti-arylmetallative cyclization to occur. The ring system of the products are substructures of certain diarylindolizidine alkaloids.

Nickel-catalyzed formation of quaternary carbon centers using tertiary alkyl electrophiles

This review provides a comprehensive summary of recent advances in nickel-catalyzed reactions employing tertiary alkyl electrophiles for the construction of quaternary carbon centers.

Stereoselective synthesis of pentasubstituted 1,3-dienes via Ni-catalyzed reductive coupling of unsymmetrical internal alkynes

The reductive coupling of alkynes represents a powerful strategy for the rapid synthesis of highly substituted 1,3-dienes. This method has the advantages of high atom and step economy, and readily available substrates. Unfortunately, the intermolecular coupling of unsymmetrical internal alkynes remains extremely challenging due to the difficulty in controlling self-dimerization and cross-coupling, as well as stereo- and regioselectivity. Previous reports are still limited to intramolecular processes or the use of stoichiometric amounts of metal catalyst. Herein, we report that nickel-catalyzed reductive coupling of two unsymmetrical internal alkynes can overcome the above-mentioned limitations by using a hemilabile directing group strategy to control the regioselectivity. A series of synthetically challenging penta-substituted 1,3-dienes are obtained in good yields with high regio- and enantioselectivity (mostly > 20/1 rr, >90% ee).

The reductive coupling of alkynes represents a powerful strategy for the rapid synthesis of highly substituted 1,3-dienes.

Ni-Catalyzed Reductive Antiarylative Cyclization of Alkynones

A new catalyst system for the antiarylative cyclization of alkynones and aryl halides through a reductive cross-coupling strategy is developed. The transformation proceeds smoothly in the absence of organometallic reagents and features high functional group tolerance. This method provides an effective platform to access a wide variety of synthetically useful endocyclic tetrasubstituted allylic alcohols in a stereoselective manner.

Ni-Catalyzed stereoselective difunctionalization of alkynes

We summarize the progress of the nickel-catalyzed alkyne difunctionalization reaction for the synthesis of tri- and tetrasubstituted olefins, with an emphasis on the strategy and control of stereochemistry.