Non-stabilized nucleophiles in Cu-catalysed dynamic kinetic asymmetric allylic alkylation

Enantioselective Decarboxylative C(sp3)-C(sp3) Cross-Coupling of Aliphatic Redox-Active Esters with gem-Borazirconocene Alkanes

Asymmetric decarboxylative cross-couplings of carboxylic acids are powerful methods for synthesizing chiral building blocks essential in medicinal chemistry and material science. Despite their potential, creating versatile chiral alkylboron derivatives through asymmetric decarboxylative C(sp3)-C(sp3) cross-coupling from readily available primary aliphatic acids and mild organometallic reagents remains challenging. In this study, we present a visible light-induced Ni-catalyzed enantioconvergent C(sp3)-C(sp3) cross-coupling of unactivated primary aliphatic acid NHPI esters with gem-borazirconocene alkanes, producing a diverse array of valuable chiral alkylboron building blocks. The method boasts a broad substrate scope, high functional group tolerance, and the ability for late-stage modification of complex drug molecules and natural products with high enantioselectivity, showcasing its synthetic potential. Mechanistic investigations suggest a nickel-catalyzed enantioconvergent radical cross-coupling pathway, wherein the primary radical from a redox-active ester is generated through single-electron reduction with ZrIII species. This represents an unprecedented example of enantioselective radical C(sp3)-C(sp3) cross-coupling in the absence of photocatalysts.

Desymmetrization of Inert meso-Diethers through Copper-Catalyzed Asymmetric Allylic Alkylation with Grignard Reagents

We have developed a highly regio-, diastereo-, and enantioselective Cu-catalyzed desymmetrization of inert meso-diethers using Grignard reagents. Moreover, previous inaccessible sterically hindered organometallic reagents are realized in the reaction with broad secondary alkyl Grignard reagents. Finally, detailed control experiments and density functional theory calculations revealed the desymmetrization of meso-diethers exploits a direct anti-SN2' pathway, in the absence of an in situ-generated allyl bromine intermediate. The following oxidative addition is the crucial rate-determining and enantioselectivity-determining step.

Copper-catalyzed asymmetric allylic substitution of racemic/meso substrates

The synthesis of enantiomerically pure compounds is a pivotal subject in the field of chemistry, with enantioselective catalysis currently standing as the primary approach for delivering specific enantiomers. Among these strategies, Cu-catalyzed asymmetric allylic substitution (AAS) is significant and irreplaceable, especially when it comes to the use of non-stabilized nucleophiles (pK a > 25). Although Cu-catalyzed AAS of prochiral substrates has also been widely developed, methodologies involving racemic/meso substrates are highly desirable, as the substrates undergo dynamic processes to give single enantiomer products. Inspired by the pioneering work of the Alexakis, Feringa and Gennari groups, Cu-catalyzed AAS has been continuously employed in deracemization and desymmetrization processes for the synthesis of enantiomerically enriched products. In this review, we mainly focus on the developments of Cu-catalyzed AAS with racemic/meso substrates over the past two decades, providing an explicit outline of the ligands employed, the scope of nucleophiles, the underlying dynamic processes and their practical applications.

Recent Advances in the Catalytic Synthesis of the Cyclopentene Core

Five-membered carbocycles are ubiquitously found in natural products, pharmaceuticals, and other classes of organic compounds. Within this category, cyclopentenes deserve special attention due to their prevalence as targets and as well as key intermediates for synthesizing more complex molecules. Herein, we offer an overview summarizing some significant recent advances in the catalytic assembly of this structural motif. A great variety of synthetic methodologies and strategies are covered, including transition metal-catalyzed or organocatalyzed processes. Both inter- and intramolecular transformations are documented. On this ground, our expertise in the application of C-H functionalization reactions oriented towards the formation of this ring and its subsequent selective functionalization is embedded.

Catalytic asymmetric defluorinative allylation of silyl enol ethers

The stereocontrolled installation of alkyl fragments at the alpha position of ketones is a fundamental yet unresolved transformation in organic chemistry. Herein we report a new catalytic methodology able to construct α-allyl ketones via defluorinative allylation of silyl enol ethers in a regio-, diastereo- and enantioselective manner. The protocol leverages the unique features of the fluorine atom to simultaneously act as a leaving group and to activate the fluorophilic nucleophile via a Si-F interaction. A series of spectroscopic, electroanalytic and kinetic experiments demonstrate the crucial interplay of the Si-F interaction for successful reactivity and selectivity. The generality of the transformation is demonstrated by synthesising a wide set of structurally diverse α-allylated ketones bearing two contiguous stereocenters. Remarkably, the catalytic protocol is amenable for the allylation of biologically significant natural products.

Migratory allylic arylation of 1,n-enols enabled by nickel catalysis

Transition-metal-catalyzed allylic substitution reactions (Tsuji-Trost reactions) proceeding via a π-allyl metal intermediate have been demonstrated as a powerful tool in synthetic chemistry. Herein, we disclose an unprecedented π-allyl metal species migration, walking on the carbon chain involving 1,4-hydride shift as confirmed by deuterium labeling experiments. This migratory allylic arylation can be realized under dual catalysis of nickel and lanthanide triflate, a Lewis acid. Olefin migration has been observed to preferentially occur with the substrate of 1,n-enols (n ≥ 3). The robust nature of the allylic substitution strategy is reflected by a broad scope of substrates with the control of regio- and stereoselectivity. DFT studies suggest that π-allyl metal species migration consists of the sequential β-H elimination and migratory insertion, with diene not being allowed to release from the metal center before producing a new π-allyl nickel species.

Dynamic kinetic asymmetric arylation and alkenylation of ketones

Despite the importance of enantioenriched alcohols in medicinal chemistry, total synthesis, and materials science, the efficient and selective construction of enantioenriched tertiary alcohols bearing two contiguous stereocenters has remained a substantial challenge. We report a platform for their preparation through the enantioconvergent, nickel-catalyzed addition of organoboronates to racemic, nonactivated ketones. We prepared several important classes of α,β-chiral tertiary alcohols in a single step with high levels of diastereo- and enantioselectivity through a dynamic kinetic asymmetric addition of aryl and alkenyl nucleophiles. We applied this protocol to modify several profen drugs and to rapidly synthesize biologically relevant molecules. We expect this nickel-catalyzed, base-free ketone racemization process to be a widely applicable strategy for the development of dynamic kinetic processes.

Copper-catalyzed asymmetric allylic alkylation of racemic inert cyclic allylic ethers under batch and flow conditions

The Cu-catalyzed AAA reactions employing challenging racemic inert cyclic allylic ethers with sterically hindered Grignard reagents have been disclosed under batch and flow conditions.

Cobalt(III)-Catalyzed and DMSO-Involved Allylation of 1,3-Dicarbonyl Compounds with Alkenes

Cobalt(III)-catalyzed allylation of 1,3-dicarbonyl compounds has been reported with in situ generated allyl reagents from alkenes and dimethyl sulfoxide (DMSO). This novel protocol enables a high regio- and stereoselective access for a broad range of allyl 1,3-dicarbonyl compounds. In the transformation, DMSO plays the role of a C1 source, and it incorporates with alkenes to form the allyl reagent allylic methyl thioether. Moreover, a multiple-step pathway has been proposed to rationalize the mechanism study, which involves silver-mediated coupling, Co(III)-catalyzed π-allylation, and intermolecular nucleophilic substitution.

Enantio- and Diastereoselective Copper-Catalyzed Allylboration of Alkynes with Allylic gem-Dichlorides

Allylic gem-dichlorides are shown to be efficient substrates for catalytic asymmetric allylboration of alkynes. The method employs a chiral NHC-Cu catalyst capable of generating in a single step chiral skipped dienes bearing a Z-alkenyl chloride, a trisubstituted E-alkenyl boronate and a bis-allylic stereocenter with excellent levels of chemo-, regio- enantio- and diastereoselectivity. This high degree of functionalization makes these products versatile building blocks as illustrated with the synthesis of several optically active compounds. DFT calculations support the key presence of a metal cation bridge ligand-substrate interaction and account for the stereoselectivity outcome.

Enantioselective Lactonization by π-Acid-Catalyzed Allylic Substitution: A Complement to π-Allylmetal Chemistry

Asymmetric allylic alkylation (AAA) is a powerful method for the formation of highly useful, non-racemic allylic compounds. Here we present a complementary enantioselective process that generates allylic lactones via π-acid catalysis. More specifically, a catalytic enantioselective dehydrative lactonization of allylic alcohols using a novel Pd^II -catalyst containing the imidazole-based P,N-ligand (S)-StackPhos is reported. The high-yielding reactions are operationally simple to perform with enantioselectivities up to 99 % ee. This strategy facilitates the replacement of a poor leaving group with what would ostensibly be a better leaving group in the product avoiding complications arising from racemization by equilibration.

Additions to Racemates: A Strategy for Developing Asymmetric Cross-Coupling Reactions

In this Account, the authors describe their progress in developing catalytic asymmetric C(sp3)–C(sp3) and C(sp3)–C(sp2) cross-coupling reactions. Whereas most catalytic enantioselective transformations rely on prochiral or meso starting materials, strategies that use racemic starting materials are rare. Key features of these reactions are efficient mechanisms for deracemization. Here, the authors present copper-catalyzed alkylation and rhodium-catalyzed Suzuki–Miyaura-type arylation reactions, their underlying mechanisms, and their applications in complex-molecule syntheses.

Rhodium(i)/bisoxazolinephosphine-catalyzed regio- and enantioselective amination of allylic carbonates: a computational study

DFT calculations were performed to investigate the rhodium(i)/bisoxazolinephosphine-catalyzed regio- and enantioselective amination of allylic carbonates.

Are Organozirconium Reagents Applicable in Current Organic Synthesis?

The search for mild, user-friendly, easily accessible, and robust organometallic reagents is an important feature of organometallic chemistry. Ideally, new methodologies employing organometallics should be developed with respect to practical applications in syntheses of target compounds. In this short review, we investigate if organozirconium reagents can fulfill these criteria. Organozirconium compounds are typically generated via in situ hydrozirconation of alkenes or alkynes with the Schwartz reagent. Alkyl and alkenylzirconium reagents have proven to be convenient in conjugate additions, allylic substitutions, cross-coupling reactions, and additions to carbonyls or imines. Furthermore, the Schwartz reagent itself is a useful reducing agent for polar functional groups.

1 Introduction

2 Synthesis and Generation of the Schwartz Reagent

3 Structure and Properties of Cp2Zr(H)Cl

4 Reactivity of Organozirconium Reagents

4.1 Asymmetric Conjugate Addition

4.2 Asymmetric Allylic Alkylations

4.3 Desymmetrization Reactions

4.4 Cross-Coupling Reactions

4.5 1,2-Additions

5 Conclusions

Asymmetric synthesis of γ-chiral borylalkanes via sequential reduction/hydroboration using a single copper catalyst

The synthesis of γ-chiral borylalkanes through copper-catalyzed enantioselective SN2'-reduction of γ,γ-disubstituted allylic substrates and subsequent hydroboration was reported. A copper-DTBM-Segphos catalyst produced a range of γ-chiral alkylboronates from easily accessible allylic acetate or benzoate with high enantioselectivities up to 99% ee. Furthermore, selective organic transformations of the resulting γ-chiral alkylboronates generated the corresponding γ-chiral alcohol, arene and amine compounds.

Chemoselective Cross-Coupling of gem-Borazirconocene Alkanes with Aryl Halides

The direct and chemoselective conversion of the carbon-metal bond of gem-dimetallic reagents enables rapid and sequential formation of multiple carbon-carbon and carbon-heteroatom bonds, thus representing a powerful method for efficiently increasing structural complexity. Herein, we report a visible-light-induced, nickel-catalyzed, chemoselective cross-coupling reaction between gem-borazirconocene alkanes and diverse aryl halides, affording a wide range of alkyl Bpin derivatives in high yields with excellent regioselectivity. This practical method features attractively simple reaction conditions and a broad substrate scope. Additionally, we systematically investigated a Bpin-directed chain walking process underlying the regioselectivity of alkylzirconocenes, thus uncovering the mechanism of the remote functionalization of internal olefins achieved with our method. Finally, DFT calculations indicate that the high regioselectivity of this reaction originates from the directing effect of the Bpin group.

Light-Triggered Catalytic Asymmetric Allylic Benzylation with Photogenerated C-Nucleophiles

Herein is reported the asymmetric allylic benzylation of Morita–Baylis–Hillman (MBH) carbonates with 2-methylbenzophenone (MBP) derivatives as nonstabilized photogenerated C-nucleophiles. The dual activation of both reaction partners, chiral Lewis-base activation of the electrophile and light activation of the nucleophile, enables the stereoselective installation of benzyl groups at the allylic position to forge tertiary and quaternary carbon centers.

Direct Stereoconvergent Allylation of Chiral Alkylcopper Nucleophiles with Racemic Allylic Phosphates

Copper-catalyzed stereoconvergent allylation of chiral sp³ -hybridized carbon nucleophiles with a racemic mixture of acyclic secondary allylic phosphates is reported. In the presence of a copper-catalyst complexed with chiral BenzP* ligand, tandem coupling reaction of vinyl arenes, bis(pinacolato)diboron, and racemic allylic phosphates provided β-chiral alkylboronates possessing (E)-alkenyl moiety through a direct stereoconvergent allylic coupling with concomitant generation of a C(sp³ )-stereogenic center. A range of vinyl (hetero)arenes and secondary allylic phosphates bearing 1°, 2°, 3° alkyl and phenyl α-substituents were suitable for the reaction, forming products with high enantioselectivities up to 95 % ee. Density functional theory calculations were conducted in detail to elucidate the origin of the observed regioselectivity of borylcupration and stereoconvergent (E)-olefin formation from racemic allylic phosphates.

Enantioconvergent alkylation of ketones with racemic secondary alcohols via hydrogen borrowing catalysis

An enantioconvergent hydrogen borrowing strategy enables the catalytic asymmetric alkylation of ketone enolates with unactivated, racemic secondary alcohols.

Highly Enantioselective Hiyama Cross-Coupling via Rh-Catalyzed Allylic Arylation of Racemic Allyl Chlorides

Highly enantioselective Hiyama cross-coupling reactions have been achieved through rhodium(I)-catalyzed dynamic kinetic asymmetric transformations between aryl siloxanes and cyclic racemic allyl halides. This process affords valuable enantiomerically enriched aryl-substituted cyclic allyl products and is compatible with heterocyclic allyl chloride electrophiles.

Sulfinate-Engaged Nucleophilic Addition Induced Allylic Alkylation of Allenoates

A strategically novel Pd-catalyzed nucleophilic addition induced allylic alkylation reaction (NAAA) of allenoates has been successfully accomplished. By judiciously integrating ZnCl₂-promoted Michael addition with Pd-catalyzed allylic alkylation, allenoates readily undergo allyl-sunfonylation at the internal double bond, thus providing a straightforward avenue for the rapid assembly of a host of structurally diversified α-allyl-β-sufonylbut-3-enoate derivatives. The success of this transformation profits from a delicate control of the reaction kinetic of each elementary step, thanks to the synergistic interaction of Pd/Zn bimetallic system, thus suppressing either direct allylic sulfonylation or premature quenching of therein in situ generated ester enolate intermediate. Furthermore, by expanding the scope of workable Michael acceptor beyond those previously required doubly activated ones, such as methylenemalononitrile, the present work substantially enriches the repertoire of NAAA reactions.

Enantio- and Diastereoselective Suzuki-Miyaura Coupling with Racemic Bicycles

Herein, we describe a rhodium‐catalyzed enantio‐ and diastereoselective Suzuki–Miyaura cross‐coupling between racemic fused bicyclic allylic chlorides and boronic acids. The highly stereoselective transformation allows for the coupling of aryl, heteroaryl, and alkenyl boronic acids and gives access to functionalized bicyclic cyclopentenes, which can be converted into other five‐membered‐ring scaffolds with up to five contiguous stereocenters. Preliminary mechanistic studies suggest that these reactions occur with overall retention of the relative stereochemistry and are enantioconvergent for pseudo‐symmetric allylic chloride starting materials. In addition, a bicyclic allylic chloride starting material without pseudo‐symmetry undergoes a highly enantioselective regiodivergent reaction.

Chiral Brønsted Acid Catalyzed Dynamic Kinetic Asymmetric Hydroamination of Racemic Allenes and Asymmetric Hydroamination of Dienes

The first highly efficient and practical chiral Brønsted acid catalyzed dynamic kinetic asymmetric hydroamination (DyKAH) of racemic allenes and asymmetric hydroamination of unactivated dienes with both high E/Z selectivity and enantioselectivity are described herein. The transformation proceeds through a new catalytic asymmetric model involving a highly reactive π-allylic carbocationic intermediate, generated from racemic allenes or dienes through a proton transfer mediated by an activating/directing thiourea group. This method affords expedient access to structurally diverse enantioenriched, potentially bioactive alkenyl-containing aza-heterocycles and bicyclic aza-heterocycles.

Desymmetrization of meso-bisphosphates using copper catalysis and alkylzirconocene nucleophiles

The desymmetrization of meso-compounds is a useful synthetic method, as illustrated by numerous applications of this strategy in natural product synthesis. Cu-catalyzed allylic desymmetrizations enable the enantioselective formation of carbon-carbon bonds, but these transformations are limited in substrate scope and by the use of highly reactive premade organometallic reagents at cryogenic temperatures. Here we show that diverse meso-bisphosphates in combination with alkylzirconium nucleophiles undergo highly regio-, diastereo- and enantio-selective Cu-catalyzed desymmetrization reactions. In addition, C₂-symmetric chiral bisphosphates undergo stereospecific reactions and a racemic substrate undergoes a Cu-catalyzed kinetic resolution. The reaction tolerates functional groups incompatible with many common organometallic reagents and provides access to a broad range of functionalized carbo- and hetero-cyclic structures. The products bear up to three contiguous stereogenic centers, including quaternary centers and spirocyclic ring systems. We anticipate that the method will be a useful complement to existing catalytic enantioselective reactions.

Synthesis of 1,3-disubstituted cyclohexenes from dienylethers via sequential hydrozirconation/deoxygenative cyclisation

The preparation of 1,3-disubstituted cyclohexenes from 3-methoxyhexa-1,5-dienes involving a sequential hydrozirconation/TMSOTf-mediated activation is described.

Iridium-Catalyzed Asymmetric Allylic Substitution Reactions

In this review, we summarize the origin and advancements of iridium-catalyzed asymmetric allylic substitution reactions during the past two decades. Since the first report in 1997, Ir-catalyzed asymmetric allylic substitution reactions have attracted intense attention due to their exceptionally high regio- and enantioselectivities. Ir-catalyzed asymmetric allylic substitution reactions have been significantly developed in recent years in many respects, including ligand development, mechanistic understanding, substrate scope, and application in the synthesis of complex functional molecules. In this review, an explicit outline of ligands, mechanism, scope of nucleophiles, and applications is presented.