Pd-Catalyzed Spirocyclization via C–H Activation and Benzyne Insertion

A Cascade C(sp3)-H Annulation Involving C(alkyl),C(alkyl)-Palladacycle Intermediates

C-H bond functionalization involving C,C-palladacycle intermediates provides a unique platform for developing novel reactions. However, the vast majority of studies have been limited to the transformations of C(aryl),C-palladacycles. In sharp contrast, catalytic reactions involving C(alkyl),C(alkyl)-palladacycles have rarely been reported. Herein, we disclose an unprecedented cascade C(sp3)-H annulation involving C(alkyl),C(alkyl)-palladacycles. In this protocol, alkene-tethered cycloalkenyl bromides undergo intramolecular Heck/C(sp3)-H activation to generate C(alkyl),C(alkyl)-palladacycles, which can be captured by α-bromoacrylic acids to afford tricyclic fused pyridinediones. In addition, this strategy can also be applied to indole-tethered cycloalkenyl bromides to construct pentacyclic fused pyridinediones via suquential Heck dearomatization/C(sp3)-H activation/decarboxylative cyclization. Notably, the removal of α-bromoacrylic acids in the reaction of alkene-tethered cycloalkenyl bromides can build an interesting tricyclic skeleton containing a four-membered ring. Preliminary mechanistic experiments indicate that five-membered C(alkyl),C(alkyl)-palladacycles serve as the key intermediates. Meanwhile, density functional theory (DFT) calculations have provided insights into the reaction pathway.

Palladium-Catalyzed Dearomative Heck/C(sp2)-H Activation/Decarboxylative Cyclization of C2-Tethered Indoles

Until now, palladium-catalyzed dearomative Heck reactions of indoles were largely limited to β-H elimination and nucleophilic capture of the transient alkyl-Pd(II) species. Herein, we disclose a novel palladium-catalyzed dearomative Heck/C(sp2)-H activation/decarboxylative cyclization of C2-tethered indoles. In this protocol, the alkyl-Pd(II) species formed by dearomatization of C2-tethered indoles is not terminated by common β-H elimination or nucleophilic capture, but rather generates C,C-palladacycle via C-H activation. The latter is intercepted by α-bromoacrylic acids to produce pentacyclic and heptacyclic fused indolines.

Constructing spirooxindoles from non-oxindole precursors: a one-pot nitro-reduction/double lactamization approach to spiro[indoline-3,3'-quinoline]-2,2'-diones

2-(2-Nitrobenzyl)-2-(2-nitrophenyl)malonates, readily prepared by SNAr-arylation of diethyl malonate with o-fluoronitrobenzenes, followed by SN2-alkylatioin of the resulting products with o-nitrobenzyl bromides, undergo a tandem Fe/AcOH-promoted nitro-reduction and double lactamization sequence to afford spiro[indoline-3,3'-quinoline]-2,2'-diones in high overall yields. The method is operationally simple, economical, and has a broad substrate scope. The synthetic practicality of this methodology was illustrated by performing the reaction on a gram scale with the same efficiency.

A diastereoselective strategy for dihydrophenanthrene-fused spirooxindoles via [1,2]-phospha-Brook rearrangement

A highly diastereoselective, one-pot strategy for spirooxindoles bearing dihydrophenanthrenes from readily available isatins and p-quinone methides (p-QMs) has been disclosed. Here, a sequential umpolung process via [1,2]-phospha-Brook rearrangement followed by Lewis acid-mediated intramolecular cyclization was employed to furnish the desired spiro product. This protocol provides access to potential medicinally relevant varieties of spirooxindolyl dihydrophenanthrenes in good to excellent yields and diastereoselectivity (>20 : 1).

Harnessing the benzyne insertion consequence to enable π-extended pyrido-acridine and quinazolino-phenanthridine

Distinct protocols have been devised for the preparation of hybrid heterocyclic scaffolds like π-extended pyrido-acridines and quinazolino-phenanthridines duly materialized through Rh(III)- and Pd(II)-mediated catalytic courses commencing from acridine and quinazolimine scaffolds. Interestingly, the parent compounds (acridines and quinazolimines) are actualized from 2-aminobenzonitrile and anthranilic acid, where 2-aminobenzonitrile acts as the 1,4-dipolarophilic species and anthranilic acid as the benzyne precursor. The molecular assembly of acridine suggests the participation of two benzyne units. In addition, the structural motif of the quinazolimine ring features one benzyne unit. Further, indolizine ring containing the enaminonitrile skeleton upon exposure to benzyne forms an indolizine fused quinoline ring, decorated with three benzyne units.

Pd-Catalyzed Cascade Heck/C(sp3)-H Activation for Spirocyclopropyl Oxindoles

We have demonstrated a Pd(0)-catalyzed Heck/C(sp3)-H activation cascade for the synthesis of spirocyclopropyl oxindoles in high yields from easily accessible ortho-bromoacrylamides. The formation of spirocyclopropyl oxindole is guided by an unconventional four-membered palladacycle through C(sp3)-H activation. The reaction exhibits a wide range of substrate scope and operates efficiently with a mere 0.5 mol % of Pd-catalyst. In addition, the use of microwave conditions facilitates rapid completion of the reaction. Furthermore, this spirocyclopropanation strategy can be coupled with [3 + 2] cycloaddition to produce spiropyrrolidine oxindoles, offering a valuable approach for the preparation of alkaloids such as (±)-horsfiline and (±)-coerulescine.

Origin of Enantio- and Chemoselectivity in the Synthesis of Spirocycles via Palladium/Xu-Phos-Catalyzed Cascade Heck/Remote C(sp2)-H Alkylation: A Computational Mechanistic Study

Density functional theory (DFT) calculations were performed to study the mechanism and factors affecting the enantio-, regio-, and chemoselectivities in the palladium/Xu-Phos-catalyzed cascade Heck/remote C(sp2)-H alkylation reaction. The active catalyst is found to be able to sustain coordination with P and S atoms and can adapt its coordination mode to accommodate the significant steric hindrance between the ligand and substrate, unlike previous findings that showed coordination with P and O atoms. The reaction is established to occur in sequence through the oxidative addition of the aryl iodide to Pd(0), intramolecular alkene insertion, C(sp2)-H bond activation, and C(sp2)-C(sp3) bond reductive elimination. The C(sp2)-C(sp3) bond reductive elimination is identified as the rate-determining step, and the intramolecular alkene insertion as the enantioselectivity-determining step. The high enantioselectivity originates from the stronger electronic interaction between the catalyst and substrate; the exclusive 5-exo-regioselectivity is due to the stronger nucleophilicity of the terminal alkene carbon atom, and the chemoselectivity of C-H activation over carboiodination is driven by thermodynamics.

Synthesis of spirooxindoles via formal acetylene insertion into a common palladacycle intermediate

A palladium-catalyzed spirocyclization reaction is reported, which is proposed to arise via insertion of an oxabicycle into a palladacycle, formed from carbocyclization and a C-H functionalization sequence. Mechanistic studies suggest the insertion is diastereoselective and a post-catalytic retro-Diels-Alder step furnishes an alkene, wherein the oxibicycle has served as an acetylene surrogate. Aryl iodides and carbamoyl chlorides were compatible as starting materials under the same reaction conditions, enabling the convergent and complementary synthesis of spirooxindoles, as well as other azacycles. These spirooxindoles allowed further transformations that were previously unaccessible.

2-Oxindole and related heterocycles: synthetic methodologies for their natural products and related derivatives

Natural goods, medications, and pharmaceutically active substances all contain substituted oxindoles. Generally, the C-3 stereocenter of the substituents of oxindoles and their absolute arrangement have a substantial impact on the bioactivity of these substances. In this case, the desire for contemporary probe and drug-discovery programs for the synthesis of chiral compounds using desirable scaffolds with high structural diversity further drives research in this field. Also, the new synthetic techniques are generally simple to apply for the synthesis of other similar scaffolds. Herein, we review the distinct approaches for the synthesis of diverse useful oxindole scaffolds. Specifically, the research findings on the naturally existing 2-oxindole core and a variety of synthetic compounds having a 2-oxindole core are discussed. We present an overview of the construction of oxindole-based synthetic and natural products. In addition, the chemical reactivity of 2-oxindole and its related derivatives in the presence of chiral and achiral catalysts are thoroughly discussed. The data compiled herein provides broad information related to the bioactive product design, development, and applications of 2-oxindoles and the reported techniques will be helpful for the investigation of novel reactions in the future.

Pd(II)-Catalyzed Synthesis of Polycyclic Heteroarenes via an Aminopalladation/C-H Activation/Dealkylation/Decarboxylative Cyclization Cascade

Until now, cascade reactions involving five-membered C,C-palladacycles rely heavily on Pd(0)-catalyzed C-H functionalization of aryl halides initiated by carbopalladation. Herein, we report a novel Pd(II)-catalyzed cascade decarboxylative cyclization of o-alkynylanilines initiated by aminopalladation. In this protocol, o-alkynylanilines undergo sequential anti aminopalladation, C-H activation, and dealkylation to form C,C-palladacycles, which are then trapped by o-bromobenzoic acids or 8-bromo-1-naphthoic acid to produce diverse polycyclic heteroarenes, such as dibenzo[a,c]carbazoles and multiple arene-fused cyclohepta[1,2-b]indoles.

Palladium-Catalyzed Sequential Heck Reactions of Olefin-Tethered Aryl Iodides with Alkenes

An efficient approach to functionalized (E)-3-cinnamyl-3-methyl-2,3-dihydrobenzofurans and (E)-(3-methyl-2,3-dihydrobenzofuran-3-yl)but-2-enones has been developed through a Pd-catalyzed one-pot cascade process involving two sequential Heck reactions, that is, an intramolecular Heck reaction of olefin-tethered aryl iodides and an intermolecular Heck reaction with substituted styrenes and α,β-unsaturated ketones. As a result, a series of desired products were obtained in moderate to good yields and with exclusive E-form selectivities.

Research advances in palladium-catalysed intermolecular C-H annulation of aryl halides with various aromatic ring precursors

Transition-metal-catalysed C-H functionalization has emerged as a powerful approach for the transformation of organic molecules due to its high atom and step economy. Palladium-catalysed intermolecular C-H annulation of aryl halides, especially those involving annulation of a five-membered C,C-palladacycle with coupling reagents, have attracted considerable attention in the past decades. This review summarizes the progress on palladium-catalysed intermolecular C-H annulation of aryl halides with various aromatic ring precursors. Mechanistically, five-membered C,C-palladacycles as intermediates are involved in the majority of reactions.

Highly Diastereoselective Synthesis of Oxindoles Containing Vicinal Quaternary and Tertiary Stereocenters by a Domino Heck/Decarboxylative Alkynylation Sequence

A palladium-catalyzed domino Heck/decarboxylative alkynylation reaction of trisubstituted alkenes or enamines is reported. For two different types of substrates, the current domino reaction employing different solvents and bases led to 3,3-disubstituted oxindoles and hydropyrimidinyl spirooxindoles containing vicinal quaternary and tertiary stereocenters in moderate to good yields, respectively. The general applicability of this method was shown by gram-scale syntheses and diverse transformations of the reaction products. The enantioselective version for this domino process was also studied.

Regioselective synthesis of spirocyclic pyrrolines via a palladium-catalyzed Narasaka-Heck/C-H activation/[4 + 2] annulation cascade reaction

A novel palladium-catalyzed spirocyclization through sequential Narasaka-Heck cyclization, C-H activation and [4 + 2] annulation has been developed. In this reaction, cheap and readily available 2-chlorobenzoic acid or ethyl phenylpropiolate was employed as the C2 insertion unit to react with γ,δ-unsaturated oxime ester. The key step in this transformation is the regioselective insertion of the C2 synthon into the spiro-palladacycle intermediate that is formed by the δ-C-H activation process, thereby efficiently assembling a series of spirocyclic pyrrolines with high regiocontrol. Furthermore, density functional theory (DFT) calculations and control experiments were performed to gain some insights into the reaction mechanism.

Pd-Catalyzed C-H Functionalization of Indole-Containing Alkene-Tethered Aryl Halides with Alkynes To Construct Indole Alkaloid Scaffolds

A convenient and straightforward approach for the construction of indole alkaloid scaffolds from indole-containing alkene-tethered aryl halides and alkynes through a sequential C-H activation, five-membered palladacycle formation, and alkyne insertion process has been described. The approach provides a series of indole alkaloid compounds in moderate to excellent yields with good functional tolerance.

Efficient synthesis of spiro diheterocycles via multi-component dicyclization reaction

Spiro diheterocycles with one valuable quaternary carbon were constructed in one pot via an in situ cyclization–respiroannulation strategy.

Decarboxylative cyclization of o-chlorobenzoic acids with C,C-palladacycles formed by an aminopalladation/dealkylation strategy to access dibenzo[a,c]carbazoles

A novel decarboxylative cyclization of o-chlorobenzoic acids with C,C-palladacycles formed by an aminopalladation/dealkylation strategy for the assembly of dibenzo[a,c]carbazoles has been reported.

Palladium-Catalyzed Difunctionalization of Alkenes by Relay Coupling with Propargylic Pyridines: Synthesis of Indolizine and Indolizinone-Containing Bisheterocycles

Palladium-catalyzed arylation/heteroarylation of aryl halide-tethered alkenes with propargylic pyridines has been established, which provides direct and efficient access to various oxindole, azaoxindole, dihydrobenzopyran, indole, and benzofuran-linked indolizines in good yields with a broad substrate scope and high functional group tolerance. This process enables the formation of one C-N and two C-C bonds in a single operation through an intramolecular carbopalladation and cycloisomerization sequence. Furthermore, an indolizinone-linked bisheterocyclic framework containing indole and benzofuran could be synthesized conveniently from tertiary propargylic alcohols involving methyl or phenyl migration.

A Modular Approach for the Palladium-Catalyzed Synthesis of Bis-heterocyclic Spirocycles

A simple and modular approach toward bis-heterocyclic spirocycles using palladium catalysis is reported. The enclosed methodology leverages a Mizoroki-Heck-type reaction to generate a neopentylpalladium species. This species can undergo intramolecular C-H activation on a wide array of (hetero)aryl C-H bonds, generating a variety of [4.4] and [4.5] bis-heterocyclic spirocycles in up to 95% yield. A diverse range of bis-heterocyclic spirocycles were possible, with 24 examples and 18 different combinations of heterocycles were synthesized. Biologically relevant aza-heterocycles such as purine, pyrazole, (benz)imidazole, (aza)indole, and pyridine were readily incorporated into the spirocyclic core. The reaction was readily scalable to 1 mmol using a lower catalyst loading and number of base equivalents, and the product was purified without the use flash column chromatography.

Synthesis of Spiroindenyl-2-Oxindoles through Palladium-Catalyzed Spirocyclization of 2-Bromoarylamides and Vinyl Bromides

An expeditious approach to the construction of spiroindenyl-2-oxindoles was developed via a palladium-catalyzed spirocyclization reaction of 2-bromoarylamides with vinyl bromides. The reaction formed spiropalladacycles as the intermediates via carbopalladation and the C–H functionalization of 2-bromoarylamides. The spiropalladacycles reacted with vinyl bromides to form spiroindenyl-2-oxindoles. A Heck process rather than vinylic C–H functionalization was involved in the reaction.

Me3SiSiMe2(O n Bu): a disilane reagent for the synthesis of diverse silacycles via Brook- and retro-Brook-type rearrangement

Herein, a readily available disilane Me₃SiSiMe₂(OⁿBu) has been developed for the synthesis of diverse silacycles via Brook- and retro-Brook-type rearrangement. This protocol enables the incorporation of a silylene into different starting materials, including acrylamides, alkene-tethered 2-(2-iodophenyl)-1H-indoles, and 2-iodobiaryls, via the cleavage of Si–Si, Si–C, and Si–O bonds, leading to the formation of spirobenzosiloles, fused benzosiloles, and π-conjugated dibenzosiloles in moderate to good yields. Preliminary mechanistic studies indicate that this transformation is realized by successive palladium-catalyzed bis-silylation and Brook- and retro-Brook-type rearrangement of silane-tethered silanols.

A readily available disilane Me₃SiSiMe₂(OⁿBu) as a silylene source has been developed for the synthesis of diverse silacycles via Brook- and retro-Brook-type rearrangement.

Palladium-catalyzed cascade carbonylative annulation between alkene-tethered aryl iodides and carbon monoxide

Rapid construction of molecules bearing all-substituted quaternary stereocenters represents a highly significant but challenging task in organic synthesis. Herein, we report a novel palladium-catalyzed cascade between alkene-tethered aryl iodides and carbon monoxide, which has resulted in a practical and powerful method for the synthesis of complex polycyclic molecules containing aryl-substituted quaternary stereocenters. Mechanistic studies suggested that the reaction proceeded via a Heck-type carbonylative cyclization, followed by a ketene-involved Friedel-Crafts acylation.

Palladium-Catalyzed Chemoselective Oxidative Addition of Allyloxy-Tethered Aryl Iodides: Synthesis of Medium-Sized Rings and Mechanistic Studies

This Letter describes a Pd-catalyzed Tsuji-Trost-type/Heck reaction with allyloxy-tethered aryl iodides and aziridines. The strategy provides efficient access to benzannulated medium-sized rings via intermolecular cyclization. The substrate aryl iodide has two oxidative addition sites, that is, the aromatic C-I bond and the allyl-oxygen bond. The chemoselective oxidative addition of allyl-oxygen bonds is favored, followed by the activation of aromatic C-I bonds. Aziridine plays a key role. Mechanistic studies shed light on the reaction pathway.

Experimental and Computational Studies of Palladium-Catalyzed Spirocyclization via a Narasaka-Heck/C(sp3 or sp2)-H Activation Cascade Reaction

The first synthesis of highly strained spirocyclobutane-pyrrolines via a palladium-catalyzed tandem Narasaka-Heck/C(sp³ or sp²)-H activation reaction is reported here. The key step in this transformation is the activation of a δ-C-H bond via an in situ generated σ-alkyl-Pd(II) species to form a five-membered spiro-palladacycle intermediate. The concerted metalation-deprotonation (CMD) process, rate-determining step, and energy barrier of the entire reaction were explored by density functional theory (DFT) calculations. Moreover, a series of control experiments was conducted to probe the rate-determining step and reversibility of the C(sp³)-H activation step.

Palladium-Catalyzed Three-Component Carbocarbonation of Arynes: Expeditious Synthesis of o-Alkylated Arylacrylates and Stilbenes

A palladium-catalyzed multicomponent reaction involving olefin-tethered aryl iodides, arynes, and electrophilic alkenes has been developed for straightforward synthesis of o-alkylated arylacrylates and stilbenes through tandem intramolecular Heck cyclization/aryne dicarbofunctionalization.

Palladium-Catalyzed Domino Heck/Sulfination: Synthesis of Sulfonylated Hetero- and Carbocyclic Scaffolds Using DABCO-Bis(sulfur dioxide)

The synthesis of a broad variety of hetero- and carbocyclic scaffolds via a Pd-catalyzed domino Heck/SO₂ insertion reaction is reported. This reaction utilizes DABSO, a safe and easy-to-handle alternative to SO₂ gas. The reaction proceeds through a sulfinate intermediate, which can act as a lynchpin for the in situ generation of sulfones, sulfonamides, and sulfonyl fluorides. Good yields and scalability are demonstrated.

Transition metal-catalyzed synthesis of spirooxindoles

Spirooxindole is a principal bioactive agent and is observed in several natural products including alkaloids. They are broadly studied in the pharmaceutical field and have a significant role in the evolution of drugs such as anti-viral, anti-cancer, anti-microbial etc. In organic chemistry, an indispensable role is presented by transition metal catalysts. An effective synthetic perspective to spirooxindoles is the use of transition metals as the catalyst. This review discusses the synthesis of spirooxindoles catalyzed by transition metals and covers literature up to 2020.

Directed Cobalt-Catalyzed C-H Activation to Form C-C and C-O Bonds in One Pot via Three-Component Coupling

Herein, we disclose an efficient cobalt-catalyzed three-component coupling of benzamides, diazo compounds, and tert-butyl hydroperoxide, which provides an efficient approach to construct C(sp²)-C(sp³) and C-O bonds in one-pot accompanied with C-H activation. This protocol features low catalyst loading (4 mol %), the avoidance of additives, and excellent functional group compatibility, providing three-component coupling adducts with high yields under mild conditions (up to 88%). Mechanism studies show that the reaction may involve a radical process.

Palladium-catalyzed domino spirocyclization of [60]fullerene: synthesis of diverse [60]fullerene-fused spiro[4,5]/[5,5] derivatives

Herein a new, general and practical method for the spirocyclization of [60]fullerene through a palladium-catalyzed domino Heck/C-H activation reaction is presented. A wide range of novel [60]fullerene-fused spirocyclic derivatives can be easily and flexibly synthesized with a broad substrate scope and excellent functional-group tolerance. A plausible mechanism involving an alkyl Pd(ii) species as a key intermediate has been proposed.

A palladium-catalyzed Heck/[4 + 1] decarboxylative cyclization cascade to access diverse heteropolycycles by using α-bromoacrylic acids as C1 insertion units

A novel palladium-catalyzed Heck/[4 + 1] decarboxylative cyclization cascade of alkene-tethered aryl iodides by employing α-bromoacrylic acids as C1 insertion units is reported.

Stereoselective synthesis and applications of spirocyclic oxindoles

This review summaries recent synthetic developments towards spirocyclic oxindoles and applications as valuable medicinal and synthetic targets.

The role of allyl ammonium salts in palladium-catalyzed cascade reactions towards the synthesis of spiro-fused heterocycles

There is a continuous need for designing new and improved synthetic methods aiming at minimizing reaction steps while increasing molecular complexity. In this respect, catalytic, one-pot cascade methodologies constitute an ideal tool for the construction of complex molecules with high chemo-, regio-, and stereoselectivity. Herein, we describe two general and efficient cascade procedures for the synthesis of spiro-fused heterocylces. This transformation combines selective nucleophilic substitution (S_N2′), palladium-catalyzed Heck and C–H activation reactions in a cascade manner. The use of allylic ammonium salts and specific Pd catalysts are key to the success of the transformations. The synthetic utility of these methodologies is showcased by the preparation of 48 spiro-fused dihydrobenzofuranes and indolines including a variety of fluorinated derivatives.

Synthetic methods aiming at minimizing reaction steps while increasing molecular complexity are highly sought after by organic chemists. Here, the authors report two cascade procedures combining nucleophilic substitution, palladium-catalyzed Heck and C–H activation reactions for the synthesis of spiro-fused heterocycles.

Recent Advances in Palladium-Catalyzed Bridging C–H Activation by Using Alkenes, Alkynes or Diazo Compounds as Bridging Reagents

Transition-metal-catalyzed direct inert C–H bond functionalization has attracted much attention over the past decades. However, because of the high strain energy of the suspected palladacycle generated via C–H bond palladation, direct functionalization of a C–H bond less than a three-bond distance from a catalyst center is highly challenging. In this short review, we summarize the advances on palladium-catalyzed bridging C–H activation, in which an inert proximal C–H bond palladation is promoted by the elementary step of migratory insertion of an alkene, an alkyne or a metal carbene intermediate.

1 Introduction

2 Palladium-Catalyzed Alkene Bridging C–H Activation

2.1 Intramolecular Reactions

2.2 Intermolecular Reactions

3 Palladium-Catalyzed Alkyne Bridging C–H Activation

3.1 Intermolecular Reactions

3.2 Intramolecular Reactions

4 Palladium-Catalyzed Carbene Bridging C–H Activation

5 Conclusion and Outlook

Metal-Catalyzed Approaches toward the Oxindole Core

The oxindole scaffold is a privileged structural motif that is found in a variety of bioactive targets and natural products. Moreover, derivatives of the oxindole structure are widely present in a number of biologically relevant compounds and are key intermediates in the synthesis of diverse natural products and pharmaceuticals. Therefore, novel methods to obtain oxindoles remain of high priority in synthetic organic chemistry.Over the past several decades, novel transition-metal-catalyzed methodologies have been applied toward the synthesis of a variety of heterocycles. A detailed mechanistic understanding facilitates the disruption of traditional catalytic pathways to access useful synthetic intermediates. The strategies employed have generally revolved around the generation of high-energy organometallic intermediates, which undergo cyclization reactions through domino processes. Domino cyclization methodologies are therefore attractive, as they allow facile access to functionalized oxindoles containing all-carbon quaternary centers or tetrasubstituted olefins with high chemo- and stereoselectivities. Furthermore, these developed synthetic strategies can often be easily applied in the syntheses of other related scaffolds.In this Account, we discuss the three unique strategies that our group has leveraged for the synthesis of valuable oxindole scaffolds. The first section in this Account outlines the use of an initial oxidative addition to a C(sp²)-X bond, followed by a migratory insertion, yielding a neopentyl species amenable to a variety of subsequent functionalizations. From this reactive neopentyl metal species, we have reported C-X reductive eliminations, anionic capture cascade reactions, and intramolecular C-H functionalization processes. The second section of this Account summarizes our group's findings on 1,2-insertions of a metal-nucleophile species across an unsaturation, generating a reactive organometallic intermediate; subsequent reactions with tethered electrophiles form the desired heterocyclic core. We have explored a wide array of transition metal-catalyzed strategies using this approach, including rhodium-catalyzed conjugate additions, an asymmetric copper-catalyzed borylcupration, and a palladium(II)-catalyzed chloropalladation protocol. The final section of this Account details the use of dual-metal catalysis to perform a cyclization through a C-H functionalization-allylation domino reaction. Throughout this Account, we provide details of mechanistic studies that better enabled our understanding of the domino processes.Overall, our group has developed methods exploiting the unique reactivity of palladium, nickel, copper, rhodium, and ruthenium catalysts to develop methods toward a wide array of oxindole scaffolds. On the basis of the utility, diversity, and applicability of the strategies developed, we believe that they will prove to be highly useful in the syntheses of other important targets and inspire further development and mechanistic understanding of various metal-catalyzed processes.

Cobalt-Catalyzed Enantioselective Hydroarylation of 1,6-Enynes

An asymmetric hydroarylative cyclization of enynes involving a C-H bond cleavage is reported. The cobalt-catalyzed cascade generates three new bonds in an atom-economical fashion. The products were obtained in excellent yields and excellent enantioselectivities as single diastereo- and regioisomers. Preliminary mechanistic studies indicate that the reaction shows no intermolecular C-H crossover. This work highlights the potential of cobalt catalysis in C-H bond functionalization and enantioselective domino reactivity.