Iridium‐Catalyzed Enantioselective Hydroarylation of Alkenes through C−H bond Activation: Experiment and Computation

Rhodium-catalyzed atroposelective access to trisubstituted olefins via C-H bond olefination of diverse arenes

The atroposelective synthesis of axially chiral acyclic olefins remains a daunting challenge due to their relatively lower racemization barriers, especially for trisubstituted ones. In this work, atroposelective C-H olefination has been realized for synthesis of open-chain trisubstituted olefins via C-H activation of two classes of (hetero)arenes in the coupling with sterically hindered alkynes. The employment of phenyl N-methoxycarbamates as arene reagents afforded phenol-tethered olefins, with the carbamate being a traceless directing group. The olefination of N-methoxy-2-indolylcarboxamides afforded the corresponding chiral olefin by circumventing the redox-neutral [4 + 2] annulation. The reactions proceeded with excellent Z/E selectivity, chemoselectivity, regioselectivity, and enantioselectivity in both hydroarylation systems.

Asymmetric Hydroarylation Reactions Catalyzed by Transition Metals: Last 10 Years in a Mini Review

Hydroarylation reactions play a pivotal role in organic chemistry due to their versatility and efficiency. In the last 10 years, the scientific production around this reaction has been very high, but in its asymmetric version, the results are less. In this mini review, selected literature examples are considered to draw attention to directions of the asymmetric hydroarylation reaction mediated by transition metal catalysts. The selected works were grouped in two main sections. In the first, we reported examples relating the narrower definition of hydroarylation, namely the metal-catalyzed processes where inactivated aryl moiety undergoes a direct functionalization via insertion of an unsaturated compound. In the second part, hydroarylation reactions take place with the use of pre-activated aryl substrates, usually aryl-iodides or aryl-boronated.

Transition-metal-catalyzed C-H bond alkylation using olefins: recent advances and mechanistic aspects

Transition metal catalysis has contributed immensely to C-C bond formation reactions over the last few decades, and alkylation is no exception. The superiority of such methodologies over traditional alkylation is evident from minimal reaction steps, shorter reaction times, and atom economy while also allowing control over regio- and stereo-selectivity. In particular, hydrocarbonation of alkenes has grabbed increased attention due its fundamental ability to effectively and selectively synthesise a wide range of industrially and pharmaceutically relevant moieties. This review attempts to provide a scientific viewpoint and a systematic analysis of the recent developments in transition-metal-catalyzed alkylation of various C-H bonds using simple and activated olefins. The key features and mechanistic studies involved in these transformations are described briefly.

Looking deep into C-H functionalization: the synthesis and application of cyclopentadienyl and related metal catalysts

Metal catalyzed C-H functionalization offers a versatile platform for methodology development and a wide variety of reactions now exist for the chemo- and site-selective functionalization of organic molecules. Cyclopentadienyl-metal (CpM) complexes of transition metals and their correlative analogues have found widespread application in this area, and herein we highlight several key applications of commonly used transition-metal Cp-type catalysts. In addition, an understanding of transition metal Cp-type catalyst synthesis is important, particularly where modifications to the catalyst structure are required for different applications, and a summary of this aspect is given.

DFT Case Study on the Comparison of Ruthenium-Catalyzed C-H Allylation, C-H Alkenylation, and Hydroarylation

Density functional calculations at the B3LYP-D3+IDSCRF/TZP-DKH(-dfg) level of theory have been performed to understand the mechanism of ruthenium-catalyzed C-H allylation reported in the literature in depth. The plausible pathway consisted of four sequential processes, including C-H activation, migratory insertion, amide extrusion, and recovery of the catalyst, in which C-H activation was identified as the rate-determining step. The amide extrusion step could be promoted kinetically by trifluoroacetic acid since its mediation lowered the free-energy barrier from 32.1 to 12.2 kcal/mol. Additional calculations have been performed to explore other common pathways between arenes and alkenes, such as C-H alkenylation and hydroarylation. A comparison of the amide extrusion and β-H elimination steps established the following reactivity sequence of the leaving groups: protonated amide group > β-H group > unprotonated amide group. The suppression of hydroarylation was attributed to the sluggishness of the Ru-C protonation step as compared to the amide extrusion step. This study can unveil factors favoring the C-H allylation reaction.

Gold-Catalyzed Hydroarylation Reactions: A Comprehensive Overview

The hydroarylation of alkynes, alkene, and, allene is a cost-effective and efficient way to incorporate unsaturated moieties into aromatic substrates. This review focuses on gold-catalyzed hydroarylation, which produces aromatic alkenes,...

Iridium-catalyzed enantioselective intramolecular hydroarylation of allylic aryl ethers devoid of a directing group on the aryl group

Although intramolecular hydroarylation is an attractive transformation of allylic aryl ethers, it has suffered from narrow substrate scope. We herein describe Ir/(S)-DTBM-SEGPHOS-catalyzed intramolecular hydroarylation of allylic aryl ethers. The reaction eliminates the structural requirement from the aryl group, affording 2,3-dihydrobenzofurans bearing a stereogenic carbon center at the C3 position with up to 99% enantiomeric excess.

Cp*Co(III)-Catalyzed Enantioselective Hydroarylation of Unactivated Terminal Alkenes via C-H Activation

Enantioselective hydroarylation of unactivated terminal akenes constitutes a prominent challenge in organic chemistry. Herein, we reported a Cp*Co(III)-catalyzed asymmetric hydroarylation of unactivated aliphatic terminal alkenes assisted by a new type of tailor-made amino acid ligands. Critical to the chiral induction was the engaging of a novel noncovalent interaction (NCI), which has seldomly been disclosed in the C-H activation area, arising from the molecular recognition among the organocobalt(III) intermediate, the coordinated alkene, and the well-designed chiral ligand. A broad range of C2-alkylated indoles were obtained in high yields and excellent enantioselectivities. DFT calculations revealed the reaction mechanism and elucidated the origins of chiral induction in the stereodetermining alkene insertion step.

Highly Enantioselective Iridium(I)-Catalyzed Hydrocarbonation of Alkenes: A Versatile Approach to Heterocyclic Systems Bearing Quaternary Stereocenters

We report a versatile, highly enantioselective intramolecular hydrocarbonation reaction that provides a direct access to heteropolycyclic systems bearing chiral quaternary carbon stereocenters. The method, which relies on an iridium(I)/bisphosphine chiral catalyst, is particularly efficient for the synthesis of five-, six- and seven-membered fused indole and pyrrole products, bearing one and two stereocenters, with enantiomeric excesses of up to >99 %. DFT computational studies allowed to obtain a detailed mechanistic profile and identify a cluster of weak non-covalent interactions as key factors to control the enantioselectivity.

Iridium-Catalyzed Hydroarylation via C-H Bond Activation

Hydroarylation reactions via C-H activation, which compensate for shortcomings of classical methods based on the Friedel-Crafts reaction, is one of the most attractive methods to synthesize substituted arenes. This Personal Account reviews our recent studies on iridium-catalyzed intermolecular hydroarylation of vinyl ethers, alkynes, bicycloalkenes, and 1,3-dienes, and intramolecular hydroarylation of m-allyloxyphenyl ketones, where asymmetric addition reactions are included. A cationic iridium catalyst, which is generated from chloroiridium [IrCl] and NaBAr^F ₄ [Ar^F =3,5-(CF₃ )₂ C₆ H₃ ], or a hydroxoiridium [Ir(OH)] complex is effective in catalyzing the hydroarylation depending on the substrates. 1,5-Cyclooctadiene (cod), chiral dienes, and conventional bisphosphines function as ligands controlling the high reactivity and selectivity of the catalysts in the hydroarylation. H/D exchange reaction of alkenes by use of a key intermediate of the hydroarylation reaction is also described.

Enantioselective Intermolecular Murai-Type Alkene Hydroarylation Reactions

Strategies that enable the efficient assembly of complex building blocks from feedstock chemicals are of paramount importance to synthetic chemistry. Building upon the pioneering work of Murai and co-workers in 1993, C–H-activation-based enantioselective hydroarylations of alkenes offer a particularly promising framework for the step- and atom-economical installation of benzylic stereocenters. This short review presents recent intermolecular enantioselective Murai-type alkene hydroarylation methodologies and the mechanisms by which they proceed.

1 Introduction

2 Enantioselective Hydroarylation Reactions of Strained Bicyclic Alkenes

3 Enantioselective Hydroarylation Reactions of Electron-Rich Acyclic Alkenes

4 Enantioselective Hydroarylation Reactions of Electron-Poor Acyclic Alkenes

5 Enantioselective Hydroarylation Reactions of Minimally Polarized Acyclic Alkenes

6 Conclusion and Outlook

Strong and Confined Acids Catalyze Asymmetric Intramolecular Hydroarylations of Unactivated Olefins with Indoles

In recent years, several organocatalytic asymmetric hydroarylations of activated, electron-poor olefins with activated, electron-rich arenes have been described. In contrast, only a few approaches that can handle unactivated, electronically neutral olefins have been reported and invariably require transition metal catalysts. Here we show how an efficient and highly enantioselective catalytic asymmetric intramolecular hydroarylation of aliphatic and aromatic olefins with indoles can be realized using strong and confined IDPi Brønsted acid catalysts. This unprecedented transformation is enabled by tertiary carbocation formation and establishes quaternary stereogenic centers in excellent enantioselectivity and with a broad substrate scope that includes an aliphatic iodide, an azide, and an alkyl boronate, which can be further elaborated into bioactive molecules.

Enantioselective synthesis of 3-substituted dihydrobenzofurans through iridium-catalyzed intramolecular hydroarylation

The enantioselective cyclization was efficiently catalyzed by a cationic iridium complex coordinated with a conventional chiral bisphosphine ligand to give benzofurans in high yields with high enantioselectivity.