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

Construction of Nonadjacent Stereocenters Through Iridium-Catalyzed Desymmetric Hydroheteroarylation of Cyclopentenes

Transition metal-catalyzed direct addition of (hetero)aryl C─H bond to an alkene provides an expedited route to construct benzylic stereocenter from readily available arene and alkene feedstocks with complete atom-economy. However, creation of more than one stereocenter through enantioselective C─H (hetero)arylation remains a challenging goal. Here we report an iridium-catalyzed desymmetric hydroheteroarylation of cyclopentenes to construct 1,3-nonadjacent stereocenters. A series of heteroaryl C─H bonds were cleaved site-selectively and added regio- and enantioselectively to an unactivated alkene containing an amide coordinating group, delivering valuable enantioenriched cyclopentane scaffolds containing 1,3-tertiary-tertiary or 1,3-quaternary-tertiary stereocenters with exclusive diastereoselectivity and excellent enantioselectivity.

Enantioselective Construction of Oxindoles Bearing a Quaternary Carbon via Ni-Al Bimetal-Catalyzed Formyl C-H Alkylation

Enantioselective transition metal-catalyzed C-H alkylation emerges as one of the most atom- and step-economical routes to chiral quaternary carbons, while big challenges still remain with acyl C-H alkylations. Herein, we use a Ni-Al bimetallic catalyst to facilitate a highly regioselective and highly enantioselective C-H alkylation of formamides with alkenes, constructing various oxindoles bearing a chiral quaternary carbon in up to 94 % yield and up to 95 % ee.

Gold(I)-Catalyzed 6-exo-dig Hydroamination/7-endo-dig Cycloisomerization Domino Approach to 3,7a-Diazacyclohepta[jk]fluorene Derivatives

A series of 3,7a-diazacyclohepta[jk]fluorene derivatives were synthesized via a gold(I)-catalyzed 6-exo-dig hydroamination/7-endo-dig cycloisomerization domino method. The method exhibits a broad substrate scope, and a plausible mechanism has been proposed. The efficacy of this strategy is further validated by the successful derivatization of 3,7a-diazacyclohepta[jk]fluorene.

Synthesis of chiral systems featuring the pyrrole unit: a review

Synthetic strategies towards pyrroles within chiral frameworks are summarised, focussing on reports published 2010-2023. The synthesis of pyrroles featuring substituents bearing chiral centres are summarised, as are those whereby pyrroles are located within axially chiral systems courtesy of restricted bond rotation.

Skeletal and Mechanistic Diversity in Ir-Catalyzed Cycloisomerizations of Allene-Tethered Pyrroles and Indoles

Pyrroles and indoles bearing N-allenyl tethers participate in a variety of iridium-catalyzed cycloisomerization processes initiated by a C-H activation step, to deliver a diversity of synthetically relevant azaheterocyclic products. By appropriate selection of the ancillary ligand and the substitution pattern of the allene, the reactions can diverge from simple intramolecular hydrocarbonations to tandem processes involving intriguing mechanistic issues. Accordingly, a wide range of heterocyclic structures ranging from dihydro-indolizines and pyridoindoles to tetrahydroindolizines, as well as cyclopropane-fused tetrahydroindolizines can be obtained. Moreover, by using chiral ligands, these cascade processes can be carried out in an enantioselective manner. DFT studies provide insights into the underlying mechanisms and justify the observed chemo- regio- and stereoselectivities.

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.

Enantioselective Synthesis of N-N Biaryl Atropisomers through Iridium(I)-Catalyzed C-H Alkylation with Acrylates

Enantioselective synthesis of N-N biaryl atropisomers is an emerging area but remains underexplored. The development of efficient synthesis of N-N biaryl atropisomers is in great demand. Herein, the construction of N-N biaryl atropisomers through iridium-catalyzed asymmetric C-H alkylation is reported for the first time. In the presence of readily available Ir precursor and Xyl-BINAP, a variety of axially chiral molecules based on indole-pyrrole skeleton were obtained in good yields (up to 98 %) with excellent enantioselectivity (up to 99 % ee). In addition, N-N bispyrrole atropisomers could also be synthesized in excellent yields and enantioselectivity. This method features perfect atom economy, wide substrate scope, and multifunctionalized products allowing diverse transformations.

Synthesis of 1-Aryltetralins via Re2O7/HReO4 Mediated Intramolecular Hydroarylations

Here, we describe highly efficient intramolecular hydroarylations mediated by Re2O7/HReO4. Styrene derivatives of different electronic properties have been activated to effect a challenging intramolecular hydroarylation for the facile access to various substituted 1-aryltetralin structures. This method is characterized by mild reaction conditions, broad substrate scope, high chemical yields, and 100% atom economy. The potential synthetic application of this methodology was exemplified by the efficient total synthesis of an isoCA-4 analogue.

Ir-Catalyzed Distal Branch-Selective Hydroarylation of Unactivated Internal Alkenes with Benzanilides via C-H Activation along with Consecutive Isomerization

We herein report a synergistic strategy of C-H activation and consecutive isomerization catalyzed by an Ir catalyst to selectively obtain branched isomers as C-H alkylated products of benzanilide derivatives. A well-tuned ligand and a directing group are crucial to achieve this selectivity. The scope of this reaction is demonstrated by the use of a variety of substituents and complex molecules.

Palladium-Catalyzed Oxidative Annulation Leading to Substituted Pyrrolo[3,2,1-jk]carbazoles by Sequential C-N and C-C Bond Formation

A novel regioselective annulation of propargylic alcohols with simple carbazoles for the construction of [3,2,1-jk]carbazole scaffolds is described to be the first example of intermolecular synthesis of [3,2,1-jk]carbazoles from simple carbazoles. In situ synthesis of propargyl alcohols from simple, cheap, and easily accessible ketones has also been developed during the one-pot synthesis of [3,2,1-jk]carbazoles.

Catalyst-Controlled Nickel-Catalyzed Intramolecular endo-Selective C-H Cyclization of Benzimidazoles with Alkenes

Compared with the widely explored exo-selective C-H cyclization, transition metal-catalyzed endo-selective C-H cyclization of benzimidazoles with alkenes has been a formidable challenge. Previous efforts mainly rely on substrate-controlled methods, rendering the product complexity restricted. Herein we report a catalyst-controlled method to facilitate endo-cyclization, in which a bulky N-heterocyclic carbene ligand and ^tBuOK base-enabled Ni-Al bimetallic catalyst prove critical to the endo selectivity.

Synthesis of Unsymmetrical Ketones Using Chelation-Controlled Sequential Substitution of N-Triazinylamide/Weinreb Amide by Organometallic Reagents

N-(2,4-Dimethoxy-1,3,5-triazinyl)amide was found to exhibit similar behavior to N-methoxy-N-methylamide (Weinreb amide) but higher reactivity for nucleophilic substitution by organometallic reagents. Triazinylamide suppresses overaddition, leading to the formation of a tertiary alcohol by the chelating ability of the triazinyl and carbonyl groups. Ureas possessing both triazinylamino and methoxy(methyl)amino groups underwent sequential nucleophilic substitution with different organometallic reagents, which furnished unsymmetrical ketones without any detectable tertiary alcohols.

Iridium-Catalyzed Branch-Selective and Enantioselective Hydroalkenylation of α-Olefins through C-H Cleavage of Enamides

Catalytic branch-selective hydrofunctionalization of feedstock α-olefins to form enantioenriched chiral compounds is a particularly attractive yet challenging transformation in asymmetric catalysis. Herein we report an iridium-catalyzed asymmetric hydroalkenylation of α-olefins through directed C-H cleavage of enamides. This atom-economical addition process is highly branch-selective and enantioselective, delivering trisubstituted alkenes with an allylic stereocenter. DFT calculations reveal the origin of regio- and enantioselectivity.

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.

Visible-Light-Irradiated Cascade Reaction of Indole-Tethered Alkenes to Access Tetracyclic Tetrahydro-γ-carbolines

A series of indole-derived alkenes have been designed and applied in a photocatalytic cascade reaction with bromodifluoroacetate esters, affording an unknown type of tetracyclic tetrahydro-γ-carboline derivative in up to 90% yields. Mechanistic studies suggest that the reaction proceeds with tetrahydro-γ-carboline as a key intermediate. The reaction tolerates a diverse pool of substrates, which provides an efficient method for the construction of tetracyclic tetrahydro-γ-carboline compounds.

Atom and step economical synthesis of acyclic quaternary centers via iridium-catalyzed hydroarylative cross-coupling of 1,1-disubstituted alkenes

Quaternary benzylic centers are accessed with high atom and step economy by intermolecular Ir-catalyzed hydroarylation of non-polarized 1,1-disubstituted alkenes.

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.