Synthesis of Chiral Spirolactams via Sequential C-H Olefination/Asymmetric [4+1] Spirocyclization under a Simple CoII /Chiral Spiro Phosphoric Acid Binary System

Cobalt-Catalyzed Domino Transformations via Enantioselective C-H Activation/Nucleophilic [3 + 2] Annulation toward Chiral Bridged Bicycles

Selective synthesis of chiral bridged (hetero)bicyclic scaffolds via asymmetric C-H activation constitutes substantial challenges due to the multiple reactivities of strained bicyclic structures. Herein, we develop the domino transformations through an unprecedented cobalt-catalyzed enantioselective C-H activation/nucleophilic [3 + 2] annulation with symmetrical bicyclic alkenes. The methods offer straightforward access to a wide range of chiral molecules bearing [2.2.1]-bridged bicyclic cores with four and five consecutive stereocenters in a single step. Two elaborate salicyloxazoline (Salox) ligands were synthesized based on the rational design and mechanistic understanding. The well-defined chiral pockets generated from asymmetric coordination around the trivalent cobalt catalyst direct the orientation of bicyclic alkenes, leading to excellent enantioselectivity.

Arenethiolate-Catalyzed 1,5-HAT of Aryl Halides: Synthesis of γ-Spirolactams

γ-Spirolactam is a privileged building block that is found in a wide range of natural products and bioactive compounds. Herein, we report an arenethiolate-catalyzed 1,5-HAT of aryl halides to obtain γ-spirolactams through a SET reduction/intramolecular 1,5-HAT/cyclization/HAT process. This protocol features metal-free conditions and a broad substrate scope, furnishing the γ-spirolactams in moderate to excellent yields. Notably, aryl bromides, aryl chlorides and even aryl fluorides are well tolerated in this transformation. A mechanism involving arenethiolate as a SET catalyst is proposed based on DFT calculation.

Recent advances in spirocyclization of maleimides via transition-metal catalyzed C-H activation

In recent years, the maleimide scaffold has received a great deal of attention in C-H activation. Several types of products can be constructed using maleimides as a coupling partner. Alkylation, alkenylation, annulation, dehydrogenative annulation and spirocyclization are various reactions shown by maleimides in C-H activation. Thus, the maleimide scaffold has been extensively studied in the last few years in C-H activation owing to its unique reactivity. Among the diverse class of reactions of maleimides, spirocyclization is a less explored reaction. The spirocycles, in particular the spirosuccinimides are interesting candidates in drug discovery and materials chemistry. Therefore the method of spirocyclization of maleimides via C-H activation becomes an important strategy for the synthesis of a diverse array of spirosuccinimides. This review summarizes the reports available in this field from 2015-2023 and also highlights the scopes and prospects of this method.

Brønsted Acid-Catalyzed Diastereoselective Synthesis of Spiroisoindolinones from Enamides

A highly diastereoselective synthesis of spiroisoindolinones from enamides and 3-hydroxy-isoindolinones is reported. The reaction proceeds rapidly in the presence of p-toluenesulfonic acid as a Brønsted acid catalyst and affords a variety of densely substituted spiroisoindolinones with three contiguous stereogenic centers in high yields (≤98%) and diastereoselectivities (up to dr >98:<2:0:0).

Enantioselective C-H bond functionalization under Co(III)-catalysis

While progress in enantioselective C-H functionalization has been accomplished by employing 4d and 5d transition metal-based catalysts, the rapid depletion of these metals in the earth's crust poses a serious threat to making these protocols sustainable. On the other hand, because of their unique reactivity, low toxicity, and high earth abundance, newer strategies utilizing affordable 3d transition metals have come to the forefront. Among the first-row transition metals, high-valent cobalt has recently attracted a lot of attention for catalytic C-H functionalization with mono and bidentate directing groups. This approach was extended for asymmetric catalysis due to a fairly thorough knowledge of its catalytic cycles. Four major themes have been investigated as a result of this insight: (1) rational design of a chiral Cp#Co(III)-catalyst, (2) chiral carboxylic acid with achiral Cp*Co(III)-catalysts using monodentate directing groups, (3) cobalt/salox-based systems, and (4) cobalt/chiral phosphoric acid-based hybrid systems with bidentate directing groups. Herein, we highlight the recent developments in high-valent cobalt-catalyzed enantioselective C-H functionalization up to October 2023, with the strong belief that the current state-of-the-art can attract considerable interest in the synthetic community, encouraging discoveries in the evolving landscape of asymmetric catalysis.

Cobalt-Catalyzed Enantioselective C-H Carbonylation towards Chiral Isoindolinones

Transition metal-catalyzed enantioselective C-H carbonylation with carbon monoxide, an essential and easily available C1 feedstock, remains challenging. Here, we disclosed an unprecedented enantioselective C-H carbonylation catalyzed by inexpensive and readily available cobalt(II) salt. The reactions proceed efficiently through desymmetrization, kinetic resolution, and parallel kinetic resolution, affording a broad range of chiral isoindolinones in good yields with excellent enantioselectivities (up to 92 % yield and 99 % ee). The synthetic potential of this method was demonstrated by asymmetric synthesis of biological active compounds, such as (S)-PD172938 and (S)-Pazinaclone. The resulting chiral isoindolinones also serve as chiral ligands in cobalt-catalyzed enantioselective C-H annulation with alkynes to construct phosphorus stereocenter.

Cobalt-Catalyzed Enantioselective C-H Annulation of Benzylamines with Alkynes: Application to the Modular and Asymmetric Syntheses of Bioactive Molecules

The transition metal-catalyzed enantioselective C-H functionalization strategy has revolutionized the logic of natural product synthesis. However, previous applications have heavily relied on the use of noble metal catalysts such as rhodium and palladium. Herein, we report the efficient synthesis of C1-chiral 1,2-dihydroisoquinolines (DHIQs) via enantioselective C-H/N-H annulation of picolinamides with alkynes catalyzed by a more sustainable and cheaper 3d metal catalyst, cobalt(II) acetate tetrahydrate. A wide range of enantiomerically enriched DHIQs were obtained in good yields with excellent enantioselectivities (up to 98% yield and >99% ee). The robustness and synthetic potential of this method were demonstrated by the modular and asymmetric syntheses of several tetrahydroisoquinoline alkaloids, including (S)-norlaudanosine, (S)-laudanosine, (S)-xylopinine, (S)-sebiferine, and (S)-cryptostyline II, and the asymmetric syntheses of key intermediates of (+)-solifenacin, FR115427, and (+)-NPS R-568.

Synthesis of Axially Chiral Biaryls through Cobalt(II)-Catalyzed Atroposelective C-H Arylation

Highly efficient synthesis of axially chiral biaryl amines through cobalt-catalyzed atroposelective C-H arylation using easily accessible cobalt(II) salt and salicyloxazoline ligand has been reported. This methodology provides a straightforward and sustainable access to a broad range of enantioenriched biaryl-2-amines in good yields (up to 99 %) with excellent enantioselectivities (up to 99 % ee). The synthetic utility of the unprecedented method is highlighted by its scalability and diverse transformations.

Rh(III)-Catalyzed C8-Spiroannulation of 1-Aminonaphthalenes with Maleimides

The rhodium(III)-catalyzed C8-spiroannulation of 1-aminonaphthalenes with maleimides is described herein. Initially formed C8-alkenylated 1-aminonaphthalenes can intercept nucleophilic 1-amino groups through the intramolecular aza-Michael reaction, resulting in the formation of spirofused tetracyclic frameworks. This protocol displayed a wide substrate scope and a broad functional group compatibility. The synthetic utility of this process is demonstrated by the gram-scale synthesis, late-stage modification, and synthetic transformations.

Data-driven design of new chiral carboxylic acid for construction of indoles with C-central and C-N axial chirality via cobalt catalysis

Challenging enantio- and diastereoselective cobalt-catalyzed C-H alkylation has been realized by an innovative data-driven knowledge transfer strategy. Harnessing the statistics of a related transformation as the knowledge source, the designed machine learning (ML) model took advantage of delta learning and enabled accurate and extrapolative enantioselectivity predictions. Powered by the knowledge transfer model, the virtual screening of a broad scope of 360 chiral carboxylic acids led to the discovery of a new catalyst featuring an intriguing furyl moiety. Further experiments verified that the predicted chiral carboxylic acid can achieve excellent stereochemical control for the target C-H alkylation, which supported the expedient synthesis for a large library of substituted indoles with C-central and C-N axial chirality. The reported machine learning approach provides a powerful data engine to accelerate the discovery of molecular catalysis by harnessing the hidden value of the available structure-performance statistics.

Access to 3-Aminomethylated Maleimides via a Phosphine-Catalyzed Aza-Morita-Baylis-Hillman Type Coupling

A designed method for the preparation of 3-aminomethylated maleimides via Morita-Baylis-Hillman (MBH) reaction was developed. This phosphine-catalyzed coupling adopted maleimides and 1,3,5-triazinanes as the substrate, giving a series of 3-aminomethylated maleimide derivatives with a double bond retained on the maleimide ring in 41-90% yield. Acylation, isomerization, and Michael addition of the obtained products demonstrated the synthetic application of the present protocol. The results of control experiments indicated that phosphorus ylide formation and elimination take place during the reaction pathway.

Enantio- and Regioselective Electrooxidative Cobalt-Catalyzed C-H/N-H Annulation with Alkenes

In recent years, the merging of electrosynthesis with 3d metal catalyzed C-H activation has emerged as a sustainable and powerful technique in organic synthesis. Despite the impressive advantages, the development of an enantioselective version remains elusive and poses a daunting challenge. Herein, we report the first electrooxidative cobalt-catalyzed enantio- and regioselective C-H/N-H annulation with olefins using an undivided cell at room temperature (up to 99 % ee). ^t Bu-Salox, a rationally designed Salox ligand bearing a bulky tert-butyl group at the ortho-position of phenol, was found to be crucial for this asymmetric annulation reaction. A strong cooperative effect between ^t Bu-Salox and 3,4,5-trichloropyridine enabled the highly enantio- and regioselective C-H annulation with the more challenging α-olefins without secondary bond interactions (up to 96 % ee and 97 : 3 rr). Cyclovoltametric studies, and the preparation, characterization, and transformation of cobaltacycle intermediates shed light on the mechanism of this reaction.

Enantioselective Synthesis of Spiro Heterocyclic Compounds Using a Combination of Organocatalysis and Transition-Metal Catalysis

Over the last ten years, the combination of organocatalysis with transition metal (TM) catalysis has become one of the most important toolboxes used for synthesizing optically pure compounds containing chiral quaternary centers, including spiro heterocyclic molecules. The dominant method in the enantioselective synthesis of spiro heterocyclic compounds based on synergistic catalysis includes chiral aminocatalysis and NHC catalysis, as already established covalent organocatalytic strategies. Another area of organocatalysis widely combined with TM catalysis producing enantiomerically enriched spiro heterocyclic compounds is non-covalent catalysis, dominated by chiral phosphoric acids, thiourea, and squaramide derivatives. This review article aims to summarize enantioselective methods used for constructing spirocyclic heterocycles based on a combination of organocatalysis and transition metal catalysis.

(SCp)Rhodium-Catalyzed Asymmetric Satoh-Miura Reaction for Building-up Axial Chirality: Counteranion-Directed Switching of Reaction Pathways

Satoh-Miura reaction is an important method for extending π-systems by forging multi-substituted benzene rings via double aryl C-H activation and annulation with alkynes. However, the development of highly enantioselective Satoh-Miura reaction remains rather challenging. Herein, we report an asymmetric Satoh-Miura reaction between 1-aryl benzo[h]isoquinolines and internal alkynes enabled by a SCpRh-catalyst. Judiciously choosing the counteranion of the Rh-catalyst is crucial for the desired reactivity over the competitive formation of azoniahelicenes. Detailed mechanistic studies support the proposal of counteranion-directed switching of reaction pathways in Rh-catalyzed asymmetric C-H activation.

Lewis Acid-Catalyzed [3 + 2]-Cyclization of Iodonium Ylides with Azadienes: Access to Spiro[benzofuran-2,2'-furan]-3-ones

A highly regioselective synthesis of spiro[benzofuran-2,2'-furan]-3-ones has been explored via Lewis acid-catalyzed [3 + 2] cyclization of iodonium ylides with azadienes. The acidity of the Lewis acid was significantly strengthened with strong hydrogen bond donors, thereby promoting the enolization isomerization of iodonium ylides for the subsequent cycloaddition. This reaction was compatible with a broad range of substrates under the mild reaction conditions, and efficiently delivered spiro-heterocycles with excellent stereoselectivity.

Cobalt/Salox-Catalyzed Enantioselective C-H Functionalization of Arylphosphinamides

Previous methods on Co^III -catalyzed asymmetric C-H activation rely on the use of tailor-made cyclopentadienyl-ligated Co^III complexes, which require lengthy steps for the preparation. Herein, we report an unprecedented enantioselective C-H functionalization enabled by a simple cobalt/salicyloxazoline (Salox) catalysis. The chiral Salox ligands can be easily prepared in one step from salicylonitrile and chiral amino alcohols. A broad range of P-stereogenic compounds were synthesized in high yields with excellent enantioselectivities (45 examples, up to 99 % yield and >99 % ee). The isolation and characterization of several intermediates provided insights into the generation of active catalytic cobalt species, the action of Salox, and the mode of stereocontrol.

Chiral Brønsted Acid Catalyzed Enantioselective Synthesis of Spiro-Isoindolinone-Indolines via Formal [3 + 2] Cycloaddition

A novel organocatalytic asymmetric formal [3 + 2] cycloaddition of 3-substituted 1H-indoles with in situ generated 3-hydroxy-isoindolinone-derived β,γ-alkynyl-α-ketimines has been developed. A variety of biologically relevant chiral spiro-isoindolinone-indolines were achieved with excellent yields (up to 99%) and enantioselectivity (up to 99% ee) under mild conditions. The gram-scale reaction of this methodology and several interesting transformations of the products have been demonstrated.

Enantioselective Cobalt-Catalyzed C–H Functionalization

Co-catalyzed C–H functionalization has received great attention due to the high earth abundance, low biotoxicity, and unique reactivity of cobalt; enantioselective control of these reactions has been a formidable challenge. Various efficient strategies have recently been developed for enantioselective Co-catalyzed C–H functionalization, but there is no topical review of this field. Herein, we give a detailed summary of this rapidly growing field, highlighting critical progress, current challenges, and future trends.

1 Introduction

2 Enantioselective C–H Functionalization via Low-Valent Co Catalysis

2.1 Chiral Diphosphines for Enantioselective Control

2.2 Chiral Monophosphines or N-Heterocyclic Carbenes for Enantioselective Control

3 Enantioselective C–H Functionalization via High-Valent Co Catalysis

3.1 Chiral Acids for Enantioselective Control

3.2 Chiral Cp Ligands for Enantioselective Control

4 Conclusions and Outlook

Asymmetric Ru/Cinchonine Dual Catalysis for the One-Pot Synthesis of Optically Active Phthalides from Benzoic Acids and Acrylates

Herein, we report the asymmetric Ru/cinchonine dual catalysis that provides straightforward access to enantioselective synthesis of C-3 substituted phthalides via tandem C-H activation/Michael addition cascade. The use of readily accessible and less expensive [RuCl₂(p-cym)]₂ and cinchonine catalyst for the one-pot assembly of chiral phthalides greatly overcomes the present trend of using highly sophisticated catalysts. The developed method provides access to both enantiomers of a product using pseudoenantiomeric cinchona alkaloids as catalysts streamlining the synthesis of phthalide in both the optically active forms.

Electrooxidative palladium- and enantioselective rhodium-catalyzed [3 + 2] spiroannulations

Despite indisputable progress in the development of electrochemical transformations, electrocatalytic annulations for the synthesis of biologically relevant three-dimensional spirocyclic compounds has as of yet not been accomplished. In sharp contrast, herein, we describe the palladaelectro-catalyzed C-H activation/[3 + 2] spiroannulation of alkynes by 1-aryl-2-naphthols. Likewise, a cationic rhodium(iii) catalyst was shown to enable electrooxidative [3 + 2] spiroannulations via formal C(sp3)-H activations. The versatile spiroannulations featured a broad substrate scope, employing electricity as a green oxidant in lieu of stoichiometric chemical oxidants under mild conditions. An array of spirocyclic enones and diverse spiropyrazolones, bearing all-carbon quaternary stereogenic centers were thereby accessed in a user-friendly undivided cell setup, with molecular hydrogen as the sole byproduct.

Total Synthesis of (-)-Amathaspiramide A via One-pot Aldol Addition/Transamidification Reaction

The total synthesis of (-)-amathaspiramide A was accomplished through an efficient construction of chiral aza-spirobicyclic core by aldol addition/transamidification cascade. The scope of the efficient construction methodology was investigated. Configuration...

Reaction Path Determination of Rhodium(I)-Catalyzed C-H Alkylation of N-8-Aminoquinolinyl Aromatic Amides with Maleimides

The rhodium(I)-catalyzed reaction of N-8-aminoquinolinyl aromatic amides with maleimides results in C-H alkylation at the ortho position of the amide. The reaction path and formation of the alkylation product with density functional theory (DFT) calculations were done. The detailed computational study showed that the reaction proceeds in the following steps: (I) deprotonation of the NH amide proton, (II) oxidative addition of the ortho C-H bond, (III) migratory insertion of the maleimide, (IV) reductive elimination with the C-C bond formation, and (V) protonation. The energetic span model showed that the turnover frequency (TOF)-determining transition state (TDTS) is the oxidative addition, while the TOF-determining intermediate (TDI) is the formation of an Rh(I)-complex after N-H deprotonation. It was also found that the change in the oxidation number of the Rh catalyst is a key determinant of the reaction path.