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).

Palladium(0) π-Lewis Base Catalysis: Concept and Development

The development of a new catalytic strategy plays a vital role in modern organic chemistry since it permits bond formation in an unprecedented and more efficient manner. Although the application of preformed metal complexes as π-base-activated reagents have enabled diverse transformations elegantly, the concept and strategy by directly utilizing transition metals as efficient π-Lewis base catalysts remain underdeveloped, especially in the field of asymmetric catalysis. Here, we outline our perspective on the discovery of palladium(0) as an efficient π-Lewis base catalyst, which is capable of increasing the highest occupied molecular orbital (HOMO) energy of both electron-neutral and electron-deficient 1,3-dienes and 1,3-enynes upon flexible η2-complexes formed in situ and resultant π-backdonation. Thus, fruitful carbon-carbon-forming reactions with diverse electrophiles can be achieved enantioselectively in a vinylogous addition pattern, which is conceptually different from the classical oxidative cyclization mechanism. Emphasis will be given to the concept and mechanism elucidation, catalytic features, and reaction design together with perspective on the further development of this emerging field.

Propargylic Dialkyl Effect for Cyclobutene Formation through Ir(III)-Catalyzed Cycloisomerization of 1,6-Enynes

The propargylic dialkyl effect (PDAE) has a significant impact on the cyclization reaction of enynes, partly reflected in changing the types of products. Herein, we described the influence of the propargylic dialkyl effect on the Ir(III)-catalyzed cycloisomerization of 1,6-enynes to provide strained cyclobutenes. A series of substituted 1,6-enynes were proved to be excellent substrate candidates in the presence of [Cp*IrCl2]2 in toluene. Mechanistic investigation, based on deuterium labeling experiments and control experiments, indicated that the propargylic dialkyl effect might boost C(sp)-H activation by preventing the coordination of active iridium species to the C(sp)≡C(sp) bond of enynes. This finding contributes to the fundamental understanding of enyne cyclization reactions and offers valuable insight into the propargylic dialkyl effect.

Metal-Catalyzed Enantioconvergent Transformations

Enantioconvergent catalysis has expanded asymmetric synthesis to new methodologies able to convert racemic compounds into a single enantiomer. This review covers recent advances in transition-metal-catalyzed transformations, such as radical-based cross-coupling of racemic alkyl electrophiles with nucleophiles or racemic alkylmetals with electrophiles and reductive cross-coupling of two electrophiles mainly under Ni/bis(oxazoline) catalysis. C-H functionalization of racemic electrophiles or nucleophiles can be performed in an enantioconvergent manner. Hydroalkylation of alkenes, allenes, and acetylenes is an alternative to cross-coupling reactions. Hydrogen autotransfer has been applied to amination of racemic alcohols and C-C bond forming reactions (Guerbet reaction). Other metal-catalyzed reactions involve addition of racemic allylic systems to carbonyl compounds, propargylation of alcohols and phenols, amination of racemic 3-bromooxindoles, allenylation of carbonyl compounds with racemic allenolates or propargyl bromides, and hydroxylation of racemic 1,3-dicarbonyl compounds.

Enantioselective Synthesis of 1-Aminoindanes via [3 + 2] Annulation of Aldimines with Alkenes by Scandium-Catalyzed C-H Activation

Multisubstituted chiral 1-aminoindanes are important components in many pharmaceuticals and bioactive molecules. Therefore, the development of efficient and selective methods for the synthesis of chiral 1-aminoindanes is of great interest and importance. In principle, the asymmetric [3 + 2] annulation of aldimines with alkenes through C-H activation is the most atom-efficient and straightforward route for the construction of chiral 1-aminoindanes, but such a transformation has remained undeveloped to date probably due to the lack of suitable catalysts. Herein, we report for the first time the enantioselective [3 + 2] annulation of a wide range of aromatic aldimines and alkenes via ortho-C(sp2)-H activation by chiral half-sandwich scandium catalysts, which provides a straightforward route for the synthesis of multisubstituted chiral 1-aminoindanes. This protocol features 100% atom-efficiency, broad functional group compatibility, and high regio-, diastereo-, and enantioselectivity (up to >19:1 dr and 99:1 er). Remarkably, by fine-tuning the sterics of the chiral ligand around the catalyst metal center, the diastereodivergent asymmetric [3 + 2] annulation of aldimines and styrenes has been achieved with a high level of diastereo- and enantioselectivity, offering an efficient method for the synthesis of both the trans and cis diastereomers of a novel class of chiral 1-aminoindane derivatives containing two contiguous stereocenters from the same set of starting materials. Moreover, the asymmetric [3 + 2] annulation of aldimines with aliphatic α-olefins, norbornene, and 1,3-dienes has also been achieved.

Rh-Catalyzed [3+2] Annulation of Cyclic Ketimines and Alkynyl Chloride: A Strategy for Accessing Unsymmetrically Substituted and Highly Functionalizable Indenes

Alkynyl chlorides were found to be extraordinarily novel electrophiles, which could afford a single regioisomer of the [3+2] annulation adducts with cyclic ketimines by rhodium catalysis. The alkenyl chloride moiety in the products provided a valuable functional handle for further diverse transformations. Therefore, this research provided not only a synthetic protocol for accessing unsymmetrically substituted indenyl amines but also a highly divergent solution for decorating the substituting group by postmanipulation of the chloride.

Chiral Diene Ligands in Asymmetric Catalysis

Asymmetric catalysis has emerged as a general and powerful approach for constructing chiral compounds in an enantioselective manner. Hence, developing novel chiral ligands and catalysts that can effectively induce asymmetry in reactions is crucial in modern chemical synthesis. Among such chiral ligands and catalysts, chiral dienes and their metal complexes have received increased attention, and a great progress has been made over the past two decades. This review provides comprehensive and critical information on the essential aspects of chiral diene ligands and their importance in asymmetric catalysis. The literature covered ranges from August 2003 (when the first effective chiral diene ligand for asymmetric catalysis was reported) to October 2021. This review is divided into two parts. In the first part, the chiral diene ligands are categorized according to their structures, and their preparation methods are summarized. In the second part, their applications in asymmetric transformations are presented according to the reaction types.

Stereoselective Synthesis of Allenyl Alcohols by Cobalt(III)-Catalyzed Sequential C-H Bond Addition to 1,3-Enynes and Aldehydes

An efficient and stereoselective CoIII -catalyzed sequential C-H bond addition to 1,3-enynes and aldehydes is disclosed. This transformation represents the first example of sequential C-H bond additions to 1,3-enynes and a second coupling partner and provides the first example of preparing allenes by C-H bond addition to 1,3-enynes. A wide range of aldehydes, C-H bond substrates and 1,3-enynes with large substituents on the alkynes are effective substrates. The allenyl alcohol products can be further converted to dihydrofurans with high stereoselectivity either in situ or under Ag-mediated cyclization conditions. The allenyl silyl group can also be transferred to the adjacent alcohol by a Brook rearrangement. Moreover, a mechanism for the transformation is proposed supported by X-ray structural characterization of a cobaltacycle intermediate.

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.

Rh(III)-Catalyzed spiroannulation of ketimines with cyclopropenones via sequential C-H/C-C bond activation

An unprecedented Rh(III)-catalyzed [3+3]-spiroannulation of ketimines with cyclopropenones to access spiro[4,5]dienones has been developed. Sequential C-H/C-C bond activation and subsequent nucleophilic addition are disclosed in this process. This procedure represents the first example of the construction of spirolactams utilising cyclopropenones as 3C synthons. The remarkable advantages of this protocol are excellent chemo- and regio-selectivity, wide functional group tolerance, high reaction yields, and tolerance towards H₂O.

Chemoselective and Regioselective Synthesis of Spiroisoindolinone Indenes via an Intercepted Meyer-Schuster Rearrangement/Intramolecular Friedel-Crafts Alkylation Relay

A Brønsted acid-catalyzed reaction between isoindolinone-derived propargylic alcohols and external aromatic nucleophiles for the construction of spiroisoindolinone indenes is described. The reaction proceeds rapidly with a broad range of substrates to generate spiroindenes chemoselectively and regioselectively in moderate to high yields. Key to the success of this transformation is an intercepted Meyer-Schuster rearrangement/intramolecular Friedel-Crafts alkylation relay that offers a modular approach in the synthesis of target compounds.

Diastereoselective synthesis of chiral 3-substituted isoindolinones via rhodium(III)-catalyzed oxidative C-H olefination/annulation

A new method for the direct and stereoselective synthesis of 3-substituted isoindolinones via Rh(iii)-catalyzed chiral N-sulfinyl amide directed asymmetric [4 + 1] annulation of benzamides with acrylic esters has been developed. The reaction proceeded through an oxidative C-H olefination and a subsequent cyclization by intramolecular aza-Michael addition, producing a series of diastereoisomeric chiral isoindolinones (20 examples) in generally good yields with a dr value up to 5.5 : 1. The absolute configurations of the newly formed C-stereocenters in the major and minor diastereomers of the catalysis product have been determined by X-ray crystal diffraction analysis to be S and R, respectively. The separation of the major diastereoisomers from the catalysis products and subsequent removal of the N-sulfinyl chiral auxiliary afforded enantiomerically pure (S)-isoindolinones. The application of the obtained (S)-isoindolinones in the synthesis of several biologically active isoindolinones such as (S)-PD172938, (S)-pazinaclone and (S)-pagoclone is presented.

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.

Synthesis and stereoselective catalytic transformations of 3-hydroxyisoindolinones

This review focuses on the synthesis of 3-hydroxyisoindolinones, and their application as substrates in stereoselective catalytic transformations reported from 2010 to date. These compounds have attracted much attention among synthetic chemists, as they are integral structural parts of a number of natural products and biologically active compounds. The first part of this review covers methods based on electrochemical, photochemical, and thermal reactions for the synthesis of 3-hydroxyisoindolinones. The second part focuses on their employment as substrates in transition metal-catalyzed and organocatalyzed stereoselective transformations for the preparation of chiral 3-substituted isoindolinone derivatives.

Intramolecular Formal [4 + 2] Cycloadditions: Synthesis of Spiro Isoindolinone Derivatives and Related Molecules

Acid-catalyzed intramolecular reactions of isoindolinone-derived hydroxylactam derivatives bearing enones or enals that afford spiro isoindolinone derivatives and related molecules have been developed. From the hydroxylactam moieties, N-acylenamides were generated in situ and reacted with the enone and the enal moieties via formal [4 + 2] cycloaddition reactions to construct cyclohexanone- and dihydropyran-fused ring systems and the spiro ring systems.

Strategies and methodologies for the construction of spiro-γ-lactams: an update

This review gives an insight into the most recent synthetic methodologies towards spiro-γ-lactams, a class of compounds that are present in a wide range of synthetic bioactive and naturally occurring 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.

Palladium(II)-catalyzed asymmetric C-H carbonylation to diverse isoquinoline derivatives bearing all-carbon quaternary stereocenters

Enantioselective synthesis of tetrahydroisoquinolines bearing an all-carbon quaternary stereogenic center, was achieved via asymmetric C-H activation with high enantioselectivities (up to 93% ee). Fair substrate tolerance was indicated throughout the scope investigation and no evident loss of enantioselectivity was exhibited in late-stage derivatization. This study provides incentives for the construction of diverse chiral isoquinoline derivatives, which are prevalent among pharmaceuticals, natural products, etc.

Ruthenium(II)-Catalyzed Regioselective [3 + 2] Spiroannulation of 2H-Imidazoles with 2-Alkynoates

The C═N double bond of 2H-imidazole has been employed as a C-electrophile for the ruthenium(II)-catalyzed [3 + 2] spiroannulation reaction of 4-phenyl-2H-imidazoles and 2-alkynoates to synthesize spiroimidazole-4,1'-indenes. This strategy features high regioselectivity, broad functional group tolerance, and use of ruthenium as a catalyst, providing a new method to synthesize spirocycles with potential applications in pharmaceuticals.

BF3·OEt2-Catalyzed Vinyl Azide Addition to in Situ Generated N-Acyl Iminium Salts: Synthesis of 3-Oxoisoindoline-1-acetamides

BF₃·OEt₂-catalyzed nucleophilic addition of vinyl azides to in situ generated N-acyl iminium salts obtained from 3-hydroxyisoindolinones is described in this article. The procedure is operationally simple, mild, additive, and metal-free. The reaction proceeds smoothly at ambient temperature with a wide range of 3-hydroxyisoindol-1-ones and vinyl azides to afford 3-oxoisoindoline-1-acetamides (32 examples) in high yields (up to 97%). Furthermore, the synthetic utility of this methodology is depicted by exploiting the reactivity of an amide functionality in the products.

Rapid assembly of cyclopentene spiroisoindolinones via a rhodium-catalysed redox-neutral cascade reaction

A rhodium-catalysed redox-neutral cascade reaction starting from benzamides and cyclopropenones for the rapid assembly of cyclopentene spiroisoindolinones has been developed.

Asymmetric aerobic decarboxylative Povarov reactions of N-aryl α-amino acids with methylenephthalimidines via cooperative photoredox and chiral Brønsted acid catalysis

This work realizes a new synthetic utility of methylenephthalimidines as a 1,2-synthon and the synthesis of valuable chiral isoindolin-1-ones featuring a 3,3-spiro-tetrahydroquinoline-based stereocenter.

Chiral phosphoric acid catalyzed enantioselective N-alkylation of indoles with in situ generated cyclic N-acyl ketimines

A chiral SPINOL derived phosphoric acid-catalyzed asymmetric N-alkylation reaction of indoles with cyclic α-diaryl-substituted N-acyl imines, which are generated in situ from 3-aryl 3-hydroxyisoindo-linones, has been demonstrated.