Asymmetric Formal Vinylogous Iminium Ion Activation for Vinyl-Substituted Heteroaryl and Aryl Aldehydes

Heteroatom-Controlled Three-Component [4 + 3] or [3 + 2] Annulation of Isatin-Derived Azomethine Ylide with Azadiene: Selective Synthesis of Spirooxindole-diazepines and Density Functional Theory Studies

A novel three-component [4 + 3] annulation reaction of isatin-derived azomethine ylides with azadienes was developed for the first time to efficiently synthesize spirooxindole-diazepines incorporating a benzothiophene moiety under catalyst-free conditions. Effects of the heteroatom of azadiene on the chemoselectivity was investigated. With the use of the azadiene bearing a benzofuran moiety as a substrate, the dominant reaction pathway was changed to an α-[3 + 2] annulation. When azadiene bearing an indenone moiety was used, a distinct γ-[3 + 2] annulation was observed. Density functional theory calculations revealed that a delicate balance between kinetic accessibility and the thermodynamic driving force controlled the competition of different annulation reactions.

Chiral-Boron Complex-Catalyzed Asymmetric [3 + 2] Cycloaddition of 2'-Hydroxychalcones with N-2,2,2-Trifluoroethylisatin Ketimines

A highly efficient asymmetric [3 + 2] cycloaddition reaction of 2'-hydroxychalcones with N-2,2,2-trifluoroethylisatin ketimines catalyzed by a (R)-3,3'-I2-BINOL-boron complex was developed. A broad range of 3,2'-pyrrolidinyl spirooxindole derivatives bearing a CF3-substituted pyrrolidine moiety with four contiguous stereocenters was prepared in high yields with excellent diastereo- and enantioselectivities (up to >20:1 dr and >99% ee). This protocol had the characteristics of mild reaction conditions, high efficiency, and excellent stereocontrol.

K2CO3-Catalyzed (3 + 2) Cycloaddition Reaction of N-2,2,2-Trifluoroethylisatin Ketimines with Azodicarboxylates: Access to Spirooxindoles Containing Trifluoromethyl-1,2,4-triazolines

Potassium carbonate-catalyzed (3 + 2) cycloaddition reaction between N-2,2,2-trifluoroethylisatin ketimines and azodicarboxylates has been developed, constructing a series of novel N-heterocycle infused spirooxindoles in good to excellent yields (up to 98%) under milder conditions. The presence of both biologically active oxindole and trifluoromethyl-1,2,4-triazoline moieties in these novel spirocyclic compounds would provide new lead structures in the discovery of heterocyclic compounds with potential pharmaceutical activities.

Hydrazone Activation in the Aminocatalytic Cascade Reaction for the Synthesis of Tetrahydroindolizines

In this Letter, we demonstrate the usefulness of hydrazone activation for the synthesis of biologically relevant tetrahydroindolizines. A pyrrol-derived hydrazone bearing a Michael acceptor moiety in the N-alkyl side chain has been designed with the aim of participating in the aminocatalytic cascade reaction leading to the annulation of the new six-membered heterocyclic scaffold. The application of (S)-(-)-α,α-diphenyl-2-pyrrolidinemethanol trimethylsilyl ether as the aminocatalyst allows for the iminium ion-enamine-mediated cascade to proceed in a fully stereoselective manner.

Recent Advances of N-2,2,2-Trifluoroethylisatin Ketimines in Organic Synthesis

The special properties of fluorine atoms and fluorine-containing groups have led to an increasing number of applications for fluorine-containing organic compounds, which are also extremely widely used in the field of new drug development. Unfortunately, naturally fluorinated organics are rare in nature, so the selective introduction of fluorine atoms or fluorine-containing groups into organic molecules is very important for pharmaceutical/synthetic chemists. N-2,2,2-trifluoroethylisatin ketimines have received the attention of many chemists since they were first developed as fluorine-containing synthons in 2015. This paper reviews the organic synthesis reactions in which trifluoroethyl isatin ketimine has been involved in recent years, focusing on the types of reactions and the stereoselectivity of products, and also provides a prospect of its application in this field.

Cu-Catalyzed Asymmetric 1,3-Dipolar Cycloaddition of N-2,2,2-Trifluoroethylisatin Ketimines Enables the Desymmetrization of N-Arylmaleimides: Access to Enantioenriched F3C-Containing Octahydropyrrolo[3,4-c]pyrroles

With a Cu(OTf)₂/chiral ferrocenyl P,N-ligand complex as a catalyst, the enantioselective desymmetrization of N-arylmaleimides was successfully realized by taking advantage of the asymmetric 1,3-dipolar cycloaddition reaction of N-2,2,2-trifluoroethylisatin ketimines. A series of structurally diverse F₃C-containing octahydropyrrolo[3,4-c]pyrroles, bearing four contiguous carbon stereocenters and one stereogenic chiral C-N axial bond, were obtained with excellent results (≤99% yield, >20:1 dr, and 99% ee).

Dearomative Michael addition involving enals and 2-nitrobenzofurans realized under NHC-catalysis

In this manuscript, the first enantioselective dearomative Michael addition between α,β-unsaturated aldehydes and 2-nitrobenzofurans realized under N-heterocyclic carbene activation has been described. The reaction proceeds via addition of homoenolate to Michael acceptors leading to the formation of biologically important heterocycles with high yields and stereoselectivities. Their functionalization potential has been confirmed in selected, diastereoselective transformations.

Synthesis of functionalized 3,2′-pyrrolidinyl spirooxindoles via domino 1,6-addition/annulation reactions of para-quinone methides and 3-chlorooxindoles

A highly efficient diastereoselective [4 + 1] cycloaddition of ortho-tosylaminophenyl-substituted p-QMs with 3-chlorooxindoles has been developed to afford 3,2′-pyrrolidinyl spirooxindoles.

Oxyenamides as Versatile Building Blocks for a Highly Stereoselective One-Pot Synthesis of the 1,3-Diamino-2-ol-Scaffold Containing Three Continuous Stereocenters

A highly diastereoselective one-pot synthesis of the 1,3-diamino-2-alcohol unit bearing three continuous stereocenters is described. This method utilizes 2-oxyenamides as a novel type of building block for the rapid assembly of the 1,3-diamine scaffold containing an additional stereogenic oxygen functionality at the C2 position. A stereoselective preparation of the required (Z)-oxyenamides is reported as well.

Regiodivergent Organocatalytic Reactions

Organocatalysts are abundantly used for various transformations, particularly to obtain highly enantio- and diastereomeric pure products by controlling the stereochemistry. These applications of organocatalysts have been the topic of several reviews. Organocatalysts have emerged as one of the very essential areas of research due to their mild reaction conditions, cost-effective nature, non-toxicity, and environmentally benign approach that obviates the need for transition metal catalysts and other toxic reagents. Various types of organocatalysts including amine catalysts, Brønsted acids, and Lewis bases such as N-heterocyclic carbene (NHC) catalysts, cinchona alkaloids, 4-dimethylaminopyridine (DMAP), and hydrogen bond-donating catalysts, have gained renewed interest because of their regioselectivity. In this review, we present recent advances in regiodivergent reactions that are governed by organocatalysts. Additionally, we briefly discuss the reaction pathways of achieving regiodivergent products by changes in conditions such as solvents, additives, or the temperature.

Asymmetric Dearomative (3+2)-Cycloaddition Involving Nitro-Substituted Benzoheteroarenes under H-Bonding Catalysis

In our studies, the organocatalytic 1,3-dipolar cycloaddition between 2-nitrobenzofurans or 2-nitrobenzothiophene and N-2,2,2-trifluoroethyl-substituted isatin imines has been developed. The reaction has been realized by employing bifunctional organocatalysis, with the use of squaramide derivative being crucial for the stereochemical efficiency of the process. The usefulness of the cycloadducts obtained has been confirmed in selected transformations, including aromative and non-aromative removal of the nitro group.

Enantioselective H-bond-directed vinylogous iminium ion strategy for the functionalization of vinyl-substituted heteroaryl aldehydes

In this work the first H-bond-directed vinylogous iminium ion strategy has been developed as a convenient strategy for the γ,δ-functionalization of vinyl-substituted heteroaromatic aldehydes. Their reaction with α-mercaptoketones proceeds in a cascade manner involving 1,6-addition followed by intramolecular aldol reaction. Excellent stereoselectivities have been obtained as a result of the H-bond interactions controlling the outcome of the cyclization step. The application of the strategy for the synthesis of tricyclic compounds bearing furan, tetrahydrothiophene and dihydropyran moieties has also been demonstrated.

Remote asymmetric conjugate addition catalyzed by a bifunctional spiro-pyrrolidine-derived thiourea catalyst

A novel spiro-pyrrolidine (SPD)-derived bifunctional thiourea catalyst has been developed and used in a stereoselective conjugate addition of furfurals to β,γ-unsaturated α-ketoesters.

Synthesis of novel pyridinium 1,5-zwitterions and their reactivity with isatin-based α-(trifluoromethyl)imines: a sulfur-controlled domino reaction

A new stable pyridinium 1,5-zwitterion, generated from azadiene and 4-dimethylaminopyridine, was isolated. The reaction of pyridinium 1,5-zwitterion and isatin-derived α-(trifluoromethyl)imine was regulated by temperature.

Enantioselective organocatalytic formal [3+2]-cycloaddition of isatin-derived ketimines with benzylidenemalononitriles and benzylidineindanones

Electron-deficient alkenes undergo organocatalysed formal [3+2]-cycloaddition with isatin-derived imines, generating complex spirocyclic products with high yield and stereoselectivity.

Asymmetric β,γ′-regioselective [4 + 3] and [4 + 2] annulations of α-vinylenals via cascade iminium ion-dienamine catalysis

α-Vinylenal substrates have been designed and applied in β,γ′-regioselective asymmetric [4 + 3] and [4 + 2] annulation reactions via cascade aminocatalysis.

Bifunctional Brønsted Base Catalyzed [3 + 3] Annulations of Indolin-2-imines and α,β-Unsaturated Imides: An Enantioselective Approach to α-Carbolinones

Asymmetric construction of α-carbolinones with easily available starting materials has recently attracted considerable attention from the synthesis community, and the development of effective catalysis for this target is in great demand. Here, a bifunctional Brønsted base catalyzed asymmetric [3 + 3] cyclization of indolin-2-imines and α,β-unsaturated N-acylated succinimides was developed by using the strategy of noncovalent bonding catalysis. With this organocatalytic protocol, a variety of tetrahydro-α-carbolinones bearing different substituents were synthesized with up to 99% yield and up to 96:4 er.