Highly regio- and diastereoselective [3 + 2]-cycloadditions involving indolediones and α,β-disubstituted nitroethylenes

A highly diastereoselective [3 + 2]-cycloaddition strategy involving multiple oxindoles and several α,β-disubstituted nitroethylenes is developed to access tetra-substituted α-spiropyrrolidine frameworks. A variety of α-amino acids were employed for the first time in order to generate azomethine ylides under thermal conditions, affording regioisomers 13 and 14 merely by changing the α-substituents (R = H and substituted carbons) of the α-amino acids. The reaction tolerates various sterically demanding, electron-rich and electron-deficient aryl and nitrogen substituents on glycines, oxindoles and nitroethylenes. The operational simplicity, such as the use of a metal-free and non-inert environment, the utilization of non-halogenated solvents and the ease of isolation, adhering to the principles of green chemistry, makes this process attractive for scale-up opportunities. The reaction delivers good yields (80-94%) and diastereoselectivities (up to 98 : 2) in favor of (cis,cis)-spirooxindoles, with opposite regioselectivity compared to β-nitrostyrenes under identical conditions. Two spiropyrrolidine cycloadducts with unprotected amides exhibited significant activity against Gram-positive MRSA.

Application of isatin-derived saturated esters in the synthesis of 3,3'-spirooxindole γ-butyrolactams

Stable while reactive isatin-derived saturated esters have been utilized as 3-carbon synthons in a base-promoted formal [3 + 2] annulation with N-Boc imines. The developed protocol offers a direct pathway for the rapid and divergent construction of two classes of 3,3'-spirooxindole γ-butyrolactam skeletons that are recognized as the privileged structures of various bioactive compounds. This protocol also has the advantages of mild reaction conditions, scalability and wide reaction scope.

Stereochemical diversity in pyrrolidine synthesis by catalytic asymmetric 1,3-dipolar cycloaddition of azomethine ylides

The pyrrolidine ring is a privileged structural motif in synthetic and medicinal chemisty. This review aims to highlight the high versatility of the catalytic asymmetric 1,3-dipolar cycloaddition of azomethine ylides for access to different types of stereochemical patterns in enantioselective pyrrolidine synthesis. Special attention will be paid to stereodivergent procedures giving rise to different stereoisomers from the same starting materials.

Diastereodivergent Asymmetric 1,3-Dipolar Cycloaddition of Azomethine Ylides and β-Fluoroalkyl Vinylsulfones: Low Copper(II) Catalyst Loading and Theoretical Studies

A Cu^II -catalyzed asymmetric 1,3-dipolar cycloaddition using β-fluoroalkyl alkenyl arylsulfones as dipolarophiles and glycine/alanine iminoesters as azomethine ylide precursors has been developed. Remarkably, a catalyst loading as low as 0.5 mol % is highly efficient. Accordingly, a wide range of enantioenriched 3-fluoroalkyl pyrrolidines, as well as Δ² -pyrroline and pyrrole derivatives, are generated in good to excellent yields with high asymmetric induction. This synthetic approach is diastereodivergent in that exo-adducts could be converted into the corresponding exo'-adducts by 1,8-diazabicyclo[5.4.0]undec-7-ene mediated epimerization at C2 of the pyrrolidine core. The free-energy profiles from DFT calculations suggest the Michael addition of the 1,3-dipole to be the rate- and enantiodetermining step, and the origin of stereoselectivity is studied by means of the noncovalent interaction (NCI) analysis.

Catalytic Asymmetric and Divergent Synthesis of Tricyclic and Tetracyclic Spirooxindoles: Controllable Site-Selective Electrophilic Halocyclization of 1,6-Enynes

Catalytic asymmetric and divergent assembly of tricyclic and tetracyclic 3,3'-pyrrolidonyl spirooxindoles was developed, involving a one-pot chiral Brønsted base catalyzed asymmetric propargylation for the synthesis of oxindole 1,6-enynes and a subsequent switchable site-selective and highly diastereoselective electrophilic iodocyclization of 1,6-enynes. In addition, antitumor properties of the newly synthesized compounds were evaluated.

Synthesis of DNA-coupled isoquinolones and pyrrolidines by solid phase ytterbium- and silver-mediated imine chemistry

DNA-encoded libraries of chemically synthesized compounds are an important small molecule screening technology. The synthesis of encoded compounds in solution is currently restricted to a few DNA-compatible and water-tolerant reactions. Encoded compound synthesis of short DNA-barcodes covalently connected to solid supports benefits from a broad range of choices of organic solvents. Here, we show that this encoded chemistry approach allows for the synthesis of DNA-coupled isoquinolones by an Yb(iii)-mediated Castagnoli-Cushman reaction under anhydrous reaction conditions and for the synthesis of highly substituted pyrrolidines by Ag(i)-mediated 1,3-dipolar azomethine ylide cycloaddition. An encoding scheme for these DNA-barcoded compounds based on a DNA hairpin is demonstrated.

Ag/P-Stereogenic Phosphine-Catalyzed Enantioselective 1,3-Dipolar Cycloadditions: A Method to Optically Active Pyrrolidines

A Ag/P-stereogenic phosphine-complex-catalyzed 1,3-dipolar cycloaddition of azomethine ylides with electron-deficient olefins is reported. In this reaction, highly functionalized pyrrolines with a spiro-quaternary stereogenic center were obtained in good yields (up to 99%) with excellent levels of diastereo- (up to >20:1 dr) and enantioselectivities (up to >99% ee). The chirality of adducts was controlled predominantly by the P-stereogenic phosphines.

Proline bulky substituents consecutively act as steric hindrances and directing groups in a Michael/Conia-ene cascade reaction under synergistic catalysis

In this study, we report a highly stereoselective and versatile synthesis of spiro pyrazolones, promising motifs that are being employed as pharmacophores. The new synthetic strategy merges organocatalysis and metal catalysis to create a synergistic catalysis using proline derivatives and Pd catalysts. This protocol is suitable for late-stage functionalization, which is very important in drug discovery. Additionally, a thorough computational study proved to be very useful to elucidate the function of the different catalysts along the reaction, showing a peculiar feature: the -CPh2OSiMe3 group of the proline catalyst switches its role during the reaction. In the initial Michael reaction, this group plays its commonly-assumed role of bulky blocking group, but the same group generates π-Pd interactions and acts as a directing group in the subsequent Pd-catalyzed Conia-ene reaction. This finding might be very relevant especially for processes with many steps, such as cascade reactions, in which functional groups are assumed to play the same role during all reaction steps.

Double 1,3-Dipolar Cycloadditions of Two Nonstabilized Azomethine Ylides for Polycyclic Pyrrolidines

Nonstabilized azomethine ylides derived from decarboxylation of oxazolidin-5-ones were used for double 1,3-dipolar cycloadditions in diastereoselective synthesis of pyrrolidine-containing tetracyclic compounds. This is the first example of one-pot and five-component reactions involving two nonstabilized azomethine ylides. Only CO₂ and water were generated as byproducts.

Stereocontrolled [3+2] Cycloaddition of Donor-Acceptor Cyclopropanes to Iminooxindoles: Access to Spiro[oxindole-3,2'-pyrrolidines]

A novel stereocontrolled assembly of spiro[oxindole-3,2'-pyrrolidines] via [3+2]-cycloaddition of donor-acceptor cyclopropanes to electron-poor ketimines, iminooxindoles, was developed. The method allows for efficient employment of common readily available donor-acceptor cyclopropanes, functionalized with ester, keto, nitro, cyano etc. groups, and N-unprotected iminooxindoles. The stereospecificity of the initial S_N2-like imine attack on a cyclopropane molecule together with a high diastereoselectivity of further C-C bond formation facilitate a rapid access to spiro[oxindole-3,2'-pyrrolidines] in their optically active forms. Preliminary in vitro testing of the synthesized compounds against LNCaP (p53+) and PC-3 (p53-) cells revealed good antiproliferative activities and p53-selectivity indices for several compounds that are intriguing in terms of their further investigation as inhibitors of MDM2-p53 interaction.

Copper(I)-Catalyzed Kinetic Resolution of exo-3-Oxodicyclopentadienes and endo-3-Oxodicyclopentadiene

The first example of highly efficient kinetic resolution of exo-3-oxodicyclopentadienes and endo-3-oxodicyclopentadiene has been developed by means of Cu(I)-catalyzed asymmetric 1,3-dipolar cycloaddition of azomethine ylide. Compared with the existing methodologies for those synthetically important optically active convex molecules, the current protocol provides an alternative but more practical approach from the readily available racemic starting materials, which is free from the repetitive reduction/oxidation steps in the enzymatic resolution or the indispensable stoichiometric amount of chirality-induction reagents.

Asymmetric domino 1,6-addition/annulation reaction of 3-cyano-4-alkenyl-2H-chromen-2-ones with isatin-derived MBH carbonates: enantioselective synthesis of 3,3′-cyclopentenylspirooxindoles bearing 2H-chromen-2-ones

An asymmetric domino 1,6-addition/annulation reaction of 3-cyano-4-alkenyl-2H-chromen-2-ones with isatin-derived MBH carbonates was achieved by using a modified cinchona alkaloid as a catalyst.

1,3-Dipolar cycloaddition of nitrones to oxa(aza)bicyclic alkenes

A new 1,3-dipolar cycloaddition of oxa(aza)bicyclic alkenes with nitrones has been developed without any catalyst and additive under mild conditions. The proposed concerted mechanism is investigated by DFT calculations of the reaction pathways.

The catalytic asymmetric synthesis of CF3-containing spiro-oxindole–pyrrolidine–pyrazolone compounds through squaramide-catalyzed 1,3-dipolar cycloaddition

Pharmaceutically important compounds were synthesized through the organocatalytic 1,3-dipolar cycloaddition reaction.

Recent advances in the synthesis of C2-spiropseudoindoxyls

This review summarizes the recent development of novel approaches to construct structurally unique oxindoles featuring a spirocycle at the C2 position.

The asymmetric construction of CF3-containing spiro-thiazolone-pyrrolidine compoundsvia[3 + 2] cycloaddition

An organocatalytic method for the asymmetric construction of CF₃-containing spiro-thiazolone-pyrrolidine compounds has been developed.

A [3+2] cycloaddition reaction for the synthesis of spiro[indoline-3,3′-pyrrolidines] and evaluation of cytotoxicity towards cancer cells

A new type of azomethine ylides, which was in situ generated by the reaction of ethyl glycinate hydrochloride and dimethyl acetylenedicarboxylate, reacted with 3-phenacylideneoxindoline-2-ones in ethanol to give polysubstituted spiro[indoline-3,3′-pyrrolidines] in good yields.

Ligand-controlled switch in diastereoselectivities: catalytic asymmetric construction of spirocyclic pyrrolidine-azetidine/oxe(thie)tane derivatives

An asymmetric [3+2] cycloaddition of azomethine ylides with four-membered ring-containing dipolarophiles was developed, and either exo or endo spirocyclic pyrrolidine-azetidine/oxe(thie)tanes were obtained.

Asymmetric synthesis of polycyclic 3-fluoroalkylproline derivatives by intramolecular azomethine ylide cycloaddition

The asymmetric intramolecular dipolar cycloaddition of azomethine ylides was developed for fluorinated dipolarophiles, being the RF group crucial for selectivity.

Highly efficient enantioselective synthesis of bispiro[benzofuran-oxindole-pyrrolidine]s through organocatalytic cycloaddition

The first organocatalyzed [3 + 2] cyclisation of N-2,2,2-trifluoroethylisatin ketimines with aurones has been developed.

Organocatalyzed asymmetric formal [3 + 2] cycloaddition of isocyanoacetates withN-itaconimides: facile access to optically active spiropyrroline succinimide derivatives

This reaction provides facile access to a variety of optically active spiropyrroline succinimide derivatives in moderate to good yields and good to excellent stereoselectivities.

Regiodivergent Synthesis of Pyrazolines with a Quaternary Carbon Center via Cycloaddition of Diazoesters to N-Purine-Substituted Allenes

Diversity-oriented synthesis of pyrazoline derivatives that contain a quaternary carbon center has been achieved via the 1,3-dipolar cycloaddition between N-purine-substituted allenes and α-alkyl/aryl diazoesters. Using Pd₂(dba)₃ as a catalyst, only 1-pyrazoline derivatives are produced in a regioselective manner. When DPPB is used as a catalyst, diverse 1-pyrazolines and 2-pyrazolines are obtained in moderate to good total yields.

Diastereoselective synthesis of dispirooxindoles via [3+2] cycloaddition of azomethine ylides to 3-phenacylideneoxindoles and evaluation of their cytotoxicity

The three-component reaction of 1,2,3,4-tetrahydroisoquinoline, isatins and 3-phenacylideneoxindoles in refluxing ethanol afforded dispiro[indoline-3,1'-pyrrolo[2,1-a]isoquinoline-3',3'-indolines] (4a-4x) in good yields via 1,3-dipolar cycloaddition of in situ generated azomethine ylide with the exocyclic double bond of 3-phenacylideneoxindoles. 1H NMR spectra and single crystal structures indicated the reaction has high regioselectivity and diastereoselectivity. Furthermore, their biological activities have been preliminarily demonstrated by in vitro evaluation against mouse breast cancer cells 4T1 and human liver cancer cells HepG2 by MTT assay. The results demonstrated that some of the compounds showed cytotoxicities to cell lines of 4T1 and HepG2, and indicated that novel spirooxindoles may become potential lead compounds for further biological screenings of their medicinal applications.

Catalytic asymmetric synthesis of spirooxindoles: recent developments

The past four years have witnessed significant developments in the field of the catalytic asymmetric synthesis of spirooxindoles, and this feature article outlines the recent progress in this area, including the contributions of our group. This article is divided into sections according to the size and type of the generated spiro-ring fused at the C3-position of the oxindole core.

Diastereoselective construction of pyrrolo[2,1-a]isoquinoline-based bispirooxindoles through a three-component [3 + 2] cycloaddition

An efficient and highly diastereoselective three-component one-pot [3 + 2] cycloaddition of isatins, 1,2,3,4-tetrahydroisoquinolines and methyleneindolinones has been developed to afford a wide range of pyrrolo[1,2-a]isoquinoline-based bispirooxindoles in up to 91% yields.