An update on the progress of cycloaddition reactions of 3-methyleneindolinones in the past decade: versatile approaches to spirooxindoles

Highly regio- and stereoselective (3 + 2) annulation reaction of allenoates with 3-methyleneindolin-2-ones catalyzed by a planar chiral [2.2]paracyclophane-based bifunctional phosphine-phenol catalyst

A planar chiral [2.2]paracyclophane-based phosphine-phenol catalyst catalyzed the (3 + 2) annulation reaction of ethyl 2,3-butadienoate with 3-methyleneindolin-2-ones to produce 2,5-disubstituted cyclopentene-fused C3-spirooxindoles in high yields with high regio-, diastereo-, and enantioselectivities. This catalyst was suitable for reactions of not only benzylideneindolinones but also alkylideneindolinones, the chiral phosphine-catalyzed reactions of which have not yet been reported. Density functional theory calculations suggested that the formation of hydrogen bonds between the phenolic OH group of the catalyst and the allenoate carbonyl group, rather than between the OH group and the carbonyl group of indolinone, contributed to the formation of an efficient reaction space at the enantiodetermining step.

Metal-Free Regioselective Oxa-Michael Approach to Access Spirooxindole-Fused Tetrahydrofuran/Tetrahydropyran through [3 + 2]/ [4 + 2] Spirocyclization of Methyleneindolinones with Haloalcohols

An efficient one-pot metal-free, base-catalyzed method has been developed for the regioselective [3 + 2]/[4 + 2] annulation reactions of electrophilic methyleneindolinones with haloalcohols to furnish spirooxindole derivatives under mild reaction conditions. This reaction afforded the corresponding products with two contiguous stereocenters including a quaternary center in good to excellent yield (up to 95%) with moderate to good diastereoselectivities (up to 12.5:1 dr) with complete regioselectivity.

Construction of diazepine-containing spiroindolines via annulation reaction of α-halogenated N-acylhydrazones and isatin-derived MBH carbonates

A straightforward synthetic protocol for the efficient construction of diazepine-containing spiroindolines has been developed and proceeds through a by base-promoted annulation reaction of α-halogenated N-acylhydrazones and isatin-derived MBH carbonates. The reaction mechanism of this formal [4 + 3] annulation includes the in situ generated allylic ylide, nucleophilic substitution, Michael additon, and elimination processes. Additionally, the similar reaction with α-halogenated N-tosylhydrazones also afforded N-tosyl-substituted spiro[indoline-3,5'-[1,2]diazepine] in satisfactory yields. This protocol provides a convenient approach for the assembly of diverse highly functionalized spiro[indoline-3,5'-[1,2]diazepines] and also features a broad substrate scope, simple reaction conditions, and high molecular convergence.

Selective construction of dispiro[indoline-3,2'-quinoline-3',3''-indoline] and dispiro[indoline-3,2'-pyrrole-3',3''-indoline] via three-component reaction

A convenient synthetic procedure for the construction of novel dispirooxindole motifs was successfully developed by base-promoted three-component reaction of ammonium acetate, isatins and in situ-generated 3-isatyl-1,4-dicarbonyl compounds. The piperidine-promoted three-component reaction of ammonium acetate, isatins and the in situ-generated dimedone adducts of 3-ethoxycarbonylmethyleneoxindoles afforded mutlifunctionalized dispiro[indoline-3,2'-quinoline-3',3''-indoline] derivatives in good yields and with high diastereoselectivity. On the other hand, a similar reaction of the dimedone adducts of 3-phenacylideneoxindoles afforded unique dispiro[indoline-3,2'-pyrrole-3',3''-indoline] derivatives with a cyclohexanedione substituent. A plausible reaction mechanism is proposed to explain the formation of the different spirooxindoles.

Convenient Synthetic Protocols for Diverse Functionalized Dihydrobenzofuran-Fused Spiro-indanedione-oxindole Scaffolds

Diverse functionalized dihydrobenzofuran spiro-indanedione-oxindole scaffolds were conveniently synthesized by base-promoted cyclization reaction of Morita-Baylis-Hillman (MBH) carbonates of isatins and 2-(o-hydroxybenzylidene)-1,3-indanediones. The two diastereomeric dispiro[indene-2,1'-cyclopenta[b]benzofuran-2',3″'-indolines] could be selectively synthesized by using DABCO or DMAP as a base promoter. More importantly, DABCO or DMAP facilitated the annulation reaction of MBH formates of isatins and 2-(o-hydroxybenzylidene)-1,3-indanediones selectively, resulting in spiro[cyclopropa[c]chromene-1,2'-indene]-1',3'-diones or dispiro[indene-2,1'-cyclopenta[b]benzofuran-2',3″'-indolines]. Additionally, a similar reaction with MBH maleimides of isatins afforded dispiro[indene-2,5'-benzofuro[2',3':1,5]cyclopenta[1,2-c]pyrrole-4',3″'-indolines] in high yields and with high diastereoselectivity.

Regioselective synthesis and in vitro cytotoxicity evaluation of 3-thiooxindole derivatives: Tubulin polymerization inhibition and apoptosis inducing studies

Herein, regiospecific nucleophilic ring-opening of spiroaziridine oxindoles has been established to afford 3-substituted-thiooxindole derivatives as anticancer agents. Among the new series, compounds 7d and 9c exhibited promising cytotoxic activity toward HCT-116 cells with IC₅₀ values of 6.73 ± 0.36 and 6.64 ± 0.95 µM, respectively. Further, AO/EB, DCFDA, and DAPI staining studies were executed to establish the underlying apoptosis mechanism which displayed significant nuclear and morphological alterations. JC-1 staining and annexin V binding assay inferred the loss of mitochondrial membrane potential in HCT-116 cancer cells. Cell cycle analysis showed the treatment of 9c against HCT-116 cells, arrested the cell cycle in G2-M phase. In addition, tubulin binding assay revealed that compound 9c exhibited tubulin polymerase inhibition with IC₅₀ value of 9.73 ± 0.18 μM. This inhibition of tubulin polymerase was further supported by binding interactions of 9c with tubulin through docking studies on PDB ID: 3E22.

Stereoselective synthesis of CF3-containing spirocyclic-oxindoles using N-2,2,2-trifluoroethylisatin ketimines: an update

The introduction of fluorine-containing groups into organic molecules either changes or improves the characteristics of the target compounds. On the other hand, spirocyclic-oxindoles featuring C-3 functionalized sp3-hybridized carbon atoms of three-dimensional orthogonally shaped molecules were well recognized in the core structure of varied natural products and synthetic pharmaceutical targets. Consequently, the construction of spirooxindoles by an elegant synthetic approach with efficient stereocontrol has received tremendous interest over the past decades. In this context of the synergic combination of the features associated with fluorine-containing compounds and the synthetic and medicinal efficiency associated with spirooxindoles, the stereodivergent installation of CF3 groups embedded with spirooxindoles is of increasing academic and scientific interest. This mini-review article is dedicated to demonstrating a critical overview of the recent stereoselective synthesis of spirocyclic-oxindoles featuring trifluoromethyl groups by employing the reactivity of N-2,2,2-trifluoroethylisatin ketimines as an efficient and easily prepared synthon, and covers the literature reports from 2020 to date. Besides exploring the advancements accomplished in this area, we also investigate the limitations associated with reaction discovery, mechanistic rationalization, and future applications.

An Access to Highly Functionalized Dihydrobenzofuran Spirooxindole Scaffolds

We have developed an efficient protocol for the construction of polycyclic dihydrobenzofuran spirooxindole scaffolds via base promoted cascade annulation of Morita-Baylis-Hillman (MBH) carbonates of isatins with ortho-hydroxychalcones or ortho-hydroxy-β-nitrostyrenes. The complex polycyclic compounds were conveniently synthesized in satisfactory yields and with high diastereoselectivity. This protocol provides a swift and convenient approach for the assembly of diverse highly functionalized dihydrobenzofuran spirooxindoles and also features broad substrate scope, high molecular convergence, and excellent atomic economy.

Expeditious entry into carbocyclic and heterocyclic spirooxindoles

Spirocyclic frameworks have attracted synthetic practitioners due to their unique three-dimensional assembly, improved metabolic stability, solubility, and increased molecular complexity with regard to planar architectures. A recent surge in the number of spirocyclic oxindoles inhibiting enzymes, moderating unique protein-protein interactions, modulating receptors and transporters is testament to their prevalence. Against this background, the construction of spirocyclic frameworks containing an oxindole moiety as a torsional switch via stereoselective methods is in great demand. Herein we present a summary of the past three years in the progress of metal, organic molecule, nanostructured particle mediated, and even uncatalyzed versions of the highly diastereo- and enantioselective pathways leading to oxindole spirocycles.

Asymmetric α-Regioselective [3 + 2] Annulation of Morita-Baylis-Hillman Carbonates: Construction of Three Contiguous Stereocenters with Vicinal Quaternary Carbon Centers

Asymmetric α-regioselective annulation of MBH carbonates with 4-arylmethylisoxazol-5-ones has been developed to afford spirocyclic oxindole derivatives containing three contiguous stereogenic centers and vicinal all-carbon quaternary chiral centers. This reaction exhibits a broad substrate scope and excellent functional group tolerance. Excellent yields with high diastereo- and enantioselectivities were obtained in this efficient organocatalytic reaction.

Substrate-Controlled Regioselectivity Switchable [3 + 2] Annulations To Access Spirooxindole Skeletons

The additive-free [3 + 2] annulation from isatins, amino acids with 2-styrylbenzoxazoles, was described, providing a series of functional and structurally complex 3,3'-pyrrolidinyl-spirooxindole derivatives containing four contiguous and two quaternary stereogenic centers in high yields (up to 95%) and excellent diastereoselectivities (up to >25:1 dr). Interestingly, the reaction exhibits switchable regioselectivity depending on the substrate of amino acids. With proline or thioproline as the substrate, the reaction afforded α-regioselective spirooxindole skeletons. In contrast, when piperidine acid is the substrate, the reaction provided γ-regioselective spirooxindole skeletons.

Diastereoselective aldol-type interception of phenolic oxonium ylides for the direct assembly of 2,2-disubstituted dihydrobenzofurans

A Rh₂(OAc)₄ catalyzed intermolecular aldol-type interception of phenolic oxonium ylides with isatins has been developed, which provides an effective access to 2,2-disubstituted dihydrobenzofuran derivatives containing 3-hydroxyoxindole in high yields and with high diastereoselectivities under mild reaction conditions. The antiproliferation activity of these synthesized dihydrobenzofuran and 3-hydroxyoxindole hybrid products has been tested via the CCK8 assay in different cancer cell lines; compounds 3s and 3t exhibit good anticancer potency against human colon cancer cells (HCT116 cells, 3s: IC₅₀ = 15.99 μM; 3t: IC₅₀ = 14.48 μM) compared to other tested compounds.

Organocatalytic Regio- and Enantioselective [3 + 2]-Annulations of Ninhydrin-Derived Morita-Baylis-Hillman Carbonates with 3-Methyleneoxindoles

A type of Morita-Baylis-Hillman (MBH) carbonates has been developed from ninhydrin. These MBH carbonates have been successfully employed as 3C-synthons in the organocatalytic asymmetric [3 + 2]-annulations of the isatin-derived electron-deficient olefins, affording structurally diverse spirooxindoles in high yield with excellent stereoselectivity. In particular, the regioselectivity of MBH carbonates was controlled by the reaction partner, 3-methyleneoxindoles with carbonyl groups (R = ArCO), affording β-selective products and 3-methyleneoxindoles with ester groups (R = CO₂Me) furnishing γ-selective products. The representative scale-up reactions and transformation of product were examined. The reaction mechanism was expounded by control experiments.

Dithiocarbamation of spiro-aziridine oxindoles: a facile access to C3-functionalised 3-thiooxindoles as apoptosis inducing agents

Herein, we report the first dithiocarbamation of spiro-aziridine oxindoles involving regiospecific ring-opening by using in situ generated nucleophilic dithiocarbamates as an instant source of sulfur. This approach afforded C3-functionalised-3-thiooxindoles in good to excellent yields with a wide substrate scope under catalyst-free and mild reaction conditions. These compounds were screened for their anticancer activity against a panel of human cancer cell lines, wherein compound 3u exhibited significant cytotoxic activity against human lung cancer cells with an IC50 value of 4.31 ± 1.88 μM. Phase contrast microscopy as well as different staining assays such as acridine orange/ethidium bromide (AO/EB), DAPI and DCFDA demonstrated the induction of apoptosis in A549 lung cancer cells after treatment with compound 3u. In addition, the clonogenic assay and migration assay demonstrated the ability of compound 3u to inhibit colony formation and cell migration, respectively, in A549 cells in a dose-dependent manner.