Recent Advances in Asymmetric Organocatalytic Construction of 3,3′-Spirocyclic Oxindoles

Quantitative structure-activity relationship and ADME prediction studies on series of spirooxindoles derivatives for anti-cancer activity against colon cancer cell line HCT-116

Forty-one derivatives of spirooxindoles, active against HCT-116 colon cancer cells, underwent pharmacophore-based 3D-QSAR analysis to understand their correlation with anti-cancer activity. The study identified a seven-point pharmacophore model (ADHHRRR1) and QSAR models, offering insights for lead optimization and novel analogue design, thus advancing anti-cancer drug discovery. This research underscores the value of molecular modeling in elucidating structure-activity relationships and enhancing drug development efforts.

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.

Copper-Catalyzed Tunable Oxygenative Rearrangement of Tetrahydrocarbazoles

Herein, we report a general copper-catalyzed method for the tunable oxygenative rearrangement of tetrahydrocarbazoles to cyclopentyl-bearing spiroindolin-2-ones and spiroindolin-3-ones. The method demonstrates excellent chemoselectivity, regioselectivity, and product control simply by using the H2O and O2 as oxygen source, respectively. This open-flask method is safe and simple to operate, and no other chemical oxidants are required. Besides, inspired from the unique pathway of 1, 2-migration rearrangement, a highly controllable hydroxylation of indoles for the construction of C3a-hydroxyl iminium indolines was also developed. Mechanistic experiments suggest that a single-electron transfer-induced oxidation process is responsible for the tunable selectivity control.

Enantioselective Synthesis of Spiro[cyclopentane-1,3'-oxindole] Scaffolds with Five Consecutive Stereocenters

A highly diastereo- and enantioselective cascade annulation reaction of Morita-Baylis-Hillman (MBH) maleimides of isatins with ortho-hydroxychalcones was achieved by a chiral N,N'-dioxide/Mg(II) complex Lewis acid catalyst. This strategy provides a concise and efficient route to densely functionalized spiro[cyclopentane-1,3'-oxindole] compounds with five consecutive stereocenters. The reaction itself features mild conditions, good functional group compatibility, and broad substrate scope (62 examples, up to 99% yield, up to >20:1 dr, 97% ee). In addition, an obvious ligand acceleration effect and chiral amplification effect were observed. DFT calculations were performed to elucidate the stereoselectivity observed. The gram-scale synthesis and the inhibitory effect of two products on the viability of A549 cells demonstrate the potential utility of the current method.

Spirooxadiazoline-oxindoles derived from imatinib show antimyeloproliferative potential in K562 cells

Imatinib mesylate was the first representative BCR-ABL1 tyrosine kinase inhibitor (TKI) class for the treatment of chronic myeloid leukemia. Despite the revolution promoted by TKIs in the treatment of this pathology, a resistance mechanism occurs against all BCR-ABL1 inhibitors, necessitating a constant search for new therapeutic options. To develop new antimyeloproliferative substances, we applied a medicinal chemistry tool known as molecular hybridization to design 25 new substances. These compounds were synthesized and biologically evaluated against K562 cells, which express BCR-ABL1, a constitutively active tyrosine kinase enzyme, as well as in WSS-1 cells (healthy cells). The new compounds are conjugated hybrids that contain phenylamino-pyrimidine-pyridine (PAPP) and an isatin backbone, which are the main pharmacophoric fragments of imatinib and sunitinib, respectively. A spiro-oxindole nucleus was used as a linker because it occurs in many compounds with antimyeloproliferative activity. Compounds 2a, 2b, 3c, 4c, and 4e showed promise, as they inhibited cell viability by between 45% and 61% at a concentration of 10 µM. The CC50 of the most active substances was determined to be within 0.8-9.8 µM.

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.

Synthesis of gem-Difluorinated Oxa/Azaspiro[2.4]heptanes via Palladium-Catalyzed Spirocyclopropanation

A palladium-catalyzed spirocyclopropanation of gem-difluoroalkenes with π-allylpalladium 1,4-dipoles has been successfully developed, which gives a powerful and straightforward synthetic strategy for the construction of novel gem-difluorinated spirocyclic compounds, 6,6-difluoro-5-oxa/azaspiro[2.4]heptanes. The scope of gem-difluoroalkenes can be extended to styrenes, acrylic esters, and acrylamides to realize the installment of various functional groups and different heteroatoms on the spirocyclic skeletons, which could be converted to valuable compounds with potential biological activity. The mechanistic investigations revealed the competition between spirocyclopropanation and β-F elimination of π-allylpalladium zwitterionic intermediates.

COAP-Pd Catalyzed Asymmetric Formal [3+2] Cycloaddition for Optically Active Multistereogenic Spiro Cyclopentane-Indandiones Bearing Cyclic N-Sulfonyl Ketimine Skeletons

We reported a chiral oxamide-phosphine ligand (COAP-Ph)-Pd-catalyzed asymmetric [3+2] cycloaddition reaction between vinyl cyclopropane compounds derived from 1,3-indanedione and 2-vinylcyclopropane-1,1-dicarboxylates with cyclic sulfonyl 1-azadienes. The corresponding reactions provided a series of enantiomerically active spiro cyclopentane-indandione and cyclopentane structures bearing three consecutive stereogenic centers in good yields with good diastereo- and enantioselectivity. The COAP-Pd complex serves not only to promote generation of chiral π-allyl-palladium intermediates and induce the asymmetry of the reaction, but also depress the background reaction.

Highly enantio- and diastereoselective construction of spirocyclic oxindoles via a palladium-catalyzed decarboxylative asymmetric [4 + 2] annulation strategy

A palladium-catalyzed decarboxylative asymmetric [4 + 2] annulation of methyleneindolinones with a zwitterionic oxo-1,4-dipole intermediate was successfully developed to access spirocyclic oxindoles bearing two vicinal stereocenters in good yields with high diastereoselectivities and enantioselectivities. This strategy features a broad substrate scope (28 examples), allowing for efficient scale-up. Further selective transformation of the product and preliminary mechanistic studies were conducted.

Enantioselective synthesis of spirooxindole-pyran derivatives via a remote inverse-electron-demand Diels-Alder reaction of β,γ-unsaturated amides

Novel construction methods for obtaining 3,4'-pyran spirooxindole heterocyclic skeletons have always been the focus of attention. Herein, we report a highly enantioselective inverse-electron-demand oxa-Diels-Alder cycloaddition reaction of a β,γ-unsaturated pyrazole amide and a N-diphenyl isatin-derived oxodiene using a bifunctional catalyst. In addition, large-scale experiments confirmed the reliability of the reaction. The resultant products of this study can be further transformed.

Asymmetric Tandem Michael Addition/Interrupted Nef Reactions of Nitromethane with Oxindole-Derived Alkenes: Enantioselective Synthesis of Spiro-polycyclic Oxindoles

Chiral spiro-polycyclic oxindoles are valuable heterocyclic ring systems that are widely distributed in natural alkaloids and biologically active compounds. Herein, we reported an asymmetric tandem Michael addition/interrupted Nef reaction of nitromethane with oxindole-derived alkenes catalyzed by a chiral 2-aminobenzimidazole bifunctional organocatalyst. A series of novel enantiomerically enriched spiro-polycyclic oxindole derivatives bearing an oxime group were synthesized in moderate to excellent isolated yields (up to 99%) with an excellent level of enantioselectivities (up to 99% ee). Furthermore, the antiproliferation activity of the resulting oxindoles derivatives were evaluated, and compound 2d demonstrated promising anticancer properties against HCT116 (IC50 = 14.08 μM) and HT29 (IC50 = 15.46 μM) cell lines.

Diastereoselective Three-Component 1,3-Dipolar Cycloaddition to Access Functionalized β-Tetrahydrocarboline- and Tetrahydroisoquinoline-Fused Spirooxindoles

A chemselective catalyst-free three-component 1,3-dipolar cycloaddition has been described. The unique polycyclic THPI and THIQs were creatively employed as dipolarophiles, which led to the formation of functionalized β-tetrahydrocarboline- and tetrahydroisoquinoline-fused spirooxindoles in 60-94% of yields with excellent diastereoselectivities (10: 1->99: 1 dr). This reaction not only realizes a concise THPI- or THIQs-based 1,3-dipolar cycloaddition, but also provides a practical strategy for the construction of two distinctive spirooxindole skeletons.

Catalytic Asymmetric Synthesis of 3,4'-Piperidinoyl Spirooxindoles via [3 + 3] Annulation of 3-Aminobenzofurans and Isatin-Derived Enals

A chiral NHC-catalyzed [3 + 3] cycloaddition reaction of 3-aminobenzofurans with isatin-derived enals has been documented, furnishing 3,4'-piperidinoyl spirooxindoles bearing a quaternary stereocenter with good yields and excellent enantioselectivities. Further gram-scale preparation and synthetic transformation of the cycloadducts to δ-amino acid derivative demonstrated good practicality and applicability of this reaction.

Substrate-directed divergent annulations of sulfur ylides: synthesis of functionalized bispirocyclopentane and bispirocyclopropane derivatives

Herein, an efficient, substrate-directed divergent [2 + 3]/[2 + 1] annulation of tetra-substituted oxa-dienes and allylic sulfur ylides has been successfully developed. Under precise annulation regulation, a series of functionalized bispirocyclopentane and bispirocyclopropane derivatives were synthesized in a highly stereoselective and economical manner (up to 95% yield, >20 : 1 dr or >20 : 1 E/Z). This protocol offers the advantages of mild conditions, high chemo-, regio- and diastereoselectivity and broad substrate compatibility. In addition, the synthetic practicality of this protocol was evaluated through a scale-up preparation and a series of three-component reactions utilizing in situ generated sulfur ylides.

Alkene carboamination/oxidative denitrogenation of 3-allyl-3-hydrazinylindolin-2-ones: one-pot entry to spirocyclopropyloxindoles

A one-pot protocol, consisting of a Pd-catalysed carboamination reaction, followed by N-deprotection and oxidative denitrogenation, has been developed for the synthesis of diversely substituted spirocyclopropyloxindoles, in yields up to 73% and with diastereoselectivity close to 1 : 1. Readily accessible starting materials, mild reaction conditions, an easy to operate one-pot procedure and good functional group tolerance make this transformation a versatile tool for the synthesis of substituted spirocyclopropyloxindoles. This protocol successfully works on the gram-scale and allows access to both diastereoisomers separately. A plausible mechanism was proposed, and a series of post-transformations were performed on the obtained products, showing their remarkable synthetic versatility.

Eco-friendly K-10 Clay-Mediated [3 + 3] Spiroannulation of Morita-Baylis-Hillman Adduct of Isatin with Anthracene: Synthesis of Green Fluorophore Compounds

An easy and simple spiroannulation of the Morita-Baylis-Hillman adduct of isatin derivatives with anthracene was achieved in moderate-to-good yields (37-75%). The spiroderivatives synthesized in this work exhibited green fluorescence properties. The reaction occurred in metal-free eco-friendly K-10 clay-mediated conditions. The final products have multiple structural features such as 3-spirooxindole, fluorophoric anthracene, phenanthracene, phenalene, and perylene cores.

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.

Sequential organo and metal catalyzed reaction between 3-pyrrolyloxindoles and linear nitroenynes: access to cyclic aza-spirooxindoles

An asymmetric Michael addition/hydroarylation reaction sequence, catalyzed by a sequential catalytic system consisting of a squaramide and a combination of silver and gold salts, provides a new series of cyclic aza-spirooxindole derivatives in excellent yields (up to 94%) and high diastero- and enantioselectivities (up to 7 : 1 dr, up to >99% ee). Computational study has also been performed.

Evaluation of antibiofilm properties of dehydroacetic acid (DHA) grafted spiro-oxindolopyrrolidines synthesized via multicomponent 1,3-dipolar cycloaddition reaction

The current work involves the use of dehydroacetic acid based chalcone derivatives for the synthesis of spirooxindole grafted pyrrolidine moieties. All the synthesized compounds have been characterized using spectroscopic techniques such as NMR (1H-NMR and 13C-NMR), IR, mass and elemental analysis. Molecular mechanics studies were performed to comprehend the regioselectivity in the product formation. Molecular docking of the synthesized compounds was performed with few bacterial proteins of Bacillus subtilis and Pseudomonas aeruginosa responsible for biofilm formation followed by molecular dynamics simulations with the potential lead compound. Further, to corroborate the results obtained via in silico study, anti-biofilm activity etc. of the synthesized compounds (4a-e) was checked for effectiveness against biofilm formation. Taken together, this study opens up to explore these compounds' multiple roles in diverse fields in the arena of medical sciences.

Engaging Isatins and Amino Acids in Multicomponent One-Pot 1,3-Dipolar Cycloaddition Reactions-Easy Access to Structural Diversity

Multicomponent reactions (MCRs) have undoubtedly emerged as the most indispensable tool for organic chemists worldwide, finding extensive utility in the synthesis of intricate natural products, heterocyclic molecules with significant bioactivity, and pharmaceutical agents. The multicomponent one-pot 1,3-dipolar cycloaddition reactions, which were initially conceptualized by Rolf Huisgen in 1960, find extensive application in contemporary heterocyclic chemistry. In terms of green synthesis, the multicomponent 1,3-dipolar cycloaddition is highly favored owing to its numerous advantages, including high step- and atom-economies, remarkable product diversity, as well as excellent efficiency and diastereoselectivity. Among the numerous pieces of research, the most fascinating reaction involves the utilization of azomethine ylides generated from isatins and amino acids that can be captured by various dipolarophiles. This approach offers a highly efficient and convenient method for constructing spiro-pyrrolidine oxindole scaffolds, which are crucial building blocks in biologically active molecules. Consequently, this review delves deeper into the dipolarophiles utilized in the 1,3-dipolar cycloaddition of isatins and amino acids over the past six years.

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.

Confronting the Challenge of Asymmetric Carbonyl Addition to Sterically Bulky Isatins: Upgrading Dirhodium(II)/Biphosphine Catalytic System

Catalytic asymmetric addition of arylboronic acids to ketones is a powerful transformation for directly delivering chiral tertiary alcohols. However, there is no successful example of enantioselective addition to steric bulky isatins, which contain bulky substituent at the 4-position. To confront this challenge, in this work a dirhodium/(BTFM-Garphos) system was developed that showed extremely high activity and stereoselectivity, and the reactions were usually finished within a few minutes.

Substrate-Controlled Diastereo- and Enantiodivergent Synthesis of Bis-Spirocyclopropyloxindoles from Available Isatin as a Single Starting Material

The first diastereo- and enantiodivergent asymmetric synthesis of new bis-spirocyclopropyloxindole scaffolds has been accomplished from the readily available isatin as a single starting material. Four rel-(1R,2R,3R), rel-(1S,2S,3R), rel-(1R,2R,3S), and rel-(1S,2S,3S) configurations of desired products were constructed in excellent enantiopurity via a simple switch in substrates using the chiral auxiliary-controlled method. The absolute configuration of cycloadducts with three contiguous quaternary/tertiary stereogenic centers was confirmed through X-ray diffraction analysis. A facile synthesis of versatile precursor 3-chlorooxindoles was also introduced.

Dipolarophile-Controlled Regioselective 1,3-Dipolar Cycloaddition: A Switchable Divergent Access to Functionalized N-Fused Pyrrolidinyl Spirooxindoles

N-fused pyrrolidinyl spirooxindole belongs to a class of privileged heterocyclic scaffolds and is prevalent in natural alkaloids and synthetic pharmaceutical molecules. To realize the switchable synthesis of divergent N-fused pyrrolidinyl spirooxindoles for further biological activity evaluation via a substrate-controlled strategy, a chemically sustainable, catalysis-free, and dipolarophile-controlled three-component 1,3-dipolar cycloaddition of isatin-derived azomethine ylides with diverse dipolarophiles is described in this work. A total of 40 functionalized N-fused pyrrolidinyl spirooxindoles were synthesized in 76-95% yields with excellent diastereoselectivities (up to >99:1 dr). The scaffolds of these products can be well-controlled by employing different 1,4-enedione derivatives as dipolarophiles in EtOH at room temperature. This study provides an efficient strategy to afford a spectrum of natural-like and potentially bioactive N-fused pyrrolidinyl spirooxindoles.

Trienamine catalysed unprecedented remote olefin E/Z isomerisation/[4 + 2]-cycloaddition reaction to access spirooxindole hexahydroindoles

Herein, for the first time, we report the asymmetric synthesis of an unexpected stereoisomer of spirohexahydroindole via a trienamine-catalysed remote olefin E/Z isomerisation/[4 + 2]-cycloaddition reaction. The reaction afforded a vast library of aesthetically pleasing spirooxindole hexahydroindole scaffolds with exceptional enantio- and diastereo-selectivities (up to 95% yield, 99% ee and >99 : 1 dr). In addition, we demonstrated the synthetic transformation of enantiomerically pure spirooxindole hexahydroindoles to synthesize alkyl homologated spirooxindole hexahydroindole and fluoro-pyranooctahydroindole moieties with four and seven contiguous stereocenters, respectively, in excellent yield and selectivities. We have also demonstrated the evidence for the proposed pathway through NMR investigations.

Photoinduced Synthesis of Functionalized Oxacyclic Spirooxindoles Via Ring Expansion

A versatile photochemical ring-expansion protocol for the synthesis of oxacyclic spirooxindoles under catalyst-free conditions is described. The reaction is enabled by the use of unstrained O-containing heterocycles with 3-diazoindolin-2-ones under visible-light irradiation. Several synthetic advantages for this method are exhibited, including mild conditions, good functional group tolerance, operational simplicity, and scalability. Mechanistic studies indicate that the transformation may proceed through the formation of oxonium ylide intermediate followed by an ionic cyclization.

Asymmetric synthesis of the perhydroepoxyethanoindole core via sequential [4 + 2]-addition/reduction/fluoroannulation reactions

Herein, we present the sequential aminocatalytic [4 + 2]-addition/reduction and fluoroannulation reactions to afford a novel class of bridged fluoro-perhydroepoxyethanoindole spiropyrazolone and fluoro-perhydroepoxyethanoindole spirooxindole moieties with six contiguous stereocenters. An array of perhydroepoxyethanoindole core derivatives (up to 31 examples) mimicking aspidosperma alkaloids were obtained with moderate to good yields and excellent enantio- and diastereo-selectivities (up to 69% overall yield, up to 99.9% ee and up to >20 : 1 dr). Furthermore, we have also disclosed the synthesis of the unexpected tribromo derivative of hexahydroepoxyethanoindole spiropyrazolone in a moderate yield with excellent selectivity by employing the developed protocol in sequential bromoannulation reactions.

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.

Asymmetric α-spirocyclopropanation of oxindoles and benzofuranones via dynamic kinetic resolution

Chiral benzo five-membered heterocyclic spirocyclopropanes are an important class of parent core structures with pharmacological activity. A novel organocatalytic one-pot cascade ether oxidation iminium-ion activation strategy for the asymmetric spirocyclopropylation of benzofuran-2-ones and indolin-2-ones from allyl tert-butyl ethers/ pent-2,4-dienyl ethyl ethers with excellent enantioselectivity (ee% up to > 99) and diastereoselectivity(dr.% up to 91:9) has been developed. This process involves the successful dynamic kinetic resolution of racemic 3-bromobenzofuran-2-ones or 3-bromoindolin-2-ones. Its synthetic application will provide a new aminocatalytic cascade tool for the efficient synthesis of complex molecules.

Efficient construction of diverse spiro[indoline-3,4'-pyrrolo[3,4-b]pyridines] via [3 + 3] cycloaddition of MBH carbonates of isatins with β-enamino maleimides

An efficient method to construct unique spiro[indoline-3,4'-pyrrolo[3,4-b]pyridines] was successfully developed via a DABCO promoted formal [3 + 3] cycloaddition reaction of MBH carbonates of isatins with β-enamino maleimides in acetonitrile at room temperature. This reaction afforded multifunctionalized spiro[indoline-3,4'-pyrrolo[3,4-b]pyridines] and spiro[dipyrrolo[3,4-b:3',4'-e]pyridine-8,3'-indolines] in good yields and with lower diastereoselectivity. The relative configuration of the two diasteromers of the spiro compounds was clearly elucidated by the determination of eight single crystal structures.

N-Heterocyclic Carbene-Catalyzed [3 + 2] Annulation of 3,3'-Bisoxindoles with α-Bromoenals: Enantioselective Construction of Contiguous Quaternary Stereocenters

An NHC-catalyzed enantio- and diastereoselective [3 + 2] annulation of α-bromoenals with bisoxindoles is developed, affording efficient access to various spirocyclic bisoxindole alkaloids. This protocol tolerates a broad substrates scope, with various spirocyclic bisoxindoles obtained in generally excellent enantioselectivities. More importantly, two contiguous sterically congested all-carbon quaternary stereocenters are successfully created during this process.

Cobalt-promoted synthesis of sulfurated oxindoles via radical annulation of N-arylacrylamides with disulfides

An efficient radical annulation of N-arylacrylamides with disulfides is developed for the synthesis of sulfurated oxindoles. The reaction occurs in a facile manner using CoBr₂ as both an initiator and a promoter for the first time and (NH₄)₂S₂O₈ as the oxidant. By controlling the CoBr₂/(NH₄)₂S₂O₈ ratio, a wide range of sulfurated and brominated/sulfurated oxindoles are selectively prepared in good to excellent yields. The present protocol is simple and highly atom economical, and can tolerate a broad range of substrates.

Dearomatizing Cyclization of 2-Iodoindoles by Oxidative NHC Catalysis to Access Spirocyclic Indolenines and Oxindoles Bearing an All Carbon Quaternary Stereocenter

An intramolecular dearomatizing spirocyclization of indoles by oxidative N-heterocyclic carbene catalysis is reported. C2-iodinated indoles are used as substrates in combination with aroyl azolium ions as acceptors, which provides C2-iodinated indolenines containing an all carbon quaternary stereocenter. The products are readily further C2-functionalized and give access to valuable oxindoles by simple hydrolysis in very good overall yields and excellent enantioselectivities.

Catalytic asymmetric Michael/cyclization reaction of 3-isothiocyanato thiobutyrolactone: an approach to the construction of a library of bispiro[pyrazolone-thiobutyrolactone] skeletons

Here, we demonstrate the first example of 3-isothiocyanato thiobutyrolactone serving as a useful building block in the Michael/cyclization reaction with alkylidene pyrazolones for the enantioselective construction of optically active structural bispiro[pyrazolone-thiobutyrolactone] skeletons containing three contiguous stereocenters with two spiroquaternary stereocenters. These products were smoothly afforded in up to 90% yield, >20 : 1 dr and >99% ee with chiral squaramide as the catalyst under mild conditions. Notably, this is also the first example of the merger of a spirocyclic pyrazolone scaffold with a spirocyclic thiobutyrolactone scaffold, potentially useful in medicinal chemistry.

Highly stereoselective synthesis of spirocyclopropylthiooxindoles and biological evaluation

We present a novel highly stereoselective Rh-catalyzed cyclopropanation of diazothiooxindoles with a broad range of α-functionalized styrenes, enabling facile access of chiral spirocyclopropylthiooxindoles in high to excellent enantiomeric excess.

Dinuclear zinc catalyzed asymmetric [3 + 2] spiroannulation for the synthesis of diverse bispirocyclic saccharines

A highly atom-economical and novel enantioselective [3 + 2] spiroannulation reaction of saccharine-derived cyclic 1-azadienes with α-hydroxy-1-indanones has been developed.

Diastereoselective construction of a library of structural bispiro[butyrolactone/valerolactone-pyrrolidine-indanedione] hybrids via 1,3-dipolar cycloaddition reactions

Herein, a highly efficient strategy that allows the diversity synthesis of a library of structural bispiro[butyrolactone-pyrrolidine-indanedione] hybrids is achieved effectively by means of 1,3-dipolar cycloadditions of α,β-unsaturated butyrolactones/valerolactones as dipolarophiles...