Enantioselective Synthesis of Dihydrospiro[indoline-3,4′-pyrano[2,3-c]pyrazole] Derivatives via Michael/Hemiketalization Reaction

Enantioselective Synthesis of Spirooxindole-Pyran and Furan Scaffolds via Copper-Catalyzed Formal (3+3) and (3+2) Cycloaddition of Isatin-Derived Propargylic Esters

Herein, we report a copper-catalyzed enantioselective formal (3+3) and (3+2) cycloaddition reaction of isatin-derived tertiary propargylic esters with N,N-dimethylbarbituric acid and 4-hydroxycoumarins, respectively. In this process, the tertiary propargylic ester serves as both C3- and C2-synthons, facilitating the synthesis of optically active spirooxindole-pyran and furan scaffolds featuring an all-carbon quaternary stereocenter. The reaction delivers these spirocyclic frameworks in good yields with high enantioselectivities. Additionally, the scalability of both the reactions and the transformation of chiral intermediates into valuable structures emphasize the synthetic and practical importance of this strategy.

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 Construction of Tetrahydro-Dispiro[indolinone-3,2'-pyran-5',4″-pyrazolone] Scaffolds via an Oxa-Michael Cascade [4 + 2] Annulation Reaction

A straightforward metal-free oxa-Michael cascade [4 + 2] annulation reaction was established between isatin-derived Morita-Baylis-Hillman (Is-MBH) alcohols with alkylidene pyrazolones to access structural diverse tetrahydro-dispiro[indolinone-3,2'-pyran-5',4″-pyrazolone] scaffolds bearing two tertiary and two quaternary stereocenters. The Is-MBH alcohol was utilized as an oxa-Michael donor for the first time as a new approach in highly atom-economical transformations. This method offered a wide range of bioinspired novel tetrahydro-dispirooxindole-pyran-pyrazolone derivatives in excellent yields (up to 96%) and diastereoselectivities (up to >20:1) in a shorter reaction time (15 min).

Organocatalytic Asymmetric Inverse-Electron-Demand Diels-Alder Reaction between Alkylidene Pyrazolones and Allyl Ketones: Access to Tetrahydropyrano[2,3-c]pyrazoles

Herein we report a catalytic asymmetric inverse-electron-demand Diels-Alder reaction between alkylidene pyrazolones and allyl ketones. Allyl ketone gets activated by a bifunctional thiourea catalyst and acts as a dienolate in this reaction. The trisubstituted tetrahydropyrano[2,3-c]pyrazoles were obtained in moderate to good yields with high diastereo- and enantioselectivities. Few applications, including a decarbonylation reaction, have been demonstrated.

Access to Spirooxindole-Fused Cyclopentanes via a Stereoselective Organocascade Reaction Using Bifunctional Catalysis

The present study reports an asymmetric organocascade reaction of oxindole-derived alkenes with 3-bromo-1-nitropropane efficiently catalyzed by the bifunctional catalyst. Spirooxindole-fused cyclopentanes were produced in moderate-to-good isolated yields (15-69%) with excellent stereochemical outcomes. The synthetic utility of the protocol was exemplified on a set of additional transformations of the corresponding spirooxindole compounds.

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.

Catalytic Efficiency of Primary α-Amino Amides as Multifunctional Organocatalysts in Recent Asymmetric Organic Transformations

Chiral primary α-amino amides, consisting of an adjacent enamine bonding site (Bronsted base site), a hydrogen bonding site (Bronsted acid site), and flexible bulky substituent groups to modify the steric factor, are proving to be extremely valuable bifunctional organocatalysts for a wide range of asymmetric organic transformations. Primary α-amino amides are less expensive alternatives to other primary amino organocatalysts, such as chiral diamines and cinchona-alkaloid-derived primary amines, as they are easy to synthesize, air-stable, and allow for the incorporation of a variety of functional groups. In recent years, we have demonstrated the catalytic use of simple primary α-amino amides and their derivatives as organocatalysts for the aldol reaction, Strecker reaction, Michael tandem reaction, allylation of aldehydes, reduction of N-Aryl mines, opening of epoxides, hydrosilylation, asymmetric hydrogen transfer, and N-specific nitrosobenzene reaction with aldehydes.

Synthesis, Characterization, and Cytotoxicity of New Spirooxindoles Engrafted Furan Structural Motif as a Potential Anticancer Agent

A new series of spirooxindoles based on ethylene derivatives having furan aryl moiety are reported. The new hybrids were achieved via [3 + 2] cycloaddition reaction as an economic one-step efficient approach. The final constructed spirooxindoles have four contiguous asymmetric carbon centers. The structure of 3a is exclusively confirmed using X-ray single crystal diffraction. The supramolecular structure of 3a is controlled by O···H, H···H, and C···C intermolecular contacts. It includes layered molecules interconnected weak C-H···O (2.675 Å), H···H (2.269 Å), and relatively short Cl···Br interhalogen interactions [3.4500(11)Å]. Using Hirshfeld analysis, the percentages of these intermolecular contacts are 10.6, 25.7, 6.4, and 6.2%, respectively. The spirooxindoles along with ethylene derivatives having furan aryl moiety were assessed against breast (MCF7) and liver (HepG2) cancer cell lines. The results indicated that the new chalcone 3b showed excellent activity in both cell lines (MCF7 and HepG2) with IC₅₀ = 4.1 ± 0.10 μM/mL (MCF7) and 3.5 ± 0.07 μM/mL (HepG2) compared to staurosporine with 4.3 and 2.92 folds. Spirooxindoles 6d (IC₅₀ = 4.3 ± 0.18 μM/mL), 6f (IC₅₀ = 10.3 ± 0.40 μM/mL), 6i (IC₅₀ = 10.7 ± 0.38 μM/mL), and 6j (IC₅₀ = 4.7 ± 0.18 μM/mL) exhibited potential activity against breast adenocarcinoma, while compounds 6d (IC₅₀ = 6.9 ± 0.23 μM/mL) and 6f (IC₅₀ = 3.5 ± 0.11 μM/mL) were the most active hybrids against human liver cancer cell line (HepG2) compared to staurosporine [IC₅₀ = 17.8 ± 0.50 μM/mL (MCF7) and 10.3 ± 0.23 μM/mL (HepG2)]. Molecular docking study exhibited the virtual mechanism of binding of compound 3b as a dual inhibitor of EGFR/CDK-2 proteins, and this may highlight the molecular targets for its cytotoxic activity.

Asymmetric Synthesis of Structurally Sophisticated Spirocyclic Pyrano[2,3-c]pyrazole Derivatives Bearing a Chiral Quaternary Carbon Center

A carbene-catalyzed enantio- and diastereoselective [2 + 4] cycloaddition reaction is developed for quick and efficient access to structurally complex multicyclic pyrano[2,3-c]pyrazole molecules. The reaction tolerates a broad scope of substrates bearing various substitution patterns, with the multicyclic pyrano[2,3-c]pyrazole products afforded in generally good to excellent yields and optical purities. The chiral molecules obtained from this approach has found promising applications in the development of novel bacteriacides for plant protection.

Chemo- and regioselective defluorinative annulation of (trifluoromethyl)alkenes with pyrazolones: synthesis and insecticidal activity of 6-fluoro-1,4-dihydropyrano[2,3-c]pyrazoles

The chemo- and regioselective defluorinative [3 + 3] annulation of (trifluoromethyl)alkenes and pyrazolones gives useful 6-fluoro-1,4-dihydropyrano[2,3-c]pyrazoles.

Enantioselective synthesis of functionalized 1,4-dihydropyrazolo-[4',3':5,6]pyrano[2,3-b]quinolines through ferrocenyl-phosphine-catalyzed annulation of modified MBH carbonates and pyrazolones

An enantioselective synthesis of highly functionalized 1,4-dihydropyrazolo[4',3':5,6]pyrano[2,3-b]quinolines from modified MBH carbonates and pyrazolones via a chiral phosphine-mediated alkylation/annulation sequence has been realized. The chiral dihydropyrano[2,3-c]pyrazoles bearing bio-active condensed heterocycles were facilely formed in good chemical yields and with high to excellent enantioselectivity by utilizing low catalyst loading.

Solvent-specific, DAST-mediated intramolecular Friedel-Crafts reaction: access to dibenzoxepine-fused spirooxindoles

A facile, DAST-mediated intramolecular cyclization of 3-hydroxy-3-(2-((3-methoxybenzyl)oxy)phenyl)indolin-2-one derivatives for the synthesis of spirooxindoles fused with dibenzoxepine moieties is described. The success of this reaction is highly dependent on the choice of solvent (promoted by DCM and 1,2-DCE) and the electronic nature of the pendant aromatic ring, which is favored by the presence of electron-donating substituents. The reaction is believed to proceed through an intramolecular Friedel-Crafts-type reaction. Various dibenzoxepine-fused spirooxindoles were successfully synthesized in up to 98% yield. This methodology provides libraries of structurally diverse and medicinally important small molecules that could aid in the search for new bioactive molecules.

DMAP Catalyzed Domino Rauhut-Currier Cyclization Reaction between Alkylidene Pyrazolones and Nitro-olefins: Access to Tetrahydropyrano[2,3-c]pyrazoles

Herein, we employ unsaturated pyrazolones in the Rauhut-Currier reaction for the first time. A domino Rauhut-Currier cyclization reaction has been developed between unsaturated pyrazolones and nitro-olefins. The trisubstituted tetrahydropyrano[2,3-c]pyrazoles were obtained in moderate to high yields with excellent diastereoselectivities. A few applications including a synthesis of disubstituted tetrahydropyrano[2,3-c]pyrazole have been demonstrated. A preliminary catalytic asymmetric version of this process was also studied with chiral DMAP catalysts.

Stereoselective synthesis and applications of spirocyclic oxindoles

This review summaries recent synthetic developments towards spirocyclic oxindoles and applications as valuable medicinal and synthetic targets.

Recent advances in reactions promoted by amino acids and oligopeptides

During the last 20 years, Organocatalysis has become one of the major fields of Catalysis. Herein, we provide a recent overview on reactions where the use of amino acids and peptides as the organocatalysts was employed. All aspects regarding aldol reactions, Michael reactions, epoxidation, Henry reactions and many others that are crucial for the reaction conditions and reaction mechanisms are discussed.

Ligand Free One-Pot Synthesis of Pyrano[2,3-c]pyrazoles in Water Extract of Banana Peel (WEB): A Green Chemistry Approach

Here, we have developed a novel, simple, efficient, and green protocol for one-pot synthesis of pyrano[2,3-c]pyrazole using arylidene malononitrile and pyrazolone in Water Extract of Banana Peels (WEB) as a reaction medium at room temperature (r.t.). This is a green and general synthetic protocol without utilization of any toxic organic solvent, ligand, base that could be applicable for the wide substrate scope in good to excellent yields. This protocol has various advantages such as fast reactions, eco-friendly reaction conditions, easy isolation of the product without using column chromatography. The green chemistry matrices calculation like atom economy reaction, environmental factor, as well as process mass intensity indicates the eco-friendly nature of the protocol.

Access to highly enantioselective and diastereoselective spirooxindole dihydrofuran fused pyrazolones

Access to highly enantioselective and diastereoselective spirooxindole dihydrofuran fused pyrazolones from MBH-carbonates and pyrazole 4,5-diones.

Cascade annulation reaction (CAR): highly diastereoselective synthesis of pyranopyrazole scaffolds

An unprecedented domino protocol for the novel synthesis of highly diverse and functionalized tetrahydro pyranopyrazole scaffolds using chalcone epoxide has been reported for the first time. This synthetic protocol generates three consecutive stereogenic centres in a highly diastereoselective manner with the formation of vicinal diol and a quaternary carbon centre. A wide range of substrates were utilized for the scope of this methodology and provided very good yields of pyranopyrazoles. The pyranopyrazoles were also transformed into densely functionalized tetrasubstituted olefins.

An unprecedented domino protocol for the novel synthesis of highly diverse and functionalized tetrahydro pyranopyrazole scaffolds using chalcone epoxide has been reported.

Organocatalytic enantioselective conjugate addition of pyrazolin-5-ones to arylomethylidene malonates

An efficient asymmetric organocatalytic conjugate addition reaction of pyrazolin-5-ones with arylomethylidene malonates has been successfully developed by employing bifunctional Cinchona derived thiourea organocatalysts. The protocol provides straightforward access to pyrazole substituted scaffolds in good yields with high stereocontrol.

Lewis base catalyzed regioselective cyclization of allene ketones or α-methyl allene ketones with unsaturated pyrazolones

A nitrogen-containing Lewis base catalyzed highly regioselective [4 + 2] cycloaddition of allene ketones or α-methyl allene ketones with unsaturated pyrazolones has been disclosed to give the corresponding tetrahydropyrano [2,3-c] pyrazoles in moderate to good yields under mild conditions. High regioselectivity, 100% atom-economy, broad substrate scope and good functional group tolerance are attractive features of this process and make it a practical and versatile transformation.