Divergent Cyclization Reactions of Morita–Baylis–Hillman Carbonates of 2-Cyclohexenone and Isatylidene Malononitriles

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.

Formation of bis-spiropyrrolidines from isatin, secondary amines, and alkylidene Meldrum's acids

A catalyst-free synthesis of stable bis-spiropyrrolidines from isatin, secondary amines, and alkylidene Meldrum's acids in MeCN in 75-95% yield is described. The antioxidant and antimicrobial properties of the synthesized compounds are investigated. For this purpose, the radical scavenging activities of four derivatives were studied by radical trapping of diphenylpicrylhydrazine and ferric reduction power experiments. Disk diffusion test on Gram-positive and Gram-negative bacteria was employed to investigate antibacterial activities of five derivatives.

Four-component one-pot synthesis of novel dicyanoaniline anchored triazoles

A four-component reaction was developed by taking the advantage of the reactivity of the propargyl functional groups, residing on the primarily formed dicyanoaniline products. Various enolizable cyclic ketones were reacted with malononitrile and 4-(prop-2-yn-1-yloxy)benzaldehyde derivatives in an aqueous <i>t</i>-BuOH/NaOH medium, and the resulting dicyanoanilines were subjected to a subsequent in situ click reaction to afford the final dicyanoaniline-anchored-triazole products. The enhanced photophysical properties of the novel products are under current study.

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.

Stereoselective synthesis and applications of spirocyclic oxindoles

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

Phosphine-Catalyzed Asymmetric Umpolung Addition of Trifluoromethyl Ketimines to Morita-Baylis-Hillman Carbonates

A novel phosphine-catalyzed, highly enantioselective umpolung addition of trifluoromethyl ketimines to Morita-Baylis-Hillman carbonates was developed and it provides facile access to optically active trifluoromethyl amines with a chiral tertiary stereocenter under mild reaction conditions. The salient features of this reaction include general substrate scope, mild reaction conditions, good yields, high enantioselectivity, ease of scale-up to gram scale, and further transformations of the products.

A DBU-catalyzed Michael–Pinner–isomerization cascade reaction of 3-hydroxyoxindoles with isatylidene malononitriles: access to highly functionalized bispirooxindoles containing a fully substituted dihydrofuran motif

The first DBU-catalyzed Michael/Pinner/isomerization cascade reaction of 3-hydrooxindoles with isatylidene malononitriles was developed.

Catalyst-free [3 + 2] cyclization of imines and Morita–Baylis–Hillman carbonates: a general route to tetrahydropyrrolo[2,1-a]isoquinolines and dihydropyrrolo[2,1-a]isoquinolines

A mild and efficient catalyst-free [3 + 2] cyclization of isoquinoline imines and Morita–Baylis–Hillman carbonates has been developed.

Application of 7-azaisatins in enantioselective Morita-Baylis-Hillman reaction

7-Azaisatin and 7-azaoxindole skeletons are valuable building blocks in diverse biologically active substances. Here 7-azaisatins turned out to be more efficient electrophiles than the analogous isatins in the enantioselective Morita-Baylis-Hillman (MBH) reactions with maleimides using a bifunctional tertiary amine, β-isocupreidine (β-ICD), as the catalyst. This route allows a convenient approach to access multifunctional 3-hydroxy-7-aza-2-oxindoles with high enantiopurity (up to 94% ee). Other types of activated alkenes, such as acrylates and acrolein, could also be efficiently utilized.

Cupreines and cupreidines: an established class of bifunctional cinchona organocatalysts

Cinchona alkaloids with a free 6'-OH functionality are being increasingly used within asymmetric organocatalysis. This fascinating class of bifunctional catalyst offers a genuine alternative to the more commonly used thiourea systems and because of the different spacing between the functional groups, can control enantioselectivity where other organocatalysts have failed. In the main, this review covers the highlights from the last five years and attempts to show the diversity of reactions that these systems can control. It is hoped that chemists developing asymmetric methodologies will see the value in adding these easily accessible, but underused organocatalysts to their screens.