Enantioselective Addition of 1,3,5,7-Tetramethyl-BODIPYs to Isatins by Bifunctional Quinine-Based Squaramides

This work describes the development of the first enantioselective addition reaction between 1,3,5,7-tetramethyl-BODIPYs and isatin derivatives. The reaction utilizes bifunctional quinine/squaramide organocatalysts and affords nine novel chiral BODIPY dyes under mild conditions, with enantioselectivities reaching up to 60%. The synthesized BODIPY-oxindoles exhibit high fluorescence emissions, consistent with their parent BODIPYs, and display tunable colors. A representative example demonstrates a remarkably high quantum yield of 0.78 compared to fluorescein. Notably, the newly created carbon-stereocenter on the isatin skeleton induces detectable asymmetry in the electronically decoupled BODIPY chromophore. This is confirmed by the presence of Cotton effects in the visible region of the electronic circular dichroism (ECD) spectra. Density Functional Theory calculations suggested that the model oxindole 3aa adopts an (R) absolute stereochemical configuration, unveiling key interactions between the catalyst and substrates.

Tandem Condensation-Cycloaddition of Propargylic Amines with α-Azido Ketones and β-Alkoxy-γ-Azido Enones

α-Azido ketones and their vinylogous relatives β-alkoxy-γ-azido enones are versatile building blocks for constructing diverse heterocyclic products, but are prone to azide decomposition. Here, we report their condensation with propargylic amines and investigate the fate of the intermediate azido-enamine condensation products, both experimentally and theoretically. Efficient intramolecular cycloaddition was observed for electron-poor azide substrates, and a range of diversely substituted [1,2,3]triazolo[1,5-a]pyrazine products is reported. For electron-rich substrates, azide decomposition predominated. Computational modeling of possible pathways from the azido-enamine intermediates revealed two alternative mechanisms for azide decomposition, which were consistent with observed side products.

Enantioselective synthesis of 2,3-dihydrofurans using a bifunctional quinine/squaramide organocatalyst

Enantioselective synthesis of 2,3-dihydrofurans is carried out via domino type Michael/SN2 reactions using α-bromonitroalkenes and 1,3-dicarbonyl compounds catalyzed by a quinine/squaramide organocatalyst.

Organocatalytic enantioselective synthesis of dihydronaphthofurans and dihydrobenzofurans: reaction development and insights into stereoselectivity

Squaramide/cinchona alkaloid-derived bifunctional organocatalysts are in high demand in asymmetric transformations.

An enantioselective aza-Friedel-Crafts reaction of 5-aminoisoxazoles with isatin-derived N-Boc ketimines

By employing a chiral phosphoric acid as a catalyst, an enantioselective aza-Friedel-Crafts reaction of 5-aminoisoxazoles with isatin-derived N-Boc ketimines was realized. The reaction provided a wide variety of novel 3-isoxazole 3-amino-oxindoles with good yields (up to 99%) and moderate to good enantioselectivities (up to 99%). The absolute configuration of one product was assigned by X-ray crystal structural analysis and a plausible reaction mechanism was proposed. In addition, a scale-up reaction was performed successfully. Finally, one product was subjected to Suzuki-Miyaura coupling with phenylboronic acid to afford the product in a moderate yield without erosion of the enantioselectivity.

A Bispidine-Based Chiral Amine Catalyst for Asymmetric Mannich Reaction of Ketones with Isatin Ketimines

A unique chiral amine organocatalyst with a bispidine structure was found to be efficient for the diastereo- and enantioselective Mannich reaction of isatin ketimines with ketones. A series of 3-substituted 3-amino-2-oxindoles bearing vicinal tertiary and quaternary chiral stereogenic centers were obtained in excellent yields with excellent dr and ee values. The gram-scale synthesis and transformation of the product showed the practicability of this methodology. In addition, a possible transition state model was proposed to explain the origin of the stereoselectivity.

Recent advances in the catalytic synthesis of 3-aminooxindoles: an update

3-Substituted-3-aminooxindoles are versatile scaffolds and these motifs constitute the core structure of number of natural products and biologically active compounds.