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

This work describes\nthe development of the first enantioselective\naddition reaction between 1,3,5,7-tetramethyl-BODIPYs and isatin derivatives.\nThe reaction utilizes bifunctional quinine/squaramide organocatalysts\nand affords nine novel chiral BODIPY dyes under mild conditions, with\nenantioselectivities reaching up to 60%. The synthesized BODIPY–oxindoles\nexhibit high fluorescence emissions, consistent with their parent\nBODIPYs, and display tunable colors. A representative example demonstrates\na remarkably high quantum yield of 0.78 compared to fluorescein. Notably,\nthe newly created carbon-stereocenter on the isatin skeleton induces\ndetectable asymmetry in the electronically decoupled BODIPY chromophore.\nThis is confirmed by the presence of Cotton effects in the visible\nregion of the electronic circular dichroism (ECD) spectra. Density\nFunctional Theory calculations suggested that the model oxindole <b>3aa</b> adopts an (<i>R</i>) absolute stereochemical\nconfiguration, unveiling key interactions between the catalyst and\nsubstrates.