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.