Domino Ring‐Opening Cyclization of Aziridines with Isatogens: A Stereoselective Synthetic Route to Fluorescent Tetrahydrooxadiazino[2,3‐ a ]indolones

A highly regio‐ and stereoselective Cu(I)‐catalysed domino ring‐opening cyclisation (DROC) of activated aziridines with isatogens has been developed, providing access to tricyclic fluorescent tetrahydrooxadiazino[2,3‐ a ]indolones bearing a substituted quaternary carbon center. The reaction proceeds under mild conditions, delivering products in up to 99% yield with excellent diastereo‐ (up to 99% dr ) and enantioselectivity (99% ee for non‐racemic aziridines). A representative one‐pot sequence merging nitroalkyne cycloisomerisation with DROC of aziridines further demonstrates the versatility of this methodology. The resulting heterocycles display promising photophysical properties, including UV–visible absorption, fluorescence emission, and lifetime measurements, as well as pronounced solvatochromism. Cyclic voltammetry was employed to estimate electrochemical band gaps and HOMO–LUMO energy levels, and the compounds exhibit high fluorescence efficiency (quantum yields up to 0.6), highlighting their potential for opto‐electronic applications.