K-10 Clay-Promoted Oxidative [3+3] Spiroannulation of Bromo-Isomerized MBH Isatin Adducts with Anthracene: A Versatile Route to Green, Orange Fluorophores and Domino Hydrogen Harvesting Method

Green-emissive spirooxindole fluorophores were efficiently synthesized through a K-10 clay-mediated [3+3] spiroannulation of bromine-isomerized Morita–Baylis–Hillman (MBH) adducts of isatin derivatives with anthracene. The transformation, conducted at 120 °C under metal-free conditions, furnished the desired products in excellent yields (82–88%) within 45 minutes. Additionally, a domino reductive cyclization led to a tetrahydrofuran-fused indole derivative, showcasing a novel hydrogen-harvesting transformation. Furthermore, the methodology was successfully extended to a double-side [3+3] annulation strategy, enabling access to bis-spiro frameworks. The synthetic approach and its photophysical consequences are elaborated in this communication, highlighting the potential of clay-driven catalysis for sustainable fluorophore development.