Organohalogenite-Catalyzed Spiroketalization: Enantioselective Synthesis of Bisbenzannulated Spiroketal Cores

A new core structure-motivated strategy for the intramolecular aromatic spiroketalization process was found and used for the enantioselective synthesis of bisbenzannulated spiroketals, the bioactive core of rubromycins, with high levels of enantioselectivity (up to 98% ee) via an organohalogenite-mediated asymmetric intramolecular aromatic spiroketalization. This is the first organocatalytic method for the construction of optically pure bisbenzannulated spiroketals.