Pd-Catalyzed Formal [3 + 3] Heteroannulation of Allylic <i>gem</i>-Diacetates: Synthesis of Chromene-Based Natural Products and Exploration of Photochromic Properties
Prashant Kumar, Pravesh Kumar, Sugumar Venkataramani, S. S. V. Ramasastry
Abstract
Palladium-catalyzed allylic alkylation reactions of allylic gem-diacetates are rarely explored. This work unveils an unusual chemical reactivity pattern of allylic gem-diacetates and establishes them as new prototypes to synthesize complex benzo[f]chromene systems. Under the reaction conditions, the diacetates behave as 1,3-dicationic equivalents and undergo a [3 + 3] heteroannulation with 2-naphthols (and meta-substituted phenols) to produce novel polycyclic chromenes possessing spiro-, tri-, and tetrasubstituted carbon centers. The versatility of the method is demonstrated in the synthesis of several chromene-based bioactive natural products. Further, interesting photochromic properties of the new classes of benzo[f]chromenes are also discovered.