A Palladium-Catalyzed Cascade Double Annulation Strategy for Modular Access to Dihydrocyclopenta[]chromenes.

The cyclopentachromene skeleton is a key structural motif in pharmaceutical and fluorescent materials. We here introduce a Pd-promoted double ring-closure strategy for tackling the modular synthesis of densely functionalized dihydrocyclopenta[]chromenes, which proceeds simply from two reaction partners with high diversity. This scheme features a reaction sequence beginning with 1,6-conjugate addition of -alkynyl quinone methide, followed by annulation and migratory insertion. This approach is compatible with functional groups, providing a streamlined pathway to access complex five-membered ring-fused chromenes.