Silver-Catalyzed Unusual Cyclization and Skeletal Rearrangement to Selectively Synthesize 2D Benzo[a]fluorenones and 3D Barbaralone Rings

A silver-catalyzed strategy that divergently constructs either planar benzo[a]fluorenones or three-dimensional barbaralones from common alkynol precursors, governed solely by ligand and silver salt, is reported. This protocol enables rapid molecular complexity enhancement (up to a 91% yield). In addition, mechanistic studies suggest that the alkalinity of silver salt is the key point to distinguish the two types of reaction and binuclear silver complexes would be more likely to be a transition state rather than the radical species. The cyclic spatial configuration of Meldrum's acid can form a stable binuclear complex with silver salts, promoting the reconstruction of the bridged ring.