Accessing Dihydroazepines and Cyclopentanes from Enynyl Ketones.

The stereocontrolled construction of polycyclic architectures from linear precursors remains a significant challenge, particularly for medium-sized rings, where strain and conformational flexibility hinder efficient cyclization. Herein, we report a tandem cyclization strategy converting linear precursors to polysubstituted dihydroazepines. The resulting compounds undergo acid-promoted ring contraction to cyclopentanes with five contiguous stereocenters. Overall, this strategy provides a streamlined route to architecturally sterically congested azepine- and cyclopentane-fused dihydrofuran products with a broad substrate scope and functional group tolerance.