Stereocontrolled Assembly of Benzofulvenes and Dihydronaphthalenes via a Tandem Chromium Catalyzed NHK/Cyclization Cascade.

Functionalized benzofulvenes and dihydronaphthalenes are privileged scaffolds with profound utility in medicinal chemistry and materials science. However, their modular synthesis is often bottlenecked by a reliance on complex, pre-functionalized precursors and a persistent challenge to control exocyclic E/Z stereochemistry. Herein, we report a step-economical cascade methodology that successfully bridges reductive radical-involved carbonyl addition with Lewis acid-catalyzed cyclization. By orchestrating a one-pot, chromium-mediated tandem Nozaki-Hiyama-Kishi (NHK) coupling with Lewis acid-catalyzed cyclization, this protocol enables the rapid assembly of complex benzofulvenes and dihydronaphthalene directly from commercially abundant propargyl bromides and aromatic aldehydes or ketones. For benzofulvene synthesis, this cascade generates kinetically sensitive allenol intermediates strictly in situ-circumventing their isolation-and exerts rigorous thermodynamic control to deliver the exocyclic olefin with unprecedented >20:1 E/Z selectivity.