Type I [4σ+4π] versus [4σ+4π−1] Cycloaddition To Access Medium‐Sized Carbocycles and Discovery of a Liver X Receptor β‐Selective Ligand

Transition-metal-catalyzed [4+4] cycloaddition leading to cyclooctanoids has centered on dimerization between 1,3-diene-type substrates. Herein, we describe a [4σ+4π-1] and [4σ+4π] cycloaddition strategy to access 7/8-membered fused carbocycles through rhodium-catalyzed coupling between the 4σ-donor (benzocyclobutenones) and pendant diene (4π) motifs. The two pathways can be controlled by adjusting the solvated CO concentration. A broad range (>40 examples) of 5-6-7 and 5-6-8 polyfused carbocycles was obtained in good yields (up to 90 %). DFT calculations, kinetic monitoring and