Enantioselective Synthesis of Fused Bicyclic Cyclohexadienes by Rh/Si-SDP-Catalyzed [2 + 2 + 2] Cycloaddition of 1,6-Diynes with Acrylamides or Enamides

[2 + 2 + 2] Cycloaddition reactions have emerged as one of the most powerful approaches for constructing highly substituted six-membered rings. However, enantioselective [2 + 2 + 2] cycloadditions catalyzed by transition metal catalysts and chiral ligands are often limited by narrow substrate scopes and insufficient catalyst/ligand diversity. In this study, we employ an innovative Si-centered spirodiphosphine (Si-SDP) ligand that enables Rh-catalyzed asymmetric [2 + 2 + 2] cycloadditions of 1,6-diynes with 2π-components; this achieves high yields and enantioselectivities (up to 99% ee). The Rh/Si-SDP catalyst has broad substrate versatility and functional group tolerance and enables the synthesis of more than 60 examples of cyclohexadienes bearing chiral centers with carbon or nitrogen substituents. The incorporation of silicon at the center of the spirodiphosphine ligand is crucial for high catalytic activity and stereoselectivity. This work highlights the potential of the Rh/Si-SDP catalytic system for synthesizing complex chiral molecules and addresses the challenging problems in asymmetric catalysis.