Asymmetric Trapping of Siloxyketenes In Situ Generated from [1,3]-Silyl Migration of α-Ketoacylsilanes: A Visible-Light-Driven Palladium-Catalyzed [4 + 2] Cycloaddition

The transition metal-catalyzed asymmetric [n + 2] cycloaddition reaction with oxy-substituted ketene intermediates remains a synthetic challenge due to the limited availability of suitable ketene precursors. Herein, we report a visible-light-driven, palladium-catalyzed asymmetric [4 + 2] cycloaddition of vinyl benzoxazinanones with siloxyketene intermediates, generating structurally diverse chiral quinolinone derivatives with satisfactory diastereo- and enantioselectivities. The transient generation of siloxyketenes from α-ketoacylsilylanes through visible-light-induced Brook rearrangement is important for the success of the present cycloaddition. The 13C-labeling experiments reveal a Brook rearrangement pathway involving a [1,3]-silyl migration process. The side arm effects of BOX ligand and silyl steric hindrance of α-ketoacylsilanes play crucial roles in the stereoselectivity control, and theoretical calculations provide crucial insights into the stereochemical outcome in the reaction.