Enantioselective [4 + 2] Cycloaddition Enabled by Sequential Photoinduced [1,3]‐Silyl Migration and Isothiourea Catalysis

Comprehensive Summary Chiral isothioureas represent a highly efficient class of organocatalysts, which can activate substrates such as anhydrides, esters, and ketenes to generate C(1)‐ammonium enolate intermediates, and have been widely used in the construction of chiral heterocyclic compounds and biologically active molecules. However, the accessible C(1)‐ammonium enolate intermediates are largely limited to those bearing hydrogen, alkyl, or aryl substituents. The corresponding oxygen‐substituted variants, which would provide valuable access to α‐hydroxy ketone motifs, remain inaccessible due to the scarcity of suitable starting materials. α‐Ketoacylsilanes can undergo photoinduced [1,3]‐silyl migration to in situ generate siloxyketenes, providing a new strategy for the construction of oxy‐substituted ketene intermediates. Herein, we developed an enantioselective [4+2] cycloaddition reaction combining sequential photoinduced [1,3]‐silyl migration and isothiourea catalysis. Under the irradiation of blue LEDs at room temperature, α‐ketoacylsilanes and acyclic azadienes were used as readily available substrates, with chiral HyperBTM as the optimal catalyst to realize highly stereoselective cycloaddition. The reaction features mild reaction conditions, operational simplicity, a broad substrate scope, and generates structurally diverse chiral dihydropyridinone derivatives in good yields (up to 88%) with high enantioselectivities (up to 99% ee). This transition‐metal‐free methodology not only expands the scope of C(1)‐ammonium enolates but also provides a new and reliable platform for the construction of δ‐lactam scaffolds bearing chiral tertiary alcohol motifs.