S _N 2′-Type Alkylation of <i>gem</i> -Dichlorocyclobutenones with Organotrifluoroborates Enabled by Organophotoredox Catalysis

Nucleophilic alkylation of <i>gem</i>-dichlorocyclobutenones with alkyl-organometallics is relatively challenging in accessing C(sp³)-enriched α-chlorocyclobutenones. Leveraging single-electron oxidation ability, herein, we report readily accessible alkyltrifluoroborates, enabling a photoinduced SOMOphilic allylic alkylation of <i>gem</i>-dichlorocyclobutenones under metal-free conditions. Additionally, alkene feedstocks are exploited as latent C(sp³) partners in this C(sp³)-C(sp³) bond-forming transformation. This reaction proceeds with high fidelity, expanding the previously limited scope of β-alkyl cyclobutenones beyond β-aryl analogues and enabling access to pharmaceutically relevant scaffolds. Conceptual DFT calculations rationalize the preferential α-radical addition over β-addition, alongside other experimental supports, including an EPR study, for the SET-mediated mechanism.