Photoinduced Boryl Radical-Promoted Stepwise Dehalogenative Functionalization of Polyhaloalkyl Groups

Partially halogenated alkyl motifs are prevalent in pharmaceuticals and functional materials, yet their synthesis via selective, stepwise dehalogenative functionalization of readily available polyhalogenated precursors constitutes a marked challenge. Furthermore, a general method capable of functionalizing C─F, C─Cl, and C─Br bonds under unified conditions has remained elusive because of their markedly different reactivities. Herein, we report a visible-light-driven, photocatalyst-free strategy for selective dehalogenative alkylation and hydrodehalogenation of polyhaloalkyl molecules across three C─X (X = F, Cl, or Br) bond types. The method relies on a unique photoactive complex formed from 4-dimethylaminopyridine (DMAP)-BH₃ and thiophenol through synergistic noncovalent interactions. Visible-light excitation triggers a previously unrecognized thiol-to-borane charge transfer, ultimately generating the DMAP-boryl radical for selective C─X bond activation. The protocol accommodates tetra-, tri-, and dihaloalkyl substrates with broad functional group tolerance. Sequential C─X bond functionalization further provides modular access to structurally diverse partially halogenated alkyl architectures. Time-resolved spectroscopic studies and density functional theory (DFT) calculations support the proposed mechanistic pathway.