Chemoselective Divergence via Substrate Control: Decarboxylative and Decarbonylative Coupling of 2-Oxoacids with Allylic Difluorides

Herein, we report the photocatalytic decarboxylative coupling of allylic difluorides and carbon-centered radicals, which are formed from 2-oxoacids. This mild and operationally simple protocol enables selective synthesis of monofluoroalkenes via defluorinative C–C bond formation. Primary and aryl-substituted α-ketoacids undergo direct acyl radical addition to allylic difluorides, yielding exclusively acylated products. In contrast, secondary 2-oxoacids afford mixtures of acylated and alkylated products, while tertiary 2-oxoacids selectively deliver alkylated products via a decarboxylative/decarbonylation cascade. Thus, the product distribution can be tuned by the substitution pattern on the 2-oxoacid. The rate of decarbonylation vs radical addition is based on the stability and reactivity of the radical intermediate formed. Computational studies confirm a substrate-dependent divergence in reaction pathways, with primary 2-oxoacid undergoing direct acyl radical addition, while secondary and tertiary substrates exhibit competing decarbonylation leading to alkylated products. This study therefore helps establish a mechanistic rationale for the competitive acylation/alkylation processes.