An in situ masking strategy enables radical monodecarboxylative C–C bond coupling of malonic acid derivatives

The utilization of malonic acids in radical decarboxylative functionalization is still underexploited, and the few existing examples are primarily limited to bisdecarboxylative functionalization. While radical monodecarboxylative functionalization is highly desirable, it is challenging because of the difficulty in suppressing the second radical decarboxylation step. Herein, we report the successful radical monodecarboxylative C–C bond coupling of malonic acids with ethynylbenziodoxolone (EBX) reagents enabled by an in situ masking strategy, affording synthetically useful 2(3H)-furanones in satisfactory yields. The keys to the success of this transformation include (1) the dual role of a silver catalyst as a single-electron transfer catalyst to drive the radical decarboxylative alkynylation and as a Lewis acid catalyst to promote the 5-endo-dig cyclization and (2) the dual function of the alkynyl reagent as a radical trapper and as an in situ masking group. Notably, the latent carboxylate group in the furanones could be readily released, which could serve as a versatile synthetic handle for further elaborations. Thus, both carboxylic acid groups in malonic acid derivatives have been well utilized for the rapid construction of molecular complexity.