Zinc-Mediated Radical-Type Cross-Electrophile Couplings of Trifluoromethyl Alkenes with Alkyl Iodides for Accessing gem-Difluoroalkenes in Aqueous Media

The cross-electrophile couplings of trifluoromethyl alkenes with alkyl iodides could be successfully realized in aqueous media in the presence of Zn powder, CuI, and TBAI. The defluorinative reactions proceeded effectively at ambient temperature under transition metal catalyst-free conditions via C-F bond cleavage to afford a broad range of synthetically useful gem-difluoroalkenes in moderate to excellent yields. Both wide substrate generality (broadly applicable to primary, secondary, and tertiary alkyl iodides) and excellent functional group compatibility could be achieved. Control experiments disclosed that the employment of zinc(0) powder as a metal promoter, copper(I) iodide and TBAI as additives, and H2O/THF (2:1) as reaction solvent are all critical for the efficient progress of the defluorinative couplings; without any of them, the reaction either could not occur or proceeded very sluggishly. Preliminary mechanistic explorations indicated that a radical-type mechanism might be involved in the transformation. The present method employing earth-abundant and environmentally benign water as reaction medium not only meets the requirement of sustainable chemistry but also functions as an appealing surrogate to existing methodologies for the facile entry to value-added gem-difluoroalkenes.