Air- and light-stable electrophilic difluoromethylating reagents, S-(difluoromethyl)- S-phenyl- S-(2,4,6-trialkoxyphenyl) sulfonium salts were successfully developed, and the introduction of intramolecular hydrogen bonds plays a crucial role for the stabilities and reactivities of these reagents. C-selective difluoromethylation of a broad range of β-ketoesters and malonates proceeded smoothly under mild reaction conditions to give good to excellent yields with excellent C/O regioselectivities.