Bench‐Stable S ‐(Monofluoromethyl)sulfonium Salts: Highly Efficient C ‐ and O ‐Regioselective Monofluoromethylation of 1,3‐Dicarbonyl Compounds

The new bench‐stable electrophilic monofluoromethylating reagents, S ‐(monofluoromethyl)‐S‐phenyl‐S‐(2,4,6‐trialkoxyphenyl)sulfonium salts, were successfully developed, which were readily prepared from inexpensive starting materials 1,3,5‐trimethoxybenzene and monofluoromethyl phenyl sulfoxides. The reactivity of these reagents was demonstrated through the C ‐ and O ‐regioselective monofluoromethylation of 1,3‐dicarbonyl compounds. Employing this reagent, a wide range of β‐keto esters easily underwent O ‐regioselective monofluoromethylation reaction to afford their corresponding O ‐monofluoromethylated products in good to excellent yields under mild reaction conditions. Contrastively, various malonates were smoothly transferred into their corresponding C ‐monofluoromethylated products in good to excellent yields under the standard reaction conditions.