Deoxofluorination

Deoxofluorination is a chemical transformation in which a carbonyl group, typically present in aldehydes and ketones, is converted into a difluoromethylene moiety by replacing the carbonyl oxygen with two fluorine atoms. The result is a difluorinated carbon center, described as converting C=O to C–F2, and the method is valued for its ability to install difluoromethylene units into small molecules and complex structures.

Most widely used reagents are diethylaminosulfur trifluoride (DAST) and Deoxo-Fluor, along with related fluorinating systems such as XtalFluor reagents. These reagents react with aldehydes and ketones under controlled temperatures to give difluoromethylene products. The mechanism involves formation of an activated intermediate that transfers fluorine to the carbonyl carbon, followed by loss of a leaving group to furnish the C–F2 unit.

Applications include medicinal chemistry and agrochemistry, where the CF2 group is used to modulate lipophilicity, metabolic stability, and conformational properties of compounds. The difluoromethylene motif can serve as a bioisostere for carbonyl-containing moieties and as a handle for further synthetic elaboration.

Limitations and hazards: The reagents are moisture sensitive and can be hazardous, with potential for exothermic decomposition and generation of hydrogen fluoride. Reactions can be sensitive to substitution and may give rearrangements or overfluorination under forcing conditions. Workups and purifications require appropriate safety measures and ventilation.