The
effects of the CF2H moiety on H-bond (HB) acidity
and lipophilicity of various compounds, when attached directly to
an aromatic ring or to other functions like alkyls, ethers/thioethers,
or electron-withdrawing groups, are discussed. It was found that the
CF2H group acts as a HB donor with a strong dependence
on the attached functional group (A = 0.035–0.165).
Regarding lipophilicity, the CF2H group may act as a more
lipophilic bioisostere of OH but as a similar or less lipophilic bioisostere
of SH and CH3, respectively, when attached to Ar or alkyl.
In addition, the lipophilicity of ethers, sulfoxides, and sulfones
is dramatically increased upon CH3/CF2H exchange
at the α position. Interestingly, this exchange significantly
affects not only the polarity and the volume of the solutes but also
their HB-accepting ability, the main factors influencing log P
oct. Accordingly, this study may be helpful
in the rational design of drugs containing this moiety.
A practical, convenient, and general method for the difluoromethylation of tertiary amines, using diethyl bromodifluoromethylphosphonate and fluoride, is described. This commercially available phosphonate smoothly reacts with a fluoride ion to liberate a difluorocarbene intermediate that in the presence of a proton source and a tertiary amine generates the corresponding α-difluoromethylammonium compound in good to excellent yields. Despite the involvement of a difluorocarbene intermediate, this difluoromethylation occurs almost exclusively on the nitrogen atom with diverse molecular structures, including drugs, surfactants, chiral phase transfer catalysts, polymers, ionic liquids, and other fine chemicals. A preliminary assessment of the effects that an α-difluoromethyl groupT has on hydrogen bonding and logP of quaternary ammonium salts is also described.
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