Esterification of Carboxylic Acids with Difluoromethyl Diazomethane and Interrupted Esterification with Trifluoromethyl Diazomethane: A Fluorine Effect

It is demonstrated
that difluoromethyl diazomethane (HCF2CHN2)
can react with a broad range of carboxylic acids.
The reaction is convenient, operationally simple, mild, and tolerant
of a variety of different functional groups. In sharp contrast, trifluoromethyl
diazomethane (CF3CHN2) fails to react with carboxylic
acids in most solvents, and in acetonitrile this reagent instead undergoes
an interrupted esterification (a Mumm reaction) to yield N-trifluoroethyl imides. This striking example of the ability of a
single F-for-H substitution to alter a reaction pathway was rationalized
through a DFT study.