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

It is demonstrated that difluoromethyl diazomethane (HCFCHN) 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 (CFCHN) 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.