The Conversion of Amides to Esters with Meerwein'S Reagent. Application to the Synthesis of a Carfentanil Precursor.

Abstract An efficient two step transformation of 1° and 2° amides to methyl and ethyl esters has been developed using trimethyl- and triethyloxonium tetrafluoroborates, and dilute acid. This methodology was applied to 1-benzyl-4-phenylamino-4-piperidinecarboxamide, a precursor in the synthesis of carfentanil, to produce the methyl ester in 60% yield and the ethyl ester in 80% yield.