A Direct and Mild Conversion of Tertiary Aryl Amides to Methyl Esters Using Trimethyloxonium Tetrafluoroborate: A Very Useful Complement to Directed Metalation Reactions

The scope and generality of a direct process for the conversion of tertiary amides directly to methyl esters has been investigated. The process involves a two-step, one pot procedure in which a tertiary amide is first treated with trimethyloxonium tetrafluoroborate to generate an imidate intermediate which is then hydrolyzed, generally by the addition of saturated aqueous sodium bicarbonate solution. Although this process fails for aliphatic amides, very good yields are realized for a variety of amides derived from aromatic carboxylic acids. Steric hindrance at the N-alkyl group is well tolerated; thus N,N-dimethyl, -diethyl, and -diisopropyl amides can all be utilized successfully.