Trimethylsilyldiazomethane esterification

The scope of the multi-residue method is extended permanently by testing and then including further active substances that can be determined by GC. Acidic analytes (such as phenoxyacetic acids or RCOOH metabolites) are included into the homogeneous partitioning by acidifying the raw extracts to a pH below the pKs value of the carboxylic acids. To include these analytes in the GC determination scheme they have to be derivatized with diazomethane, diazoethane, trimethylsilyldiazomethane, acidic esterification or benzylation, or by silanizing the COOH moiety. 

Initially, the oxidation conditions chosen for 154 to 157 were the modified ruthenium tetraoxide conditions of Sharpless and co-workers.44 The crude oxidation products were converted to methyl esters 106,160, 161, and 162 and their C-2 epimers 163 to 166 using either diazomethane or trimethylsilyldiazomethane.77 The epimer ratios were determined from integration of the H NMR spectra of the crude esterification products to ensure that accurate ratios were obtained without losing minor isomers during chromatography. The results obtained are summarized in Scheme 60 and Table 15. 

Trimethylsilyldiazomethane is a commercially available equivalent to diazomethane. It reliably converts an acid to the methyl ester. Methanol is an essential co-solvent for this esterification. 

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