The reaction of carboxylic acids with tosylhydrazones in basic media gives rise to the corresponding esters through an O–H insertion reaction in the in situ generated diazo compound. The process is operationally very simple, catalyst free, and very general with regard to the structure of both coupling partners. In particular, the esterification can be accomplished by employing tosylhydrazones derived from enolizable carbonyl compounds. Considering the ready availability of tosylhydrazones from carbonyl compounds, this reaction can be visualized as a reductive esterification of carbonyl compounds.

A stepwise approach is found to be suitable especially for the preparation of benzhydryl or benzyl esters [cf.(VI)] via diazo intermediates.