Abstract: Process for the preparation of an ester of formula (1), wherein R1 represents a leaving group, CN, OH or a COOR5 group, R3 and R4 each independently represent a 1-3 C alkyl group, and R2 and R5 each independently represent an ester residue, wherein the corresonding salt with formula (2), wherein M represents H or an alkali (earth) metal in an inert solvent is contacted with an acid chloride forming agent to form the corresponding acid chloride, and the acid chloride is contacted with an alcohol with formula R2OH in the presence of N-methyl-morpholine. Preferably M represents an alkali metal, and R2 represents an alkyl group, particularly a t.-butyl group.