Hydrolytic enzymes regioselectively catalyze the hydrolysis of diethyl itaconate 5a to the monoester 5c and opening of itaconic anhydride 6 to the regioisomeric monoester 5b that was tranformed into the hydroxy esters 2. This was used for the synthesis of β-methylene-, γ- butyrolactone 7 and of the racemic epoxyalcohol 3, that was resolved by a highly enantioselective Pseudomonas fluorescens lipase-catalyzed transesterification into (S)-3 ...