Compounds of the formula I ##STR1## where R.sup.1 is ##STR2## where A is C.sub.1 -C.sub.4 -alkyl, phenyl or C.sub.7 -C.sub.12 -aralkyl and l is 0 or 1, R.sup.2 is C.sub.1 -C.sub.4 -alkyl, n is 0, 1, 2 or 3, m is 1, 2 or 3 and Y is hydrogen, fluorine, chlorine, bromine, C.sub.1 -C.sub.3 -alkyl, C.sub.1 -C.sub.3 -alkoxy, trifluoromethyl, phenyl or phenoxy, and, when m is greater than 1, the individual atoms or groups Y are identical or different, are prepared by a process in which, in a first stage, a diester of the formula II ##STR3## is hydrolyzed with one equivalent of an aqueous alkali metal hydroxide to give the alcohol of the formula IIIa ##STR4## in a second stage this alcohol is converted with a halogenating agent or a sulfonyl chloride or bromide into a compound of the formula IIIb ##STR5## where X is a nucleophilically displaceable leaving group, such as chlorine, bromine, mesyl or tosyl, and then, in a third stage, the compound IIIb is reacted with a phenolate of the formula IV ##STR6## where y and m have the abovementioned meanings, in the presence of an aprotic solvent to give compound I. Furthermore, diesters of the formula II and a process for their preparation are provided, the said diesters being prepared by reacting a lactone of the formula V ##STR7## with a Grignard compound VIR.sup.1 MgZ VIwhere Z is chlorine or bromine, in a nonpolar organic solvent, from 2 to 3 moles of the Grignard compound being used per mole of lactone, and the reaction mixture then being treated with from 2 to 3 moles of anhydride VII ##STR8## per mole of lactone.