Process for the manufacture of 4-acetoxy-3-hydroxyethyl-azetidinone

A process for the manufacture of the optically active diastereoisomerically pure compound of the formula ##STR11## which is characterized in that a) an enantiomerically pure (4R)-compound of the formula ##STR12## in which R.sup.1 represents lower alkyl and Z.sup.1 represents amino, arylmethylamino, acylamino or azido, or a salt thereof, is catalytically reduced with hydrogen and, if desired, an acylamino group Z.sup.1 and/or the lower alkoxycarbonyl group COOR.sup.1 is hydrolyzed, resulting in a compound of the formula ##STR13## in which R.sup.2 represents hydrogen or lower alkyl, R.sup.3 and R.sup.4 together represent a bond, and Z.sup.2 represents amino or acylamino, or in a salt thereof,

• b) epimerising an obtained 2S,3R,4R-compound or an obtained mixture consisting of a 2S,3S,4R-, a 2R,3S,4R- and a 2S,3R,4R-compound of the formula III by treatment in an anhydrous polar solvent with a tertiary amine, an amidine base, sodium or potassium carbonate or potassium fluoride and isolating the pure 2S,3S,4R-compound of the formula ##STR14## wherein the substituents have the meanings given above, c) opening the lactone ring by treatment with an aqueous base, and if Z.sup.2 is an acylamino group, this acylamino group Z.sup.2 is hydrolyzed, to give a 2S,3S,4R-compound of the formula IIIa, in which R.sup.2 is hydrogen or lower alkyl, R.sup.3 is hydroxy, R.sup.4 is hydrogen, and Z.sup.2 is amino, or a salt thereof,
• d) protecting in an obtained compound or in a salt thereof the hydroxy group R.sup.3 and a carboxyl group --COOR.sup.2 and --COOR.sup.4 with a protecting group,
• e) closing the .beta.-lactam ring by treatment with a non-nucleophilic alkalimetal amide, a lower alkyllithium or lower alkylmagnesium compound branched in the 1-position, and removing the protecting groups to give a compound of the formula ##STR15## or a salt thereof, f) which compound of the formula IV or salt thereof is oxidatively decarboxylated in the presence of an acetate-yielding agent.