Racemic and enantiomeric p-nitrobenzyl carbapen-2-em-3-carboxylates 3, 3a, and 3b were prepared starting from inexpensive sorbic acid through the key intermediates, azetidinone esters 4, thus establishing a total synthesis of the p-nitrobenzyl ester of a natural product SQ 27,860. Optical resolution was achieved readily on azetidinone menthyl esters, 12. The absolute configurations were also established.

Aus dem Methylester (Ia) und Sorbinsäure (Ib) werden zunächst die β‐Ketoester (VI) synthetisiert.

A short synthesis of (±)-2-alkylthiocarbapen-2-em-3-carboxylic acid (2) from sorbic acid via a key intermediate 4 is described.

Die Reaktion zwischen dem Methylester (I) und dem Ester (III) dient als Ausgangspunkt zur Synthese des Racemats (V).