Use of π-allyltricarbonyliron lactam complexes in the preparation of nocardicin derivatives: synthesis of (–)-3-oxo-1-[(p-benzyloxyphenyl)-benzyloxycarbonylmethyl]azetidin-2-one

Abstract

A short five-step synthesis, in 79% overall yield, of (–)-3-Oxo-1 -[(p-benzyloxyphenyl) benzyloxy-carbonylmethyl]azetidin-2-one (3), a precursor for nocardicin synthesis has been developed from isoprene monoepoxide. The key steps of the procedure rely on the efficient transformation of 2–4-η³-(1-formyloxy-2-methylbut-3-en-2-ylato)tricarbonyliron into the corresponding diastereoisomeric lactam complexes (6) and (7) using D-(–)-benzyl-(p-benzyloxyphenyl)glycinate (5) and ZnCl₂·TMEDA (TMEDA = tetramethylethylenediamine), and their oxidation with ceric ammonium nitrate to 3-isopropenylazetidinone derivatives.