Preparation of 3‐Benzoylpenems and Penem Amides by Wittig Methodology.

Abstract Condensation of phenyl glyoxal with azetidin-2-ones (1a-c) gave the hemi-aminals (2a-c). Subsequent conversions produced the 4-(formylthio)phosphoranes (4a-c) which gave on heating the 3-benzoylpenems (5a-c), formed by intramolecular Wittig cyclisation. Thermal isomerisation of trans -6-substituted-3-benzoylpenems allowed the preparation of the cis -6-substituted-3-benzoylpenems (7a-c). Using similar methodology the penem amides (7d-e) were synthesised.