Olivanic acid analogues. Part 1. Total synthesis of the 7-oxo-1-azabicyclo[3.2.0]hept-2-ene-2-carboxylate system and some related β-lactams

Abstract

4-Allylazetidin-2-one, prepared from penta-1,4-diene and chlorosulphonyl isocyanate, has been used to synthesise the parent 7-oxo-1-azabicyclo[3.2.0] hept-2-ene-2-carboxylate system of the naturally occurring olivanic acids, using an intramolecular Witting reaction to construct the 2,3-double bond. Cyclisation of ketones derived from the 4-allyl grouping produced 3-substituted derivatives, while use of the azetidin-2-one prepared from hexa-1,5-diene and chlorosulphonyl isocyanate has given the homologous 8-oxo-1-azabicyclo[4.2.0]oct-2-ene system.