Olivanic acid analogues. Part 9. Allylic oxidative functionalisation of substituted azetidinones: synthesis of some 4-acyloxy-7-oxo-1-azabicyclo[3.2.0]hept-2-ene-2-carboxylates

Abstract

Sharpless oxidation (Bu^tO₂H, SeO₂) of the protected allyl azetidinone 7 gave the allylic alcohol 8 which was transformed to the 5,6-trans-4α-acetoxyolivanic acid derivative 16. Kharasch–Sosnovsky benzoyloxylation (PhCO₃Bu^t, CuCl, PhH, heat) of the silylated 7-azabicyclo[4.2.0]oct-3-enes 17b,c provided inter alia allylic benzoates 18b,c and 21b,c. These were synthetic precursors of the 5,6-cis-olivanic acid analogues 23 and 26, which contain 8- and 4α-benzoyloxy groups, respectively.