Towards EPC-syntheses of the structural class of cochleamycins and macquarimicins. Part 3: EPC-syntheses of the β-keto lactone subunits and first attempts towards the syntheses of the pentacyclic antibiotics of this group
Practical EPC-syntheses of δ-substituted-β-keto δ-lactones, subunits of the cochleamycins and macquarimicins, are presented. In consequence Tietze's tandem reaction is employed to combine δ-allyl-β-keto δ-lactone with a hydrindene derivative, the second subunit of these acetogenic antibiotics. Model reactions for the final oxidative radical tandem cyclization reveal that the electrophilic radical cyclizes