Abstract
Partial saponification of ethyl 11-ethoxycarbonyl-3-oxoeusanton-4-enate (I) produces two kinds of monoesters (II and XII), which are epimers at C11-position. Bromination-dehydrobromination of these esters affords the corresponding dienonelactonic esters (V and XV) and their saponification followed by decarboxylation give, from both, 6β-hydroxy-3-oxo-11-epi-eusantona-1, 4-dienic acid lactone (XI) or rac-santonin D, which is also obtained by the bromination-dehydrobromination of 11-carboxy-3-oxoeusanton-4-enic acid (XVI).
