The stereocontrolled synthesis of the C(17)--C(28) fragment 3 of didemnaketal B was accomplished in 21 steps from the natural (R)-(+)-pulegone and (S)-(--)-citronellal. The key steps involved diastereoselective construction of two chiral carbon centers through the intramolecular chiral induction and uncommon Julia olefination of ketone forming the E-trisubstituted C(22)--C(23) double bound.
The fully substituted cyclopentenedione core of madindoline A (1) and B (2) as potent and selective inhibitor of IL-6 has been synthesized efficiently. The quaternary carbon center C-2' was constructed on the basis of a newly developed AIEt3-promoted tandem reductive rearrangement of α-hydroxy epoxides.