Unified Total Synthesis of Madangamines A, C, and E.

A stereodivergent strategy for the synthesis of skipped dienes is developed. The method consists of hydroboration of allenes and Migita-Kosugi-Stille coupling, which allows for access to all four possible stereoisomers of the skipped dienes. The hydroboration is especially useful for providing both E-allylic and Z-allylic alcohols from the same allene by simply changing the organoborane reagent. The strategy was successfully applied to a unified total synthesis of the madangamine alkaloids via a common ABCE-tetracyclic intermediate with a (Z,Z)-skipped diene. The late-stage variation of the D-ring enabled the supply of synthetic madangamines A, C, and E for the first time.