Pentadienyl sulfoxide in triene synthesis. Efficient assembly of the Northern fragment of polycavernoside A

Various polyunsaturated fragments, akin to the polycavernoside A Northern fragment, can be synthesized efficiently using as key steps a double Mislow-Braverman-Evans rearrangement of bis-allylic sulfoxides and a novel Julia-type 1,6-reductive elimination.