Two routes are reported for the synthesis of the title marine metaboli
te 1. The routes converge at the trienoic aldehyde 4, and are complete
d by chain extension to the tetraenoic ketone 5 and intramolecular Die
ls-Alder cyclization. - Daylight lamp irradiation offers a convenient
means for converting a cis/trans mixture from a Wittig reaction into t
he pure trans isomer.