In this study, we synthesized the C8–C20 and C21–C30 segments of the diarrhetic shellfish toxin pectenotoxin 2. The C8–C20 segment was assembled from a phosphonate corresponding to the C8–C15 segment (prepared from l-malic acid in 19 steps) and an aldehyde corresponding to the C16–C20 segment (synthesized from 3-methyl-3-butenol in nine steps) by a twelve-step process including the Horner–Wadsworth–Emmons reaction, ...