Synthesis of Principal Building Blocks of Amphidinolides of the G and H Families

Unsaturated lactones, (6R)- and (6S)-6-[(2R)-1,4-dioxaspiro[4.5]dec-2-yl]-4-methyl-5,6-dihydro-2H-pyran-2-ones, have been synthesized by diastereoselective allylation of (R)-2,3-O-cyclohexylidene­glycer­aldehyde with methyl 3-(bromomethyl)but-3-enoate and its allylstannyl derivative. These lactones have been subjected to highly diastereoselective reduction and utilized in a new retrosynthetic scheme for obtaining C5–C14, C15–C19, and C20–C26 building blocks of amphidinolide G and H families.