Synthesis of the methylene bis-tetrahydropyran motif of (−)-exiguolide

A chiral-pool approach for the construction of methylene bis-tetrahydropyran subunit, C1–C16 fragment, of (−)-exiguolide is described. The synthesis was efficiently accomplished starting from l-glutamic acid and l-aspartic acid involving oxa-Michael reaction and an aldol-driven-reductive etherification as key steps for the formation of tetrahydropyran ring.