The C12–C24 fragment of peloruside A has been synthesized using, as a key step, a silyl- tethered ring closing metathesis reaction to form the C16–C17 (Z)-alkene. The metathesis reaction discriminates between diastereoisomers of the starting material. A diphenylsilyl bis- ether provides simultaneous protection for the C15 and C24 hydroxyl groups, and is expected to lead to high 1, 5-anti selectivity in subsequent aldol reactions of the methyl ...