Two esterifications and an RCM to create the challenging trisubstituted C12-C13 double bond were required in the total synthesis of amphidinolideX (1) reported here. Assembling the three fragments in this order, no RCM occurred or the process yielded mainly isomer Z. However, generating the E double bond first, by a new variant of a Si-tethered metathesis (using Schrock's catalyst), and carrying out