Abstract The synthesis of the C22–C37 segment of prorocentin, isolated from the dinoflagellate Prorocentrum lima , was achieved. Because the relative stereochemical relationship between C26 and other stereocenters (C28/C31/C32 established as R */ R */ R *) in the C22–C37 region of natural prorocentin has not yet been determined, both epimers at C26 of the C22–C37 segment were selectively constructed. The synthesis was based on a 5- exo epoxide ring opening reaction to form an oxolane (E-ring), Brown asymmetric methallylation to install the C26-stereocenter, acryloylation of the resulting alcohol, and ring-closing olefin metathesis to establish the Z -olefin at C23/C24.