Total Synthesis of Methyl Sarcophytoate, a Marine Natural Biscembranoid

The total synthesis of methyl sarcophytoate (1), a marine natural biscembranoid, has been achieved by the thermal Diels−Alder reaction between the 14-membered dienophile unit, methyl sarcoate (2), and the 14-membered diene unit 64. Methyl sarcoate (2) was prepared using n-BuLi-Bu₂Mg-mediated dithiane coupling, Kosugi−Migita−Stille coupling, and Grubbs ring-closing metathesis. The diene unit 64 was prepared using Sharpless asymmetric epoxidation, Grubbs ring-closing metathesis, 6-exo-tet epoxide opening, and n-BuLi-Bu₂Mg-mediated Ito−Kodama cyclization. The final Diels−Alder reaction between 2 and 64 proceeded with high site, endo/exo, π-face, and regioselectivities. During this reaction, partial E → Z isomerization at the C4 position was observed.