| The total synthesis of the medium ring ether (+)-Rogioloxepane A and the total synthesis of the polyether Bistramide A will be described. Rogioloxepane A was isolated in 1992 from the red seaweed Laurencia microladia collected in the Mediterranean Sea off the torrent Il Rogiolo. Rogioloxepane A is a seven membered oxepene ring with alpha,alpha'-transdisubstitution, two halogen substituents, and a terminal Z enyne moiety. The key stereogenic centers were set using a Sharpless kinetic resolution, an asymmetric glycolate alkylation, and a diastereoselective acetate aldol reaction. The total synthesis was completed in twenty-one linear steps. Bistramide A was isolated in 1988 from the marine ascidian Lissoclinum bistratum. Interesting structural features include a functionalized THP ring, two amide linkages, and a spiroketal. An efficient and convergent synthetic strategy for Bistramide A will be described. The approach involves the use of an asymmetric glycolate alkylation, an asymmetric aldol addition, and a Sharpless asymmetric epoxidation to synthesize the three key fragments. The synthesis was completed with a longest linear sequence of eighteen steps. |
