Total Syntheses of the Cytotoxic Marine Natural Product, Aplysiapyranoid C1

The first total syntheses of the cytotoxic marine natural product, aplysiapyranoid C, 1c, are reported. The Wittig reaction of 4-methyl-3-pentenyltriphenylphosphorane with the THP ether of hydroxyacetone gave in 88% yield the Z-alkene 4 which was hydrolyzed to the alcohol 5 in 72% yield. Sharpless asymmetric epoxidation of 5 afforded the epoxy alcohol 6 in 91% yield and 81% ee. Opening of the epoxide of 6 with ammonium chloride in DMSO gave in 76% yield the chloro diol 7 which was converted to the primary TBS ether 8 in 95% yield. Opening of the epoxy alcohol 6 with HCl and Ti(OiPr)4 afforded the desired chloro diol 7 as the minor product along with the rearranged chloromethyl diol 9. This compound is presumably formed by opening of the protonated epoxide to give a butenyl cation which rearranges to the cyclopropylcarbinyl cation and is then trapped by chloride ion at the unsubstituted cyclopropyl carbon, regenerating the alkene. Cyclization of the TBS ether 8 with tetrabromocyclohexadienone (TBCO) afford...