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Several synthetic strategies for amphidinolide A, 2 B, C, G, H, and L have been reported to date and the total synthesis of three amphidinolides, J, 7 K, and P was recently completed by Williams group. Herein, we describe the stereoselective synthesis of the C12-C17 fragment 3 of amphidinolide O ( 1) using a titanium-mediated diastereoselective anti-aldol reaction as a key step. Retrosynthetically, the amphidinolide O ( 1) can be bisected into two fragments: the C1-C11 fragment 2 bearing the epoxide and the hemiketal moieties and C12-C17 vinyl iodide fragment 3 (Scheme 1). The synthesis of vinyl iodide fragment 3 started from chiral propionate ester 4 (Scheme 2). The (1 S,2R)-cis-1-(pmethyl)benzenesulfonamido-2-indanyl ester 4 was prepared in 2 steps from commercially available optically active (1S,2R)-cis-aminoindan-2-ol. 10 The titanium enolate of 4 was generated by the following sequence of reactions, .e., treatment of 4 with TiCl4 (1.2 equiv.) in CH2Cl2 at 0 C-25 C for 15 min, addition of N-ethyldiisopropylamine (4.0 equiv.) at 25 C, and finally stirring of the resulting dark brown solution for 2 hr. The titanium enolate of 4 was then treated with 3trimethylsilyl-2-propyn-1-al ( 5) (2.0 equiv.), 11 which was already precomplexed with TiCl 4 (2.4 equiv.) at -78 C, to provide the anti-aldol product 6 as a major product in 55% isolated yield. 10 TMS group of anti-aldol ester 6 was removed with tetran-butylammonium fluoride (1.5 equiv., 1.0 M in THF) in THF. The chiral auxiliary ester 7 was directly esterified with a solution of methyl magnesium chloride (6 equiv., 3.0 M in THF) in methanol. 13 Hydrostannylation of acetylene 8 with tributyltin hydride (1.5 equiv.) and AIBN (cat.) followed by metal-halogen exchange with iodine (1 equiv.) in diethyl ether yielded the desired ( E)-vinyl iodide 10 in 54% yield over 2 steps. 14

Studies on the Toral Synthesis of Amphidinolide O. A Stereoselective Synthesis of C12-C17 Fragment