Total Synthesis of Plakortide E and Biomimetic Synthesis of Plakortone B

The total synthesis of plakortide E ( 1 a ) is reported. A novel palladium‐catalyzed approach towards 1,2‐dioxolanes as well as an alternative substrate‐controlled route leading exclusively to cis ‐highly substituted 1,2‐dioxolanes have been developed. A lipase‐catalyzed kinetic resolution was employed to provide optically pure 1,2‐dioxolane central cores. Coupling of the central cores and side chains was achieved by a modified Negishi reaction. All four isomeric structures of plakortide E methyl ester, namely, 26 a – d were synthesized. One of the structures, 26 d , was shown to be identical with the natural plakortide E methyl ester on the basis of 1 H, 13 C NMR spectra and specific rotation comparisons. With the plakortide E methyl ester (4 S ,6 R ,10 R )‐(−)‐ cis ‐ 26 d and its other three isomers in hand, we successfully converted them into (3 S ,4 S ,6 R ,10 R )‐plakortone B ( 2 a ), and its isomers ent ‐ 2 a , 2 b and ent ‐ 2 b via an intramolecular oxa‐Michael addition/lactonization cascade reaction. Finally, saponification converted 1,2‐dioxolane 26 d into plakortide E ( 1 a ) whose absolute configuration (4 S ,6 R ,10 R ) was confirmed by comparison of spectral and physical data with those reported.