THE FIRST TOTAL SYNTHESIS OF (+)-BULLATACIN, A POTENT ANITITUMOR ANNONACEOUS ACETOGENIN, AND (+)-(15,24)-BISEPI-BULLATACIN

This paper reports the first total synthesis of the natural product (+)-bullatacin (1), a representative of potent antitumor Annonaceous acetogenins, as well as a stereoisomer (+)-(15,24)-bisepi-bullatacin (2). In this synthesis, a new, efficient method has been developed to introduce the gamma-lactone into the bistetrahydrofuran skeleton through in situ alkylation of epoxide 4 by the alpha-sulfonyl carbanion of phenyl sulfone 5. The methylated gamma-lactone was successfully synthesized by a sequence of reactions comprising an aldol reaction, an acidic lactonization, and elimination under mild, basic condition.