Asymmetric Total Synthesis of (+)-Crassalactone D

The asymmetric total synthesis of (+)-crassalactone D (4), a naturally occurring antitumor agent, has been achieved by employing an oxidative spirocyclization of furan 11 as the key step. Two close analogues, 7-epi-crassalactone D (14) and 5-epi-7-epi-crassalactone D (15), also have been prepared in the course of the synthesis of (+)-crassalactone D.