Phomopsidin was isolated from Phompsis sp. TUF95F47 by Namikoshi and co-workers in 1997, and its absolute structure and biological activity have been reported. Phomopsidin and its geometrical isomer (MK8383) showed potent inhibitory activity against assembly of microtubule proteins, exhibiting strong antitumor activity. It has been proposed that phomopsidin could be generated via the IMDA reaction of 1. Therefore, the potent antitumor activity and this biosynthetic background draw our attention to the synthesis of phomopsidin. We planned to synthesize the cis-decalin core 2 of phomopsidin f...