Totalsynthesis of surugatoxin 1, isolated from the toxic Japanese ivory shell (), was achieved from 6-bromoisatin by a stepwise ring construction involving two key steps: the stereospecific cyclization (17 → 18) and hydration (33b → 1).
The Diels-Alder adduct obtained from (E)-6-bromo-3-ethoxycarbonylmethylene-2-oxoindoline and trans-1, 3-pentadiene was successfully transformed into the diacetate of the aglycone of neosurugatoxin, which is the key intermediate in our first total synthesis of neosurugatoxin in 16 steps.
Details on a second synthetic procedure of neosurugatoxin framework are described using a Diels–Alder adduct obtained from 6-bromo-3-ethoxycarbonylmethylene-2-oxoindoline and 1,3-pentadiene.