nitric acid then afforded the anthraquinone spirolactone core of cyclo-mumbaistatin
436 in high yield.
2.18.2 Ferrier Rearrangement
Smith et al. [28] have made use of an initially unanticipated Ferrier rearrangement
for the synthesis of the southern hemisphere of spirastrellolide B (Scheme 106).
The spiroacetal 438 was initially targeted through a dehydrative spirocyclization
strategy. However, following antiselective reduction of ketone 437, treatment of the
mixture with aq. HClO 4 afforded the spiroacetal 438 in moderate yield in addition
to the Ferrier rearrangement byproducts 439 and 440.
Ultimately, downstream modification of 438 toward the target molecule was
unsuccessful; nevertheless the authors recognized the potential to make use of
unsaturated spiroacetal 439 instead. Thus, the reaction sequence was optimized to
maximize the yield of 439, proposed to arise from dehydration of the intermediate
hemiacetal 441, followed by Ferrier rearrangement (Scheme 107). By inclusion of
Scheme 105 Anionic homo-Fries rearrangement in the synthesis of a spiroacetal [202]
260
M.A. Brimble and L.A. Stubbing