A practical route for the total synthesis of
8,9-secokaurene diterpenes is described. The central step is
the
[3.3]sigmatropic rearrangement of spirocyclic intermediates such
as 35, 40, and 41. All three
compounds must
necessarily respond identically to properly install the absolute
configuration of the bridgehead methine carbon. The
total synthesis of (−)-O-methylshikoccin (2b)
was realized in 8% overall yield from the Wieland−Miescher
ketone
9. Its naturally occurring epoxide 47 was
prepared with comparable efficiency. The preparative route
developed
herein should provide a general entry into this important class of
diterpenoids.
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