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Abstract
For nearly two decades, synthetic chemists have been fascinated by the structural
complexity and synthetic challenges afforded by the guanacastepene and heptemerone
diterpenoids.Numerous synthetic approaches to these compounds have been reported,
but to date the application of enantioselective catalysis to this problem has not
been realized. Herein we report an enantioselective synthesis of an advanced intermediate
corresponding to the tricyclic core common to the guanacastepenes and heptemerones.
Highlights of this work include sequential Pd-catalyzed decarboxylative allylic alkylation
reactions to generate the two all carbon quaternary stereocenters, the use of ring-closing
metathesis to close the A ring in the presence of a distal allyl sidechain, and a
region and diastereoselective oxidation of an trienol ether to introduce oxygenation
on the A ring.