A practical and mild set of conditions for the Sonogashira reaction
utilizing CsF-mediated in situ TMS-alkyne desilylation followed by
Sonogashira coupling has been developed for the synthesis of a variety
of alkynyl benzenes and heteroarenes in good to excellent yields.
This methodology demonstrates excellent functional group tolerance
and simple purification, which allows large-scale industrial applications.
This one-pot protocol enables a high-yielding Sonogashira coupling
with volatile alkynes by avoiding challenging isolation of free alkynes.
The evolution of a successful strategy for the synthesis
of the
strained, cage-like antiviral diterpenoids wickerols A and B is described.
Initial attempts to access the carbocyclic core were surprisingly
challenging and in retrospect, presaged the many detours needed to
ultimately arrive at the fully adorned wickerol architecture. In most
cases, conditions to trigger desired outcomes with respect to both
reactivity and stereochemistry were hard-won. The successful synthesis
ultimately leveraged alkenes in virtually all productive bond-forming
events. A series of conjugate addition reactions generated the fused
tricyclic core, a Claisen rearrangement was used to install an otherwise
unmanageable methyl-bearing stereogenic center, and a Prins cyclization
closed the strained bridging ring. This final reaction proved enormously
interesting because the strain of the ring system permitted diversion
of the presumed initial Prins product into several different scaffolds.
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