A Concise Synthetic Route to the Stereotetrad Core
of the Briarane Diterpenoids
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Abstract
A concise
synthesis (under 10 steps) of the stereotetrad core of
the briarane diterpenoids is reported. This approach harnesses the
unique reactivity of salicylate ester derived 2,5-cyclohexadienones
to quickly build complexity. In particular, a highly diastereoselective
acetylide conjugate addition/β-ketoester alkylation sequence
was used to set the relative configuration of the C1 (quaternary)
and C10 (tertiary) vicinal stereocenters. The sterochemical outcome
of the β-ketoester alkylation appears to be governed by torsional
steering in the transition state
