Structural
reassignments for littordial E, littordial F, and drychampone
B are proposed on the basis of consideration of their biosynthetic
origin. The key step in the proposed biosynthesis of each of these
meroterpenoids is an intermolecular hetero-Diels–Alder reaction
between an o-quinone methide and caryophyllene or
humulene. Biomimetic total synthesis of the natural products gave
sufficient material to allow their structure revision by NMR studies.
A concise synthesis of a stereochemically complex meroterpenoid, peshawaraquinone, via the unsymmetrical dimerization of its achiral precursor, dehydro-α-lapachone, is reported. Enabled by reversible oxa-6π-electrocyclizations of (2H)-pyran intermediates, the base-catalyzed dimerization...
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