Total Synthesis of (±)-Taiwaniaquinol B via a Domino Intramolecular Friedel−Crafts Acylation/Carbonyl α-tert-Alkylation Reaction

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Abstract
The first synthesis of taiwaniaquinol B, a 6-nor-5(6→7)abeoabietane-type diterpenoid exhibiting the uncommon fused 6−5−6 tricyclic carbon skeleton, was accomplished in 15 steps. A Lewis acid-promoted tandem intramolecular Friedel−Crafts/carbonyl α-tert-alkylation reaction was exploited as the core strategy for the synthesis of the sterically congested 1-indanone-containing tricyclic structure. This multiple carbon−carbon bond forming reaction exploits the unique reactivity of Meldrum's acid. The facile precursor synthesis makes this a useful methodology for the expedient modification and assembly of sterically congested 1-indanone-containing ring systems.