Synthesis of Quadrangularin A and Pallidol

Key words

cationic cyclization - Ramberg-Bäcklund reaction - Friedel-Crafts alkylation

Significance

Resveratrol-based oligomers are produced combinatorially by plants in response to environmental stress. Snyder and co-workers report that the core structure A can be transformed to every member of the family by simply altering reagents and reaction conditions. Pallidol, quadrangularin, ampelopsins D and F, paucifloral F, and hemsleyanol E were all synthesized by related cationic cyclization cascades.

Comment

Treatment of A with acid generated carbocation C that cyclized regioselectively followed by cation capture by thiol B. The resultant thioether E was used in a Ramberg-Bäcklund rearrangement to install the fourth aromatic ring of F, the precursor to quadrangularin A. A further cationic cyclization of F generated the tetracyclic array of H, a precursor to pallidol.