Pepper HP, Lam HC, Bloch WM, George JH * University of Adelaide, Australia
Biomimetic Total Synthesis of (±)-Garcibracteatone.
Org. Lett. 2012;
14: 5162-5164
Key words
radical cascade - polyprenylated acylphloroglucinol - biomimetic synthesis
Significance
Garcibracteatone (K) is the structurally most complex polycyclic polyprenylated acylphlorogucinol natural product that has so far been isolated. The four-step total synthesis presented makes use of a biomimetic radical cascade reaction to build up four rings in one transformation. Additionally, the previously unknown relative stereochemistry at C-5 was assigned.
Comment
Precursor F for the key transformation is synthesized from phloroglucinol A in three steps by Friedel–Crafts acylation followed by subsequent diprenylation and alkylation with (±)-lavandulyl iodide (E). Oxidation of F by using Mn(OAc)3–Cu(OAc)2 initiates a radical cascade, which ultimately leads to the formation of the natural product garcibracteatone K (14% yield) along with its C5-epimer L (8% yield). This key transformation constructs four rings and five stereocenters.
