Synthesis of arieianal, a prenylated benzoic acid from Piper arieianum.

Arieianal (1) is a complex prenylated benzoic acid that was isolated from Piper arieianum. It has been synthesized through a convergent sequence that joins a functionalized diterpenoid chain to a protected aromatic core. Key steps include use of a copper enolate for selective displacement of an allylic bromide in the presence of an allylic acetate and a stereoselective Horner-Wadsworth-Emmons condensation to afford the desired E olefin of the isoprenoid side chain. After the diterpenoid chain was joined to the aromatic ring, use of sodium metal in hot sBuOH allowed selective cleavage of two benzyl ether protecting groups, and a sequence of oxidations gave the target compound. This synthesis confirms the structure assigned to the natural product and establishes a route that may be used to prepare more active analogues.