Starting from juglone derivative 5, a series of frenolicin B analogs 15 (R1 = R2 = Me), 19a (R1 = H, R2 = Ph), and 19b (R1 = Ph, R2 = H) were obtained via the key β-hydroxy ester intermediate 10 in a twelve step synthesis.
A synthesis of the pyranonaphthoquinone antibiotic (±)-frenolicin B[(±)-1] is described. Key step is the intramolecular palladium-catalyzed aryloxycarbonylation of the 2-allyl-1-naphthol derivatives 8a,b to give the tricyclic λ-lactones 6a,b. Only the former (6a) is converted successfully into (±)-deoxyfrenolicin, the immediate precursor of (±)-1.