Novel oxidative phenol-coupling reaction with phosphomolybdic acid on silica gel support: Regioselective biomimetic synthesis of dimeric phenanthrene derivatives

Article abstract of DOI:10.1016/S0040-4020(01)82403-0

Biomimetic synthesis of the naturally occurring dimeric phenanthrene derivatives, cirrhopetalanthrin (3a) and flavanthrin (7a), and their structural analogues 3c, 3e, 5a and 7c was achieved in very high yields by regioselecxtive oxidative coupling of their respective phenolic monomers 2a, 6a, 2c, 2e, 4a and 6c with phosphomolybdic acid on a silical gel support. Unlike coelonin (6a) and lusianthridin (6c), 2,7-dihydroxy-3,4,6-trimethoxy-9-10-dihydrophenanthrene (6e) gave, on similar oxidation, the phenanthrene dimer 3e, instead of the expected 9,10-dihydrophenanthrene dimer 7e. β-Naphthol afforded the corresponding 1,1'-dimer 1a in almost quantitative yield. The structures of the new dimeric compounds were established from various spectral data of the compounds and their respective acetyl derivatives.