Tandem pericyclic reactions in a new FeCl3-promoted synthesis of catechol analogues of restrytisol C

The uncommon stilbene, 3,4-dimethoxy-12-acetoxy stilbene, has been synthesised by Heck coupling methodology in three steps. Treatment of this stilbene with ferric chloride in dichloromethane (room temperature) gave the unnatural stilbenoid dimers; 8,8′-(12,12′-bisacetoxyphenyl)-7′-(3′,4′-dimethoxyphenyl)-3,4-dimethoxy-7′,8′-dihydro-naphthalene and 8-(12-acetoxyphenyl)-8′-(12′-hydroxy-phenyl)-7′-(3′,4′-dimethoxyphenyl)-3,4-dimethoxy-7′,8′-dihydro-naphthalene. The structures of both stilbene dimers were unambiguously confirmed by 1D (1H, 13C) and 2D NMR experiments (COSY, HMQC, HMBC and NOESY). This is the first report of a FeCl3-promoted sequential pericyclic pathway leading to a highly oxygenated oligostilbenoid dimer (incorporating two asymmetric centres). The NMR spectroscopic evidence and a mechanistic interpretation consistent with these structures are discussed.