Aromatics to bis-triquinane: a tandem oxidative dearomatization of bis-phenol, cycloaddition, photorearrangement and a rapid entry into carbocyclic framework of Xeromphalinone E

摘要

A novel approach for the synthesis of a bird-shaped bis-triquinane 3, a fascinating carbocyclic framework closely related to the skeleton of Xeromphalinone E 1 from readily available 2,6-dimethyl phenol 8 has been reported. The synthesis of bis-cyclohexadienones 6, 22aee by oxidative acetylation of tetramethyl bisphenols 7, 20aee has been investigated using two different reagents under varying reaction conditions. The cycloaddition of bis-cyclohexadienone 6 gives two carbocycles, bis-adduct 4b and monoadduct 5d in a stereocontrolled manner. The photochemical sigmatropic 1,2-acyl shift in 4b furnished 3 and monotriquinane 9 linked with a 9-acetoxy-9-methyl-endo-tricyclo[5,2,2,0~(2,6)]undeca-4,10-diene-8- one system. Two different pentasubstituted phenols 13 and 14 were also isolated during an attempted oxa-di-p-methane (ODPM) rearrangement of mono-adduct 5d via aromatisation of the cyclohexadienone ring. The photochemical behaviour of bis-cyclohexadienones 6, 22aee has also been investigated under UV irradiation and two different aromatized products were isolated for each biscyclohexadienone by migration and elimination of acetate groups.