Acid-catalysed intramolecular cyclization of geranyl hydroquinone derivatives from Cordia alliodora. X-Ray crystal and molecular structure of 1,2,3,3a,4,9,10,10a-octahydro-5,8-dimethoxy-3,10-dimethyl-3a,9-epoxybenz[f]azulene

Abstract

The aqueous acid-catalysed intramolecular cyclization of dimethylated alliodorin (2) obtained from the heartwood of Cordia alliodora has been characterized by X-ray analysis as the unusual tetracyclic di-O-methyl hydroquinone title compound (8). A new synthesis of di-O-methylalliodorin (2) from a terminal methylallylic sulphide derivative of 2-geranyl-1,4-dimethoxybenzene is described.

Crystals of the title compound (8) are monoclinic, space group P2₁/c, unit cell dimensions a= 14.984(7), b= 5.206(4), c= 20.131(9)Å, β= 99.77(1)°, Z= 4. The structure was solved by direct methods and refined by least-squares calculations to an R value of 0.078 for 1 832 independent reflections measured on a diffractometer using Cu-K_α radiation.