Studies in the xanthone series. Part XII. A general synthesis of polyoxygenated xanthones from benzophenone precursors

Abstract

Various 2-mono-, 2,3- and 1,7-di-, 1,3,7-, 1,5,6-, 1,6,7- and 2,3,4-tri-, 1,3,4,7-, 1,3,5,6-, 1,3,6,7-, 1,5,6,7- and 2,3,4,5-tetra-, and 1,3,5,6,7-penta-oxygenated xanthones have been synthesised by preparation of 2-hydroxy-2′-methoxybenzophenones under Friedel–Crafts conditions, and subsequent base catalysed cyclisation to eliminate methanol. Acid or base catalysed selective demethylations of polymethoxyxanthones, and of benzophenones lead to efficient synthesis of natural hydroxymethoxyxanthones, and of hydroxymethoxybenzophenones. Selective methylation procedures are also given.