Synthesis and study of 2-C- and 4-C-methylxanthones

Abstract

2-C- and 4-C-methylxanthones with different oxygenation patterns have been synthesized by two methods: (1) nuclear methylation of 1,3-dihydroxyxanthones (I) to the corresponding 2-C-methyl derivatives (II) and (2) condensation of 2-methyl-(VI) and 4-methyl-(IX) 3,5-dimethoxyphenols with substituted salicylic acids. The 2-methylphenol (VI) gives 2-C-methyl-3-methoxy-1-hydroxyxanthones (VIII) and the 4-methylphenol (IX) gives 4-C-methyl isomers (XI). These observations might be of significance in understanding the mechanism of xanthone formation. C-Methylphloroglucinol (XII) yields exclusively 2-C-methyl-1,3-dihydroxyxanthones (IIa and XIV). The NMR spectra of these xanthones distinguish between 2-C- and 4-C-methylxanthones.