Synthesis and Substituent Effects in the Nuclear Magnetic Resonance and Mass Spectra of Dimethyl- and Dihaloxanthones

Halogen- and methyl-substituted xanthones have been prepared by three routes. The main approach has been Friedel-Crafts acylation-cyclization of aromatic ethers with oxalyl chloride or with chloroacetyl chloride followed by permanganate oxidation. The substituent shifts in the ¹H NMR spectra of the compounds studied are in good agreement with those predicted for substituted benzene derivatives. The typical electron-impact-induced CO expulsion from the molecular ion of xanthone decreases or even disappears in the halogenated derivatives owing to the competing halogen elimination.