Xanthone undergoes regioselective substitution and nucleophically triggered ring opening to the corresponding ketone. Hydrazone of the latter oxidatively rearranges to ortho-diacylarenes, which, then, with hydrazine gives regioselectively substituted phthalazines. Molecular modeling analysis and H-1 NMR spectra indicate an intramolecular H-bonding engaging phenol OH and phthalazine N-3 atom.
The direct photo-oxygenation of 10-phenyl and 10-methoxy-9-dimethylaminoanthracenes 1a and 1b gives the corresponding 9,10-endoperoxides 2a and 2b. The latter are unstable owing to their high reactivity towards nucleophiles.