Jh. Li et Jk. Snyder, SELECTIVE OXIDATION OF CANTHINES TO CANTHIN-6-ONES WITH TRIETHYLBENZYLAMMONIUM PERMANGANATE, Tetrahedron letters, 35(10), 1994, pp. 1485-1488
Oxidation of canthines, prepared from intramolecular inverse electron
demand Diels-Alder reactions of indole with tethered triazines, produc
ed the corresponding canthin-6-ones regiospecifically, with no detecte
d canthin-4-ones.