The treatment of natural chlorins with 2,3-dichloro-5,6-dicyanobenzoquinone resulted not only in the intramolecular cyclization of the propionic acid residue in position 17 with the formation of an additional delta-lactone cycle at the pyrrole ring D, but also in the oxygen-assisted oxidation of 8-ethyl group in ring B to an alpha-methoxyethyl substituent.