Intramolecular Oxidative O‐Demethylation of an Oxoferryl Porphyrin Complexed with a Per‐O‐methylated β‐Cyclodextrin Dimer

Abstract

The intramolecular oxidation of ROCH3 to ROCH2 OH, where the latter compound spontaneously decomposed to ROH and HCHO, was observed during the reaction of the supramolecular complex (met-hemoCD3) with cumene hydroperoxide in aqueous solution. Met-hemoCD3 is composed of meso-tetrakis(4-sulfonatophenyl)porphinatoiron(III) (FeIII TPPS) and a per-O-methylated β-cyclodextrin dimer having an -OCH2 PyCH2 O- linker (Py=pyridine-3,5-diyl). The O=FeIV TPPS complex was formed by the reaction of met-hemoCD3 with cumene hydroperoxide, and isolated by gel-filtration chromatography. Although the isolated O=FeIV TPPS complex in the cyclodextrin cage was stable in aqueous solution at 25 °C, it was gradually converted to FeII TPPS (t1/2 =7.6 h). This conversion was accompanied by oxidative O-demethylation of an OCH3 group in the cyclodextrin dimer. The results indicated that hydrogen abstraction by O=FeIV TPPS from ROCH3 yields HO-FeIII TPPS and ROCH2. . This was followed by radical coupling to afford FeII TPPS and ROCH2 OH. The hemiacetal (ROCH2 OH) immediately decomposed to ROH and HCHO. This study revealed the ability of oxoferryl porphyrin to induce two-electron oxidation.