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

The intramolecular oxidation of ROCH₃ to ROCH₂OH, 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) (Fe^IIITPPS) and a per‐O‐methylated β‐cyclodextrin dimer having an ‐OCH₂PyCH₂O‐ linker (Py=pyridine‐3,5‐diyl). The O=Fe^IVTPPS complex was formed by the reaction of met‐hemoCD3 with cumene hydroperoxide, and isolated by gel‐filtration chromatography. Although the isolated O=Fe^IVTPPS complex in the cyclodextrin cage was stable in aqueous solution at 25 °C, it was gradually converted to Fe^IITPPS (t_1/2=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=Fe^IVTPPS from ROCH₃ yields HO‐Fe^IIITPPS and ROCH₂^.. This was followed by radical coupling to afford Fe^IITPPS and ROCH₂OH. The hemiacetal (ROCH₂OH) immediately decomposed to ROH and HCHO. This study revealed the ability of oxoferryl porphyrin to induce two‐electron oxidation.