The Photooxygenation of Heptamethyl Coα, Coβ‐Dicyanocobyrinate

Irradiation with visible light of an oxygen‐saturated methanolic solution of heptamethyl Coα, Coβ‐dicyanocobyrinate and of the sensitizer methylene blue causes the efficient photooxygenation of this vitamin B12 derivative. Use of CD3OD instead of CH3OH strongly accelerates the reaction. This solvent H/D‐isotope effect is consistent with a mechanism involving ‘singlet oxygen’ and is exploited preparatively. Two photooxygenation products can be isolated from such preparative experiments. One of these, isolated in 47% yield, has NMR.‐spectral characteristics identical with those of Inhoffen's heptamethyl Coα,Coβ‐dicyano‐5,6‐dioxo‐5,6‐secocobyrinate (2a). To the other photoproduct, isolated in 25% yield, the structure of the unknown isomeric heptamethyl Coα, Coβ‐dicyano‐14,15‐dioxo‐14, 15‐secocobyrinate (3a) is assigned.