Li-Mei Jin

Copper-induced fluoroalkylation of porphyrins: solvent-dependent synthesis of fluoroalkyl chlorins and porphyrins from fluoroalkyl iodides

Treatment of copper(II) or nickel(II) porphyrins with fluoroalkyl iodides (RfI) in the presence of copper powder in dioxane, diglyme(DG) or tetrahydrofuran (THF) at 70-90°C gave β-fluoroalkyl chlorins in moderate yields. Unexpectedly, when dimethylsulphoxide (DMSO), hexamethylphosphoric triamide (HMPA) or N,N-dimethylformamide (DMF) was used as the solvent, with chlorobenzene as a co-solvent, the β-fluoroalkylporphyrins were obtained. In the first three solvents the reaction can be completely suppressed by p-dinitrobenzene (p-DNB) or hydroquione (HQ), but not at all in the last three solvents. Apparently, a single electron-transfer mechanism may be involved in the formation of β-fluoroalkyl chlorins while fluoroalkylcopper intermediates may play a role in the production of β-fluoroalkylporphyrins. The metallofluoroalkylchlorins can be converted quantitatively to 2-hydoxyl-3-fluoroalkylchlorins by air/SiO2 or air/Al2O3. Additionally, the metallofluoroalkylchlorins and metallofluoroalkylporphyrins can be converted into the corresponding free-base chlorins and porphyrins, respectively, with H2SO4. On the other hand, the metallohydoxyfluoroalkylchlorins under the same conditions afforded β-fluoroalkylporphyrins. Metallohydroxyfluoroalkylchlorins were readily also etherified to the corresponding metallomethoxyfluoroalkylchlorins with dimethyl sulfate (Me2SO4).