Regioselective synthesis of antipodal β-tetrabrominated meso-tetraarylporphyrins

A series of meso-tetraarylporphyrins bearing electron-donor or electron-withdrawing substituents at the meso-phenyl groups were examined for antipodal β-pyrrole tetrabromination using different brominating agents. Porphyrins bearing electron-donor substituents undergo bromination at moderate temperatures with N-bromosuccinimide as the brominating agent while the electron-deficient porphyrins require Hq. Br2 at room temperature. The brominated porphyrins were isolated in moderate to very good yields. Synthesized compounds were characterized by electronic absorption, 1HNMR, and mass spectroscopic methods. Regioselectivity of an electron-deficient porphyrin, 2,3,12,13-tetrabromo-5,10,15,20-tetrakis(4- methoxycarbonylphenyl)porphyrin was examined by single-crystal X-ray structure analysis and showed antipodal β-pyrrole bromo substitution. © 2008 The Chemical Society of Japan.