Rational Synthesis of 2-Bromoporphyrins and 2,12-Dibromoporphyrins

Bromoporphyrins were prepared by the metal-mediated self-condensation of brominated 1-formyldipyrromethanes. Depending on the conditions, Mg(II)-2,12-dibromoporphyrin and Mg(II)-2-bromoporphyrin could be obtained in up to 11% and 17% isolated yield, respectively. Zn(II) was also a viable templating metal. The positions of the bromine substituents were confirmed by 2D-NMR spectroscopic analysis and the X-ray crystal structure of a derivative. Suzuki and Sonogashira reactions of the bromoporphyrins yielded 2-substituted or 2,12-disubstituted porphyrins with red-shifted absorption and emission spectra. This method provides access to the minimalist core of β-mono- and β,β'-disubstituted porphyrins from readily available starting materials.