The Bromination of Dipyrromethanes for Porphyrin Synthesis
Paine, J.B. III, Hiom, J., and David Dolphin
J. Org. Chem.
5'-Bromo-5-(bromomethyl)-2,2'-dipyrromethenium bromides I (R = Me, Et, R1 = Me; R = Et, R1 = CH2CH2CO2Me) were prepared in 90% yield from dipyrromethenium bromides II (R2 = H, CO2H, Br) by treatment with Br2 and CF3CO2H in chlorocarbon solvents at room temperature. I are important intermediates in the Johnson regioselective synthesis of porphyrins via biladienes, exemplified by the preparation of etioporphyrin III and mesoporphyrin II di-Me ester.