Bromination of Dipyrromethenes for Porphyrin Synthesis

Article abstract of DOI:10.1021/jo00247a025

5'-Bromo-5-(bromomethyl)-2,2'-dipyrromethenium bromides (1) and dimers were prepared in 90percent yield from 5'-unsubstituted (16), 5'-carboxy- (15),or 5'-bromo-5-methyl-2,2'-dipyrromethenium bromides (17) by treatment of the latter with bromine and trifluoroacetic acid in chlorocarbon solvents at room temperature.Dipyrromethenes (1) are important intermediates in the Johnson regioselective synthesis of porphyrins via biladienes (3).Improvements in porphyrin synthetic methodology are exemplified by the preparation of etioporphyrin III (4a) and mesoporphyrin II dimethyl ester (4b)