An alternative synthesis of benziporphyrins starting from isophthaloyl chloride

Abstract

An alternative route to benziporphyrins has been developed. Reaction of an α-unsubstituted pyrrole ethyl ester with isophthaloyl chloride in the presence of aluminum chloride afforded a diketone that underwent selective reduction with diborane to give a benzitripyrrane. Cleavage of the ethyl esters with sodium hydroxide in refluxing ethylene glycol, followed by acid catalyzed condensation with a pyrrole dialdehyde and oxidation with DDQ, generated the targeted benziporphyrin product. Spectrophotometric titration of the benziporphyrin with trifluoroacetic acid (TFA) demonstrated the sequential formation of mono-and dicationic species. At lower dilutions, the free base benziporphyrin showed unusually strong 5 J HH coupling between two adjacent methyl substituents, indicating that the connecting unit has substantial olefinic characteristics.

Synthesis of Selenium and Tellurium Core-Modified Azuliporphyrinogens and Benziporphyrinogens and Corresponding Carbaporphyrinoids

“…The pyrrolic and tellurophene protons further shifted downfield compared with the values of tellurabenziporphyrin in the absence of TFA. The presence of a +2 charge on the system contributed to the downfield shifts, and the data was found to be consistent with the emergence of weak diatropic character over the macrocycle as has been noted for related structures. ,− …”