Synthesis and characterization of derivatized capped porphyrins

Abstract

The syntheses of porphyrins carrying either a fully hydrophobic cavity with a benzene moiety (32a,b) or a polar cavity with an amidobenzene (32c–d) are described. Terephthaldehyde (1) was converted to benzene-bisalkanoic acids (8, 10) and nitrobenzene-bisalkanoic acids (13 and 16) by using standard methods. The corresponding diacid chlorides 17a–d were used to acylate two equivalents of a β-unsubstituted pyrrole, and the ketonic groups were reduced by diborane. Following the transformation of the nitro function to the acetamide, appropriate modifications of the ethyl ester functions afforded the key bisformylpyrroles 25a–d. The cyanoacrylate-protected formyl pyrrole derivatives were mono-chlorinated at the α-methyl groups and condensed with two equivalents of an α-unsubstitutued pyrrole to give the dipyrromethane dimers. Strong aqueous alkali caused saponification of the two ester groups and deprotection of the formyl functions to produce the dipyrromethane dimer 30, which, after thermal decarboxylation, was cyclized intramolecularly in acidic medium to give the porphyrins 32 (n = 4 or 5, X = H or NHCOCH3).