Acid-catalyzed exocyclic ring formation in meso-tetrakis(3Ј,5Ј-dimethoxyphenyl)-2-aza-21-carbaporphyrin takes place regioselectively between the external carbon atom of the confused pyrrole and the ortho-carbon atom of the adjacent meso-aryl group. The ring fusion strongly alters the spectroscopic properties of the macrocycle, but its aromaticity is preserved, as shown by NMR spectroscopy as well as DFT calculations. A tendency to self-associate is observed for

Reaction of paraformaldehyde with meso-tetraaryl-2-aza-21-carbaporphyrins (NCP) in the presence of a basic catalyst afforded fused lactam derivatives comprising a >C═O bridge linking the internal carbon C21 with one of the internal nitrogens. The isomer 2 with C21-C(O)-N24 bridge is formed with about 9-fold molar excess over that with C21-C(O)-N22 bridge (3). The (1)H NMR and UV-vis spectral characteristics indicate aromatic character of the derivatives. For meso-tetrakis(3',5'-dimethoxy)- and meso-tetrakis(3',4',5'-trimethoxy)-21,24-carbonyl-NCP an efficient external ring fusion by linking C3, i.e., the external carbon of the confused pyrrole, with an ortho carbon of the adjacent aryl was observed under acidic conditions, yielding derivatives 4c and 4d, comprising a linear system of five fused rings. The chirality and configurational stability of these carbonylated systems were established by a chiral stationary phase HPLC and circular dichroism. The interaction of 2 with chiral acids and alcohols leading to the formation of diastereomers was observed by (1)H NMR. Slow racemization of 2 under acidic conditions was established by HPLC and (1)H NMR and a mechanism for this process was proposed.

Bis- and tris(methylated) derivatives of 3,3'-bis(N-confused porphyrin) were obtained. Methylation of C21 stabilizes the geometry of the axially chiral system allowing separation of enantiomers and assignment of an absolute configuration by X-ray methods.

A fully conjugated system 4 consisting of two 2-aza-21-carbaporphyrin (NCP) subunits bridged by dipyrrin was synthesized by a highly selective condensation of 3-pyrrole-NCP 2 with aryl aldehydes. The free base 4 as well as its silver(III) complex 5 exhibited flexibility of the bridge allowing synergetic binding of Ag , thus leading to a mixed-valence tetraporphyrinic assembly consisting of eight silver atoms which was characterized both in the solid state and in solution. Binding of chiral acid by 4 and 5 was shown by observation of an induced optical activity of the adducts.

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