Efficient Regiospecific Conjugated Ring Fusion in N‐Confused Porphyrin

Abstract

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

Heterocyclic Nanographenes and Other Polycyclic Heteroaromatic Compounds: Synthetic Routes, Properties, and Applications

“…Chmielewski et al reported that the acid-catalyzed exocyclic ring formation in meso -tetrakis­(3′,5′-dimethoxyphenyl)-2-aza-21-carbaporphyrin 263.1 ( N -confused porphyrin, NCP) took place regioselectively between the external carbon of the confused pyrrole and the ortho -carbon of the adjacent meso -aryl group (Scheme ). This reaction was not observed with other meso -substituents, which only yielded the corresponding 3,3′-linked homodimers. The resulting indeno-fused product 263.2 remained aromatic, although a reduction of the diatropic ring current was observed, consistent with the antiaromatic resonance contributions characteristic of dehydropurpurin systems.…”

Blooming of confused porphyrinoids—fusion, expansion, contraction, and more confusion

“…142 Although the compound is rather specific, an example of peripherally fused NCP derivative at the 3-position (a-carbon atom of the confused pyrrole ring) is also reported (Scheme 26). 143 Relatively high reactivity of the 3-position is also applicable for the reactions with active methylene compounds. 144 Recently, N-heterocyclic carbene rhenium(I) complexes embedded in the NCTPP core (Fig.…”

Regioselective Internal Carbonylation of the 2-Aza-21-carbaporphyrin: Access to Configurationally Stable Chiral Porphyrinoids

“…The transformation was combined with a color change from olive green to purple, and after deacidification, the solution turned deep red. The electronic spectrum of 4 is considerably different from the porphyrin-like spectrum of the starting 2 and similar to that of externally 3,5 o -fused porphyrin 5 with no internal ring fusion (Figure ). Mass spectra of 4 indicate the loss of two hydrogens upon reaction.…”

“…In the NOESY spectrum (CDCl 3 , 233 K), 7-H correlates strongly with a doublet of the 5- o ′-H, i.e., proton at the ortho position of the aryl fused with the confused pyrrole. Analogously to the parent compounds 2c , the ortho protons are magnetically distinct due to a nonplanar character of 4c and some restrictions in the rotation freedom of the meso -substituents, while for the effectively flat 5 a pairwise degeneration of the ortho signals has been observed . The macrocyclic aromaticity of 4 is less affected by the external ring fusion compared to the internally nonbridged system 5 .…”

“…The internal fusion does not prevent the formation of an externally fused ring involving C3 and an ortho carbon of the 5-aryl. For the systems comprising meso -aryls with electron-donating methoxy groups, which activate ortho-positions, the C3–C5 o bond formation is facile . It was already accomplished after 30 min of reflux in toluene for 2c or 2d acidified with trifluoracetic acid, and the conversion into 4c or 4d was practically quantitative (Scheme ).…”