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Carbaporphyrins exhibit rich and unique reactivities that form stable organometallic derivatives and unique oxidation reactions. In this review, the regioselective oxidation of carbaporphyrinoids is surveyed. True carbaporphyrins undergo core oxidation to give aromatic carbaporphyrin ketals and weakly aromatic oxycarbaporphyrins, while carbaporphyrin carbaldehydes are converted into aromatic trioxycarbaporphyrins. Azuliporphyrins are easily oxidized to benzocarbaporphyrins and nonaromatic 21-oxyazuliporphyrins. Oxidative metalations are also commonly observed in this system. In addition, other carbaporphyrinoids, including N-confused porphyrins and benziporphyrins, give rise to remarkable oxidation reactions that afford intriguing new structures. 

A series of porphyrinoids fused to highly electron-withdrawing bis(thiadiazolo)benzene units have been prepared and spectroscopically characterized. These structures have modified chromophores and exhibit large bathochromic shifts. The nickel(II), copper(II) and zinc complexes of a bis(thiadiazolo)benzoporphyrin were prepared, and these showed strong absorptions above 600 nm that shifted to longer wavelengths with increasing atomic number for the coordinated metal cations. Although the investigated porphyrinoids were poorly soluble, proton NMR data could be obtained, and these demonstrated that the structures possess global aromatic character. This was confirmed with nucleus-independent chemical shift (NICS) calculations and anisotropy of induced current density (AICD) plots. The AICD plots also demonstrate that the fused heterocyclic unit is disconnected from the porphyrinoid π-system, and in this respect, it differs from phenanthroline-fused porphyrinoids as it shows the presence of extended conjugation pathways. 

A series of porphyrin analogues with fused 1,10-phenanthroline units were synthesized. The proton NMR spectra for phenanthroline-fused heteroporphyrins showed significantly upfield shifted meso-proton resonances compared to related porphyrinoid systems and the peaks corresponding to alkyl substituents directly attached to these macrocycles were also observed further upfield. These results indicate that the presence of the phenanthroline unit leads to reduced diatropicity, but the internal NH resonance was also further upfield, a result that is inconsistent with this interpretation. A phenanthrene-fused carbaporphyrin gave an unexpectedly upfield singlet for the internal C−H at nearly −9 ppm, while the NH protons appeared at −6.8 ppm. These unusual chemical shifts again imply enhanced diatropicity but the reduced downfield shifts for the external protons indicates that the aromatic ring current has been significantly reduced. Similar results were obtained for phenanthroline-fused oxybenzi- and oxypyriporphyrins. Detailed analyses of the spectroscopic properties for these systems are reported and protonation studies were conducted. The conjugation pathways and aromatic properties were computationally analyzed using nucleus independent chemical shifts (NICS) and anisotropy of induced current density plots. 

cid catalyzed condensation of N-alkyltripyrranes with trialdehydes derived from 1,3-cyclopentadiene or methyl-1,3-cyclopentadiene, followed by oxidation with aqueous ferric chloride solutions, gave 23-alkyl-21- carbaporphyrin-2-carbaldehydes in 22−27% yield together with weakly aromatic oxycarbaporphyrins. The carbaporphyrins reacted with palladium(II) acetate or nickel(II) acetate to give organometallic complexes but in both cases alkyl group migration took place to generate 21-alkyl derivatives. Although this type of reactivity had been observed previously for palladium complexes, this is the first time the phenomenon has been seen in nickel(II) carbaporphyrins. Reactions with nickel(II) acetate in refluxing DMF for longer time periods primarily led to decomposition but unusual byproducts were identified. These could be obtained in higher yields by reacting the carbaporphyrin aldehydes with 5 equiv of (bis(trifluoroacetoxy)iodo)benzene in the presence of grade 3 alumina. Decarbonylation and oxidation generate a trioxocyclopentane moiety that is embedded in the porphyrinoid macrocycle. The new system has strongly aromatic properties that are evident from the proton NMR spectra, nucleus independent chemical shift (NICS) calculations and anisotropy of induced ring current plots. 

Acid-catalyzed condensation of a nitronaphthalene-fused dipyrrylmethane with dipyrrylmethane dialdehydes afforded unique dipyrromethene-naphthoporphyrin conjugates together with expected nitronaphthoporphyrins. The unusual conjugated system retained aromatic porphyrin-type characteristics but afforded highly modified UV−vis spectra with multiple absorptions throughout the visible region. 

A series of 5-alkoxy-1,3-benzenedicarbaldehydes and related dimers were prepared in three steps from dimethyl 5-hydroxyisophthalate. Acid catalyzed condensation of the dialdehydes with a tripyrrane dicarboxylic acid, followed by oxidation with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone, afforded good yields of 3-alkoxybenziporphyrins, although dimeric tetraaldehydes failed to give isolatable porphyrinoid products. Proton NMR spectroscopy gave no indication of an aromatic ring current, but addition of trifluoroacetic acid resulted in the formation of dications that exhibited weakly diatropic characteristics. Spectroscopic titration with TFA demonstrated that stepwise protonation took place, generating monocationic and dicationic species. 3-Alkoxybenziporphyrins reacted with nickel(II) or palladium(II) acetate to give the related nickel(II) or palladium(II) complexes. These stable organometallic derivatives showed increased diatropic properties that were most pronounced for the palladium(II) complexes. These unique porphyrinoids provide further insights into the properties of benziporphyrins.