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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.
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Regioselective oxidation of carbaporphyrinoid systems
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.
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- Award ID(s):
- 2247214
- PAR ID:
- 10620590
- Publisher / Repository:
- World Scientific
- Date Published:
- Journal Name:
- Journal of Porphyrins and Phthalocyanines
- Volume:
- 29
- Issue:
- 05n06
- ISSN:
- 1088-4246
- Page Range / eLocation ID:
- 557 to 582
- Subject(s) / Keyword(s):
- carbaporphyrins regioselective oxidation methylation aromaticity
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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