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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.
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Synthesis, Reactivity and Aromatic Characteristics of Porphyrinoids Derived from N -Alkylcarbaporphyrin-2-Carbaldehydes: Isolation of Nickel(II) and Palladium(II) Complexes, Weakly Diatropic 21-Oxycarbaporphyrins and Strongly Aromatic Trioxycarbaporphyrins
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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- Award ID(s):
- 2247214
- PAR ID:
- 10620571
- Publisher / Repository:
- American Chemical Society
- Date Published:
- Journal Name:
- The Journal of Organic Chemistry
- Volume:
- 90
- Issue:
- 1
- ISSN:
- 0022-3263
- Page Range / eLocation ID:
- 202 to 216
- Subject(s) / Keyword(s):
- Carbaporphyrins regioselective oxidation metalation aromaticity
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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