1.1 Porphyrins - Friedrich-Alexander-Universität Erlangen-Nürnberg

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3 Discussion and Results 3.2.2.1.2 An Alternative Route Using Cyanide Another approach to carboxylic acids involves nitrile precursors which can be introduced via cyanides. This alternative seemed to be adequate since cyanide is a good nucleophile, which could be saponified to the corresponding carboxylic acid. Thus, o-(cyanomethyl) porphyrin system 50 has been the logical sub-ordinate target: 36 Br N NH HN N S N reaction Scheme 27. Formation of sub-ordinate target 50. NC N NH HN N According to literature, the substitution of the benzylic bromide can be managed by reaction with NaCN or KCN in DMF at elevated temperature. 94 Correspondingly, free base bromomethyl porphyrin 45 has been treated for 12 h. After acidic work-up, a crude product material was obtained which consisted of the desired cyanomethyl porphyrin 50 being accompanied by two by-products, which were identified as the corresponding hydroxymethyl porphyrin and as the (N,N-dimethylamino)methyl porphyrin derivative. Repeating the experiment showed that the formation of these by-products, which arose from water and free amine in the used DMF, could not be suppressed. Nevertheless, the desired sub-ordinate target 50 could be obtained in pure after (repeated) FC in yields ranging between 60 % and 84 %. 45 50 To eliminate side reactions originating from the used solvent DMF, other reaction media have been considered. Typical organic solvents like THF or chlorinated solvents are well suited since the porphyrin precursor 45 is concerned, but fail in dissolving the salt providing the nucleophile. So crown ethers would have to be used or biphasic mixtures of solvents have to be applied together with phase transfer catalysts. That problem drew our attention to polyethylene glycols (PEGs) being capable to act as appropriate solvents as well as to efficiently complex alkali metal cations and thus enhance the substitution reaction. 95
NC N NH HN N N NH HN N Discussion and Results 3 With this in hand, trials were done using KCN as reagent in PEG 400 to react with bromomethyl porphyrin 45. These furnished the desired product in comparable yield without any observable by-products. By applying the corresponding zinc(II) porphyrin precursor Zn(II)-45, the yield could be risen reproducibly to 95 %. This enhancing effect results from the coordination of the generated ‘naked’ cyanide to the zinc(II) metal center increasing its local concentration close to the substitution site. This coordination phenomenon showed up by a color change of the solution from purple to dark turquoise. 96 Unfortunately, the same coordinative effect hampered the isolation and characterization, as the zinc(II) complexes eagerly aggregated becoming poorly soluble. This could be easily overcome by adding an acidic work-up step, which removed the zinc(II) metal center quantitatively 96 providing well soluble and pure samples for further reactions. For the final conversion into a carboxylic acid, the nitrile functionality had to be hydrolyzed. This can be generally achieved under acidic as well as under nucleophilic conditions (see Scheme 28). Several standard saponification methods were therefore tried. A summary including conditions and outcomes is presented in Table 4. catalyzed by H + or OH - /Nu - + 2 H 2 O - NH 3 HO 2 C 50 51 Scheme 28. Saponification of porphyrin ethanoic acid nitrile 50. 37
Page 1 and 2: Semi-Natural and Synthetic Chiral C
Page 3 and 4: Die vorliegende Arbeit entstand in
Page 5 and 6: Table of Contents 1 Introduction 1
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Page 22 and 23: 1 Introduction 1.2 Photodynamic The
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3 Discussion and Results phenyl sub
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3 Discussion and Results 3.2.6.5.4
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3 Discussion and Results 90 5 μA -
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3 Discussion and Results 3.2.7 Appr
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3 Discussion and Results (75 eq.) w
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3 Discussion and Results 3.2.7.2 Sy
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3 Discussion and Results of rotatio
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3 Discussion and Results Thus, the
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3 Discussion and Results Time-resol
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3 Discussion and Results first redu
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3 Discussion and Results correspond
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3 Discussion and Results The remain
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3 Discussion and Results 3.2.8.1 Us
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3 Discussion and Results With all t
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3 Discussion and Results The interm
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3 Discussion and Results 116 HO 2 C
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3 Discussion and Results nitro comp
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3 Discussion and Results The effect
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3 Discussion and Results 3.2.8.2.7
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3 Discussion and Results 3.2.9 Pote
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3 Discussion and Results peak at m/
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3 Discussion and Results Table 25.
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3 Discussion and Results 130
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4 Summary As the characterization d
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5 Zusammenfassung 5 Zusammenfassung
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5 Zusammenfassung Da in guten Ausbe
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6 Experimental Section UV/Vis spect
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6 Experimental Section 6.2 Studied
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6 Experimental Section 13 C NMR (10
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6 Experimental Section (cyanomethyl
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6 Experimental Section 6.2.4 AB3-Ty
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6 Experimental Section 6.2.4.3 5 4
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6 Experimental Section 6.2.4.11 10
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6 Experimental Section EA: C57H56N4
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6 Experimental Section 6.2.4.15 10
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6 Experimental Section 6.2.5 A2B2-T
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6 Experimental Section 6.2.5.5 αβ
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6 Experimental Section 6.2.5.7 αβ
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6 Experimental Section 6.2.5.9 αα
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6 Experimental Section 6.2.5.11 α
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6 Experimental Section 6.2.5.13 α
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6 Experimental Section 6.2.6 AB2C-T
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6 Experimental Section UV/Vis (CH2C
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6 Experimental Section UV/Vis (CH2C
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6 Experimental Section broad signal
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7 References 16 H. Fischer, K. Zeil
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7 References 57 S. Schwartz, K. Abs
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7 References 89 (a) R. C. Fuson, J.
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7 References 131 (a) J. Perdew, Phy
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S. Jasinski, N. Jux, “Investigati
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Ein großer Dank gilt auch den Ange
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Cirruculum vitae Stefan Jasinski Ge
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1.1 Porphyrins - Friedrich-Alexander-Universität Erlangen-Nürnberg

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