1.1 Porphyrins - Friedrich-Alexander-Universität Erlangen-Nürnberg

3 Discussion and Results
3.2.7.2 Synthesis of Bis-Annulated Cycloketo-Porphyrin Systems (BCKPs)
As copper(II) complexes turned out to be best suited to access free-base systems after
annulation, the obtained porphyrin di-ethanoic acids were firstly converted thereto by
application of the acetate method 96,97 . Subsequently, they were transformed into their
corresponding acid chlorides by reaction with oxalyl chloride, C2O2Cl2, and finally cyclized
using tin tetrachloride, SnCl4, as appropriate FRIEDEL-CRAFTS catalyst. 96 Upon acidic
demetallation (TFA : H2SO4 = 5 : 1, rt, 45 min 96 ), five BCKPs were obtained in pure after
chromatography (67-71, Scheme 46, p. 93). The corresponding yields for those compounds
are summarized in Table 19. Thereby is to be kept in mind that 67 and 68 as well as 69 and
70 arose from one sole reaction each.
Table 19. Yields in which BCKPs 67-71 were isolated after the applied annulation protocols
based on the corresponding porphyrin di-ethanoic acids 75, 76 and 77 (Scheme 47, p. 94).
96
67 from 77 68 from 77 69 from 76 70 from 76 71 from 75
Overall Yield 51 % 12 % 58 % 14 % 70 %
Although the combined yields turned out to be excellent (> 60 %), 68 and 70 were only
formed in very low quantities implying some sort of directing effect in the formation of the
second exocycle disfavoring a diagonal positioning. Further discussion on that is done in
paragraph 3.2.7.7. Firstly, it should be focused on characterization and photophysical data.
3.2.7.3 NMR Spectroscopy
As already deducible from introductive Scheme 46, the BCKPs under investigation exhibit
quite different symmetry patterns majorly determining their NMR spectroscopic data. While
the chiral members of that group are of C2 symmetry (68, 69 and 71), the achiral “meso-
forms” appear to be of higher symmetries (Cs for 67 and Ci for 70). These assignments
concerning symmetry patterns thereby renounce the appearance of NH-tautomers since
those will not be observable at room temperature by NMR.
To sustain clarity, the spectra will not be compared to each other on the whole but step-wise
focusing on corresponding decisive regions. The complete data is summarized in the
experimental section. To start with, it should be concentrated on the assignment of the
abovementioned symmetry patterns.