1.1 Porphyrins - Friedrich-Alexander-Universität Erlangen-Nürnberg

3 Discussion and Results
cyanomethyl porphyrin system 63 in high isolated yield (95 % based on 62). Upon acidic
saponification, the corresponding porphyrin carboxylic acid 64 could be obtained in 85 %
yield and provided the basis compound for the FRIEDEL-CRAFTS annulation procedure. Also
here, the full characterization of the intermediates is displayed in the experimental section.
For brief monitoring of the transformations not only the rising polarity from 62 over 63 to 64
could be used but also MS (for 63: m/z = 823 [M+H] +· and for 64: m/z = 841 [M] +· ) and 1 H
NMR data as the methylene group in the side chain underwent the already discussed
characteristic shift from 4.31 ppm (62) over 3.42 ppm (63) to 3.35 ppm (64).
For the build-up of the exocyclic ketone, 64 was firstly converted into the corresponding
copper(II) complex. Then, according to paragraph 3.2.2.2, the carboxylic acid was treated
with oxalyl chloride, C2O2Cl2, and tin tetrachloride, SnCl4. Upon acidic demetallation, free
base cycloketo-porphyrin 57 was isolated in 65 % yield based on 64 as a dark green
powder. 96
Like for 58, the detailed discussion of characterization data will be done later (paragraph
3.2.5.6) while here, only the 1 H NMR spectrum is to be presented (Figure 31).
For 57, the splitting pattern for the β-pyrrolic protons again reflects the present C1
symmetry. The signals appear mostly clearly resolved as one singlet (9.16 ppm) and three
sets of doublets in between 9.09 and 8.71 ppm ( 3 J ∼ 4.8 Hz). More upfield, the signals for the
phenyl substituents are visible but partially show an intense line broadening and strong
overlays. Thus, 57 is sharing major spectral characteristics with 53, which is also reflected by
the remainder of the resonances apart from the ones arising from the ABCD spin system in
the 5-phenyl substituent since that is not present in 53. These signals can be definitely
assigned as outstanding doublets of doublets (7.84 and 7.23 ppm) or doublets of triplets
(7.56 and 7.50 ppm). The exocyclic methylene group expectedly provides a pair of doublets
at 5.63 and 4.23 ppm with geminal couplings of about 11.7 Hz due to diastereotopicity. Like
for 53, the t-butyl groups of the system give rise to three well resolved singlets around
1.63 ppm being in full accordance to the system’s C1 symmetry. The inner-ring NH-protons
resonate at -1.70 ppm. That is being well comparable to the situation in 53, where the signal
is also shifted upfield by of over 1 ppm compared to the precursor.
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