1.1 Porphyrins - Friedrich-Alexander-Universität Erlangen-Nürnberg

3 Discussion and Results
(75 eq.) was used. The subsequent acidic saponification 96 , conducted in complete analogy,
furnished porphyrin di-ethanoic acids 75-77. While the reactions and the compounds are
depicted in Scheme 47, the corresponding yields, being throughout good to excellent, are
given in Table 18.
R 1
94
Br
N
NH HN
N
R 3
46 R 1 =Br, R 2 =R 3 =H
R 2
47 R 1 =H, R 2 =CH2Br, R 3 =CH3
48 R 1 =H, R 2 =CH3, R 3 =CH2Br
a.
R 1
CN
N
NH HN
N
R 3
R 2
b.
R 1
CO 2 H
N
NH HN
N
Scheme 47. Synthetic access to porphyrin di-ethanoic acids 75-77 via cyanation and
subsequent saponification. Applied conditions: a. 1. Zn(OAc)·2 H2O, CH2Cl2/MeOH, rt, 6h; 2.
KCN, PEG400, rt, 24h; 3. aq. HCl, CH2Cl2, rt, 10 min; b. AcOH/H2SO4/H2O, 95 °C, 96h.
Table 18. Overview on the isolated yields for the reactions depicted in Scheme 46.
Pathway Yield of bis-cyanation Yield of full saponification Overall yield
46 → 75 95 % 88 % 83.6 %
47 → 76 88 % 83 % 73.0 %
48 → 77 95 % 85 % 80.8 %
Thus, the direct precursors for the next step – the bis-annulation – were obtained providing
the abovementioned pre-organization: 75, having both acid functionalities on the same
phenyl substituent, one above one below the porphyrin plane, and 76 and 77 carrying those
groups on trans-standing phenyl rings. Thereby, both side chains are situated in one half-
space for 77 (αα-conformation) and oppositely for 76 (αβ-conformation). Both purity and
conformation were verified by 1 H-NMR spectroscopy like it is depicted in Figure 37 before
the bis-annulations were tackled.
72 R 1 =CN, R 2 =R 3 =H
73 R 1 =H, R 2 =CH2CN, R 3 =CH3
74 R 1 =H, R 2 =CH3, R 3 =CH2CN
R 3
75 R 1 =CO2H, R 2 =R 3 =H
R 2
76 R 1 =H, R 2 =CH2CO2H, R 3 =CH3
77 R 1 =H, R 2 =CH3, R 3 =CH2CO2H