1.1 Porphyrins - Friedrich-Alexander-Universität Erlangen-Nürnberg

3 Discussion and Results
3.2.6.2 10 4 ,15 4 ,20 4 -Tri-t-Butyl-5 2 -(Methoxycarbonyl)-5,10,15,20-Tetraphenylporphyrin
76
60 as General Precursor for 57 and 58
To access both model systems, the same precursor porphyrin 60 was used arising from the
condensation of methyl 2-formylbenzoate 59 and 4-t-butylbenzaldehyde with pyrrole under
LINDSEY conditions (Scheme 42). 96 This approach delivering the desired target in high yield
(17.4 % based on 59) was preferred to the corresponding dipyrromethane approach as that
only gave 1.8 % of 60 overall.
H
CO2Me + 3
O
H
59
O
+ 4 NH
MeO 2 C
N
NH HN
Scheme 42. Chosen synthesis of precursor porphyrin 60. Conditions: 1. BF3·OEt2, CHCl3, rt,
1 h; 2. add. DDQ, 2 h.
Since 60 exhibits a great resemblance to precursors like 45, 50 and 51 previously dealt with,
the discussion on characterization data will focus on specialties.
The aromatic region of the 1 H NMR spectrum of 60 shows up far more complex as the
lacking of the alkyl substituents gives rise to the typical resonance pattern of an ABCD spin
system in the 5-substituent. Thus, four signals are observed at 8.39 (dd), 8.15 (dd), 7.86 (dt)
and 7.81 (dt) ppm, respectively. The methyl group of the ester provides a singlet at 2.72 ppm
strongly shifted upfield compared to the parental aldehyde (3.91 ppm) implying a
positioning above the porphyrin core.
The ester functionality is also clearly visible in the 13 C NMR spectrum where the carboxylic
carbon atom characteristically resonates at 168.2 ppm while the signal for the methyl group
is found at 51.4 ppm.
By MS only the molecular mass peak was found at m/z = 841 and in the IR spectrum the
pronounced carbonyl vibration for the ester was detected at 1735 cm -1 .
N
60