Unexpectedly, the protonation of N-confused 21-thiapyriporphyrin 7-S did not
follow the track detected for 7. Thus, for 6,21-diphenyl-11,16-bis( p-tolyl)-24-thia3-aza-m-benziporphyrin 7-S, the addition of acid afforded 6-hydroxy-24-thia-3-azam-benziphlorin 32 (Scheme 15). The process was reversed by neutralization using
the nitrogen base. The outcome of adding water is regioselective and depends
strongly on the macrocyclic structure. Namely, the presence of bulky mesityl substituents at the meso position adjacent to the m-pyridine ring inhibited a nucleophilic
attack, leading to 32. Thus, the hydroxylation of 6,21-dimesityl-11,16-bis( p-tolyl)24-thia-3-aza-m-benziporphyrin 7-S occurred at the perimeter of the pyridine,
affording the aromatic 2-hydroxy-24-thia-3-aza-m-benzichlorin 31-OH or 2-ethoxy-24-thia-3-aza-m-benzichlorin 31-OEt when ethanol was added (Scheme 15).
The clear diatropicity of 31, detected by
1 H NMR, is consistent with 18π-electron
delocalization pathways, warranting the observation of the macrocyclic ring current
effect in the
1 H NMR spectra.
H
N
N
N
N
Ar 1
Ar 1
Ar 2
Ar 2
H
N
NH
N
N
Ar 1
Ar 1
Ar 2
Ar 2
H
N
NH
HN
N
Ar 1
Ar 1
Ar 2
Ar 2
H
N
NH
HN
H
N
Ar 1
Ar 1
Ar 2
Ar 2
H
+
H
+
H
+
H
+
H
+
7-H A
+
7-H 2
2+
7-H B
+
7-H 3
3+
7
N
NH
HN
N
Ar 1
Ar 1
Ar 2
Ar 2
Scheme 14 The protonation of meso-substituted 3-aza-m-benziporphyrin 7
HN
NH
N
Ar 1
Ar 1
S
+
HO
HO
Ar 2
Ar 2
1. TFA
2. DDQ
S
N
N
N
Ar 1
Ar 1
Ar 2
Ar 2
30
24
7-S
Scheme 13 Synthesis of meso-tetraryl-24-thia-3-aza-m-benziporphyrin 7-S
192
K. Hurej and L. Latos-Grażyński