The pyridinium species 52 underwent quantitative isomerization to 55 (Scheme
24) [73]. Presumably, the placement of a pyridinium moiety in the center of mbenziporphyrin triggered the peculiar rearrangement of 52, albeit observed solely on
the
1 H NMR scale. Eventually, m-benziphlorin 55 was formed with the
22-pyridiniumyl ring fused to the adjacent meso position. Formally, this resulted
in the incorporation of a new heterocyclic unit, 4a-azafluorene, into the porphyrinoid
skeleton.
3.2 Perimeter Modifications: Hydroxy and Alkoxy
Substituents
X 1
X 2
Essential perimeter modifications of the m-phenylene ring are addressed to C(2) or C
(2) and C(4) positions via hydroxy or alkoxy substitution, affording mesosubstituted 58 and β-substituted 60 derivatives [76–79]. The representative synthetic
route to the meso-substituted macrocycle 58 is shown in Scheme 25 [76]. However,
OHC
CHO PhMgBr
OH
Ar
Ar
OH
pyrrole,
ArCHO,
BF 3
.
Et 2 O
58
59
H
N
N
N
Ar
Ar
Ar
Ar
57
56
HO
HO
HO
H
N
NH
HN
Ar
Ar
Ar
Ar
O
58'-H 2
2+
58''-H 2
2+
59-H 2
2+
H
N
NH
HN
Ar
Ar
Ar
Ar
HO
H
N
NH
HN
Ar
Ar
Ar
Ar
O
H
N
NH
HN
Ar
Ar
Ar
Ar
HO
H
+
H
+
Scheme 25 Synthesis of meso-tetraaryl-2-hydroxy-m-benziporphyrin 59
A Pincer Motif Etched into a meta-Benziporphyrin Frame
199