Alternatively, β-alkylated 2-oxypyriporphyrin 66 was synthesized by a rather
atypical procedure which involved the ring expansion step of dihydroxychlorin 65
(Scheme 29) [82].
A spectacular approach to synthesize the derivatives of meso-tetraaryl-22-aza-3oxa-m-benziporphyrin 68 involves the controlled expansion of a pyrrole ring
[68]. Pandey and coworkers showed that the reaction of 2,3-dioxo-mesotetraphenylchlorin 67 with an excess of diazomethane creates the pyridinone frame
of 68 (Scheme 30) [83].
N
NH
HN
N
O
65
66
N
HN
N
NH
HO
OH
NaIO 4 –silica
Scheme 29 Synthesis of β-alkylated 2-oxypyriporphyrin via ring expansion
N
OHC
CHO
NH HN
HN
ROOC
ROOC
N
NH
HN
+
63
N
40
HO
O
64
1. TFA
2. DDQ
Scheme 28 Synthesis of
2-oxypyriporphyrin 64
N
NH
HN
N
Ar
Ar
Ar
Ar 2
N
NH
N
HN
Ar
Ar
Ar
Ar
O
O
O
MeO
CH 2 N 2
68
69
Scheme 30 Expansion of pyrrole ring to form 22-aza-3-oxa-m-benziporphyrin 68
A Pincer Motif Etched into a meta-Benziporphyrin Frame
201