Pyrazole analogues of porphyrins and oxophlorins

Article abstract of DOI:10.1039/c1ob05603d

A series of porphyrin analogues with pyrazole rings replacing one of the usual pyrrole subunits have been synthesized. This was accomplished by reacting 1-phenyl, 1-methyl and 1-ethyl pyrazole-1,3-dicarbaldehydes with a tripyrrane in the presence of TFA, followed by an oxidation step. The initially formed phlorin product was sufficiently stable for the N-phenyl system to be isolated and characterized, although the related N-alkyl phlorin analogues were less stable. Attempts to dehydrogenate the intermediary phlorins with DDQ resulted in decomposition, but the N-alkylphlorins could be oxidized with 0.2% aqueous ferric chloride solutions. Although the phenyl-substituted phlorin could not be oxidized under these conditions, it did afford the pyrazoloporphyrin upon treatment with silver acetate under acidic conditions. Oxidations with silver acetate also afforded oxophlorin analogues where the oxo-linkage was selectively formed at the 5-position. The pyrazole-containing porphyrin analogues are cross-conjugated and exhibit only a small degree of diatropic character. The internal CH resonances were observed between 5.27 and 5.87 ppm, while the external meso-protons fell into a range of 6.84-7.88 ppm. The borderline overall aromatic character was attributed to dipolar resonance contributors. Protonation considerably increased the diatropicity and the diprotonated dications formed from these porphyrin analogues gave the internal CH resonance at upfield values of 2.65-3.20 ppm. The aromatic character was enhanced by the presence of an electron-donating alkyl substituent on the nitrogen compared to the phenyl-substituted species. The pyrazoloporphyrins reacted with nickel(ii) acetate in DMF, or palladium(ii) acetate in acetonitrile, to give the corresponding organometallic derivatives. The metal complexes showed increased diatropic character but protonation afforded nonaromatic cations. The oxophlorin analogues were also nonaromatic in the free base and protonated forms. This work extends our understanding of carbaporphyrinoid systems and provides the first detailed studies on pyrazole-containing porphyrin analogues.

Full text of DOI:10.1039/c1ob05603d

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PAPER
Pyrazole analogues of porphyrins and oxophlorins†‡
Alexandra M. Young, Amber L. Von Ruden and Timothy D. Lash*
Received 14th April 2011, Accepted 14th June 2011
DOI: 10.1039/c1ob05603d
A series of porphyrin analogues with pyrazole rings replacing one of the usual pyrrole subunits have
been synthesized. This was accomplished by reacting 1-phenyl, 1-methyl and 1-ethyl pyrazole-1,3-
dicarbaldehydes with a tripyrrane in the presence of TFA, followed by an oxidation step. The initially
formed phlorin product was sufficiently stable for the N-phenyl system to be isolated and characterized,
although the related N-alkyl phlorin analogues were less stable. Attempts to dehydrogenate the
intermediary phlorins with DDQ resulted in decomposition, but the N-alkylphlorins could be oxidized
with 0.2% aqueous ferric chloride solutions. Although the phenyl-substituted phlorin could not be
oxidized under these conditions, it did afford the pyrazoloporphyrin upon treatment with silver acetate
under acidic conditions. Oxidations with silver acetate also afforded oxophlorin analogues where the
oxo-linkage was selectively formed at the 5-position. The pyrazole-containing porphyrin analogues are
cross-conjugated and exhibit only a small degree of diatropic character. The internal CH resonances
were observed between 5.27 and 5.87 ppm, while the external meso-protons fell into a range of
6
.84–7.88 ppm. The borderline overall aromatic character was attributed to dipolar resonance
contributors. Protonation considerably increased the diatropicity and the diprotonated dications
formed from these porphyrin analogues gave the internal CH resonance at upfield values of 2.65–3.20
ppm. The aromatic character was enhanced by the presence of an electron-donating alkyl substituent
on the nitrogen compared to the phenyl-substituted species. The pyrazoloporphyrins reacted with
nickel(II) acetate in DMF, or palladium(II) acetate in acetonitrile, to give the corresponding
organometallic derivatives. The metal complexes showed increased diatropic character but protonation
afforded nonaromatic cations. The oxophlorin analogues were also nonaromatic in the free base and
protonated forms. This work extends our understanding of carbaporphyrinoid systems and provides
the first detailed studies on pyrazole-containing porphyrin analogues.
1
4
Introduction
type tetraarylporphyrin syntheses. NCPs attracted considerable
15
interest due to their unusual properties. They have relatively
long wavelength absorptions compared to porphyrins and this
could lead to applications as photosensitizers in photodynamic
therapy. NCPs readily form organometallic derivatives and can
act as dianionic and trianionic ligands. In addition, coordination
can occur on the external nitrogen and this can lead to the
formation of supramolecular systems. These investigations have
been facilitated by the development of high yielding conditions for
the synthesis of NCPs. NCPs are generally isolated as the fully
aromatic tautomer 2, but this species is only slightly more stable
than the less aromatic cross-conjugated form 3 which is favored
in polar aprotic solvents. Alkylation of the external nitrogen
can also be used to trap the less aromatic form, and a rational
synthesis of N-methyl and N-phenyl NCPs 4 has been developed.
Although porphyrin analogues were first investigated in the
1,2
1
960s, it was not until 1986 that the first example of a porphyrin
3
,4
isomer 1 was reported by Vogel and coworkers. This system,
named porphycene due to its structural relationship to the acenes,
proved to be a stable aromatic system that readily forms metalated
16
17
5,6
derivatives. In the mid to late 1990s, further examples of
18
7,8
9,10
porphyrin isomers, specifically corrphycene, hemicorphycene
11
and isoporphycene, were synthesized. In these systems, all four
nitrogens are orientated into the macrocyclic cavity. However,
another type of porphyrin isomer 2 with an inverted pyrrole ring
was also discovered around this time.
isomer was named N-confused porphyrin (NCP) by Furuta,
19
12,13
This type of porphyrin
20
12
21
and was obtained as a by-product from Rothemund or Lindsey-
22
NCPs have a core arrangement of three nitrogens and one
carbon atom, and may be considered to be carbaporphyrinoids.
Contemporaneously with the initial studies on NCPs, other
examples of carbaporphyrinoids were also synthesized in the
Department of Chemistry, Illinois State University, Normal, Illinois, 61790-
4
160. E-mail: tdlash@ilstu.edu
†
Part 57 in the series ‘Conjugated Macrocycles Related to the Porphyrins’.
For part 56, see reference 52b.
23,24
25
1990s.
These included benzocarbaporphyrins 5, carbachlo-
‡
1
Electronic supplementary information (ESI) available. See DOI:
0.1039/c1ob05603d
26
27
28
rins 6, azuliporphyrins 7, tropiporphyrins 8, benziporphyrins
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29,30
30
9
and oxybenziporphyrins 10. Carbaporphyrinoids 5–10 were
all synthesized by using a ‘3 + 1’ version of the MacDonald
31,32
condensation.
In this methodology, a dialdehyde 11 is reacted
with a tripyrrane 12 in the presence of an acid catalyst, usually
TFA, and following oxidation, fully conjugated carbaporphyri-
31
been prepared using Lindsey–Rothemund type conditions. Tria-
noids can be generated (Scheme 1). This approach is quite ver-
2
2,33,34
zole analogues of the porphyrins 13 have also been prepared using
satile and can also be used to prepare NCPs.
More recently,
3
7,38
35
36
the MacDonald ‘3 + 1’ approach
and an alternative procedure
tetraaryl substituted benziporphyrins and azuliporphyrins have
39,40
was used to prepare imidazole-containing porphyrinoids 14.
However, pyrazole analogues of the porphyrins were not known.
Non-conjugated hexaphyrin analogues with two pyrazole subunits
41
(
e.g. 15) were investigated some time ago, but attempts to convert
this system into a fully aromatic macrocycle were unsuccessful.
More recently, Schiff base macrocycles 16 containing a pyrazole
subunit were reported by Br u¨ ckner and coworkers, but again
this system could not be oxidized to the related fully conjugated
42
texaphyrin analogue. However, very recently a fully conjugated
octaphenyl hexaphyrin analogue with two pyrazole rings was
43
reported. This “Siamese-twin” porphyrin is not aromatic but al-
43
lows the formation of bimetallic complexes. Our earlier attempts
to prepare a pyrazole-containing porphyrinoid system 18 by the
‘
3 + 1’ condensation of 1,3-pyrazoledicarbaldehyde (19) with a
44
tripyrrane were unsuccessful (Scheme 1). Nevertheless, pyrazole
analogues of the porphyrins are of interest because they extend
the “confused” aspect of these porphyrinoid macrocycles while
retaining the carbaporphyrinoid arrangement of core atoms. In
this paper, the synthesis of pyrazole-containing porphyrin ana-
45,46
logues and related oxophlorins is presented.
These porphyrin
analogues proved to have very different properties from regular
porphyrins or N-confused porphyrins.
Scheme 1
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294 | Org. Biomol. Chem., 2011, 9, 6293–6305
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Scheme 2
Scheme 3
conjugated pyrazoloporphyrin 25. However, attempts to oxidize
the crude product with DDQ led to complete decomposition.
In related work, it was found that dilute aqueous solutions of
ferric chloride could be used as a mild oxidant and may give
Results and discussion
The presence of substituents often aids in the formation
of porphyrin systems, and for this reason the synthesis of
pyrazole-containing porphyrin analogues from N-substituted
pyrazole dialdehydes 20 was investigated (Scheme 2). 1-Phenyl-
33,49
superior yields of conjugated porphyrinoid macrocycles.
This
transformation is usually carried out by vigorously shaking the
reaction solution in a separatory funnel with 0.1% aqueous ferric
chloride solution. Prolonged shaking (ca. 10 min) again led to
decomposition, but shorter exposure times failed to oxidize the
intermediate. Extraction and column chromatography on grade 3
basic alumina, eluting with dichloromethane, gave a blue fraction
that corresponded to the phlorin analogue 24a. This species was
moderately stable and could be recrystallized from chloroform–
methanol to give the macrocyclic product in 40% yield. The
position of the methylene bridge was confirmed by nOe difference
proton NMR spectroscopy. Reactions of dialdehydes 20b and 20c
were also carried out, and unstable phlorin products 24b and 24c
were observed by proton NMR spectroscopy prior to oxidation.
However, in these cases oxidation with 0.2% aqueous ferric
chloride solution gave the fully conjugated pyrazole-containing
porphyrin analogues 25b and 25c (Scheme 2). The reaction
3
,5-pyrazoledicarbaldehyde (20a) was prepared by a literature
47
method from the osazone of D-xylose. The corresponding N-
methyl and N-ethyl dialdehydes, 20b and 20c, were generated from
dimethyl pyrazole-1,3-dicarboxylate (21, Scheme 3). Alkylation
of pyrazole 21 with methyl or ethyl iodide affords N-alkylpyrazoles
48
22 and subsequent reduction with lithium aluminum hydride gave
the related dicarbinols 23. Subsequent oxidation with freshly
activated manganese dioxide in refluxing dioxane then gave the
required diformyl pyrazoles 20b and 20c in good yields. The methyl
substituted dialdehyde 20b has been reported previously but the
ethyl version 20c has been synthesized for the first time.
Phenylpyrazole dialdehyde 20a was reacted with tripyrrane 12 in
the presence of TFA in dichloromethane for 16 h (Scheme 2). This
affords a phlorin 24 that must then be oxidized to afford the fully
48a
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mixtures were shaken for 7–8 min with the ferric chloride solution,
and porphyrin analogues 25b and 25c were isolated as blue–green
crystals in 16–21% yield following column chromatography on
grade 3 basic alumina and recrystallization from chloroform–
ligroin.
Metalation studies were performed on phlorin 24a and
pyrazole-porphyrins 25b and 25c (see later). Silver(I) acetate has
50
been shown to react with tetraphenyl NCP 2, benzocarbapor-
51
52
52
phyrins 5, oxybenziporphyrins 10, oxynaphthiporphyrins and
28b
tropiporphyrins 8 to give silver(III) derivatives. With this in
mind, N-phenylphlorin analogue 21a was reacted with silver(I)
acetate in an attempt to generate the corresponding silver(III)
complex (Scheme 4). Although these conditions failed to form
any metallo-derivative, the conjugated macrocyclic product 25a
was unexpectedly formed instead. Based on these observations,
a modified ‘3 + 1’ procedure was carried out to prepare 25a
(
Scheme 2) where tripyrrane 12 was reacted with pyrazole
Fig. 1 UV-vis spectra of pyrazoloporphyrin 25a in 1% Et
3
N–chloroform
dialdehyde 20a for 4 h, followed by treatment with silver acetate
for 16 h. The alternative oxidation conditions gave the phenyl
substituted porphyrin analogue 25a in 18% yield, and thereby
provided us with a third member of the pyrazoloporphyrin series.
2+
(
free base, solid line) and 1% TFA–chloroform (dication 25aH
2
, dashed
line).
Scheme 4
Scheme 5
nowhere near as far downfield as those seen for true porphyrins
The phenyl substituted pyrazole porphyrin analogue gave a UV-
visible spectrum in 1% triethylamine–chloroform with a Soret-like
band at 395 nm and broad absorptions through the visible region
Fig. 1). Titration of this species in chloroform with TFA showed
the formation of a new species with 5–10 equiv TFA which was
assigned as the monoprotonated cation 25aH (Scheme 5). In the
presence of a larger excess of TFA, a bathochromically shifted
Soret-like band was observed at 403 nm (Fig. 1) and this new
species was attributed to the dication 25aH
UV-vis absorption spectra for 25b and 25c in 1% Et
53
(ca. 10 ppm), but the shifts are consistent with a system that has
a degree of diatropic character. This interpretation is reinforced
by the presence of relatively upfield NH resonances for 25b and
25c around 6.7 ppm, and the presence of a 1H singlet for the
internal CH near 5.3 ppm. The aliphatic region shows the methyl
resonances at 2.5 ppm, which is slightly downfield from values seen
for nonaromatic porphyrinoids, but again much less deshielded
than the values for fully aromatic porphyrinoid systems (ca.
(
+
2
+
2
(Scheme 5). The
N–CHCl
53
3
3
3.5 ppm). The proton NMR spectrum of 25a in CDCl gave
3
gave similar results showing Soret-like bands at 393 and 392 nm,
respectively, and broad absorptions at higher wavelengths. In the
presence of excess TFA, a stronger Soret band was observed near
four 1H singlets for the meso-protons at 6.84, 6.89, 7.39 and
7.87 ppm, a broadened peak for the NH at 7.19 ppm and the
internal CH singlet showing up near 5.9 ppm (Table 1). Again,
the internal protons show a small but significant upfield shift
demonstrating that the system has some diatropic character, and
the external meso-protons are slightly downfield compared to
4
10 nm.
The proton NMR spectra of 25a, 25b and 25c in CDCl were
3
very insightful, showing a series of 1H singlets for the meso-
protons between 6.8 and 7.9 ppm (Fig. 2). These values are
30b
nonaromatic porphyrinoids like benziporphyrin 9. However, the
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1
1
Table 1 H NMR shifts (ppm) for free base N-substituted pyrazole
Table 2 H NMR shifts (ppm) for protonated pyrazole porphyrins 25a–
2+
porphyrins 25a–c in CDCl
3
cH
2
in TFA–CDCl
3
5
-CH
20-CH
10,15-CH
21-CH
NH
5-CH
8.83
25b (R = Me) 8.72
25c (R = Et) 8.82
20-CH 10,15-CH 21-CH NH
2
2
2
5a (R = Ph)
5b (R = Me)
5c (R = Et)
7.87
7.82
7.88
7.39
7.45
7.47
6.84, 6.89
6.89, 6.95
6.92, 6.98
5.87
5.34
5.27
7.19
6.75
6.70
25a (R = Ph)
7.94
8.27
8.31
7.45, 7.49 3.20
7.47, 7.52 2.77
7.51, 7.56 2.64
Not observed
Not observed
Not observed
+
2+
formation of monocations 25H and dications 25H
2
. Addition
of trace amounts of TFA (1–10 eq.) to NMR solutions of 25b
or 25c gave poor quality spectra but a species could be observed,
for both methyl and ethyl substituted versions, where the meso-
protons were shifted downfield to between 7.6 and 8.8 ppm. The
internal CH was likely overlapped by the upfield multiplet at 1.5
ppm for the methyl version, as this integrated for an extra proton.
This spectrum also showed two broad peaks at 1.25 and 1.34
ppm that may correspond to shielded internal NHs. The ethyl
version, however, showed messy broad peaks upfield and was less
clearly identifiable. Nonetheless, these observations are consistent
+
with the formation of a monoprotonated species 25H that has a
slightly increased diatropic ring current compared to the free base
forms 25. Addition of one drop of TFA to an NMR solution of
2
5 in CDCl
3
changed the dark green colored solutions to brown
2
+
and gave a new species, attributed to dication 25H
2
, where the
meso-protons were shifted downfield to values between 6.9 and
8.8 ppm (Table 2, Fig. 3). The resonances for the two exterior
pyrrole methyl groups were also shifted downfield to between 2.6
and 3.2 ppm. Although the shifts for the external protons may be
attributable in part to the positive charges, these results suggest
that the diprotonated species has significantly increased diatropic
characteristics compared to the free base. The presence of the
internal CH resonances near 3 ppm provides the best evidence
for the presence of an enhanced diatropic ring current (Table 2,
Fig. 3). The observed increase in diatropicity is likely due to
resonance forms like 27 (Scheme 5) that aid in generating an 18 p
electron delocalization pathway. This type of contributor is more
favorable for the protonated form as charge separation is no longer
a factor and indeed this electronic interaction will aid in charge
delocalization. The pyrazole-substituents play a similar role in
stabilizing this canonical form, as the ethyl substituted version
Fig. 2 500 MHz proton NMR spectrum of pyrazole porphyrin 25c in
CDCl
3
.
proton NMR spectra of 25b and 25c in CDCl showed the meso-
3
protons a little further downfield between 6.8 and 7.9 ppm (e.g.,
Fig. 2), and the internal protons are also more upfield than the
resonances for 25a. Even so, the latter values are nowhere near
as far upfield as those seen in cross-conjugated azuliporphyrins
27
22
7
or 2-substututed NCPs 4. For instance, 2-methyl NCP 4a
shows the internal CH and NH resonances at 1.50 and 2.75 ppm,
respectively, while the external meso-protons give rise to four 1H
22
singlets between 8.00 and 8.47 ppm. Even the methyl resonances
for 4a are further downfield than in 25a–c, giving rise to two 3H
22
singlets at 2.83 and 2.84 ppm. The aromatic character of these
cross-conjugated porphyrinoids is attributed to dipolar resonance
contributors like 26 (Scheme 2). The comparative favorability of
this type of canonical form (i.e., structure 4¢) for 21-substituted
NCPs 4 is most likely because the positive charge is not placed
next to a nitrogen atom as is the case for 25a–c. If this hypothesis is
correct, an electron-donating alkyl group would stabilize this form
and lead to increased diatropicity compared to the poorly electron-
donating characteristics of a phenyl substituent. Hence, the lesser
diatropic character of phenyl-substituted pyrazole porphyrin 25a
is consistent with this proposal (Table 1). It is also worth
noting that an ethyl group is a more effective electron-donating
substituent than methyl, and the slightly increased downfield shifts
for the external protons and upfield shifts to the internal protons
for 25c also supports this interpretation.
Although the aromatic character of 25a–c can be attributed to
the presence of dipolar canonical forms like 26 (Scheme 2), this
contributor is not likely to be very favorable due to the requirement
for charge separation, as well as the placement of a positive charge
next to a nitrogen atom. Protonation studies were also carried out
Fig. 3 500 MHz proton NMR spectrum of pyrazole porphyrin dication
(
Scheme 5). Addition of TFA to solutions of 25 may lead to the
3
25c in TFA–CDCl .
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shows the largest shifts and the phenyl version the smallest shifts.
The porphyrin analogues were also characterized by carbon-13
NMR spectroscopy and mass spectrometry.
A new and unexpected oxidation product 28a was also observed
when phlorin 24a was oxidized using silver acetate (Scheme 6).
This oxophlorin product was first noted as a brightly colored blue
band that eluted after the turquoise porphyrin analogue 25a during
product purification by column chromatography. Following re-
crystallization from chloroform–ligroin, the oxophlorin analogue
28a was isolated as dark blue crystals in 9% yield. This type of
oxidation product could also be generated for the methyl and
ethyl-substituted systems, and a minor regioisomeric product 29
could also be identified for the ethyl series. The yield of oxophlorin
product was low for the methyl version (approximately 3%) but the
major oxophlorin analogue for the ethyl version was isolated in
1
4% yield. Proton NMR spectroscopy for the major blue oxidation
products gave very different spectra from the porphyrin analogues
5a–c. For example, oxophlorin 28a gave four singlets between 5.8
2
and 7.0 ppm, as well as two broad resonances for the NHs near 9.2
ppm (Fig. 4). As expected, these new macrocycles appear to have
no overall diatropic character based on the downfield resonances
for the internal NHs and the relatively upfield positions of the
meso-protons.
Fig. 4 Partial 500 MHz proton NMR spectrum showing the downfield
region for 28a in CDCl .
3
1
Table 3 H NMR shifts (ppm) for pyrazole oxophlorins 28a–c in TFA–
CDCl
3
1
0-CH
15-CH
20-CH
21-CH
NHs
2
2
2
8a (R = Ph)
8b (R = Me)
8c (R = Et)
6.90
6.89
6.90
6.07
6.05
6.06
6.14
6.13
6.15
5.79
5.56
5.50
9.08, 9.28
8.94, 9.17
8.91, 9.13
that these corresponded to three of the four possible meso-
protons (Table 3). The absence of the fourth meso-proton from
the spectra indicated that an oxidation had occurred at one of
these positions (identified as carbon 5). A carbonyl stretch was
-
1
present in the IR spectrum at 1625 cm , and the proposed
structures 28 were supported by carbon-13 NMR spectroscopy
and high resolution mass spectrometry. The UV-visible spectra
for 28 gave weak Soret-like bands near 380 nm and a broad lower
intensity band that stretched between 600 and 700 nm, confirming
that these compounds are not porphyrin-like and suggesting the
absence of an aromatic delocalization pathway. These results fit
the anticipated properties for compounds with a carbonyl at a
meso-position that interrupts any fully conjugated pathway. As
noted above, a second oxophlorin analogue 29 was also isolated
from oxidations of the ethyl substituted phlorin. This less favored
oxidation product was seen as a faint blue band that eluted in front
of the other oxidation products during column chromatography.
Proton NMR spectroscopy and NOE difference proton NMR
data for this compound indicate that the oxidation occurred at the
other meso-position flanking the pyrazole moiety. It is reasonable
to assume that the steric interactions between the N-substituent
and the carbonyl group leads to this product being less favored.
Addition of TFA to oxophlorins 28 gave rise to a color change
from dark blue to a bright green. The internal CHs shifted from
5.5–5.8 ppm to 6.69–6.94 ppm, which is farther downfield than
two of the meso-protons in this protonated form. These results
are likely due to the positive charges on the macrocycle resulting
from protonation, and the new species were attributed to dications
Scheme 6
NOE difference proton NMR spectroscopy was used to confirm
the identity of the oxophlorins and to assign the meso-proton
resonances. Irradiation of the peak near 5.5 ppm for 28c enhanced
both of the broad downfield NH peaks, indicating that this
singlet was due to the internal pyrazole CH. The other three
singlets between 6.0 and 7.0 ppm enhanced the methyl and
ethyl peaks around the exterior of the macrocycle confirming
2
+
28H
2
. There is no evidence for these species having an aromatic
6
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1
2+
Table 4 H NMR shifts (ppm) for pyrazole oxophlorins 28a–cH
TFA–CDCl
2
in
3
1
0-CH 15-CH 20-CH 21-CH NHs
2
2
2
8a (R = Ph)
8b (R = Me) 6.97
8c (R = Et) 6.96
7.07
6.32
6.21
6.19
6.37
6.72
6.68
6.69
6.90
6.94
8.53, 9.11, 9.85
9.25, 9.63, 10.57
9.28, 9.71, 10.62
delocalization pathway and the meso-protons are too far upfield to
be affected by any significant diamagnetic ring current (Table 4).
The color change observed may be due to tautomerization to a
cross-conjugated hydroxyporphyrin species 30 (Scheme 6). The
UV-vis spectra also showed the transformation to this species,
where the Soret-like band is slightly red shifted towards 400 nm
and a broad intense band appears between 700 and 800 nm (Fig. 5).
Further changes in the UV-vis spectrum were noted at higher
concentration of TFA (see ESI section).
Scheme 7
Fig. 5 UV-vis spectra of ethyl pyrazole oxophlorin 28c in chloroform
2+
(
free base, solid line) and 1% TFA–chloroform (28cH
2
, dashed line).
The pyrazole-containing porphyrin analogues 25 were all re-
acted with nickel(II) acetate in refluxing DMF to give the fully
conjugated nickel(II) derivatives 31 in 41–45% yield (Scheme 7);
the nickel complex for the phenyl version could also be prepared
directly from the unoxidized phlorin 24a. Similarly, porphyrin
analogues 25 or phlorin 24a could be reacted with palladium(II)
acetate in refluxing acetonitrile to give the corresponding palla-
dium(II) organometallic complexes 32 in 54–61% yield (Scheme 7).
The nickel(II) complexes gave green colored solutions that pro-
duced very different UV-vis spectra from the red–brown solutions
of the palladium(II) derivatives (Fig. 6 and 7). The nickel complexes
showed two strong bands near 340 and 390 nm, and a series of
weaker bands between 500 and 700 nm (Fig. 6). The palladium
complexes gave one major Soret-like band at 414–416 nm and
a series of broad absorptions extending into the far red region
Fig. 6 UV-vis spectra of nickel(II) complex 31c in chloroform (dashed
line) and in chloroform with 500 equiv TFA (31cH , solid line).
+
the diatropic character as palladium(II) is a better fit for the
macrocyclic core and the palladium derivatives would be expected
54
to be more planar than the nickel complexes. The substituent
on the pyrazole nitrogen also had little effect on these shifts
for the metal chelates, unlike the free base pyrazole porphyrins
and their diprotonated dications. An X-ray crystal structure for
palladium complex 32a was obtained and this demonstrated that
the macrocycle is quite planar. The structure exhibits framework
bond distances that are consistent with a localized p-bonding
system and the planarity was attributed to the requirements
(
Fig. 7). The proton NMR data for these Pd(II) and Ni(II)
55
derivatives all showed similar downfield shifts for the external
protons, with singlets showing up between 7.38 and 8.02 ppm
corresponding to the meso-resonances. These derivatives showed
significant downfield shifts compared to the parent porphyrinoid,
possibly due to dipolar resonance contributors like 33. However,
it is somewhat surprising that there is so little difference between
for metal binding. Addition of TFA to solutions of nickel or
palladium complexes 31 and 32 gave rise to simplified UV-vis
absorptions with a Soret-like band at 368–377 nm for 31a–c and
387–396 nm for the palladium derivatives 32a–c (Fig. 6 and 7).
Both series also showed a broad band running through most of
the visible region. The new species were attributed to monocations
This journal is © The Royal Society of Chemistry 2011
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1
3
(
1H, s); C NMR (CDCl
3
): d 15.9, 48.4, 52.40, 52.42, 114.4, 133.0,
1
42.0, 159.7, 162.2. Anal. calcd for C
9
H
12
N
2
4
O : C, 50.94; H, 5.70;
N, 13.20. Found: C, 51.06; H, 5.59; N, 12.91%.
1
-Ethyl-3,5-bis(hydroxymethyl)pyrazole (23c)
A solution of diethyl 1-ethyl-3,5-pyrazoledicarboxylate (4.00 g,
1
8.9 mmol) in sodium dried ether (100 mL) was added dropwise
to a suspension of lithium aluminum hydride (3.1 g, 80 mmol) in
sodium dried ether (100 mL), and the resulting mixture was stirred
under reflux overnight. The excess LiAlH was then hydrolyzed by
4
the slow dropwise addition of methanol (25 mL), followed by
the addition of saturated aqueous ammonium chloride solution
(
100 mL). Insoluble inorganic materials were removed by suction
filtration and these were washed with ether, ethyl acetate and
water. The combined filtrates were evaporated to give a solid, and
traces of water were removed azeotropically with ethanol. The
solid residue was then extracted using a Soxhlet apparatus with
Fig. 7 UV-vis spectra of palladium(II) complex 32c in chloroform (solid
line) and in chloroform with 500 equiv TFA (32cH , dashed line).
+
ethyl acetate to give 1-ethyl-3,5-bis(hydroxymethyl)pyrazole as a
1
pale yellow oil (2.91 g, 19 mmol, quantitative). H NMR (D
2
O):
+
+
3
1H and 32H , where protonation has taken place on the
d 1.38 (3H, t, J = 7.3 Hz), 4.16 (2H, q, J = 7.3 Hz), 4.58 (2H, s),
external nitrogen. The protonated species showed no signs of
1
3
4
1
.68 (2H, s), 6.35 (1H, s); C NMR (D
2
O): d 14.9, 44.0, 53.8, 57.0,
: 156.0898.
macrocyclic aromaticity by proton NMR spectroscopy. The meso-
04.6, 142.6, 150.7; HR MS (EI): Calc. for C
7
H
12
N
2
O
2
+
proton resonances in the nickel series 31H were shifted upfield
Found: 156.0904.
and showed up between 6.47–6.86 ppm, while the protonated
+
palladium complexes 32H gave these resonances slightly further
1
-Ethylpyrazole-3,5-dicarboxaldehyde (20c)
upfield between 6.33—6.86 ppm. The pyrrolic methyls were also
shifted upfield in all of the metalated species by 0.4–0.6 ppm, which
is consistent with the formation of a nonaromatic species. These
results are to be expected if the aromatic characteristics of the
nonprotonated metallo-derivatives are drawn from 18p electron
delocalized contributors like 33 because the protonated species
would have to place two positive charges directly next to one
another (structure 34) in order to obtain this type of interaction.
Activated MnO (3.20 g, 36.8 mmol) was added to refluxing
2
1
-ethyl-3,5-bis(hydroxymethyl)pyrazole (500 mg, 3.20 mmol) in
freshly distilled 1,4-dioxane (45 mL). The mixture was stirred
under reflux overnight, after which the insoluble material was
removed by filtration through Celite and the residues washed with
ether and dichloromethane. The filtrate was evaporated under
reduced pressure and the residue further purified on a silica column
eluting with dichloromethane. Upon evaporation of the solvent,
the dialdehyde (287 mg, 1.89 mmol, 59%) was obtained as a white
Conclusion
◦
1
solid, mp 40–41 C; H NMR (CDCl
3
) d 1.48 (3H, t, J = 7.2 Hz),
The first fully conjugated porphyrinoid systems with pyrazole
subunits have been synthesized and the nature of the N-substituent
has been shown to be a crucial factor for the stabilization of
this species. Interesting and unexpected oxidation side products
were also isolated and these results provide some insights into the
reactivity of this system. In addition, these diazacarbaporphyrins
readily form stable organometallic derivatives and in this respect
parallel the properties of the N-confused porphyrins.
4.65 (2H, q, J = 7.2 Hz), 7.39 (1H, s), 9.89 (1H, s), 9.99 (1H, s);
1
3
C NMR (CDCl ) d 15.4, 48.6, 114.7, 140.0, 150.4, 179.8, 185.7.
3
Anal. calcd for C H N O : C, 55.26; H, 5.30; N, 18.41. Found: C,
7
8
2
2
55.29; H, 5.18; N, 18.01%.
8,12,13,17-Tetraethyl-2,7,18-trimethyl-2,3-diaza-21-
carbaporphyrin (25b)
3
2d,56
Tripyrrane dicarboxylic acid 12
(100 mg, 0.22 mmol)
, then di-
luted with dichloromethane (99 mL) and 1-methylpyrazole-3,5-
was stirred for 1 min in TFA (1 mL) under N
2
Experimental
48a
dicarbaldehyde (31 mg, 0.22 mmol) was immediately added.
The reaction mixture was stirred under nitrogen in the dark for
16 h. The reaction solution was then shaken vigorously with 0.2%
w/v aqueous ferric chloride solution (100 mL) for 7–8 min. The
two layers were separated, the aqueous solution was extracted
with chloroform, and the combined organic solutions were washed
with water (100 mL) and saturated sodium bicarbonate solution
(100 mL). The solvent was evaporated under reduced pressure
and the dark colored residue was run through a grade 3 basic
alumina column, eluting with dichloromethane. A dark fraction
was collected and rechromatographed on grade 3 basic alumina,
eluting initially with 50% dichloromethane–hexanes and then with
Dimethyl 1-ethyl-3,5-pyrazoledicarboxylate (22c)
Iodoethane (6.8 g, 43.6 mmol) was added dropwise to a stirred mix-
48b
ture of dimethyl 3,5-pyrazoledicarboxylate (4.00 g, 21.7 mmol)
and potassium carbonate (3.0 g) in 80 mL of methyl ethyl ketone.
The mixture was stirred under reflux overnight, suction filtered,
and evaporated under reduced pressure. The residue was dissolved
in dichloromethane, washed with water and dried over sodium
sulfate. Recrystallization from hexanes gave dimethyl 1-ethyl-3,5-
pyrazoledicarboxylate (4.04 g, 19.0 mmol, 88%) as white crystals,
◦
1
mp 48–49 C; H NMR (500 MHz, CDCl
3
) d 1.46 (3H, t, J =
7
.2 Hz), 3.90 (3H, s), 3.93 (3H, s), 4.67 (2H, q, J = 7.2 Hz), 7.34
6
300 | Org. Biomol. Chem., 2011, 9, 6293–6305
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1
7
0% dichloromethane–hexanes. Green and blue colored fractions
H NMR (TFA–CDCl
3
): d 1.38–1.43 (12H, m), 1.71 (3H, t, J =
eluted initially, followed by a turquoise fraction that corresponded
to the pyrazole-containing porphyrin analogue. Evaporation of
the solvent gave the title compound (21.6 mg, 0.0465 mmol, 21%)
as blue–green crystals, mp >300 C. A sample was recrystallized
from chloroform–ligroin to give dark blue–green crystals, mp >
7.3 Hz), 2.65 (1H, s), 2.80 (3H, s), 2.84 (3H, s), 3.08–3.15 (8H, 4
overlapping quartets), 4.89 (2H, q, J = 7.3 Hz), 7.51 (1H, s), 7.56
1
3
(1H, s), 8.31 (1H, s), 8.82 (1H, s); C NMR (CDCl ): d 10.17,
3
◦
10.26, 15.7, 16.38, 16.45, 17.1, 18.44, 18.47, 18.61, 18.66, 45.7,
92.7, 94.2, 104.1, 108.9, 115.0, 137.4, 139.5, 140.0, 140.5, 141.1,
141.6, 142.8, 146.1, 146.7, 147.3, 157.4, 157.9, 166.4, 167.3; HR
◦
3
00 C; UV-vis (1% Et
3
N-CHCl
3
): lmax (log e) 323 (4.65), 393
): lmax (log e) 403
4.67), 526 (3.65), 567 (3.85), 711 (4.22), 787 nm (3.97); UV-vis
(
(
(
4.77), 639 nm (3.82); UV-vis (5 eq TFA–CHCl
3
MS (ESI): Calc. for C31
H
37
5
N + H: 480.3127. Found: 480.3122.
5% TFA–CHCl
88 (3.62), 735 nm (3.84); H NMR (CDCl
3
): lmax (log e) 348 (4.60), 408 (4.80), 546 (3.58),
8
,12,13,17-Tetraethyl-5,22-dihydro-7,18-dimethyl-2-phenyl-2,3-
1
5
3
): d 1.31–1.35 (6H, 2
diaza-21-carbaporphyrin (pyrazolophlorin 24a)
overlapping triplets), 1.39–1.43 (6H, 2 overlapping triplets), 2.49
6H, s), 2.84–2.90 (2H, 2 overlapping quartets), 2.97–3.03 (4H,
overlapping quartets), 4.50 (3H, s), 5.34 (1H, s), 6.75 (1H, br
32,56
(
Tripyrrane dicarboxylic acid 12
(100 mg, 0.220 mmol) was
2
stirred with TFA (1 mL) under nitrogen for 2 min. The mixture
was diluted with dichloromethane (99 mL) and 1-phenylpyrazole-
1
s), 6.89 (1H, s), 6.95 (1H, s), 7.45 (1H, s), 7.82 (1H, s); H NMR
trace TFA–CDCl ): d 1.46–1.51 (13H, m), 2.92 (6H, 2 overlapping
47
(
3
3,5-dicarbaldehyde (48.0 mg, 0.24 mmol) was immediately added
in a single portion. The resulting solution was stirred overnight
under nitrogen and then washed with water, 0.1% ferric chloride
solution, water, and saturated sodium bicarbonate (the aqueous
solutions were back-extracted with chloroform at each stage in the
extractions). The solvent was removed under reduced pressure and
the residue chromatographed on grade 3 basic alumina, eluting
with dichloromethane. The solvent was removed under reduced
pressure and recrystallized from chloroform–methanol to yield
singlets), 3.13–3.18 (4H, 2 overlapping quartets), 3.20–3.26 (4H, 2
overlapping quartets), 4.73 (3H, s), 7.69 (1H, s), 7.73 (1H, s), 8.65
1
(
1H, s), 8.76 (1H, s); H NMR (TFA–CDCl
3
): d 1.37–1.43 (12H,
s), 2.77 (1H, s), 2.79 (3H, s), 2.83 (3H, s), 3.06–3.14 (8H, m), 4.56
1
3
(
3H, s), 7.47 (1H, s), 7.52 (1H, s), 8.27 (1H, s), 8.72 (1H, s); C
NMR (CDCl ): d 10.17, 10.23, 15.6, 16.4, 18.45, 18.47, 18.6, 37.7,
3
9
2.7, 94.3, 104.3, 109.0, 114.9, 138.4, 139.4, 140.05, 140.52, 141.1,
1
3
1
41.6, 142.8, 146.2, 146.7, 147.5, 157.5, 157.9, 166.5, 167.5;
): d 10.7, 10.9, 14.62, 14.66, 15.4, 15.5, 18.46,
8.50, 18.80, 18.86, 39.9, 93.6, 94.9, 95.9, 109.2, 120.9, 137.5, 142.9,
43.9, 144.3, 145.2, 145.5, 146.8, 147.3, 147.7, 147.9, 153.3, 154.8,
C
NMR (TFA–CDCl
3
the pyrazole phlorin analogue (47.5 mg, 0.090 mmol, 41%) as
◦
1
1
1
4
dark blue crystals, mp >300 C; UV-vis (1% Et
3
N-CHCl ): lmax
3
1
(log e) 377 (4.67), 528 (sh, 4.08), 578 (4.27), 627 (4.28); H NMR
(CDCl ): d 1.16–1.25 (12H, m), 2.09 (3H, s), 2.15 (3H, s), 2.56–
2.63 (4H, m), 2.64–2.74 (4H, m), 4.17 (2H, s), 5.84 (1H, s), 5.90
1H, s), 6.34 (1H, s), 6.84 (1H, s), 7.35 (1H, t, J = 7.0 Hz), 7.44 (2H,
59.1, 159.9; HR MS (EI): Calc. for C30
65.2893.
H
35
N
5
: 465.2893. Found:
3
(
1
3
t, J = 7.8 Hz), 7.51 (2H, d, J = 8.0 Hz), 9.17 (2H, br s); C NMR
CDCl ): d 9.1, 9.5, 14.8, 16.0, 16.5, 17.3, 17.8, 18.27, 18.29, 18.4,
6.1, 87.2, 89.4, 104.7, 111.8, 116.7, 124.7, 127.6, 129.0, 129.2,
129.3, 132.1, 133.5, 136.2, 137.5, 140.5, 141.4, 146.0, 147.3, 147.8,
148.1, 165.1; HR MS (FAB): Calc. for C35 : 529.3205. Found:
529.3206. Anal. calcd for C35
·0.6CHCl
N, 11.64. Found: C, 70.79; H, 6.70; N, 11.22%.
2
,8,12,13,17-Pentaethyl-7,18-dimethyl-2,3-diaza-21-
(
2
3
carbaporphyrin (25c)
32d,56
Tripyrrane dicarboxylic acid 12
1
(100 mg, 0.22 mmol) and
-ethylpyrazole-3,5-dicarbaldehyde (36.5 mg, 0.24 mmol) were
H
39
N
5
reacted under the foregoing conditions. The crude product was
run through a grade 3 basic alumina column eluting with
dichloromethane. A dark fraction was collected and rechro-
matographed on grade 3 basic alumina, eluting first with 50%
dichloromethane–hexanes and then with 70% dichloromethane–
hexanes. Blue colored fractions eluted initially, followed by a
turquoise fraction that corresponded to the pyrazole-containing
porphyrin analogue. Evaporation of the solvent and recrystalliza-
H
39
N
5
3
: C, 71.10; H, 6.30;
8
,12,13,17-Tetraethyl-7,18-dimethyl-2-phenyl-2,3-diaza-21-
carbaporphyrin (25a)
32d,56
Tripyrrane dicarboxylic acid 12
(100 mg, 0.22 mmol) was
stirred with TFA (1 mL) under nitrogen for 2 min. The mixture
47
tion from chloroform–ligroin gave 25c (16 mg, 0.035 mmol, 16%)
as dark blue–green crystals, mp > 300 C. UV-vis (1% Et
was diluted with dichloromethane (99 mL) and dialdehyde 20a
◦
3
N–
(48.0 mg, 0.24 mmol) was immediately added in a single portion.
The resulting solution was stirred for 4 h under nitrogen and
then oxidized overnight with silver acetate (77 mg, 0.46 mmol).
The mixture was then washed with water, followed by saturated
sodium bicarbonate (the aqueous solutions were back-extracted
with chloroform at each stage in the extractions). The solvent was
removed under reduced pressure and the residue chromatographed
on grade 3 basic alumina, eluting with dichloromethane, to give an
early turquoise fraction. The solvent was removed under reduced
pressure and the residue was recrystallized from chloroform–
CHCl
3.77), 694 nm (sh, 3.57); UV-vis (20 equiv TFA–CHCl
e) 293 (4.46), 320 (4.33), 364 (4.64), 406 (4.81), 489 (3.49), 526
3.78), 566 (3.95), 720 (4.00), 789 nm (4.27); UV-vis (1% TFA–
3
): lmax (log e) 324 (4.64), 393 (4.78), 594 (sh, 3.57), 643
(
3
): lmax (log
(
CHCl
5
3
): lmax (log e) 277 (4.25), 304 (4.34), 348 (4.59), 411 (4.81),
1
47 (3.38), 590 (3.42), 740 (3.83), 794 nm (sh, 3.77); H NMR
(CDCl
3
): d 1.32–1.36 (6H, 2 overlapping triplets), 1.42 (6H, t, J =
7
2
4
.7 Hz), 1.72 (3H, t, J = 7.3 Hz), 2.505 (3H, s), 2.507 (3H, s),
.89 (4H, q, J = 7.7 Hz), 2.98–3.04 (4H, 2 overlapping quartets),
.85 (2H, q, J = 7.3 Hz), 5.27 (1H, s), 6.70 (1H, br s), 6.92 (1H,
methanol to yield the pyrazoloporphyrin (20 mg, 18%) as dark
1
◦
s), 6.98 (1H, s), 7.47 (1H, s), 7.88 (1H, s); H NMR (trace TFA–
blue–green crystals, mp >300 C; UV-vis (1% Et
3
N–CHCl ): lmax
3
CDCl
3
): d 1.43–1.47 (12H, m), 1.74 (3H, t, J = 7.3 Hz), 1.96 (1H,
(log e) 318 (4.49), 395 (4.70), 595 (sh, 3.65), 643 (3.70), 695 nm (sh,
br s), 2.87 (3H, s), 2.88 (3H, s), 3.10–3.21 (8H, m), 4.98 (2H, q,
3.51); UV-vis (10 equiv TFA–CHCl ): lmax (log e) 292 (sh, 4.38),
3
J = 7.3 Hz), 7.60 (1H, s), 7.64 (1H, s), 8.43 (1H, s), 8.75 (1H, s);
302 (4.39), 372 (sh, 4.55), 408 (4.64), 489 (sh, 3.63), 529 (3.77), 570
This journal is © The Royal Society of Chemistry 2011
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◦
(
(
3.91), 727 (3.87), 798 nm (4.05); UV-vis (1% TFA–CHCl
3
): lmax
0.0073 mmol, 41%) as dark green crystals, mp >300 C; UV-
log e) 322 (4.45), 416 (4.66), 550 (3.72), 594 (3.72), 738 (3.73), 804
vis (CHCl
3
): lmax (log e) 342 (4.61), 394 (4.60), 499 (3.73), 535
): lmax (log e)
368 (4.65), 458 (4.19), 670 nm (3.52); H NMR (CDCl ): d 1.35–
1.39 (6H, 2 overlapping triplets), 1.44–1.47 (6H, 2 overlapping
triplets), 1.81 (3H, t, J = 7.3 Hz), 2.57 (3H, s), 2.58 (3H, s), 2.95–
3.08 (8H, 4 overlapping quartets), 4.90 (2H, q, J = 7.4 Hz), 7.46
1
nm (sh, 3.65); H-NMR (CDCl
triplets), 1.39–1.43 (6H, 2 overlapping triplets), 2.37 (3H, s), 2.49
3H, s), 2.82–2.88 (4H, 2 overlapping quartets), 2.96–3.01 (4H,
3
): d 1.30–1.35 (6H, 2 overlapping
(3.92), 613 nm (3.83); UV-vis (500 eq TFA–CHCl
3
1
3
(
2
7
overlapping quartets), 5.87 (1H, s), 6.84 (1H, s), 6.89 (1H, s),
.19 (1H, br s), 7.39 (1H, s), 7.54 (1H, t, J = 7.7 Hz), 7.65 (2H,
1
1
t, J = 7.7 Hz), 7.79 (2H, d, J = 7.3 Hz), 7.87 (1H, s); H NMR
(1H, s), 7.50 (1H, s), 7.62 (1H, s), 8.02 (1H, s); H NMR (TFA–
(
trace TFA–CDCl
s), 3.02–3.12 (8H, m), 7.44 (1H, s), 7.48 (1H, s), 7.60 (1H, t, J =
.4 Hz), 7.67 (2H, t, J = 7.4 Hz), 7.74 (2H, d, J = 7.4 Hz), 7.89
3
): d 1.37–1.42 (13H, m), 2.63 (3H, s), 2.75 (3H,
CDCl ): d 1.18–1.23 (6H, 2 overlapping triplets), 1.26–1.30 (6H,
3
2 overlapping triplets), 1.64 (3H, t, J = 7.3 Hz), 2.17 (3H, s), 2.22
(3H, s), 2.58–2.62 (4H, 2 overlapping quartets), 2.66–2.70 (4H, 2
overlapping quartets), 4.73 (2H, quartet, J = 7.3 Hz), 6.54 (3H,
7
(
4
4
7
1
1H, s), 8.51 (1H, s); H NMR (TFA–CDCl ): d 1.37–1.43 (12H,
3
1
3
overlapping triplets), 2.68 (3H, s), 2.84 (3H, s), 3.04–3.13 (8H,
br s), 6.86 (1H, br s); C NMR (CDCl ): d 10.5, 10.6, 15.6, 15.7,
3
overlapping quartets), 3.20 (1H, s), 7.45 (1H, s), 7.49 (1H, s),
16.74, 16.76, 16.9, 18.67, 18.72, 18.8, 45.6, 53.6, 95.3, 96.2, 101.8,
109.6, 113.7, 136.7, 138.9, 139.9, 140.7, 141.5, 144.60, 144.63,
146.7, 149.1, 149.8, 153.3, 154.0, 158.4, 159.1; HR MS (EI): Calc.
1
3
.63–7.76 (5H, m), 7.94 (1H, s), 8.83 (1H, s); C NMR (CDCl ):
3
d 10.2, 15.6, 16.32, 16.39, 18.40, 18.43, 18.58, 18.60, 92.9, 94.1,
106.1, 109.5, 114.7, 127.0, 128.3, 129.6, 138.2, 139.7, 140.1, 140.6,
for C31
H
35
N
5
Ni 535.2246. Found: 535.2232.
141.1, 141.8, 142.7, 146.6, 147.7, 148.2, 157.9, 158.8, 167.2, 167.8;
HR MS (EI): Calc. for C35
H
37
5
N : 527.3049. Found: 527.3044.
[
8,12,13,17-Tetraethyl-7,18-dimethyl-2-phenyl-2,3-diaza-21-
carbaporphyrinato]nickel(II) (31a)
[
8,12,13,17-Tetraethyl-2,7,18-trimethyl-2,3-diaza-21-
Two equivalents of nickel(II) acetate tetrahydrate (12.0 mg,
carbaporphyrinato]nickel(II) (31b)
0.048 mmol) were added to a solution of 2,3-diaza-21-
Porphyrin analogue 25b (34 mg, 0.0731 mmol) and nickel(II)
acetate tetrahydrate (36 mg; 0.145 mmol; 2 equiv) were reacted
in DMF (37 mL) and the solution was stirred under reflux for
carbaporphyrin 25a (12.7 mg, 0.024 mmol) in DMF (13 mL), and
the solution was stirred under reflux for 30 min. The solution
was cooled, diluted with chloroform, and washed with water.
The organic layer was separated, evaporated to dryness and chro-
matographed on grade 3 basic alumina, eluting with chloroform,
to give a dark green band. The solvent was removed under reduced
pressure and the residue recrystallized from chloroform–methanol
3
0 min. The solution was cooled, diluted with chloroform, and
washed with water. The organic layer was separated, evaporated
to dryness and chromatographed on grade 3 basic alumina, eluting
with chloroform, to give a dark green band. Recrystallization
from chloroform–methanol gave the nickel complex (17.0 mg,
to yield the nickel(II) complex (6.0 mg, 43%) as dark purple
◦
◦
0
.0326 mmol, 45%) as dark green crystals, mp >300 C; UV-vis
crystals, mp >300 C; (UV-vis CHCl
3
): lmax (log e) 343 (4.66), 394
(
6
l
CHCl
3
): lmax (log e) 340 (4.64), 393 (4.62), 497 (3.72), 533 (3.91),
(4.67), 498 (4.08), 535 (4.18), 624 (4.06), 883 nm (3.84); (UV-vis
TFA–CHCl ): lmax (log e) 377 (4.71), 529 (3.98), 632 (4.01), 883 nm
(3.83); H-NMR (CDCl ): d 1.33–1.39 (6H, m), 1.43–1.47 (6H, m),
14 (3.85), 731 (2.86), 870 nm (2.83); UV-vis (1% TFA–CHCl ):
3
1
3
1
max (log e) 325 (4.44), 370 (4.70), 683 (3.69), 842 nm (3.08); H
): d 1.34–1.39 (6H, 2 overlapping triplets), 1.42–1.47
6H, 2 overlapping triplets), 2.54 (3H, s), 2.56 (3H, s), 2.93–3.07
8H, m), 4.53 (3H, s), 7.43 (1H, s), 7.47 (1H, s), 7.56 (1H, s), 7.96
3
NMR (CDCl
3
2.53 (3H, s), 2.62 (3H, s), 2.92–3.06 (8H, 2 overlapping quartets),
7.38 (1H, s), 7.45 (1H, s), 7.54 (1H, t, J = 8.0 Hz), 7.58 (1H, s),
7.68 (2H, t, J = 7.8 Hz), 7.86 (2H, d, J = 7.6 Hz), 8.02 (1H, s);
(
(
(
1
1
1H, s); H NMR (TFA–CDCl
3
): d 1.16–1.21 (6H, 2 overlapping
H-NMR (TFA–CDCl3): d 1.18–1.22 (6H, m), 1.26–1.31 (6H, m),
triplets), 1.27 (6H, t, J = 7.5 Hz), 2.13 (3H, s), 2.15 (3H, s), 2.53–
2.06 (3H, s), 2.17 (3H, s), 2.58–2.68 (8H, m), 6.50 (3H, br s), 6.83
1
3
2
.58 (4H, 2 overlapping quartets), 2.63–2.67 (4H, 2 overlapping
(1H, br s), 7.57 (2H, m), 7.66–7.71 (3H, m); C NMR (CDCl ): d
3
1
3
quartets), 4.31 (3H, s), 6.47 (2H, s), 6.52 (1H, s), 6.78 (1H, s);
C
10.4, 10.5, 15.4, 15.5, 15.6, 16.6, 18.66, 18.71, 18.8, 29.9, 95.5, 96.1,
104.1, 108.6, 110.8, 113.6, 126.5, 128.3, 129.6, 137.3, 139.3, 140.0,
140.4, 141.1, 141.5, 144.6, 144.9, 145.7, 148.3, 149.7, 151.1, 154.3,
NMR (CDCl ): d 10.46, 10.54, 15.6, 15.7, 16.70, 16.75, 18.65,
3
1
1
1
8.70, 18.8, 37.7, 95.3, 96.2, 102.0, 109.6, 113.6, 137.7, 138.9,
39.8, 140.7, 141.4, 144.61, 144.62, 146.7, 149.2, 149.8, 153.4,
154.4, 158.9, 160.0; HR MS (EI): Calc. for C35
Found: 583.2248. Anal. calcd for C35
H, 6.11; N, 11.79. Found: C, 70.56; H, 6.11; N, 11.33%.
H
35
N
5
Ni: 583.2246.
O: C, 70.84;
54.1, 158.5, 159.2; HR MS (EI): Calc. for C30
H
33
N
5
Ni: 521.2089.
H
35
N
5
Ni·0.5H
2
Found: 521.2093.
[
2,8,12,13,17-Pentaethyl-7,18-dimethyl-2,3-diaza-21-
[8,12,13,17-Tetraethyl-2,7,18-trimethyl-2,3-diaza-21-
carbaporphyrinato]palladium(II) (32b)
carbaporphyrinato]nickel(II) (31c)
Porphyrin analogue 25c (9.0 mg, 0.017 mmol) and nickel(II)
acetate tetrahydrate (12 mg, 0.047 mmol) were reacted in DMF
Pyrazole porphyrin analogue 25b (21.0 mg, 0.045 mmol) was
reacted with palladium(II) acetate (10.0 mg; 0.045 mmol) in
acetonitrile (65 mL) and the solution was stirred under reflux for
30 min. The solution was cooled, diluted with chloroform, washed
with water, and the organic layer separated and then evaporated
to dryness. Following chromatography on grade 3 basic alumina,
eluting with chloroform, the product was recrystallized from
chloroform–methanol to give the palladium complex (15.7 mg,
(
10 mL) and the solution was stirred under reflux for 30 min.
The solution was cooled, diluted with chloroform, and washed
with water. The organic layer was separated, evaporated to
dryness and chromatographed on grade 3 basic alumina, eluting
with chloroform, to give a dark green band. Recrystallization
from chloroform–methanol gave the nickel complex (4.3 mg,
6
302 | Org. Biomol. Chem., 2011, 9, 6293–6305
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◦
◦
0
.0276 mmol, 61%) as dark purplish brown crystals, mp >300 C;
UV-vis (CHCl ): lmax (log e) 320 (4.45), 347 (4.48), 368 (4.47), 414
4.63), 533 (3.93), 570 (3.87), 674 (3.35), 738 (3.44), 816 nm (3.24);
mp >300 C; UV-vis (CHCl
3
): lmax (log e) 416 (4.68), 523 (4.18),
3
575 (4.11), 672 (3.86), 731 (3.87), 817 (3.78), 883 nm (3.84); UV-vis
(TFA–CHCl
(4.15), 678 (3.88), 742 (3.88), 883 nm (3.85); H-NMR (CDCl3):
d 1.34–1.48 (12H, 4 overlapping triplets), 2.53 (3H, s), 2.62 (3H,
s), 2.96–3.05 (8H, m), 7.35 (1H, s), 7.40 (1H, s), 7.57 (1H, t, J =
(
3
): lmax (log e) 396 (4.66), 483 (4.09), 522 (4.16), 544
1
UV-vis (1% TFA–CHCl
3
1
3
): lmax (log e) 304 (4.52), 370 (sh, 4.63),
1
87 (4.96), 576 (3.64), 817 nm (3.47); H NMR (CDCl
3
): d 1.38–
.42 (6H, 2 overlapping triplets), 1.44–1.48 (6H, 2 overlapping
triplets), 2.62 (3H, s), 2.64 (3H, s), 2.94–3.06 (8H, m), 4.59 (3H,
s), 7.41 (1H, s), 7.45 (1H, s), 7.63 (1H, s), 7.97 (1H, s); H NMR
7.6 Hz), 7.61 (1H, s), 7.69 (2H, t, J = 7.8 Hz), 7.90 (2H, d, J =
1
1
7.6 Hz), 8.02 (1H, s); H-NMR (TFA–CDCl
3
): d 1.18–1.23 (6H, 2
(
2
(
1
1
1
5
TFA–CDCl
3
): d 1.19–1.29 (12H, m), 2.22 (3H, s), 2.23 (3H, s),
overlapping triplets), 1.25–1.29 (6H, 2 overlapping triplets), 2.09
(3H, s), 2.20 (3H, s), 2.54–2.64 (8H, 4 overlapping quartets), 6.33
(3H, br s), 6.79 (1H, br s), 7.58–7.60 (2H, m), 7.66–7.68 (3H, m);
.56–2.67 (8H, m), 4.34 (3H, s), 6.41 (2H, s), 6.49 (1H, s), 6.86
1
3
1H, s); C NMR (CDCl
3
): d 10.37, 10.45, 15.5, 15.6, 16.7, 16.8,
8.62, 18.64, 18.8, 18.9, 37.7, 95.6, 96.8, 104.3, 115.7, 119.6, 135.7,
37.8, 138.6, 140.1, 140.7, 143.85, 143.92, 144.2, 146.6, 147.4,
1
3
C NMR (CDCl ): d 10.9, 16.3, 16.4, 16.6, 16.8, 17.4, 19.17, 19.22,
3
19.5, 30.0, 96.0, 96.6, 106.7, 113.3, 119.4, 121.7, 127.2, 128.8, 130.0,
131.2, 135.5, 136.2, 136.9, 138.3, 139.3, 140.0, 140.5, 142.2, 143.4,
143.8, 144.7, 145.3, 146.0, 147.3, 149.3, 150.5; HR MS (EI): Calc.
52.1, 152.5, 155.5, 156.2; HR MS (EI): Calc. for C30
69.1771. Found: 569.1767.
H
33
5
N Pd:
for C35
H
35
5
N Pd: 631.1927. Found: 631.1930.
[2,8,12,13,17-Pentaethyl-7,18-dimethyl-2,3-diaza-21-
carbaporphyrinato]palladium(II) (32c)
Pyrazole porphyrin analogue 25c (9.0 mg, 0.017 mmol) was reacted
with palladium(II) acetate (6.0 mg, 0.026 mmol) in acetonitrile
8,12,13,17-Tetraethyl-5,22-dihydro-2,7,18-trimethyl-5-oxo-2,3-
diaza-21-carbaporphyrin (pyrazolo-oxophlorin 28b)
(
40 mL) and the solution was stirred under reflux for 30 min.
3
2d,56
Tripyrrane dicarboxylic acid 12
was stirred for 1 min in TFA (1 mL) under N
luted with dichloromethane (99 mL) and 1-methylpyrazole-3,5-
(100 mg, 0.22 mmol)
The solution was cooled, diluted with chloroform, washed with
water, and the organic layer separated and then evaporated to
dryness. Following chromatography on grade 3 basic alumina,
eluting with chloroform, the product was recrystallized from
chloroform–methanol to give the palladium complex (5.3 mg,
2
, then di-
48a
dicarbaldehyde (33 mg, 0.24 mmol) was immediately added.
The reaction mixture was stirred under nitrogen in the dark for
h and then was oxidized overnight by continued stirring with
silver acetate (77 mg, 0.46 mmol). The solution was then washed
with water (150 mL) and saturated sodium bicarbonate solution
150 mL), back extracting at each stage with chloroform. The
solvent was evaporated under reduced pressure and the dark
colored residue was run through a grade 3 basic alumina column
eluting with dichloromethane. A dark fraction was collected and
rechromatographed on grade 3 basic alumina eluting with 50%
dichloromethane–hexanes. Unidentified green and blue colored
fractions eluted initially followed by a turquoise fraction that
corresponded to the pyrazole-containing porphyrin analogue, and
finally a dark blue fraction containing the oxophlorin product.
Evaporation of the solvent and recrystallization from chloroform–
4
0
.0089 mmol, 54%) as dark purplish brown crystals, mp >300
◦
C; UV-vis (CHCl
15 (4.68), 532 (3.98), 569 (3.91), 669 (3.35), 736 nm (3.45); UV-vis
500 eq TFA–CHCl ): lmax (log e) 306 (4.54), 391 (4.65), 571 (3.67),
69 nm (3.63); H NMR (CDCl ): d 1.38–1.42 (6H, 2 overlapping
triplets), 1.45–1.48 (6H, 2 overlapping triplets), 1.83 (3H, t, J =
.3 Hz), 2.63 (3H, s), 2.64 (3H, s), 2.99–3.07 (8H, 4 overlapping
quartets), 4.91 (2H, q, J = 7.3 Hz), 7.42 (1H, s), 7.45 (1H, s), 7.62
3
): lmax (log e) 319 (4.49), 347 (4.52), 368 (4.51),
4
(
6
(
3
1
3
7
1
(
1H, s), 8.02 (1H, s); H NMR (TFA–CDCl
3
): d 1.19–1.24 (6H,
overlapping triplets), 1.27 (6H, t, J = 7.7 Hz), 1.63 (3H, t, J =
.3 Hz), 2.16 (3H, s), 2.21 (3H, s), 2.54–2.64 (8H, 4 overlapping
2
7
quartets), 4.66 (2H, q, J = 7.3 Hz), 6.33 (2H, br s), 6.41 (1H, br
s), 6.57 (1H, br s); C NMR (CDCl
1
1
1
1
3
3
): d 10.4, 10.5, 15.5, 15.7,
ligroin gave 28b (3.4 mg, 0.0071 mmol, 3.2%) as dark blue crystals,
6.7, 16.8, 17.0, 18.6, 18.86, 18.95, 45.7, 95.5, 96.8, 104.1, 115.7,
19.6, 134.7, 137.8, 138.6, 140.0, 140.7, 143.84, 143.89, 144.3,
46.5, 147.4, 152.0, 152.5, 155.3, 156.1; HR MS (EI): Calc. for
◦
mp >300 C; UV-vis (0.5% Et
3
N-CHCl
3
): lmax (log e) 326 (4.52),
):
max (log e) 322 (4.42), 386 (4.71), 681 (sh, 4.10), 734 nm (4.22);
3
80 (4.72), 62o (4.06), 651 nm (sh, 4.05); UV-vis (1% TFA–CHCl
3
l
C
31
H
35
5
N Pd: 583.1927. Found: 583.1912.
1
H NMR (CDCl
3
): d 1.21–1.28 (12H, 4 overlapping triplets), 2.27
(
(
(
(
3H, s), 2.63 (3H, s), 2.62–2.74 (6H, 3 overlapping quartets), 2.80
2H, q, J = 7.7 Hz), 4.10 (3H, s), 5.56 (1H, s), 6.05 (1H, s), 6.13
[
8,12,13,17-Tetraethyl-7,18-dimethyl-2-phenyl-2,3-diaza-21-
1
1H, s), 6.89 (1H, s), 8.94 (1H, br s), 9.17 (1H br s); H NMR
carbaporphyrinato]palladium(II) (32a)
trace TFA–CDCl ): d 1.19–1.33 (12H, m), 2.36 (3H, s), 2.55 (3H,
3
Palladium(II) acetate (5.4 mg, 0.024 mmol) was added to a solution
of 2,3-diaza-21-carbaporphyrin 25a (12.7 mg, 0.024 mmol) in
acetonitrile (40 mL), and the solution was stirred under reflux for
s), 2.68–2.83 (8H, m), 4.16 (3H, s), 6.03 (1H, br s), 6.14 (1H, s),
6.71 (1H, br s), 6.97 (1H, s), 10.12 (1H, br s); H NMR (TFA–
1
CDCl ): d 1.22–1.34 (12H, 4 overlapping triplets), 2.37 (3H, s),
3
3
0 min. The solution was cooled, diluted with chloroform, washed
2.58 (3H, s), 2.70–2.84 (8H, m), 4.28 (3H, s), 6.21 (1H, s), 6.72
with water, and the organic layer separated and then evaporated
to dryness. The residue was chromatographed with grade 3 basic
alumina, eluting with chloroform, and the product was collected
as a reddish/brown band. The solvent was evaporated to dryness
and the residue recrystallized from chloroform–methanol to yield
the palladium(II) complex (8.9 mg, 59%) as dark purple crystals,
(1H, s), 6.90 (1H, s), 6.97 (1H, s), 9.25 (1H, br s), 9.63 (1H, br
1
3
s), 10.57 (1H br s); C NMR (CDCl ): d 9.7, 11.5, 15.0, 15.9,
3
16.5, 17.1, 17.6, 17.9, 18.37, 18.44, 87.3, 89.4, 93.5, 108.7, 130.6,
131.3 132.5, 134.0, 134.2, 140.0, 140.44, 140.47, 146.1, 146.9, 148.7,
149.6, 153.0, 168.7, 176.2; HR MS (ESI): Calc. for C30
H: 482.2920. Found: 482.2915.
H
35
5
N O +
This journal is © The Royal Society of Chemistry 2011
Org. Biomol. Chem., 2011, 9, 6293–6305 | 6303

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2
,8,12,13,17-Pentaethyl-5,22-dihydro-7,18-dimethyl-5-oxo-2,3-
8,12,13,17-Tetraethyl-5,22-dihydro-7,18-dimethyl-5-oxo-2-phenyl-
2,3-diaza-21-carbaporphyrin (pyrazolo-oxophlorin 28a)
diaza-21-carbaporphyrin (pyrazolo-oxophlorin 28c)
32d,56
32d,56
Tripyrrane dicarboxylic acid 12
(100 mg, 0.22 mmol) was
Tripyrrane dicarboxylic acid 12
(100 mg, 0.22 mmol) was
stirred for 1 min in TFA (1 mL) under nitrogen, then diluted
with dichloromethane (99 mL) and dialdehyde 20c (36.5 mg,
stirred with TFA (1 mL) under nitrogen for 2 min. The mixture
was diluted with dichloromethane (99 mL) and dialdehyde 20a
47
0
.24 mmol) was immediately added. The reaction mixture was
stirred under nitrogen in the dark for 4 h, silver acetate (77 mg,
.46 mmol) was added, and stirring was continued overnight. The
(48.0 mg, 0.24 mmol) was immediately added in a single portion.
The resulting solution was stirred for 4 h under nitrogen and
then oxidized overnight with silver acetate (77 mg, 0.46 mmol).
The mixture was then washed with water followed by saturated
sodium bicarbonate (the aqueous solutions were back-extracted
with chloroform at each stage in the extractions). The solvent was
removed under reduced pressure and the residue chromatographed
on grade 3 basic alumina, eluting with dichloromethane, to
give the oxophlorin as a late dark blue fraction. The solvent
was removed under reduced pressure and recrystallized from
chloroform–ligroin to yield the pyrazole oxophlorin analogue
0
solution was then washed with water (150 mL) and saturated
sodium bicarbonate solution (150 mL), back extracting with
chloroform each time. The solvent was evaporated under reduced
pressure and the dark colored residue was run through a grade
3
basic alumina column eluting with dichloromethane. A dark
fraction was collected and rechromatographed on grade 3 basic
alumina eluting with 50% dichloromethane–hexanes. Green and
blue colored fractions eluted initially, followed by a turquoise
fraction that corresponded to the pyrazole-containing porphyrin
analogue, and finally a dark blue fraction containing the oxophlo-
rin product. Evaporation of the solvent and recrystallization from
chloroform–ligroin gave 28c (15 mg, 0.030 mmol, 14%) as dark
blue crystals, mp >300 C; UV-vis (CHCl
3
3
4
◦
(10.7 mg, 0.0020 mmol, 9%) as dark blue crystals, mp >300 C;
UV-vis (CHCl
3
): lmax (log e) 324 (4.59), 381 (4.77), 623 (4.10);
): lmax (log e) 324 (4.50), 394 (4.70), 737 (4.11);
): d 1.22–1.28 (12H, 4 overlapping triplets), 2.16
(20% TFA–CHCl
3
1
H-NMR (CDCl
3
◦
3
): lmax (log e) 325 (4.52),
): lmax (log e)
): d 1.21–1.28 (12H,
overlapping triplets), 1.51 (3H, t, J = 7.3 Hz), 2.27 (3H, s), 2.64
(3H, s), 2.65 (3H, s), 2.66 (4H, q, J = 7.7 Hz), 2.73 (2H, q, J =
7.7 Hz), 2.81 (2H, q, J = 7.7 Hz), 5.79 (1H, s), 6.07 (1H, s), 6.14
(1H, s), 6.90 (1H, s), 7.46 (1H, t, J = 7.7 Hz), 7.53 (2H, t, J =
80 (4.72), 618 nm (4.06); UV-vis (10% TFA–CHCl
3
1
88 (4.69), 734 nm (4.12); H NMR (CDCl
3
7.7 Hz), 7.64 (2H, d, J = 7.3 Hz), 9.08 (1H, br s), 9.28 (1H, br s);
1
(
7
3H, s), 2.62–2.75 (6H, 3 overlapping quartets), 2.80 (2H, q, J =
.6 Hz), 4.45 (2H, q, J = 7.3 Hz), 5.50 (1H, s), 6.06 (1H, s), 6.15
H-NMR (trace TFA–CDCl ): d 1.20–1.28 (9H, m), 1.32 (3H, t,
3
J = 7.7 Hz), 2.27 (3H, s), 2.59 (3H, s), 2.68–2.74 (4H, 2 overlapping
quartets), 2.78–2.83 (4H, 2 overlapping quartets), 6.09 (1H, s), 6.17
1
(
(
(
(
1H, s), 6.90 (1H, s), 8.91 (1H, br s), 9.13 (1H, br s); H NMR
trace TFA–CDCl ): d 1.19–1.27 (9H, 3 overlapping triplets), 1.31
3H, t, J = 7.7 Hz), 1.52 (3H, t, J = 7.3 Hz), 2.37 (3H, s), 2.56
3H, s), 2.68–2.83 (8H, 4 overlapping quartets), 4.46 (2H, q, J =
3
(1H, s), 6.55 (1H, s), 7.00 (1H, s), 7.53–7.61 (5H, m), 9.69 (1H,
1
br s), 10.11 (1H, br s); H-NMR (TFA–CDCl
3
): d 1.24–1.30 (9H,
m), 1.33 (3H, t, J = 7.7 Hz), 2.32 (3H, s), 2.66 (3H, s), 2.71–2.90
(8H, m), 6.32 (1H, s), 6.37 (1H, s), 6.69 (1H, s), 7.07 (1H, s), 7.49–
7.56 (3H, m), 7.63–7.68 (2H, m), 8.53 (1H, br s), 9.11 (1H, br s),
7
.3 Hz), 5.84 (1H, s), 6.11 (1H, s), 6.67 (1H, s), 6.98 (1H, s), 9.73
1
(
1H, br s), 10.15 (1H, br s); H NMR (TFA–CDCl
3
): d 1.21–1.27
1
3
(
9H, 3 overlapping triplets), 1.31 (3H, t, J = 7.7 Hz), 1.58 (3H, t,
9.85 (1H, br s); C NMR (CDCl ): d 9.7, 11.6, 14.9, 15.9, 16.5,
3
J = 6.8 Hz), 2.36 (3H, s), 2.57 (3H, s), 2.69–2.83 (8H, m), 4.62 (2H,
q, J = 7.3 Hz), 6.19 (1H, s), 6.68 (1H, s), 6.94 (1H, br s), 6.96 (1H,
17.1, 17.6, 17.9, 18.37, 18.45, 89.0, 89.4, 93.9, 108.5, 126.5, 128.6,
129.4, 130.9, 131.5, 132.4, 134.3, 139.7, 140.2, 140.4, 140.5, 146.0,
147.0, 149.9, 150.1, 153.1, 168.9, 176.0; HR MS (ESI): Calc. for
1
3
s), 9.28 (1H, br s), 9.71 (1H, s), 10.62 (1H, s); C NMR (CDCl
3
):
d 9.7, 11.5, 15.0, 15.89, 15.90, 16.5, 17.1, 17.6, 17.9, 18.37, 18.44,
C
35
H
37
5
N O + H: 544.3076. Found: 544.3073.
4
1
n
5.9, 87.4, 89.3, 93.4, 108.6, 130.6, 131.2, 132.5, 134.0, 134.2, 139.0,
40.35, 140.44, 145.9, 146.9, 148.9, 149.7, 153.0, 168.6, 176.3; IR:
Acknowledgements
-
1
CO 1625 cm ; HR MS (ESI): Calc. for C31
H
37
5
N O + H: 496.3076.
This work was supported by the National Science Foundation
under grant nos. CHE-0616555 and CHE-0911699, and the
Petroleum Research Fund, administered by the American Chem-
ical Society. Funding for a 500 MHz NMR spectrometer was
provided by the National Science Foundation under grant no.
CHE-0722385.
Found: 496.3067.
2
,8,12,13,17-Pentaethyl-20,22-dihydro-7,18-dimethyl-20-oxo-2,3-
diaza-21-carbaporphyrin (pyrazolo-oxophlorin 29)
An early blue colored fraction from the previous experiment
corresponded to the less favored pyrazole-containing oxophlorin
analogue. Evaporation of the solvent gave the oxophlorin product
References
1
A. W. Johnson, in Porphyrins and Metalloporphyrins, K. M. Smith, ed.,
Elsevier, Amsterdam, 1975, pp 729–754.
29 (1.0 mg, 0.002 mmol, 1%) as dark blue crystals that were
2
R. Grigg, in The Porphyrins, Vol. 2, D. Dolphin, ed., Academic Press,
New York, 1978, pp 327–391.
somewhat unstable in solution. UV-vis (CHCl
intensity) 326 (0.81), 381 (1.00), 637 (0.23), 669 nm (0.23); H
3
): lmax (relative
1
3 E. Vogel, M. Kocher, H. Schmickler and J. Lex, Angew. Chem., Int. Ed.
Engl., 1986, 25, 257.
NMR (CDCl
3H, t, J = 7.3 Hz), 2.29 (3H, s), 2.65 (3H, s), 2.65–2.76 (6H, 3
overlapping quartets), 2.82 (2H, q, J = 7.6 Hz), 4.74 (2H, q, J =
.3 Hz), 5.36 (1H, s), 6.05 (1H, s), 6.69 (1H, s), 6.86 (1H, s), 8.83
1H, br s); HR MS (EI): Calc. for: C31 O: 495.2998. Found:
3
): d 1.22–1.28 (12H, 4 overlapping triplets), 1.56
4
(a) E. Vogel, M. Balci, K. Pramod, P. Kock, J. Lex and O. Ermer,
Angew. Chem., Int. Ed. Engl., 1987, 26, 928; (b) E. Vogel, I. Grigat, M.
K
(
o¨ cher and J. Lex, Angew. Chem., Int. Ed. Engl., 1989, 28, 1655.
5
6
E. Vogel, J. Heterocycl. Chem., 1996, 33, 1461.
7
J. L. Sessler, A. Gebauer and E. Vogel, in The Porphyrin Handbook,
Vol. 2, K. M. Kadish, K. M. Smith and R. Guilard, ed., Academic
Press, San Diego, 2000, pp 1–54.
(
H
37
N
5
495.2991.
6
304 | Org. Biomol. Chem., 2011, 9, 6293–6305
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7
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(
3
3
7
55 Full details on this X-ray crystal structure are provided in the
45
preliminary communication and are not repeated in this paper .
56 J. L. Sessler, M. R. Johnson and V. Lynch, J. Org. Chem., 1987, 52,
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