Formation, structure, and reactivity of meso-tetraaryl-chlorolactones, -porpholactams, and -chlorolactams, porphyrin and chlorin analogues incorporating oxazolone or imidazolone moieties

Article abstract of DOI:10.1039/c3ob40138c

Reaction of known meso-tetraarylporpholactone free bases 3, made from the corresponding porphyrins, with hydrazine produces three products: It converts the lactone functional group into an N-aminolactam moiety, generating porphyrin-like N-aminoporpholacta

Full text of DOI:10.1039/c3ob40138c

Organic &
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Formation, structure, and reactivity of meso-tetraaryl-
chlorolactones, -porpholactams, and -chlorolactams,
porphyrin and chlorin analogues incorporating
oxazolone or imidazolone moieties†‡
Cite this: DOI: 10.1039/c3ob40138c
Joshua Akhigbe,a John Haskoor,a Jeanette A. Krause,b Matthias Zellerc and
Christian Brückner*a
Reaction of known meso-tetraarylporpholactone free bases 3, made from the corresponding porphyrins,
with hydrazine produces three products: It converts the lactone functional group into an N-aminolactam
moiety, generating porphyrin-like N-aminoporpholactams 8. It also reduces regioselectively the β,β’-
double bond of the pyrrolic moiety opposite to the imidazolone in both the starting material and the
N-aminoporpholactam, thus forming the chlorin-like chlorolactones 7 and N-aminochlorolactams 9. An
equivalent set of reaction products is also derived from the reaction of porpholactones 3 with tosylhydra-
zide. Reductive N–N cleavage of the N-aminoporpholactams 8 generated the parent porpholactams 10.
The molecular structures of all key compounds were shown by single crystal X-ray diffraction to be essen-
tially planar. Porpholactam 10a can be converted in two steps (enolization and halogenation α to the
imine, followed by reductive removal of the halogen) to known imidazoloporphyrin 5a, thus constituting
the third independent pathway to replace a β-carbon of a tetraphenylporphyrin by a nitrogen. All these
transformations show the flexibility of our ‘porphyrin breaking and mending’ strategy toward the
synthesis of novel porphyrin and chlorin analogues incorporating non-pyrrolic heterocycles that carry
functionalities at their periphery.
Received 22nd January 2013,
Accepted 12th March 2013
DOI: 10.1039/c3ob40138c
www.rsc.org/obc
biomedical applications (e.g., tumor imaging and photodynamic
Introduction
therapy).3,7 Particularly chromophores that allow a facile modu-
The synthesis of chlorins (2,3-dihydroporphyrins) has received lation of their optical or solubility properties are of interest.
considerable attention in recent years because they possess Efficient and scaleable total syntheses of chlorins have
UV-visible spectra that are generally red-shifted and endowed recently been described by the group of Lindsey.8 Alternatively,
with strongly enhanced λmax absorbance bands when com- chlorins can be made from porphyrins by removing one of
pared to the spectra of the corresponding porphyrins.1,2 These the β,β′-double bonds from macrocycle conjugation. For
properties are utilized in nature where chlorins are the most instance, 1,3-dipolar cycloadditions, Diels–Alder reactions, and
prominent photosynthetic pigments.3,4 Chlorins promise also reductions have been used to accomplish this.9 The classic
to be of use in a number of technical (light harvesting)5,6 and reductant is diimide.10,11 This reduction results in the most
straight forward formation of chlorins but, for notable excep-
tions,11 these unsubstituted chlorins and bacteriochlorins
tend to be unstable with respect to reversion (oxidation) to the
parent porphyrin.
aDepartment of Chemistry, University of Connecticut, Storrs, CT 06269-3060, USA.
E-mail: c.bruckner@uconn.edu; Fax: +1 (860) 486-2981; Tel: +1 (860) 486-2743
bDepartment of Chemistry, University of Cincinnati, Cincinnati, OH 45221-0172,
USA
We described the formal oxidation of meso-tetraarylporphyr-
ins, such as 1, with OsO4 to form the corresponding dihydroxy-
chlorins, such as 2. The chlorin diols are a versatile class
of chlorins that are relatively stable toward air oxidation
(Scheme 1).12–15
We also described multiple ways in which the diol function-
ality in 2 can be used as a synthetic handle toward the
generation of a range of other porphyrin- and chlorin-like
chromophores.14,18,19 For instance, oxidation of chlorin 2
cDepartment of Chemistry, Youngstown State University, One University Plaza,
Youngstown, OH 44555-3663, USA
†Oxazolochlorins 9. Oxazolochlorins 8: J. Ogikubo, J. L. Worlinsky, Y.-J. Fu, and
C. Brückner Tetrahedron Lett. 2013, 54, 1707–1710.
‡Electronic supplementary information (ESI) available: 1H, 13C NMR, UV-vis,
and IR spectra of all novel compounds and experimental details to the crystal
structure determination of 7a, 8c, 9c, and 15a, including their CIF files. CCDC
919810–919813. For ESI and crystallographic data in CIF or other electronic
format see DOI: 10.1039/c3ob40138c
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Porpholactones found utility as catalysts,24 or were used as
sensor dyes in pressure-sensing paints.25,26 A porpholactone
metal complex also served as a high pH-sensing chromo-
phore.15 Only relatively few organic transformations of porpho-
lactones were reported to date. We described the reduction of
porpholactones to generate oxazolochlorins, such as the oxida-
tively sensitive parent compound 4.17,27 More robust α-alkyl-
ated oxazolochlorins (and oxazolobacteriochlorins) can be
generated from porpholactone 3 by alkylation reactions.28
The alkylation reactions using Grignard reagents, hydride
reductions, and the reaction with hydroxide and methoxide,
the fundamental reaction on which the high pH sensor
relies,15 show the susceptibility of the lactone carbonyl to
nucleophilic attack.
Scheme 1 Synthesis of porpholactone 3 and oxazolochlorin 4 along the ‘por-
phyrin breaking and mending strategy’.16,17
generates porpholactone 3 in which a pyrrole was formally
replaced by an oxazolone moiety.14,15,17,20 Alternative syntheses
for porpholactones are known, several of which appeared well
before our reports.20–22 A recently described ruthenium-cata-
lyzed oxidation strategy also makes porpholactones available
from the corresponding porphyrins in a single efficient step.23
The lactone moiety in the free base porpholactones mimics
the electronic properties of the β,β′-double bond. Thus, their
UV-visible spectra are very similar to those of the correspond-
ing porphyrin (Fig. 1A).17,22
Applying our ‘porphyrin breaking and mending strategy’ to
dihydroxychlorin 2, other heterocycles could also be
introduced.12,14,16,19,29–31 For instance, a β-carbon of a por-
phyrin can also be replaced in a multi-step sequence with a
nitrogen atom, generating imidazoloporphyrin 5.16
Porphyrin analogues that maintain the principle porphyri-
noid macrocycle structure but in which one (or two) C or N
atoms were exchanged for other heteroatoms have become a
widely investigated class of porphyrinoids.32–34 The β-function-
alities of porphyrins in general,35 and those of the pyrrole-
modified porphyrins in particular, potentially enable their
application in sensing and molecular recognition appli-
cations.15,25,36 Aside from the N-confused porphyrins, a class
of carbaporphyrins carrying a 2,4-linked pyrrole pointing its
nitrogen to the outside and a β-carbon to the inside,34,37 the
introduction of nitrogens to the β-positions of (aza-)porphyrins
is, however, relatively rare. We are aware of only one other true
porphyrin analogue containing β-nitrogens, pyrazoloporphyrin
6,38 prepared by total synthesis.39
In a preliminary report we described the reaction of porpho-
lactone 3 with hydrazine, generating N-aminoporpholactams,
such as 8a.31 Incidentally, the reaction of the porpholactones
with hydrazine also led to a reduction of the porpholactones to
form the novel chlorin-like chromophores, such as chlorolac-
tone 7a.31 The reduction of porpholactam 8a to the corres-
ponding chlorolactam was observed as well.31
Fig. 1 UV-visible spectra (CH2Cl2) of the porphyrinoids indicated.
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We will disclose here the details of these transformations, carbon at 170 ppm) spectra. The absence of isomers of this
the structures of the novel chromophores, as determined by novel chromophore and the chemical shift similarity of the
single crystal X-ray diffractometry, and their reactivity. We will four sp2-hybridized β-protons suggests that a regioselective
further detail the consequences of the modifications on the reduction had taken place at the pyrrolic moiety opposite of
optical properties of these compounds, and we will report on the oxazolone moiety. The structure of 7a could be confirmed
an alternative route toward imidazoloporphyrins by step-wise by single crystal X-ray diffractometry (see below). We suggest to
manipulation of porpholactams, thus establishing a third name this chromophore chlorolactone, reflecting its chlorin-
independent pathway toward this intriguing pyrrole-modified like optical properties and the presence of the lactone moiety.
porphyrin class.16
A pronounced effect of the meso-aryl substituents on the
outcome of the reaction of porpholactones 3 with hydrazine
(or diimide generated in situ, see below) is noticeable. A switch
from meso-phenyl to the more electron-rich meso-4-methoxy-
phenyl groups (i.e., reacting meso-tetrakis(4-methoxyphenyl)-
porpholactone 3b) doubles the yield of the corresponding
meso-tetrakis(4-methoxyphenyl)chlorolactone 7b in case of the
hydrazine reaction and makes this chlorolactone the main
product in the reaction of 3b with diimide. Inversely, subject-
ing the relatively less electron-rich meso-tetrakis(α,α,α-trifluoro-
tolyl)-substituted porpholactone 3c to either reduction
conditions yields only traces (<3%) of the corresponding
chlorolactone 7c.
There is precedence for a hydrazine-induced reduction of a
porphyrin to a chlorin.40 However, the classic method for the
synthesis of hydroporphyrins from porphyrins is using
diimide (HNvNH) as the reductant. Diimide is formed by
reaction of tosylhydrazide in the presence of base (K2CO3) at
elevated temperatures (reflux temperature of pyridine). Applied
to 3a, this reaction forms chlorolactone 7a in only 6% yield
and also the N-aminoporpholactam 8 and -chlorolactam 9 (see
Results and discussion
Reaction of porpholactones with hydrazine hydrate
Reaction of porpholactones 3 with a large stoichiometric
excess of hydrazine hydrate in THF (∼1 : 2 v/v) at refluxing
temperatures forms, over the course of 3–5 days, one minor (in
12% yield) and two major products (in 37% and 25% yields) of
the compositions C43H30N4O2 (7a), C43H30N6O (8a) and
C43H32N6O (9a), respectively (compositions determined by
ESI+ HR-MS) (Scheme 2). The composition of product 7a
suggested that a two-hydrogen reduction of starting porpholac-
tone 3a (C43H28N4O2) had taken place. Indeed, the UV-vis spec-
trum of product 7a is, in contrast to the porphyrin-like
spectrum of porpholactone 3a, 46 nm red-shifted (λmax
=
1
686 nm) and chlorin-like (Fig. 1B). The H NMR spectrum of
7a identifies four non-equivalent pyrrolidine β-protons
(4.06–3.98 ppm), while the retention of the lactone moiety was
indicated by its IR (νCvO at 1757 cm−1) and 13C NMR (quaternary
Scheme 2 Formation of chlorolactones 7, N-aminoporpholactams 8, N-aminochlorolactams 9, porpholactams 10, and chlorolactam 11c by conversion of porpho-
lactones 3.
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below).41 The reaction with tosylhydrazide is significantly
faster (10–24 h) than the reaction with hydrazine hydrate.
The composition of the major product 8 (C43H30N6O for 8a)
resulting from the reaction of 3 with hydrazine hydrate is sug-
gestive of the take-up of hydrazine by porpholactone 3, with
1
concomitant loss of water (Scheme 2). H and 13C NMR spec-
troscopic data of the products were indecisive whether a hydra-
zone or an N-aminolactam had formed. IR spectroscopy
supported the lactam formulation (νCvO at 1686 cm−1). This
was confirmed by single crystal diffractometry (discussed
below; Fig. 4). In essence, the lactone oxygen was replaced by a
hydrazinyl moiety.
Fig. 2 UV-visible spectra (CH2Cl2) of the porphyrinoids indicated.
Interestingly, the O-to-NNH2 exchange had only minor
effects on the optical properties of the chromophores as
product 8 retains the porphyrin-like spectra of the porpholac-
N–N cleavage of the N-aminolactams
tones (8a: λmax = 651 nm, 8b: λmax = 653 nm, 8c: λmax
=
The reductive N–N cleavage of hydrazine derivatives using
SmI2 is known.42 This reaction can also be applied to N-amino-
porpholactams 8, generating the parent porpholactams 10 in
good yield (Scheme 2). This reaction leads to the expected
change in composition (C43H29N5O for 10a) with a significant
change in the νCvO vibrational frequency of the product
651 nm), with only ∼8 nm red-shifts of the λmax bands (Fig. 2).
Again, it appears that the lactam sp2-carbon also effectively
mimics the electronic effects of a β,β′-bond. We suggest the
trivial name porpholactam for this chromophore. Thus, deriva-
tives 8 are N-aminoporpholactams.
The third product 9, generally formed as the second most
abundant product in the hydrazine reactions, possesses a com-
position that suggested both a lactone-to-lactam conversion
and a reduction had taken place (C43H32N6O for 9a). As
observed for the reduction of porpholactone 3a to chlorolac-
tone 7a, the νCvO frequency measured for porpholactam 8a (at
1686 cm−1) and its corresponding chlorin analogue 9a (at
1678 cm−1) are close to each other. Parallel to the generation
of a red-shifted chlorin-like optical spectrum upon reduction
of porpholactone 3 to chlorolactone 7, reduction of porpholac-
tam 8 to form 9 also generates a chromophore with a chlorin-
like optical spectrum (Fig. 2). The UV-vis spectra of N-amino-
chlorolactam 9 (9a: λmax = 695 nm, 9b: λmax = 695 nm, 9c: λmax
= 697 nm) are very similar to the spectra of the corresponding
chlorolactones, except for a ∼10 nm red-shift, mirroring the
relative positions of their corresponding parent compounds.
Correspondingly, we name these chromophores chlorolactams.
The structure of the N-aminochlorolactam 9a could also be
confirmed by X-ray diffractometry (discussed below; Fig. 4).
Perceivably, chlorolactam 9a can either be formed as the
reduction product of 8a or as the substitution product of
chlorolactone 7a. Indeed, reaction of porpholactam 8a with
hydrazine forms the corresponding chlorolactam. However,
isolated chlorolactone 7a does not undergo any substitution
reaction with hydrazine, even after extended reaction times.
This may be a consequence of the generally increased HOMO
level of chlorins versus porphyrins.2
1
(1703 cm−1). The most diagnostic feature in the H NMR spec-
trum of 10a for the conversion is the replacement of the
signals assigned to the NH2-group protons at 4.13 ppm in
starting material 8a by a signal at 9.64 ppm, assigned to the
lactam NH group. The UV-visible spectrum of 10 is nearly
identical to that of the starting material (Fig. 1A), while that of
11 is chlorin-like (Fig. 3) (10a: λmax = 649 nm, 10b: λmax
=
650 nm; 11c, λmax = 701 nm). Again, suitable crystals for an
analysis by single crystal diffractometry confirmed the connec-
tivity of the chromophore (discussed below; Fig. 4).
As this N–N cleavage reaction proceeds only at elevated
temperatures (o-dichlorobenzene, reflux, bp
= 180.5 °C),
only the least electron-rich and presumably more oxidation-
resistant N-amino chlorolactam 9c could be converted to the
corresponding parent chlorolactam 11c. The more electron-
rich derivatives 9a and 9b underwent the desired N–N cleavage
but concomitantly also oxidized to the corresponding
porpholactams.
Theoretically, porpholactams 10 could be derived from
lactones 3 by reaction with ammonia. However, we failed to
Intriguingly, when the reaction of porpholactones 3 with
hydrazine is performed under anoxic conditions (N2 atmos-
phere), little to no chlorolactone 7 and chlorolactam 9 are
formed and the major product becomes the N-aminolactam 8.
We cannot provide an explanation for this finding except to
suggest that this seems to point at an oxidatively or radical-
induced step in the reduction of
hydrazine.
a porphyrinoid with
Fig. 3 UV-visible spectra (CH2Cl2) of the porphyrinoids indicated.
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Fig. 4 Single crystal X-ray structure of porpholactone 3a17 (included for comparison), chlorolactone 7a, porpholactam 10a,48 N-aminoporpholactam 8c,49 and
N-aminochlorolactam 9c,50 top (top) and side (bottom) views. All hydrogen atoms attached to sp2-hybridized carbon positions and all disorder and solvent, when
present, have been omitted for clarity; in addition, the phenyl groups were removed in the side views. For details to the crystal structures, see ESI.‡
induce this reaction under a range of conditions (aq. and
anhyd. NH3, different solvents, temperatures, slightly elevated
pressures, presence of Lewis acids, etc.). Perhaps the increased
nucleophilicity of hydrazine is required for the substitution
reaction to proceed.
Mechanistic considerations
Over the course of the reaction, we never observed any ring-
opened or other intermediates or hydrazones. The propensity
of lactones to undergo an aminolysis reaction with hydrazine
is well known.43 Also, one pot, two-step and direct, one-step
conversions of lactones to lactams are known; the conversion
of the oxazolidinones to imidazolidinones are particularly
well studied.44 Thus, the transformation of lactone 3 to lactam
10 does, in principle, not surprise. On the other hand, the
reaction is unusual in several aspects as a more detailed look
at a possible mechanism of this reaction will illustrate
(Scheme 3).
Many lactones, such as coumarins, react with hydrazine to
form ring-opened γ-hydroxyhydrazides.45 However, considering
that the five-membered lactone in 3 is being rigidly held in
position by the porphyrinic macrocycle, any ring-opening reac-
tion may be inhibited or prevented. Thus, following the
Scheme 3 Proposed mechanism of the lactone-to-lactam conversion and
nucleophilic attack of 3 by hydrazine, forming intermediate I,
the formation of hydrazone II would not have been an unrea-
sonable outcome of the reaction. However, this reaction is not
observed. Evidently, a ring-opening of intermediate I to form
III did indeed take place. The γ-hydroxy group in III thus esta-
blished is the hydroxy group of the imidol tautomeric form of
an amide that can be expected to be in equilibrium with its
amide tautomeric form IV. Amide IV is set up to undergo a
condensation reaction with either one of the hydrazide nitro-
gens. However, this reaction is highly selective as the reaction
with the terminal amine group leading to the formation of the
six-membered hydro-1,3,4-triazine V is not observed. Instead,
the five-membered imidazolidinone is formed by reaction of
the amidic NH group with the neighboring amidic carbonyl
group, thus forming intermediate VI. This subsequently dehy-
drates, thereby reestablishing the porphyrinic π-conjugated
possible other reactions.
system. We attribute the formation of the five-membered ring
to the overwhelming steric preference for five-membered rings
within the porphyrinoid macrocycle,46 though porphyrinoids
containing, for example, a pyrazine moiety, are known.30,47
This reaction highlights that the established chemistry of the
oxazolidones with amines is transferable into the context of
porphyrin chemistry, even if the reaction mechanism evokes
the temporary perturbation of the aromatic ring current. It is
reasonable to assume that the porphyrinic ring would more
strongly enforce the formation of a five-membered ring
product than any unrestricted substrate. Alas, since we are not
aware of reports on the reaction of oxazolidones with hydra-
zine, the latter conclusion must remain speculative.
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Structural characterization of chlorolactones, porpholactam,
and chlorolactams
The structures of chlorolactone 7a, porpholactam 10a,31
N-aminoporpholactam 8c, and N-aminochlorolactam 9c were
determined by single crystal X-ray diffraction (Fig. 4). The
molecular structures of the essentially planar free base por-
pholactone 3a was reported previously and is included here as
the benchmark compound.17 The structures confirm the atom
connectivities of the novel chromophores but more impor-
tantly, they also prove the conformation of the macrocycles (in
the solid state) to be all idealized planar. The structure of the
phenyl-derivatives 8a and 9a are near-identical to the struc-
tures of 8c and 9c shown,47,48 highlighting the generality
of the findings. In other words, the replacement of a pyrrole
by any one or two five-membered heterocycles pyrroline,
imidazole, imidazolone, or oxazolone does not disturb the
overall planarity of the parent porphyrin. However, as already
observed for the porpholactone and imidazoloporphyrin struc-
tures,16,17 the non-pyrrolic moiety is frequently disordered
over several positions, somewhat limiting the detailed metric
analyses of these macrocycles (for details, see ESI‡).
Nonetheless, some trends and details are discernable. The
small deviation from planarity in the solid state conformations
of porpholactam 10a and chlorolactone 7a are similar to the
deviations also observed for meso-tetraarylporphyrin free bases
1.51 In all cases, the two pyrroles carrying the NH groups are
slightly tilted out of plane to minimize the steric interaction of
the inner NH groups.
In comparison, the N-amino-substituted chromophores 8c
and 9c are slightly more non-planar, likely because of a larger
steric interaction of the N-amino group with the flanking
phenyl group. The N-amino groups in 8c and 9c are H-bonded
to solvate molecules (EtOH), highlighting their ability to inter-
act with the surroundings, a prerequisite for the utilization
of these molecules in, for instance, sensing applications.
Hydroporphyrins are generally more conformationally flexible
than porphyrins. Correspondingly, chlorin-type chromophore
9c (and 9a)48 is slightly more saddled than porphyrin-type
chromophore 8c (or 8a).47 Irrespective of the small deviations
from planarity, neither the atom positions and thermal
ellipsoids in the structures nor any broadening of the UV-vis
spectra of the compounds indicate the presence of a confor-
mationally flexible chromophore.
Scheme 4 Formation of carbaporpholactones 13 and 14 by oxidation of N-
substituted N-confused porphyrin 12 according to Chmielewski and Latos-
Grażyński.56
representative of these reactions.56 Oxidations of N-benzylated
or N-methylated N-confused porphyrin 12, as its silane
complex or free base, using oxygen or silver(I) as oxidant forms
the corresponding N-substituted carbaporpholactams 13 and
14, respectively. Internal C-oxidation or a metalation reaction
also have taken place.56 This oxidation sensitivity of the
α-carbon of the inverted pyrrole was observed previously
during the synthesis of N-confused porphyrins.55 In compari-
son, we did not observe any oxidation sensitivity of the porpho-
lactams. Except for the partial structural similarity with the
porpho- and chloro-lactams reported here, compounds 13 and
14 are much different because they are subject to very different
electronic substituent and conformational effects. Therefore,
no similarity in their optical properties with those of the
porpho- and chloro-lactams are evident.
Porpholactam to imidazoloporphyrin conversions
The amide functionality of porpholactam 10a is susceptible to
enolization with concomitant hydroxy-to-chlorine substitution
using phosphoryl chloride (POCl3) in refluxing toluene, yield-
ing 3-chloroimidazoloporphyrin 15a in excellent yield
(Scheme 5).
1
The imine-peak in the H NMR spectrum is diagnostic for
the known parent imidazoloporphyrin 5a. Chloride 15a is,
naturally, devoid of this diagnostic handle. However, the com-
pound possesses the expected porphyrin-like UV-vis spectrum
Comparison to other porphyrinoids containing a β,β′-lactam
moiety
Both the β,β′-reduction of porpholactones as well as the por- and the expected composition. 3-Chloroimidazoloporphyrin
pholactone-to-porpholactam conversions detailed above have 15a also exhibits an optical response to protonation much
not been, outside of our earlier communication,31 reported different from the parent compound 5a (Fig. 5). Exposure of
before. Nonetheless, γ-lactams have been reported in a benzi- 15a to TFA produces a UV-vis spectrum that is reminiscent of a
porphodimethene,52 calixphyrin,53 N-confused hexaphyrin,54 porphyrin protonated at the central nitrogens,57 whereas
and N-confused porphyrins.36,55 They were established by parent compound 5a responded with an unusually red-shifted
means of (often fortuitous) oxidations of a pyrrolic building spectrum we rationalized by outer imine protonation.16 The
block of the macrocycle (Scheme 4). The introduction of the difference between the two imidazoloporphyrins is presumably
β,β′-lactam moieties in carbaporpholactams 13 and 14 is a consequence of the presence of the strongly electron-
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(Cl–Phcentroid distance 3.37 Å). The crystal structure of the non-
chlorinated parent compound, also as its free base, shows no
such distortion.16
Reduction of chloro-imine 15a with Zn dust/H2SO4 formed,
in addition to the major hydrolysis product porpholactam 10a,
the known parent imidazoloporphyrin 5a in low yield.16 This
6-step pathway to formally replace a β-carbon of tetraphenyl-
porphyrin by a nitrogen is the third and – irrespective of its
overall low yield – the best pathway toward imidazoloporphyr-
ins, an intriguing porphyrinoid class combining the N4-core of
porphyrins with the peripheral nitrogen of N-confused
porphyrins.16
Conclusions
We have shown here that the lactone moiety in porpholactones
can be converted to the corresponding lactam by reaction with
hydrazine. We have also shown that the reduction of the por-
pholactones and porpholactams to the corresponding novel
chlorin-like chromophores in which the pyrrole opposite of
the lactone/lactam functionality is reduced to a pyrroline is
possible. We thus demonstrated the formal replacement of a
pyrrolic moiety in porphyrins and chlorins by an imidazolone
moiety, further highlighting the power of our ‘breaking and
mending of porphyrin’ strategy toward the synthesis of por-
phyrinoids containing non-pyrrolic heterocycles. While the
lactone-to-lactam replacement does not alter the optical prop-
erties of the porphyrin or chlorin-like chromophore much, it
introduces functionality to the porphyrin periphery that can
be further manipulated, as shown by the conversion of the
initially formed N-aminolactams to lactams and substituted
imidazoloporphyrins.
Scheme 5 Conversions of porpholactam 10a to imidazoloporphyrins.
Fig. 5 UV-visible spectra (CH2Cl2) of the porphyrinoids indicated.
The minor deviations from planarity observed in these
novel chromophores presented here are not large enough to
affect their optical properties in any major way. This further
allows the conclusion to be drawn that all observed differences
in the optical properties of the chromophores are entirely due
to the atom replacement and substituent effects.
The introduction of functionality to the periphery of the
porphyrin is important as it enables the use of these chromo-
phores as, for instance, sensors and will allow further chemi-
cal modifications. To a significant portion, the increasing
popularity of porpholactones and the immense importance of
N-confused porphyrins33,34,58 are due to their β-functionalities
that are part of their macrocycles, a property that distinguishes
them sharply from substituted porphyrins or chlorins. With
the facile syntheses of porpholactams and the chlorin ana-
logues chlorolactone and chlorolactam described herein, we
expect these derivatives over time to gain utility and promi-
Fig. 6 Single crystal X-ray structure of the 3-chloroimidazoloporphyrin 15a, top
view (top) and side view (bottom). All hydrogen atoms attached to carbon posi-
tions in both views have been omitted for clarity; in addition, the phenyl groups
were removed in the side view. For details to the crystal structures, see ESI.‡
withdrawing chlorine substitution next to the imine, rendering nence for their optical properties, stability, and functionality.
it less basic than the inner nitrogens.
The crystal structure analysis of 3-chloroimidazolopor-
phyrin 15a ultimately proved its connectivity (Fig. 6). The sub-
stituted imidazole moiety is slightly tilted out of the mean
Experimental
X-Ray single crystal diffractometry
chromophore plane, likely as a result of the interaction of the Intensity data for a single crystal of chlorolactone 7a (0.04 ×
(large) chlorine atom with the flanking phenyl group 0.04 × 0.005 mm, MiTeGen mount with paratone-N oil) were
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collected on a D8 goniostat equipped with a Bruker APEXII thickness) TLC plates, and basic alumina gel (50–200 μm, pH
CCD detector at Beamline 11.3.1 at the Advanced Light Source 10) were used.
(Lawrence Berkeley National Laboratory) using synchrotron
1H and 13C NMR spectra were recorded on a Bruker DRX
radiation tuned to λ = 0.8856 Å. Data collection frames were 400, or Avance 500 instrument. High and low resolution mass
measured for a duration of 5 s at 0.3° intervals of ω with a spectra were provided by the Mass Spectrometry Facilities at
maximum resolution of ∼0.60 Å. The data frames were col- the Department of Chemistry, University of Connecticut. UV-
lected using the program APEX2 and processed using the vis spectra were recorded on a Varian Cary 50 spectropho-
program SAINT within APEX2. The data were corrected for tometer. IR spectra were acquired on a JASCO FT-IR-410 using
absorption and beam corrections based on the multi-scan an ATR (ZnSe) unit.
technique as implemented in SADABS.59
Single crystals of N-aminoporpholactam 8c, N-aminochloro-
meso-Tetrakisphenyl-12-oxa-13-oxochlorin (chlorolactone 7a),
lactam 9c, and chloro-imidazoloporphyrin 15a were mounted
meso-tetrakisphenyl-2-(N-amino-aza)-3-oxoporphyrin
on MiTeGen micromesh mounts with the help of a trace of
(N-aminoporpholactam 8a), and meso-tetrakisphenyl-12-
(N-amino-aza)-13-oxochlorin (chlorolactam 9a)
meso-Tetraphenyl-2-oxa-3-oxoporphyrin 3a (56 mg, 8.85 × 10−5
mol) was dissolved in THF (20 mL) and magnetically stirred.
Hydrazine hydrate (N2H4·2H2O, 11 mL) was added and the
mixture was heated to reflux for 5 d. When the starting
material was consumed (reaction monitored by TLC), the reac-
mineral oil, mounted on a pin and placed a goniometer head
under a stream of cold nitrogen. The data were collected on a
Bruker APEX CCD diffractometer with Mo source Kα radiation
(λ = 0.71073 Å) using ω scans. The frames were integrated with
the Bruker SAINT software package using a narrow frame
algorithm. Data were corrected for absorption effects using the
multiscan method (SADABS). All structures were solved and
tion mixture was allowed to cool and was evaporated to
refined using the Bruker SHELXTL Software Package until the
final anisotropic full-matrix, least-squares refinement on F2
dryness by rotary evaporation. The residue was taken up in
CH2Cl2, washed with H2O (2 × 10 mL), dried over anhyd.
Na2SO4, and reduced by rotary evaporation. The reaction
converged.60
Data collection and structural parameters for the structure
mixture was separated by preparative TLC (silica–CH2Cl2/2%
elucidations can be found in Table 1 and the ESI.‡
MeOH), providing 7a in 12% (7.0 mg) as a red-purple solid, 8a
as a purple solid in 37% (21.0 mg), and 9a as a purple solid in
25% (15.0 mg) yields. When the reaction was performed under
Materials and instrumentation
an atmosphere of N2, the formation of 7a is almost totally sup-
All solvents and reagents (Aldrich, Acros, CIL) were used as pressed, and 8a and 9a were isolated in 81–90% and 3–5%
received. meso-Tetrakisarylporpholactones 3a, 3b, and 3c were yields, respectively. 7a: Rf (silica–CH2Cl2) = 0.50; 1H NMR
synthesized as reported in the literature.17 Analytical (alumi- (400 MHz, CDCl3): δ 8.48 (dd, 3J = 5.0, 4J = 1.6 Hz, 1H), 8.24
num backed, silica gel 60, 250 μm thickness) and preparative (dd, 3J = 4.6, 4J = 1.9 Hz, 1H), 8.15 (dd, 3J = 5.0, 4J = 1.5 Hz, 1H),
3
(20 × 20 cm, glass backed, silica gel 60, 500 or 1000 μm 8.00 and 7.99 (overlapping d, J = 7.8 Hz, and s, 2H), 7.93 (dd,
Table 1 Crystal dataa
7a
8c·2EtOH
9c·2EtOH
15a
Formula
C43H30N4O2
634.71
Monoclinic
P2/n
C51H38F12N6O3
1010.87
Triclinic
ˉ
P1
C51H40F12N6O3
1012.89
Triclinic
ˉ
P1
C43H28ClN5
650.15
Monoclinic
P2(1)/n
M/g mol−1
Crystal system
Space group
a, b, c/Å
11.016(3), 6.7826(18),
21.878(6)
12.801(4), 12.814(4),
14.782(5)
12.6859(12), 12.9511(12),
14.5378(13)
14.440(4), 16.901(5),
14.820(4)
α, β, γ (°)
90, 101.024(4), 90
81.419(5), 75.271(5),
84.415(5)
2314.3(12)
150(2)
81.7260(10), 76.306(2), 84.1850
(10)
2290.8(4)
100(2)
90, 117.629(4), 90
V/Å3
T/K
1604.6(7)
150(2)
3204.4(17)
100(2)
Z
2
2
2
4
Reflections measured
14 751
20 289
19 920
16 647
Unique (Rint
)
3227 (0.0474)
3227/248/13
8112 (0.0529)
8112/771/327
9252 (0.0261)
9252/703/125
7763 (0.0724)
7763/561/51
Data/parameters/
restraints
Goodness-of-fit on F2
R(F) [all data]
1.033
1.024
1.051
0.984
0.0729
0.0446
0.1149
0.1028
919810
0.1336
0.0693
0.2130
0.1809
919811
0.0979
0.0674
0.2038
0.1846
919812
0.1966
0.0733
0.2002
0.1599
919813
R(F) [I > 2σ(I)]
wR(F2) [all data]
wR(F2) [I > 2σ(I)]
CCDC number
a For details, particularly with respect to the disorder models used, see ESI.
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4
3
3J = 4.6, J = 1.8 Hz, 1H), 7.89 and 7.88 (overlapping s and d, J (400 MHz, CDCl3 neutralized with basic alumina): δ 8.49 (dd,
= 7.6 Hz, 2H), 7.82–7.80 (m, 4H), 7.68–7.65 (m, 12H), 4.06–3.98 3J = 5.2, J = 1.8 Hz, 1H), 8.27 (dd, J = 4.7, 4J = 2.0 Hz, 1H),
(m, 4H), −0.78 (s, 1H, exchangeable with D2O), −1.20 (s, 1H, 8.17 (dd, 3J = 5.0, 4J = 1.9 Hz, 1H), 7.95 (dd, 3J = 4.9 Hz, 4J = 1.9
exchangeable with D2O) ppm; 13C NMR (100 MHz, CDCl3 neu- Hz, 1H), 7.91 (d, 8.6 Hz, 2H), 7.79 (d, 8.6 Hz, 2H), 7.69 (dd, 3J =
tralized in basic alumina): δ 170.0, 167.6, 164.2, 152.6, 142.8, 8.6, 4J = 2.9 Hz, 4H), 7.22–7.18 (m, 8H), 4.02–4.00 (m, 16H),
142.1, 141.0, 139.1, 139.0, 138.5, 137.5, 134.8, 133.9, 132.3, −0.78 (s, 1H, exchangeable with D2O), −1.21 (s, 1H, exchange-
132.2, 131.9, 128.4, 128.3, 128.2, 128.1, 128.0, 127.9, 127.6, able with D2O) ppm. 13C NMR (100 MHz, CDCl3): δ 170.3,
126.6, 125.9, 125.5, 122.9, 121.7, 116.0, 114.6, 104.9, 36.8, 167.8, 164.6, 159.8, 159.7, 159.5, 159.3, 152.6, 141.3, 139.4,
34.7 ppm; UV-vis (CH2Cl2) λmax (log ε) 412 (5.35), 512 (4.02), 139.2, 135.2, 135.1, 135.0, 134.4, 133.5, 133.2, 132.9, 130.8,
547 (4.02), 625 (3.83), 686 (4.67) nm; HR-MS (ESI+, cone 129.9, 127.9, 126.5, 125.8, 125.5, 122.7, 121.6, 115.4, 113.9,
voltage = 30 V, 100% CH3CN, TOF) m/z calcd for C43H31N4O2 113.8, 113.7, 113.5, 113.2, 104.6, 55.71, 55.68, 55.66, 55.55,
635.2447 ([M·H]+), found 635.2432. 8a: Rf (silica–CH2Cl2/2% 36.74, 34.73 ppm; UV-vis (CH2Cl2) λmax (log ε) 416 (5.31), 516
4
3
MeOH) = 0.45; H NMR (400 MHz, CDCl3 neutralized in basic (4.03), 554 (4.13), 625 (3.92), 686 (4.69) nm; HR-MS (ESI+, cone
1
3
3
alumina): δ 8.80 (d, J = 4.0 Hz, 1H), 8.77 (d, J = 4.0 Hz, 1H), voltage = 30 V, 100% CH3CN, TOF) m/z calcd for C47H39N4O6
3
3
3
8.71 (d, J = 4.0 Hz, 1H), 8.68 (d, J = 4.0 Hz, 1H), 8.64 (d, J = 755.2870 ([M·H]+), found 755.2878. 8b: Rf (silica–CH2Cl2/2%
4.0 Hz, 1H), 8.58 (d, 3J = 4.0 Hz, 1H), 8.17–8.15 (m, 4H), MeOH) = 0.39; 1H NMR (400 MHz, CD2Cl2 neutralized with
3
3
8.11–8.09 (m, 2H), 8.04–8.02 (m, 2H), 7.78–7.72 (m, 12H), 4.73 basic alumina): δ 8.80 (d, J = 5.0 Hz, 1H), 8.77 (d, J = 4.9 Hz,
(s, 2H, exchangeable with D2O), −2.08 (s, 1H, exchangeable 1H) 8.71 (d, 3J = 5.0 Hz, 1H), 8.65 (d, 3J = 4.9 Hz, 1H) 8.62 (d, 3J
with D2O), −2.35 (s, 1H, exchangeable with D2O) ppm; 13C = 4.6 Hz, 1H) 8.57 (d, J = 4.6 Hz, 1H) 8.05–8.02 (m, 4H), 7.95
3
3
4
3
4
NMR (100 MHz, CDCl3): δ 168.3, 156.3, 154.3, 147.4, 141.8, (d, J = 8.7, J = 2.1 Hz, 2H), 7.87 (d, J = 8.7, J = 2.3 Hz, 2H)
141.7, 141.4, 140.5, 140.1, 139.2, 138.4, 137.3, 135.5, 134.8, 7.26–7.23 (m, 8H), 4.74 (s, 2H), 4.04–4.02 (m, 12H), −2.08 (s,
134.6, 134.4, 133.8, 133.6, 132.8, 129.5, 128.3, 128.23, 128.2, 1H, exchangeable with D2O), −2.34 (s, 1H, exchangeable with
128.1, 127.8, 127.7, 127.1, 127.0, 127.0, 124.3, 121.4, 118.3, D2O) ppm. 13C NMR (100 MHz, CD2Cl2): δ 167.7, 160.0, 159.9,
105.8 ppm; UV-vis (CH2Cl2) λmax (log ε) 424 (5.47), 522 (4.35), 159.8, 159.7, 156.4, 154.4, 147.8, 141.8, 139.6, 138.6, 137.4,
556 (4.04), 597 (3.93), 651 (3.68) nm; HR-MS (ESI+, cone 136.0, 135.6, 135.5, 134.6, 134.4, 134.1, 134.0, 133.4, 132.7,
voltage = 30 V, 100% CH3CN, TOF) m/z calcd for C43H31N6O 132.6, 129.2, 127.6, 127.5, 126.7, 123.9, 121.0, 117.5, 113.2,
647.2559 ([M·H]+), found 647.2603. 9a: Rf (silica–CH2Cl2/2% 112.9, 112.6, 112.5, 105.2, 55.74, 55.71, 55.6 ppm; UV-vis
1
MeOH) = 0.17; H NMR (400 MHz, CDCl3 neutralized in basic (CH2Cl2) λmax (log ε) 429 (5.60), 525 (4.45), 562 (4.24), 600
3
4
3
alumina): δ 8.43 (dd, J = 5.0, J = 1.6 Hz, 1H), 8.37 (dd, J = (4.08), 653 (3.72) nm; HR-MS (ESI+, cone voltage = 30 V, 100%
4.7, 4J = 1.8 Hz, 1H), 8.15 (dd, 3J = 4.9, 4J = 1.6 Hz, 1H), CH3CN, TOF) m/z calcd for C47H39N6O5 767.2982 ([M·H]+),
8.02–7.98 (m, 3H), 7.95–7.93 (m, 2H), 7.84–7.82 (m, 4H), found 767.2953. 9b: Rf (silica–CH2Cl2/5% MeOH) = 0.77; 1H
7.72–7.66 (m, 12H), 4.62 (s, 2H, exchangeable with D2O), 4.06 NMR (400 MHz, CD2Cl2 neutralized with basic alumina): δ
(s, 4H), −1.27 (s, 1H, exchangeable with D2O), −1.51 (s, 1H, 8.42 (dd, 3J = 5.1, 4J = 1.9 Hz, 1H), 8.31 (dd, 3J = 4.7, 4J = 2.1 Hz,
3
4
3
4
exchangeable with D2O) ppm; 13C NMR (100 MHz, CDCl3): δ 1H), 8.16 (dd, J = 5.1, J = 1.9 Hz, 1H), 8.00 (dd, J = 4.7, J =
168.8, 167.4, 164.6, 144.8, 142.8, 142.5, 140.8, 140.4, 140.2, 2.1 Hz, 1H), 7.87 (d, 8.6 Hz, 2H), 7.78 (d, 3J = 8.6 Hz, 2H), 7.72,
139.3, 138.7, 134.8, 133.2, 132.4, 132.3, 132.1, 131.3, 128.34, 7.70 (two overlapping d, 3J = 8.5 Hz, 4H), 7.21–7.17 (m, 8H),
128.33, 128.1, 127.98, 127.93, 127.8, 127.6, 126.7, 125.7, 125.6, 4.65 (s, 2H), 4.07–4.00 (m, 16H), −1.31 (s, 1H, exchangeable
121.9, 121.7, 115.2, 114.0, 107.8, 36.6, 34.9 ppm; UV-vis with D2O), −1.55 (s, 1H, exchangeable with D2O) ppm; 13C
(CH2Cl2) λmax (log ε) 414 (5.46), 509 (4.23), 542 (4.17), 634 NMR (100 MHz, CD2Cl2): δ 169.5, 166.8, 165.1, 159.8, 159.6,
(3.88), 695 (4.75) nm; HR-MS (ESI+, cone voltage = 30 V, 100% 159.5, 159.4, 145.1, 141.0, 139.4, 139.1, 135.1, 135.0, 134.7,
CH3CN, TOF) m/z calcd for C43H33N6O 649.2716 ([M·H]+), 134.1, 133.7, 133.3, 133.1, 132.7, 132.6, 131.7, 127.7, 126.2,
found 649.2735.
125.4, 121.6, 120.9, 114.6, 113.6, 113.5, 113.2, 112.8, 107.3,
55.67, 55.62, 55.61, 55.55, 36.5, 34.8 ppm; UV-vis (CH2Cl2) λmax
(log ε) 418 (5.10), 512 (3.92), 547 (3.90), 634 (3.60), 695 (4.42)
nm; HR-MS (ESI+, cone voltage = 30 V, 100% CH3CN, TOF) m/z
calcd for C47H41N6O5 769.3138 ([M·H]+), found 769.3111.
meso-Tetrakis(4-methoxyphenyl)-12-oxa-13-oxochlorin
(chlorolactone 7b), meso-tetrakis(4-methoxyphenyl)-2-(N-
amino-aza)-3-oxoporphyrin (N-aminoporpholactam 8b), and
meso-tetrakis(4-methoxyphenyl)-12-(N-amino-aza)-13-
oxochlorin (chlorolactam 9b)
meso-Tetrakis(4-trifluoromethylphenyl)-12-oxa-13-oxochlorin
(chlorolactone 7c), meso-tetrakis(4-trifluoromethylphenyl)-2-
(N-amino-aza)-3-oxoporphyrin (N-aminoporpholactam 8c), and
meso-tetrakis(4-trifluoromethylphenyl)-12-(N-amino-aza)-13-
oxochlorin (chlorolactam 9c)
Prepared by reaction of meso-tetrakis(4-methoxyphenyl)-2-oxa-
3-oxoporphyrin (3b) (33 mg, 4.45 × 10−5 mol) with N2H4·2H2O
as described for the preparation of 3a. Isolated yields for 7b
are 21% (6.9 mg) as a purple solid, for 8b 30% (8.4 mg) as a
purple solid, and for 9b 27% (11.0 mg) as a purple solid. Prepared by reaction of meso-tetrakis(4-trifluoromethylphenyl)-
When the reaction was performed under an atmosphere of N2, 2-oxa-3-oxoporphyrin (3c) (105 mg, 1.16 × 10−4 mol) with
only products 8b and 9b were isolated in 78% and 3% yields, N2H4·2H2O as described for the preparation of 3a. Isolated
1
respectively. 7b: Rf (silica–CH2Cl2/2% MeOH) = 0.46; H NMR yields for 7c were traces (<3%; identified by MS, but not
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further characterized), 8c 56% (59.3 mg) as a purple solid, and 128.8, 128.2, 128.1, 127.9, 127.7, 127.1, 126.9, 126.8, 126.4,
9c 16% (16.0 mg) as a purple solid. When the reaction was per- 124.8, 121.2, 118.0, 103.9, 55.85, 55.74, 55.57 ppm; UV-vis
formed under an atmosphere of N2, only products 8c and 9c (CH2Cl2) λmax (log ε) 421 (5.49), 519 (4.28), 554 (4.08), 595
were isolated in 60–65% and 3–7% yields, respectively. 8c: Rf (3.87), 649 (3.84) nm; HR-MS (ESI+, cone voltage = 30 V, 100%
(silica–CH2Cl2/2% petroleum ether 30–60) = 0.54; 1H NMR CH3CN, TOF) m/z calcd for C43H30N5O 632.2450 ([M·H]+),
3
(400 MHz, CDCl3 neutralized with basic alumina): δ 8.74 (t, J found 632.2398.
= 5.7 Hz, 2H), 8.64 (d, 3J = 5.2 Hz, 1H) 8.62 (d, 3J = 4.8 Hz, 1H),
3
3
meso-Tetrakis(4-methoxyphenyl)-2-aza-3-oxoporphyrin
(porpholactam 10b)
8.58 (d, J = 4.6 Hz, 1H) 8.52 (d, J = 4.6 Hz, 1H) 8.28 and 8.26
3
(two overlapping d, 7.8 Hz, 4H), 8.17 (d, J = 7.8 Hz, 2H), 8.12
(d, 3J = 8.0 Hz, 2H) 8.04–7.99 (m, 8H), 4.56 (s, 2H), −2.12 (s, Prepared in 65% yield (19.0 mg) as a purple solid from N-
1H, exchangeable with D2O), −2.38 (s, 1H, exchangeable with aminoporpholactam 8b (30 mg, 3.91 × 10−5 mol) by SmI2
D2O) ppm; 13C NMR (100 MHz, CDCl3): δ 168.7, 155.9, 154.1, reduction as described for the preparation of 10a. Rf (silica–
1
147.8, 144.9, 144.1, 143.5, 141.3, 138.9, 138.2, 136.9, 135.5, CH2Cl2/2% MeOH) = 0.22; H NMR (400 MHz, CD2Cl2): δ 9.76
3
134.9, 134.6, 134.4, 133.9, 133.7, 132.9, 130.8, 130.5, 129.5, (s, 1H, exchangeable with D2O), 8.81 (d, J = 5.0 Hz, 1H), 8.74
128.0, 127.9, 127.1, 124.8, 124.2, 123.2, 122.9, 120.2, 116.9, (d, 3J = 5.0 Hz, 1H) 8.65 (d, 3J = 5.0 Hz, 1H), 8.60 (d, 3J = 5.0 Hz,
3
104.8 ppm; UV-vis (CHCl2) λmax (log ε) 423 (5.44), 519 (4.26), 1H) 8.55 (m, 2H), 8.04–7.97 (m, 6H), 7.84 (d, J = 7.8 Hz, 2H),
552 (3.91), 598 (3.81), 651 (3.66) nm; HR-MS (ESI+, cone 7.31–7.22 (m, 8H), 4.04 (d, 3J = 7.4 Hz, 12H), −1.87 (s, 1H,
voltage = 30 V, 100% CH3CN, TOF) m/z calcd for C47H27F12N6O exchangeable with D2O), −2.15 (s, 1H, exchangeable with D2O)
919.2055 ([M·H]+), found 919.2022. 9c: Rf (silica–CH2Cl2) = ppm; 13C NMR (100 MHz, CD2Cl2): δ 169.4, 160.5, 160.0, 159.9,
0.10; 1H NMR (400 MHz, CDCl3 neutralized with basic 159.6, 147.9, 140.7, 140.3, 138.6, 136.9, 135.5, 135.4, 134.7,
3
4
3
alumina): δ 8.36 (dd, J = 5.2, J = 1.9 Hz, 1H), 8.29 (dd, J = 134.6, 134.2, 133.9, 133.1, 132.0, 130.7, 129.4, 127.8, 126.9,
4.7, 4J = 2.1 Hz, 1H), 8.12 (dd, 3J = 5.2, 4J = 1.9 Hz, 1H), 8.08 (d, 126.1, 124.5, 120.8, 117.3, 114.2, 112.9, 112.6, 112.5, 103.7,
3
3J = 7.8 Hz, 2H), 8.02 (d, J = 7.8 Hz, 2H), 7.99–7.93 (m, 13H), 55.9, 55.7, 55.6 ppm; UV-vis (CH2Cl) λmax (log ε) 426 (5.32), 523
4.44 (s, 2H), 4.06–4.04 (m, 4H), −1.31 (s, 1H, exchangeable (4.22), 559 (4.11), 598 (4.00), 650 (3.84) nm; HR-MS (ESI+, cone
with D2O), −1.52 (s, 1H, exchangeable with D2O) ppm; 13C voltage = 30 V, 100% CH3CN, TOF) m/z calcd for C47H38N5O5
NMR (100 MHz, CDCl3): δ 168.6, 167.9, 164.5, 146.2, 145.1, 752.2873 ([M·H]+), found 752.2798.
143.6, 140.5, 138.9, 138.7, 134.5, 133.2, 132.6, 132.5, 132.4,
meso-Tetrakis(4-trifluoromethylphenyl)-2-aza-3-oxoporphyrin
(porpholactam 10c)
131.3, 130.6, 130.3, 129.3, 129.2, 128.2, 126.8, 125.8, 125.5,
124.6, 122.1, 120.3, 114.2, 113.1, 106.9, 36.7, 34.9 ppm; UV-vis
(CH2Cl2) λmax (log ε) 412 (5.43), 503 (4.25), 538 (4.03), 637 Prepared in 83% yield (26.0 mg) as a purple solid from N-ami-
(3.95), 697 (4.75) nm; HR-MS (ESI+, cone voltage = 30 V, 100% noporpholactam 8c (32 mg, 3.48 × 10−5 mol) by SmI2 reduction
CH3CN, TOF) m/z calcd for C47H29F12N6O 921.2211 ([M·H]+), as described for the preparation of 10a. Rf (silica–CH2Cl2/2%
found 921.2197.
petroleum ether 30–60) = 0.49; 1H NMR (400 MHz, CDCl3): δ
3
9.61 (s, 1H, exchangeable with D2O), 8.79 (d, J = 5.0 Hz, 1H),
meso-Tetrakisphenyl-2-aza-3-oxoporphyrin (porpholactam 10a)
3
3
3
8.70 (d, J = 4.8 Hz, 1H) 8.64 (d, J = 5.0 Hz, 1H), 8.57 (d, J =
3
3
meso-Tetrakisphenyl-2-(N-amino-aza)-3-oxoporphyrin
(8a) 4.6 Hz, 1H), 8.54 (d, J = 5.0 Hz, 1H), 8.51 (d, J = 4.7 Hz, 1H),
(27 mg, 4.18 × 10−5 mol) was dissolved in anhyd. 1,2-dichloro- 8.28–8.23 (m, 6H), 8.11–8.08 (m, 4H), 8.05–7.98 (m, 6H), −1.88
benzene (10 mL) and magnetically stirred. To this was added (s, 1H, exchangeable with D2O), −2.13 (s, 1H, exchangeable
SmI2 (2.5 mL of a 0.1 M solution in THF, 6 equiv.) and the with D2O) ppm; 13C NMR (100 MHz, CDCl3): δ 169.2, 156.1,
mixture was heated to reflux for 14 h. When the starting 153.7, 147.4, 145.2, 144.9, 142.9, 142.0, 140.1, 139.7, 138.4,
material was consumed (reaction monitored by TLC), the 138.1, 136.5, 135.1, 134.5, 134.3, 133.9, 133.7, 132.9, 132.0,
reaction mixture was allowed to cool and was evaporated to 131.7, 131.0, 130.9, 130.7, 130.6, 130.3, 129.7, 128.2, 127.1,
dryness by rotary evaporation. The residue was taken up in 126.6, 126.1, 125.96, 125.93, 125.6, 124.8, 124.7, 124.29,
CH2Cl2, filtered and washed with water (2 × 10 mL), and dried 124.26, 124.14, 124.11, 123.5, 123.4, 123.2, 122.9, 120.1, 116.7,
over anhydrous Na2SO4. The crude product was purified by 102.9 ppm; UV-vis (CH2Cl2) λmax (log ε) 420 (5.54), 517 (4.32),
preparative TLC (CH2Cl2/1% MeOH) to furnish 10a as a purple 551 (4.02), 595 (3.86), 650 (3.88) nm; HR-MS (ESI+, cone
solid in 72% (19.0 mg) yield. Rf (silica–CH2Cl2) = 0.20; 1H NMR voltage = 30 V, 100% CH3CN, TOF) m/z calcd for C47H26F12N5O
(400 MHz, CDCl3): δ 9.64 (s, 1H, exchangeable with D2O), 8.80 904.1946 ([M]+), found 904.1917.
(d, 3J = 4.0 Hz, 1H), 8.72 (d, 3J = 4.0 Hz, 1H), 8.64 (d, 3J =
3
3
meso-Tetrakis(4-trifluoromethylphenyl)-2-aza-3-oxochlorin
(chlorolactam 11c)
4.0 Hz, 1H), 8.61 (d, J = 4.0 Hz, 1H), 8.58 (d, J = 4.0 Hz, 1H),
3
8.55 (d, J = 4.0 Hz, 1H), 8.14–8.12 (m, 4H), 8.09–8.07 (m, 2H),
7.99–7.97 (m, 2H), 7.81–7.79 (m, 3H), 7.77–7.73 (m, 9H), −1.86 Prepared in 57% yield (6.0 mg) as a purple solid from N-
(s, 1H, exchangeable with D2O), −2.13 (s, 1H, exchangeable aminochlorolactam 9c (∼11 mg, 1.16 × 10−5 mol) by SmI2
with D2O) ppm; 13C NMR (100 MHz, CDCl3): δ 169.5, 156.4, reduction as described for the preparation of 10a. Rf (silica–
1
153.9, 147.4, 141.9, 141.7, 140.2, 139.9, 139.6, 138.6, 138.3, CH2Cl2/2% MeOH) = 0.58; H NMR (400 MHz, CDCl3 neutral-
136.8, 134.9, 134.5, 134.3, 133.7, 133.4, 132.7, 129.6, 129.2, ized with basic alumina): δ 9.41 (s, 1H), 8.35 (d, 3J = 4.8 Hz,
Org. Biomol. Chem.
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3
4
1H), 8.20 (d, J = 4.5 Hz, J = 1.5 Hz, 1H) 8.15 (d, 7.2 Hz, 3H),
8.05–7.92 (m, 15H), 4.08–4.01 (m, 4H), −1.11 (s, 1H, exchange-
Acknowledgements
able with D2O), −1.44 (s, 1H, exchangeable with D2O) ppm; Support from the NSF (CHE-0517782, CHE-1058846, and
13C NMR (100 MHz, CDCl3): δ 168.8, 168.7, 163.9, 146.5, 145.8, CMMI-0730826 to CB) is gratefully acknowledged. The
144.6, 140.3, 138.4, 137.6, 135.1, 133.6, 132.6, 132.5, 132.3, 400 MHz NMR spectrometer at UConn was supported by the
127.2, 126.2, 126.0, 125.9, 125.6, 124.7, 122.2, 120.1, 114.6, NSF (CHE-1048717). The diffractometer at YSU was funded by
113.2, 105.0, 36.7, 35.1 ppm; UV-vis (CH2Cl2) λmax (log ε) 413 NSF grant 0087210, Ohio Board of Regents grant CAP-491, and
(5.10), 506 (3.93), 538 (3.87), 636 (3.61), 701 (4.44) nm; HR-MS by YSU. Crystallographic data for 7a were collected through the
(DART+, orifice voltage = 20 V, 100% CH3CN, TOF) m/z calcd SCrALS (Service Crystallography at Advanced Light Source)
for C47H28F12N5O 906.2102 ([M·H]+), found 906.2097.
program at the Small-Crystal Crystallography Beamline 11.3.1
at the Advanced Light Source (ALS), Lawrence Berkeley
National Laboratory. The ALS is supported by the U.S. Depart-
ment of Energy, Office of Energy Sciences Materials Sciences
Division, under contract DE-AC02-05CH11231.
meso-Tetrakisphenyl-2-aza-3-chloroporphyrin (15a)
meso-Tetrakisphenyl-2-aza-3-oxo-porphyrin 10a (10 mg, 1.58 ×
10−5 mol) was dissolved in dry toluene (10 mL) and magneti-
cally stirred. To this was added phosphoryl chloride (POCl3;
100 μL, ∼50 equiv.) and the mixture was heated to reflux for
3–5 h. When the starting material was consumed (reaction
monitored by UV-visible and TLC), the reaction mixture was
quenched by the addition of triethylamine (∼0.1 mL), allowed
to cool to room temperature and was evaporated to dryness by
rotary evaporation. The residue was taken up in CH2Cl2,
washed with water (2 × 10 mL), and dried over anhydrous
Na2SO4. The product was purified by preparative TLC (CH2Cl2/
20% petroleum ether 30–60) to furnish 15a in 97% (10.0 mg)
as a purple solid: Rf (silica–CH2Cl2) = 0.55; 1H NMR (400 MHz,
Notes and references
1 W. Flitsch, Adv. Heterocycl. Chem., 1988, 43, 73–126.
2 M. Gouterman, in The Porphyrins, ed. D. Dolphin,
Academic Press, New York, 1978, pp. 1–165.
3 Chlorophylls and Bacteriochlorophylls, ed. B. Grimm,
R. J. Porra, W. Rüdinger and H. Scheer, Springer,
Dordrecht, NL, 2006.
4 Chlorophylls, ed. H. Scheer, CRC Press, Boca Raton, 1991.
5 H. Imahori, K. Kurotobi, M. G. Walter, A. B. Rudine and
C. C. Wamser, in Handbook of Porphyrin Science, ed.
K. M. Kadish, K. M. Smith and R. Guilard, World Scientific,
River Edge, NY, 2012, 18, pp. 58–123; L.-L. Li and
E. W.-G. Diau, Chem. Soc. Rev., 2013, 42, 291–304.
6 See also Artificial Photosynthesis & Solar Fuels thematic
issue of Acc. Chem. Res., 2009, 42, e.g.: D. Gust, T. A. Moore
and A. L. Moore, Acc. Chem. Res, 2009, 42, 1890; N. Aratani,
D. Kim and A. Osuka, Acc. Chem. Res, 2009, 42, 1992.
7 E. D. Sternberg, D. Dolphin and C. Brückner, Tetrahedron,
1998, 54, 4151–4202; R. Bonnett, Chemical Aspects of Photo-
dynamic Therapy, Gordon & Breach, Langhorne, PA, 2000;
R. K. Pandey and G. Zheng, in The Porphyrin Handbook, ed.
K. M. Kadish, K. M. Smith and R. Guilard, Academic Press,
San Diego, 2000, 6, pp. 157–230; M. Ethirajan, Y. Chen,
P. Joshi and R. K. Pandey, Chem. Soc. Rev., 2011, 40, 340–
362.
3
CDCl3): δ 9.05 (d, J = 4.9 Hz, 1H), 8.92 (d, 5.1 Hz, 1H), 8.86 (s,
3
2H) 8.72 (s, 2H), 8.25 (dd, J = 7.8 Hz, 2H), 8.21–8.17 (m, 4H),
8.05 (dd, 3J = 6.7, 1.4 Hz, 2H) 7.81–7.74 (m, 12H) −2.51 (s,
1H, exchangeable with D2O) ppm; 13C NMR (100 MHz, CDCl3):
δ 159.5, 157.3, 157.1, 156.7, 141.8, 141.7, 141.6, 140.9,
140.2, 139.8, 139.7, 139.4, 135.7, 135.4, 135.3, 134.8, 134.7,
133.7, 130.1, 129.5, 128.8, 128.4, 128.3, 127.9, 127.6,
127.2, 127.1, 121.4, 120.8, 119.9, 119.8 ppm; UV-vis (CH2Cl2)
λmax (log ε) 423 (5.68), 522 (4.30), 560 (3.74), 599 (3.78), 655
(4.06) nm, UV-vis (CH2Cl2 + 10% TFA) λmax (log ε) 448 (5.46),
679 (4.58) nm; HR-MS (ESI+, cone voltage = 30 V, 100%
CH3CN, TOF) m/z calcd for C43H29ClN5 650.2111 ([M·H]+),
found 650.2118.
meso-Tetrakisphenyl-2-azaporphyrin (5a)
8 J. K. Laha, C. Muthiah, M. Taniguchi, B. E. McDowell,
M. Ptaszek and J. S. Lindsey, J. Org. Chem., 2006, 71, 4092–
4102; H. L. Kee, C. Kirmaier, Q. Tang, J. R. Diers,
C. Muthiah, M. Taniguchi, J. K. Laha, M. Ptaszek,
J. S. Lindsey, D. F. Bocian and D. Holten, Photochem. Photo-
biol., 2007, 83, 1125–1143; H. L. Kee, C. Kirmaier, Q. Tang,
J. R. Diers, C. Muthiah, M. Taniguchi, J. K. Laha,
M. Ptaszek, J. S. Lindsey, D. F. Bocian and D. Holten, Photo-
chem. Photobiol., 2007, 83, 1110–1124; M. Ptaszek,
B. E. McDowell, M. Taniguchi, H.-J. Kim and J. S. Lindsey,
Tetrahedron, 2007, 63, 3826–3839; M. Taniguchi,
M. Ptaszek, B. E. McDowell, P. D. Boyle and J. S. Lindsey,
Tetrahedron, 2007, 63, 3850–3863; M. Taniguchi,
M. Ptaszek, B. E. McDowell and J. S. Lindsey, Tetrahedron,
meso-Tetrakisphenyl-2-aza-3-chloroporphyrin 15a (10 mg,
1.54 × 10−5 mol) was dissolved in dry toluene (7 mL) and mag-
netically stirred. To this was added zinc dust (45 mg) and 2 N
aq. H2SO4 (3 mL) and the mixture was heated to reflux for 5 h.
The reaction mixture was added to an aq. sat’d. Na2CO3 solu-
tion (caution: gas evolution, foam formation) until all acid was
neutralized. The products were extracted with CH2Cl2. The
organic phase was dried over anhyd. Na2SO4 and after evapo-
ration under reduced pressure, the residue was separated on a
preparative TLC plate (silica–CH2Cl2/1% MeOH) to furnish 5a
in 10% and 10a in 72% yields. The spectroscopic and analyti-
cal properties of this product were identical to those reported
previously.16
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Paper
2007, 63, 3840–3849; M. Ptaszek, D. Lahaye, M. Krayer,
C. Muthiah and J. S. Lindsey, J. Org. Chem., 2010, 75, 1659–
1673.
9 A. M. G. Silva and J. A. S. Cavaleiro, Prog. Heterocycl. Chem.,
2008, 19, 44–69; A. C. Tome, M. G. P. M. S. Neves and
J. A. S. Cavaleiro, J. Porphyrins Phthalocyanines, 2009, 13,
408–414.
Organic & Biomolecular Chemistry
K. Jayaraj, A. Gold, R. N. Austin, L. M. Ball, J. Terner,
D. Mandon, R. Weiss, J. Fischer, A. DeCian, E. Bill,
M. Müther, V. Schünemann and A. X. Trautwein, Inorg.
Chem., 1997, 36, 4555–4566; H. Lv, B. Yang, J. Jing, Y. Yu,
J. Zhang and J.-L. Zhang, Dalton Trans., 2012, 41, 3116–
3118.
22 M. Gouterman, R. J. Hall, G. E. Khalil, P. C. Martin,
E. G. Shankland and R. L. Cerny, J. Am. Chem. Soc., 1989,
111, 3702–3707.
10 H. W. Whitlock Jr., R. Hanauer, M. Y. Oester and
B. K. Bower, J. Am. Chem. Soc., 1969, 91, 7485–7489;
R. Bonnett, R. D. White, U. J. Winfield and 23 Y. Yu, H. Lv, X. Ke, B. Yang and J.-L. Zhang, Adv. Synth.
M. C. Berenbaum, Biochem. J., 1989, 261, 277–280; Catal., 2012, 354, 3509–3516.
M. O. Senge, W. W. Kalisch and S. Runge, Tetrahedron, 24 A. Cetin and C. J. Ziegler, Dalton Trans., 2005, 25–26;
1998, 54, 3781–3798; M. M. Pereira, A. R. Abreu,
N. P. F. Goncalves, M. J. F. Calvete, A. V. C. Simões,
C. J. P. Monteiro, L. G. Arnaut, M. E. Eusébio and
J. Canotilho, Green Chem., 2012, 14, 1666–1672.
R. Rahimi, A. A. Tehrani, M. A. Fard, B. M. M. Sadegh and
H. R. Khavasi, Catal. Commun., 2009, 11, 232–235; L. Liang,
H. Lv, Y. Yu, P. Wang and J.-L. Zhang, Dalton Trans., 2012,
41.
11 M. M. Pereira, C. J. P. Monteiro, A. V. C. Simoes, 25 M. Gouterman, J. Callis, L. Dalton, G. Khalil, Y. Mebarki,
S. M. A. Pinto, A. R. Abreu, G. F. F. Sa, E. F. F. Silva,
L. B. Rocha, J. M. Dabrowski, S. J. Formosinho, S. Simoes
and L. G. Arnaut, Tetrahedron, 2010, 66, 9545–9551.
12 C. Brückner, S. J. Rettig and D. Dolphin, J. Org. Chem.,
1998, 63, 2094–2098.
13 L. P. Samankumara, M. Zeller, J. A. Krause and
C. Brückner, Org. Biomol. Chem., 2010, 8, 1951–1965;
M. A. Hyland, M. D. Morton and C. Brückner, J. Org.
Chem., 2012, 77, 3038–3048.
K. R. Cooper and M. Grenier, Meas. Sci. Technol., 2004, 15,
1986–1994.
26 G. E. Khalil, C. Costin, J. Crafton, G. Jones, S. Grenoble,
M. Gouterman, J. B. Callis and L. R. Dalton, Sens. Actuators,
B, 2004, 97, 13–21; B. Zelelow, G. E. Khalil, G. Phelan,
B. Carlson, M. Gouterman, J. B. Callis and L. R. Dalton,
Sens. Actuators, B, 2003, 96, 304–314; K. S. F. Lau, Syntheses
and Evaluation of Novel Porpholactones for Photonic Appli-
cations (PhD thesis), University of Washington, Seattle,
2006.
14 K. K. Lara, C. K. Rinaldo and C. Brückner, Tetrahedron,
2005, 61, 2529–2539; S. Banerjee, M. Zeller and 27 C. Brückner, J. R. McCarthy, H. W. Daniell, Z. D. Pendon,
C. Brückner, J. Org. Chem., 2010, 75, 1179–1187.
15 G. E. Khalil, P. Daddario, K. S. F. Lau, S. Imtiaz, M. King,
M. Gouterman, A. Sidelev, N. Puran, M. Ghandehari and
C. Brückner, Analyst, 2010, 135, 2125–2131.
R. P. Ilagan, T. M. Francis, L. Ren, R. R. Birge and
H. A. Frank, Chem. Phys., 2003, 294, 285–303;
J. R. McCarthy, M. J. Perez, C. Brückner and R. Weissleder,
Nano Lett., 2005, 5, 2552–2556.
16 J. Akhigbe, G. Peters, M. Zeller and C. Brückner, Org. 28 J. Ogikubo and C. Brückner, Org. Lett., 2011, 13, 2380–
Biomol. Chem., 2011, 9, 2306–2313.
2383; J. Ogikubo, E. Meehan, J. T. Engle, C. Ziegler and
C. Brückner, J. Org. Chem., 2012, 77, 6199–6207;
J. Ogikubo, E. Meehan, J. T. Engle, C. J. Ziegler and
C. Brückner, J. Org. Chem., 2013, DOI: 10.1021/jo400031r,
ASAP.
17 C. Brückner, J. Ogikubo, J. R. McCarthy, J. Akhigbe,
M. A. Hyland, P. Daddario, J. L. Worlinsky, M. Zeller,
J. T. Engle, C. J. Ziegler, M. J. Ranaghan, M. N. Sandberg
and R. R. Birge, J. Org. Chem., 2012, 77, 6480–6494.
18 J. R. McCarthy, H. A. Jenkins and C. Brückner, Org. Lett., 29 C. Brückner, E. D. Sternberg, J. K. MacAlpine, S. J. Rettig
2003, 5, 19–22; J. Akhigbe, C. Ryppa, M. Zeller and
C. Brückner, J. Org. Chem., 2009, 74, 4927–4933.
and D. Dolphin, J. Am. Chem. Soc., 1999, 121, 2609–2610;
J. R. McCarthy, M. A. Hyland and C. Brückner, Org. Biomol.
Chem., 2004, 2, 1484–1491; C. Brückner, M. A. Hyland,
E. D. Sternberg, J. MacAlpine, S. J. Rettig, B. O. Patrick and
D. Dolphin, Inorg. Chim. Acta, 2005, 358, 2943–2953;
C. Ryppa, D. Niedzwiedzki, N. L. Morozowich, R. Srikanth,
M. Zeller, H. A. Frank and C. Brückner, Chem.–Eur. J., 2009,
15, 5749–5762.
19 C. Brückner, D. C. G. Götz, S. P. Fox, C. Ryppa,
J. R. McCarthy, T. Bruhn, J. Akhigbe, S. Banerjee,
P. Daddario, H. W. Daniell, M. Zeller, R. W. Boyle and
G. Bringmann, J. Am. Chem. Soc., 2011, 133, 8740–8752;
L. P. Samankumara, S. Wells, M. Zeller, A. M. Acuña,
B. Röder and C. Brückner, Angew. Chem., Int. Ed., 2012, 51,
5757–5760.
20 J. R. McCarthy, P. J. Melfi, S. H. Capetta and C. Brückner,
Tetrahedron, 2003, 59, 9137–9146.
21 M. J. Crossley and L. G. King, J. Chem. Soc., Chem.
30 C. J. Campbell, J. F. Rusling and C. Brückner, J. Am. Chem.
Soc., 2000, 122, 6679–6685.
31 J. Akhigbe, J. Haskoor, M. Zeller and C. Brückner, Chem.
Commun., 2011, 47, 8599–8601.
Commun., 1984, 920–922; G. Khalil, M. Gouterman, 32 T. D. Lash, in The Porphyrin Handbook, ed. K. M. Kadish,
S. Ching, C. Costin, L. Coyle, S. Gouin, E. Green,
M. Sadilek, R. Wan, J. Yearyean and B. Zelelow, J. Porphy-
rins Phthalocyanines, 2002, 6, 135–145; T. Köpke, M. Pink
and J. M. Zaleski, Chem. Commun., 2006, 4940–4942;
K. M. Smith and R. Guilard, Academic Press, San Diego,
2000, 2, pp. 125–200; L. Latos-Grażyński, in The Porphyrin
Handbook, ed. K. M. Kadish, K. M. Smith and R. Guilard,
Academic Press, San Diego, 2000, 2, pp. 361–416;
Org. Biomol. Chem.
This journal is © The Royal Society of Chemistry 2013

View Article Online
Organic & Biomolecular Chemistry
Paper
M. O. Pawlicki and L. A. Latos-Grażyński, in Handbook of 44 L. Wu and K. Burgess, J. Am. Chem. Soc., 2008, 130, 4089–
Porphyrin Science, ed. K. M. Kadish, K. M. Smith and
R. Guilard, World Scientific, Singapore, 2010, 2,
pp. 103–192; T. D. Lash, in Handbook of Porphyrin Science,
ed. K. M. Kadish, K. M. Smith and R. Guilard, World Scien-
tific, Singapore, 2010, 16, pp. 1–330.
4096; J. Dong, K. M. Solntsev, O. Poizat and L. M. Tolbert,
J. Am. Chem. Soc., 2007, 129, 10084–10085; B. Prueger and
T. Bach, Synthesis, 2007, 1103–1106; K.-Y. Chen,
Y.-M. Cheng, C.-H. Lai, C.-C. Hsu, M.-L. Ho, G.-H. Lee and
P.-T. Chou, J. Am. Chem. Soc., 2007, 129, 4534–4535;
P. K. Tripathy and A. K. Mukerjee, Synthesis, 1985, 285–288.
33 M. Toganoh and H. Furuta, in Handbook of Porphyrin
Science, ed. K. M. Kadish, K. M. Smith and R. Guilard, 45 C. F. H. Allen and E. Weismann Magder, J. Heterocycl.
World Scientific, Singapore, 2010, 2, pp. 295–367. Chem., 1969, 6, 349–360.
34 M. Toganoh and H. Furuta, Chem. Commun., 2012, 48, 937– 46 J. Akhigbe, L. Samankumara and C. Brückner, Tetrahedron
954. Lett., 2012, 53, 3524–3526.
35 S. Richeter, C. Jeandon, J.-P. Gisselbrecht and R. Ruppert, 47 J. Akhigbe and C. Brückner, Eur. J. Org. Chem., 2013, DOI:
in Handbook of Porphyrin Science, World Scientific Publish-
ing, Singapore, 2010, 3, pp. 429–483.
10.1002/ejoc.201300274.
48 CCDC 821398; ref. 31.
36 Y. Xie, T. Morimoto and H. Furuta, Angew. Chem., Int. Ed., 49 The corresponding effectively isostructural meso-phenyl
2006, 45, 6907–6910.
derivative 8a was also crystallographically characterized,
37 A. Srinivasan and H. Furuta, Acc. Chem. Res., 2005, 38, 10–
CCDC 821399; ref. 31.
20; H. Maeda and H. Furuta, Pure Appl. Chem., 2006, 78, 50 The corresponding effectively isostructural meso-phenyl
29–44.
derivative 9a was also crystallographically characterized,
38 T. D. Lash, A. M. Young, A. L. Von Ruden and
CCDC 821400; ref. 31.
G. M. Ferrence, Chem. Commun., 2008, 6309–6311; 51 CCDC Code TPHPOR04.
A. M. Young, A. L. Von Ruden and T. D. Lash, Org. Biomol. 52 G.-F. Chang, A. Kumar, W.-M. Ching, H.-W. Chu and
Chem., 2011, 9, 6293–6305.
39 We shall exclude here expanded porphyrins containing 53 H. Furuta, T. Ishizuka, A. Osuka, Y. Uwatoko and
pyrazoles, see e.g., L. K. Frensch, K. Proepper, M. John, Y. Ishikawa, Angew. Chem., Int. Ed., 2001, 40, 2323–2325.
S. Demeshko, C. Brückner and F. Meyer, Angew. Chem., Int. 54 A. Srinivasan, T. Ishizuka, A. Osuka and H. Furuta, J. Am.
Ed., 2011, 50, 1420–1424; L. K. Blusch (née Frensch), Chem. Soc., 2003, 125, 878–879.
Y. Hemberger, K. Pröpper, B. Dittrich, F. Witterauf, 55 I. Schmidt and P. J. Chmielewski, Tetrahedron Lett., 2001,
M. John, G. Bringmann, C. Brückner and F. Meyer, Chem.– 42, 6389–6392.
Eur. J., 2013, DOI: 10.1002/chem.201204296, accepted for 56 P. J. Chmielewski, Org. Lett., 2005, 7, 1789–1792;
C.-H. Hung, Chem.–Asian J., 2009, 4, 164–173.
publication.
J. Skonieczny, L. Latos-Grażyński and L. Szterenberg, Inorg.
Chem., 2009, 48, 7394–7407.
57 C. Brückner, P. C. D. Foss, J. O. Sullivan, R. Pelto, M. Zeller,
R. R. Birge and G. Crundwell, Phys. Chem. Chem. Phys.,
2006, 8, 2402–2412.
40 A. R. Genady and D. Gabel, Tetrahedron Lett., 2003, 44,
2915–2917.
41 The earlier report that this compound cannot be made
along that route (ref. 31) is to be revised; once we gained
deeper insight into the products, we were also able to opti- 58 J. D. Harvey and C. J. Ziegler, Coord. Chem. Rev., 2003, 247,
mize the diimide reaction and identify all products.
42 For reviews of the use of SmI2 as reductant:
1–19; P. J. Chmielewski and L. Latos-Grażyński, Coord.
Chem. Rev., 2005, 249, 2510–2533.
D. B. G. Williams, K. Blan and J. Caddy, Org. Prep. Proced. 59 APEX2 v2010.3.0 and SAINT v7.60A data collection and data
Int., 2001, 33, 565–602; G. A. Molander, in Organic Reac-
tions, ed. L. Paquette, Wiley, New York, 1994, vol. 46,
pp. 211–367.
processing programs, respectively. Bruker Analytical X-ray
Instruments, Inc., Madison, WI; G. M. Sheldrick, SADABS
v2008/1 semi-empirical absorption and beam correction
program. University of Göttingen, Germany.
43 M. A. Ogliaruso and J. F. Wolfe, Synthesis of Lactones and
Lactams. (Updates to the Chemistry of Functional Groups). 60 Apex2 v2009.7-0 (Bruker, 2009), Apex2 v2009.7-0, SHELXTL
Wiley, Chichester, UK, 1993.
6.14 (Bruker, 2000–2003; Sheldrick, 2008), SHELXTL 6.14.
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