Further Studies on the Synthesis of meso-Tetraarylazuliporphyrins under Lindsey-Rothemund Reaction Conditions and Their Conversion into Benzocarbaporphyrins

Article abstract of DOI:10.1002/ejoc.200300530

Azulene has been shown to react with pyrrole and a series of aromatic aldehydes in the presence of boron trifluoride etherate to give meso-tetraarylazuliporphyrins 6. Good yields of azuliporphyrins were obtained for benzaldehyde, 4-chlorobenzaldehyde, 4-bromobenzaldehyde, and 4-iodobenzaldehyde, and under dilute conditions p-tolualdehyde gave respectable yields. In each case, substantial amounts of meso-tetraarylporphyrins were also formed and a minor fraction of carbaporphyrin by-products could be detected, but otherwise no other macrocyclic products could be identified. 4-Nitrobenzaldehyde gave relatively poor yields of the corresponding azuliporphyrin, while p-anisaldehyde only gave trace amounts of product. Pentafluorobenzaldehyde gave variable results, although in this case a large number of additional by-products were identified including N-fused pentaphyrin, hexaphyrin, and higher order porphyrinoids, but no expanded azulene-containing macrocycles could be detected. Azuliporphyrins undergo reversible nucleophilic substitution on the seven-membered ring with pyrrolidine, benzenethiol, hydrazine, or benzylamine to give carbaporphyrin adducts. This property appears to facilitate an oxidative ring contraction of azuliporphyrins 6 with tert-butyl hydroperoxide in the presence of potassium hydroxide to produce mixtures of benzocarbaporphyrins 19 and 20. Tetraaryl-benzocarbaporphyrins exhibit slightly reduced diatropic ring currents compared to their meso-unsubstituted counterparts, although their UV/Vis spectra are very porphyrin-like and exhibit strong Soret bands near 450 nm. The benzocarbaporphyrins undergo reversible protonation to give monocationic and dicationic species. The latter involves C-protonation to generate an internal CH2 within the macrocyclic cavity. X-ray crystallography of tetraphenylbenzocarbaporphyrin 19a confirms that the preferred tautomer has the two NHs on either side of the indene subunit, in agreement with previous theoretical and spectroscopic studies. In addition, the presence of phenyl substituents at the 5,20-positions was found to tilt the indene moiety substantially by 27.4(1)° relative to the [18]annulene substructure. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003.

Full text of DOI:10.1002/ejoc.200300530

FULL PAPER
Further Studies on the Synthesis of meso-Tetraarylazuliporphyrins under
Lindsey؊Rothemund Reaction Conditions and Their Conversion into
Benzocarbaporphyrins[‡]
Timothy D. Lash,*[a] Denise A. Colby,[a] and Gregory M. Ferrence[a]
Keywords: Azulene / Azuliporphyrins / Porphyrinoids / Synthetic design
Azulene has been shown to react with pyrrole and a series
of aromatic aldehydes in the presence of boron trifluoride
etherate to give meso-tetraarylazuliporphyrins 6. Good
yields of azuliporphyrins were obtained for benzaldehyde, 4-
adducts. This property appears to facilitate an oxidative ring
contraction of azuliporphyrins 6 with tert-butyl hydroperox-
ide in the presence of potassium hydroxide to produce mix-
tures of benzocarbaporphyrins 19 and 20. Tetraaryl-benzo-
chlorobenzaldehyde, 4-bromobenzaldehyde, and 4-iodobenz- carbaporphyrins exhibit slightly reduced diatropic ring cur-
aldehyde, and under dilute conditions p-tolualdehyde gave
respectable yields. In each case, substantial amounts of
meso-tetraarylporphyrins were also formed and a minor frac-
tion of carbaporphyrin by-products could be detected, but
otherwise no other macrocyclic products could be identified.
4-Nitrobenzaldehyde gave relatively poor yields of the cor-
responding azuliporphyrin, while p-anisaldehyde only gave
trace amounts of product. Pentafluorobenzaldehyde gave
variable results, although in this case a large number of addi-
tional by-products were identified including N-fused penta-
phyrin, hexaphyrin, and higher order porphyrinoids, but no
rents compared to their meso-unsubstituted counterparts, al-
though their UV/Vis spectra are very porphyrin-like and
exhibit strong Soret bands near 450 nm. The benzocarbapor-
phyrins undergo reversible protonation to give monocationic
and dicationic species. The latter involves C-protonation to
generate an internal CH2 within the macrocyclic cavity. X-
ray crystallography of tetraphenylbenzocarbaporphyrin 19a
confirms that the preferred tautomer has the two NHs on
either side of the indene subunit, in agreement with previous
theoretical and spectroscopic studies. In addition, the pres-
ence of phenyl substituents at the 5,20-positions was found
expanded azulene-containing macrocycles could be de- to tilt the indene moiety substantially by 27.4(1)° relative to
tected. Azuliporphyrins undergo reversible nucleophilic sub- the [18]annulene substructure.
stitution on the seven-membered ring with pyrrolidine, ben- ( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
zenethiol, hydrazine, or benzylamine to give carbaporphyrin
Germany, 2003)
Introduction
syntheses of carbaporphyrinoid systems relied upon the
‘‘3ϩ1’’ MacDonald condensation.[1,2,46] This approach has
been extraordinarily successful and has allowed the syn-
thesis of diverse structures including oxybenziporphyrins
2,[5,14,19] azuliporphyrins 3,[8,22] and benzocarbaporphyrins
Carbaporphyrinoid systems, porphyrin analogues with
carbocyclic units in place of one or more of the usual pyr-
role rings, have attracted a considerable amount of interest
in recent years,[1Ϫ36] in part due to their unique reactivity
and spectroscopic properties.[2,15] Of particular note, many
carbaporphyrinoids have been shown to form organometal-
lic derivatives under mild conditions[20,21,25Ϫ28,34Ϫ36] and
these ligands are starting to rival the N-confused porphy-
rins (NCPs, 1)[37Ϫ38] and the corroles[39Ϫ44] in their ability
to stabilize higher transition metal oxidation states.[26,34Ϫ36]
Furthermore, carbaporphyrinoids often show strong ab-
sorptions in the far red that make them potentially good
candidates as photosensitizers for photodynamic therapy
(PDT).[1,2,45] Until recently, virtually all of the reported
4
[7,24,31]. However, the ‘‘3ϩ1’’ methodology relies upon the
availability of tripyrranes[47,48] or related precursors.[22] Al-
though an excellent route has been developed for synthesiz-
ing these crucial intermediates,[47] this involves multistep
procedures which place severe limitations on the quantities
of carbaporphyrinoid products that can be conveniently
prepared. Clearly, if carbaporphyrinoids are to find any ap-
plications in industry or medicine, far more straightforward
synthetic procedures need to be devised. meso-Tetrasubsti-
tuted porphyrins are easily prepared by treating pyrrole
with simple aldehydes, usually under acidic conditions.[49]
This chemistry was first observed by Rothemund,[50] who
carried out reactions of pyrrole and various aldehydes in
sealed tubes at elevated temperatures, but the approach was
popularised by the efforts of Adler and Longo who con-
densed the reactants in refluxing acetic or propionic acid in
the presence of atmospheric oxygen.[51] The AdlerϪLongo
[‡]
Conjugated Macrocycles Related to the Porphyrins, 28. Part 27:
T. D. Lash, M. A. Muckey, M. J. Hayes, D. Liu, J. D. Spence,
G. M. Ferrence, J. Org. Chem., in press.
Department of Chemistry, Illinois State University,
[a]
Normal, Illinois 61790-4160, U.S.A.
Fax: (internat.) ϩ 1-309-438-5538
E-mail: tdlash@ilstu.edu
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T. D. Lash, D. A. Colby, G. M. Ferrence
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conditions are particularly convenient for the synthesis of of a series of meso-tetraarylazuliporphyrins.[58] The oxidat-
simple tetrasubstituted porphyrins using aromatic alde- ive ring contraction of azuliporphyrins to afford benzocar-
hydes. However, these conditions are too harsh for acid lab- baporphyrins has been further investigated. In addition, the
ile side chains and fail to afford any porphyrin product in structural characterization of the first tetraphenylcarbapor-
some cases. In order to overcome the limitations of this phyrin by X-ray diffraction has been accomplished.
chemistry, many researchers have explored alternative pro-
cedures for porphyrin synthesis. By far the most important
of these investigations were conducted by Lindsey and co-
workers.[52,53] Lindsey separated the condensation and oxi-
dation steps and optimized the conditions to allow the syn-
Results and Discussion
thesis of diverse porphyrin structures under mild con-
In most syntheses of porphyrins and related macrocycles,
ditions. The most common reaction conditions involved the the key carbonϪcarbon bond forming reactions involve
condensation of pyrrole and an aldehyde in dichlorometh- electrophilic substitution on to the electron-rich pyrrole nu-
ane in the presence of boron trifluoride etherate. Sub- cleus. The propensity of pyrrole to react at its α-positions
sequent oxidation with an electron-deficient quinone, such also facilitates porphyrin formation. We have investigated
as DDQ, affords the macrocyclic products. In 1994, two azulene as a substitute for pyrrole in this type of chemistry.
groups reported that a porphyrin isomer, NCP 1, is formed Azulene favors electrophilic substitution at the 1 and 3 posi-
under modified Rothemund or Lindsey reaction con- tions, which are structurally analogous to the α or 2,5-posi-
ditions.[54] Subsequently, Lindsey demonstrated that NCPs tions of pyrrole, and this feature is ideal for generating
were formed as minor products under virtually any con- macrocyclic systems. For instance, azulene was shown to
ditions that produce significant quantities of porphyrin react with two equivalents of an acetoxymethylpyrrole un-
products.[55] However, under optimal conditions using der mildly acidic conditions to give a tripyrrane analogue
methanesulfonic acid as a catalyst, NCP was produced in and this was utilized in the synthesis of azuliporphyrins and
up to 40% yield.[56] This high yielding one pot synthesis of related systems using the ‘‘3ϩ1’’ methodology.[22] In ad-
NCPs has been instrumental in promoting a surge of inter- dition, azulene was shown to react with paraformaldehyde
est in these porphyrin analogues.[57] The availability of a in the presence of florisil to give calix[4]azulene 5 in excel-
direct synthesis of carbaporphyrinoids is likely to allow a lent yields.[23] These results suggested that azulene might
renaissance in this research area as well. Towards this end, be a suitable reactant for Rothemund-type condensations.
we have developed a one pot synthesis of meso-tetraaryla- Indeed, azulene, pyrrole, and benzaldehyde were shown to
zuliporphyrins under RothemundϪLindsey reaction con- react in the presence of boron trifluoride etherate at room
ditions.[3][58] In a recent paper,[3] we reported our initial re- temperature under nitrogen to give, following oxidation
sults on the synthesis of tetraphenylazuliporphyrin and sev- with DDQ, tetraphenylazuliporphyrin 6a in good yields
eral related benzocarbaporphyrins. We now report further (Scheme 1).[3]
details on these synthetic studies and the characterization
Initially, azulene, pyrrole, and benzaldehyde were com-
bined in a molar ratio of 1:3:4 in dichloromethane and con-
densed in the presence of boron trifluoride for 16 hours.
Following oxidation and extraction, azuliporphyrin was iso-
lated in approximately 3% yield. Although the yield was
relatively poor, the formation of azuliporphyrin demon-
strated that the concept of a one pot synthesis was feasible.
Lindsey has shown that ethanol can modify the reactivity of
the boron trifluoride etherate catalyst and the 0.8% ethanol
present as a stabilizer in commercially available chloroform
gives close to optimal results for sterically hindered meso-
tetrasubstituted porphyrins.[53] In addition, chloroform gave
far better results than dichloromethane in the synthesis of
tetraphenanthroporphyrin[60] and meso-tetraaryltetraacen-
aphthoporphyrins.[61][62] Chloroform also proved to be a su-
perior solvent for the synthesis of meso-tetraarylazulipor-
phyrins. Reaction of 0.29 mmoles of azulene with 3 equiva-
lents of pyrrole and 4 equivalents of benzaldehyde in
120 mL of chloroform for 16 hours, followed by oxidation
for 1 hour with DDQ, afforded 6a in 10Ϫ11% yield. The
yield was slightly improved under more dilute conditions
giving 13% of the desired macrocyclic product using
480 mL of chloroform (Table 1). The crude product was
chromatographed on Grade III basic alumina eluting with
80:20 dichloromethane/hexanes. Initially, a major fraction
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meso-Tetraarylazuliporphyrins under LindseyϪRothemund Reaction Conditions
FULL PAPER
quoted yields correspond to isolated material following
chromatography and recrystallization.
The chemistry also works well for a number of aromatic
aldehydes and a series of related meso-tetraarylporphyrino-
ids 6bϪh were generated (Table 1). p-Chlorobenzaldehyde
gave better results, affording 16% and 17% yields of 6b un-
der the more concentrated and dilute conditions, respec-
tively. p-Bromo- and p-iodobenzaldehyde also gave excellent
results (Table 1), although purification of these azulipor-
phyrins required the use of flash chromatography. The
tetrakis(4-chlorophenyl)azuliporphyrin product 6b was par-
ticularly convenient for our studies due to the relatively
good yield and reasonable solubility. In addition, the pro-
ton NMR spectra for the 4-chlorophenyl-substituted carba-
porphyrinoids were far easier to interpret than is the case
for the related tetraphenyl-substituted porphyrinoids (Fig-
ure 1) and for this reason most of our detailed investi-
gations were carried out on both 6a and 6b. Other alde-
hydes gave poorer results. p-Tolualdehyde gave inferior
yields of 6e under the more concentrated conditions, but
this reactant gave a four fold improvement in yield under
the more dilute conditions (Table 1). p-Nitrobenzaldehyde
gave low yields under concentrated or dilute conditions, al-
though it is worth noting that this aldehyde also affords
poor yields of porphyrin in Lindsey’s studies.[52] p-Anisal-
dehyde also gave inferior results, and less than 2% yield of
impure 6g was noted under the conditions investigated. Fi-
nally, pentafluorobenzaldehyde was investigated and this
was found to give low, poorly reproducible yields of carba-
porphyrinoid 6h. Although yields as high as 8% were noted
for 6h under dilute conditions, the yields were often far
lower. During chromatography, a ‘‘rainbow’’ of nonpolar
products ranging from blue to green to yellow to red eluted
from the column. A later red colored band was isolated
and recrystallized from chloroform/hexanes. This showed a
molecular ion by FAB MS at m/z ϭ 1217.8, while field de-
sorption mass spectrometry gave a molecular ion at 1217.1.
Further consideration of the UV/Vis and proton NMR
spectra for this product demonstrated that it corresponded
to the nonaromatic form of N-fused pentaphyrin 7. This
porphyrinoid was recently reported by Furuta and co-work-
ers in Lindsey-type reactions using pentafluorobenzal-
dehyde,[63] and this group also noted the formation of a
series of expanded porphyrinoids 8 with 6Ϫ12 pyrrole
rings.[64] A comparison of our data for the colored by-prod-
ucts from our chemistry showed that the same series of
products were formed under our conditions and hexaphyrin
8b was present as a major fraction.[64,65] A small amount
of porphyrin 8a was noted, and in some cases a trace of
carbaporphyrin was identified as well. The surprisingly
large number of products that can be formed for penta-
fluorobenzaldehyde presumably leads to the poor yields of
azuliporphyrin 6h. Unfortunately, no expanded porphy-
rinoids incorporating azulene units could be identified in
these reactions.
Scheme 1. LindseyϪRothemund synthesis of meso-tetraaryl azuli-
porphyrins from pyrrole, azulene, and aryl aldehydes
Table 1. Isolated yields of meso-tetraarylazuliporphyrins for reac-
tions of 0.29 mmol. azulene with 3 equiv. of pyrrole and 4 equiv.
of ArCHO
Azuliporphyrin
Product
% Yield
120 mL of CHCl3
480 mL of CHCl3
6a
6b
6c
6d
6e
6f
10Ϫ11%
16%
12%
17%
2.2%
1.8%
0Ϫ5.8%
13%
17%
21.5%
17%
9.0%
1.9%
0Ϫ8%
6h
corresponding to tetraphenylporphyrin was collected, and
this was followed by small amounts of carbaporphyrin by-
products (the quantity of these by-products, which probably
arise from oxidative rearrangement of the azuliporphyrin,
varied somewhat from one experiment to another). A dark
brown fraction was then collected corresponding to meso-
tetraphenylazuliporphyrin (6a). Recrystallization from
Alternative conditions were investigated for the synthesis
chloroform/methanol gave lustrous green flaky crystals. It of tetraphenylazuliporphyrin 6a, although none of them
should be noted that, unless otherwise specified, all of the provided any improvements and most gave only small
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Figure 1. 400 MHz proton NMR spectra of meso-tetrakis(4-chlorophenyl)carbaporphyrinoids in deuteriochloroform. A. Downfield region
for azuliporphyrin 6b. B. Downfield region for meso-tetrakis(4-chlorophenyl)benzocarbaporphyrin 20a. Inset: upfield singlet for the in-
ternal CH. C. Downfield region for major aldehyde 20b. D. Downfield region for minor aldehyde 20c. Inset: downfield singlet for the
aldehydic proton
tity used in the reported experiments, but significantly re-
duced yields were obtained. Methanesulfonic acid (80 mg
for 0.29 mol of azulene) was used in place of boron trifluor-
ide etherate, but only low yields of 6a were noted. However,
in this case substantial amounts of NCP 1 were generated
as a by-product (this was formed to a greater extent in a 30
minute experiment than was found to be formed over 16
hours, in agreement with Lindsey’s investigations into NCP
formation[56]). TFA as a catalyst afforded no azuliporphyrin
product, as was the case for Montmorillonite clay[66] (1.0 g
clay for 0.29 mmoles of azulene). Finally, Florisil[23] (1.0 g)
amounts of the required macrocyclic product. Reactions
with a 1:7:8 molar ratio of azulene to pyrrole to benzal-
dehyde gave a slightly reduced yield of 6a. Although a
gave a complex mixture of products but only a trace
amount of azuliporphyrin could be detected.
Under Lindsey’s reaction conditions, pyrrole and benzal-
larger quantity of tetraphenylporphyrin would be expected dehyde react in the presence of boron trifluoride etherate
under these conditions, we had speculated that the excess to give an equilibrium mixture of oligopyrrolic species and
of reactants relative to azulene would lead to an increase in porphyrinogen 9 (Scheme 1). On addition of DDQ, the pyr-
yield, but this proved not to be the case. The amount of rolic species are irreversibly oxidized and porphyrinogen 9
boron trifluoride was decreased to one quarter of the quan- is converted into meso-tetraphenylporphyrin. The distrubu-
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meso-Tetraarylazuliporphyrins under LindseyϪRothemund Reaction Conditions
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tion of products is highly time dependent and optimal ion substructure (hybrid structure 14). In meso-unsubsti-
yields are often obtained after only 30 minutes.[67] Longer tuted azuliporphyrins 3, the internal CH is shifted further
reaction times generally lead to lower yields. In our synth- upfield to δ ϭ 1.3 ppm,[8] indicating that this series of azuli-
eses of azuliporphyrins, the azulene is consumed very slowly porphyrins possesses a higher degree of aromatic character.
and longer reaction times are necessary. This indicates that The decrease in diatropicity for 6 is probably due to steric
the azuliporphyrinogen intermediate 10 is formed relatively crowding as the aryl substituents prevent the macrocycle
slowly, but that it accumulates to a significant equilibrium from taking on a planar conformation. Nonetheless, the up-
concentration at longer reaction times. Upon addition of field shifts for the interior protons of tetraarylazuliporphyr-
DDQ, this species is converted into the azuliporphyrin ins are significant. The slightly electron-withdrawing 4-hal-
product.
ophenyl units in 6bϪd presumably induce a small upfield
Diphenyldicarbinols have recently been used in the syn- shift by helping to stabilize the dipolar canonical form 13,
thesis of tetraphenylbenziporphyrins.[21,30] In principle, a di- while the slightly electron-donating p-tolyl groups in 6e
phenylcarbinol 11 might be prepared from 1,3-azulene- have the opposite effect. This hypothesis is confirmed to
dicarbaldehyde (12)[59b] by reaction with phenylmagnesium a certain extent by the observation that the 4-nitrophenyl
bromide (Scheme 2). Although this species is probably not substituents in azuliporphyrin 6f cause the interior CH to
involved in the Rothemund syntheses described above, it resonate at δ ϭ 2.94 ppm, while the highly electron-with-
nonetheless incorporates the required carbonϪazulene drawing pentafluorophenyl groups in 6h cause this peak to
bonds and represents a reasonable intermediate for carba- shift to δ ϭ 2.84 ppm. The external pyrrolic protons in azuli-
porphyrin synthesis. Unfortunately, reaction of 12 with porphyrins did not vary to the same extent but produced
PhMgBr gave complex mixtures of products rather than the two doublets and a singlet, each for 2 H, in the chemical
anticipated dialcohol.[68] Nonetheless, the crude mixture shift range of δ ϭ 7.3Ϫ8.0 ppm. The external azulene pro-
was combined with three equivalents of pyrrole and two tons of 6aϪe were easily identified by the relatively large
equivalents of benzaldehyde in the presence of BF3·Et2O in coupling constants (ca. 10 Hz) and produced a 2H triplet
chloroform for two hours. Oxidation with DDQ and chro- at δ ϭ 6.92Ϫ7.08 ppm, a 1H triplet at δ ϭ 7.25Ϫ7.37 ppm
matography on basic alumina gave three major fractions: and a 2H doublet at δ ϭ 7.64Ϫ7.71 ppm. The 4-nitrophenyl
meso-tetraphenylporphyrin, NCP 1, and the desired azuli- substituents of 6f gave rise to downfield shifts, producing
porphyrin 6a. The latter product was isolated in 8% yield. these resonances at δ ϭ 7.13, 7.46, and 7.70 ppm, and this
This route appears to offer no particular advantages, al- effect was even more pronounced for 6h where the penta-
though the formation of NCP as a major by-product in this fluorophenyl groups caused the three sets of azulene reson-
chemistry is interesting.
ances to appear at δ ϭ 7.33, 7.56, and 8.09 ppm, respec-
tively. These results indicate that the seven-membered ring
is taking on more tropylium ion character as would be ex-
pected if the electron-withdrawing groupings help to stabil-
ize the dipolar contributors 13. The presence of a plane of
symmetry in these macrocycles was evident from the proton
NMR spectra, and this was also confirmed by carbon-13
NMR spectroscopy.
Addition of TFA to solutions of 6 gave rise to the corre-
sponding dications 15 (Scheme 3). These show a large in-
crease in the macrocyclic ring current, a feature that we
attribute to the associated enhancement of charge delocaliz-
ation due to resonance hybrid 16 (the free base forms can
only take on aromatic character at the expense of charge
separation). In particular, the internal CH for 15aϪe shows
Scheme 2. Alternative synthesis of meso-tetraphenylazuliporphyrin
The proton NMR spectra for azuliporphyrins 6 indicate up in the range of δ ϭ Ϫ0.4 to Ϫ0.6 ppm while the NHs
that the macrocycle possesses a weak diatropic ring current give rise to a two singlets at δ ϭ 0.8Ϫ1.5 ppm (1 H) and
(Figure 1, a). The internal CH for 6a appears at δ ϭ δ ϭ 2.3Ϫ2.6 ppm (2 H). The 4-nitrophenyl substituents for
3.35 ppm, while the values for 6bϪd fall into the range of dication 15g gave a small additional upfield shift for the
δ ϭ 3.06Ϫ3.13 ppm and 6e gives a peak at δ ϭ 3.40 ppm. internal CH, which was observed at δ ϭ Ϫ0.63 ppm, while
The NH resonance is observed for 6aϪe in the range of δ ϭ the more electron-withdrawing pentafluorophenyl moieties
4.80Ϫ5.16 ppm, where the 4-halophenyl-substituted azuli- of 15h resulted in the CH producing a peak at δ ϭ
porphyrins gave resonances that were again shifted slightly Ϫ0.94 ppm. Again, these data suggest that electron-with-
upfield compared to 6a while 6e shows a small downfield drawing aryl substituents can enhance aromatic character
shift. Although azuliporphyrins are cross-conjugated, they by increasing charge delocalization. The external pyrrolic
can take on some aromatic character due to dipolar reson- protons in dications 15 fell into the range δ ϭ 8.0Ϫ8.5 ppm,
ance contributors (e.g. 13), where the seven-membered ring although these were partially obscured by the aryl reson-
can take on tropylium characteristics while donating elec- ances in some cases. The pyrrole singlet corresponding to
trons into the macrocycle to give a carbaporphyrin-type cat- the ring furthest removed from the azulene unit was clearly
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T. D. Lash, D. A. Colby, G. M. Ferrence
FULL PAPER
resolved in all of the spectra, and showed the greatest
downfield shift for 15h (δ ϭ 8.31 ppm), followed by 15f
(δ ϭ 8.26 ppm), while 15aϪe gave resonances in the range
δ ϭ 8.18Ϫ8.23 ppm. The dication proton NMR spectra
showed considerable broadening to the aryl resonances that
sharpened up somewhat at higher temperatures (ca. 50 °C).
This feature was attributed to conformational restrictions
due in part to the presence of 4 protons within the porphy-
rinoid internal cavity.
Figure 2. UV/Vis spectra of azuliporphyrin 6b (5.66·10Ϫ6 ) in
chloroform (dotted line, free base) and 1% PhSH/CHCl3 (bold
line). The latter spectrum corresponds to the thioether adduct 18b
gave a Soret band at 451 nm, while the pentafluorophenyl-
substituted system 6h showed this absorption at 427 nm,
again demonstrating the typical bathochromic and hyp-
sochromic shifts, respectively, for these substituents.[73] The
influence of other nucleophiles on the UV/Vis spectra of 6a
and 6b were also examined. Benzenethiol gave an adduct
18a with 6a that showed a Soret band at 443 nm, while 18b,
generated from 6b, gave this band at 445 nm, and a long
wavelength Q band was noted in both cases at 750 nm.
Similar results were obtained with hydrazine and benzyla-
mine.
Scheme 3. Protonation of meso-tetraarylazuliporphyrins
The UV/Vis spectra for tetraarylazuliporphyrins 6aϪh
show broad, ill-defined bands between 350 and 540 nm and
weaker broad absorptions through the remainder of the vis-
ible region (Figure 2). Although the spectra for 6aϪe were
very similar, the 4-nitrophenyl groups in 6f gave rise to
small bathochromic shifts to the major absorptions (ca.
8 nm), while 6h showed significant hypsochromic shifts.
These effects for 4-nitrophenyl and pentafluorophenyl sub-
stituents are similar to those observed for tetraarylporphyr-
ins,[69] tetraaryltetraacenaphthoporphyrins,[62][70] and triar-
ylcorroles.[71,72] While the pentafluorophenyl units would be
expected to modify the chromophore through the inductive
effect, the 4-nitrophenyl substituents presumably allow for
a small amount of conjugation (although this is very limited
as the aryl groups must be highly tilted relative to the mean
macrocyclic plane). Addition of TFA to solutions of 6 in
chloroform gave the dications 15 which exhibit more por-
phyrin-like spectra. Azuliporphyrin dication 15a gave a So-
ret-like band at 519 nm, while 15bϪe gave this band at
523Ϫ525 nm. As expected, the 4-nitrophenyl-substituted di-
cation 15f gave a longer wavelength absorption at 532 nm,
while 15h showed a blue shift to 508 nm.
Scheme 4. Nucleophilic additions to meso-tetraarylazuliporphyrins
Addition of pyrrolidine to solutions of azuliporphyrins
has been reported to produce equilibria with the nucleo-
philic addition products 17 (Scheme 4).[3,12] These adducts
Although the adducts could not be isolated, proton
have fully aromatic carbaporphyrin delocalization pathways NMR spectra were obtained for the pyrrolidine and ben-
and exhibit porphyrin-like UV/Vis spectra. In the presence zenethiol adducts of 6a and 6b (Scheme 4). Pyrrolidine gave
of trace pyrrolidine, tetraphenylazuliporphyrin 6a gave a good quality NMR spectra for the downfield region but
Soret band at 437 nm, while 6bϪe gave this absorption at obscured much of the aliphatic portion of the spectrum.
440Ϫ442 nm (Figure 2). In addition, a series of Q bands Greatly improved spectra were obtained with [D8]pyrrolid-
are present at longer wavelengths. Addition of pyrrolidine ine. For instance, the proton spectrum for 6b in CDCl3 with
to solutions of nitrophenyl-substituted azuliporphyrin 6f one drop of [D8]pyrrolidine is shown in Figure 3. The pres-
4538
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meso-Tetraarylazuliporphyrins under LindseyϪRothemund Reaction Conditions
FULL PAPER
Figure 3. 400-MHz proton NMR spectrum of 6b in the presence of [D8]pyrrolidine. This spectrum corresponds to the pyrrolidine adduct
17b. Inset A: Upfield singlet corresponding to the internal CH. Inset B: Details of the triplet of triplets corresponding to the CH connected
to the pyrrolidine nitrogen. Inset C: details of the resonances for the remaining protons on the seven-membered ring
ence of a powerful diatropic ring current is evident from the phyrin 6a was shown to react with tert-butyl hydroperoxide
presence of a singlet at δ ϭ Ϫ5.76 ppm for the internal CH, in the presence of potassium hydroxide to give a mixture
while the pyrrolic protons are shifted downfield to give res- of three carbaporphyrin products 19aϪc (Scheme 5).[3] This
onances at δ ϭ 8.33 (s, 2 H), 8.38 (d, 2 H), and 8.65 ppm chemistry has been further investigated and applied to the
(d, 2 H). The seven-membered ring shows a 2H doublet of 4-chlorophenyl-substituted azuliporphyrin 6b. Reaction of
doublets (J ϭ 1.6, 9.2 Hz) at δ ϭ 5.82 ppm, a 2 H doublet 6a with 5Ϫ6 equiv. of tBuOOH for 2 hours gave 50Ϫ60%
of doublets (J ϭ 5.6, 9.2 Hz) at δ ϭ 5.32 ppm and a 1 H yield of carbaporphyrins 19aϪc. Benzocarbaporphyrin 19a
triplet of triplets (J ϭ 1.6, 5.4 Hz) at δ ϭ 2.93 ppm. The and the related 22-formyl derivative 19b were formed as the
latter resonance corresponds to the central carbon that has major products in roughly equal proportions, while the
been attacked by the nucleophilic pyrrolidine nitrogen. The more sterically hindered aldehyde 19c was also isolated as
data are consistent with the presence of a major substi- a minor product. When the amount of tBuOOH was re-
tution product that retains a plane of symmetry and indi- duced to 1.5 equiv., the reaction was far slower taking 6
cates a strong thermodynamic preference for attack at the hours to go to completion, but the yields were roughly the
23-carbon of azuliporphyrin. However, as this chemistry is same. Addition of 50 equiv. of tBuOOH gave the carbapor-
reversible, nucleophilic attack at other sites may be possible. phyrin products in approximately 10 min, but again the
Similar NMR spectra could be obtained for 6a and 6b in yields and relative proportions of the three carbaporphyrin
the presence of benzenethiol. For instance, the proton products were essentially unchanged. The use of potassium
NMR spectrum of 6b with a trace of PhSH in CDCl3 gave tert-butoxide as the base instead of KOH gave poor results
a resonance for the internal CH at δ ϭ Ϫ5.65 ppm and the and little carbaporphyrin product was isolated. Finally, hy-
external pyrrolic protons appeared downfield at δ ϭ 8.36 drogen peroxide could be used in place of tBuOOH, but
(s, 2 H), 8.39 (d, 2 H), 8.67 (d, 2 H). The azulene protons this appeared to give slightly more of the major aldehyde
for the thioether adduct 18b gave rise to a doublet at δ ϭ 19b compared to 19a. As most of our studies were carried
6.03 ppm (2 H), a doublet of doublets at 5.43 (2 H), and a out on the more symmetrical product 19a, the H2O2 con-
triplet at δ ϭ 4.52 ppm (1 H). Again, these data are consist- ditions were less convenient. Azuliporphyrin reacted with
ent with a single major product that retains a plane of sym- KOH and tBuOOH to give superior yields of the related
metry (i.e. the nucleophile must be attached to carbon 23).
benzocarbaporphyrins 20aϪc. Prior to recrystallization the
The reactivity of azuliporphyrins towards nucleophilic combined yields of these products was often Ͼ80%. The
substitution has previously been utilized in the oxidative carbaporphyrins can easily be separated by flash chroma-
ring contraction of the seven-membered ring to produce tography. In addition to the improved yields, both at the
benzocarbaporphyrins.[3,12] Previously, tetraphenylazulipor- Rothemund and oxidative ring contraction stages, the pro-
Eur. J. Org. Chem. 2003, 4533Ϫ4548
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4539

T. D. Lash, D. A. Colby, G. M. Ferrence
FULL PAPER
ton NMR spectra for the chlorophenyl-substituted benzo-
carbaporphyrin series were relatively easy to interpret
(Figure 1, BϪD). These considerations made these new car-
baporphyrins a convenient set of compounds to compare
and contrast to 19aϪc.
Scheme 5. Oxidative ring contraction of azuliporphyrins to afford
meso-tetraarylbenzocarbaporphyrins
The formation of the benzocarbaporphyrins is believed
to involve an initial nucleophilic attack by the tert-butyl
hydroperoxide anion (Scheme 6). The adduct 21 resulting
from attack at position 23 undergoes a Cope rearrangement
pinching off a cyclopropane ring, to give the cyclohexadiene
22. Abstraction of a proton from position 22 with elimin-
ation of tert-butoxide would give the major aldehyde prod-
uct. The minor aldehyde must arise by initial nucleophilic
attack at position 22, rather than 23, to give 23. Subsequent
Cope rearrangement and loss of tert-butyl alcohol could
give both of the observed formyl products. Deprotonation
of 22 at position 23, on the other hand, followed by chelo-
tropic extrusion of carbon monoxide, would generate the
unsubstituted benzocarbaporphyrin (Scheme 6).
Scheme 6. Proposed mechanism for the oxidative ring contraction
of azuliporphyrins to give benzocarbaporphyrins
from our laboratory suggest that a single tautomer X
(Scheme 7) with the NH protons flanking the indene unit
is favored for carboporphyrins and tautomers of type Y are
not observed. The structures of the new carbaporphyrins
were confirmed by carbon-13 NMR spectroscopy, mass
spectrometry and where possible combustion analysis. The
UV/Vis spectra for 19a,b and 20a,b gave very porphyrin-
like absorptions with a Soret band at 446Ϫ459 nm and a
series of four Q bands that extend well beyond 700 nm (Fig-
ure 4). The absorptions were at slightly longer wavelengths
(1Ϫ3 nm) for the 4-chlorophenyl-substituted species and
the aldehydes were red shifted by 7Ϫ11 nm compared to
the unsubstituted porphyrinoids. The minor aldehydes 19c
and 20c also gave slightly longer wavelength absorptions
than the less crowded major aldehydes 19b and 20b.
Benzocarbaporphyrins show strong macrocyclic ring cur-
rents, and in particular the internal CH for 19a, 19b, 20a,
and 20b are shifted downfield to between δ ϭ Ϫ5.1 and
Ϫ5.5 ppm. Although these shifts are much larger than those
observed for the azuliporphyrins, they are still somewhat
smaller than those observed for the meso-unsubstituted
series 4 where the resonance falls near δ ϭ Ϫ7 ppm.[7,24]
This is attributed to the decreased planarity in the tetraaryl-
substituted carbaporphyrins. The minor aldehydes 19c and
20c gave resonances for the indene CH near δ ϭ Ϫ4.9 ppm,
possibly due to a further distortion of the macrocycle due
to steric crowding. The external pyrrolic protons for 19aϪc
and 20aϪc were observed between δ ϭ 8.2 and 8.8 ppm.
The NMR spectra for 19a and 20a were relatively simple
due to the presence of a plane of symmetry (Figure 1, B).
The benzo-protons for these compounds gave multiplets
near δ ϭ 6.8 and 7.0 ppm, values that are somewhat upfield
from those expected for fused benzene rings. These reson-
ances indicate that the benzene protons point towards the
aryl substituents and fall into the shielding region for these
units. This is particularly significant for the protons lying
next to the carbaporphyrin core because these would other-
wise be observed near δ ϭ 8.8 ppm.[7,24] Previous results Scheme 7. Tautomers of tetraarylbenzocarbaporphyrins
4540  2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim www.eurjoc.org
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meso-Tetraarylazuliporphyrins under LindseyϪRothemund Reaction Conditions
FULL PAPER
Figure 4. UV/Vis spectra of 8.78·10Ϫ6  solutions of tetraphe-
nylbenzocarbaporphyrin 19a. A. Free base in 1% Et3N/chloroform
(bold line). B. Monocation in 1% TFA/chloroform (dashed line).
C. Dication in 50% TFA/chloroform (dotted line)
Addition of small amounts of TFA to benzocarbapor-
phyrins leads to the formation of monocations 24
(Scheme 8),[3,24] and these show broadened Soret bands be-
tween 467 and 479 nm (Figure 4). At higher acid concen-
trations, C-protonated dications 25 are generated. Although
the dication appears to be the major species present in 50%
Scheme 8. Protonation of tetraarylbenzocarbaporphyrins
TFA/chloroform, the Soret band underwent a significant
hypsochromic shift in neat TFA possibly due to stabiliz-
ation of the ground state due to the polar solvent. In any partially attributed to the relief of steric crowding due to
case, the Soret bands for the dications fell into the range of the presence of three hydrogen atoms in the central cavity,
458Ϫ478 nm in 50% TFA and 446Ϫ463 nm in 100% TFA. the closely related meso-unsubstituted carbaporphyrin 4b
The proton NMR spectra for the carbaporphyrins in the exhibits only a 15.5° tilt out of the mean macrocyclic
presence of trace TFA were variable and additional species plane.[24] The additional 11.9° tilt of the indene unit for 19a
appeared to be present in many of these spectra. These is attributable to steric interactions with the 5,20-phenyl
minor species have not been identified, but it is possible substituents. Many meso-tetraarylporphyrins have been
that these correspond to ion associated species by analogy shown to distort substantially from planarity, particularly
to studies reported on related systems by others.[74] In 50% when isoindole units have been incorporated.[75] The re-
TFA/CDCl3, the dication derived from 19a showed the in- maining structural parameters for 19a are as expected and
ternal CH2 at δ ϭ Ϫ2.22 ppm, while 20a gave the corre- are indistinguishable from 4b. All CϪN bond lengths
sponding resonance at δ ϭ Ϫ2.12 ppm. In the latter case, are essentially equivalent with an average bond length
˚
however, the second protonation had not gone to com- equal to 1.374(5) A. The C(6)ϪN(22)ϪC(9) and
pletion, a result that suggests that the dication is slightly C(16)ϪN(24)ϪC(19) bond angles, 110.9(1)° and 110.9(1)°,
destabilized by the presence of the slightly more electron- respectively, are similarly equivalent; however, the 105.4(1)°
withdrawing 4-chlorophenyl substituents. Addition of deut- bond angle of C(11)ϪN(23)ϪC(14) is significantly com-
erated TFA to solutions of 19a or 20a in CDCl3 leads to a pressed and may be attributed to the presence of the non-
rapid exchange of the internal CH, as well as the NH reson- bonding lone pair of electrons on N(23). The three core
ances, confirming that C-protonation is indeed occurring. hydrogen atoms were located by a difference Fourier follow-
For meso-unsubstituted carbaporphyrins 4, slow proton ex- ing anisotropic refinement of all non-hydrogen atoms and
change was observed at the meso-positions under these con- allowed to freely refine. These hydrogens remained associ-
ditions.[24] However, even after a week at room temperature ated with C(21), N(22), and N(24) lending further support
no further exchange occurs on the pyrrolic rings for 19a to the structural assignment. Thus, as has been demon-
or 20a.
strated in both solution from extensive NMR studies,[3,24,31]
Crystals of tetraphenylazuliporphyrin 19a were obtained and by solid state diffraction data for a meso-unsubstituted
that were suitable for X-ray diffraction analysis and this benzocarbaporphyrin,[24] the preferred tautomer for tetra-
data provides further insights into the properties of the phenylbenzocarbaporphyrin 19a has the two NHs flanking
meso-tetraarylbenzocarbaporphyrin series. The macrocy- the pyrroline nitrogen. This result is also in agreement with
cle’s tripyrrolic core is slightly saddled as evidenced by the theoretical studies by Ghosh and co-workers that indicate
tilts for the individual pyrrole rings relative to the mean that tautomers of this type (structure X, Scheme 7) are fav-
plane of the [18]annulene substructure of 11.3(1)°, 8.7(1)°, ored over alternative forms Y by approximately 6 kcal/
and 3.5(1)°; however, the structure’s most striking feature is mol.[76] The phenyl groups are tilted between 52 and 74°
the 27.4(1)° rotation of the indene unit out of the mean out of the carbaporphyrin plane and therefore, as expected,
[18]annulene plane (Figure 5). While this feature may be are not significantly conjugated to the macrocycle’s π sys-
Eur. J. Org. Chem. 2003, 4533Ϫ4548
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4541

T. D. Lash, D. A. Colby, G. M. Ferrence
FULL PAPER
6b and its derivatives. Azuliporphyrins undergo reversible
nucleophilic additions with various nucleophiles including
pyrrolidine, benzylamine, benzenethiol, and hydrazine. This
type of nucleophilic attack appears to trigger oxidative ring
contractions of azuliporphyrins in the presence of KOH
and tert-butyl hydroperoxide, and 6a and 6b were also easily
converted into mixtures of the corresponding benzocarba-
porphyrins. Although three carbaporphyrins are generated
in each case, these were easily separated by flash chroma-
tography. The carbaporphyrins are highly diatropic by pro-
ton NMR spectroscopy, although X-ray crystallography
demonstrates that the indene unit is considerably tilted out
of the mean macrocyclic plane by more than 27°. These
results provide the foundations for future investigations into
these important meso-substituted porphyrin analogue sys-
tems, including the synthesis of novel organometallic de-
rivatives.[34,35]
Experimental Section
Azulene was prepared by a modification of the procedure reported
by Hafner and Meinhardt.[23,77] tert-Butyl hydroperoxide (5Ϫ6 
in decane), phenylmagnesium bromide (1  in THF), and penta-
fluorobenzaldehyde were purchased from Aldrich. UV/Vis spectra
were obtained on a Beckman DU-40 spectrophotometer. NMR
spectra were recorded on a Varian Gemini-400 MHz NMR spec-
trometer at 18Ϫ21 °C, unless otherwise indicated, and recorded in
ppm relative to CDCl3 (residual chloroform at δ ϭ 7.26 ppm in
proton NMR and CDCl3 triplet at δ ϭ 77.23 ppm in carbon-13
NMR spectra). Mass spectroscopic data were obtained from the
Mass Spectral Laboratory, School of Chemical Sciences, University
of Illinois at Urbana-Champaign, supported in part by a grant
from the National Institute of General Medical Sciences (GM,
27029). Elemental analyses were obtained from the School of
Chemical Sciences Microanalysis Laboratory at the University of
Illinois.
Figure 5. RASTEP drawings of tetraphenylbenzocarbaporphyrin
19a showing the atom labeling scheme. Non-hydrogen atoms are
represented by Gaussian ellipsoids at the 50% probability level.
Hydrogen atoms have been drawn arbitrarily small and are not
labeled. a) View perpendicular to the macrocyclic ring. b) View
illustrating the tilt of the indene subunit relative to the porphy-
rinoid ring
5,10,15,20-Tetrakis(4-chlorophenyl)azuliporphyrin (6b): Azulene
(37 mg, 0.29 mmol), 4-chlorobenzaldehyde (165 mg, 1.17 mmol),
and pyrrole (60 mg, 0.895 mmol) were dissolved in chloroform
(480 mL) and the resulting solution purged with nitrogen for
10 min. A 10% solution of boron trifluorideϪdiethyl ether in
chloroform (0.3 mL) was then added and the reaction stirred for
16 h under nitrogen in the dark. DDQ (200 mg) was added and the
solution stirred for an additional 1 h. The mixture was washed with
water and sat. NaHCO3 solution, back extracting with chloroform
at each stage, and the combined organic solutions dried over so-
dium sulfate, filtered and the solvents evaporated under reduced
pressure. The residue was purified by column chromatography on
Grade III basic alumina, eluting with 20:80 hexanes/CH2Cl2. Tetra-
kis(4-chlorophenyl)porphyrin eluted initially, followed by trace
amounts of carbaporphyrins, and then a deep reddish-brown frac-
tion corresponding to the azuliporphyrin product was collected.
Further purification by flash chromatography, loading the column
with CH2Cl2 and eluting with a gradient of CH2Cl2/CHCl3, was
then carried out. Recrystallization from chloroform/methanol af-
forded the azuliporphyrin (41 mg, 0.0501 mmol, 17%) as a lustrous
green powder, m.p. 282Ϫ285 °C, dec. UV/Vis (1% Et3N/CHCl3):
λmax (log10ε) ϭ 383 (4.66), 401 (4.67), 420 (4.66), 473 (4.68, infl),
499 (4.81), 619 (3.92), 668 nm (3.99). UV/Vis (1% TFA/CHCl3):
tem. The crystal packing for structure 19a is unremarkable
and shows no evidence of π-stacking interactions; the in-
terplane separation between the parent and the closest
stacked molecule, related crystallographically by 1 Ϫ x, Ϫy,
˚
Ϫz, is approximately 4.2 A. This pair possesses
a
˚
centroid···centroid distance of 5.137(2) A, corresponding to
an intermolecular lateral displacement of ca. 2.9 A parallel
˚
to the N(22), N(24) axis.
Conclusions
A series of meso-tetraarylazuliporphyrins have been syn-
thesized in a one pot procedure from azulene, pyrrole, and
aryl aldehydes. Although the chemistry is not completely
general, good yields can be obtained using benzaldehyde, p-
halobenzaldehydes, and p-tolualdehyde. In addition, the 4-
chlorophenyl-substituted azuliporphyrin 6b is particularly
useful in these investigations due to the relatively high yields
obtained and the well resolved proton NMR spectra for λmax (log10ε) ϭ 331 (4.38), 410 (4.73), 467 (4.83), 523 (5.02), 618
4542  2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim www.eurjoc.org
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meso-Tetraarylazuliporphyrins under LindseyϪRothemund Reaction Conditions
(4.01), 683 (3.94), 862 nm (4.29). UV/Vis (1% pyrrolidine/CHCl3): Method B:
FULL PAPER
solution of phenylmagnesium bromide
A
1.0

λmax (log10ε) ϭ 357 (4.345), 440 (5.18), 552 (4.11), 596 (4.06), (0.70 mL) was added slowly via syringe to a stirred solution of 1,3-
745 nm (3.75). UV/Vis (0.1% PhSH/CHCl3): λmax (log10ε) ϭ 445 azulenedicarbaldehyde (50 mg, 0.27 mmol) in THF that had been
(5.15), 553 (4.15), 598 (4.025), 752 nm (3.78). UV/Vis (5%
cooled with the aid of an ice bath to 10 °C. The burgandy red
PhCH2NH2/CHCl3): λmax (log10ε) ϭ 442 (5.10), 550 (4.28), 593
solution immediately turned dark green upon addition of the Grig-
(4.19), 748 nm (4.00). UV/Vis (0.5% hydrazine/CHCl3): λmax nard reagent. The ice bath was removed and the reaction mixture
(log10ε) ϭ 442 (5.08), 550 (4.16), 596 (4.03), 748 nm (3.85). 1H stirred at room temperature for 30 min. The reaction was quenched
NMR (400 MHz, CDCl3): δ ϭ 3.13 (s, 1 H), 4.92 (s, 1 H), 7.06 (t,
by the dropwise addition of a saturated aqueous solution of am-
J ϭ 10 Hz, 2 H), 7.31 (d, J ϭ 4.8 Hz, 2 H), 7.36 (t, J ϭ 9.6 Hz, 1 monium chloride (20 mL), and the mixture extracted with dichloro-
H), 7.56 (AAЈBBЈ system, 4 H), 7.61 (s, 2 H), 7.65 (AAЈBBЈ system, methane (2 ϫ 20 mL). The purplish grey-blue solution was washed
4 H), 7.69 (d, J ϭ 9.6 Hz, 2 H), 7.73 (AAЈBBЈ system, 4 H), 7.89
(AAЈBBЈ system, 4 H), 7.92 (d, J ϭ 4.8 Hz, 2 H) ppm. H NMR a rotary evaporator. The residue was further dried under vacuum
(400 MHz, TFA/CDCl3): δ ϭ Ϫ0.41(s, 1 H), 1.43 (br. s, 1 H), 2.53 overnight to give the crude dicarbinol 11 (100 mg, quantitative)
with water, dried over sodium sulfate and the solvent removed on
1
(br. s, 2 H), 7.77 (t, J ϭ 9.8 Hz, 2 H), 7.84 (d, J ϭ 8.4 Hz, 4 H),
7.90 (t, J ϭ 10 Hz, 1 H), 7.94Ϫ7.98 (br. m, 4 H), 7.99 (d, J ϭ chloroform with pyrrole (55 mg, 0.82 mmol) and benzaldehyde
5.2 Hz, 2 H), 8.02 (d, J ϭ 10 Hz, 2 H), 8.04Ϫ8.12 (br. m, 4 H), (58 mg, 0.55 mmol), and a 10% solution of boron trifluoride ether-
as a dark purplish-blue tar. This crude material was dissolved in
8.18 (s, 2 H), 8.2Ϫ8.3 (br. m, 4 H), 8.41 (d, J ϭ 4.8 Hz, 2 H) ppm. ate in chloroform (0.3 mL) was added to the resulting solution un-
1H NMR (400 MHz, [D8]pyrrolidine/CDCl3): δ ϭ Ϫ5.76 (s, 1 H), der nitrogen. The solution was stirred in the dark under nitrogen
2.93 (tt, J ϭ 5.4, 1.6 Hz, 1 H), 5.32 (dd, J ϭ 9.2, 5.6 Hz, 2 H), 5.82
(dd, J ϭ 9.2, 1.6 Hz, 2 H), 7.67Ϫ7.70 (2 overlapping doublets, J ϭ
at room temperature for 2 h, DDQ (185 mg) was added and the
mixture stirred for a further 1 h. The mixture was washed with
8 Hz, 2 H), 7.73Ϫ7.77 (m, 6 H), 7.90Ϫ7.93 (2 overlapping doublets, saturated aqueous sodium hydrogen carbonate solution and the
J ϭ 8 Hz, 2 H), 8.15Ϫ8.19 (2 overlapping doublets, J ϭ 8 Hz, 2 solvents evaporated to dryness under reduced pressure. The residue
H), 8.21 (d, J ϭ 8.4 Hz, 4 H), 8.33 (s, 2 H), 8.38 (d, J ϭ 4.8 Hz, 2 was columned on grade 3 basic alumina, initially eluting with 70%
H), 8.65 (d, J ϭ 4.8 Hz, 2 H) ppm. 1H NMR (400 MHz, trace dichloromethane/hexanes and then increasing the polarity of the
PhSH/CDCl3, major addition product): δ ϭ Ϫ5.65 (s, 1 H), Ϫ2.5
(v br, 2 H), 4.52 (t, J ϭ 7 Hz, 1 H), 5.43 (dd, J ϭ 9.6, 7.2 Hz, 2
H), 6.03 (d, J ϭ 9.6 Hz, 2 H), 7.38 (t, J ϭ 7.2 Hz, 1 H), 7.48Ϫ7.58
eluting solvent to 80%, 90%, and finally 100% dichloromethane.
A deep red colored tetraphenylporphyrin fraction was collected,
followed by a yellow band that corresponded to N-confused por-
(m, 4 H), 7.67 (d, J ϭ 8 Hz, 4 H), 7.72Ϫ7.76 (m, 4 H), 8.03 (d, phyrin 1. Finally, a brown band eluted corresponding to the re-
J ϭ 8 Hz, 2 H), 8.09 (d, J ϭ 8 Hz, 2 H), 8.27 (d, J ϭ 8 Hz, 4 H), quired azuliporphyrin. Recrystallization from chloroform/meth-
8.36 (s, 2 H), 8.39 (d, J ϭ 5 Hz, 2 H), 8.67 (d, J ϭ 5 Hz, 2 H) ppm. anol gave 6a as a dark green powder (15 mg, 0.022 mmol, 8%) that
13C NMR (100 MHz, CDCl3): δ ϭ 114.5, 123.2, 126.6, 127.9,
128.1, 129.3, 130.4, 131.2, 133.8, 134.5, 134.9, 135.1, 135.9, 138.9,
139.1, 139.8, 140.1, 141.0, 144.0, 155.6, 165.5 ppm. 13C NMR
(100 MHz, TFA/CDCl3): δ ϭ 114.8, 116.6, 127.6, 129.3, 130.0,
130.2, 131.3, 132.5, 135.2, 137.0, 137.2, 137.4, 139.5 (2), 141.0,
142.9, 143.9, 145.3, 147.0, 151.0 ppm. HRMS (FAB): calculated
for C50H29N3Cl4 ϩ H: m/z ϭ 812.1194; found 812.1195; elemental
analysis calcd. (%) for C50H29Cl4N3·1/4CHCl3: calcd. C 71.56, H
3.49, N 4.98; found C 71.66, H 3.49, N 5.01.
was identical to the material prepared by method A.
5,10,15,20-Tetrakis(4-bromophenyl)azuliporphyrin (6c): Prepared by
the procedure described for 6b from azulene (37 mg, 0.29 mmol),
pyrrole (60 mg, 0.895 mmol), 4-bromobenzaldehyde (218 mg,
1.18 mmol), chloroform (480 mL), and 10% BF3·Et2O in chloro-
form (0.3 mL). Following oxidation with DDQ (200 mg), the prod-
uct was loaded onto a Grade 3 basic alumina column with di-
chloromethane and eluted with a gradient of 60:40 dichlorometh-
ane/hexanes to 100% dichloromethane. Further purification was
accomplished by loading the crude product in dichloromethane
onto a flash column and eluting with a gradient of 100% dichloro-
5,10,15,20-Tetraphenylazuliporphyrin (6a). Method A: Azuliporphy-
rin 6a was prepared by the foregoing procedure from azulene
(37 mg, 0.29 mmol), pyrrole (60 mg, 0.895 mmol), benzaldehyde
(120 mg, 1.17 mmol), chloroform (480 mL), and 10% BF3·Et2O in methane to 80% chloroform/dichloromethane. Recrystallization
chloroform (0.3 mL). Following oxidation with DDQ (200 mg), the
product was chromatographed on a Grade 3 basic alumina column
from chloroform/methanol gave the azuliporphyrin (62 mg,
0.062 mmol, 21.5%) as a lustrous dark green powder, m.p. Ͼ 300
with 20:80 hexanes-dichloromethane. Recrystallization from °C. UV/Vis (1% Et3N/CHCl3): λmax (log10ε) ϭ 381 (4.66), 403
chloroform/methanol gave tetraphenylazuliporphyrin (25 mg,
(4.65), 422 (4.70), 432 (4.69), 440 (4.68), 467 (4.675), 500 (4.78),
0.037 mmol, 13%) as a lustrous green powder, m.p. Ͼ 300 °C. UV/
634 (3.98), 672 nm (4.005). UV/Vis (1% TFA-CHCl3): λmax
Vis (0.1% PhSH/CHCl3): λmax (log10ε) ϭ 443 (5.03), 550 (4.21), 592 (log10ε) ϭ 333 (4.405), 411 (4.71), 467 (4.85), 524 (4.99), 617 (4.07),
(infl., 4.00), 750 nm (3.81). UV/Vis (1% PhCH2NH2/CHCl3): λmax 683 (4.01), 854 nm (4.29). UV/Vis (1% pyrrolidine/CHCl3): λmax
(log10ε) ϭ 439 (5.05), 545 (4.19), 594 (4.00), 744 nm (3.795). UV/
Vis (0.5% hydrazine/CHCl3): λmax (log10ε) ϭ 442 (5.01), 547 (4.19),
(log10ε) ϭ 355 (4.40), 440 (5.14), 550 (4.13), 596 (4.05), 739 nm
1
(3.74). H NMR (400 MHz, CDCl3): δ ϭ 3.10 (s, 1 H), 4.89 (s, 1
592 (3.98), 741 nm (3.80). 1H NMR (400 MHz, [D8]pyrrolidine/ H), 7.06 (t, J ϭ 10 Hz, 2 H), 7.32 (d, J ϭ 4.4 Hz, 2 H), 7.36 (t,
CDCl3): δ ϭ Ϫ5.66 (s, 1 H), Ϫ2.3 (v br, 2 H), 2.93 (t, J ϭ 5.6 Hz,
J ϭ 9.8 Hz, 1 H), 7.61 (s, 2 H), 7.65Ϫ7.73 (AAЈBBЈ system, 8 H),
1 H), 5.25 (dd, J ϭ 9.2, 5.2 Hz, 2 H), 5.84 (d, J ϭ 10 Hz, 2 H), 7.81 (collapsed AAЈBBЈ system, 8 H), 7.92 (d, J ϭ 4.4 Hz, 2 H)
1
7.69Ϫ7.80 (m, 12 H), 8.07 (d, J ϭ 6.4 Hz, 2 H), 8.3Ϫ8.4 (m, 6 H), ppm. H NMR (400 MHz, TFA/CDCl3): δ ϭ Ϫ0.49 (s, 1 H), 1.29
8.47 (d, J ϭ 4.8 Hz, 2 H), 8.50 (s, 2 H), 8.77 (d, J ϭ 4.8 Hz, 2 (br. s, 1 H), 2.48 (br. s, 2 H), 7.79 (t, J ϭ 9.8 Hz, 2 H), 7.91 (t, J ϭ
1
H) ppm. H NMR (400 MHz, trace PhSH/CDCl3, major addition 9.6 Hz, 1 H), 7.66Ϫ8.05 (m, 12 H), 8.07Ϫ8.25 (m, 8 H), 8.19 (s, 2
product): δ ϭ Ϫ5.53 (s, 1 H), Ϫ2.5 (v br, 2 H), 4.41 (t, J ϭ 6.8 Hz,
1 H), 5.31 (dd, J ϭ 9.6, 6.8 Hz, 2 H), 6.06 (d, J ϭ 9.6 Hz, 2 H),
7.43Ϫ7.56 (m, 5 H), 7.70Ϫ7.77 (m, 6 H), 8.18Ϫ8.22 (m, 4 H),
8.35Ϫ8.39 (m, 4 H), 8.46 (d, J ϭ 4.8 Hz, 2 H), 8.52 (s, 2 H), 8.77
(d, J ϭ 4.8 Hz, 2 H) ppm.[78]
H), 8.42 (d, J ϭ 4.4 Hz, 2 H) ppm. 13C NMR (100 MHz, CDCl3):
δ ϭ 114.5, 122.1, 123.2, 123.5, 126.5, 129.3, 130.4, 130.8, 131.0,
131.2, 134.5, 135.1, 135.2, 136.2, 138.9, 139.1, 140.1, 140.2, 141.4,
143.9, 155.5, 165.4 ppm. HRMS (FAB): calculated for
C50H29N3Br4 ϩ H: m/z ϭ 987.9173; found 987.9171; elemental
Eur. J. Org. Chem. 2003, 4533Ϫ4548
www.eurjoc.org
 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
4543

T. D. Lash, D. A. Colby, G. M. Ferrence
analysis calcd. (%) for C50H29Br4N3: calcd. C 60.57, H 2.95, N 129.11, 130.10, 130.35, 133.69, 134.91, 135.76, 136.92, 138.30,
FULL PAPER
4.24; found C 60.01, H 2.88, N 4.23.
138.69, 138.99, 139.38, 139.95, 144.14, 155.65, 165.76 ppm. HRMS
(FAB): calculated for C54H41N3 ϩ H: m/z ϭ 732.3379; found
732.3382.
5,10,15,20-Tetrakis(4-iodophenyl)azuliporphyrin (6d): Prepared by
the foregoing procedure from azulene (37 mg, 0.29 mmol), pyrrole
(60 mg, 0.895 mmol), 4-iodobenzaldehyde (270 mg, 1.16 mmol),
chloroform (480 mL), and 10% BF3·Et2O in chloroform (0.3 mL).
Following oxidation with DDQ (200 mg), the product was chroma-
tographed on a Grade 3 basic alumina column, eluting with di-
chloromethane. The crude product was further purified on two
sequential flash chromatography columns, loading the sample in
dichloromethane and eluting with a gradient of 100% dichloro-
methane to 90% chloroform/dichloromethane. Recrystallization
from chloroform/methanol gave the azuliporphyrin (58 mg,
0.049 mmol, 17%) as dark blue green crystals, m.p. Ͼ 300 °C. UV/
5,10,15,20-Tetrakis(4-nitrophenyl)azuliporphyrin (6f): Prepared by
the foregoing procedure from azulene (37 mg, 0.29 mmol), pyrrole
(60 mg, 0.895 mmol), 4-nitrobenzaldehyde (175 mg, 1.16 mmol),
chloroform (120 mL), and 10% BF3·Et2O in chloroform (0.3 mL).
Following oxidation with DDQ (200 mg), the product was chroma-
tographed on a Grade 3 basic alumina column eluting with di-
chloromethane. The crude product was further purified on two
sequential flash chromatography columns, loading the sample in
dichloromethane and eluting with a gradient of 100% dichloro-
methane to 30% chloroform/dichloromethane. Recrystallization
Vis (1% Et3N/CHCl3): λmax (log10ε) ϭ 383 (4.68), 400 (4.66), 420 from chloroform/methanol gave the azuliporphyrin (4.5 mg,
(4.63), 474 (4.64, infl), 501 (4.77), 668 nm (3.94). UV/Vis (1% TFA/ 0.00526 mmol, 1.8%) as a blue-black powder, m.p. Ͼ 300 °C. UV/
CHCl3): λmax (log10ε) ϭ 390 (4.53), 422 (4.62), 471 (4.85), 525 Vis (1% Et3N/CHCl3): λmax (log10ε) ϭ 368 (4.60), 479 (4.69), 526
(5.00), 620 (3.98), 686 (3.95), 864 nm (4.31). UV/Vis (1% pyrroli- (4.79), 642 (3.96), 692 (4.03), 745 nm (4.00). UV/Vis (1% TFA/
dine/CHCl3): λmax (log10ε) ϭ 360 (4.385), 441 (5.11), 552 (4.13), CHCl3): λmax (log10ε) ϭ 411 (4.75), 478 (4.80), 532 (5.10), 629
1
597 (4.06), 742 nm (3.76). H NMR (400 MHz, CDCl3): δ ϭ 3.06 (4.06), 688 (3.86), 779 (3.90), 857 nm (4.30). UV/Vis (1% pyrroli-
(s, 1 H), 4.85 (br. s, 1 H), 7.08 (t, J ϭ 9.8 Hz, 2 H), 7.32 (d, J ϭ dine/CHCl3): λmax (log10ε) ϭ 372 (4.46), 451 (5.00), 609 (4.03),
4.8 Hz, 2 H), 7.37 (t, J ϭ 10 Hz, 1 H), 7.53 (AAЈBBЈ system, 4 H),
7.62 (s, 2 H), 7.67 (AAЈBBЈ system, 4 H), 7.71 (d, J ϭ 10 Hz, 2
751 nm (3.72). 1H NMR (400 MHz, CDCl3): δ ϭ 2.94 (s, 1 H),
7.13 (t, J ϭ 10 Hz, 2 H), 7.34 (d, J ϭ 4.4 Hz, 2 H), 7.46 (t, J ϭ
H), 7.91 (AAЈBBЈ system, 4 H), 7.92 (d, J ϭ 4.8 Hz, 2 H), 8.01 9.4 Hz, 1 H), 7.68 (s, 2 H), 7.70 (d, J ϭ 10 Hz, 2 H), 7.94 (d, J ϭ
(AAЈBBЈ system, 4 H) ppm. 1H NMR (400 MHz, 40 °C, TFA/
4.8 Hz, 2 H), 8.00 (d, J ϭ 8.4 Hz, 4 H), 8.16 (d, J ϭ 8.8 Hz, 4 H),
CDCl3): δ ϭ Ϫ0.60 (s, 1 H), 0.91 (br. s, 1 H), 2.34 (br. s, 2 H), 7.82 8.49 (d, J ϭ 8.8 Hz, 4 H), 8.57 (d, J ϭ 8.4 Hz, 4 H) ppm. 1H NMR
(t, J ϭ 10 Hz, 2 H), 7.83Ϫ7.86 (4 H, doublet overlapping with (400 MHz, TFA/CDCl3): δ ϭ Ϫ0.63 (s, 1 H), 0.88 (br. s, 1 H), 2.62
previous triplet, J ϭ 7.2 Hz, 4 H), 7.94 (t, J ϭ 9 Hz, 1 H), (br. s, 2 H), 7.87 (t, J ϭ 9.8 Hz, 2 H), 8.04 (t, J ϭ 9.6 Hz, 1 H),
7.98Ϫ8.06 (v br. m, 4 H), 8.03 (d, J ϭ 4.8 Hz, 2 H), 8.08 (d, J ϭ 8.05Ϫ8.09 (m, 4 H), 8.26 (s, 2 H), 8.37Ϫ8.40 (m, 4 H), 8.46Ϫ8.49
9.6 Hz, 2 H), 8.22 (d, J ϭ 7.6 Hz, 4 H), 8.23 (s, 2 H), 8.34 (d, J ϭ (m, 2 H), 8.59 (br. m, 4 H), 8.76 (d, J ϭ 8.8 Hz, 4 H), 8.83 (br. m,
7.6 Hz, 4 H), 8.45 (d, 4.8 Hz, 2 H) ppm. 13C NMR (100 MHz, 4 H) ppm. 13C NMR (100 MHz, TFA/CDCl3): δ ϭ 115.0, 116.5,
CDCl3): δ ϭ 97.9, 100.7, 114.7, 116.9, 127.7, 130.0, 131.4, 132.5, 124.2, 124.5, 128.1, 129.9, 131.7, 132.7, 134.2, 137.0, 140.9, 142.6,
135.7, 137.6, 137.8, 137.9, 138.3, 139.1, 139.6, 141.0, 143.0, 143.7,
145.5, 146.8, 148.0, 150.9 ppm. HRMS (FAB): calculated for
C50H29N3I4 ϩ H: m/z ϭ 1179.8619; found 1179.8620.
142.9, 143.6, 143.8, 143.9, 146.4, 147.3, 149.1, 149.7, 150.7 ppm.
FAB MS: m/z (rel. int.) 857.2 (10), 774.6 (100); FD MS: m/z (rel.
int.) 856.1 (100). MALDI MS: m/z ϭ 856.29 [Mϩ].
5,10,15,20-Tetrakis(4-methylphenyl)azuliporphyrin (6e): Prepared
5,10,15,20-Tetrakis(pentafluorophenyl)azuliporphyrin (6h): Prepared
by the foregoing procedure from azulene (37 mg, 0.29 mmol), pyr-
by the foregoing procedure from azulene (37 mg, 0.29 mmol), pyr-
role (60 mg, 0.895 mmol), 4-methylbenzaldehyde (140 mg, role (60 mg, 0.895 mmol), pentafluorobenzaldehyde (230 mg,
1.17 mmol), chloroform (480 mL), and 10% BF3·Et2O in chloro-
form (0.3 mL). Following oxidation with DDQ (200 mg), the prod-
uct was chromatographed on a Grade 3 basic alumina column elut-
1.16 mmol), chloroform (480 mL), and 10% BF3·Et2O in chloro-
form (0.3 mL). Following oxidation with DDQ (200 mg), the prod-
uct was loaded chromatographed on a Grade 3 basic alumina col-
ing with dichloromethane. Further purification was accomplished umn eluting with 80:20 hexanes/CH2Cl2 and then 60:40 hexanes/
by loading the crude product in dichloromethane onto a flash col-
umn and eluting with chloroform. Recrystallization from chloro-
form/methanol gave the azuliporphyrin (19 mg, 0.026 mmol, 9.0%)
CH2Cl2. Multiple colored bands were noted that corresponded to
N-fused pentaphyrin, hexaphyrin, octaphyrin, and related meso-po-
lyaryl expanded porphyrins,[63][64] although a small amount of
as a shiny green crystals, m.p. Ͼ 300 °C. UV/Vis (1% Et3N/CHCl3): tetrakis(pentafluorophenyl)porphyrin was also seen. The crude
λmax (log10ε) ϭ 382 (4.66), 404 (4.66), 418 (4.65), 501 (4.81), 611 product was further purified twice by flash chromatography on sil-
(3.90), 667 (3.94), 753 nm (3.88). UV/Vis (1% TFA/CHCl3): λmax ica, eluting initially with 80:20 hexanes/CH2Cl2, and gradually in-
(log10ε) ϭ 335 (4.31), 386 (4.55), 415 (4.66), 469 (4.825), 524 (4.99),
617 (3.94), 685 (4.00), 866 nm (4.29). UV/Vis (1% pyrrolidine/
creasing the polarity to 50:50 hexanes/CH2Cl2. Evaporation of the
solvent under reduced pressure afforded the tetrakis(pentafluoro-
CHCl3): λmax (log10ε) ϭ 355 (4.34), 442 (5.075), 549 (4.09), 596 phenyl)azuliporphyrin as a shiny green powder in variable quantit-
1
(4.04), 744 nm (3.76). H NMR (400 MHz, CDCl3): δ ϭ 2.55 (s, 6 ies (trace amounts up to 25 mg, 0Ϫ8%). UV/Vis (CHCl3): λmax
H), 2.60 (s, 6 H), 3.40 (s, 1 H), 5.16 (s, 1 H), 6.94 (t, J ϭ 9.8 Hz, 2 (log10ε) ϭ 367 (4.69), 394 (4.67), 455 (infl., 4.68), 479 (4.78), 632
H), 7.25 (t, J ϭ 9.6 Hz, 1 H), 7.31 (d, J ϭ 4.8 Hz, 2 H), 7.37 (d, (infl., 4.11), 680 nm (4.24). UV/Vis (1% TFA/CHCl3): λmax
J ϭ 7.6 Hz, 4 H), 7.45 (d, J ϭ 8 Hz, 4 H), 7.60 (s, 2 H), 7.65Ϫ7.71 (log10ε) ϭ 394 (4.71), 508 (5.11), 618 (3.96), 673 (4.09), 730 (3.92),
(m, 4 H), 7.83 (d, J ϭ 7.6 Hz, 4 H), 7.94 (d, J ϭ 4.4 Hz, 2 H) ppm.
809 nm (4.10). UV/Vis (1% pyrrolidine/CHCl3): λmax (log10ε) ϭ 427
1
1H NMR (400 MHz, TFA/CDCl3): δ ϭ Ϫ0.41 (s, 1 H), 0.86 (br. s, (5.005), 470 (4.81), 580 (3.98), 632 (3.75), 704 nm (3.48). H NMR
1 H), 2.49 (br. s, 2 H), 2.68 (s, 6 H), 2.74 (s, 6 H), 7.65 (d, J ϭ (400 MHz, CDCl3): δ ϭ 2.84 (s, 1 H), 4.57 (br. s, 1 H), 7.33 (t, J ϭ
8 Hz, 4 H), 7.68 (t, J ϭ 10 Hz, 2 H), 7.7Ϫ7.8 (br. m, 4 H), 7.83 (t, 9.8 Hz, 2 H), 7.41 (d, J ϭ 4.4 Hz, 2 H), 7.56 (t, J ϭ 9.6 Hz, 1 H),
J ϭ 9.6 Hz, 1 H), 7.96Ϫ8.03 (m, 8 H), 8.19 (s, 2 H), 8.15Ϫ8.25 (br.
7.67 (s, 2 H), 7.84Ϫ7.88 (m, 2 H), 8.09 (d, J ϭ 10 Hz, 2 H) ppm.
m, 4 H), 8.42 (d, J ϭ 5.2 Hz, 2 H) ppm. 13C NMR (100 MHz, 1H NMR (400 MHz, 40 °C, TFA/CDCl3): δ ϭ Ϫ0.94 (s, 1 H), 0.9
CDCl3): δ ϭ 21.59, 21.75, 115.32, 123.50, 127.17, 128.25, 128.43, (br. s, 1 H), 2.92 (br. s, 2 H), 8.08Ϫ8.18 (m, 5 H), 8.31 (s, 2 H),
4544
 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
Eur. J. Org. Chem. 2003, 4533Ϫ4548

meso-Tetraarylazuliporphyrins under LindseyϪRothemund Reaction Conditions
8.47Ϫ8.52 (m, H) ppm. HRMS (FAB): calculated for 108.6, 117.6, 117.8, 122.0, 122.1, 123.9, 125.8, 125.9, 126.3, 127.1,
FULL PAPER
4
C50H13F20N3 ϩ H: m/z ϭ 1036.0868; found 1036.0865.
127.4, 127.5, 127.6, 128.5, 128.7, 128.8, 132.8, 133.1, 134.2, 134.3,
134.7, 134.8, 135.1, 135.8, 135.9, 136.4, 138.1, 138.2, 138.3, 139.2,
139.3, 139.9, 140.0, 140.3, 140.4, 142.2, 155.9, 192.2 ppm. HRMS
(FAB): calculated for C50H29N3Cl4O ϩ H: m/z ϭ 828.1143; found
828.1139; elemental analysis calcd. (%) for C50H29N3O·1/8CHCl3:
calcd. C 71.29, H 3.47, N 4.97; found C 71.19, H 3.44, N 4.98.
Oxidative Ring Contraction of 6b: A solution of KOH (800 mg)
in methanol (100 mL) was added to 6b (110 mg, 0.135 mmol) in
dichloromethane (110 mL), followed by the addition of 150 µL of
a solution of tert-butyl hydroperoxide in decane (5Ϫ6 ). The mix-
ture was stirred at room temperature in the dark under nitrogen
for 2 h. The mixture was diluted with chloroform, washed twice
with water, dried with sodium sulfate, filtered, and the solvents eva-
porated to dryness. The residue was loaded onto a silica flash chro-
matography column with CH2Cl2, and eluted with 30% hexanes/
dichloromethane. Three carbaporphyrin fractions corresponding to
20a (least polar), 20b, and 20c (most polar) were collected. Each
sample was recrystallized from chloroform/methanol to give pure
20a (28.7 mg, 26.5%, 0.0359 mmol), 20b (29.5 mg, 0.0351 mmol,
26.4%), and 20c (10.4 mg, 0.0126 mmol, 9.3%). Although the over-
all yields remained consistent, significant variations in the yield of
the minor product 20c was noted. However, the yield of 20c was
always Ͻ 10% and was commonly Ͻ 5%.
21-Formyl-5,10,15,20-tetrakis(4-chlorophenyl)benzo[b]carba-
porphyrin (20c): Blue-black solid, m.p. Ͼ 300 °C. UV/Vis (1% Et3N/
CHCl3): λmax (log10ε) ϭ 459 (5.22), 551 (4.15), 593 (3.97), 653
(3.56), 725 nm (3.80). UV/Vis (1% TFA/CHCl3): λmax (log10ε) ϭ
353 (4.47), 479 (5.01), 669 (4.02), 736 nm (4.025). UV/Vis (50%
TFA/CHCl3): λmax (log10ε) ϭ 368 (4.54), 478 (5.09), 559 (4.04), 662
(4.24), 742 nm (4.11). UV/Vis (TFA): λmax (log10ε) ϭ 347 (4.53),
463 (5.10), 598 (3.89), 648 (4.22), 732 nm (4.11). 1H NMR
(400 MHz, CDCl3): δ ϭ Ϫ4.96 (s, 1 H), Ϫ2.2 (v br, 2 H), 7.08 (d,
J ϭ 7.6 Hz, 1 H), 7.16 (t, J ϭ 7.6 Hz, 1 H), 7.49 (d, J ϭ 7.2 Hz, 1
H), 7.73Ϫ7.80 (m, 6 H), 7.88 (AAЈXXЈ system, 2 H), 8.02
(AAЈXXЈ system, 2 H), 8.10 (AAЈXXЈ system, 2 H), 8.26 (s, 2 H),
8.30 (AAЈXXЈ system, 2 H), 8.34 (d, J ϭ 5.2 Hz, 1 H), 8.38 (d, J ϭ
4.8 Hz, 1 H), 8.41 (AAЈXXЈ system, 2 H), 8.60 (d, J ϭ 4.8 Hz, 1
H), 8.70 (d, J ϭ 4.8 Hz, 1 H), 9.74 (s, 1 H) ppm. 13C NMR
(100 MHz, CDCl3): δ ϭ 105.4, 117.2, 118.0, 121.5, 123.6, 125.6,
126.2, 126.6, 126.7, 127.0, 127.1, 127.6, 127.7, 127.8, 128.8, 129.3,
129.4, 131.9, 132.6, 133.8, 134.1, 134.8, 134.9, 135.8, 135.9, 136.0,
136.1, 136.4, 136.6, 137.3, 137.8, 138.3, 138.8, 139.7, 139.9, 140.0,
140.1, 140.4, 155.7, 156.3, 189.9 ppm. HRMS (FAB): calculated
for C50H29N3Cl4O ϩ H: m/z ϭ 828.1143; found 828.1139.
5,10,15,20-Tetrakis(4-chlorophenyl)benzo[b]carbaporphyrin (20a):
Lustrous dark purple crystals, m.p. Ͼ 300 °C. UV/Vis (1% Et3N/
CHCl3): λmax (log10ε) ϭ 449 (5.28), 538 (4.21), 580 (3.93), 644
(3.58), 711 nm (3.69). UV/Vis (1% TFA/CHCl3): λmax (log10ε) ϭ
344 (4.50), 471 (5.11), 656 (4.18), 723 nm (4.01). UV/Vis (50% TFA/
CHCl3): λmax (log10ε) ϭ 464 (5.12), 675 nm (4.28). UV/Vis (TFA):
λmax (log10ε) ϭ 319 (4.47), 451 (5.33), 565 (3.89), 615 (4.07), 671 nm
1
(4.50). H NMR (400 MHz, CDCl3): δ ϭ Ϫ5.41 (s, 1 H), Ϫ2.7 (v
br, 2 H), 6.85Ϫ6.89 (m, 2 H), 7.03Ϫ7.06 (m, 2 H), 7.74 (AAЈBBЈ
system, 4 H), 7.82 (AAЈBBЈ system, 4 H), 8.07 (AAЈBBЈ system, 4
H), 8.26 (AAЈBBЈ system, 4 H), 8.45 (s, 2 H), 8.47 (d, J ϭ 4.8 Hz,
2 H), 8.63 (d, J ϭ 4.8 Hz, 2 H) ppm. 1H NMR (400 MHz, trace
TFA/CDCl3): δ ϭ Ϫ4.99 (s, 1 H), Ϫ3.82 (s, 1 H), Ϫ0.59 (s, 2 H),
6.86Ϫ6.90 (m, 2 H), 7.01Ϫ7.04 (m, 2 H), 7.86Ϫ7.89 (m, 8 H),
8.25Ϫ8.28 (m, 6 H), 8.37 (d, J ϭ 4 Hz, 2 H), 8.40 (d, J ϭ 8 Hz, 4
Oxidative Ring Contraction of 6a. Method A: Under the same con-
ditions reported above for the ring contraction of 6b, tetraphe-
nylazuliporphyrin 6a (105 mg, 0.156 mmol) and KOH (800 mg) in
CH2Cl2 (100 mL) and methanol (100 mL) was treated with 150 µL
of a 5  solution of tert-butyl hydroperoxide in decane. The crude
product was chromatographed on a silica flash column eluting with
20% hexanes/CH2Cl2, and then dichloromethane. Two carbapor-
phyrin fractions corresponding to 19a (least polar) and 19b were
collected. When the eluting solvent was changed to 50% CHCl3/
CH2Cl2, a third minor fraction 19c was obtained. Each sample was
recrystallized from chloroform/methanol to give pure 19a (29.8 mg,
29%), 19b (23.1 mg, 21.5%) and 19c (5.2 mg, 4.8%).
1
H), 8.66 (s, 2 H) ppm. H NMR (400 MHz, 50% TFA/CDCl3, up-
field region only): δ ϭ Ϫ2.12 (s, 2 H) ppm. 13C NMR (100 MHz,
CDCl3): δ ϭ 108.0, 117.4, 121.2, 123.8, 125.4, 126.7, 127.5, 128.6,
133.8, 134.6, 135.3, 135.9, 136.3, 138.2, 138.3, 138.5, 140.3, 140.5,
155.2 ppm. HRMS (EI): calculated for C49H29N3Cl4: m/z ϭ
799.1115; found 799.1112; elemental analysis calcd. (%) for
C49H29N3Cl4: calcd. C 73.42, H 3.65, N 5.24; found C 73.18, H
3.59, N 5.20.
Method B: Tetraphenylazuliporphyrin 6a (20.0 mg, 0.0296 mmol)
and KOH (230 mg) in CH2Cl2 (25 mL) and methanol (25 mL) was
treated with 150 µL of a 30% aqueous solution of hydrogen per-
oxide and stirred at room temperature for 2 hours. Following
workup and chromatography as described above, recrystallization
gave pure samples of 19a (3.5 mg, 18%) and 19b (6.0 mg, 29%).
A small amount of 19c was formed but this was not isolated in
pure form.
22-Formyl-5,10,15,20-tetrakis(4-chlorophenyl)benzo[b]carba-
porphyrin (20b): Brown-black solid, m.p. Ͼ 300 °C. UV/Vis (1%
Et3N/CHCl3): λmax (log10ε) ϭ 347 (4.52), 456 (5.34), 541 (4.31),
581 (3.86), 646 (3.59), 715 nm (3.85). UV/Vis (1% TFA/CHCl3):
λmax (log10ε) ϭ 347 (4.56), 472 (5.22), 653 (4.19), 729 nm (4.08).
UV/Vis (50% TFA/CHCl3): λmax (log10ε) ϭ 361 (4.56), 474 (5.17),
553 (4.20), 652 (4.225), 728 nm (4.12). UV/Vis (TFA): λmax
(log10ε) ϭ 348 (4.59), 462 (5.22), 593 (3.95), 642 (4.19), 722 nm 5,10,15,20-Tetraphenylbenzo[b]carbaporphyrin (19a): UV/Vis (1%
1
(4.11). H NMR (400 MHz, CDCl3): δ ϭ Ϫ5.20 (s, 1 H), Ϫ2.8 (v TFA/CHCl3): λmax (log10ε) ϭ 341 (4.49), 467 (5.115), 654 (4.16),
br, 2 H), 6.98 (d, J ϭ 8 Hz, 1 H), 7.24 (d, J ϭ 1 Hz, 1 H), 7.57
720 nm (4.015). UV/Vis (TFA): λmax (log10ε) ϭ 446 (5.26), 564
(dd, J ϭ 8, 1 Hz, 1 H), 7.75 (d, J ϭ 8.4 Hz, 4 H), 7.85 (d, J ϭ (3.71), 615 (3.935), 669 nm (4.22). 1H NMR (400 MHz, trace TFA/
8.4 Hz, 2 H), 7.87 (d, J ϭ 8.4 Hz, 2 H), 8.07Ϫ8.11 (2 overlapping CDCl3, monocation): δ ϭ Ϫ4.96 (s, 1 H), Ϫ3.83 (s, 1 H), Ϫ1.16 (s,
doublets, 4 H), 8.25Ϫ8.30 (2 overlapping doublets, 4 H), 8.50 (s, 2 2 H), 6.78Ϫ6.83 (m, 2 H), 6.94Ϫ6.98 (m, 2 H), 7.82Ϫ7.94 (m, 12
H), 8.50Ϫ8.53 (2 overlapping doublets, 2 H), 8.71 (d, J ϭ 4.8 Hz,
H), 8.30 (d, J ϭ 4 Hz, 2 H), 8.32Ϫ8.36 (m, 4 H), 8.42 (d, J ϭ
1 H), 8.73 (d, J ϭ 4.8 Hz, 1 H), 9.71 (s, 1 H) ppm. 1H NMR 4.8 Hz, 2 H), 8.44Ϫ8.49 (m, 4 H), 8.68 (s, 2 H) ppm. 13C NMR
(400 MHz, trace TFA/CDCl3): δ ϭ Ϫ4.66 (s, 1 H), Ϫ3.65 (s, 1 H), (100 MHz, trace TFA/CDCl3, monocation): δ ϭ 127.1, 127.2,
Ϫ0.52 (s, 2 H), 7.04 (d, J ϭ 8 Hz, 1 H), 7.33 (s, 1 H), 7.58 (d, J ϭ
8 Hz, 1 H), 7.88Ϫ7.94 (2 overlapping doublets, 8 H), 8.25Ϫ8.30
127.3, 127.9, 129.4, 130.0, 130.3, 130.7, 131.5, 132.0, 132.2, 133.2,
134.6, 137.4, 138.2, 138.7, 142.5, 145.5, 146.0, 146.5, 158.1 ppm.
(m, 6 H), 8.39Ϫ8.42 (m, 4 H), 8.45 (d, J ϭ 4.4 Hz, 2 H), 8.68 (s, 2 Elemental analysis calcd. (%) for C49H33N3·0.3CHCl3: calcd. C
H), 9.54 (s, 1 H) ppm. 13C NMR (100 MHz, CDCl3, 40 °C): δ ϭ
www.eurjoc.org
84.64, H 4.80, N 6.00; found C 84.78, H 4.74, N 6.00.[78]
Eur. J. Org. Chem. 2003, 4533Ϫ4548
 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
4545

T. D. Lash, D. A. Colby, G. M. Ferrence
FULL PAPER
22-Formyl-5,10,15,20-tetraphenylbenzo[b]carbaporphyrin (19b): UV/
acknowledges funding from the Barry M. Goldwater Foundation,
Vis (1% TFA/CHCl3): λmax (log10ε) ϭ 348 (4.53), 469 (5.22), 647 the ISU Honors summer research scholarship program, the John-
(4.15), 724 nm (4.05). UV/Vis (TFA): λmax (log10ε) ϭ 341 (4.44), son and Johnson Travel Award Program, Pfizer Inc. and Abbott
451 (5.15), 592 (3.85), 655 (4.10), 713 nm (3.93). 1H NMR Laboratories. We also thank Dr. Robert McDonald and The Uni-
(400 MHz, trace TFA/CDCl3, monocation): δ ϭ Ϫ4.68 (s, 1 H), versity of Alberta Structure Determination Laboratory for the col-
Ϫ3.70 (s, 1 H), Ϫ0.51 (s, 2 H), 6.94 (d, J ϭ 8.4 Hz, 1 H), 7.21 (s, lection of low temperature, CCD X-ray data.
1 H), 7.53 (dd, J ϭ 1.2, 8 Hz, 1 H), 7.88Ϫ7.94 (m, 12 H), 8.30Ϫ8.38
(m, 6 H), 8.44Ϫ8.50 (m, 6 H), 8.69 (s, 2 H), 9.49 (s, 1 H) ppm. 13
C
[1]
[2]
T. D. Lash, Synlett 2000, 279Ϫ295.
NMR (100 MHz, 2 drops TFA/CDCl3, monocation): δ ϭ 124.1,
126.0, 126.9, 127.7, 128.0, 128.5, 128.8, 129.2, 129.4, 129.5, 129.6,
130.3, 134.2, 135.0, 135.4, 136.2, 136.6, 138.0, 140.0, 143.2, 144.1,
194.7 ppm. Elemental analysis calcd. (%) for C50H33N3O: calcd. C
86.80, H 4.81, N 6.07; found C 86.54, H 4.72, N 6.03.[78]
T. D. Lash, in: The Porphyrin Handbook, Vol. 2 (Eds.: K. M.
Kadish, K. M. Smith, R. Guilard), Academic Press, San Diego,
2000, pp. 125Ϫ199.
[3]
[4]
D. A. Colby, T. D. Lash, Chem. Eur. J. 2002, 8, 5397Ϫ5402.
The first example of a nonaromatic ‘‘benziporphyrin’’ was re-
ported in 1994: K. Berlin, E. Breitmaier, Angew. Chem. 1994,
106, 1356Ϫ1357; Angew. Chem. Int. Ed. Engl. 1994, 33,
1246Ϫ1247. For related chemistry, see: K. Berlin, E. Breitma-
ier, Angew. Chem. 1994, 106, 229Ϫ230; Angew. Chem. Int. Ed.
Engl. 1994, 33, 219Ϫ220. However, it is worth noting that non-
aromatic examples of benzene and pyridine containing conju-
gated macrocycles related to the phthalocyanines have been
known for over 50 years. See: R. P. Linstead, J. Chem. Soc.,
1953, 2873Ϫ2884.
The first example of an aromatic carbaporphyrinoid system,
‘‘oxybenziporphyrin’’, was reported by our group in 1995. See:
T. D. Lash, Angew. Chem. 1995, 107, 2703Ϫ2705; Angew.
Chem. Int. Ed. Engl. 1995, 34, 2533Ϫ2535. See also: T. D. Lash,
S. T. Chaney, Chem. Eur. J. 1996, 2, 944Ϫ948.
T. D. Lash, S. T. Chaney, Tetrahedron Lett. 1996, 37, 8825Ϫ
8828.
21-Formyl-5,10,15,20-tetraphenylbenzo[b]carbaporphyrin (19c): UV/
Vis (1% TFA/CHCl3): λmax (log10ε) ϭ 353 (4.42), 474 (5.07), 657
(4.14), 732 nm (4.00). UV/Vis (TFA): λmax (log10ε) ϭ 341 (4.42),
457 (4.97), 594 (3.98), 647 (4.17), 721 nm (3.97).[78]
Crystal Structure Determination of 19a: X-ray quality crystals were
obtained by slow diffusion of hexanes into a solution of 19a in
dichloroethane containing a small amount of benzene. A purple
prism thereby obtained of approximate dimensions 0.33 ϫ 0.30 ϫ
0.27 mm was mounted on a glass fiber with super-glue and trans-
ferred to a Bruker P4/R4/SMART 1000 CCD diffractometer.[79]
The X-ray diffraction data were collected at Ϫ80 °C using Mo-Kα
radiation. Data collection and cell refinement were performed
using SMART.[79a] The unit cell parameters were obtained from a
[5]
[6]
[7]
least-squares refinement of 4448 centered reflections. The system-
T. D. Lash, M. J. Hayes, Angew. Chem. 1997, 109, 868Ϫ870;
Angew. Chem. Int. Ed. Engl. 1997, 36, 840Ϫ842.
T. D. Lash, S. T. Chaney, Angew. Chem. 1997, 109, 867Ϫ868;
Angew. Chem. Int. Ed. Engl. 1997, 36, 839Ϫ840.
K. Berlin, C. Steinbeck, E. Breitmaier, Synthesis 1996, 336Ϫ
340.
[80]
¯
atic absences indicated the space group P1 (no. 02).
Carbapor-
[8]
phyrin 19a was found to crystallize in the triclinic crystal system
˚
with the following cell parameters: a ϭ 10.6433(7) A, b ϭ 13.058(9)
[9]
˚
˚
A, c ϭ 13.750(9) A, α ϭ 81.986(1)°, β ϭ 71.249(1)°, and γ ϭ
73.011(1)°, Z ϭ 2. A total of 9646 reflections were collected, of
which 6922 were unique, and 5293 were observed F2o Ͼ 2σ(F2o).
Data reduction was accomplished using SAINT.[79b] The data were
corrected for absorption through use of the SADABS pro-
cedure.[79c] Solution and data analysis was performed using the
WinGX software package.[81] The structure of 19a was solved using
the direct method program SIR-92[82] and the refinement com-
pleted using the program SHELXL-97.[83] With the exception of
the three core hydrogen atoms, hydrogen atoms were assigned posi-
tions based on the geometries of the attached carbon atoms, and
were given thermal parameters of 20% greater than the attached
atoms. The three core hydrogen atoms, H21, H22, and H24, were
located by a difference Fourier and were allowed to freely refine.
Full-matrix least-squares refinement on F2 using 481 parameters
and zero restraints led to convergence (shift esd. max./min. ϭ
0.000:0.000) with R1 ϭ 0.0451 and wR2 ϭ 0.1097, and a goodness
of fit ϭ 1.043 for 5293 data with F2o Ͼ 2σ(F2o). A final difference
Fourier synthesis showed features in the range of ϩ0.263 to Ϫ0.174
[10]
[11]
K. Berlin, Angew. Chem. 1996, 108, 1955Ϫ1957; Angew. Chem.
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M. Scherer, J. L. Sessler, A. Gebauer, V. Lynch, J. Org. Chem.
1997, 62, 7877Ϫ7881.
T. D. Lash, Chem. Commun. 1998, 1683Ϫ1684.
M. J. Hayes, T. D. Lash, Chem. Eur. J. 1998, 4, 508Ϫ511.
T. D. Lash, S. T. Chaney, D. T. Richter, J. Org. Chem. 1998,
63, 9076Ϫ9088.
M. J. Hayes, J. D. Spence, T. D. Lash, Chem. Commun. 1998,
2409Ϫ2410.
T. D. Lash, D. T. Richter, J. Am. Chem. Soc. 1998, 120,
9965Ϫ9966.
D. T. Richter, T. D. Lash, Tetrahedron Lett. 1999, 40,
6735Ϫ6738.
T. D. Lash, J. L. Romanic, M. J. Hayes, J. D. Spence, Chem.
Commun. 1999, 819Ϫ820.
D. T. Richter, T. D. Lash, Tetrahedron 2001, 57, 3659Ϫ3673.
M. Stepien, L. Latos-Grazynski, T. D. Lash, L. Szterenberg,
Inorg. Chem. 2001, 40, 6892Ϫ6900.
M. Stepien, L. Latos-Grazynski, Chem. Eur. J. 2001, 7,
5113Ϫ5117.
S. R. Graham, D. A. Colby, T. D. Lash, Angew. Chem. 2002,
114, 1429Ϫ1432; Angew. Chem. Int. Ed. 2002, 41, 1371Ϫ1374.
D. A. Colby, T. D. Lash, J. Org. Chem. 2002, 67, 1031Ϫ1033.
T. D. Lash, M. J. Hayes, J. D. Spence, M. A. Muckey, G. M.
Ferrence, L. F. Szczepura, J. Org. Chem. 2002, 67, 4860Ϫ4874.
S. R. Graham, G. M. Ferrence, T. D. Lash, Chem. Commun.
2002, 894Ϫ895.
M. A. Muckey, L. F. Szczepura, G. M. Ferrence, T. D. Lash,
Inorg. Chem. 2002, 4840Ϫ4842.
D. Liu, T. D. Lash, Chem. Commun. 2002, 2426Ϫ2427.
S. Venkatraman, V. G. Anand, S. K. Pushpan, J. Sankar, T. K.
Chandrashekar, Chem. Commun. 2002, 462Ϫ463.
S. Venkatraman, V. G. Anand, V. PrabhuRaja, H. Rath, J. San-
[12]
[13]
[14]
[15]
[16]
[17]
[18]
[19]
[20]
[21]
[22]
Ϫ
3
[81]
˚
e /A . A RASTEP
drawing of the refined structure is shown
in Figure 5. Complete X-ray structural data has been deposited at
the Cambridge Crystallographic Data Center CCDC no. 217671.
Copies of this information can be obtained free of charge from The
Director, CCDC, 12 Union Road, Cambridge CB2 1EZ, UK [Fax:
(internat.) ϩ 44-1223-336033; E-mail: deposit@ccdc.cam.ac.uk or
www: http://www.ccdc.cam.ac.uk].
[23]
[24]
[25]
[26]
Acknowledgments
This work was supported by the National Science Foundation, un-
der Grant No. CHE-0134472, and the Petroleum Research Fund,
administered by the American Chemical Society. D.A.C. also
[27]
[28]
[29]
4546
 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
Eur. J. Org. Chem. 2003, 4533Ϫ4548

meso-Tetraarylazuliporphyrins under LindseyϪRothemund Reaction Conditions
FULL PAPER
[56]
kar, T. K. Chandrashekar, W. Teng, K. R. Senge, Chem. Com-
mun. 2002, 1662Ϫ1663.
M. Stepien, L. Latos-Grazynski, J. Am. Chem. Soc. 2002,
124, 3838Ϫ3839.
G. R. Geier III, D. M. Haynes, J. S. Lindsey, Org. Lett. 1999,
1, 1455Ϫ1458.
H. Furuta, H. Maeda, A. Osuka, Chem. Commun. 2002,
1795Ϫ1804.
These results were initially disclosed, in part, as a seminar pres-
entation by T. D. Lash at the Peoria Section American Chemi-
cal Society Meeting held at Bradley University, Peoria, Illinois
on April 16, 2002. Further details of these studies were re-
ported at the following meetings:
ference on Porphyrins and Phthalocyanines (ICPP-2), Kyoto,
Japan, June 30-July 5, 2002 (D. A. Colby, T. D. Lash, Book of
Abstracts, Abstract No. P-247).
of the American Chemical Society, Boston, Massachusetts, U.
S. A., August 18Ϫ22, 2002 (D. A. Colby, T. D. Lash, Book
of Abstracts, CHED 218).
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T. D. Lash, D. A. Colby, M. A. Muckey, D. Liu, G. M. Ferr-
ence, Book of Abstracts for the 225th National Meeting of the
American Chemical Society, New Orleans, LA, March 2003,
INOR 672.
T. D. Lash, D. A. Colby, S. R. Graham, G. M. Ferrence, Book
of Abstracts for the 225th National Meeting of the American
Chemical Society, New Orleans, LA, March 2003, INOR 673.
K. Miyake, T. D. Lash, Book of Abstracts for the 225th
National Meeting of the American Chemical Society, New Orle-
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H. Furuta, T. Ogawa, Y. Uwatoko, K. Araki, Inorg. Chem.
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[58a]
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2nd International Con-
[58b]
224th National Meeting
[35]
[36]
[58c]
225th National Meeting of the
American Chemical Society, New Orleans, Louisiana, U. S. A.,
March 23Ϫ27, 2003 (D. A. Colby, T. D. Lash, Book of Ab-
stracts, ORGN 330).
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P. J. Chmielewski, L. Latos-Grazynski, K.
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Received June 20, 2003
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 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
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