Synthesis and luminescence of soluble meso-unsubstituted tetrabenzo- and tetranaphtho[2,3]porphyrins

Article abstract of DOI:10.1021/jo051580r

Syntheses of soluble tetrabenzoporphyrins (TBP) and tetranaphtho[2,3] porphyrins (TNP), with multiple substituents in the conjugated aromatic rings but bearing no substituents in the meso-positions, is reported. Both types of porphyrins were obtained by direct aromatization of precursor porphyrins, annealed with either cyclohexene or dihydronaphthalene fragments. TBPs and TNPs possess powerful absorption bands in the near-infrared (λ = 610-710 nm, ε = 100,000-300,000 M^-1 cm^-1) and exhibit strong luminescence. Free bases and Zn complexes fluoresce with quantum yields of up to 50%, whereas Pd and Pt complexes phosphoresce in solutions at ambient temperatures. Remarkably, the phosphorescence quantum yields of Pd and Pt TBPs reach as high as 20-50%, which places them among the brightest near-infrared phosphors known to date.

Full text of DOI:10.1021/jo051580r

Synthesis and Luminescence of Soluble meso-Unsubstituted
Tetrabenzo- and Tetranaphtho[2,3]porphyrins
Olga S. Finikova,† Andrei V. Cheprakov,‡ and Sergei A. Vinogradov*,†
Department of Biochemistry and Biophysics, University of Pennsylvania,
Philadelphia, Pennsylvania 19104, and Department of Chemistry, Moscow State University,
Moscow 119899, Russia
vinograd@mail.med.upenn.edu
Received July 28, 2005
Syntheses of soluble tetrabenzoporphyrins (TBP) and tetranaphtho[2,3]porphyrins (TNP), with
multiple substituents in the conjugated aromatic rings but bearing no substituents in the meso-
positions, is reported. Both types of porphyrins were obtained by direct aromatization of precursor
porphyrins, annealed with either cyclohexene or dihydronaphthalene fragments. TBPs and TNPs
possess powerful absorption bands in the near-infrared (λ ) 610-710 nm, ꢀ ) 100,000-300,000
M-1 cm-1) and exhibit strong luminescence. Free bases and Zn complexes fluoresce with quantum
yields of up to 50%, whereas Pd and Pt complexes phosphoresce in solutions at ambient
temperatures. Remarkably, the phosphorescence quantum yields of Pd and Pt TBPs reach as high
as 20-50%, which places them among the brightest near-infrared phosphors known to date.
Introduction
field3b,4,5 but also include the design of optical limiters6
and other nonlinear optical materials,7 as well as the
development organic semiconductors,8 sensitizers for
photovoltaic cells9 and fluorescent STM enhancers.10
Our interest in π-extended porphyrins stems from their
usefulness as probes for biological oxygen measurements
using phosphorescence quenching.11 Pt and Pd porphy-
Porphyrins extended via conjugation with exocyclic
aromatic rings form a large group of tetrapyrroles that
have received much attention in the recent years.1 This
interest is explained primarily by the photophysical effect
of the π-conjugation, known to induce red shifts in the
absorption spectra of porphyrins. Absorption in the red
region of the spectrum is generally useful for those
biomedical applications, which rely on exogenous dyes
and/or contrast agents, e.g., PDT,2 in vivo optical sensing
and imaging.3 Potential applications of π-extended por-
phyrins, therefore, exist primarily in the biomedical
(2) (a) Bonnett, R. Chem. Soc. Rev. 1995, 24, 19. (b) Sessler, J. L.;
Dow, W. C.; Oconnor, D.; Harriman, A.; Hemmi, G.; Mody, T. D.; Miller,
R. A.; Qing, F.; Springs, S.; Woodburn, K.; Young, S. W. J. Alloys
Compd. 1997, 249, 146. (c) Pandey, R. K. In ref 1a, Chapter 43. (d)
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Moan, J.; Peng, Q. Anticancer Res. 2003, 23, 3591. (f) Nyman, E. S.;
Hynninen, P. H. J. Photochem. Photobiol., B 2004, 73, 1.
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C.; Mody, T. D.; Hemmi, G. W.; Hao, Y. P.; Miller, R. A. Proc. Natl.
Acad. Sci. U.S.A. 1996, 93, 6610. (b) Vinogradov, S. A.; Lo, L.-W.;
Jenkins, W. T.; Evans, S. M.; Koch, C.; Wilson, D. F. Biophys. J. 1996,
70, 1609. (c) Liebsch, G.; Klimant, I.; Frank, B.; Holst, G.; Wolfbeis,
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1.
* To whom correspondence should be addressed. Phone: (215)-898-
6382. FAX: (215)-573-3787.
† University of Pennsylvania.
‡ Moscow State University.
(1) (a) Lash, T. D. In The Porphyrin Handbook, Kadish, K. M.;
Smith, K. M.; Guilard, R. Eds.; Academic Press: New York; 2000,
Chapter 10. (b) Lash, T. D. J. Porphyrins Phthalocyanines 2001, 5,
267. (c) Vicente, M. G. H.; Smith, K. M. J. Porphyrins Phthalocyanines
2004, 8, 26.
10.1021/jo051580r CCC: $30.25 © 2005 American Chemical Society
Published on Web 10/14/2005
9562
J. Org. Chem. 2005, 70, 9562-9572

Soluble Tetrabenzo- and Tetranaphtho[2,3]porphyrins
CHART 1
rins show high rates of intersystem crossing from their
excited singlet states to the triplet states, from which
they decay by emitting phosphorescence.12 The triplet
lifetimes of Pt and Pd porphyrins in solutions at ambient
temperatures are usually in the order of tens to hundreds
of microseconds, which makes their phosphorescence
extremely sensitive to oxygen. For biomedical applica-
tions, such as oxygen imaging in tissue in vivo,3b,13 it is
crucial that the absorption bands of the phosphorescent
sensors overlap minimally with those of endogenous
tissue chromophors (e.g., hemoglobin, myoglobin, cyto-
chromes, etc.). Accordingly, dyes with absorption in the
near-infrared and with strong oxygen-dependent phos-
phorescence have been the focus of our interest. While a
large number of porphyrinoids with absorption in the
infrared are known to date (e.g., chlorophylls, expanded
porphyrins, phthalocyanines, etc.), the list of compounds
that simultaneously possess strongly emissive triplet
states is very short.14 Some metal complexes of sym-
metrically π-extended porphyrins, i.e., tetrabenzoporphy-
rins (TBPs) and tetranaphtho[2,3]porphyrins (TNPs)
(Chart 1), apparently combine both of these properties
and, in fact, are superior to the other chromophors due
to their particularly intense and narrow transitions in
the near-infrared window of tissue.15
Some water-soluble Pd meso-tetraaryltetrabenzopor-
phyrins (Ar4TBP) indeed have been shown to be effective
as in vivo phosphorescent oxygen indicators.3b,15a,b,16 meso-
Tetraarylated TNPs (Ar4TNP), although studied much
less,17 also revealed potential in the oxygen-sensing
application.15b,c At the same time, meso-unsubstituted
TBPs and TNPs (Chart 1) and their metal complexes
have remained practically unexplored in this, as well as
in many other, areas of research. This is due largely to
the difficulties in their synthesis, their extremely poor
solubility and strong aggregation.
Metal complexes of meso-unsubstituted TBPs and
TNPs, if made adequately soluble, are on the other hand
likely to be very potent luminescent chromophores. Core
macrocycles in their meso-tetraarylated analogues (Ar4-
TBPs and Ar4TNPs), which already exhibit quite strong
luminescence, are severely nonplanar.18,40b,41 Nonplanar-
ity is known to dramatically affect photophysical proper-
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J. Org. Chem, Vol. 70, No. 23, 2005 9563

Finikova et al.
ties of porphyrins19 by shifting their absorption bands to
the red20 and by reducing their luminescence quantum
yields.21 According to both the X-ray data8b,c and the
computational studies,22 TBPs and TNPs possess nearly
ideally planar geometries. Therefore, it would be reason-
able to expect that the luminescence quantum yields of
TBPs and TNPs would be considerably higher than those
of nonplanar Ar4TBPs and Ar4TNPs. Given that the
absorption Q-bands of TBPs and TNPs are already
positioned in the red as a consequence of the π-conjuga-
tion, these porphyrins should be superior as biological
luminescent sensors.
Understanding the effects of nonplanarity is interest-
ing not only for practical reasons. The interplay between
the porphyrin structure and porphyrin photophysics has
been intensely discussed in the recent literature.19,20,23
Not surprisingly, only a few experimental studies address
the effects of nonplanarity in π-conjugated porphy-
rins,6d,15c,24,25 which is explained by their limited synthetic
availability. In the past several years considerable progress
has been made in the synthesis of meso-tetraarylated
extended porphyrins (vide infra), and some of studies of
their photophysical properties have been conducted. At
the same time, soluble, nonaggregating planar TBPs and
TNPs still remain a much less accessible target. Synthe-
sis of these molecules constitutes the main focus of the
present work.
Synthesis of meso-unsubstituted tetrabenzoporphyrin
(TBP) was originally described by Helberger and co-
workers26 and later by Linstead and co-workers.27 The
TBP macrocycle was assembled by self-condensing o-
cyanoacetophenone in the presence of metal salts at high
temperature,26 an approach resembling classic phthalo-
cyanine chemistry. A number of similar precursors, such
as o-acetylbenzoic acid,28 phthalimides,29 phthalim-
idines,26,27,30 isoindoles31 and isoindoline,32 were used later
to prepare differently substituted TBPs. The first syn-
thesis of tetranaphtho[2,3]porphyrin (TNP) also relied on
the “template condensation” method.33 TNP was synthe-
sized by condensing 3-carboxymethyl-5,6-benzophthali-
midine with Zn acetate at high temperature. Several
peripherally substituted TNPs, as well as isomeric
tetranaphtho[1,2]porphyrins, were later prepared by
similar methods from the corresponding benzophthali-
midines or naphthalenedicarboximides.34
(26) (a) Helberger, J. H., von Rebay, A., and Hever, D. B. Just.
Liebigs Ann. Chem. 1938, 533, 197. (b) Helberger, J. H., Hever, D. B.
Just. Liebigs Ann. Chem. 1938, 536, 173.
(27) (a) Barrett, P. A.; Linstead, R. P.; Rundall, F. G.; Tuey, G. A.
P. J. Chem. Soc. 1940, 1079. (b) Linstead, R. P.; Weiss, F. T. J. Chem.
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Aside from low yields and the large number of side
products, the template condensation approach suffers
because of the extremely harsh conditions required for
the macrocycle assembly (i.e., fusion at 350-400 °C).
Only a few TBPs and TNPs with inert substituents could
be synthesized using this method.29b,30b,31,32 Over the past
decade, several new approaches to π-extended porphyrins
have emerged, all of them relying on more traditional
porphyrin chemistry. A number of π-extended porphyrins
were synthesized by Lash and co-workers and Ono and
co-workers from the corresponding porphyrinogenic pyr-
roles, annealed with external aromatic rings.1b,35,36 Ap-
plying the same methodology to tetrabenzo- and tetra-
naphtho[2,3]porphyrins, however, was impossible because
of the very low stability of the required isoindoles.37 As
a result, approaches based on the use of masked isoindole
moiety received increasing attention. Two methods of
synthesis of the TBP system have been subsequently
devised by Cavaleiro’s38 and Ono’s groups.39 In the first
method, TBP was synthesized form the precursor cyclo-
hexenoporphyrin by base-catalyzed elimination of sulfi-
nate, followed by oxidation with DDQ.38 In the second,
TBP, TNP and their meso-arylated analogues were syn-
thesized by thermal extrusion of ethylene from porphy-
(35) (a) Lash, T. Energy Fuels 1993, 7, 166. (b) Lash, T. D.; Roper,
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(37) Synthesis of Ph4TBP from isoindole has been described, but it
also required a condensation at high temperature: Remy, D. E.
Tetrahedron Lett. 1983, 24, 1452.
(38) Vicente, M. G. H.; Tome, A. C.; Walter, A.; Cavaleiro, J. A. S.
Tetrahedron Lett. 1997, 38, 3639.
rins fused with bicyclo[2.2.2]octadiene fragments.39
A
(39) (a) Ito, S.; Murashima, T.; Uno, H.; Ono, N. Chem. Commun.
1998, 1661. (b) Ito, S.; Ochi, N.; Murashima, T.; Uno, H.; Ono, N.
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(40) (a) Finikova, O.; Cheprakov, A.; Beletskaya, I.; Vinogradov, S.
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69, 522.
recent version of the latter approach makes it possible
to synthesize polyfunctionalized TBPs at low tempera-
tures;39e however, the synthesis of bicyclo-fused pyrroles
themselves is rather complicated, and no TNPs with
substituents in the fused aromatic rings could be pro-
duced by this method.
In the course of our own work on the synthesis of
polyfunctionalized π-extended porphyrins we came across
a useful strategy based on the direct oxidative aromati-
zation of precursor porphyrins, annealed with nonaro-
matic hydrocarbon rings.5,40,41,42 Using this method, a
variety of Ar4TBPs5,40 and Ar4TNPs41 were synthesized
(41) (a) Finikova, O. S.; Cheprakov, A. V.; Carroll, P. J.; Vinogradov,
S. A. J. Org. Chem. 2003, 68, 7517. (b) Finikova, O. S.; Aleshchenkov,
S. E.; Brinas, R. P.; Cheprakov, A. V.; Carroll, P. J.; Vinogradov, S. A.
J. Org. Chem. 2005, 70, 4617.
9564 J. Org. Chem., Vol. 70, No. 23, 2005

Soluble Tetrabenzo- and Tetranaphtho[2,3]porphyrins
SCHEME 1a
a Reagents and conditions: (a) (i) PhSCl, CH2Cl2, rt; (ii) MCPBA, CH2Cl2; (iii) DBU (80-85% for 3 steps); (b) CNCH2CO2X, tBuOK,
THF, 0 °C (60-95%); (c) for R ) Bn: (i) H2, Pearlman catalyst, THF-MeOH-Et3N, rt; (ii) (CH2OH)2, reflux, 30 min (82-90% for 2 steps);
for R ) tBu: TFA-CH2Cl2, Ar, rt, 30 min (30-40%); (d) (i) (CH2O)n, PhH, TsOH‚H2O, Ar, reflux, 6-8 h, then air, (rt), overnight (30-
45%); (ii) for M ) Zn: Zn(OAc)2‚2H2O, THF, reflux, 15 min (95-97%); (e) R ) Bu: DDQ, toluene, reflux (95-97%); R ) Me: DDQ,
dioxane, reflux (20-96%); (f) PdCl2 or PtCl2, PhCN, reflux, Pd: 5-10 min, Pt: 7-8 h (84-90%), or Fe/FeCl2‚4H2O, CH3CH2CO2H, Ar,
reflux 1 h (74%).
in good yields from readily available starting materials.
In the present paper we extend our methodology on the
synthesis of soluble meso-unsubstituted TBPs and TNPs
and report their basic photophysical properties.
(30-40%). The increase in the yield was probably caused
by the better solubility of the reaction intermediates,
containing multiple butoxycarbonyl residues. Similarly,
porphyrin 5b is very well soluble in most organic solvents
(CH2Cl2, THF, diethyl ether), whereas porphyrin 5a is
only moderately soluble.
Results and Discussion
TCHPs 5a,b were oxidized into the corresponding
TBPs 6a,b by DDQ. The aromatization required substan-
tially longer reaction times than did the recently reported
aromatization of meso-tetraarylated TCHPs (Ar4TC-
HPs).5,40 However, the processes could be driven to com-
pletion, and the products were isolated in moderate (6a)
to quantitative (6b) yields. The most striking difference
between the reactivities of meso-unsubstituted TCHPs
and Ar4TCHPs was that in the latter case it was neces-
sary to preconvert Ar4TCHPs into their Cu, Ni or Pd
complexes,5,40 whereas 5a,b could be oxidized into TBPs
directly as free bases. Removing the metalation/demeta-
lation step is obviously an advantage from the practical
point of view but is also curious mechanistically.40b Metal
assistance in the case of Ar4TCHPs was necessary
because when these porphyrins, taken as free bases, were
subjected to aromatization, they instantaneously formed
dications, completely inert with respect to the oxidation.
We have speculated that the protonation of the free bases
occurred either directly, due to the acidification of the
medium, or via the hydrogen abstraction from the solvent
by an intermediate free-base cation radical.40b The fact
that the rate of the aromatization appears to be reciprocal
to the proton affinities of the free bases argues for the
former pathway. The basicities of nonplanar Ar4TCHPs
are much higher than those of their planar counterparts
TCHPs,18b and the latter, as evidenced by our present
results, can be aromatized as free bases.
Synthesis of meso-Unsubstituted Tetrabenzopor-
phyrins (TBPs). Synthesis of TBP-octaesters 6a,b is
shown in Scheme 1. Esters 1a,b were obtained from
commercially available 1,2,3,6-tetrahydrophthalic anhy-
dride using standard procedures. Conversion of 1a (R )
Me) into sulfone 2a and then into pyrroles 3a and 4a
followed the published method.40b The same general
procedures were used in the case of dibutoxycarbonyl
derivatives, although both sulfone 2b and pyrrole ester
3b (X ) Bn) were isolated as oils. To allow adequate
characterization, these oils could be purified by simple
flash chromatography (90-95% purity). Benzyl ester 3b
was subjected to Pd-catalyzed hydrogenolysis, followed
by decarboxylation of the pyrrole acid to give pyrrole 4b
in 82% overall yield. Alternatively, tert-butyl ester 3c
could be used as a precursor to 4b. 3c has an advantage
of being a solid compound, and its conversion into 4b
could be accomplished in a single step by being treated
with TFA. However, the yield of 4b in this case was only
30-40%.
Syntheses of tetracyclohexenoporphyrins (TCHPs) 5a,b
from pyrroles 4a,b followed the classic synthesis of
octaethylporphyrin (OEP).43 Porphyrin 5b with eight
butoxycarbonyl groups was obtained in a higher yield
(40-45%) than its octamethoxycarbonylated analogue 5a
(42) The oxidation aromatization approach has been used before to
synthesize aromatically π-extended porphyrins (for examples, see ref
35), but it has never been applied to the synthesis of meso-unsubsti-
tuted TBPs and TNPs.
(43) Sessler, J. L.; Mozaffari, A.; Johnson, M. R. In Organic
Synthesis; Freeman, J. P., Ed.; Wiley & Sons: New York, 1998; Vol.
70, p 68.
J. Org. Chem, Vol. 70, No. 23, 2005 9565

Finikova et al.
SCHEME 2a
a Reagents and conditions: (a) Me2SO4 (for 8a), or BrCH2CO2Et (for 8b), or Br(CH2)3CO2Et-NaI (for 8c), K2CO3, acetone, reflux, 1-3
days (70-98%); (b) PhSCl, CH2Cl2, then MCPBA, CH2Cl2 (65-85%); (c) CNCH2CO2R, tBuOK, THF, reflux 30 min. (70-80%); (d) for R )
Et: KOH, (CH2OH)2, reflux, 30 min (90-97%); for R ) tBu: TFA-CH2Cl2, Ar, rt, 30 min (98%); (e) (CH2O)n, PhH, TsOH‚H2O, Ar, reflux,
5 h, then air, rt, overnight; (g) DDQ, rt of reflux 30 min (e + g: 25-33%); (h) PdCl2 or Zn(OAc)2‚2H2O, pyridine or PhCN/pyridine, reflux
(80-95%).
Overall, more soluble octabutoxycarbonyl-TCHP 5b
performed much better in the aromatization than its
octamethoxycarbonyl analogue 5a, whose oxidation was
additionally complicated by side reactions. For example,
the oxidation of 5b and Zn-5b in toluene was completed
after 4 h and required a 1.5- to 2-fold excess of DDQ.
Under the same conditions, oxidation of 5a gave only
undefined insoluble green solids, possibly products of the
oxidative oligomerization. Aromatization of both 5a and
Zn-5a could be accomplished in dioxane, but required a
larger excess of DDQ (5- to 6-fold) and longer reaction
times. Notably, neither Cu(II) nor Ni(II) nor Pd(II)
complexes of 5a gave metallo-TBPs in good yields,
whereas these metals have proven to be the best in the
aromatization of Ar4TCHPs.40b
TBP 6b was further used to synthesize its Pd, Pt and
Fe complexes, all of which showed excellent solubility in
most common organic solvents. The structure and purity
of the newly synthesized complexes were confirmed by
1H and 13C NMR, MALDI-TOF spectrometry and elemen-
tal analysis. Pd and Pt derivatives were obtained by
refluxing 6b with the corresponding chlorides in ben-
zonitrile. For insertion of Fe, 6b was refluxed with a large
excess of FeCl2 in propionic acid in the presence of iron
wire. The UV-vis spectrum of the resulting Fe-6b was
very similar to that of Fe(II) (bis)pyridine TBP.28a Fe-6b
was stable on air for days both in the solid state and in
solution when stored in the dark. A well-resolved NMR
spectrum of Fe-6b suggests that this compound is a
diamagnetic complex.44
cently.41 The key starting material, 5,8-dihydroxy-1,4-
dihydronaphthalene 7, was prepared from butadiene and
1,4-benzoquinone45 and converted into its alkoxy deriva-
tives using Williamson alkylation. Dimethoxy derivative
8a was prepared as described previously,45 whereas
dialkoxy derivatives 8b and 8c, terminated with ester
groups, were prepared from 7 and ethyl bromoacetate or
ethyl 4-bromobutyrate, respectively.
R-Chlorosulfone 9a (X ) OMe) was obtained from 8a
following the published method.41 Synthesis of pyrrole
11a from 9a was performed as described earlier.41 9a was
introduced into the modified Barton-Zard reaction with
ethyl isocyanoacetate to give pyrrole ester 10a, which was
further converted into 2,5-unsubstituted pyrrole 11a
upon refluxing with KOH in ethylene glycol.
R-Chlorosulfones 9b,c were prepared from alkenes 8b,c
by the same method as 9a.41 However, because both 9b
and 9c contained ethyl ester groups, which were intended
to be kept intact throughout the rest of the transforma-
tions, the use of ethyl isocyanoacetate in the subsequent
Barton-Zard synthesis (step c in Scheme 2) was not
feasible. Indeed, hydrolytic cleavage of the pyrrole-ethyl
ester in the following step (step d in Scheme 2) would
require heating this compound with KOH, and that
would simultaneously destroy the peripheral ethyl ester
groups. Consequently, we turned our attention to isocy-
anoacetates containing selectively cleavable benzyloxy-
carbonyl and tert-butoxycarbonyl groups. To our surprise,
benzyl isocyanoacetate did not react with chlorosulfones
9a-c at all. tert-Butyl isocyanoacetate, on the other hand,
reacted readily with sulfone 9c (X ) O(CH2)3CO2Et,
Synthesis of meso-Unsubstituted Tetranaphtho-
[2,3]porphyrins (TNP). TNPs 13a,b were synthesized
as shown in Scheme 2. The starting materials and
reagents used in these syntheses were similar to those
employed in the synthesis of the meso-tetraarylated
analogues of porphyrin 13a (X ) OMe), reported re-
(44) Oxidation states and spin states of FeTBP complexes depend
strongly on the nature of their axial ligation. For examples, see:
Kobayashi, N.; Koshiyama, M.; Osa, T. Inorg. Chem. 1985, 24, 2502
and ref 28a,b.
(45) Rama Rao, A. V.; Yadav, J. S.; Bal Reddy, K.; Mehendale, A.
R. Tetrahedron 1984, 40, 4643.
9566 J. Org. Chem., Vol. 70, No. 23, 2005

Soluble Tetrabenzo- and Tetranaphtho[2,3]porphyrins
Scheme 2), giving pyrrole ester 10b in 70-80% yield, but
did not react with 9b (X ) OCH2CO2Et, Scheme 2). Only
trace amounts of the corresponding pyrrole ester could
be isolated, and there was a similar result when 9b
reacted with ethyl isocyanoacetate.
being reacted with the corresponding metal salts in
refluxing pyridine or benzonitrile-pyridine mixtures.
NMR characterization of porphyrins 13a and Pd-13a
was impossible due to their extremely low solubilities.
The solubility of 13b and its complexes was significantly
higher, but at the level of concentrations required for the
NMR analysis aggregation still presented a considerable
problem, especially for the Pd complex. Consequently, the
aromatic signals in the spectra of Pd-13b appeared to
be severely broadened. At the same time, the spectra of
the free base 13b and of Zn-13b were quite well resolved,
with aromatic resonances appearing at 11-12 ppm.
Photophysical Properties of meso-Unsubstituted
TBPs and TNPs. Original photophysical studies of tetra-
benzoporphyrin and its metal complexes were performed
by Soloviev and co-workers50 and by Gouterman and co-
workers.30c,51 Later, a number of investigators studied
metallo-TBPs, primarily with respect to their applica-
tions.4a,15a,52 The photophysics of the TNP system,34a,17d,53
however, remains seriously understudied. Just the basic
photophysical characteristics of Ar4TNPs have been
recently reported,6d,15c,17g,41 whereas the properties of
meso-unsubstituted TNPs have not yet been explored.
We have measured the absorption and emission char-
acteristics of TBPs M-6b and TNPs M-13b and have
compared them with those of Ph4TBPs5,40 and Ph4TNPs,41
substituted with similar functional groups in the fused
aromatic rings. In this way, the influence of the side
substituents on the photophysical properties can be
excluded, whereas the effects of the nonplanar deforma-
tion and/or extra π-conjugation involving meso-aryl rings
can be emphasized. The data are summarized in Table
1, and some absorption and emission spectra are shown
in Figures 1 and 2.
The reasons for the unexpected behavior of benzyl
isocyanoacetate is not well understood. In our past
experience, benzyl isocyanoacetate did consistently show
a somewhat lower reactivity in the Barton-Zard syn-
thesis than did ethyl and tert-butyl isocyanoacetates but
still usually gave pyrrole esters in reasonably good
yields.40 Lash and co-workers, who originally introduced
benzyl isocyanoacetate,46 used it successfully in many
different syntheses;1b however, they also commented on
its lower reactivity.46 On the other hand, for 9a-c the
equilibrium between the vinyl sulfone47 and allyl sulfone
forms48 is most certainly shifted toward the latter. Allyl
sulfones are inactive in the Barton-Zard reaction, and
thus, reduction in the concentration of the substrate
(vinyl sulfone), combined with less active reagent (benzyl
isocyanoacetate), led to such a dramatic decrease in the
reaction rate, that virtually no condensation could be
observed.
One possible explanation of the low reactivity of 9b is
that this chlorosulfone, as well as the corresponding vinyl
sulfone, possesses relatively easily ionizable CH2 groups
in the side chains (-OCH2CO2R). Abstraction of a proton
from one of these groups, under conditions of the Barton-
Zard condensation49 would produce an anionic species,
which is likely to be inert in the condensation with
isocyanoacetates.
Pyrrole ester 10b, synthesized from sulfone 9c and tert-
butyl isocyanoacetate, was cleaved and decarboxylated
by TFA to give 11b in 98% yield. Pyrroles 11a (vide
supra) and 11b were further reacted with formaldehyde
under conditions similar to those used in the synthesis
of 5a,b (Scheme 1). The UV-vis spectra of the reaction
mixtures after the condensation closely resembled the
spectra of OEP, evidencing formation of the intermediate
octahydro-TNPs of type 12 (Scheme 2). These porphyrins,
however, were not isolated. Instead, the mixtures were
treated with DDQ or p-chloranil, and within minutes the
conversion of 12 into TNPs was complete.
Octamethoxy-TNP 13a appeared to be insoluble in
most organic solvents. It was purified by washing it with
pyridine and THF, followed by recrystallization from
refluxing benzonitrile. Porphyrin 13b, on the contrary,
is very well soluble in many organic solvents, and it was
purified by repetitive precipitation from CH2Cl2 by ac-
etonitrile. Porphyrins 13a,b were isolated in 25-33%
yields and converted into their Zn and Pd complexes by
The absorption bands of meso-unsubstituted TBPs and
TNPs are blue-shifted by about 20-40 nm compared to
the corresponding bands of Ar4TBPs and Ar4TNPs. This
reflects the severe nonplanarity of the latter, confirmed
earlier by both computational6d,15c and X-ray data.18,40b,41
Along with its own effect on the absorption spectra,20,21
the nonplanar deformation causes the meso-aryl rings in
Ar4TBPs and Ar4TNPs to be partially drawn into the
π-conjugation, which additionally contributes to the red
shifts of the absorption bands.6d Consistent with flat
structures of porphyrins of M-6b and M-13b, their
(50) For example see: (a) Sevchenko, A. N.; Soloviev, K. N.;
Shkirman, S. F.; Kachura, T. F. Proc. Natl. Acad. Sci. USSR (Russian)
1965, 161, 1313. (b) Sevchenko, A. N.; Soloviev, K. N.; Gradushko, A.
T.; Shkirman, S. F. Soviet Phys. Proc. (Russian) 1967, 11, 349. (c)
Tsvirko, M. P.; Sapunov, V. V.; Soloviev, K. N. Opt. Spectrosc. (Russian)
1973, 34, 1094. Also see: Kobayashi, N. In Phthalocyanines. Properties
and Applications; Leznoff, C. C., Lever, A. B. P. Eds.; VCH Publish-
ers: New York, 1993 and references therein.
(51) (a) Gouterman, M. J. Mol. Spectrosc. 1961, 6, 138. (b) Bajema,
L.; Gouterman, M.; Rose, C. J. Mol. Spectrosc. 1971, 39, 421. (c)
Aartsma, T. J.; Gouterman, M.; Jochum, C.; Kwiram, A. L.; Pepich, B.
V.; Williams, L. D. J. Am. Chem. Soc. 1982, 104, 6278.
(46) Lash, T. D.; Bellettini, J. R.; Bastian, J. A.; Couch, K. B.
Synthesis 1994, 170.
(47) The common substrates for Barton-Zard reaction are 2-ni-
troolefines and vinyl sulfones.49 In the case of R-chlorosulfones, such
as 9a-c, the elimination of HCl, leading to the corresponding vinyl
sulfones, and the subsequent Barton-Zard reaction can be combined
in one step.41b
(48) (a) Savoia, D.; Trombini, C.; Umani-Ronci, A. J. Chem. Soc.,
Perkin Trans. 1 1977, 123. (b) Inomata, K.; Hirata, T.; Kinoshita, H.;
Kotake, H.; Senda, H. Chem. Lett. 1988, 2009.
(49) (a) Barton, D.; Zard, S. J. Chem. Soc., Chem. Commun. 1985,
1098. (b) Barton, D.; Kervagoret, J.; Zard, S. Tetrahedron 1990, 46,
7587. (c) Arnold, D. P.; Burgess-Dean, L.; Hubbard, J.; Abdur Rahman,
M. Aust. J. Chem. 1994, 47, 969. (d) Abel, Y.; Haake, E.; Haake, G.;
Schmidt, W.; Struve, D.; Walter, A.; Montforts, F. P. Helv. Chim. Acta
1998, 81, 1978.
(52) For examples, see: (a) Aaviksoo, J.; Frieberg, A.; Savikhin, S.;
Stelmakh, G. F.; Tsvirko, M. P. Chem. Phys. Lett. 1984, 111, 275. (b)
Ehrenberg, B.; Johnson, F. M. Spectrochim. Acta 1990, 46a, 1521. (c)
Luo, B. Z.; Tian, M. Z.; Li, W. L.; Huang, S. H.; Yu, J. Q. J. Lumin.
1992, 53, 247. (d) Vacha, M.; Machida, S.; Horie, K. Chem. Phys. Lett.
1995, 242, 169. (e) Stiel, H.; Volkmer, A.; Ruckmann, I.; Zeug, A.;
Ehrenberg, B.; Roder, B. Opt. Commun. 1998, 155, 135. (f) Khodykin,
O. V.; Zilker, S. J.; Haarer, D.; Kharlamov, B. M. Opt. Lett. 1999, 24,
513. (g) Zhou, X.; Ren, A. M.; Feng, J. K.; Liu, X. J. Can. J. Chem.
2004, 82, 19.
(53) Sapunov, V. V.; Solovev, K. N.; Kopranenkov, V. N.; Vorotnikov,
A. M. Zh. Prikl. Spektrosk. 1986, 45, 56.
J. Org. Chem, Vol. 70, No. 23, 2005 9567

Finikova et al.
TABLE 1. Selected Photophysical Data of meso-Unsubstituted TBPs and TNPs
a Solvent: pyridine for Zn-6b, Pt-6b, M-13b and for all M-Ph4TNP(OMe)8; DMF for 6b, Pd-6b and for all M-Ph4TBP(CO2Me)8. b Solvent:
DMF, deoxygenated by Ar for the phosphorescence measurements. c f ) fluorescence, p ) phosphorescence. d φ ) emission quantum
yield, τ ) phosphorescence lifetime. Lifetime was not measured for fluorescence. e Syntheses and photophysical properties of
M-Ph4TBP(CO2Me)8 and M-Ph4TNP(OMe)8 were reported previously.5,40,41
Q-bands are much narrower and generally more intense
than those of Ar4TBPs and Ar4TNPs. The emission bands
of M-6b and M-13b are also much sharper and in some
cases (e.g., fluorescence of 6b and 13b, Figure 1) display
relatively well resolved vibronic structures. The Stokes
shifts of the fluorescence of free bases 6b and 13b are
very small (66 cm-1 for 6b; 94 cm-1 for 13b), whereas
the Stokes shifts of the fluorescence of Ar4TBP free bases
are typically in the order of several thousands of cm-1
(Table 1). All together, these facts consistently point
toward the greatly increased rigidity of planar meso-
unsubstituted porphyrins and suggest an increase in
their radiative transitions.
Indeed, the values of the fluorescence quantum yields
of meso-unsubstituted TBPs and TNPs free bases are in
the range of 15-50%, which is significantly higher than
for the analogous Ar4TBP(CO2Me)8’s and Ar4TNP(OMe)8’s
(Table 1). As expected, Pd and Pt complexes of either
TBPs or TNPs do not show fluorescence, which is due to
a dramatic enhancement of their intersystem crossing.
9568 J. Org. Chem., Vol. 70, No. 23, 2005

Soluble Tetrabenzo- and Tetranaphtho[2,3]porphyrins
923 nm). Such a low energy triplet state is probably
effectively overlapped by many ground-state vibrations,
which enhance the rate of its internal conversion and
cause the decrease in the emission quantum yield.
Nevertheless, the phosphorescence quantum yield of Pd-
13b, although below expected, is still entirely adequate
for considering this chromophor in practical biological
applications.
In conclusion, a convenient method of synthesis of
meso-unsubstituted tetrabenzo- (TBP) and tetranaphtho-
[2,3]porphyrins (TNP) with solubilizing groups at the
periphery is described. The porphyrins were synthesized
in 33-45% yields from readily available precursors. TBPs
and TNPs and their metal complexes exhibit powerful
absorption bands in the red region of the spectrum and
luminesce with quantum yields of up to 50%. This places
them among the brightest near-infrared absorbing lu-
minescent tetrapyrroles known to date. Because of their
exceptionally strong phosphorescence in solutions at
ambient temperatures, Pd and Pt complexes of meso-
unsubstituted π-extended porphyrins show great promise
as luminescent probes for biological applications.
FIGURE 1. Absorption and fluorescence (inset) spectra of 6b
(s) and 13b (- - -) in DMF. The spectra are scaled to reflect
the relative extinction coefficients (absorption) and quantum
yields (fluorescence).
Experimental Section
Ethyl isocyanoacetate,55 benzyl isocyanoacetate46 and tert-
butyl isocyanoacetate56 were prepared according to the pub-
lished methods. Dimethyl 1,2,3,6-tetrahydrophthalate 1a was
obtained from 1,2,3,6-tetrahydrophthalic anhydride as de-
scribed previously.57 5,8-Dihydroxy-1,4-dihydronaphthalene 745
and 5,8-dimethoxy-1,4-dihydronaphthalene 8a45 were synthe-
sized as reported previously. Vinyl sulfone 2a40b and R-chlo-
rosulfone 9a41 were prepared following the published methods.
Pyrrole esters 3a40b and 10a41 and pyrroles 4a40b and 11a41
were synthesized according to the published procedures. The
equipment used for the analytical characterization of the
compounds was described elsewhere.40b,41 Melting points are
reported uncorrected.
Dibutyl 1,2,3,6-Tetrahydrophthalate (1b). 1b was ob-
tained from 1,2,3,6-tetrahydrophthalic anhydride by a stan-
dard esterification method. 1,2,3,6-Tetrahydrophthalic anhy-
dride (15 g, 99 mmol), butyl alcohol (40 mL), benzene (100 mL)
and TsOH‚H2O (0.1 g, 0.53 mmol) were refluxed with a Dean-
Stark refluxing condenser until the separation of water
stopped. NaHCO3 (0.5 g, 5.95 mmol) was added to the mixture
and the excess of butyl alcohol was removed in a vacuum. The
resulting material was dissolved in diethyl ether (100 mL),
washed with 10% aqueous Na2CO3 (100 mL) and dried over
K2CO3. After evaporation of the solvent, 1b was obtained as a
FIGURE 2. Absorption and phosphorescence (inset) spectra
of Pd-6b (s) and Pd-13b (- - -) in deoxygenated DMF. The
spectra are scaled to reflect the relative extinction coefficients
(absorption) and quantum yields (phosphorescence).
Instead, they emit from their triplet states. The quantum
yields of the phosphorescence of TBPs Pd-6b and Pt-6b
were found to be as high as 25% and 51% respectively,
placing these metalloporphyrins among the brightest
near-infrared phosphors known to date. The phospho-
rescent quantum yields of these porphyrins, as well as
their triplet lifetimes are considerably larger than those
of Ar4TBPs.
1
colorless oil. Yield: 21.1 g, 75%. H NMR (CDCl3) δ 5.65 (s,
2H), 4.07 (t, 4H, J ) 6.5 Hz), 3.02 (m, 2H), 2.56-2.31 (m, 4H)
1.58 (m, 4H), 1.34 (m, 4H), 0.91 (t, 6H, J ) 7.5 Hz); 13C NMR
(CDCl3) δ 173.3, 125.2, 64.42, 39.8, 30.6, 25.9, 19.2, 13.7.
Vinyl Sulfone (2b). Synthesis of sulfone 2b from the ester
1b followed the general procedure described previously.58 The
product was purified by flash chromatography on a short silica
gel column (eluent CH2Cl2) and isolated as a yellow oil. Yield:
Based on the trends observed for TBPs and because of
the high fluorescence quantum yield of 13b (45%), a
similarly high quantum yield of the phosphorescence of
Pd-TNP was expected. To our surprise, the phosphores-
cence of Pd-13b appeared to be quite moderate (φ ) 4%),
resembling that of Pd-Ph4TNP(OMe)8 (φ ) 2.5%).54 It is
possible that the lower emission yield of Pd-13b is due
1
83%. H NMR (CDCl3) δ 7.85-7.50 (m, 5H), 7.06 (d, 1H, J )
2 Hz), 4.03-3.86 (m, 4H), 3.10 (m, 1H), 3.00 (m, 1H), 2.90 (m,
1H), 2.60 (m, 3H), 1.45 (m, 4H), 1.28 (m, 4H), 0.88 (m, 6H);
13C NMR (CDCl3) δ 172.1, 171.8, 139.2, 138.5, 136.8, 133.5,
129.3, 128.3, 128.2, 65.1, 39.7, 39.0, 30.7, 30.6, 26.6, 24.4, 19.3,
13.9.
to the very low energy of the triplet band itself (λmax
)
(55) Tietze L. F.; Eicher, T. Reaktionen und Synthesen im organisch-
chemischen Praktikum und Forschungslaboratorium; Georg Thieme
Verlag: New York, 1991.
(54) Earlier, we have pointed out41b that precise measurements of
emission quantum yields in the range of the spectrum around 1 µm
are difficult because of the rapidly fading sensitivity of the detection
systems (PMTs). Therefore, the reported quantum yield values should
be considered as approximate.
(56) Novak, B. H.; Lash, T. D. J. Org. Chem. 1998, 63, 3998.
(57) Toyota, M.; Yokota, M.; Ihara, M. J. Am. Chem. Soc. 2001, 123,
1856.
(58) Hopkins, P. B.; Fuchs, P. L. J. Org. Chem. 1978, 43, 1208.
J. Org. Chem, Vol. 70, No. 23, 2005 9569

Finikova et al.
Pyrrole Esters (3b,c). Esters 3b,c were synthesized from
vinyl sulfone 2b and the corresponding alkyl isocyanoacetates
following the published method,49d used previously to synthe-
size pyrrole 3a from sulfone 2a and alkyl isocyanoacetates.40b
Benzyl ester 3b was purified by chromatography on a silica
gel column (eluent CH2Cl2) and isolated as a yellow oil. Yield
of 3b: 65%. 1H NMR (CDCl3) δ 8.89 (br s, 1H), 7.42-7.31 (m,
5H), 6.67 (d, 1H, J ) 1.5 Hz), 5.29 (m, 2H), 4.06 (m, 4H), 3.41-
2.83 (m, 6H), 1.56 (m, 4H), 1.32 (m, 4H), 0.89 (m, 6H); 13C NMR
(CDCl3) δ 174.5, 173.3, 170.3, 136.6, 128.7, 128.3, 128.2, 127.3,
119.8, 119.3, 117.8, 65.9, 64.8, 64.7, 41.2, 41.1, 30.7, 24.1, 22.6,
19.6, 16.3, 13.9.
48H); MALDI-TOF m/z 1054.05, calcd 1052.27; UV-vis, CH2-
Cl2, λmax nm (ꢀ) 402 (240,000), 533 (16,000), 568 (12,000). Anal.
Calcd for C52H52N4O16Zn: C, 59.23; H, 4.97; N, 5.31. Found:
1
C, 58.80; H, 4.96; N, 5.20. Yield of Zn-5b: 95-97%. H NMR
(DMSO-d6) δ 9.89 (s, 4H), 4.60-4.40 (m, 16H), 4.2-4.0 (m,
24H), 1.60 (m, 16H), 1.36 (m, 16H0, 0.85 (m, 16H); MALDI-
TOF m/z 1405.51, calcd 1403.67; UV-vis, CH2Cl2, λmax nm (ꢀ)
402 (220,000), 533 (16,000), 568 (12,000). Anal. Calcd for
C77H103N4O16Zn: C, 65.77; H, 7.38; N, 3.98. Found: C, 65.25;
H, 7.45; N, 3.60.
Tetrabenzoporphyrins (6a,b and Zn-6a,b). To synthe-
size porphyrins 6a and Zn-6a, 5a or Zn-5a (0.1 mmol),
respectively, was dissolved in dioxane (75 mL), DDQ (450 mg,
2.0 mmol) was added, and the mixture was refluxed under Ar
for 3 h. An extra portion of DDQ (450 mg, 2.0 mmol) was added
and the mixture was refluxed for additional 2-3 h. The
conversion was monitored by UV-vis spectroscopy (solvent
CH2Cl2-pyridine).39d If required, more DDQ was added and
the refluxing was continued until the conversion was complete.
In the case of 6b or Zn-6b, 5b or Zn-5b (0.1 mmol), respec-
tively, was dissolved in toluene (100 mL), DDQ (363 mg, 1.6
mmol) was added, and the mixture was refluxed under Ar for
4-5 h, after which the conversion (monitored by UV-vis
spectroscopy) was complete.
tert-Butyl ester 3c was purified by flash chromatography
on a short silica gel column (eluent CH2Cl2-THF, 30:1),
followed by recrystallization from methanol. Yield of 3c: 60%,
1
colorless crystals, mp 88-90 °C. H NMR (CDCl3) δ 8.96 (br
s, 1H), 6.63 (d, 1H, J ) 3 Hz), 4.07 (m, 4H), 3.32-2.82 (m,
6H), 1.59-1.55 (s+m, 9+4H), 1.34 (m, 4H), 0.89 (m, 6H); 13C
NMR (CDCl3) δ 173.5, 173.4, 161.6, 124.5, 119.5, 119.4, 118.4,
80.7, 64.74, 64.69, 41.23, 41.19, 30.8, 28.7, 24.1, 22.9, 19.3, 13.8.
Anal. Calcd for C25H35NO6: C, 65.53; H, 8.37; N, 3.32. Found:
C, 65.42; H, 8.33; N, 3.44.
Pyrrole 4b. 4b was synthesized from either benzyl ester
3b or tert-butyl ester 3c following the procedures described
earlier for the synthesis of pyrrole 4a.40b 4b was purified by
flash chromatography on a short silica gel column (eluent CH2-
The workup in all the cases, i.e., 6a, Zn-6a, 6b and Zn-6b,
followed the same protocol. The mixture was reduced to a small
volume (5-10 mL), CH2Cl2 (150 mL) was added, and the
resulting solution was washed with 10% aqueous Na2SO3 and
10% aqueous Na2CO3 and dried over K2CO3. After evaporation
of the solvent, the resulting material was purified on a silica
gel column (eluent CH2Cl2-THF, 20:1). The bright green
fraction was collected, its volume was reduced down to about
5 mL, and the solution was layered over with methanol and
left in a closed vial overnight. The resulting green precipitate
was collected by centrifugation and dried in a vacuum. Yield
of 6a:39f 20-30%, green powder. Yield of Zn-6a:39d 96%, green
1
Cl2). Yield: 82% (from 3b) or 35% (from 3c), colorless oil. H
NMR (CDCl3) δ 8.32 (br s, 1H), 6.37 (d, 2H, J ) 2 Hz), 3.97
(m, 4H), 3.10-2.80 (m, 6H), 1.50 (m, 4H), 1.25 (m, 4H), 0.83
(m, 6H); 13C NMR (CDCl3) δ 173.7, 116.6, 113.5, 64.6, 41.7,
30.7, 22.8, 19.2, 13.7.
Tetracyclohexenoporphyrins (5a,b). Syntheses of por-
phyrins 5a,b followed the procedure described for the synthesis
of OEP.43 The pyrrole (4a or 4b, 1.6 mmol) was dissolved in
benzene (90 mL), the reaction flask was flushed with Ar and
shaded from light by a piece of aluminum foil. Formaldehyde
(37% aqueous solution, 0.18 mL) and TsOH‚H2O (10 mg, 0.05
mmol) were added, and the mixture was refluxed with a
Dean-Stark condenser for 6-8 h under Ar. The mixture was
cooled to room temperature, and the flow of air was passed
through the mixture overnight under continuous stirring. The
solvent was evaporated, and the remaining material was
purified on a silica gel column (eluent CH2Cl2-THF; 5a, 20:
1-10:1; 5b, 100:1-50:1). The red fraction was collected,
evaporated to dryness, dissolved in a small volume of THF,
layered over with ∼20-fold excess volume of MeOH-H2O (3:
1) and left overnight in a closed vial. The resulting precipitate
was collected by centrifugation and dried in a vacuum. Yield
of 5a: 30-40%, red powder. 1H NMR (CDCl3) δ 9.98-9.85 (m,
4H), 4.70-3.60 (m, 48H), -3.80 (br, 4H); MALDI-TOF: m/z
990.82, calcd 990.35; UV-vis, CH2Cl2, λmax nm (ꢀ) 399 (185,-
000), 498 (14,300), 533 (13,000), 566(7,000), 620 (5,000). Anal.
Calcd for C52H54N4O16: C, 63.02; H, 5.49; N, 5.65. Found: C,
1
powder. Yield of 6b: 95%, green powder. H NMR (CDCl3) δ
9.55 (s, 4H), 9.22 (s, 8H), 4.74 (t, 16H, J ) 7 Hz); 2.08 (m,
16H), 1.74 (m, 16H), 1.19 (t, 24H, J ) 7.5 Hz), -5.06 (br, 2H);
1H NMR (TFA-d) δ 11.99 (s, 4H), 10.52 (s, 8H), 4.90 (t, 16H, J
) 7 Hz); 2.13 (m, 16H), 1.75 (m, 16H), 1.20 (t, 24H, J ) 7.5
Hz); 13C NMR (CDCl3) δ 168.1, 131.7, 122.1, 94.0, 66.4, 31.2,
19.7, 14.3; MALDI-TOF m/z 1311.54, calcd 1310.60; UV-vis,
DMF, λmax nm (ꢀ) 404 (46,500), 432 (240,000), 447 (325,000),
579 (20,000), 617 (66,500), 626 (70,000), 673 (46,000). Anal.
Calcd for C76H86N4O16: C, 69.60; H, 6.61; N, 4.27. Found: C,
69.19; H, 6.66; N, 4.54. Yield of Zn-6b: 97%, green powder.
1H NMR (pyridine-d5, 50 °C) δ 11.25 (s, 4H), 10.26 (s, 8H),
4.85 (t, 16H, J ) 7 Hz); 2.05 (m, 16H), 1.69 (m, 16H), 1.11 (t,
24H, J ) 7.5 Hz); 13C NMR (pyridine-d5, 50 °C) δ 169.5, 144.
9, 140.6, 132.2, 97.6, 66.5, 31.6, 20.1, 14.4; MALDI-TOF m/z
1373.11, calcd 1372.52; UV-vis, pyridine, λmax nm (ꢀ) 433 (55,-
400), 460 (434,000), 589 (22,200), 647 (139,000). Anal. Calcd
for C76H84N4O16Zn: C, 66.39; H, 6.16; N, 4.08. Found: C, 66.20;
H, 6.19; N, 4.19.
1
62.28; H, 5.31; N, 5.51. Yield of 5b: 40-45%, red powder. H
NMR (CDCl3) δ 9.95-9.80 (m, 4H), 4.50-3.80 (m, 40H), 1.90-
0.80 (m, 56H), -3.85 (br, 4H); MALDI-TOF: m/z 1329.02, calcd
1326.73; UV-vis, CH2Cl2, λmax nm (ꢀ) 400 (180,000), 498 (14,-
000), 533 (13,000), 566 (7,000), 620 (5,000). Anal. Calcd for
C76H102N4O16: C, 68.75; H, 7.74; N, 4.22. Found: C, 68.37; H,
7.57; N, 4.19.
Pd and Pt Tetrabenzoporphyrins (Pd-6b and Pt-6b).
Free base tetrabenzoporphyrin 6b (35 mg, 0.027 mmol) was
dissolved in PhCN (5 mL), PdCl2 (10 mg, 0.053 mmol) or PtCl2
(15 mg, 0.053 mmol) was added, and the mixture was refluxed
under Ar. The metal insertion required 5-10 min in the case
of Pd complex and 8 h in the case of Pt complex. The conversion
was monitored by UV-vis spectroscopy (solvent DMF), and
Zn Tetracyclohexenoporphyrins (Zn-5a,b). An excess
of Zn(OAc)2‚2H2O (100 mg, ∼0.5 mmol) was added to a solution
of porphyrin 5a or 5b (0.1 mmol) in THF (20 mL), and the
mixture was refluxed for 15-20 min. The conversion was
monitored by UV-vis spectroscopy (solvent THF). The reaction
was stopped when the absorption band of the free base
porphyrin (λmax ) 620 nm) disappeared. The mixture was
evaporated to dryness, and the remaining material was
purified on a silica gel column (eluent CH2Cl2-THF, 20:1). The
first pink fraction was collected and evaporated to dryness to
give the product as a red amorphous solid. Yield of Zn-5a: 95-
97%. 1H NMR (DMSO-d6) δ 9.95-9.80 (m, 4H), 4.80-3.60 (m,
the reaction was stopped when the free-base Q-band (λmax
)
673 nm) disappeared. The mixture was evaporated to dryness
at 0.1 mmHg, and the remaining material was washed with
methanol, dried, and purified on a silica gel column (eluent
CH2Cl2-THF, 20:1) to give the product as a blue-green
amorphous solid. Yield of Pd-6b: 90%. 1H NMR (pyridine-d5,
70 °C) δ 9.74 (br s, 4H), 9.33 (s, 8H), 4.95 (t, 16H, J ) 7 Hz);
2.20 (m, 16H), 1.83 (m, 16H), 1.28 (t, 24H, J ) 7.5 Hz); 13C
NMR (pyridine-d5, 70 °C) δ 168.7, 137.3, 135.1., 132.4, 124.2,
97.3, 66.7, 31.6, 20.1, 14.4. MALDI-TOF m/z 1413.33, calcd
9570 J. Org. Chem., Vol. 70, No. 23, 2005

Soluble Tetrabenzo- and Tetranaphtho[2,3]porphyrins
1414.49; UV-vis, DMF, λmax nm (ꢀ) 426 (305,000), 565 (17,-
000), 618 (160,000). Anal. Calcd for C76H84N4O16Pd: C, 64.47;
H, 5.98; N, 3.96. Found: C, 64.29; H, 5.62; N, 4.03. Yield of
Pt-6b: 84%. 1H NMR (pyridine-d5, 80 °C) δ 9.99 (s, 4H), 9.46
(s, 8H), 4.92 (t, 16H, J ) 7 Hz); 2.16 (m, 16H), 1.80 (m, 16H),
1.23 (t, 24H, J ) 7.5 Hz); 13C NMR (pyridine-d5, 50 °C) δ 168.8,
137.3, 134.8, 132.6, 122.6, 98.1, 66.8, 31.8, 20.2, 14.5; MALDI-
TOF m/z 1503.49, calcd 1503.55; UV-vis, pyridine, λmax nm
(ꢀ) 416 (170,000), 557 (19,000), 609 (165,000). Anal. Calcd for
C76H84N4O16Pt: C, 60.67; H, 5.63; N, 3.72. Found: C, 59.84;
H, 5.23; N, 3.92.
Fe tetrabenzoporphyrin (Fe-6b). Porphyrin 6b (27 mg,
0.02 mmol) was dissolved in propionic acid (10 mL). FeCl2‚
4H2O (100 mg, 0.5 mmol) and iron wire (∼100 mg) were added,
and the mixture was refluxed under Ar for ∼1 h. The
conversion was monitored by UV-vis spectroscopy (solvent
DMF), and the reaction was stopped when the free-base
Q-band (λmax ) 673 nm) disappeared. The mixture was filtered,
the filtrate was evaporated to dryness, and the remaining
material was washed with methanol-pyridine mixture and
dried in a vacuum. The product was isolated as a blue-green
amorphous solid. Yield of Fe-6b: 20 mg, 74%. 1H NMR
(pyridine-d5) δ 11.38 (s, 4H), 10.12 (s, 8H), 4.72 (t, 16H, J ) 7
Hz); 1.92 (m, 16H), 1.59 (m, 16H), 1.02 (t, 24H, J ) 7.5 Hz);
13C NMR (pyridine-d5) δ 169.5, 143.2, 143.3, 131.2, 121.7, 98.3,
66.4, 31.5, 19.9, 14.2; MALDI-TOF m/z 1365.17, calcd 1364.52;
UV-vis, pyridine, λmax nm (ꢀ) 422 (110,000), 446 (99,500), 613
(100,000). Anal. Calcd for C76H84N4O16Fe: C, 66.86; H, 6.20;
N, 4.10. Found: C, 66.29; H, 6.45; N, 3.98.
5,8-Dialkoxy-1,4-dihydronaphthalenes (8b,c). Synthesis
of compound 8b generally followed the procedure described
for the synthesis of 5,8-dimethoxy-1,4-dihydronaphthalene
8a.45 Ethyl bromoacetate was used in the present synthesis
instead of dimethyl sulfate. Yield of 8b: 85%, colorless solid,
mp 117-118 °C. 1H NMR (CDCl3) δ 6.50 (s, 2H), 5.87 (s, 2H),
4.56 (s, 4H), 4.24 (q, 4H, J ) 7.5 Hz), 3.35 (s, 4H), 1.28 (s,
6H); 13C NMR (CDCl3) δ 174.2, 169.4, 125.7, 123.5, 108.5, 66.2,
61.3, 24.4, 14.3. Anal. Calcd for C18H22O6: C, 64.66; H, 6.63.
Found: C, 64.50; H, 6.58. Compound 8c was synthesized using
a similar procedure. A mixture of 5,8-dihydroxy-1,4-dihy-
dronaphthalene 7 (3.24 g, 20 mmol), ethyl 3-bromobutirate
(11.7 g, 9.0 mL, 60 mmol), NaI (1.5 g, 10 mmol) and K2CO3
(15 g) was refluxed in acetone (100 mL) for 48-60 h. The solid
was filtered off, washed with CH2Cl2 (100 mL), and the filtrate
was evaporated under reduced pressure. The resulting mater-
ial was recrystallized from ethyl alcohol to afford 2c as a
cream-colored solid. Yield of 8c: 5.45 g, 69%, mp 117-118 °C.
1H NMR (CDCl3) δ 6.58 (s, 2H), 5.86 (s, 2H), 4.13 (q, 4H,
3J(H,H) ) 6.5 Hz), 3.93 (t, 4H, J ) 6 Hz), 3.25 (s, 4H), 2.51 (t,
4H, J ) 7.5 Hz), 2.10 (m, 4H), 1.25 (t, 6H, J ) 7.5 Hz); 13C
NMR (CDCl3) δ 173.5, 150.4, 124.9, 123.8, 108.2, 67.2, 60.6,
31.2, 25.1, 24.5, 14.5. Anal. Calcd for C22H30O6: C, 67.67; H,
7.74. Found: C, 67.52; H, 7.77.
R-Chlorosulfones (9b,c). Synthesis of compounds 9b,c
generally followed the procedure described earlier for the
synthesis of R-chlorosulfone 9a.41 The products were purified
by flash chromatography on a silica gel column (eluent 9a,
CH2Cl2-THF, 20:1; 9b, CH2Cl2) with subsequent crystalliza-
tions from ether-petroleum ether mixtures. Yield of 9b: 65%,
yellowish solid, mp 111-112 °C. 1H NMR (CDCl3) δ 7.95-7.53
(m, 5H), 6.53 (s, 2H), 4.85 (m, 1H), 4.85 (m, 1H), 4.57 (s, 2H),
4.53 (s, 2H), 4.23 (m, 4H), 3.74 (m, 1H), 3.48-3.26 (m, 4H),
1.26 (m, 6H); 13C NMR (CDCl3) δ 174.3, 169.1, 150.4, 150.1,
138.2, 134.2, 129.4, 129.1, 123.4, 122.7, 109.8, 109.5, 66.5, 66.3,
64.4, 61.4, 51.8, 30.5, 24.6, 20.2, 14.3. Anal. Calcd for C24H27-
ClO8S: C, 56.41; H, 5.33. Found: C, 56.46; H, 5.27. Yield of
9c: 75%, yellowish solid, mp 86-87 °C. 1H NMR (CDCl3) δ
7.92-7.55 (m, 5H), 6.60 (s, 2H), 4.86 (m, 1H), 4.13 (m, 4H),
3.90 (m, 4H), 3.70 (m, 1H), 3.38-3.15 (m, 4H), 2.47 (m, 4H),
2.10 (m, 4H), 1.25 (m, 6H); 13C NMR (CDCl3) δ 173.5, 173.4,
150.4, 150.1, 138.4, 134.3, 129.5, 129.1, 122.3, 121.5, 109.2,
108.9, 67.4, 67.2, 64.5, 60.7, 52.0, 31.2, 31.1, 30.7, 25.0, 20.4,
14.5. Anal. Calcd for C28H35ClO8S: C, 59.30; H, 6.22. Found:
C, 59.27; H, 6.18.
Pyrrole Ester (10b). Compound 10b was prepared from
R-chlorosulfone 9c and tert-butyl isocyanoacetate following the
procedure described previously for the synthesis pyrrole ester
10a.41 The product was purified by flash chromatography on
a short silica gel column (eluent CH2Cl2-THF, 20:1), followed
by recrystallization from methanol. Yield of 10b: 77%, light
1
yellow crystals, mp 103-104 °C. H NMR (CDCl3) δ 8.92 (br
s, 1H), 6.81 (d, 1H, J ) 2.5 Hz), 6.64 (s, 2H), 4.14 (m, 4H),
4.03 (m, 2H), 3.98 (t, 4H, J ) 6 Hz), 3.80 (m, 2H), 2.55 (m,
4H), 2.13 (m, 4H), 1.57 (s, 9H), 1.25 (m, 6H); 13C NMR (CDCl3)
δ 173.6, 173.5, 161.7, 151.1, 150.8, 125.7, 125.3, 124.2, 119.3,
119.2, 118.1, 108.0, 107.9, 80.6, 67.3, 67.2, 60.6, 60.5, 31.3, 31.2,
28.7, 25.2, 25.1, 23.0, 21.2, 14.4, 14.3. Anal. Calcd for C29H39-
NO8: C, 65.77; H, 7.42; N, 2.64. Found: C, 65.71; H, 7.29; N,
2.66.
Pyrrole (11b). tert-Butyl ester 10b (300 mg, 0.57 mmol)
was dissolved in CH2Cl2 (15 mL), and the solution was flushed
with Ar for 5 min under stirring. The mixture was cooled on
an ice bath, TFA (10 mL) was added, and the mixture was
refluxed for 30 min. CH2Cl2 (20 mL) was added to the mixture,
after which it was poured into a beaker with ice-cold solution
of Na2CO3 (10% aqueous, 100 mL). The resulting mixture was
transferred into a separatory funnel, the organic layer was
separated, the water phase was additionally extracted with
CH2Cl2 (2 × 30 mL), and the combined organic solutions were
washed with 10% aqueous Na2CO3 (50 mL). After drying over
K2CO3, the solution was passed through a short silica gel
column (eluent CH2Cl2-THF, 20:1), and the solvent was
evaporated to yield the product as a colorless solid. Yield of
11b: 255 mg, 98%. 1H NMR (CDCl3) δ 8.09 (br s, 1H), 6.67 (d,
2H, J ) 2 Hz), 6.63 (s, 2H), 4.14 (q, 4H, J ) 8 Hz), 3.98 (t, 4H,
J ) 6 Hz), 3.85 (s, 4H), 2.56 (t, 4H, J ) 7 Hz), 2.14 (m, 4H),
1.26 (t, 6H, J ) 7 Hz); 13C NMR (CDCl3) δ 173.7, 151.0, 126.8,
117.4, 113.1, 108.2, 67.4, 60.6, 31.5, 25.2, 21.2, 14.3.
Tetranaphtho[2,3]porphyrins (13a,b). The syntheses of
porphyrins 13a,b from pyrroles 11a,b generally followed the
procedure, described above for the synthesis of TCHPs 5a,b.
The pyrrole (11a or 11b, 1.2 mmol) was dissolved in benzene
(60 mL), and the solution was flushed with Ar. Formaldehyde
(37% aqueous solution, 0.11 mL) and TsOH‚H2O (30 mg, 0.16
mmol) were added to the mixture under vigorous stirring, and
the mixture was refluxed for 4-5 h under Ar and then stirred
overnight on air. The solvent was evaporated, and the remain-
ing material was treated with DDQ (100 mg, 4 mmol). In the
case of 13a, the reaction was performed in refluxing dioxane,
whereas in the case of 13b, DDQ was added to the solution in
CH2Cl2 at room temperature. In the latter case, the oxidation
also could be done using p-chloranil (100 mg, 4 mmol) in
refluxing toluene. The progress of the reaction was monitored
by UV-vis spectroscopy (13a in DMF; 13b in CH2Cl2). The
spectrum changed gradually from the etio type, corresponding
to the porphyrins of type 12 (Scheme 2) to characteristic TNP
spectrum with an intense Q-band at ∼720 nm.
In the case of 13a, a green residue precipitated from the
reaction mixture. It was collected by centrifugation and
washed with pyridine and THF. For further purification, it
was recrystallized from refluxing PhCN and dried in a vacuum.
Yield of 13a: 25%, dark green powder. MALDI-TOF m/z
949.07, calcd 950.33; UV-vis, pyridine, λmax nm (ꢀ) (86500),
471 (198,000), 656 (29,500), 721 (191,000). Anal. Calcd for
C60H46N4O8: C, 75.77; H, 4.88; N, 5.89. Found: C, 75.24; H,
4.99; N, 5.75.
In the case of 13b, the reaction mixture was washed with
10% aqueous Na2SO3, with 10% aqueous Na2CO3, dried over
K2CO3 and reduced in volume of about 5 mL. Acetonitrile (60
mL) was added, resulting in formation of a green precipitate.
The precipitate was collected by centrifugation, washed with
acetonitrile and methanol and dried in a vacuum. Yield of
13b: 33%, green powder. 1H NMR (pyridine-d5-PhNO2-d5, 1:1,
50 °C) δ 11.51 (s, 4H), 10.92 (s, 8H), 4.71 (br t, 16H), 4.56 (q,
J. Org. Chem, Vol. 70, No. 23, 2005 9571

Finikova et al.
16H, J ) 7 Hz), 3.23 (t, 16H, J ) 7 Hz), 2.88 (m, 16H), 1.35 (t,
24H, J ) 7 Hz), -1.27 (br s, 2H); MALDI-TOF m/z 1752.66,
calcd 1750.75; 13C NMR (pyridine-d5-PhNO2-d5, 1:1, 80 °C) δ
174.4, 151.2, 127.6, 115.9, 105.6, 93.6, 69.5, 61.2, 32.6, 26.2,
15.0; UV-vis, pyridine, λmax nm (ꢀ) 441 (90,000), 471 (205,-
000), 656 (31,500), 721 (199,500). Anal. Calcd for C100H110N4O24:
C, 68.56; H, 6.33; N, 3.20. Found: C, 67.29; H, 6.02; N, 3.03.
Zn Tetranaphtho[2,3]porphyrin (Zn-13b). An excess of
Zn(OAc)2‚2H2O (30 mg, 0.16 mmol) was added to a solution of
porphyrin 13b (17 mg, 0.01 mmol) in pyridine (20 mL), and
the mixture was refluxed for 15-20 min. The conversion was
monitored by UV-vis spectroscopy (solvent pyridine). The
reaction was stopped when the absorption band of 13b (λmax
) 722 nm) disappeared. The mixture was diluted with water,
the green precipitate was collected by centrifugation, washed
with methanol and dried in a vacuum. Yield of Zn-13b: 16
mg, 95%, green solid. 1H NMR (pyridine-d5) δ 11.80 (br s, 4H),
11.10 (br, 8H), 7.22 (br, 8H, ovlpd. w/solv), 4.60-4.53 (ovlpd.
t+q, 16+16H), 3.15 (t, 16H, J ) 7 Hz), 2.77 (m, 16H), 1.16 (t,
24H, J ) 7 Hz); 13C NMR (pyridine-d5) δ 174.5, 151.1, 146.2,
138.2, 127.2, 115.5, 104.8, 92.6, 69.2, 61.1, 32.5, 25.6, 14.7;
MALDI-TOF m/z 1815.50, calcd 1812.66; UV-vis, pyridine,
λmax nm (ꢀ) 439 (11,500), 467 (270,000), 645 (32,000), 674 (32,-
000), 708 (320,000). Anal. Calcd for C100H108N4O24Zn: C, 66.16;
H, 6.00; N, 3.09. Found: C, 65.73; H, 5.90; N, 3.04.
were added, and the mixture was allowed to cool to room
temperature. The solvents were removed in a vacuum (0.1
mmHg), and the remaining material was washed with metha-
nol, dried and purified on a silica gel column (eluent CH2Cl2-
THF, 20:1) to give the product as a green amorphous solid.
1
Yield of Pd-13b: 82%. H NMR (pyridine-d5, 100 °C) δ 9.71
(br s, 4H), 9.02 (br, 8H), 4.71 (br, 16H), 4.50 (br, 16H), 3.17
(br, 16H), 2.84 (br, 16H), 1.37 (br, 24H); 13C NMR (pyridine-
d5, 80 °C) δ 174.0, 69.4, 60.8, 32.3, 26.0, 14.7; MALDI-TOF
m/z 1856.58, calcd 1854.64; UV-vis, pyridine, λmax nm (ꢀ) 428
(140,000), 633 (34,000), 665 (44,000), 696 (315,000). Anal.
Calcd for C100H108N4O24Pd: C, 64.70; H, 5.86; N, 3.02. Found:
C, 63.77; H, 5.42; N, 3.54.
Acknowledgment. Support of the grant EB003663-
01 from the NIH (USA) and the contract 02-5403-21-2
with Anteon Inc. (USA) are gratefully acknowledged.
A.V.C. acknowledges the support of the grant RFBR 04-
03-32650-a` from Russian Foundation for Basic Re-
search. The authors thank Ms. Natalie Kim for proof-
reading the manuscript.
Supporting Information Available: Copies of the NMR
spectra of newly synthesized porphyrins and metalloporphy-
rins. This material is available free of charge via the Internet
at http://pubs.acs.org.
Pd Tetranaphtho[2,3]porphyrin (Pd-13b). Free-base
porphyrin 13b (17 mg, 0.01 mmol) was dissolved in PhCN (5
mL), PdCl2 (5 mg, 0.028 mmol) was added, and the mixture
was refluxed under Ar for 1-3 min. A few drops of pyridine
JO051580R
9572 J. Org. Chem., Vol. 70, No. 23, 2005