New Selective Synthesis of Substituted Tetrabenzoporphyrins

Full text of DOI:10.1023/A:1025340804084

Doklady Chemistry, Vol. 391, Nos. 4–6, 2003, pp. 222–224. Translated from Doklady Akademii Nauk, Vol. 391, No. 6, 2003, pp. 781–783.
Original Russian Text Copyright © 2003 by Finikova, Chernov, Cheprakov, Filatov, Vinogradov, Beletskaya.
CHEMISTRY
New Selective Synthesis of Substituted Tetrabenzoporphyrins
O. S. Finikova, S. Yu. Chernov, A. V. Cheprakov,
M. A. Filatov, S. A. Vinogradov, and Academician I. P. Beletskaya
Received April 29, 2003
Porphyrins with an extended π-system, represented used for preparing a number of important tetraaryltet-
by tetrabenzoporphyrins (TBPs) as the simplest exam- rabenzoporphyrins having no substituents in the fused
benzene rings.
ples, possess a set of unique properties. This accounts
for the extensive practical application of these com-
pounds, for example, in photodynamic therapy [1], in
nonlinear optics [2], and as organic semiconductors [3].
In terms of their optical characteristics, meso-tetra-
aryltetrabenzoporphyrins Ar4TBPs were shown to be
excellent phosphorescent sensors of oxygen [4], suit-
able, in particular, for in vivo measurements [5]. Never-
theless, more profound studies or practical use of com-
pounds of this class have been impossible due to the
lack of convenient and selective methods for their syn-
thesis. The known synthetic protocols are based on
high-temperature template condensation of, for exam-
ple, phthalimide or its derivatives with arylacetic acids
[6]. Due to exceptionally drastic reaction conditions (a
temperature above 350°ë), this method is applicable
only to a narrow range of products containing only sim-
ple substituents (alkyl groups, halogens) and does not
allow one to obtain interesting, functionally substituted
Ar4TBPs. The yields of target porphyrins are very low
and isolation of the products requires repeated chroma-
tography. Moreover, it was found that this method actu-
ally yields complex mixtures of arylated tetrabenzopor-
As target compounds, we chose (a) the parent
compound Ph4TBP (6‡) and (b) porphyrin 6b carry-
ing carboxy substituents at the 3- and 5-positions of
the 6b benzene rings. Owing to the presence of eight
ester groups, porphyrin 6b can be readily modified to
give derivatives readily soluble in water and other
solvents.
Cyclohexene 1 was converted into cyclic α-vinyl
sulfone 2 by a known procedure [2]. Product 2 was
made to react with ethyl isocyanoacetate in the pres-
ence of potassium tert-butoxide to give ethyl 4,5,6,7-
tetrahydroisoindole-1-carboxylate 3 [11]. The inter-
mediate 4,5,6,7-tetrahydroisoindole 4 was prepared
in one step from ethyl ester 3 and introduced, with-
out isolation, in the porphyrin synthesis according to
the Lindsey method [12]. The overall yield of por-
phyrins 5‡ and 5b from ester 3 was about 50%. The
key step of the whole sequence is aromatization of
porphyrins 5a and 5b to give tetrabenzoporphyrins
6a and 6b. Complexes 5a and 5b with some double-
charged ions (Cu2+, Ni2+, Pd2+) were found to be
phyrins with one to four meso-aryl groups even when readily oxidized by 2,3-dichloro-5,6-dicyano-1,4-
Ar is Ph; furthermore, Ph4TBP is not a major compo- benzoquinone to the corresponding TBPs. Interest-
ingly, 5a and 5b, as free bases, cannot be aromatized
under these conditions. Instead, the reaction affords
the dication (diprotonated porphyrin), totally inert
with respect to 2,3-dichloro-5,6-dicyano-1,4-benzo-
quinone, as the only product. Free bases of porphy-
rins 6 can be obtained by demetallation of their cop-
per complexes by treatment with hot polyphosphoric
acid.
nent of this mixture [7]. The few existing alternative
methods (see, for example, [8]) use complicated syn-
thetic routes and compounds difficult to obtain as the
starting reactants.
Previously, we described a simple and convenient
method for the synthesis of Ar4TBPs bearing methox-
ycarbonyl substituents in the condensed benzo rings
[9]. The method is based on oxidative aromatization
of hexadecahydrotetrabenzoporphyrinates of a num-
ber of metals. In the present study, we demonstrate
that the strategy we developed can be successfully
This strategy allows the synthesis of gram quanti-
ties of pure 6a–M and 6b–M in one operation using
standard laboratory equipment and without using
chromatography. The data of electronic and NMR
spectroscopy and MALDI-TOF mass spectrometry
confirmed the purity of all the products. All TBP com-
plexes, except for 6a–Pd [4], were synthesized for the
first time.
Department of Chemistry, Moscow State University,
Vorob’evy gory, Moscow, 119992 Russia
0012-5008/03/0008-0222$25.00 © 2003 åÄIä “Nauka /Interperiodica”

NEW SELECTIVE SYNTHESIS OF SUBSTITUTED TETRABENZOPORPHYRINS
223
PhO2S
a
c
b
95%
HN
HN
85%
CH3CH2OOC
1
2
4
3
45–50% d
Ar
Ar
Ar
Ar
Ar
N
Ar
Ar
N
e
N
M
N
N
M
N
N
N
30–95%
Ar
6a: Ar = –Ph
6b: Ar =
5a: Ar = –Ph
5b: Ar =
COOCH3
COOCH3
COOCH3
COOCH3
(M = Cu, Ni, Pd)
(M = 2H)
f
5a–M, 5b–M (M = Cu, Ni, Pd)
Scheme 1. Synthesis of substituted tetrabenzoporphyrins.
Note: (a) (i) PhSCl, CH Cl , 20°C; (ii) m-chloroperbenzoic acid, CH Cl , 20°C; (iii) 1,8-diazabicyclo[5.6.0]undec-7-ene,
2
2
2
2
CH Cl , 20°C; (b) CNCH COOEt, t-BuOK, THF, 0°C; (c) KOH, ethylene glycol, 200°C, 1 h; (d) ArCHO, BF · Et O, CH Cl ,
2
2
2
3
2
2
2
20°C, 2 h, then 2,3-dichloro-5,6-dicyano-1,4-benzoquinone; (e) Cu(OAc) · 2H O, Ni(OAc) · 2H O, or PdCl ; (f) 2,3-dichloro-
2
2
2
2
2
5,6-dicyano-1,4-benzoquinone, THF or dioxane.
The signals in the 13ë NMR spectrum of 6b–Pd
were assigned using HMBQ/HMBC 2D experiments
(Scheme 2).
The properties of the TBPs we obtained can be con-
veniently illustrated by comparing them with the prop-
erties of 5,10,15,20-tetraphenylporphin (TPP) deriva-
tives. As expected, the absorption bands of 5a, 5b, 6a,
and 6b are markedly shifted to longer wavelengths with
respect to those of TPP. In the case of derivatives 5a and
5b, the red shift equals 30–40 nm and is due to macro-
cycle distortion [13]. For derivatives 6a and 6b, which
are also distorted [14], an additional shift (equal to 15–
20 nm) is observed due to the π extension.
MeO
O
5M2.8e2O
131.64
138.64
126.15
123.88
166.24
131.91
O
138.65
116.26
137.86
142.65
N
Scheme 2.
EXPERIMENTAL
Attention is attracted by the substantial upfield shift of
the signals of benzo rings, related apparently to the fact
that they fall in the anisotropy cone of the meso-phenyl
groups. It should be noted that these chemical shifts are
typical of the tetraaryltetrabenzoporphyrin system;
thus, they can be used to assign the spectra of other rep-
resentatives of this series.
The reagents and solvents were purified by standard
methods. NMR spectra were recorded on a Bruker
DRX-500 instrument, electronic absorption spectra
were measured on an HP 8542A spectrophotometer,
and MALDI-TOF mass spectra were run on a Micro-
mass TofSpec instrument (USA) equipped with a pulse
N2 laser (337 nm, 4-ns pulses) using a 1-cyano-4-
hydroxycinnamic acid cryogenic matrix.
The electronic absorption spectra of porphyrins 5a,
5b, 6a, and 6b are summarized in the table.
DOKLADY CHEMISTRY Vol. 391 Nos. 4–6 2003

224
FINIKOVA et al.
Electronic absorption spectra*
7.02–7.13 (m, 16H), 7.74–7.84 (m, 12H), 8.47 (m, 8H);
MALDI-TOF, m/z: calcd. 871.65, found 869.33. 6b–
Pd; 1H NMR (CDCl3, δ): 9.35 (s, 4H), 9.16 (s, 8H), 7.24
(m, 8H), 7.00 (m, 8H), 4.06 (s, 24H); 13C NMR
(CDCl3): see Scheme 2; MALDI-TOF, m/z: calcd.
1382.24, found 1383.40.
Compound
TPP
M
λSoret (nm)
λQ (nm)
H2
414
412
439
426
442
428
514, 548, 588, 646
526
Pd
H2
Pd
H2
Pd
5a
5b
537, 580, 608, 674
536, 572
ACKNOWLEDGMENTS
This work was supported by the Russian Foundation
for Basic Research, project no. 01–03–33097–A.
O.S. Finikova is grateful to INTAS, grantYSF 2001/1-161.
538, 580, 614, 676
537, 575
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**
H2
6a
462
589, 635, 696
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General Procedure for the Synthesis
of Tetrabenzoporphyrins 6a–M and 6b–M
2,3-Dichloro-5,6-dicyano-1,4-benzoquinone (2.7 g,
12 mmol) was added to a solution of porphyrin 5a–M
and 5b–M (M = Cu, Ni, Pd) (1 mmol, ~1 g) in anhy-
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refluxed for 40–60 min. During this period, the solution
color changed from red-brown to bright green. The sol-
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DOKLADY CHEMISTRY Vol. 391 Nos. 4–6 2003