Synthesis, separation and UV/Vis spectroscopy of pyrazino- quinoxalinoporphyrazine macrocycles

Article abstract of DOI:10.1002/ejoc.200700275

Unsymmetrical metal-free and zinc complexes of pyrazinoquinoxalino- porphyrazines (PQP) bearing eight diethylamino groups have been synthesized by statistical tetramerization of 2,3-bis(diethylamino)quinoxaline-6,7- dicarbonitrile and 5,6-bis(diethylamino)pyrazine-2,3-dicarbonitrile in lithium butanolate. For this purpose, a new heteroatom-substituted quinoxaline precursor, 2,3-dichloro-6,7-dicarbonitrile, was prepared and characterized. It is a flexible starting material for new building blocks of quinoxaline-6,7- dicarbonitrile derivatives. All the PQPs (including adjacent and opposite isomers) from the statistical mixture were detected and separated by column chromatography on silica and characterized by MALDI-TOF mass spectrometry, IR, UV/Vis and NMR spectroscopy. The effect of the insertion of benzene rings into the tetrapyrazinoporphyrazine (TPP) system is discussed. Each benzene ring insertion into the TPP system causes a bathochromic shift of 22 nm; the dependence is linear. The final tetra[6,7]quinoxalinoporphyrazines were red-shifted to 744 and 763 nm for the zinc and metal-free derivative, respectively. Splitting of the Q-band was observed for PQPs with lower symmetry. Wiley-VCH Verlag GmbH & Co. KGaA, 2007.

Full text of DOI:10.1002/ejoc.200700275

FULL PAPER
DOI: 10.1002/ejoc.200700275
Synthesis, Separation and UV/Vis Spectroscopy of Pyrazino-quinoxalino-
porphyrazine Macrocycles
[a]
[a]
[a]
[a]
[b]
Zbynek Musil, Petr Zimcik,* Miroslav Miletin, Kamil Kopecky, and Juraj Lenco
Keywords: Phthalocyanines / Asymmetric synthesis / UV/Vis spectroscopy / Nitrogen heterocycles
Unsymmetrical metal-free and zinc complexes of pyrazino-
quinoxalino-porphyrazines (PQP) bearing eight diethyl-
amino groups have been synthesized by statistical tetrameri-
zation of 2,3-bis(diethylamino)quinoxaline-6,7-dicarbonitrile
and 5,6-bis(diethylamino)pyrazine-2,3-dicarbonitrile in lith-
ium butanolate. For this purpose, a new heteroatom-substi-
tuted quinoxaline precursor, 2,3-dichloro-6,7-dicarbonitrile,
was prepared and characterized. It is a flexible starting mate-
rial for new building blocks of quinoxaline-6,7-dicarbonitrile
derivatives. All the PQPs (including adjacent and opposite
isomers) from the statistical mixture were detected and sepa-
rated by column chromatography on silica and characterized
by MALDI-TOF mass spectrometry, IR, UV/Vis and NMR
spectroscopy. The effect of the insertion of benzene rings into
the tetrapyrazinoporphyrazine (TPP) system is discussed.
Each benzene ring insertion into the TPP system causes a
bathochromic shift of 22 nm; the dependence is linear. The
final tetra[6,7]quinoxalinoporphyrazines were red-shifted to
744 and 763 nm for the zinc and metal-free derivative,
respectively. Splitting of the Q-band was observed for PQPs
with lower symmetry.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2007)
Introduction
In our previous work we have focused on the investiga-
tion of tetrapyrazinoporphyrazines (TPP), aza-analogues of
Phthalocyanine (Pc) derivatives and their analogues are
a group of compounds that have very stable physical and
chemical properties; they absorb strongly in different re-
gions of the electromagnetic spectrum.[ Symmetrically tet-
ra- and octasubstituted Pc have been intensely investigated
with respect to their physical properties and they are used in
[4,5,8,14]
Pc
(Figure 1). Their advantage is the relatively simple
preparation of synthetic precursors (substituted pyrazine-
,3-dicarbonitriles) and a wide range of available peripheral
substitutions not always achievable with Pc. On the other
hand, these derivatives suffer from a hypsochromic shift of
2
1]
[2]
[3]
different areas, such as chemical sensors, liquid crystals,
photodynamic therapy (PDT)[
4–6]
and laser dyes.[7] In some
of these applications, absorption at longer wavelengths is
very advantageous, for example, in PDT it enables the depth
of the therapeutic intervention to be increased. An increase
of λmax of Pc can be achieved by peripheral substitution
with suitable substituents, the electrons of which will con-
[
8,9]
tribute to the conjugation of the π-conjugated system.
Protonation, unsymmetrical substitution or metal complex-
ation are also known to lead to some bathochromic shift.
However, the largest bathochromic shift of the Q-band is
usually achievable by linear annelation of the aromatic
[
10,11]
rings.
Naphthalocyanines (Nc) are well-known organic
dyes and pigments characterized by a significant 80–100 nm
red shift of absorption compared with the corresponding
Pc.[12,13]
[
[
a] Department of Pharmaceutical Chemistry and Drug Control,
Faculty of Pharmacy, Charles University,
Heyrovskeho 1203, Hradec Kralove 50005, Czech Republic
Fax: +420-49-5067167
E-Mail: petr.zimcik@faf.cuni.cz
b] Institute of Molecular Pathology, Faculty of Military Health
Sciences, University of Defence,
Hradec Kralove 50005, Czech Republic
Figure 1. General structures of macrocycles discussed in this work.
Eur. J. Org. Chem. 2007, 4535–4542
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Z. Musil, P. Zimcik, M. Miletin, K. Kopecky, J. Lenco
FULL PAPER
the Q-band of around 30–40 nm compared with the parent
Our syntheses (Scheme 1) led to preparation of 2,3-
Pc.[ This undesirable property can be eliminated by the dichloroquinoxaline-6,7-dicarbonitrile (3), a flexible build-
linear annelation of aromatic rings to the macrocyclic sys- ing block suitable especially for the synthesis of heteroatom-
tem, thus resulting in tetra[2,3]quinoxalinoporphyrazines or substituted quinoxalinoporphyrazines. The synthesis re-
their isomers, tetra[6,7]quinoxalinoporphyrazines (TQP), quired two steps: the formation of dioxo derivative 2 and
the aza-analogues of Nc (Figure 1). The tetra[6,7]quinoxal- its subsequent chlorination. The preparation of 2 has al-
15]
[
22]
inoporphyrazines are characterized by a stronger red shift of ready been reported using a different, quite complicated
around 40 nm compared with their corresponding isomers, synthetic approach. Our method of heating 1 in dimethyl
[
11]
tetra[2,3]quinoxalinoporphyrazines.
Tetra[2,3]quinoxal- oxalate is simple and gives very good yields of 2. The for-
[
11,16–18]
inoporphyrazines have been known for some time,
mation of two tautomeric forms (lactam and lactim) is pos-
however, to the best of our knowledge their isomers, which sible for compound 2, but very strong carbonyl bands in
are more suitable from the point of view of the spectral the IR spectrum and only one set of 13C and H NMR
properties, have been investigated in more detail in only one signals show that the equilibrium is shifted exclusively to
1
[
19]
case recently.
the lactam form. The next step, chlorination of 2, proceeded
In this work we have focused on porphyrazines contain- best by refluxing with thionyl chloride and a catalytic
ing the [6,7]quinoxalino moiety. They combine good spec- amount of DMF in 1,2-dichloroethane. Reactions with
tral properties, considering the bathochromic shift of the Q- thionyl chloride in other solvents (dioxane and THF) as
band, and simple synthetic availability with a very wide well as chlorination with POCl in these solvents (THF, di-
3
range of possible peripheral substitutions allowing, in the oxane and 1,2-dichloroethane) were unsuccessful. The
future, the preparation of compounds with desired proper- chemical properties of 3 are very similar to 5,6-dichloropyr-
ties and behaviour. For this purpose, we synthesized the azine-2,3-dicarbonitrile (5), which is widely used in the
[
4,8,23–25]
promising precursor 2,3-dichloroquinoxaline-6,7-dicar- preparation of precursors for TPP.
The carbons at
bonitrile which undergoes simple nucleophilic substitution positions 2 and 3 are strongly electron-deficient because of
and thus is an excellent substrate for the synthesis of vari- the electron-withdrawing ability of the nitrogen atoms in
ous quinoxalinoporphyrazine building blocks. To elucidate the quinoxaline heterocycle and the peripheral chlorine
the effect of the insertion of benzene rings into the macro- atoms. This makes them suitable for nucleophilic attack by,
cycle system, a series of macrocycles with different numbers for example, amines, thiolates or alkoxides leading to the
of pyrazine and quinoxaline moieties were prepared and replacement of one or both chlorine atoms with the desired
their UV/Vis spectral properties investigated. They will be substituents. Thanks to this variability of peripheral substi-
referred to in the text as pyrazinoquinoxalinoporphyrazines tution this compound is a very interesting starting material
(PQP) and, according to the number of each moiety and for the preparation of macrocycles with variable properties
the central atom, will be abbreviated as H2P4–xQ P and (e.g., spectral properties, solubility, hydrophilicity and hy-
x
ZnP4–xQ P, where x = 0–4. For a unified labelling system, drophobicity, the amount of peripheral charges). Moreover,
x
this abbreviation will be used throughout the article, that is, substituted heterocycles containing the pyrazine-2,3-dicar-
also for the members of this series containing only pyrazine
(
i.e., H P Q P = H TPP) or only quinoxaline (i.e. H P Q P
2 4 0 2 2 0 4
=
H TQP) heterocycles even though we are aware that they
2
are not actually PQPs.
Results and Discussion
Synthesis and Characterization
The synthesis of the starting material 4,5-diamino-
phthalonitrile (1) has been reported in the literature using
[
19]
either 1,2-diamino-4,5-dibromobenzene
4
or 1,2-diamino-
[
20]
,5-diiodobenzene. As experienced in our laboratory and
also reported in the literature, the limiting step in the prepa-
ration of 1 is the cyanation of halogenated diaminobenzene.
In the case of 1,2-diamino-4,5-diiodobenzene, the yields
that we obtained were considerably higher and therefore the
[
20]
synthesis reported by Youngblood
was chosen as more
suitable. In previous work,[
19,21]
phthalonitrile 1 was treated
directly with different diketones, yielding quinoxaline-5,6-
dicarbonitriles in one step. This approach, however, re-
quires the previous complicated synthesis of the desired di-
ketone and some substitutions cannot be achieved by this
approach. We therefore opted for an alternative approach.
Scheme 1. Synthetic strategy. Reagents and conditions: a) EtOH,
diethyl oxalate, 140 °C, 8 h; b) 1,2-dichloroethane, SOCl , DMF,
reflux, 3 h; c) diethylamine, THF, room temp., overnight; d) NH ,
3
2
butanol, 90 °C, 30 min; e) diethylamine, THF, reflux, 6 h.
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Pyrazinoquinoxalinoporphyrazine Macrocycles
bonitrile core have also been investigated for their herbici- ABAB[35–37] or AABB[35,38,39] derivatives have also been de-
dal[
26,27]
and antineoplastic
a promising starting material for derivatives of quinoxal-
inedicarbonitriles, investigated also for their potential in the tetramerization of quinoxaline derivative 4 and pyrazine
these interesting applications. derivative 6. The synthesis had to be therefore performed
[28,29]
activities. Compound 3 is veloped.
Our aim was to isolate all metal-free PQPs arising from
The aggregation of planar macrocyclic systems of Pc, Nc by statistical condensation followed by chromatographic
or TPP dyes is a well-known problem and it results in poor separation of the PQP derivatives (7–12, Figure 2). For sim-
solubility and consequently problems with purification, iso- plification, symmetrical 12 was not isolated from the mix-
lation and characterization of synthesized products. Intro- ture but prepared in a separate reaction (see above). The
duction of bulky substituents onto the periphery of these bulkiness of the diethylamino groups inhibits efficiently the
macrocycles hinders the stacking of the macrocycle mole- aggregation of all the PQP molecules and therefore they
cules and thus efficiently inhibits aggregation.[
12,15]
Bulky could be separated on a silica gel column by step-gradient
diethylamino groups were therefore chosen as peripheral chromatography. The compounds were readily soluble in
substituents for the final PQP to ensure very good mono- common organic solvents (chloroform, dichloromethane,
merization in organic solvents, consequently allowing good acetone, tetrahydrofuran and toluene) showing a negligible
isolation of all the synthesized dyes. Thus the reaction of 3 tendency to aggregate in dilute solution. We succeeded in
and 5 with diethylamine gave the final precursors for tetra- isolating all the compounds in the reaction mixture; even
merization, 4 and 6, respectively. The nucleophilic substitu- two isomers (adjacent and opposite) were well separated.
tions proceeded easily for both the pyrazine- and quinoxal- Compounds were eluted from the column in the following
inedicarbonitriles, giving high yields of over 70%.
order: 7, 8, 9, 10, 11 and 12. Using toluene/tetrahydrofuran
The tetramerization of one precursor gives rise to sym- (20:1) as the mobile phase the R values were 0.62, 0.60,
f
metrical dyes. Because of our good experience[8] (satisfac- 0.55, 0.24, 0.10 and 0.02 for compounds 7, 8, 9, 10, 11 and
tory yields) in the tetramerization of TPP using butanolate 12, respectively. Owing to the different masses of the two
we decided to use lithium butanolate as the cyclization precursors, the fractions could be assigned to the correct
agent. Tetrapyrazinoporphyrazine H P Q P (12) was pre- PQP unequivocally on the basis of MS. Assignment of the
2
4
0
pared with no further problems from 6 and isolated from adjacent and opposite isomers to two fractions with the
the reaction mixture. Preparation of tetraquinoxalinopor- same mass was achieved on the basis of their NMR spectra.
phyrazine H P Q P (7) proved to be very difficult. The self-
2
0
4
condensation of 4 was not successful using various pro-
cedures (lithium or magnesium butanolate, DMF or (di-
methylamino)ethanol with zinc acetate). Compound 4 was
also treated with ammonia to form the diiminoisoindoline
analogue 4a (Scheme 1). Cyclotetramerization of 4a in di-
methylaminoethanol alone or in the presence of zinc acetate
gave results similar to all the above-mentioned procedures.
The product was always detected in the reaction mixtures
through the use of UV/Vis spectroscopy (Q-bands in the
expected area) but its amount was insignificant. Surpris-
ingly, the yield of compound 7 was higher in the case of
statistical condensation (see below). However, it was iso-
lated as a mixture of two very similar compounds and we
did not succeed in the isolation of pure metal-free 7. NMR
spectroscopy indicated the presence of another substance
and MALDI-TOF mass spectrometry showed two signals
at m/z = 1291 (7) and 1281 (impurity) in a ratio of approxi-
mately 3:1. Owing to identical R values in all tested mobile
f
phases it was impossible to separate these substances even
by TLC.
The tetramerization of two different precursors (A and
B) in one reaction usually results in a mixture of six dif-
ferent compounds (AAAA, AAAB, ABAB, AABB, BBBA
and BBBB) which must be separated using chromato-
graphic procedures. This approach in the synthesis of un-
symmetrical Pc and related compounds is sometimes called
[
30]
a statistical condensation.
Different selective strate-
[
30–32]
gies
approach
leading to only AAAB (the sub-phthalocyanine
[
33]
[34]
or the polymer support approach ),
Figure 2. Structures of the PQPs in the reaction mixture.
Eur. J. Org. Chem. 2007, 4535–4542
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Z. Musil, P. Zimcik, M. Miletin, K. Kopecky, J. Lenco
FULL PAPER
1
The diethylamine H NMR signals of H P Q P 9 and 10 sponding metal-free PQPs were detected. In the case of
2
2
2
in CDCl were broad and unsplit and therefore they did H P Q P (7), the metal was also introduced into the centre
3
2
0
4
not allow exact differentiation of the two isomers. The di- of the impurity (see above). The R values of the resulting
f
1
3
ethylamine C NMR signals of H P Q P, however, were zinc complexes were different enough to isolate the
2
2
2
sharp and allowed the isomers to be distinguished (Fig- ZnP Q P using TLC, allowing this zinc complex to be
0
4
ure 3). Owing to different symmetry, the two carbons of the studied by UV/Vis spectroscopy in a pure form. The ident-
ethyl groups on the periphery gave only two signals each in ity of the impurity remains unknown, but its porphyrazine
the case of 9 but four signals each in the case of 10 in the character with perhaps a tetraquinoxaline core is implicated
expected areas. Moreover, in the case of 10 we were able to because it complexes the metals and its UV/Vis spectrum
detect all 16 signals of the aromatic carbons. This con- (not shown) is strongly red-shifted. Also its signal at m/z =
firmed unequivocally the assignment of the isomers to each 1281 suggests a metal-free system with a tetraquinoxaline
fraction.
core.
UV/Vis Absorption Spectroscopy
The successive insertion of benzene rings into TPP be-
tween the porphyrazine system and the pyrazine ring show
interesting effects in the UV/Vis spectra of these com-
pounds. It is well known that the position and bandwidth
of the Q-bands of Pcs vary with the central metal, the ring
system, molecular symmetry, size and number of substitu-
[
10]
ents.
The Q-band shifts to the red also because of an
expansion of the π-conjugated system by the insertion of
benzene rings into the periphery of Pc, thus forming Nc.[
As shown in Figure 4, a bathochromic shift of the Q-band
from 654 to 744 nm for zinc PQPs and from 686 to 763 nm
for metal-free PQPs is observed with increasing number of
inserted benzene rings. By considering the centre of the split
13]
Figure 3. 13C NMR spectra of the peripheral diethylamino groups
of 9 (opposite) and 10 (adjacent).
The zinc derivatives were prepared in minimal amounts bands as the band position, the Q-band positions of
only to study changes in the UV/Vis spectra. Metal-free H PQP and ZnPQP have a linear relationship, as shown
2
PQPs were refluxed for a few minutes in DMF/toluene with in Figure 5. The slopes of these linear plots show that the
zinc acetate to produce zinc PQPs quantitatively, as de- insertion of each benzene ring between the pyrazine ring
tected by TLC. The presence of zinc in the centre was con- and the porphyrazine macrocycle leads to a bathochromic
firmed by MS (MALDI-TOF). No signals from the corre- shift of 22 nm. The two straight lines are parallel. The
Figure 4. UV/Vis spectra of metal-free PQPs in dichloromethane and zinc PQPs in THF.
4538
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Eur. J. Org. Chem. 2007, 4535–4542

Pyrazinoquinoxalinoporphyrazine Macrocycles
metal-free PQPs are red-shifted by 18 nm on average with higher than in the case of the corresponding zinc complexes
respect to the corresponding zinc complexes. The conclu- (∆λmax = 41 nm for H P Q P compared with 18 nm for
2
3
1
sion that the Q-band centre shifts linearly with the number ZnP Q P and 39 nm for H P Q P compared with 21 nm for
3
1
2
1
3
of inserted benzene rings in the Pc/Nc series has also been ZnP Q P).
1
3
postulated by other authors.[ The positions of the Q-band
40]
The opposite isomer H P Q P (9) as well as its zinc com-
2 2 2
centre of all the unsymmetrical PQPs can therefore be plex, which are characterized by D2h symmetry, show a re-
nicely predicted by knowing the absorption of the outer markably large splitting of the Q-band. A similar depen-
macrocycles in the series (in our case TPP and TQP). Con- dence of the splitting of the Q-band of the metal-free PQP
cerning the above-mentioned findings, tuning of the absorp- and the zinc complex was observed as in the above-men-
tion maxima of the Q-band is therefore possible by success- tioned case. The Q-band is split by 82 and 41 nm in the
ive insertion of benzene rings into the TPP system. Together case of the metal-free PQP and its slightly more symmetri-
with a large variability of peripheral substitutions of the cal zinc complex, respectively. Unusually, only a single band
PQP macrocycle, it is an ideal tool for the synthesis of dyes appeared in the Q-band area for the adjacent isomer
with desired properties.
H P Q P (10) and its metal complex. These compounds are
2 2 2
also of lower C2v symmetry and therefore the Q-band is
[
13,42]
expected to be split. But similar observations,
as theoretical calculations,
as well
[
10]
have shown that this behav-
iour is typical of adjacent isomers of Pc. This spectral fea-
ture is further confirmation of the correct assignment of
adjacent and opposite isomers for the two fractions of the
same mass.
Conclusions
We have reported herein a synthesis of 2,3-dichloroquin-
oxaline-6,7-dicarbonitrile, a flexible starting material for
building blocks of tetra[6,7]quinoxalinoporphyrazines. It
easily undergoes nucleophilic substitution, so can be used
for the synthesis of heteroatom-substituted derivatives of
2 4–x x
Figure 5. The Q-band absorption centres of H P Q P (᭹) and
Zn P4–xQ
x
P (ᮀ), (x = 0–4) vs. x, the number of inserted benzene quinoxaline-6,7-dicarbonitrile. In this work, the diethyl-
rings into the macrocycle.
amino-substituted derivative was prepared as an example.
A series of PQPs containing different numbers of quinoxal-
ino and pyrazino moieties were then synthesized for the
first time by using this building block. Even the adjacent
and opposite isomers were separated and unequivocally as-
signed.
The highly symmetrical (D ) metal complexes of Pc and
4
h
related compounds show only a single maximum in the Q-
band area. This was observed in the spectra of the two sym-
metrical complexes ZnP Q P and ZnP Q P (Figure 4). In
0
4
4
0
the spectra of metal-free Pcs, the Q-band is usually split
The successive insertion of benzene rings into TPP be-
tween the pyrazine and the porphyrazine ring leads to linear
bathochromic shifts of the Q-band centre of 22 nm per ben-
zene ring. Thus the absorption wavelength of PQPs can be
tuned by increasing the number of quinoxalino moieties in
the PQP macrocycle. Owing to the linear dependence of this
shift, the position of the Q-band centre can be predicted
in the future by knowing the outer members of the series,
symmetrical TPP or TQP which are more easily accessible.
The shape of the Q-band is strongly dependent on the sym-
metry of the macrocycle molecule. Splitting of the Q-band
was observed for unsymmetrical compounds with D2h and
C2v symmetry, whereas derivatives with D4h symmetry ex-
hibited a single band. Two exceptions to this rule were ob-
served: H P Q P with D symmetry and adjacent isomer
into two maxima due to the decreased (D ) symmetry of
2
h
the molecule. In the case of H P Q P (12) this splitting is
2
4
0
clearly observable. However, the spectrum of the enlarged
H P Q P (7) is not split and exhibits only one main maxi-
2
0
4
[
41]
mum in the Q-band region. Kobayashi et al. investigated
the spectral changes of metal-free derivatives of porphyraz-
ines, Pc, Nc and antracocyanines. They found that the split-
ting of the Q-band of metal-free macrocycles decreases with
enlargement of the conjugated system; Q-bands appeared
[41]
as single bands for H Nc and larger systems.
2
In fact, H P Q P (7) is an aza-analogue of Nc so a single
2
0
4
band in the Q-band region is expected. However, the impu-
rity in this sample can also influence slightly the shape of
the spectrum.
2
0
4
2h
Unsymmetrical macrocycles of C -type symmetry show
2
v
H P Q P with C symmetry showed only a single band.
splitting of the Q-band into two bands.[
13,40,42]
This is the
case with the metal-free compounds H P Q P (11) and
2
2
2
2v
Both these exceptions have been observed previously and
2
3
1
[10,41]
explained by molecular orbital calculations.
H P Q P (8) and the corresponding zinc complexes. All
2
1
3
four compounds showed split Q-bands. In the case of
metal-free macrocycles, in which the overall symmetry is de-
Experimental Section
creased due to the presence of two central hydrogens, the All organic solvents used for synthesis were of analytical grade.
energy difference (∆λmax) between the two split bands is All chemicals and solvents were used as received without further
Eur. J. Org. Chem. 2007, 4535–4542
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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4539

Z. Musil, P. Zimcik, M. Miletin, K. Kopecky, J. Lenco
FULL PAPER
purification except for zinc acetate (Lachema, Czech Republic)
which was dried in a drying gun at 78 °C and under a pressure of
butanol (1 mL). The reaction mixture was heated slowly and kept
at 90 °C for 30 min. The reaction was monitored by TLC on silica
gel with acetone as the eluent. The solvent was removed under
reduced pressure, hexane was added to the residue and the yellow
solid was filtered off to give 4a (85 mg, 81%). M.p. 125 °C (slow
decomp.). IR (KBr): ν˜ max = 2969, 2931, 2873, 1648, 1630, 1539,
13 mbar for 8 h. TLC was performed on silica gel 60 F254 (Merck,
Darmstadt). Merck Kieselgel 60 (0.040–0.063 mm) was used for
column chromatography. Infrared spectra were measured as KBr
1
pellets with a Nicolet Impact 400 IR Spectrometer (USA). H and
1
3
–1 1
C NMR spectra were recorded with a Varian Mercury Vx BB
1448 cm . H NMR (300 MHz, CDCl
3
): δ = 8.01, (s, 2 H, imino
1
13
3
00 spectrometer ( H: 299.95 MHz; C: 75.43 MHz). Chemical NH), 7.94 (s, 2 H, arom. CH), 3.64 (q, J = 7.0 Hz, 8 H, NCH
2
),
):
1
3
shifts are given relative to internal Si(CH
3
)
4
. UV/Vis spectra were
1.11 (t, J = 7.1 Hz, 12 H, CH
3
) ppm. C NMR (75 MHz, CDCl
3
recorded with a Shimadzu UV-2401PC spectrophotometer (Shim-
adzu Europa GmbH, Duisburg, Germany). The slit width of the
instrument was set to 0.2 nm. The wavelength accuracy of the in-
strument at this slit width is Ϯ0.3 nm. MALDI-TOF mass spectra
were recorded in positive reflectron mode with a Voyager-DE STR
mass spectrometer (Applied Biosystems, Framingham, MA, USA).
For each sample, 0.5 µL of the mixture was spotted onto the target
plate, air-dried and covered with 0.5 µL of a matrix solution con-
sisting of 10 mg of α-cyano-4-hydroxycinnamic acid in 100 µL
ACN containing 0.1% TFA. The instrument was calibrated exter-
nally with a five-point calibration using Peptide Calibration Mix1
δ = 12.8, 42.7, 118.8, 129.8, 139.5, 148.3, 166.1 ppm.
5
(
3
,6-Bis(diethylamino)pyrazine-2,3-dicarbonitrile (6): Diethylamine
1.3 g, 17 mmol) was added dropwise to a solution of 5 (600 mg,
mmol) in tetrahydrofuran (100 mL) and refluxed for 6 h. At the
end of the reaction the mixture was cooled and precipitated dieth-
ylamine hydrochloride was filtered off. The solution was evaporated
under reduced pressure and a yellow crude product recrystallized
from methanol. Mother liquors from crystallization were com-
bined, evaporated, purified by column chromatography on silica
with hexane/ethyl acetate (4:1). The two fractions (from crystalli-
zation and chromatography) were combined and finally recrys-
tallized from methanol to give 6 (600 mg, 76%) as yellow plates.
M.p. 93–94 °C (lit. 94 °C[ ). IR (KBr): ν˜ max = 2978, 2935, 2876,
[20]
(
5
LaserBio Labs, Sophia-Antipolis, France). Compounds 1
and
[
43]
were prepared according to previously published methods.
44]
2,3-Dioxo-1,2,3,4-tetrahydroquinoxaline-6,7-dicarbonitrile (2):A
–1
1
2
228 (CN), 1518, 1489, 1347, 1253 cm . H NMR (300 MHz,
CDCl ): δ = 3.48 (q, J = 7.1 Hz, 8 H, NCH ), 1.07 (t, J = 7.1 Hz,
) ppm. C NMR (75 MHz, CDCl ): δ = 12.7, 42.8,
15.0, 120.3, 146.1 ppm.
suspension of 1 (1.58 g, 10 mmol) in ethanol (10 mL) was refluxed
until the heterogeneous mixture turned to a homogeneous solution
3
2
13
12 H, CH
3
3
(app. 10 min). Then diethyl oxalate (50 mL) was added and this
1
mixture was heated at 140 °C for 8 h. The boiling flask was left
opened (without condenser) to allow continual removal of ethanol.
The mixture was cooled to room temperature and the precipitate
filtered and washed with toluene to give 2 (1.6 g, 75%) as a brown
solid. M.p. Ͼ300 °C. IR (KBr): ν˜ max = 3192, 3154, 3048, 2237
General Procedure for the Synthesis of Unsymmetrical PQP: A solu-
tion of 4 (700 mg, 2.2 mmol) and the second precursor 6 (600 mg,
2.2 mmol) was refluxed in dry butanol (15 mL) and metal lithium
(196 mg, 28 mmol) was added. The mixture was refluxed for 3 h.
The solvent was evaporated under reduced pressure, aq. acetic acid
–1
1
(
6
CN), 1701, 1608, 1506, 1380 cm . H NMR (300 MHz, [D ]-
13
DMSO): δ = 12.42 (s, 2 H, NH), 7.51 (s, 2 H, CH) ppm. C NMR (50% v/v, 30 mL) was added and the mixture was stirred at room
(
75 MHz, [D
6
]DMSO): δ = 108.1, 116.1, 120.0, 130.2, 155.0 ppm.
,3-Dichloroquinoxaline-6,7-dicarbonitrile (3): DMF (55 mg,
.75 mmol) was added dropwise to a slurry of 2 (1.6 g, 7.5 mmol)
temperature for 30 min. The precipitate was filtered, washed thor-
oughly with water and dried. This mixture of the six different PQPs
was separated by column chromatography on silica. The PQPs were
obtained as fractions of various colours by using a mobile phase
of increasing polarity (reported below as the first column) starting
with 20:1 toluene/THF for 7. Each fraction was then purified on
silica once more using either the same or a slightly different mobile
phase (reported as the second column).
2
0
and thionyl chloride (7.2 g, 60 mmol) in 1,2-dichloroethane
20 mL) and the resulting mixture was refluxed for 3 h. The mixture
(
was cooled to room temperature, concentrated to dryness and ex-
tracted with hot THF (3ϫ50 mL). The extracts were combined
and evaporated to give 3 (1.2 g, 64%) as a yellow solid. M.p. 128 °C
(
decomp.). IR (KBr): ν˜ max = 3100, 3069, 3048, 2239 (CN), 1719,
2
,3,11,12,20,21,29,30-Octakis(diethylamino)tetra[6,7]quinoxalino-
–1 1
1
(
539, 1387, 1261 cm . H NMR (300 MHz, [D
6
]acetone): δ = 8.85
]acetone): δ =
porphyrazine (H P, 7): This compound was synthesized ac-
2 0 4
P Q
s, 2 H, arom. CH) ppm. 13C NMR (75 MHz, [D
6
cording to the general procedure with the following mobile phases:
the first column toluene/THF, 20:1, and the second column with
the same mobile phase. Dark solid (4 mg, 0.3%). This compound
1
15.6, 116.5, 136.6, 142.2, 151.0 ppm.
2
,3-Bis(diethylamino)quinoxaline-6,7-dicarbonitrile (4): Diethyl-
was obtained with an impurity. UV/Vis (CH
2
Cl
2
): λmax (ε) = 763
amine (1.8 g, 24 mmol) was added dropwise to a solution of 3
1.2 g, 4.8 mmol) in THF (50 mL) and stirred at room temperature
–
1
–1
(
(
182000), 685 (48000), 459 (51200), 373 nm (115600  cm ). IR
(
–
1 1
KBr): ν˜ max = 2962, 2919, 2850, 1542, 1481, 1445, 1428 cm . H
): δ = 4.02–3.72 (m, NCH ), 1.45–1.00 (m,
), 0.95–0.68 (m) ppm. MALDI-TOF MS: m/z 1291
overnight. Precipitated diethylamine hydrochloride was filtered off,
the solution was evaporated under reduced pressure and the yellow
crude product purified by column chromatography on silica with
toluene/chloroform (2:1) as eluent to give 4 (1.1 g, 71%) as a yellow
NMR (300 MHz, CDCl
CH
M + H] , 1281.
3
2
3
=
+
[
solid. M.p. 124–125 °C. UV/Vis (CHCl
3
): λmax (ε) = 391 (18600),
2 1 3
Compound 8 (H P Q P): This compound was synthesized accord-
ing to the general procedure with the following mobile phases: the
first column toluene/THF, 20:1, and the second column with the
55 (12300), 300 nm (42200 –1 cm ). IR (KBr): ν˜ max = 3012, 2971,
–1
3
2
–1
1
934, 2868, 2234 (CN), 1526, 1494, 1446, 1384 cm . H NMR
(300 MHz, CDCl
3
): δ = 7.96 (s, 2 H, arom. CH), 3.62 (q, J =
same mobile phase. Dark solid (96 mg, 7.0%). UV/Vis (CH
2
Cl
2
):
1
3
7.0 Hz, 8 H, NCH
2
), 1.11 (t, J = 7.1 Hz, 12 H, CH
3
) ppm.
C
λ
4
2
max (ε) = 752 (170000), 713 (165000), 685 (65000), 644 (40000),
NMR (75 MHz, CDCl
3
): δ = 12.9, 43.1, 108.7, 116.5, 131.9, 139.4,
–
1
–1
77 (53200), 372 nm (140000  cm ). IR (KBr): ν˜ max = 2965,
148.5 ppm.
–
1
1
930, 2869, 1541, 1479, 1445, 1428 cm . H NMR (300 MHz,
): δ = 3.95 (br. s, 32 H, CH ), 1.49–1.12 (m, 48 H, CH ) ppm.
C NMR (75 MHz, CDCl ): δ = 13.2, 43.2 ppm. MALDI-TOF
6,7-Bis(diethylamino)-1,3-diimino-2H-pyrrolo[3,4-g]quinoxaline (4a): CDCl
3
2
3
1
3
A rapid stream of ammonia was passed through a stirred mixture
of 4 (100 mg, 0.3 mmol) and sodium hydride (1 mg, 0.04 mmol) in
3
+
MS: m/z (%) = 1241 [M + H] .
4540
www.eurjoc.org
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2007, 4535–4542

Pyrazinoquinoxalinoporphyrazine Macrocycles
Opposite Isomer 9 (H P): This compound was synthesized ac-
cording to the general procedure with the following mobile phases:
the first column toluene/THF, 20:1, and the second column with
the same mobile phase. Dark solid (30 mg, 2.3%). UV/Vis
2
P
2
Q
2
was the pure product isolated by TLC for analysis and spectral
measurement.
Zinc Complex ZnP
0
Q
4
P: This compound was isolated by TLC with
toluene/THF (20:1, R
f
= 0.38) as the mobile phase and by scraping
(
6
=
CH
2
Cl
2
): λmax (ε) = 750 (134500), 690 sh, 668 (136500), 636 sh,
the silica from the TLC plate and washing it with tetrahydrofuran.
–1
–1
13 (35500), 517 (52000), 373 nm (135000  cm ). IR (KBr): ν˜ max
UV/Vis (THF): λmax = 744, 708, 665, 435, 372 nm. MALDI-TOF
–1
1
2965, 2930, 2870, 1541, 1477, 1444, 1427 cm . H NMR
): δ = 4.12 (br. s, 16 H, CH ), 3.84 (br. s, 16 H,
), 1.38 (t, J = 6.8 Hz, 24 H, CH ), 1.28 (t, J = 6.9 Hz, 24 H,
) ppm. 1 C NMR (75 MHz, CDCl
): δ = 12.9, 13.3, 42.7, 43.1,
+
MS: m/z = 1353 [M + H] .
(300 MHz, CDCl
3
2
Zinc Complex ZnP
1 3
Q P: UV/Vis (THF): λmax (ε) = 730 (193000),
CH
CH
1
2
3
3
709 (202000), 668 (42300), 638 (42000), 435 sh, 373 nm
3
3
–
1
–1
+
+
(147500  cm ). MALDI-TOF MS: m/z = 1303 [M + H] .
Opposite Isomeric Zinc Complex ZnP P: UV/Vis (THF): λmax
ε) = 720 (142200), 679 (159000), 662 (75400), 613 (37300), 435
48.3, 150.7 ppm. MALDI-TOF MS: m/z = 1191 [M + H] .
2
Q
2
Adjacent Isomer 10 (H P): This compound was synthesized
2 2 2
P Q
(
(
according to the general procedure with the following mobile
phases: the first column toluene/THF, 20:1, and the second column
with hexane/ethyl acetate, 2:1. Dark solid (105 mg, 8.0%). UV/Vis
–
1
–1
40500), 375 nm (130000  cm ). MALDI-TOF MS: m/z = 1253
M + H] .
+
[
(
3
1
CH
2
Cl
74 nm (135600  cm ). IR (KBr): ν˜ max = 2966, 2931, 2871,
2
): λmax (ε) = 718 (201500), 652 (44600), 495 (51600), Adjacent Isomeric Zinc Complex ZnP
2
Q
2
P: UV/Vis (THF): λmax
–1
–1
(ε)
(141000  cm ). MALDI-TOF MS: m/z = 1253 [M + H] .
Zinc Complex ZnP P: UV/Vis (THF): λmax (ε) = 683 (138000),
65 (156000), 633 (34300), 604 (29400), 463 (29200), 374 nm
=
694 (329000), 664 (48500), 626 (46600), 373 nm
–
1
1
–1
–1
+
640, 1539, 1478, 1445, 1427 cm . H NMR (300 MHz, CDCl
), 3.85 (br. s, 16 H, CH ), 1.40–1.24 (m,
) ppm. 13C NMR (75 MHz, CDCl
): δ = 12.9, 13.1, 13.2,
3
):
δ = 4.05 (br. s, 16 H, CH
2
2
3
Q
1
4
1
1
1
8 H, CH
3
3
6
3.3, 42.6, 42.8, 43.0, 43.3, 120.6, 121.2, 134.1, 134.2, 138.8, 139.0,
39.5, 139.7, 143.4, 146.2, 148.1, 148.4, 150.3, 150.4, 152.3,
54.0 ppm. MALDI-TOF MS: m/z = 1191 [M + H] .
–1
–1
+
(
124200  cm ). MALDI-TOF MS: m/z = 1203 [M + H] .
Zinc Complex ZnP P: UV/Vis (THF): λmax (ε) = 654 (173000),
95 (29900), 501 (33200), 374 nm (108900  cm ). MALDI-TOF
+
4 0
Q
–
1
–1
5
Compound 11 (H
2
P
3
Q
1
P): This compound was synthesized accord-
+
MS: m/z = 1153 [M + H] .
ing to the general procedure with the following mobile phases: the
first column toluene/THF, 20:1, and the second column with hex-
Acknowledgments
ane/ethyl acetate, 2:1. Dark solid (95 mg, 7.3%). UV/Vis (CH
2
Cl
2
):
λ
3
1
max (ε) = 715 (103000), 674 (88600), 653 (65000), 529 (60000),
72 nm (118000 –1 cm ). IR (KBr): ν˜ max = 2966, 2930, 2870,
–1
This work was supported by the Ministry of Education, Youth and
Sports of the Czech Republic (Research project MSM 0021620822).
The authors would like to thank Ji rˇ í Kune sˇ for recording the NMR
spectra.
–1 1
641, 1539, 1477, 1445, 1423 cm . H NMR (300 MHz, CDCl
3
):
δ = 9.83 (s, 2 H, arom. CH), 4.16–3.96 (m, 24 H, CH
6.9 Hz, 32 H, CH ), 1.42–1.24 (m, 48 H, CH ) ppm. C NMR
75 MHz, CDCl ): δ = 12.9, 13.1, 13.2, 13.3, 42.8, 42.9, 43.3, 120.5,
2
), 3.86 (q, J
1
3
=
2
3
(
3
1
1
36.9, 137.5, 138.2, 139.5, 141.3, 141.8, 148.0, 150.2, 150.7, 150.8,
51.9, 159.2 ppm. MALDI-TOF MS: m/z = 1141 [M + H] .
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Compound 12 (H
refluxed in dry butanol (15 mL) and metal lithium (196 mg,
8 mmol) was added. The mixture was refluxed for 3 h. The solvent
was evaporated under reduced pressure, aq. acetic acid (50% v/v,
2 4 0
P Q P): A solution of 6 (1.08 g, 4 mmol) was
2
[4] P. Zimcik, M. Miletin, Z. Musil, K. Kopecky, L. Kubza, D.
3
3
0 mL) was added and the mixture stirred at room temperature for
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[
[
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water and methanol. The crude product was then adsorbed on sil-
ica (5 g) and washed with methanol on a glass frit until the solution
passed through the frit was colourless. The product was dried and
purified by column chromatography with hexane/ethyl acetate, 6:1,
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(270 mg, 25%). UV/Vis (CH
2 2
Cl ): λmax (ε) = 686 (92800), 657
–1
–1
(70000), 528 (74400), 370 nm (114000  cm ). IR (KBr): ν˜ max
=
–1 1
2
4
CH
4
969, 2931, 2872, 1640 cm . H NMR (300 MHz, CDCl
.05 (q, J = 7.2 Hz, 32 H, CH
) ppm. 13C NMR (75 MHz, CDCl
2.9, 13.2 ppm. MALDI-TOF MS: m/z = 1091 [M + H] .
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[
[
[
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), 1.32 (t, J = 7.2 Hz, 48 H,
): δ = 150.5, 147.0, 140.2,
1
3
3
+
3
General Procedure for the Preparation of Zinc PQP: A mixture of
metal-free PQP (0.02 mmol) and anhydrous zinc acetate (20 mg,
0
1992, 763–766.
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Q
4
P, for which the starting material was impure,
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Eur. J. Org. Chem. 2007, 4535–4542
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
4541

Z. Musil, P. Zimcik, M. Miletin, K. Kopecky, J. Lenco
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Published Online: July 17, 2007
4542
www.eurjoc.org
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2007, 4535–4542