2-Azaanthraquinones: Building blocks for new ring-fused imidazoles and their transformation into benzo[f]isoindole-4,9-diones

Article abstract of DOI:10.1515/znb-2005-0713

The modification of 2-azaanthraquinones with selected C₁ building blocks gives a series of new imidazo-fused derivatives. Employing 2,3-dichloro-5,6-dicyanopyrazine as cyclization partner a rearrangement to yield derivatives of benzo[f]isoindol

Full text of DOI:10.1515/znb-2005-0713

2-Azaanthraquinones: Building Blocks for New Ring-Fused Imidazoles
and their Transformation into Benzo[f]isoindole-4,9-diones
Birgit Franka, Rainer Beckerta, Sven Raub, and Helmar Go¨rlsb
a Institut fu¨r Organische und Makromolekulare Chemie, Friedrich-Schiller-Universita¨t,
Humboldtstr. 10, D-07743 Jena, Germany
b Institut fu¨r Anorganische und Analytische Chemie, Friedrich-Schiller-Universita¨t,
August-Bebel-Str. 2, D-07743 Jena, Germany
Reprint requests to Prof. Dr. R. Beckert. E-mail: C6bera@uni-jena.de
Z. Naturforsch. 60b, 771 – 779 (2005); received February 22, 2005
The modification of 2-azaanthraquinones with selected C1 building blocks gives a series of new
imidazo-fused derivatives. Employing 2,3-dichloro-5,6-dicyanopyrazine as cyclization partner a re-
arrangement to yield derivatives of benzo[f]isoindole-4,9-dione takes place. The Sonogashira cross-
coupling reaction of the aminalester derivative of the azaanthraquinone resulted in well soluble silyl
substituted acetylenes as well as ethinyl aniline which allows further derivatization reactions.
Key words: Azaanthraquinones, Ring Transformation, Cross-Coupling Reactions, Crystal Structure
Introduction
Quinones – especially their ring-fused derivatives –
are interesting in many respects. They are redoxactive
compounds which are modeled after natural products
and therefore, many of their derivatives and synthetic
analogues exhibit biological activity. In addition, their
synthetic applications are manifold. For example, car-
bonyl dyes based on quinones dyes rank among the
most frequently used dyestuffs in the textile indus-
try. More recent applications of quinones are as sub-
structures in systems for studying artificial energy- and
electron transfer processes [1]. Partial replacement of
carbon by nitrogen results in azaanthraquinones, which
can be regarded as being electronically distorted vari-
ants of the parent compounds. These derivatives are
also found in nature; 1- and 2-azaanthraquinones have
been identified as natural products [2 – 4]. Many syn-
thetic representatives show interesting biological ef-
fects. Some azaanthraquinones are teratogens for in-
sects [5] and others are being tested as anti-cancer
reagents [6, 7]. 1- and 2-Azaanthraquinones are gen-
erally synthetically accessible and quite a few suc-
cessful procedures are available in the chemical lit-
erature [8 – 11]. However, a major drawback is the
fact that substitutional variety at the trinuclear core
is highly restricted. In the past, we have reported an
Scheme 1.
ily accessible pyrido[1,2-a]pyrazines 1 [12]. Reac-
tion of 1 with quinones yields, via a complex cy-
cloaddition/ring transformation cascade, novel aza-
anthraquinone derivatives featuring a 2,2’-bipyridine
substructure. We have now expanded our research to
consider the reaction of 1 with 1,4-naphthoquinone
2 which results in new azaanthraquinones of type 3
(Scheme 1). Furthermore, we demonstrate that 3 is
a useful building block for obtaining metal-chelating
substructures and redox-active dyes.
Results and Discussion
The azaanthraquinones of type 3 have been synthe-
efficient synthesis for obtaining highly substituted 2- sized starting from appropriate pyrido[1,2-a]pyrazines
azaanthraquinones by ring transformation of the eas- 2 using our proved protocol [12]. In a smooth reac-
c
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B. Frank et al. · 2-Azaanthraquinones
tion both derivatives 3a,b were obtained in yields of
about 85%. The presence of the two secondary aryl-
amine substructures at 3- and 4-positions in 3 has con-
crete advantages and disadvantages for further syn-
thetic transformations. A distinct disadvantage is the
fact that they hinder successful metal-complexation re-
actions at the bipyridine substructure. Compound 3 is
thus unsuitable for applications as a metal chelating
ligand. We therefore attempted to simply remove the
arylamine substituents via an acylation/reduction se-
quence – and failed completely. The advantage of the
arylamine substituents in 3 is the fact that their pres-
ence makes further synthetic transformations (alkyla-
tion, acylation, ring closure reactions) quite feasible. In
addition, cross-coupling reactions involving the arylic
halogens allow the introduction of further functional
groups.
Scheme 2.
In an attempt to reintroduce metal-complexing abil-
ity into 3 while retaining the synthetic advantage of
the arylamine substituents, we modified 3 by tying the
aniline nitrogen atoms together via a ring closure re-
A final building block that can be successfully
employed is 2,3-dichloro-5,6-dicyanopyrazine. This
pyrazine derivative is well-suited for the assem-
action. In the course of this study, we discovered that bly of condensed heterocycles with high fluores-
these amine substituents can be bridged by several dif- cence [16, 17]. Heating of 3 and 2,3-dichloro-5,6-
dicyanopyrazine in the presence of cesium carbonate
(as base) resulted in a mixture with the new derivatives
ferent C1 building blocks (Scheme 2). Methylene io-
dide in the presence of cesium carbonate reacts with 3
to form the desired products 4a,b, albeit in rather low 9 (ca. 40%) and 10 (ca. 35%) as the main products.
Compound 9 is red and possesses a strong orange flu-
orescence in solvents such as trichloromethane and is
remarkable because of its Stokes shift of 100 nm. The
yields (ca. 18%). Evidence for the successful cycliza-
tion are the molar mass at m/z = 638 for 4b as well
as the signals obtained at 5.91 ppm (N-CH2-N) in the
1H NMR spectra of 4b. In contrast to the deeply violet spectral data of 9 are in agreement with the structural
assignment presented in Scheme 2 and are similar to
those reported for other pyrazino-fused systems [16].
starting material 3 the products are red colored crys-
tals that, when dissolved in trichloromethane, display a
strong orange fluorescence. Another C1 building block Compound 10 is yellow and its elemental analysis as
well as its mass spectrum indicate the same molecu-
lar assembly as in compound 9. The X-ray structural
analysis obtained from a single crystal (Fig. 1) re-
that works is phosgene that is generated in situ from
diphosgene. In this manner, a bridging C=O group
can be introduced and the derivate 5b was obtained
in a moderate yield. The ring thus introduced can be vealed a fused pyrrole substructure which is connected
with an imidazo[4,5-b]pyrazine and a pyridine ring.
Compound 10 does not fluoresce; a fact which may
classified as having a cyclic urea substructure. In an
analogous manner, the corresponding sulfur derivative
(X=S) 6a was obtained in a 10% yield with thiophos- have a structural origin since the solid state structure
shows that both heteroaromatic residues are twisted
out of plane. The formation of this unexpected hete-
rocyclic quinone 10 is undoubtedly the result of a rear-
gene. However, cycloacylation with 1,1’-thiocarbonyl-
diimidazole failed. A further cyclization agent which
we have successfully employed in the past [13– 15] is
triethyl orthoformate. Heating compounds 3a,b under rangement reaction. As a mechanism (Scheme 3) for
the formation of 10, we postulate the attack of 2,3-
reflux for several hours in neat triethyl orthoformate
dichloro-5,6-dicyanopyrazine at one pyridine nitrogen
resulted in the desired products 7a,b which could be
isolated as orange solids in quite satisfactory yields of and the neighbouring NH-aryl group. The resulting
mesomeric iminium system 11/11’ is then attacked by
the remaining NH group to finally provide the novel
benzo[f]isoindole-4,9-dione 10. Although, these types
ca. 65%. Dissolved in various solvents, these deriva-
tives fluoresce orange-yellow with quantum yields of
up to 45%.
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B. Frank et al. · 2-Azaanthraquinones
773
Scheme 4.
localized the lone pair. This extension of the hetero-
cyclic system should contribute to new properties; ap-
plications as chromophores/fluorophores and/or inter-
esting biological activities. We are now investigating
whether or not these modified compounds 4 – 9 can be
employed as ligands in metalla-complexes.
Scheme 3.
The syntheses of pyrido[1,2-a]pyrazines 1 are re-
stricted to simple aryl residues due to the substituents
already present in the starting material, namely the
bis-imidoylchlorides of oxalic acid. Nonetheless, we
recently succeeded in obtaining an entry to amino
and acetylene substituted derivatives via palladium-
catalyzed cross-coupling methods [14, 15]. In order to
achieve an increased solubility of azaanthraquinones,
the Sonogashira reaction was our method of choice
(Scheme 4). Even with the standard catalytic system
PdCl2(PPh3)2/CuI both iodine atomes in 7a could be
replaced by trimethylsilylacetylene as well as by tri-
isopropylacetylene. This exchange resulted in the well
soluble derivatives 12a and 12b, respectively, which
could be purified by chromatography. Furthermore, 4-
ethinylaniline could be introduced in good yield to give
derivative 12c that due to its para-amino groups pro-
vides an access to other compounds.
Fig. 1. Molecular structure of isoindoloquinone 10b. Se-
◦
˚
lected bond lengths [A] and angles [ ]: N5-C17 1.392(7),
N5-C6 1.386(8), C1-C6 1.447(9), N1-C1 1.321(7), N4-C1
1.391(8), C6-N5-C17 109.7(5), N1-C1-N4 113.4(5).
of heterocyclic quinones are well documented [18],
Our goal was finally to construct electron-rich
derivatives which possess in 1,3-position additional tetraaminoethenes which are connected with electron-
heterocyclic substructures are unknown to date. Very accepting structures of azaquinones via dimerization of
recently, ring-fused isoindoloquinones have been iden- in situ generated carbenes. Unfortunately, all attempts
tified as novel antibiotics from a terrestrial strepto- to synthesize these dimers from 7a,b (Scheme 2) by
mycete [19] and in addition, are already patented for
the use in the treatment of cancer [20].
thermal induced α-elimination were fruitless. Treat-
◦
ment at temperatures higher than 270 C under argon
These successful modifications have resulted in a atmosphere led only to tarry pyrolysis products. En-
series of compounds 4 – 9 in which the arylamine couraged by the quantum leap in the chemistry of nu-
substituents are now bound in a heterocyclic ring cleophilic carbenes in the last years, the synthesis and
(Scheme 3). The flexibility of the arylamine sub- isolation of carbenes by deprotonation of imidazolium
stituents has thus been considerably reduced and the salts seemed feasible to us. Therefore, the transforma-
resulting planarization of the nitrogen atoms has de- tion of aminal esters 7 into imidazolium salts has been
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774
B. Frank et al. · 2-Azaanthraquinones
a Perkin Elmer Lambda 19 spectrophotometer. The 1H and
13C NMR spectra were obtained on Bruker DRX 400 and
Bruker AC 250 spectrometers. Mass spectra were obtained
with a Finnigan MAT SAQ 710 spectrometer. Elemental
analyses were carried out using an automatic analyzer LECO
CHNS 932. Microwave reactions were carried out with a
CEM “Discovery”. Synthesis of pyrido[1,2-a]pyrazine 1a:
see literature [12].
Crystallographic data
The intensity data for the compounds were collected
on a Nonius Kappa CCD diffractometer, using graphite-
monochromated Mo-Kα radiation. Data were corrected for
Lorentz and polarization effects, but not for absorption ef-
fects [21, 22]. The structures were solved by direct methods
(SHELXS [23]) and refined by full-matrix least squares tech-
Fig. 2. Molecular structure of imidazolium salt 8a. Selected
bond lengths [A] and angles [ ]: N1-C1 1.335(5), N2-C1
1.327(6), N1-C2 1.399(5), N2-C1-N1 112.2 (4).
◦
2
˚
niques against Fo (SHELXL-97 [24]). For the imidazolium
C and the pyridine N in 8a the hydrogen atoms werer located
by difference Fourier synthesis and refined isotropically. The
other hydrogen atoms were included at calculated positions
with fixed thermal parameters. All non-hydrogen atoms were
refined anisotropically [24]. XP (SIEMENS Analytical X-ray
Instruments, Inc.) was used for structure representations.
chosen as another promising way. Derivatives 7a,b
were reacted with boron trifluoride to give in a smooth
reaction salts of type 8. Alternatively, these compounds
could be prepared from 7 with gaseous hydrogen chlo-
ride. Elemental analyses and the sharp singulets at over
Crystal data for 8a [25]: C31H18B2F8I2N4O2
×
2 C4H8O, M = 1050.12 g mol−1, orange-red prism, size
0.03 × 0.03 × 0.02 mm3, monoclinic, space group P21/n,
1
10 ppm in their H NMR spectra suggest the structure
of an imidazolium salt. A single crystal X-ray analysis
of 8a allowed an unambiguous structural assignment
of these compounds, as shown in Fig. 2.
˚
a = 11.8822(3), b = 14.1197(2), c = 24.3073(5) A, β =
◦
3
◦
˚
95.941(1) , V = 4056.2(1) A , T = −90 C, Z = 4, ρcalcd.
=
1.720 g cm−3, µ (Mo-Kα ) = 16.33 cm−1, F(000) = 2064,
28532 reflections in h(−15/12), k(−18/17), l(−31/30),
measured in the range 1.84◦ ≤ Θ ≤ 27.47◦, complete-
Upon treatment of salts 8a,b with different bases
however, neither carbenes nor their dimers could be
isolated. With pyridine as solvent and sulfur as quench-
ing reagent the thione 6a (Scheme 2) was obtained in
good yields. This method is superior to the acylation
with thiophosgene described above, and is the method
of choice for the preparation of 6a. Finally, 6a was also
formed by reaction of aminalesters 7 with sulfur in a
microwave reactor.
ness Θmax = 99.8%, 9276 independent reflections, Rint
=
0.036, 6922 reflections with F > 4σ(Fo), 535 parameters,
o
0 restraints, R1obs = 0.055, wR2obs = 0.146, R1all = 0.079,
wR2all = 0.1624, GOOF = 1.009, largest difference peak and
−3
˚
hole: 1.844/–1.810 eA
.
Crystal data for 10b [25]: C36H16Br2N8O2 × 1/2 C7H8,
M = 798.46 g mol−1, colorless prism, size 0.04 × 0.04 ×
3
¯
0.03 mm , triclinic, space group P1, a = 11.2316(7),
˚
Experimental Section
Materials and methods
b = 11.3079(7), c = 15.1176(9) A, α = 96.198(3), β◦=
◦
3
˚
91.194(4), γ = 104.125(3) , V = 1848.9(2) A , T = 20 C,
Z = 2, ρcalcd. = 1.434 g cm−3, µ (Mo-Kα) = 22.38 cm−1
,
All reagents were of commercial quality (Aldrich, Fluka,
Merck). Solvents were dried and purified using standard
techniques. Reactions were monitored by thin layer chro-
matography (tlc), Polygram SIL G/UV254 from Macherey-
Nagel or Polygram Alox N/UV254 from Macherey-Nagel.
Flash chromatography was carried out on silica gel (Merck,
Silica gel 60, particle size 0.040 – 0.063 mm, 230 – 400 mesh
ASTM) or neutral aluminia (Merck, aluminium oxide 90 ac-
tive neutral, activity V, particle size 0.063 – 0.2 mm, 70 –
230 mesh ASTM). Melting points were measured with a
Galen III (Boe¨tius system) from Cambridge Instruments and
F(000) = 798, 10039 reflections in h(−14/14), k(−14/14),
l(−18/19), measured in the range 2.73◦ ≤Θ ≤ 27.50◦, com-
pleteness Θmax = 88%, 7488 independent reflections, Rint
=
0.038, 4142 reflections with F > 4σ(Fo), 449 parameters,
o
1 restraint, R1obs = 0.091, wR2obs = 0.253, R1all = 0.157,
wR2all = 0.310, GOOF =−13.017, largest difference peak and
˚
hole: 1.195/−0.692 eA
.
3-(4-Bromophenylamino)-4-(4-bromophenylimino)-4H-
pyrido[1,2-a]pyrazine (1b)
The synthesis from 1.1 g (10 mmol) of 2-(amino-
are not corrected: The UV-vis spectra were obtained using methyl)pyridine and 4.35 g (10 mmol) of oxalic acid bis(4-
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B. Frank et al. · 2-Azaanthraquinones
775
bromophenylimidoyl) chloride according to literature [12] 1,3-Bis(4-iodophenyl)-5-pyridin-2-yl-2,3-dihydro-1H-1,3,4-
yielded 3.19 g (68%); m.p. 179 ◦C. – UV/vis (acetonitrile): triazacyclopenta[a]anthracene-6,11-dione (4a)
λmax (lgε) = 324 (4.1), 428 (4.1). – 1H NMR (250 MHz,
CD2Cl2): δ = 6.29 (t, 3J = 6.3 Hz, 1 H), 6.56 – 6.66 (m,
Yield: 44 mg (17%); red crystals, decomposition at
◦
3 H), 7.09 (d, 3J = 9.1 Hz, 1 H), 7.28 – 7.34 (m, 5 H),
7.48 – 7.56 (m, 3 H), 8.20 (s, 1 H). – 13C NMR (62.5 MHz,
CD2Cl2): δ = 114.3, 118.8, 121.0, 122.4, 123.4, 125.6,
127.1, 127.9, 131.7, 137.9, 137.9, 140.1, 142.6, 148.4. –
MS (DCI, H2O): m/z (%) = 473 (47) [M++5], 471 (100)
[M++3], 469 (53) [M++1]. – C20H14Br2N4 (470.2): calcd.
C 51.09, H 3.00, Br 33.99, N 11.92; found C 50.46, H 3.12,
Br 34.06, N 12.10.
305 – 310 C. – UV/vis (CHCl3): λmax (lgε) = 395 (3.9),
509 (4.1). – 1H NMR (400 MHz, CDCl3): δ = 6.02 (s,
2 H), 6.83 (d, 3J = 8.7 Hz, 1 H), 7.14 – 8.04 (m, 14 H),
8.60 (d, 3J = 4.5 Hz, 1 H). – 13C NMR (100.6 MHz, CDCl3):
δ = 73.5, 119.5, 120.8, 122.1, 122.9, 126.4, 126.7, 126.9,
128.0, 128.9, 133.2, 133.7, 133.8, 134.6, 136.4, 137.5, 137.7,
137.8, 138.1, 138.2, 138.4, 141.0, 142.8, 146.7, 148.5, 153.1,
154.0, 154.5, 158.8, 181.3, 181.8. – MS (FAB in dmba):
m/z (%) = 733 (7) [M+], 505 (11), 439 (23), 336 (100).
– Fluorescence (CHCl3): λmax,em = 594 nm, Φ = 0.24. –
C31H18I2N4O2 (732.3): calcd. C 50.84, H 2.48, I 34.66,
N 7.65; found C 50.75, H 2.57, I 34.40, N 7.39.
Azaanthraquinone 3a
A solution of 564 mg (1 mmol) of pyrido[1,2-a]pyrazine
1a and 158 mg (1.1 mmol) of 1,4-naphthoquinone 2 in
30 ml of methylene chloride was heated at reflux, and the
progress of the reaction was controlled by TLC. The reac-
tion time was 3 – 4 h. The solvent was removed in vacuo
and the residue was separated by column chromatography
on alumina (CHCl3/n-heptane: 1/1) to yield 627 mg (87%)
dark violet solid; m.p. 256 ◦C. – UV/vis (acetonitrile):
λmax (lgε) = 360 (3.9), 509 (4.0). – 1H NMR (250 MHz,
[D6]-DMSO): δ = 6.72 (d, 3J = 8.7 Hz, 2 H), 7.39 – 7.61 (m,
9 H), 7.83 – 7.94 (m, 4 H), 7.94 – 8.12 (m, 1 H), 8.53 (d,
3J = 4.1 Hz, 1 H), 9.39 (s, 1 H) – MS (DCI, H2O):
m/z (%) = 721 (17) [M++1], 594 (9), 321 (86), 161 (100).
– C30H18I2N4O2 (720.3): calcd. C 50.02, H 2.52, I 35.24,
N 7.78; found C 49.91, H 2.65, I 35.10, N 7.89.
1,3-Bis-(4-bromophenyl)-5-pyridin-2-yl-2,3-dihydro-1H-
1,3,4-triazacyclopenta[a]anthracene-6,11-dione (4b)
Yield: 40 mg (18%); red crystals, decomposition at 289 –
294 ◦C. – UV/vis (acetonitrile): λmax (lgε) = 395 (4.0),
510 nm (4.1). – 1H NMR (400 MHz, CD2Cl2): δ = 5.91 (s,
2 H), 6.90 (d, 3J = 8.7 Hz, 1 H), 7.19 – 7.94 (m, 14 H),
8.51 (d, 3J = 4.3 Hz, 1 H). – 13C NMR (100.6 MHz,
CD2Cl2): δ = 74.1, 119.6, 121.0, 122.0, 122.3, 126.8, 127.3,
127.3, 128.2, 128.3, 129.4, 131.7, 131.9, 132.2, 132.6, 132.8,
132.9, 133.7, 143.1, 134.3, 134.4, 135.1, 136.8, 138.1, 142.7,
149.2, 153.6, 154.5, 159.2, 181.8, 182.2. – MS (DCI, H2O):
m/z (%) = 638 (3) [M], 557 (3), 427 (12), 391 (23),
279 (100), 159 (100). – C31H18Br2N4O2 (638.3): calcd.
C 58.33, H 2.84, Br 25.04, N 8.78; found C 58.23, H 3.01,
Br 25.19, N 8.57.
Azaanthraquinone 3b
Prepared in a manner analogous to that for compound
3a, Yield: 520 mg (83%); dark violet solid, m.p. 250 ◦C. –
UV/vis (acetonitrile): λmax (lgε) = 360 (4.0), 504 (4.0). –
1H NMR (400 MHz, CD2Cl2): δ = 6.87 (d, 3J = 8.7 Hz, 2
H), 7.05 (s, 1 H), 7.35 – 7.46 (m, 5 H), 7.55 – 7.65 (m, 3 H),
7.76 – 7.85 (m, 2 H), 7.92 (t, 3J = 5.0 Hz, 1 H), 8.09 (m,
1 H), 8.22 (d, 3J = 8.0 Hz, 1 H), 8.65 (d, 3J = 8.0 Hz, 1
H), 10.04 (s, 1 H). – MS (DCI, H2O): m/z (%) = 629 (43)
[M++5], 627 (100) [M++3], 625 (57) [M++1], 546 (17). –
C30H18Br2N4O2 (626.3): calcd. C 57.53, H 2.90, Br 25.52,
N 8.95; found C 57.61, H 3.04, Br 25.40, N 9.12.
1,3-Bis(4-bromophenyl)-5-pyridin-2-yl-1,3-dihydro-1,3,4-
triaza-cyclopenta[a]anthracene-2,6,11-trione (5b)
200 mg (0.32 mmol) of azaanthraquinone 3b and
61 mg (0.64 mmol) of sodium tert-butoxide were stirred at
r.t. in 50 ml of THF. After 5 min 32 mg (0.16 mmol) of
diphosgene were added and then the mixture was heated at
reflux for 6 h. After cooling to r.t. the solvent was removed
in vacuo. Purification of the yellow product by column chro-
matography on alumina (toluene/ethyl acetate: 20/1) gave
49 mg (23%) of 5b; decomposition at 274 – 307 ◦C. –
UV/vis (acetonitrile): λmax (lgε) = 247 (4.5), 409 nm (3.9).
Cyclization of azaanthraquinones 3a,b with methylene
iodide to compounds 4a,b
300 mg (0.35 mmol) of the appropriate azaanthraquinone
–
1H NMR (250 MHz, CDCl3): δ = 7.17 – 7.20 (m, 2 H),
3 were dissolved in 20 ml of DMF. After addition of 7.30 – 7.36 (m, 1 H), 7.46 (d, 3J = 6.8 Hz, 1 H), 7.57 –
226 mg (0.7 mmol) of Cs2CO3 the mixture was stirred for 7.68 (m, 8 H), 7.77 – 7.86 (m, 2 H), 7.99 – 8.02 (m, 1
10 min. and then 0.03 ml (0.37 mmol) of CH2I2 was dropped H), 8.57 (d, 3J = 4.2 Hz, 1 H). – 13C NMR (62.5 MHz,
into the mixture. After heating for 8 h and then cooling to r.t., CDCl3): δ = 119.9, 121.0, 121.1, 121.9, 122.2, 125.6, 126.3,
the crude product was precipitated by addition of water. The 126.5, 126.6, 130.1, 131.0, 131.4, 132.2, 132.9, 133.0, 133.7,
orange crude product was filtered off and purified by column 134.6, 135.7, 145.5, 148.0, 152.2, 153.3, 157.5, 180.4, 180.9.
chromatography on alumina (CHCl3/toluene: 3/1).
– MS (DCI, H2O): m/z = 653 (72) [M+], 93 (100). –
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776
B. Frank et al. · 2-Azaanthraquinones
C31H16Br2N4O3 (652.3): calcd. C 57.08, H 2.47, Br 24.50, m/z (%) = 777 (13) [M+], 731 (14), 204 (100), 181 (56),
N 8.59; found C 56.91, H 2.58, Br 24.72, N 8.41.
139 (40). – Fluorescence (CHCl3): λmax,em = 579 nm, Φ =
0.35. – C33H22I2N4O3 (776.4): calcd. C 51.05, H 2.86,
I 32.69, N 7.22; found C 51.21, H 2.71, I 32.47, N 7.35.
1,3-Bis(4-bromophenyl)-5-pyridin-2-yl-2-thioxo-2,3-
dihydro-1H-1,3,4-triazacyclopenta[a]-anthracene-6,11-
dione (6a)
2-Ethoxy-1,3-bis(4-bromophenyl)-5-pyridin-2-yl-2,3-
dihydro-1H-1,3,4-triazacyclopenta[a]-anthracene-6,11-
dione (7b)
200 mg (0.32 mmol) of azaanthraquinone 3a and
61 mg (0.64 mmol) sodium tert-butoxide were stirred at r.t.
in 50 ml of THF. After about 5 min 0.02 ml (0.32 mmol)
of thiophosgene were added and the mixture was heated
at reflux for 7 h. After cooling to r.t. and the solvent was
removed in vacuo. Chromatographic purification on alu-
mina (toluene/ethyl acetate: 20/1) gives 21 mg (10%) of a red
product. This product was obtained in a better yield (71%)
starting from 100 mg (0.11 mmol) of the imidazolium salt
8a which was heated in 10 ml of pyridine in the presence
of elemental sulphur (8 mg, 0.22 mmol). Decompostion at
312 – 317 ◦C. – UV/vis (acetonitrile): λmax(lgε) = 324 (3.8),
450 (4.1) – 1H NMR (400 MHz, [D8]-THF): δ = 7.28 –
7.32 (m, 1 H), 7.41 (d, 3J = 8.0 Hz, 2 H), 7.51 (d, 3J =
8.0 Hz, 1 H), 7.61 (d, 3J = 8.0 Hz, 2 H), 7.66 – 7.81 (m,
7 H), 7.87 (d, 3J = 8.0 Hz, 1 H), 7.99 (d, 3J = 8.0 Hz, 1
H), 8.50 (d, 3J = 4.0 Hz, 1 H). – 13C NMR (100.6 MHz,
[D8]-THF): δ = 122.7, 122.8, 123.4, 123.6, 124.4, 126.7,
127.1, 127.4, 128.8, 129.5, 130.5, 130.9, 131.4, 132.3, 132.6,
133.0, 134.3, 134.6, 134.8, 135.1, 135.4, 136.7, 138.3, 140.0,
149.5, 150.1, 156.7, 159.9, 177.6, 181.9, 182.5. – MS(CI):
m/z (%) = 670 (12) [M++2], 668 (24) [M], 666 (12) [M-2],
635 (5). – C31H16Br2N4O2S (668.4): calcd. C 55.71, H 2.41,
Br 23.91, N 8.38, S 4.80; found C 55.62, H 2.28, Br 23.76,
N 8.56, S 4.63.
Yield: 150 mg (63%); orange powder, decomposition at
261 – 265 ◦C. – UV/vis (acetonitrile): λmax (lgε) = 370 (4.1),
478 nm (4.2). – 1H NMR (250 MHz, CDCl3): δ = 1.14 (t,
3J = 7.5 Hz, 3 H), 3.22 – 3.34 (m, 1 H), 3.47 – 3.59 (m, 1
H), 6.84 (s, 1 H), 7.05 (s, br, 2 H), 7.31 – 7.37 (m, 1 H),
7.41 – 7.50 (m, 5 H), 7.60 – 7.64 (m, 2 H), 7.79 – 7.97 (m,
4 H), 8.03 – 8.06 (m, 1 H), 8.62 (d, 3J = 4.2 Hz, 1 H).
–
13C NMR (62.5 MHz, CDCl3): δ = 14.6, 56.0, 101.9,
117.9, 118.3, 118.8, 119.1, 121.3, 122.2, 122.8, 126.6, 126.9,
127.3, 131.8, 132.2, 133.5, 133.7, 134.1, 134.5, 136.1, 136.6,
141.2 149.1, 152.3, 152.8, 159.7, 181.1, 181.7. – MS (DCI,
H2O): m/z (%) = 683 (100) [M+], 637 (59), 604 (4). –
Fluorescence (CHCl3): λmax,em = 579 nm, Φ = 0.45. –
C33H22Br2N4O3 (682.4): calcd. C 58.09, H 3.25, Br 23.42,
N 8.21; found C 58.18, H 3.38, Br 23.67, N 8.10.
Transformation of aminal esters 7a,b into imidazolium salts
8a,b employing BF3-etherate or gaseous hydrogen chloride
To a solution of 0.35 mmol of the correspoding azaan-
thraquinone 7 in dry toluene an equimolar amount of BF3-
etherate was dropped slowly. Alternatively, gaseous hydro-
gen chloride was passed into the solution of 7. Immediately,
yellow precipitates were obtained which were filtered off,
washed with n-heptane and dried.
Cyclization of azaanthraquinones 3a,b with triethyl ortho-
formate to aminal esters 7a,b
Imidazolium salt 8a (tetrafluoroborate)
A mixture of 0.35 mmol of the appropriate azaan-
thraquinone 3 und 15 ml of triethyl orthoformate was heated
at reflux for about 14 h. The solvent was removed in vacuo
and the crude product was purified by column chromatogra-
phy on alumina (CHCl3/n-heptane: 1/1).
Yield: 263 mg (83%); yellow product, decomposition at
312 – 317 ◦C. – UV/vis (THF): λmax (lgε) = 371 (4.0),
483 nm (4.0). – 1H NMR (400 MHz, [D8]-THF): δ =
7.33 (d, 3J = 8.0 Hz, 2 H), 7.56 (d, 3J = 8.0 Hz, 2 H),
7.68 – 8.04 (m, 9 H), 8.23 (d, 3J = 8.0 Hz, 1 H), 8.51 –
8.59 (m, 1 H); 8.86 (d, 3J = 8 Hz, 1 H), 10.42 (s, 1
H). – MS (micro-ESI, THF): m/z (%) = 731 (100) [M+],
685 (13). – C31H18B2F8I2N4O2 (905.9): calcd. C 41.10,
H 2.00, N 6.18; found C 40.86, H 2.27, N 5.87.
2-Ethoxy-1,3-bis(4-iodophenyl)-5-pyridin-2-yl-2,3-dihydro-
1H-1,3,4-triazacyclopenta[a]-anthracene-6,11-dione (7a)
Yield: 185 mg (68%); orange powder, decomposition at
256 – 263 ◦C. – UV/vis (acetonitrile): λmax (lgε) = 370 (3.9),
1
479 nm (4.1). – H NMR (250 MHz, CDCl3): δ = 1.13 (t,
Imidazolium salt 8b (tetrafluoroborate)
3J = 7.0 Hz, 3 H), 3.26 (m, 1 H), 3.51 (m, 1 H), 6.84 (s, 1 H),
6.92 (s, br, 2 H), (d, 3J = 7.6 Hz, 1 H), 7.48 (d, 3J = 7.8 Hz, 1
Yield: 225 mg (79%); yellow product, decomposi-
H), 7.64 – 7.59 (m, 6 H), 7.82 – 7.75 (m, 3 H), 7.97 – 7.93 (m, tion at 305 – 308 ◦C. – UV/vis (THF): λmax (lgε) =
3
1 H), 8.05 – 8.02 (m, 1 H), 8.61 (d, J = 4.90 Hz, 1 H). – 370 (3.9), 483 nm (4.0). – 1H NMR (250 MHz, [D8]-
13C NMR (62.5 MHz, CDCl3): δ = 14.6, 56.0, 101.8, 117.9, THF): δ = 7.32 – 7.47 (m, 2 H), 7.61 – 7.72 (m, 4 H),
118.3, 118.8, 119.1, 121.5, 122.4, 122.8, 126.6, 126.8, 127.3, 7.80 – 8.05 (m, 8 H), 8.16 (d, 3J = 8.0 Hz, 1 H), 8.47 –
128.2, 129.0, 133.5, 133.7, 134.1, 134.5, 136.6, 136.8 141.9, 8.53 (m, 2 H); 8.80 (d, J = 8 Hz, 1 H), 10.45 (s, 1 H).
149.1, 152.3, 152.8, 159.7, 181.1, 181.7. – MS (DCI, H2O): – MS (micro-ESI, THF): m/z (%) = 639 (100) [M++1].
Unauthenticated
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B. Frank et al. · 2-Azaanthraquinones
777
1
3
– C31H18B2F8Br2N4O2 (811.9): calcd. C 45.86, H 2.66, – H NMR (250 MHz, CDCl3): δ = 6.85 (d, J = 8.7 Hz,
N 6.90; found C 45.72, H 2.83, N 6.74.
3 H), 7.17 – 7.23 (m, 2 H), 7.46 (d, 3J = 8.3 Hz, 2 H),
7.64 – 7.73 (m, 6 H), 7.97 – 8.01 (m, 1 H), 8.10 – 8.14 (m,
1 H), 8.39 (d, 3J = 4.7 Hz, 1 H). – MS (DCI, H2O):
m/z (%) = 847 (31) [M++1]. – C36H16I2N8O2 (846.4): calcd.
C 51.09, H 1.91, I 29.99, N 13.24; found C 50.85, H 2.27,
I 29.78, N 13.08.
Cyclization of azaanthraquinones 3a,b with 2,3-dichloro-
5,6-dicyanopyrazine to compounds 9a,b and 10a,b
0,35 mmol of the corresponding azaanthraquinone 3 was
mixed with 226 mg (0,7 mmol) of Cs2CO3 in 30 ml of
toluene. After stirring for about 5 min, 70 mg (0,35 mmol)
of 2,3-dichloro-5,6-dicyanopyrazine were added. The mix-
ture was heated at reflux for about 12 h. The solvent was re-
moved in vacuo and the products were separated by column
chromatography on alumina (toluene/ethyl acetate: 10/1).
1-(4-Bromophenyl)-2-[2-(4-bromophenyl)-4,9-dioxo-3-
pyridin-2-yl-4,9-dihydro-2H-benzo-[f]isoindol-1-yl]-1H-
imidazolo[4,5-b]pyrazine-5,6-dicarbonitrile (10b)
Yield: 98 mg (33%); yellow crystals, decomposition
at 264 – 268 ◦C. – UV/vis (acetonitrile): λmax (lgε) =
335 nm (4.3). – 1H NMR (250 MHz, CDCl3): δ = 7.00 (d,
3J = 8.7 Hz, 3 H), 7.02 – 7.29 (m, 4 H), 7.52 (d, 3J =
8.7 Hz, 2 H), 7.62 – 7.72 (m, 4 H), 7.98 – 8.02 (m, 1 H),
8.11 – 8.15 (m, 1 H), 8.39 (d, 3J = 4.8 Hz, 1 H). –
13C NMR (62.5 MHz, CDCl3): δ = 113.4, 119.8, 122.3,
124.0, 124.1, 124.8, 124.9, 125.3, 126.9, 127.3, 127.4,
127.8, 127.9, 128.2, 129.0, 129.4, 130.7, 132.3, 133.1,
133.8, 134.2, 134.3, 134.4, 135.4, 136.2, 137.9, 139.7, 141.0,
147.1, 148.4, 149.4, 154.7, 179.1, 179.5. – MS (DCI, H2O):
m/z (%) = 753 (25) [M++1], 335 (21), 181 (58), 93 (100). –
C36H16Br2N8O2 (752.4): calcd. C 57.47, H 2.14, Br 21.24,
N 14.89; found C 57.19, H 2.30, Br 21.13, N 15.09.
5,14-Bis(4-iodophenyl)-8,13-dioxo-7-pyridin-2-yl-
5,8,13,14-tetrahydro-1,4,5,6,14-pentaaza-pentaphene-2,3-
dicarbonitrile (9a)
Yield: 118 mg (40%); red product, decomposition at 305 –
307 ◦C. – UV/vis (acetonitrile): λmax (lgε) = 347 (4.0),
491 nm (3.9). – 1H NMR (250 MHz, CDCl3): δ = 6.91 (d,
3J = 8.7 Hz, 3 H), 7.09 – 7.30 (m, 4 H), 7.54 – 7.80 (m,
7 H), 7.85 (m, 1 H), 8.45 (d, 3J = 4.5 Hz, 1 H). –
13C NMR (62.5 MHz, CDCl3): δ = 92.3, 94.2, 112.0, 112.1,
121.9, 122.7, 123.6, 124.3, 124.8, 125.8, 126.3, 127.2, 128.0,
129.4, 129.6, 132.2, 132.5, 133.0, 133.4, 136.9, 137.4, 138.3,
139.0, 143.7, 145.1, 147.3, 147.5, 153.4, 155.5, 179.9, 180.7.
– MS (DCI, H2O): m/z (%) = 847 (17) [M+], 237 (42),
219 (100). – Fluorescence (CHCl3): λmax,em = 594 nm,
Φ = 0.07. – C36H16I2N8O2 (846.4): calcd. C 51.09, H 1.91,
I 29.99, N 13.24; found C 50.87, H 2.08, I 29.74, N 13.01.
2-Ethoxy-5-pyridin-2-yl-1,3-bis(4-trimethylsilanylethynyl-
phenyl)-2,3-dihydro-1H-1,3,4-triaza-cyclopenta[a]anthra-
cene-6,11-dione (12a)
5,14-Bis(4-bromophenyl)-8,13-dioxo-7-pyridin-2-yl-
5,8,13,14-tetrahydro-1,4,5,6,14-pentaaza-pentaphene-2,3-
dicarbonitrile (9b)
A solution of 200 mg (0.26 mmol) of azaanthraquinone
7a in 10 ml of triethylamine and 10 ml of THF was de-
gassed and then 76 mg (0.77 mmol) of trimethylsilylacety-
lene, 18 mg (5 mol%) of dichlorobis(triphenylphosphane)-
palladium(II) und 10 mg (10 mol%) of copper(I) iodide
were added. After heating for 5 h at 60 ◦C the reaction
was completed. Purification by column chromatography on
alumina (toluene/ethyl acetate: 20/1) gave 149 mg (80%)
of a red product, decomposition at 296 – 301 ◦C. –
UV/vis (acetonitrile): λmax (lgε) = 358 (4.1), 468 nm (4.0). –
1H NMR (250 MHz, CDCl3): δ = 0.08 (m, 18 H), 1.11 (t,
3J = 7.5 Hz, 3 H), 3.34 (m, 1 H), 3.52 (m, 1 H), 6.71 (s,
1 H), 6.99 – 7.51 (m, 9 H), 7.66 – 7.90 (m, 6 H), 8.5 (d,
3J = 4.8 Hz, 1 H). – 13C NMR (62.5 MHz, CDCl3): δ = 0.1,
14.6, 56.1, 86.0, 88.0, 94.5, 94.6, 101.7, 104.7, 116.5, 119.0,
119.4, 120.3, 122.9, 123.4, 125.5, 126.5, 127.0, 127.3, 127.7,
128.4, 128.6, 132.0, 132.1, 132.4, 132.9, 133.5, 133.8, 134.0,
134.4, 136.7, 136.9, 141.9, 144.9, 149.3, 152.3, 159.4, 180.8,
181.6 ppm. – MS (DEI): m/z (%) = 716 (15) [M+], 671 (100),
432 (21). – Fluorescence (CHCl3): λmax,em = 579 nm, Φ =
Yield: 100 mg (38%); red product, decomposition at
300 – 307 ◦C.- UV/vis (acetonitrile): λmax (lgε) = 345 (4.1),
491 nm (4.1). – 1H NMR (250 MHz, CDCl3): δ = 7.02 –
7.33 (m, 7 H), 7.44 – 7.62 (m, 6 H), 7.70 (d, 3J = 7.7 Hz,
1 H), 7.85 (d, 3J = 7.5 Hz, 1 H), 8.45 (d, 3J = 4,5 Hz,
1 H). – 13C NMR (62.5 MHz, CDCl3): δ = 112.0, 112.1,
120.8, 121.9, 122.5, 122.7, 123.6, 123.7, 124.3, 124.8, 125.8,
126.3, 127.2, 128.0, 129.2, 129.6, 131.4, 132.3, 132.5, 132.9,
135.9, 136.3, 143.8, 145.1, 147.3, 147.6, 153.5, 155.5, 179.9,
180.7. – MS (DCI, H2O): m/z (%) = 753 [M+], 399, 93.
– Fluorescence (CHCl3): λmax,em = 596 nm, Φ = 0.10. –
C36H16Br2N8O2 (752.4): calcd. C 57.47, H 2.14, Br 21.24,
N 14.89; found C 57.19, H 2.38, Br 21.01, N 14.73.
1-(4-Iodophenyl)-2-[2-(4-iodophenyl)-4,9-dioxo-3-
pyridin-2-yl-4,9-dihydro-2H-benzo[f]-isoindol-1-yl]-
1H-imidazolo[4,5-b]pyrazine-5,6-dicarbonitrile (10a)
Yield: 104 mg (35%); yellow crystals, decomposition at 0.25. – C43H40N4O3Si2 (717.0): calcd. C 72.03, H 5.62,
259 – 267 ◦C. – UV/vis (acetonitrile): λmax (lgε) = 334 (4.2). N 7.81; found C 71.85, H 5.82, N 8.03.
Unauthenticated
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778
B. Frank et al. · 2-Azaanthraquinones
2-Ethoxy-5-pyridin-2-yl-1,3-bis-(4-triisopropyl
silanylethynyl-phenyl)-2,3-dihydro-1H-1,3,4-triaza-
cyclopenta[a]anthracene-6,11-dione (12b)
1,3-Bis[4-(4-aminophenylethynyl)phenyl]-2-ethoxy-
5-pyridin-2-yl-2,3-dihydro-1H-1,3,4-triaza-
cyclopenta[a]anthracene-6,11-dione (12c)
To a degassed suspension of 300 mg (0,39 mmol)
A suspension of 300 mg (0.39 mmol) of 7a in 40 ml of 7a in 10 ml of triethylamine and 10 ml of toluene,
of THF and 5 ml of triethylamine was degassed for 91 mg (0.78 mmol) of 4-ethynylaniline, 27 mg (5 mol%)
10 min and then 211 mg (1.16 mmol) of triisopropylacety- of PdCl2(PPh3)2 and 15 mg (10 mol%) of CuI were
lene, 27 mg (5 mol%) of dichlorobis(triphenylphosphane)- added. Immediately, a deep red product precipitated fr◦om
the deeply orange solution. After 3 h of heating to 60 C,
palladium(II) and 15 mg (10 mol%) of CuI were added.
The orange mixture was heated at reflux for about 4 h un- the reaction was completed. The solvent was removed in
til it became clear and was red colored. The solution was vacuo and the crude product was purified by column chro-
matography on alumina (toluene/ethyl acetate: 8/1) to yield
cooled to r.t. and the solvent was removed in vacuo. Purifica-
tion by column chromatography on silica (toluene/ethyl ac- 235 mg (80%) of a red product, decomposition at 305 –
etate: 5/1) gave 293 mg (85%) of a red product, decompo- 308 ◦C. – UV/vis (acetonitrile): λmax (lgε) = 325 (4.8),
369 (4.1). – 1H NMR (250 MHz, CDCl3): δ = 1.11 (t,
sition at 298 – 314 ◦C. – UV/vis (acetonitrile): λmax (lgε) =
373 (4.1), 482 nm (4.1). – H NMR (250 MHz, CD2Cl2): 3J = 7.0 Hz, 3 H), 3.31 (m, 1 H), 3.54 (m, 1 H), 3.78 (s, 4
δ = 0.01 (m, 36 H), 1.11 (t, 3J = 7.5 Hz, 3 H), 1.47 (m, 6 H), H), 6.54 – 6.58 (m, 4 H), 6.92 (s, 1 H), 7.09 – 7.36 (m, 7 H),
1
7.43 (d, 3J = 8.9 Hz, 4 H), 7.52 (d, 3J = 7.8 Hz, 1 H), 7.59 –
3.28 (m, 1 H), 3.51 (m, 1 H), 6.90 (s, 1 H), 7.11 – 7.47 (m,
8 H), 7.61 – 7.65 (m, 2 H), 7.78 (m, 1 H), 7.91 – 7.97 (m, 7.63 (m, 2 H), 7.83 (m, 1 H), 7.92 – 8.06 (m, 4 H), 8.63 (d,
4 H), 8.54 (d, J = 4.3 Hz, 1 H). – 13C NMR (62.5 MHz, 3J = 4.3 Hz, 1 H). – 13C NMR (62.5 MHz, CDCl3): δ = 8.7,
3
46.2, 87.0, 90.5, 112.5, 114.7, 118.2, 119.0, 119.4, 120.3,
CD2Cl2): δ = 0.1, 10.6, 17.6, 55.4, 81.0, 89.2, 101.1, 105.8,
105.8, 117.7, 118.6, 118.8, 119.0, 119.6, 119.7, 121.8, 122.2, 121.2, 125.3, 127.0, 128.2, 129.0, 132.1, 132.9, 133.4, 133.8,
125.7, 126.1, 131.5, 132.0, 132.7, 133.1, 133.2, 133.8, 135.5, 134.6, 136.3, 136.6, 137.8, 141.2, 146.7, 149.0, 152.3, 152.6,
136.3, 141.3, 148.2, 151.6, 151.8, 159.1, 180.2, 180.9. – 159.7, 181.0, 181.8. – MS (FAB, dmba): m/z (%) = 755 (32)
MS (FAB, dmba): m/z (%) = 886 (41) [M++1], 870 (13), [M+], 336 (72), 210 (100). – C49H34N6O3 (754.8): calcd.
842 (21), 336 (84), 210 (100). – C55H64N4O3Si2 (858.3): C 77.97, H 4.54, N 11.13; found C 78.31, H 4.59, N 11.21.
calcd. C 74.62, H 7.29, N 6.33; found C 74.51,H 7.26,
Acknowledgement
N 6.58.
We thank the Deutsche Forschungsgemeinschaft (SFB
436) for financial support of our work.
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Unauthenticated
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