Synthesis and spectral properties of Azahetero-aromatic derivatives of 2-styrylanthracene

Article abstract of DOI:10.1007/s10593-013-1160-1

Novel azaheteroaromatic derivatives of 2-styrylanthracene: 2-styrylbenzo[g]quinoline and 3-styryl- acridine were obtained from 3-nitro-2-naphthaldehyde and 2-bromo-4-methylbenzoic acid. Spectral properties of the new compounds were studied.

Full text of DOI:10.1007/s10593-013-1160-1

Chemistry of Heterocyclic Compounds, Vol. 48, No. 10, January, 2013 (Russian Original Vol. 48, No. 10, October, 2012)
SYNTHESIS AND SPECTRAL PROPERTIES OF AZAHETERO-
AROMATIC DERIVATIVES OF 2-STYRYLANTHRACENE
V. M. Lee1* and M. F. Budyka1
Novel azaheteroaromatic derivatives of 2-styrylanthracene: 2-styrylbenzo[g]quinoline and 3-styryl-
acridine were obtained from 3-nitro-2-naphthaldehyde and 2-bromo-4-methylbenzoic acid. Spectral
properties of the new compounds were studied.
Keywords: 3-styrylacridine, 2-styrylanthracene, 2-styrylbenzo[g]quinoline, crotonic condensation,
Friedlander reaction.
Heterocyclic stilbene analogs are widely used as photosensitizers, organic luminophores, fluorescent
dyes, and as optical brightening agents [1]. They invariably cause much interest for many investigators as
evidenced by the large volume of work related to studying their spectral and photochemical properties. Among
their photochemical properties, the greatest interest is focused on those relating to trans-cis photoisomerization
reactions [2-4], photocycloaddition to form a cyclobutane [5-7], and electrocyclic reactions [8-10]. At this time,
azaheteroaromatic derivatives of 2-styrylanthracene remain unstudied, even though for 2-styrylanthracene itself
the so-called one-way cis-trans photoisomerization is widely known, when the reverse trans-cis
photoisomerization reaction does not occur [11]. In this work, we report the synthesis of two isomeric
azaheteroaromatic 2-styrylanthracenes, viz. 2-styrylbenzo[g]quinoline (1) and 3-styrylacridine (2).
Benzo[g]quinoline derivatives are difficult to obtain, since the majority of traditional methods for
constructing a quinoline system involve use of β-naphthylamine and lead to an angularly structured
benzo[f]quinolines [12]. An alternative method for building a linear benzoquinoline system is the Friedlander
reaction between 3-amino-2-naphthaldehyde and various ketones [13]. The Friedlander reaction can also be
used for the preparation of 2-styrylquinoline if methyl styryl ketone (benzalacetone) is used in the condensation
with 2-aminobenzaldehyde [14]. In a contemporary modification of the Friedlander reaction the
2-aminobenzaldehyde is generated in situ by reduction of 2-nitrobenzaldehyde using iron powder in acid
medium, and is then introduced into the reaction with the benzalacetone [15].
3-Nitro-2-naphthaldehyde (3) [16] was used as a starting material in the synthesis of compound 1 and
was reduced with iron powder in alcoholic medium containing about 10-2 mol/l HCl. The 3-amino-
2-naphthaldehyde (4) so obtained was introduced without isolation into the condensation with benzalacetone in
alkaline medium.
_______
*To whom correspondence should be addressed, e-mail: leevit@icp.ac.ru.
1Institute of Problems in Chemical Physics, Russian Academy of Sciences, 1 Academician Semenov Ave.,
Chernogolovka 142432, Russia.
________________________________________________________________________________________
Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1587-1591, October, 2012.
Original article submitted July 9, 2011.
0009-3122/13/4810-1477©2013 Springer Science+Business Media New York
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CHO
NH2
CHO
NO2
PhCH=CHCOMe
KOH, EtOH
Fe
HCl, EtOH
4
3
N
1
3-Styrylacridine (2) was prepared by a crotonic condensation of 3-methylacridine (5) with benzalaniline
(6) in the presence of potassium tert-butoxide and 18-crown-6.
t-BuOK, 18-crown-6
+
N
DMF
Me
N
5
6
N
2
Compound 5 was prepared from the 2-bromo-4-methylbenzoic acid (7) by a standard scheme for
construction of the acridine system [17, 18].
CO2H
CO2H
Br
1. POCl3
Cu, Cu2O
+ PhNH2
K2CO3
i-AmOH
Ph 2. HCl, H2O
Me
N
Me
H
7
O
O2
Na
5
EtOH
i-AmOH
Me
N
Me
N
H
H
1
The H NMR spectrum of compound 1 shows signals for the ethylenic H proton at 7.52 ppm and H
proton at 7.76 ppm, with J = 16.4 Hz indicating a trans-configured double bond. The large chemical shift of the
-ethylenic proton (relative to the heterocyclic ring) when compared to H has been seen before in analogous
compounds and is apparently due to formation of an N···H type intramolecular hydrogen bond between this
proton and the nitrogen atom [19-21]. In compound 2 formation of such a hydrogen bond is not possible, and its
1
ethylenic protons appear in the H NMR spectrum as a multiplet with the phenyl group protons in the region
7.37-7.45 pm.
H
H

N
N
.
.
.
H
.
H

1
2
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TABLE 1. Spectroscopic Parameters for Compounds 1 and 2 in the Neutral and Protonated Forms
Com-
Com-
λmax, nm
εmax, М-1·cm-1
λmax, nm
εmax, М-1·cm-1
pound
pound
309
322
376
338
411
48600
53700
13500
42900
34400
308
322
384
307
410
437
45100
44800
13700
29500
20900
18100
1
2
1·HCl
2·HCl
The IR spectra of both compounds show the presence of an out-of-plane C–H bond deformation
vibration band at 965-967 cm-1, and this also confirms the trans configuration of the double bond in compounds
1 and 2.
Fig. 1. Absorption spectra of compounds 1 and 2 in neutral (1, 2) and in the protonated forms 1·HCl and 2·HCl
(1', 2') in ethanol.
When comparing the absorption spectra of compounds 1 and 2 it is evident that the neutral forms show
two almost coincident long wavelength bands (Table 1 and Fig.1, spectra 1 and 2). Protonation of compound 1
causes a bathochromic shift of the long wavelength absorption band by 35 nm and a marked increase in its
intensity (Fig. 1, spectrum 1'). On the other hand, for compound 2 a small increase is observed in the long
wavelength band intensity, and a marked bathochromic shift of 53 nm (Fig. 1, spectrum 2'). This large
bathochromic shift for the compound 2 hydrochloride when compared to compound 1 hydrochloride is
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evidently due to the fact that there is a longer chain of conjugation between the styryl group and the protonated
nitrogen atom in compound 2.
Hence, using different methods of constructing heteroaromatic rings we have synthesized the trans
isomers of two 2-styrylanthracene aza analogs: 2-styrylbenzo[g]quinoline and 3-styrylacridine. Comparison of
the properties of the synthesized compounds has shown that introduction of an aza function into aromatic
systems has little effect on the absorption spectra for the neutral form. However, the protonated form spectra
depend markedly on the position of the nitrogen atom in the anthracene system (in the central or side benzene
ring).
EXPERIMENTAL
IR spectra were recorded on a Spectrum BX-2 Fourier spectrometer using KBr. Electronic absorption
1
spectra were recorded on a Specord M-400 spectrophotometer. H NMR spectra were recorded on a Bruker
Avance III spectrometer (500 MHz) using CDCl3 with TMS as internal standard. Elemental analysis was
performed on an Elementar vario MICRO cube analyzer. Melting points were determined on a Koffler hot stage
apparatus with a heating rate of 4°C/min.
2-[(E)-2-Phenylethenyl]benzo[g]quinoline (1). A mixture of 3-nitro-2-naphthaldehyde (250 mg,
1.24 mmol), powdered iron (312 mg, 5.58 mmol), 0.1 M HCl (1 ml), and EtOH (6 ml) was heated at 90-95ºC
for 2 h. A solution of benzalacetone (181 mg, 1.24 mmol) in EtOH (1.5 ml) and KOH (90 mg, 1.60 mmol) were
carefully added and heated at the same temperature for a further 2 h. The reaction mixture was cooled, diluted
with water (30 ml), and extracted with dichloromethane (3×25 ml). Solvent was evaporated in vacuo, and the
residue was treated with conc. HCl (1 ml) and washed with EtOAc. The hydrochloride obtained was neutralized
by heating with an aqueous-acetone solution of alkali, and the precipitated free base 1 was filtered off and
recrystallized from 80% EtOH. Yield 103 mg (30%). Yellow crystals; mp 163-165ºC. IR spectrum, , cm-1:
1
3054, 3028, 1635 (, C=C), 1604, 967 (, –CH=CH–), 887, 807, 744, 694. H NMR spectrum, , ppm (J, Hz):
7.39 (1H, t, J = 7.4, H Ph); 7.47 (2H, t, J = 7.5, H Ph); 7.52 (1H, d, J = 16.4, Ph–CH=CH–); 7.54-7.59 (2H, m,
H Ph); 7.70-7.73 (2H, m, H-7,8); 7.74 (1H, d, J = 8.8, H-3); 7.76 (1H, d, J = 16.4, Ph-CH=CH-); 8.06 (1H, d,
J = 9.0, H-6(9)); 8.12 (1H, d, J = 9.0, H-9(6)); 8.34 (1H, d, J = 8.9, H-4); 8.40 (1H, s, H-5); 8.69 (1H, s, H-10).
Found, %: C 89.33; H 5.48; N 4.76. C21H15N. Calculated, %: C 89.65; H 5.37; N 4.98.
3-[(E)-2-Phenylethenyl]acridine (2). A mixture of 3-methylacridine (5) (0.80 g, 4.1 mmol),
benzalaniline (6) (1.50 g, 8.3 mmol), t-BuOK (0.82 g, 7.3 mmol), 18-crown-6 (0.50 g, 1.9 mmol), and DMF
(10 ml) was heated at about 100ºC for 4 h under an argon atmosphere. The reaction mixture was cooled, treated
with water, and the precipitate formed was filtered off. The filtrate was extracted with benzene (2×30 ml).
Benzene was distilled off, and the solid residue formed was chromatographed together with the previously
isolated precipitate on silica gel with acetone–petroleum ether (1:5) as eluent. Yield 0.66 g (57%). Light-yellow
crystals; mp 159-161ºC. IR spectrum, , cm-1: 3054, 3025, 1626 (C=C), 1613, 1506, 965 (, –CH=CH–), 908,
791, 746, 693. 1H NMR spectrum, , ppm (J, Hz): 7.33 (1H, d, J = 7.4, H Ph); 7.37-7.45 (4H, m, Ph–CH=CH–
Ph, H Ph); 7.55 (1H, t, J = 7.4, H-7); 7.62 (2H, d, J = 7.3, H Ph); 7.81 (1H, t, J = 7.4, H-6); 7.85 (1H, d, J = 8.8,
H-2); 7.99-8.03 (2H, m, H-1,8); 8.24-8.30 (2H, m, H-5,9); 8.75 (1H, s, H-4). Found, %: C 89.43; H 5.25;
N 5.05. C21H15N. Calculated, %: C 89.65; H 5.37; N 4.98.
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