Syntheses, spectroscopic and crystallographic characterizations of 4-nitrobenzyloxy derivatives and benzofurans from ortho-substituted benzaldehydes and 4-nitrobenzyl bromide

Article abstract of DOI:10.1007/s11224-010-9618-6

A series of benzyloxybenzaldehyde derivatives (1-3) were prepared by the reactions of 4-nitrobenzyl bromide with 4-hydroxy-3-methoxybenzaldehyde (vanillin), 2-hydroxy-3-methoxybenzaldehyde (o-vanillin) and 2-hydroxy-4-methoxybenzaldehyde. When the reactio

Full text of DOI:10.1007/s11224-010-9618-6

Struct Chem (2010) 21:837–845
DOI 10.1007/s11224-010-9618-6
ORIGINAL RESEARCH
Syntheses, spectroscopic and crystallographic characterizations
of 4-nitrobenzyloxy derivatives and benzofurans from ortho-
substituted benzaldehydes and 4-nitrobenzyl bromide
•
Zeliha Hayvali Hakan Dal Pinar Koksal
•
•
¨
•
Duygu S¸ahin Tuncer Hokelek
¨
Received: 9 March 2010 / Accepted: 26 April 2010 / Published online: 9 May 2010
Ó Springer Science+Business Media, LLC 2010
Abstract A series of benzyloxybenzaldehyde derivatives
(1–3) were prepared by the reactions of 4-nitrobenzyl
bromide with 4-hydroxy-3-methoxybenzaldehyde (vanil-
lin), 2-hydroxy-3-methoxybenzaldehyde (o-vanillin) and
2-hydroxy-4-methoxybenzaldehyde. When the reaction
time is quite long, benzofuran derivatives (4 and 5) were
obtained by the reactions of ortho-hydroxyaldehydes with
the 4-nitrobenzyl bromide. Condensation reactions among
the three benzyloxybenzaldehyde derivatives (1–3) with
2-aminomethylfuran (furfurylamine) yielded the new imine
compounds (6–8). The structures of these aldehydes (1–3),
benzofuran derivatives (4 and 5) and imine compounds
(6–8) were confirmed on the basis of elemental analyses,
Introduction
Imine compounds and their metal complexes play an
important role in development of the coordination chem-
istry, resulting in an enormous number of publications,
biochemical relevant studies of metal complexes and found
wide range of applications [1–9]. Vanilline and furfuryl-
amine Schiff base derivatives are very useful biochemical
materials having biological activities [10, 11].
The benzofurans are important heterocyclic compounds,
which not only act as key structural subunits in naturally
occurring compounds that exhibit remarkable biological
activities but also represent useful building blocks in the
syntheses of natural products [12–14]. The benzofuran
nucleus is a central component of a diverse class of het-
erocyclic natural and synthetic products that possess a
broad range of biological activities [15, 16]. Some of
benzofuran derivatives have been used as potential positron
emission tomography tracers targeting amyloid plaques in
Alzheimer’s disease [17]. Additional structural changes to
the benzofuran derivatives may lead to the development of
useful amyloid-specific imaging agents [17].
1
IR, H NMR and 13C NMR and mass spectroscopy. The
solid-state structures of compounds 4–6 were determined
by single-crystal X-ray crystallography.
Keywords Cyclization reactions Á Crystal structure Á
Benzofuran compounds Á Imine compounds Á
Benzyloxy derivatives
Consequently, there has been growing interest in
developing general and versatile synthetic methods for
benzofuran derivatives [18–20]. Recently, the synthetic
methods for the construction of benzofurans mainly are
dehydrative cyclization of a-(phenoxy)-alkyl ketones [21],
decarboxylation of o-acylphenoxyacetic acids or esters
[22], phosphazene base catalyzed intramolecular cycliza-
tion for efficient synthesis of benzofurans [23], one-pot
synthesis under microwave irradiation and solvent-free
conditions [24], etc. The intramolecular cyclization reac-
tion of ortho-substituted benzaldehydes via a carbon–
oxygen bond (C–O) formation is one of the simplest
and most efficient methods for preparing benzofurans.
¨
Z. Hayvali (&) Á P. Koksal Á D. S¸ahin
Department of Chemistry, Faculty of Science,
Ankara University, 06100 Ankara, Turkey
e-mail: zhayvali@science.ankara.edu.tr
H. Dal
Department of Chemistry, Faculty of Science,
Anadolu University, 26470 Eskisehir, Turkey
¨
T. Hokelek
Department of Physics, Hacettepe University,
06800 Ankara, Turkey
123

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Struct Chem (2010) 21:837–845
Scheme 1 Structures of the
aldehydes (1–3), benzofurans
(4 and 5) and Schiff bases
(6–8)
Benzyloxybenzaldehydes
Benzofurans
Schiff bases
(1-3)
(4 and 5)
(6-8)
O
CHO
O
CH
N
O
O2
N
CH2
O2N
CH2
O
O
CH3
CH3
-
(1)
(6)
O
O2N
N
OHC
O
HC
OCH3
O
O
O2N
O
CH2
CH2
O2N
O
CH3
CH3
(2)
(4)
(7)
O
OHC
O2N
N
HC
O
O2N
OCH3
O
O
CH2
O2N
CH2
OCH3
OCH3
(3)
(5)
(8)
This reaction is effective when at least one of the substit-
uents on the benzyl subunit is an electron-withdrawing
group, such as a nitro or cyano group [25]. The catalytic
cyclization reaction of benzyloxybenzaldehyde was suc-
cessfully demonstrated using a base as the catalyst.
from Aldrich and used without further purification.
CH3CN, THF, DMF and EtOH were dried by standard
methods prior to use. Melting points were measured on a
Thomas-Hoover apparatus using a capillary tube. 1H NMR
and 13C NMR spectra were obtained on a Bruker DPX FT-
NMR (500 MHz) spectrometer (SiMe4, as internal stan-
dard). Chemical shifts for proton and carbon resonances
were reported in ppm (d). IR spectra were obtained from a
PEL-DATA spectrum 100 series spectrometer. Carbon,
nitrogen and hydrogen analyses were performed on a
LECO CHNS-932 elemental analyzer. Mass spectrometric
analysis was performed on the AGILEND 1100 MSD
spectrometer. All chemicals were of reagent grade.
Solvents were dried and distilled before use according to
standard procedures.
We have reported the syntheses of benzofuran deriva-
tives (4 and 5) without the need for a base catalyst. The
cyclization reactions were achieved by the long reaction
time. We synthesized the benzyloxybenzaldehyde deriva-
tives (1–3) in the same reaction conditions, but at a shorter
reaction than that of the cyclization reactions for getting 4
and 5. Condensation reactions among the three benzyl-
oxybenzaldehyde derivatives (1–3) with 2-aminomethylfu-
ran yielded new imine compounds (6–8). The aldehydes
(1–3), benzofuran derivatives (4 and 5) and Schiff bases
(6–8) (Scheme 1) have been characterized by the elemental
1
analyses, IR, H NMR and 13C NMR and MS. We have
X-ray crystallography
also determined the crystal structures of 4–6 by using
X-ray crystallographic techniques.
Crystallographic data were collected on a Bruker Kappa
APEXII diffractometer using Mo Ka radiation (k =
˚
0.71073 A) at T = 100 K (for 4 and 6) and at T = 296 K
Experimental
(for 5). Absorption corrections by multi-scan [26] (for 4–6)
were applied. Structures were solved by direct methods
[27] and refined by full-matrix least squares against F2
using all data [27]. All non-H atoms were refined aniso-
tropically. For compound 4, the H13 atom position was
General remarks
4-Nitrobenzyl bromide, 4-hydroxy-3-methoxybenzaldehyde
(vanillin), 2-hydroxy-3-methoxybenzaldehyde (o-vanillin)
and 2-hydroxy-4-methoxybenzaldehyde were purchased
˚
calculated geometrically at a distance of 0.93 (CH) A from
the parent atom; a riding model was used during the
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Struct Chem (2010) 21:837–845
839
refinement process and the Uiso(H) value was constrained
to be 1.2Ueq(carrier atom). The remaining H atoms were
located on a difference Fourier map and refined isotropi-
cally. For compound 5, H atoms’ positions were calculated
geometrically at the distances of 0.93 (CH) and 0.96
analysis were obtained by slow evaporation of ethanol at
room temperature.
Result and discussion
˚
(CH3) A from the parent atoms; a riding model was used
during the refinement process and the Uiso(H) values were
constrained to be 1.2Ueq(CH) and 1.5Ueq(CH3). For com-
pound 6, H atoms were located on a difference Fourier map
and refined isotropically.
Syntheses
The synthetic procedure for the preparation of the ben-
zyloxybenzaldehydes (1–3) consists of two steps. Firstly,
4-hydroxy-3-methoxybenzaldehyde, 2-hydroxy-3-methox-
ybenzaldehyde and 2-hydroxy-4-methoxybenzaldehyde
were reacted with NaOH in DMF to give the corresponding
sodium alkoxide. Secondly, the obtained sodium salts were
converted to the corresponding new benzyloxybenzalde-
hydes (1–3) by reacting with 4-nitrobenzyl bromide. The
compounds (2 and 3) were successfully synthesized with
yields in the range 44–48% (Scheme 2a). Compound 1 was
synthesized according to the previously published proce-
dure [28–30] by using different solvents and bases in the
reactions.
Syntheses of the benzyloxybenzaldehydes (1–3),
benzofurans (4, 5) and Schiff bases (6–8)
General methods for preparing the compounds (1–3)
The corresponding vanillin or methoxysalicylaldehyde
derivatives (1.0 mmol) were dissolved in DMF (15 cm3).
NaOH (2.2 mmol) was added in small amounts, and the
resulting reaction mixture was refluxed for 1 h. Subse-
quently, p-nitrobenzyl bromide (2.2 mmol) in DMF
(15 cm3) was added dropwise to the reaction mixture. The
resulting solution was refluxed for 5 h, then the complete
consumption of the starting material was observed by TLC
(silica, eluent; THF). Then, water was added until the
solution turned cloudy. The yellow precipitate formed was
isolated and recrystallized from ethanol.
The intramolecular cyclization reactions of substituted
benzaldehydes via a C–O formation are one of the simplest
and most efficient methods for preparing benzofurans. In
these reactions, electron-withdrawing groups such as nitro
or cyano substituted benzaldehydes were used and potas-
sium tert-butoxide and sodium ethoxide are typically used
to promote these reactions [31].
Herein, we report cyclization reactions of nitrobenzyl
bromide with methoxy salicylaldehyde derivatives via C–O
forming reactions. –OCH3-substituted benzofuran deriva-
tives (4 and 5) were prepared in DMF with NaOH base
(Scheme 2b). If the reaction time is short enough then the
benzyloxybenzaldehyde is formed, but if the reaction time
is quite long then the cyclization reaction is formed, in the
same reaction conditions. On the other hand, we also
observed that this reaction afforded benzofuran in better
yields in the absence of any organic base as catalyst.
Substituted benzyloxybenzaldehydes (1–3) were allowed
to react with furfurylamine to afford corresponding Schiff
bases (6–8). Analytical physical data of aldehydes (1–3),
benzofuran derivatives (4 and 5) and Schiff bases (6–8) are
given in Table 1. All of the compounds have been fully
characterized by melting points, elemental analyses, mass
spectrometry, IR, 1H NMR and 13C NMR spectroscopies.
General methods for preparing the compounds (4 and 5)
The corresponding 2-hydroxy-3-methoxybenzaldehyde or
2-hydroxy-4-methoxybenzaldehyde (1.0 mmol) was dis-
solved in DMF (15 cm3). NaOH (2.2 mmol) was added in
small amounts and the resulting solution was refluxed for
1 h. Subsequently p-nitrobenzyl bromide (2.2 mmol) in
DMF (15 cm3) was added dropwise to the reaction mix-
ture. The resulting solution was refluxed for 38 h where-
upon the cyclized products (4 and 5) were obtained by the
addition of water and the crude product was recrystallized
from acetone. Single crystals of benzofurans (4 and 5)
suitable for X-ray analyses were obtained by slow evapo-
ration of an acetone solution.
General methods for preparing the compounds (6–8)
The corresponding aldehydes (1–3) (1.0 mmol) were dis-
solved in EtOH (20 cm3). Furfuryl amine (1.0 mmol) was
dissolved in EtOH and added dropwise. The resulting
solution was stirred under reflux for 2 h and the reaction
mixture was allowed to stand 2 h at room temperature.
Yellow crystals formed and these were recrystallized from
EtOH. Single crystals of compound 6 suitable for X-ray
Mass spectra
The mass spectra of the aldehyde (2), benzofuran deriva-
tive (5) and imine compounds (6–8) are summarized in
Table 1. The mass spectrum of compound 2 displayed the
expected molecular ion peak at m/z 288 [M?1]? [the
highest peak in a multiplet, 100%, in the mass spectrum
123

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Struct Chem (2010) 21:837–845
OHC
O
Scheme 2 (a) Syntheses of
aldehydes (2 and 3);
(b) syntheses of benzofurans
(4 and 5)
DMF, 5h
CH2
O2N
(a)
OCH3
(
)
2, 3
Br
+
-
Na
O
O2N
OH
NaOH
CHO
CHO
H3CO
H3CO
(b)
O
O2N
DMF, 38h
OCH3
(
)
4, 5
Table 1 Physical characterization and analytical data of compounds (1–8)
Comp.
Colour
m.p. (°C)
Yield (%)
Elemental analyses (%) found (Calcd.)
Found (Calcd.) [M?1]?
M
C
H
N
1
2
3
4
5
6
7
8
Yellow
Yellow
Yellow
Brown
Yellow
Yellow
Yellow
Yellow
118
40
44
48
40
47
56
49
62
62.53 (62.72)
63.03 (62.72)
62.98 (62.72)
67.12 (66.91)
67.23 (66.91)
66.01 (65.57)
65.23 (65.57)
65.72 (65.57)
4.66 (4.56)
4.38 (4.56)
4.81 (4.56)
4.36 (4.12)
4.41 (4.12)
5.09 (4.95)
5.17 (4.95)
5.31 (4.95)
4.91 (4.88)
5.13 (4.88)
4.79 (4.88)
5.11 (5.20)
5.19 (5.20)
7.34 (7.65)
7.13 (7.65)
7.48 (7.65)
(287)
(287)
103–106
144–145
167–170
160–161
126–127
100–103
153–155
288 (287)
(269)
270 (269)
367 (366)
367 (366)
367 (366)
NMR spectra
obtained using the (APCI) MS technique]. The mass
spectrum of compound 5 displayed the expected molecular
ion peak at m/z 270 [M?1]? [the highest peak in a mul-
tiplet, 100%, in the mass spectrum obtained using the
(API-ES) MS technique]. The molecular ion peaks for the
Schiff bases (6–8) were observed at m/z 367 [M?1]?
(APCI) [the highest peak in a multiplet, 100%], consistent
with the proposed structure.
1
The H NMR chemical shifts of compounds (1–8) were
recorded in CDCl3 solution (Table 3). The 1H NMR
spectra of the aldehydes (1–3), benzofurans (4 and 5) and
imine compounds (6–8) show singlets at 4.00, 3.96, 3.89,
4.18, 3.92, 3.98, 3.93 and 3.90 ppm, respectively, corre-
sponding to –OCH3 protons. The aromatic protons of
aldehydes, benzofurans and imine compounds appear as
multiplets in the ranges of 6.46–8.34 (for 1–3), 6.91–8.33
(for 4 and 5) and 6.30–8.25 ppm (for 6–8), respectively.
The singlets at 9.92, 10.38 and 10.42 ppm belonging to
aldehyde protons (–CHO) (for 1–3) disappear after the
cyclization reaction for compounds (4 and 5). Furthermore,
the singlets at 5.38, 5.32 and 5.30 ppm belonging to
–OCH2 protons appear for compounds (1–3), but they
disappear for compounds (4 and 5), as expected. For the
Schiff base compounds (6–8), the characteristic azome-
thine protons (HC=N) were observed as singlets at 8.26,
8.14 and 8.32 ppm, respectively. The observations of
furfurylamine N–CH2 protons at 4.78 (for 6), 4.74 (for 7)
and 4.79 (for 8) ppm indicate the imine compounds.
The 13C NMR data of compounds (1–8) were recorded
in CDCl3 solution (Table 4). In all of the compounds (1–8),
IR spectra
The main vibration frequencies of the benzyloxybenzal-
dehydes (1–3), benzofuran derivatives (4 and 5) and Schiff
bases (6–8) were listed in Table 2. In the IR spectra of
aldehydes (1–3), the aliphatic t(C–H) vibrations exerted by
–OCH2 and –OCH3 groups were observed in 2939–
2828 cm-1. Furthermore, characteristic aldehyde t(C=O)
vibrations for carbonyl groups were observed at 1698, 1698
and 1685 cm-1, respectively. But, in the benzofuran
derivatives (4 and 5), none of the t(C=O) bands were
observed. In the imine compounds 6–8, the relatively
strong bands attributable to t(C=N) were detected at 1638,
1633 and 1635 cm-1, respectively.
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Struct Chem (2010) 21:837–845
841
Table 2 IR spectra (4000–400 cm-1) of compounds (1–8)
Comp.
t(C–H)aliph.
t(C=O)
t(C–O)
t(C=N)
t(C=C)
t(NO2)
1
2939;2834 (w)
1698 (s)
1282;1266 (s)
1135;1029 (s)
1270;1251 (s)
1188;1062 (m)
1299;1268 (m)
1193;1023 (m)
1272;1219 (s)
1183;1101 (s)
1284;1221 (s)
1148;1107 (s)
1269;1243 (s)
1129;1032 (s)
1267;1214 (s)
1076;1023 (s)
1292;1209 (s)
1121;1036 (s)
–
1585 (s)
1516;1343 (s)
1516;1349 (s)
1524;1343 (s)
1521;1330 (s)
1505;1336 (s)
1516;1340 (s)
1510;1342 (s)
1504;1342 (s)
2
3
4
5
6
7
8
2934;2838 (w)
2936;2828 (w)
2968;2902 (m)
2969;2902 (m)
2936;2859 (w)
2970;2902 (m)
2980;2845 (m)
1698 (s)
–
1586 (m)
1685 (s)
–
1581 (m)
–
–
–
–
–
–
1605;1591 (s)
1623;1596 (s)
1597 (m)
–
1638 (s)
1633 (m)
1635 (m)
1580 (m)
1581 (m)
w weak, m medium, s strong
Table 3 1H NMR spectral data
Comp. OCH3
OCH2
CHO
HC=N
N–CH2
Ar–H1,3
Ar–H2,4
Ar–H
1
2
3
4
5
6a
7
8
4.00 (s, 3H) 5.38 (s, 2H) 9.92 (s, 1H)
3.96 (s, 3H) 5.32 (s, 2H) 10.38 (s, 1H)
3.89 (s, 3H) 5.30 (s, 2H) 10.42 (s, 1H)
–
–
–
–
–
–
–
–
–
–
8.28 (s, 2H) (J = 8.6 0.3) 7.67 (s, 2H) 6.97–7.48 (m, 3H)
8.26 (s, 2H) (J = 8.3 0.3) 7.68 (s, 2H) 7.24–7.46 (m, 3H)
8.31 (s, 2H) (J = 8.5 0.3) 7.65 (s, 2H) 6.46–7.90 (m, 3H)
8.32 (s, 2H) (J = 9.0 0.3) 8.04 (s, 2H) 6.91–7.25 (m, 4H)
8.32 (s, 2H) (J = 8.9 0.3) 7.96 (s, 2H) 6.93–7.53 (m, 4H)
4.18 (s, 3H)
3.92 (s, 3H)
–
–
–
–
–
–
–
3.98 (s, 3H) 5.31 (s, 2H)
3.93 (s, 3H) 5.19 (s, 2H)
3.90 (s, 3H) 5.31 (s, 2H)
8.26 (s, 1H) 4.78 (s, 2H) 8.26 (s, 2H) (J = 8.9 0.3) 7.65 (s, 2H) 6.30–7.53 (m, 6H)
8.14 (s, 1H) 4.74 (s, 2H) 8.26 (s, 2H) (J = 7.5 0.3) 7.62 (s, 2H) 6.22–7.58 (m, 6H)
8.32 (s, 1H) 4.79 (s, 2H) 8.30 (s, 2H) (J = 8.6 0.3) 7.63 (s, 2H) 6.48–7.44 (m, 3H)
1
2
NO
2
3
4
Chemical shifts (d) are reported in ppm, coupling constants (J) are given in Hz, multiplicity is indicated as follows (s singlet, d doublet,
m multiplet)
a
HC=N peak overlapping with Ar–H1,3 peaks
the characteristic aliphatic –OCH3 carbons were detected at
56.11, 56.14, 55.74, 56.12, 55.77, 56.09, 56.13 and
55.55 ppm, respectively. The aldehyde carbons (–CHO) of
compounds (1–3) were observed at 190.75, 189.65 and
187.75 ppm, respectively. The signals of the aromatic
carbons were detected in the expected region, and equal to
the number in the proposed structures of compounds (1–8).
As expected, the imine carbons (HC=N) of the compounds
(6–8) were observed at 162.32, 158.64 and 158.04 ppm,
respectively.
X-ray crystallographic characterizations of compounds
(4–6)
The molecular and solid-state structures of compounds 4, 5
and 6 confirm the assignments of their structures from
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Struct Chem (2010) 21:837–845
Ar–CH
Table 4 13C NMR spectral
data
Comp.
OCH3
56.11
OCH2
69.61
CHO
HC=N
–
N–CH2
–
1
190.75
109.74; 112.58; 123.98; 124.00
126.27; 127.54; 128.00; 13.99
143.45; 147.81; 150.20; 152.82
113.62; 118.66; 123.80; 123.99
124.27; 124.78; 125.35; 126.19
128.39; 129.99; 144.07; 152.78
99.46; 106.32; 119.40; 124.03
124.35; 124.58; 127.54; 131.41
143.25; 147.84; 161.81, 166.07
105.40; 107.00; 107.78; 113.81
124.00; 124.25; 125.32
2
3
4
56.14
55.74
56.12
74.60
69.08
–
189.65
187.75
–
–
–
–
–
–
–
125.98 130.33; 136.14
144.88; 145.52 147.30; 153.38
95.56; 105.23; 113.02; 121.84
124.36; 124.59; 124.98; 126.02
130.36; 135.94; 144.876 145.76;
148.12; 152.98
5
6
7
8
55.77
56.09
56.13
55.55
–
–
–
–
–
–
–
69.70
74.19
69.07
163.32
158.64
158.04
57.02
57.39
55.75
107.49; 109.67; 111.38; 113.15
123.13; 123.87; 123.98; 127.54
128.00; 130.39; 142.22; 144.18
147.68; 149.94; 150.03; 152.42
107.64; 110.38; 114.61; 119.23
123.68; 124.26; 124.72; 125.34
128.47; 129.94; 142.22; 144.59
147.48; 147.68; 152.20; 152.50
99.54; 106.17; 113.02; 123.94
124.04; 124.59; 127.51; 13143
142.20; 143.25; 143.87; 147.70
147.83; 158.04; 161.80; 166.08
Chemical shifts (d) are reported
in ppm
spectroscopic data. Brown crystals of 4 and yellow crystals
of 5 and 6 were grown from acetone solutions (for 4 and 5)
and ethanol (for 6) at room temperature. Crystallographic
data are listed in Table 5 and selected bond lengths and
angles are given in Table 6. The molecular structures of 4, 5
and 6 along with the atom-numbering schemes were depicted
in Figs. 1a, 2a and 3a, respectively. In compounds 4 and 5,
rings A (C1–C6), B (O3/C7–C10) and C (C9–C14) are, of
course, planar and they are oriented at dihedral angles of
A/B = 3.30(5)°, A/C = 2.78(5)° and B/C = 0.56(4) (for
compound 4) and A/B = 7.45(5)°, A/C = 7.52(5)° and
B/C = 0.49(5) (for compound 5). So, the rings in compound
4 are more coplanar with respect to the rings in compound 5,
depending on the positions of the methoxy groups (Figs. 1a
and 2a). In compound 5, intramolecular C–HÁÁÁO hydrogen
bond (Table 7) results in the formation of a five-membered
ring D (O3/H3/C3–C7) adopting envelope conformation
5, intermolecular C–HÁÁÁO hydrogen bonds (Table 7)link the
molecules into centrosymmetric dimers (Fig. 1b) (for com-
pound 4), and into infinite chains along the c-axis (Fig. 2b)
(for compound 5), in which they may be effective in the
stabilizations of the structures. The p–p contacts between the
rings, Cg1–Cg2i and Cg1–Cg3ii [i x, y - 1, z; ii x, y ? 1, z]
(for compound 4) and Cg1–Cg2iii and Cg1–Cg3iii [iii -x, -y,
-z] (for compound 5) [where Cg1, Cg2 and Cg3 are the
centroids of the rings A (C1–C6), B (O3/C7–C10) and C
(C9–C14), respectively] may further stabilize the structures
˚
with centroid–centroid distances of 3.653(1) and 3.645(1) A
˚
(for compound 4) and 3.650(1) and 3.708(1) A (for com-
pound 5), respectively. In addition, there also exist weak
C–HÁÁÁp interactions (Table 7) involving the A, B and C
rings of compounds 4 and 5. In compound 6, rings A (C1–
C6), B (C8–C13) and C (O5/C16–C19) are, of course, planar
and they are oriented at dihedral angles of A/B = 1.60(5)°,
A/C = 84.03(5)° and B/C = 85.09(6)°. Intramolecular
C–HÁÁÁO hydrogen bond (Table 7) results in the formation of
˚
with O3 atom displaced by –0.145(1) A from the plane of the
other ring atoms. In thecrystal structures of compounds 4and
123

Struct Chem (2010) 21:837–845
843
Table 5 Crystallographic data
for compounds (4, 5 and 6)
4
5
6
Empirical formula
Fw
C15H11NO4
269.25
765429
Monoclinic
P21/n
C15H11NO4
269.25
765430
Monoclinic
P21/c
C20H18N2O5
366.36
765431
Monoclinic
P21/c
CCDC numbers
Crystal system
Space group
˚
a (A)
13.3227(3)
6.0544(2)
15.7423(3)
90.00
8.7018(2)
10.9178(3)
13.1787(3)
90.00
12.0422(6)
11.9311(6)
13.3770(7)
90.00
˚
b (A)
˚
c (A)
a (°)
b (°)
c (°)
109.997(3)
90.00
92.257(2)
90.00
115.765(3)
90.00
3
˚
V (A )
1193.23(6)
4
1251.06(5)
4
1730.89(16)
4
Z
l (Mo Ka) (mm-1
)
0.11
0.11
0.10
q (calcd.) (g cm-1
No. of refl. total
No. of refl. unique
Rint
)
1.499
1.429
1.406
10128
21502
15276
2968
3126
4316
0.026
0.034
0.043
2hmax (°)
56.8
56.8
56.8
T
min/Tmax
0.956/0.971
221
0.961/0.981
182
0.966/0.984
316
No. of Parameters
R [F2 [ 2r(F2)]
wR
0.044
0.045
0.045
0.120
0.123
0.114
Table 6 The selected bond
˚
lengths (A) and angles with the
4
5
6
selected torsion angles (°) for 4,
5 and 6
O1–N1
1.2285(17)
1.2297(16)
1.3865(16)
1.3709(17)
1.3625(16)
1.4309(19)
1.4672(19)
1.451(2)
O1–N1
1.223(2)
O1–N1
1.2260(17)
1.2182(18)
1.4278(18)
1.3684(17)
1.3770(18)
1.3722(19)
1.462(2)
O2–N1
O2–N1
1.220(2)
1.3896(18)
1.3739(17)
1.3695(19)
1.421(2)
O2–N1
O3–C7
O3–C7
O3–C7
O3–C10
O3–C10
O3–C8
O4–C11
O4–C12
O5–C16
O4–C15
O4–C15
O5–C19
N1–C1
N1–C1
1.465(2)
N1–C1
C7–C4
C7–C4
1.456(2)
N2–C14
1.272(2)
C7–C8
1.3591(19)
1.433(2)
C7–C8
1.340(2)
N2–C15
1.471(2)
C8–C9
C8–C9
1.432(2)
C15–C16
1.489(2)
O1–N1–O2
O1–N1–C1
O2–N1–C1
O3–C7–C4
O3–C7–C8
C4–C7–C8
C7–C8–C9
C8–C9–C10
O3–C10–C9
C7–O3–C10
C11–O4–C15
C3–C4–C7–C8
C5–C4–C7–O3
123.72(13)
118.16(12)
118.11(13)
115.96(11)
111.06(12)
132.97(13)
107.07(12)
105.18(12)
110.99(12)
105.69(10)
116.43(12)
-176.67(15)
-177.14(12)
O1–N1–O2
O1–N1–C1
O2–N1–C1
O3–C7–C4
O3–C7–C8
C4–C7–C8
C7–C8–C9
C8–C9–C10
O3–C10–C9
C7–O3–C10
C12–O4–C15
C3–C4–C7–C8
C5–C4–C7–O3
123.46(15)
118.32(16)
118.22(16)
116.38(13)
111.13(13)
132.48(14)
107.38(14)
105.38(13)
110.43(13)
105.68(11)
118.28(14)
171.88(17)
173.07(13)
C4–C7–O3
C7–O3–C8
C11–C14–N2
C14–N2–C15
N2–C15–C16
C16–O5–C19
O5–C16–C17
C16–C17–C18
C17–C18–C19
O5–C19–C18
C9–O4–C20
C4–C7–O3–C8
C16–C15–N2–C14
108.06(12)
117.39(12)
123.87(16)
116.11(15)
110.17(14)
106.57(12)
109.64(14)
107.06(15)
106.49(15)
110.24(14)
116.53(12)
178.48(12)
115.57(16)
123

844
Struct Chem (2010) 21:837–845
Fig. 2 a An ORTEP-3 [32] drawing of 5 with the atom-numbering
scheme. Displacement ellipsoids are drawn at the 50% probability
level. Hydrogen bond is shown as dashed line. b A partial packing
diagram. Hydrogen bonds are shown as dashed lines and hydrogen
atoms not included in hydrogen bonding have been omitted for clarity
˚
structure. A short O1ÁÁÁC20 [2.95 A] contact is observed. The
p–p contacts between the rings, Cg1–Cg2i and Cg1–Cg2ii
[i -x, y - ‘, ‘ -z; ii -x, -y, -z] [where Cg1 and Cg2 are
the centroids of the rings A (C1–C6) and B (C8–C13),
respectively] may further stabilize the structure with cen-
˚
troid–centroid distances of 3.588(1) and 3.712(1) A,
Fig. 1 a An ORTEP-3 [32] drawing of 4 with the atom-numbering
scheme. Displacement ellipsoids are drawn at the 50% probability
level. b A partial packing diagram [33]. Hydrogen bonds are shown as
dashed lines
respectively. In addition, there also exists a weak C–HÁÁÁp
interaction (Table 7) involving the C ring.
a five-membered ring D (O3/H5/C4/C5/C7) adopting enve-
˚
lope conformation with O3 atom displaced by -0.185(1) A
Conclusion
from the plane of the other ring atoms. In the crystal struc-
ture, intermolecular C–HÁÁÁO hydrogen bonds (Table 7) link
the molecules into a three-dimensional network (Fig. 3b), in
which they may be effective in the stabilization of the
In conclusion, the substituted benzyloxybenzaldehyde
derivatives (1–3) were prepared by reacting the appropriate
hydroxy benzaldehydes with p-nitrobenzyl bromide in
˚
Table 7 Hydrogen-bond geometry (A, °), where Cg1, Cg2 and Cg3 are the centroids of the rings A (C1–C6), B (O3/C7–C10) and C (C9–C14),
respectively (for compounds 4 and 5), while Cg3 is the centroid of ring C (O5/C16–C19) (for compound 6)
Compound
4
D–HÁÁÁA
D–H
HÁÁÁA
DÁÁÁA
D–HÁÁÁA
C15–H13ÁÁÁO4i
C12–H12ÁÁÁCg3ii
C3–H3ÁÁÁO3
0.95(2)
0.97(2)
0.93
2.51(2)
2.69(2)
2.49
3.218(2)
3.544(2)
2.809(2)
3.289(3)
3.664(2)
3.749(2)
3.354(2)
2.7048(19)
3.229(2)
3.510(2)
3.429(2)
3.952(2)
vi
131.1(17)
146.3(15)
100
5
C15–H15AÁÁÁO2iii
C2–H2ÁÁÁCg2iv
C15–H15AÁÁÁCg1v
C3–H3ÁÁÁO5vi
0.96
2.59
130
0.93
2.88
142
0.96
2.99
137
6
0.982(18)
0.93(2)
0.933(18)
0.99(2)
0.956(15)
0.958(18)
iv
2.399(18)
2.338(17)
2.407(19)
2.544(19)
2.529(14)
3.032(19)
v
163.8(14)
103.2(13)
147.0(15)
164.4(15)
156.8(12)
161.6(14)
C5–H5ÁÁÁO3
C12–H12ÁÁÁO2vii
C14–H14ÁÁÁO5viii
C19–H19ÁÁÁO4ix
C10–H10ÁÁÁCg3viii
i
ii
iii
-x, 1 - y, -z; ‘ - x, y - ‘, ‘ - z; x ? 1, y, z - 1; x, -y - ‘, z - 3/2; x - 1, -y - ‘; z - ‘; 2 - x, y ? ‘, 3/2 - z;
x, y - 1, z;
vii
viii
ix
1 - x, 1 - y, 1 - z; x, 3/2 - y, z - ‘
123

Struct Chem (2010) 21:837–845
845
Acknowledgements The authors gratefully acknowledge the financial
assistance of the Scientific and Technical Research Council of Turkey
(TUBITAK), Grand No. TBAG 109T034. We also thank Anadolu
University and Medicinal Plants and Medicine Research Center of
Anadolu University Eskis¸ehir, for allowing us to use the X-ray facility.
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Supplementary data
CCDC 765429, 765430 and 765431 contain the supple-
mentary crystallographic data for 4, 5 and 6. These data can
be obtained free of charge from http://www.ccdc.cam.ac.uk/
conts/retrieving.html, or from the Cambridge Crystallo-
graphic Data Centre, 12 Union Road, Cambridge CB2 1EZ,
UK; fax: (?44) 1223-336-033; or e-mail: deposit@ccdc.
cam.ac.uk.
123