Synthesis, experimental and theoretical NMR study of 2′- hydroxychalcones bearing a nitro substituent on their B ring

Article abstract of DOI:10.1016/j.tet.2004.06.005

The synthesis of several 2′-hydroxynitrochalcones has been accomplished by an aldol reaction of equimolar amounts of the appropriate 2′-hydroxyacetophenones with nitrobenzaldehydes in alkaline medium. The reaction of 2′-hydroxyacetophenones bearing a 6′-methoxy with 2- or 4-nitrobenzaldehydes gave the expected 2′-hydroxynitrochalcones and also 4-methoxynitroaurones, being the latter ones the unique reaction products when using 2molar equiv of nitrobenzaldehydes. The reaction mechanisms for the formation of both products are discussed. The ¹³C NMR chemical shifts have been discussed first by means of an empirical additive model and then by comparison with GIAO/B3LYP calculated absolute shieldings.

Full text of DOI:10.1016/j.tet.2004.06.005

Tetrahedron 60 (2004) 6513–6521
Synthesis, experimental and theoretical NMR study of
20-hydroxychalcones bearing a nitro substituent on their B ring
c
c
Ana I. R. N. A. Barros,a Artur M. S. Silva,b Ibon Alkorta and Jose Elguero
,
*
´
a
´
Department of Chemistry, University of Tras-os-Montes e Alto Douro, 5001-911 Vila Real, Portugal
bDepartment of Chemistry, University of Aveiro, 3810-193 Aveiro, Portugal
´ ´
Instituto de Quımica Medica, Juan de la Cierva, 3, E-28006 Madrid, Spain
c
Received 18 March 2004; revised 12 May 2004; accepted 3 June 2004
Abstract—The synthesis of several 20-hydroxynitrochalcones has been accomplished by an aldol reaction of equimolar amounts of the
appropriate 20-hydroxyacetophenones with nitrobenzaldehydes i0n alkaline medium. The reaction of 20-hydroxyacetophenones bearing a
60-methoxy with 2- or 4-nitrobenzaldehydes gave the expected 2 -hydroxynitrochalcones and also 4-methoxynitroaurones, being the latter
ones the unique reaction products when using 2 molar equiv of nitrobenzaldehydes. The reaction mechanisms for the formation of both
products are discussed. The 13C NMR chemical shifts have been discussed first by means of an empirical additive model and then by
comparison with GIAO/B3LYP calculated absolute shieldings.
q 2004 Elsevier Ltd. All rights reserved.
1. Introduction
synthesis of several new 20-hydroxynitrochalcone deriva-
tives. Nitroflavones are selective and competitive ligands
for central benzodiazepine receptors and possess anxiolytic
properties. The presence of nitro groups is essential for these
activities.27,28,33 Flavones bearing amino groups on the A or
B ring have been reported to be potential antineoplastic
agents26 and proved to be antimutagenic in the Ames test
using different species of mutagens.31 Some aminoflavones
derivatives are also known as specific antitumour agents
in breast cancer29 and are reported by several authors as
tyrosine kinases inhibitors25 and as antimitotic agents.32 On
the other hand, a series of aminochalcones, synthesised as
candidate of cytotoxic agents, displayed selective toxicity to
certain malignant cell and were well tolerated in mice.10
Chalcones (1,3-diaryl-2-propen-1-ones) are an import class
of natural compounds belonging to the flavonoid family,
which have demonstrated to possess an impressive array of
pharmacological and agrochemical activities, namely, anti-
protozoal, anti-inflammatory, immunomodulatory, nitric
oxide and lipid peroxidation inhibition, antileishmanial,
antimalarial, antiulcer, cytotoxic, anticancer, antitumour,
antimicrobial and antiviral activities.1–12 Certain natural
and synthetic derivatives bearing a 20-hydroxy group have
also exhibited a wide spectrum of biological activities with
potential applications as biocides and pharmaceutical
drugs.1,13–15 The presence of the enone function and the
20-hydroxy group in these compounds are important
structural features for their antibiotic activity.1
The synthesis of 20-hydroxychalcones have been exten-
sively studied,18,34–36 whereas to our knowledge only a few
synthetic methods are available for the preparation of their
nitro derivatives.37–41 Taking these facts into consideration,
we started a programme on the synthesis and trans-
formation41 of this type of compounds and on the study of
their spectroscopic features which can give some insights
about their biological activities. Recently, Lluch et al.
studied the inverse dependence of the ch0emical shift of the
hydroxyl proton of 40-dimethylamino-2 -hydroxychalcone
by theoretical calculations.42 In this communication, we
The importance of 20-hydroxychalcones is due not only to
their important biological activities, but also due to the fact
that they are intermediates in the synthesis and biosynthesis
of several flavonoids, such as flavanones, flavones,
isoflavones and aurones.1,16–21 As part of our interests in
the area of flavonoids22–24 and having in mind the potential
applications of several nitro- and aminoflavonoid-type
compounds,2,10,25–33 we have expand our studies to the
1
report the experimental and theoretical studies on the H
Keywords: 20-Hydroxynitrochalcones; 40-Methoxynitroaurones; Oxidation
reactions; Aldol reaction; NMR; B3LYP; GIAO.
and 13C NMR chemical shifts of twelve 20-hydroxynitro-
chalcones 3b–m and the comparison with those of the
parent compound 3a.
*
Corresponding author. Tel.: þ351-234-370714; fax: þ351-234-370084;
e-mail address: arturs@dq.ua.pt
0040–4020/$ - see front matter q 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2004.06.005

6514
A. I. R. N. A. Barros et al. / Tetrahedron 60 (2004) 6513–6521
Scheme 1.
2. Results and discussion
cone 3m were obtained in 17% yield together with 4,6-di-
methoxy-40-nitroaurone (4m) (27% yield) after 2 h reaction
time and only aurone 4m (44% yield) after 10 h reaction
time (Table 1). Since the yield of the expected chalcone 3m
was not increased after some changes in the experimental
procedure, it was decided to perform all the other reactions
in these conditions trying to get 20-hydroxynitrochalcones
3b–m in better yields. The aldol reactions of 20-hydroxy-
acetophenones 1a–d with 2 molar equiv of nitrobenzalde-
hydes 2b–d gave the expected chalcones 3b–g, 3i and 3l in
better yields than when using 1.1 molar equiv of benzal-
dehydes 2b–d (Table 1). However, in the cases where some
aurones 4h, 4j and 4k have been obtained using 1.1 equiv of
benzaldehyde, with 2 equiv only these compounds have
been obtained after 2 h reaction time (Table 1). These
results indicate that the presence of a 6-methoxy group in
the acetophenone moiety and a 2- and 4-nitro group in the
benzaldehyde moiety (were there is an electronic conju-
gation between the nitro substituent and the formyl group)
difficult the formation of chalcones, which after to be
formed are oxidised (dehydrogenated) into the correspond-
ing aurones 4h, 4j, 4k and 4m.43
Initial experiments considered the aldol reaction of
20-hydroxyacetophenone (1a) with 1.1 molar equiv of 2-
nitrobenzaldehyde (2b) in alkaline medium (2 molar equiv
of sodium hydride have been used, since one is consumed
by the hydroxyl group) (Scheme 1). After the disappearance
of the starting materials, controlled by TLC, the expected
20-hydroxy-2-nitrochalcone (3b) was obtained in 16% yield,
after a tedious and hard purification process by preparative
thin layer chromatography. In order to increase the yield of
the reaction and to avoid some benzaldehyde oxidation, we
have deoxygenated the reaction medium before the addition
of 2-nitrobenzaldehyde (2b) and the expected chalcone (3b)
was obtained in 24% 0 yield. After this result we carried
out the reactions of 2 -hydroxyacetophenones 1a–d with
1.1 equiv of nitrobenzaldehydes (2b–d) in the same
alkaline conditions and the expected 20-hydroxynitro-
chalcones 3c–m were obtained in moderate to good yields
(Table 1). In the case of chalcones 3h, 3j and 3k a new
compound have been obtained in each case. These new
compounds were identified as aurones 4h, 4j and 4k. The
reaction of 4-nitrobenzaldehyde (2d) and 20-hydroxy-40,60-
dimethoxyacetophenone (1d) does not gave the expected
chalcone 3m but a complex mixture of compounds where
there was some starting acetophenone 1d. Since some
starting acetophenone 1d was recovered in this case, we
decided to increase the quantity 0of04-nitrobenzaldeyde (2d)
to 2 molar equiv 20-Hydroxy-4 ,6 -dimethoxy-4-nitrochal-
In order to explain the formation of aurones 4h, 4j, 4k
and 4m, we analy0sed by preparative tlc the reaction mixture
of 20-hydroxy-4 ,60-dimethoxyacetophenone (1d) with
2 molar equiv of 4-nitrobenzaldehyde 2d and 4-nitrobenzyl
alcohol have been identified (vide experimental). This
result indicates that one can envisage the dehydrogenation
Table 1. Yields obtained in the synthesis of 20-hydroxynitrochalcones 3b–m
Equiv. nitrobenzaldehydes
Yield of 20-hydroxynitrochalcones 3b–m (%)
3b
3c
3d
3e
3f
3g
3h
3i
3j
3k
3l
3m
1.1
2
24
44
68
75
80
89
21
40
60
72
64
74
15a
—
64
81
19b
—
21c
—
60
73
—
17g
d
e
f
a
Plus 41% of 4h.
Plus 48% of 4j.
Plus 47% of 4k.
Only 89% of 4h.
Only 74% of 4j.
Only 78% of 4k.
Plus 27% of 4m.
b
c
d
e
f
g

A. I. R. N. A. Barros et al. / Tetrahedron 60 (2004) 6513–6521
Table 2. H and 13C chemical shifts (d, ppm, in DMSO-d6) and matrix of substituents
6515
1
Compound
H-a
H-b
OH
C-a
C-b
40-OMe
60-OMe
2-NO2
3-NO2
4-NO2
3a
3b
3c
3d
3e
3f
3g
3h
3i
8.05
7.98
8.23
8.15
8.00
8.22
8.20
7.15
7.34
7.35
7.69
7.85
7.70
7.84
8.06
7.92
7.85
8.07
7.91
7.88
7.64
7.48
7.45
7.87
7.71
7.59
12.50
12.11
12.35
12.15
13.13
13.31
13.23
10.41
10.42
10.41
13.15
13.22
13.21
121.8
126.6
124.7
126.2
125.3
124.1
125.5
132.3
131.0
132.0
131.8
130.4
131.7
144.9
138.8
142.0
141.3
139.6
141.6
141.1
138.2
140.9
140.3
136.6
139.3
139.0
0
0
0
0
1
1
1
0
0
0
1
1
1
0
0
0
0
0
0
0
1
1
1
1
1
1
0
1
0
0
1
0
0
1
0
0
1
0
0
0
0
1
0
0
1
0
0
1
0
0
1
0
0
0
0
1
0
0
1
0
0
1
0
0
1
3j
3k
3l
3m
of 20-hydroxychalcones 3h, 3j, 3k and 3m into the
corresponding aurones 4h, 4j, 4k and 4m by hydrogen
transfer to the corresponding benzaldehyde used in excess
which is transformed into the obtained benzyl alcohol.
have reported these values together with a presence/absence
matrix in Table 2.
2.1. Empirical analysis of Table 2 chemical shifts
We report here the full characterisation of all synthesised
20-hydroxynitrochalcones 3b–m since a major part of them
are new compounds and the references found for the others
are old and do not report these data. The NMR data of
20-hydroxychalcone 3a are reported for the comparison
study with the nitro derivatives (vide infra).
Using the presence/absence matrix the following corre-
lations are obtained (n¼13 points):
dH-a ¼ 8:05 þ 0:24pð40-OMeÞ 2 0:62pð60-OMeÞ
2 0:16pð2-NO2Þ þ 0:05pð3-NO2Þ
The main features of the NMR data of 20-hydroxychalcones
3a–m are the resonances of: (i) the hydroxyl groups at d
10.41–13.23 ppm. The high frequency resonances of these
protons are due to the intramolecular hydrogen bond formed
with the carbonyl group; (ii) the vinylic protons appearing
as doublets at dHa 7.15–8.23 ppm and dHb 7.45–8.07 ppm.
2 0:01pð4-NO2Þ; r2 ¼ 0:90
ð1Þ
ð2Þ
ð3Þ
ð4Þ
ð5Þ
dH-b ¼ 7:84 þ 0:10pð40-OMeÞ 2 0:32pð60-OMeÞ
þ 0:18pð2-NO2Þ þ 0:02pð3-NO2Þ
3
The coupling constants JHa–Hb ,15–16 Hz indicate the
trans configuration of these vinylic system; (iii) the vinylic
carbons which appear at dCa 121.8–132.3 ppm and dCb
136.6–144.9 ppm. The resonances of C-b atoms appear at
higher frequency values than those of C-a due to
deshielding mesomeric effect of the carbonyl group; (iv)
the carbonyl group appearing at d 191.1–194.0 ppm, and
(v) the aromatic carbons bonded to oxygen atoms, which
appear at d,157–166 ppm. The resonances of the hydroxyl
proton and of the vinylic proton and carbon atoms are
very sensitive to the substituents of both aryl rings of
20-hydroxychalcones 3a–m (vide infra).
2 0:04pð4-NO2Þ; p2 ¼ 0:94
dOH ¼ 12:5 þ 1:9pð40-OMeÞ 2 0:91pð60-OMeÞ
2 0:80pð2-NO2Þ 2 0:67pð3-NO2Þ
2 0:74pð4-NO2Þ; r2 ¼ 0:94
The main NMR features of aurones 4h, 4j, 4k and 4m are
the resonances of their vinylic proton, which appear at dHa
6.75–7.00 ppm. These resonance frequency are consistent
with a Z configuration of the olefinic bond of aurones, the
thermodynamically more stable isomers of these com-
pounds.44 Another important resonances to support the
structure of aurones are the carbon resonances of C-a
(d 103.4–107.4 ppm), C-2 (d 147.7–149.2 ppm) and CvO
(d 180.1–180.5 ppm).
dC-a ¼ 121:8 2 0:7pð40-OMeÞ þ 6:1pð60-OMeÞ
þ 4:5pð2-NO2Þ þ 3:0pð3-NO2Þ
þ 4:3pð4-NO2Þ; r2 ¼ 0:998
dC-b ¼ 144:9 2 0:7pð40-OMeÞ 2 1:7pð60-OMeÞ
2 5:4pð2-NO2Þ 2 2:8pð3-NO2Þ
1
The comparison of0 the H and 13C chemical shifts of the
parent compound 2 -hydroxychalcone 3a with those of the
twelve methoxy/nitro derivatives 3b–m, shed some light in
the effect of these substituents. The most sensitive signals
are those belonging to H-a, H-b, OH, C-a and C-b. We
2 3:3pð4-NO2Þ; r2 ¼ 0:95

6516
A. I. R. N. A. Barros et al. / Tetrahedron 60 (2004) 6513–6521
Since the goodness-of-fit, as represented by r 2, are not
good, except in the case of dC-a, we suspect that the effect
of the methoxy groups was not independent. We introduced
a supplementary dummy when both are present simul-
taneously (compounds 3k–m), (40,60-diOMe).
dC-a ¼ 121:8 2 0:9pð40-OMeÞ þ 5:9pð60-MeOÞ
þ 4:6pð2-NO2Þ þ 3:1pð3-NO2Þ
þ 4:4pð4-NO2Þ þ 0:4ð40; 60-diOMeÞ;
r2 ¼ 0:999
dC-b ¼ 144:9 2 0:1pð40-OMeÞ 2 0:9pð60-MeOÞ
2 5:8pð2-NO2Þ 2 3:1pð3-NO2Þ
2 3:7pð4-NO2Þ 2 1:6ð40; 60-diOMeÞ;
r2 ¼ 0:991
ð9Þ
dH-a ¼ 8:05 þ 0:02pð40-OMeÞ 2 0:84pð60-MeOÞ
2 0:05pð2-NO2Þ þ 0:16pð3-NO2Þ
2 0:10pð4-NO2Þ þ 0:45ð40; 60-diOMeÞ;
ð6Þ
r2 ¼ 0:991
ð10Þ
dH-b ¼ 7:84 þ 0:01pð40-OMeÞ 2 0:42pð60-MeOÞ
þ 0:23pð2-NO2Þ þ 0:07pð3-NO2Þ
þ 0:01pð4-NO2Þ þ 0:19ð40; 60-diOMeÞ;
ð7Þ
Eqs. (6)–(10) can be summarised graphically as represented
in Scheme 2.
r2 ¼ 0:992
Concerning the OH proton, the presence of a methoxy group
at position 40 produces a strengthening of the O–H· · ·O
hydrogen bond while a 60-methoxy group weakens the HB.
The first effect is electronic in origin, making the carbonyl
group, in para position, a better HB acceptor. The ortho
methoxy group should produce a similar effect but its steric
effect counterbalanced it, the torsion about the CO-Ca
bond weakens the HB. The presence of two methoxy groups
has a strong positive effect on the HB, and somewhat
dOH ¼ 12:5 þ 1:01pð40-OMeÞ 2 1:79pð60-MeOÞ
2 0:33pð2-NO2Þ 2 0:25pð3-NO2Þ
2 0:30pð4-NO2Þ þ 1:77ð40; 60-diOMeÞ;
r2 ¼ 0:999
ð8Þ
Scheme 2. Effects of the substituents (SCS, ppm) on 1H and 13C signals.

A. I. R. N. A. Barros et al. / Tetrahedron 60 (2004) 6513–6521
6517
Scheme 3. Conformation of the o-nitrophenyl group.
counterbalances the steric effect of the 60-methoxy group.
The same effects, although attenuated, are observed on H-a
and H-b, besides H-a is more sensitive to the closer by
60-OMe while H-b is more sensitive to the ortho nitro group
(this implies that the conformation of the nitrophenyl group
has the NO2 group close to H-b and not to H-a) (Scheme 3).
(10) is possible but not interesting due to the proportionality
between d and s (Eq. (11)). The theoretical calculated
values do not need an empirical partition into contributing
terms: they show that the experimental results are consistent
with the optimised geometries and there are no large
anomalies. Two points show the largest deviations both C-b
carbons: 3b (2-NO2) fitted 143.0, experimental 138.8
(Dd¼–4.2 ppm) and 3g (4-NO2) fitted 138.1, experimental
141.1 (Dd¼þ3.0 ppm). The NMR spectra have been
recorded again and the experimental values do not change:
we have no explanation for these differences that reflect
some factor not well taken into account by the calculations,
a rather unusual observation.
In 13C NMR, the SCS of Scheme 2 show the sensibility to
proximity effects (C-a to 60-OMe group and C-b to all NO2
groups but especially to the ortho one).
2.2. Theoretical analysis of Table 2 chemical shifts
It should be possible to verify the conclusions of the
previous empirical discussion carrying GIAO/DFT calcu-
lations. We decided to calculate, as the most representative
compounds, 3a, 3b, 3c, 3d, 3g, 3j and 3m. Initially the
structures have been optimised at the B3LYP/6-31G* level
and its minimum nature has been confirmed by frequency
calculations. A further optimisation has been carried out at
the B3LYP/6-311þþG** level and these structures have
been used to obtain the theoretical absolute chemical
shielding with the GIAO method. As this implies in a first
step the optimisation (B3LYP/6-31G*), the first result is
that of the two conformations of Scheme 3, that of the left
side is the only one stable (compound 3b). The geometrical
characteristics of the O–H· · ·O hydrogen bonds in the
different compounds are gathered in Table 3.
1
Concerning the H chemical shifts, the CH and the OH
cannot be treated together. This is an usual observation:
protons linked to heteroatoms are different, not from the
calculations, but from the experimental data. The calcu-
lations correspond to the isolated molecule and the
experimental data are from DMSO-d6 solutions. Obviously,
the solvent plays an important role on the acidic proton.
3. Computational details
The structure of the molecules have been optimised with the
hybrid B3LYP functional45,46 and the 6-31G*47 using the
Gaussian-98 program.48 At the same computational level,
the minimum nature of the structures has been confirmed by
frequency calculation. A further geometry optimisation has
been carried out at the B3LYP/6-311þþG**49 compu-
tational level. The absolute chemical shieldings have been
calculated using the GIAO method50,51 at the B3LYP/
6-311þþG** level.
˚
Table 3. Distance (A) and angle (8) of the structures optimised at the
B3LYP/6-311þþG** computational level
Compound
H· · ·O
O–H· · ·O
3a
3b
3c
3d
3g
3j
1.638
1.653
1.652
1.650
1.646
1.611
1.598
148.0
147.4
147.4
147.4
148.1
147.7
149.1
4. Experimental
3m
Melting points were measured in a Bu¨chi 535 apparatus and
are uncorrected. NMR spectra were recorded on a Bruker
DRX 300 spectrometer (300.13 for H and 75.47 MHz for
The d 13C are relatively well correlated with the calculated
absolute shielding, s. Although all nuclei of each molecule
are calculated, we will limit ourselves to those correspond-
ing to Table 1. For carbon atoms C-a and C-b, Eq. (11) is
obtained.
1
13C), with DMSO-d6 as a solvent. Chemical shifts (d) are
reported in ppm and coupling constants (J) in Hz. The
internal standard was TMS. Unequivocal 13C assignments
were made with the aid of 2D gHSQC and gHMBC (delays
for one bond and long-range J C/H couplings were
optimised for 147 and 7 Hz, respectively) experiments.
Electron impact (EI, 70 eV) MS were recorded on VG
Autospec Q spectrometer. Elemental Analyses were
obtained on a Carlo Erba 1108 CHNS analyser. Preparative
thin-layer chromatography was performed with Merck silica
gel 60 DGF254. Column chromatography was performed
with Merck silica gel 60, 70–230 mesh. All other chemicals
d13CðppmÞ ¼ 162 ppm 2 0:63s13CðppmÞ; n ¼ 14; r2
¼ 0:96
ð11Þ
The slope is far from 1 but the correlation coefficient is
acceptable taking into account that the experimental
(23 ppm) and calculated (33 ppm) ranges are quite narrow.
An analysis of the calculated values similar to Eqs. (9) and

6518
A. I. R. N. A. Barros et al. / Tetrahedron 60 (2004) 6513–6521
1
and solvents used were obtained from commercial sources
and used as received or dried using standard procedures.
161.0 8C (recrystallised from ethanol). H NMR: d 7.00
(d, 2H, H-30 and H-50, J¼7.9 Hz), 7.58 (dt, 1H, H-40, J¼1.7,
7.9 Hz), 7.71 (dt, 1H, H-4, J¼1.4, 8.2 Hz), 7.84 (dt, 1H,
H-5, J¼1.2, 8.2 Hz), 7.98 (d, 1H, H-a, J¼15.4 Hz), 8.06 (d,
1H, H-b, J¼15.4 Hz), 8.11 (dd, 1H, H-3, J¼1.2, 8.2 Hz),
8.16 (dd, 1H, H-6, J¼1.4, 8.20Hz), 8.19 (dd, 1H, H-60,
J¼1.7, 7.9 Hz), 102.11 (s, 1H, 2 -OH). 13C NMR: d 117.8
(C-30), 119.4 (C-5 ), 121.1 (C-10), 126.6 (C-a), 124.8 (C-3),
131.1 (C-600), 129.6 (C-1 and C-6), 131.3 (C-4), 133.9 (C-5),
136.5 (C-4 ), 138.8 (C-b), 148.8 (C-2), 161.5 (C-20), 193.0
(CvO). EI-MS: m/z (rel. intensity) 269 (Mþz, 10), 252 (55),
222 (38), 165 (7), 132 (5), 121 (100), 102 (8), 93 (18), 77
(10), 65 (32). IR n 1643, 1589, 1513, 1438, 1342, 1267,
1205, 1018 cm21. Anal. calcd for C15H11NO4: C 66.91, H
4.09, N 5.20. Found: C 66.70, H 4.03, N 5.12.
4.1. Synthesis of 20-hydroxychalcone (3a)
An aqueous solution of sodium hydroxide (60%, 160 mL)
was added to a methanolic solution (160 mL) of
20-hydroxyacetophenone (1a) (4 mL, 33 mmol). The
obtained solution was cooled to room temperature, benz-
aldehyde (2a) (40 mmol) was added and the reaction
mixture was stirred for 4 h. After this period, the reaction
mixture was poured into a mixture of water (100 mL), ice
and hydrochloric acid (pH adjusted to 2). The obtained solid
was filtered, taken in chloroform (300 mL) and washed with
a 5% aqueous solution of sodium hydrogen carbonate
(2£200 mL). The organic layer was collected, dried and
evaporated to dryness. The residue was crystallised from
ethanol; giving 20-hydroxychalcone 3a (75%). Mp 81–
83 8C (recrystallised from ethan0ol, lit.40 88 8C). 1H 0NMR: d
6.98–7.04 (m, 2H, H-30 and H-5 ), 7.57 (dt, 1H, H-4 , J¼1.6,
7.8 Hz), 7.45–7.50 (m, 3H, H-3, H-4 and H-5), 7.84 (d, 1H,
H-b, J¼15.6 Hz), 7.91–7.93 (m, 1H, H-2,6), 8.05 (d, 1H,
H-a, J¼105.6 Hz), 8.25 (dd, 1H, H-60, J¼1.6, 8.3 Hz), 12.50
(s, 1H, 2 -OH). 13C NMR: d 117.8 (C-30), 119.2 (C-50),
120.9 (C-10), 121.8 (C-a), 129.0 (C-3,5), 130.9 (C-60), 129.2
(C-2,6), 1304.4 (C-1), 131.0 (C-4), 136.4 (C-40), 144.9 (C-b),
161.9 (C-2 ), 193.7 (CvO).
4.2.2. 20-Hydroxy-3-nitrochalcone (3c). Mp 163.5–
163.9 8C (recrystallised from ethyl acetate, lit.40 163.0 8C).
1H NMR: d 7.02 (d, 2H, H-30 and H-50, J¼8.0 Hz), 7.58 (dt,
1H, H-40, J¼1.4, 8.0 Hz), 7.75 (t, 1H, H-5, J¼9.0 Hz), 7.92
(d, 1H, H-b, J¼15.6 Hz), 8.23 (d, 1H, H-a, J¼15.6 Hz),
8.27 (d, 1H, H-6, J¼9.0 Hz), 8.31–8.35 (m, 2H, H-4 and
H-60), 8.78 (d, 1H, H-2, J¼1.6 Hz), 12.35 (s, 1H,020-OH).
13C NMR: d 117.7 (C-30), 119.2 (C-50), 120.7 (C-1 ), 1230.1
(C-2), 124.7 (C-a), 124.9 (C-6), 130.3 (C-5), 131.1 (C-6 ),
135.2 (C-4), 136.3 (C-1), 136.5 (C-40), 142.0 (C-b), 148.4
(C-3), 161.8 (C-20), 193.3 (CvO). EI-MS: m/z (rel.
intensity) 269 (Mþz, 60), 268 (44), 252 (10), 222 (9), 194
(8), 176 (7), 152 (3), 147 (100), 121 (55), 102 (22), 93 (15),
76 (12), 65 (30). IR n 1644, 1589, 1523, 1486, 1438, 1357,
1288, 1211, 1157 cm21. Anal. calcd for C15H11NO4: C
66.91, H 4.09, N 5.20. Found: C 66.78, H 3.97, N 5.12.
4.2. Synthesis of 20-hydroxynitrochalcones 3b–m
Method A. Sodium hydride (0.88 g, 36.5 mmol) was slowly
added to a solution of the appropriate 20-hydroxyaceto-
phenone 1a–d (16.6 mmol) in dry tetrahydrofuran (10 mL)
and the reaction mixture stirred at room temperature for
20 min. After this period the adequate nitrobenzaldehyde
2b–d (18.3 mmol) dissolved in tetrahydrofuran (10 mL)
was added. The solution was stirred, under nitrogen, at room
temperature until the disappearance of the starting materials
(,8 h). The solution was poured into ice and water, and the
pH adjusted to 3 with hydrochloric acid. The obtained solid
was removed by filtration, dissolved in chloroform (30 mL)
and washed with water (2£20 mL). The organic layer was
dried over Na2SO4 and evaporated to dryness. In the case of
20-hydroxynitrochalcones 3b–g, 3i and 3l, the residue was
crystallised from ethanol, ethyl acetate or ethanol:acetone.
20-Hydroxynitrochalcones 3h, 3j and 3k and the correspond-
ing nitroaurones 4h, 4j and 4k have been isolated from the
reaction mixture by by column chromatography using
different mixtures of chloroform:n-hexane as eluent. Finally
all the synthesised compounds were recrystallised from
ethanol, ethyl acetate or ethanol:acetone, and collected in
the following yields: 3b, 24%; 3c, 68%; 3d, 80%; 3e, 21%;
3f, 60%; 3g, 64%; 3h, 15% and 4h, 41%; 3i, 64%; 3j, 19%
and 4j, 48%; 3k, 21% and 4k, 47%; 3l, 60%.
4.2.3. 20-Hydroxy-4-nitrochalcone (3d). Mp 141.8–
142.1 8C (recrystallised from ethyl acetate, lit.40 206–
20708C, lit.37 153–154 8C). H NMR: d 6.99–7.04 (m, 2H,
1
H-3 and H-50), 7.58 (dt, 1H, H-40, J¼1.5, 7.8 Hz), 7.86 (d,
1H, H-b, J¼15.5 Hz), 8.14 (d, 2H, H-2,6, J¼9.1 0Hz), 8.15
(d, 1H, H-a, J¼15.5 Hz), 8.20 (dd, 1H, H-6 , J¼1.5,
8.3 Hz), 8.27 (d, 2H, H-3,5, J¼9.1 Hz), 12.150 (s, 1H,
20-OH). 13C NMR: d 117.6 (C-30), 119.1 (C-5 ), 120.9
(C-10), 123.8 (C-3,5), 126.2 (C-a), 129.8 (C-2,6), 130.9 (C-
60), 136.5 (C-40), 140.8 (C-1), 141.3 (C-b), 148.1 (C-4),
161.5 (C-20), 193.1 (CvO). EI-MS: m/z (rel. intensity) 269
(Mþz, 82), 268 (60), 252 (16), 222 (15), 194 (6), 176 (10),
165 (13), 147 (100), 121 (62), 102 (19), 93 (15), 93 (17), 76
(9), 65 (27). IR n 1644, 1590, 1515, 1490, 1440, 1340, 1270,
1209, 1157 cm21. Anal. calcd for C15H11NO4: C 66.91, H
4.09, N 5.20. Found: C 66.64, H 3.97, N 5.17.
4.2.4. 20-Hydroxy-40-methoxy-2-nitrochalcone (3e). Mp
1
149.9–150.3 8C (recrystallised from0ethanol). H NMR: d
3.87 (s, 3H, OCH3), 6.55 (d, 1H, H-3 , J¼2.5 Hz), 6.59 (dd,
1H, H-50, J¼2.5, 9.0 Hz), 7.72 (ddd, 1H, H-4, J¼1.2, 7.6,
8.0 Hz), 7.85 (ddd, 1H, H-5, J¼1.0, 7.6, 7.7 Hz), 8.00 (d,
1H, H-a, J¼15.5 Hz), 8.07 (d, 1H, H-b, J¼15.5 Hz), 8.11
(dd, 1H, H-3, J¼1.0, 8.0 Hz), 8.22 (dd, 1H, H-6, J¼1.2,
7.7 Hz), 8.27 (d, 1H, H-60, J¼9.0 Hz),013.13 (s, 1H,020-OH).
13C NMR: d 55.9 (OCH3), 101.0 (C-3 ), 107.7 (C-5 ), 113.9
(C-10), 124.8 (C-3), 125.8 (C-a), 129.6 (C-1), 129.7 (C-6),
131.2 (C-4), 133.0 (C-60), 133.8 (C-5), 138.3 (C-b), 148.8
(C-2), 165.7 (C-20), 166.4 (C-40), 191.3 (CvO). EI-MS: m/z
(rel. intensity) 299 (Mþz, 22), 282 (54), 252 (46), 226 (10),
Method B. This method is similar to method A, except the
quantity of the adequate nitrobenzaldehyde 2b–d, which
was 33.2 mmol. The obtained yields were as follows: 3b,
44%; 3c, 75%; 3d, 89%; 3e, 40%; 3f, 72%; 3g, 74%; 4h,
89%; 3i, 81%; 4j, 74%; 4k, 78%; 3l, 78%; 3m, 17% and 4m,
27%.
4.2.1. 20-Hydroxy-2-nitrochalcone (3b). Mp 160.2–

A. I. R. N. A. Barros et al. / Tetrahedron 60 (2004) 6513–6521
6519
177 (9), 164 (8), 151 (100), 120 (5), 108 (12), 102 (7), 95
(11), 77 (6), 65 (7). IR n 1639, 1579, 1517, 1344, 1228,
1201, 1135 cm21. Anal. calcd for C16H13NO5: C 64.21, H
4.35, N 4.68. Found: C 64.12, H 4.34, N 4.60.
J¼8.0 Hz), 8.23 (dd, 1H, H-4, J¼0 1.8, 8.0 Hz), 8.51 (t, 1H,
H-2, J¼1.8 Hz), 10.42 (s, 1H, 2 -OH). 13C NMR: d 55.9
(OCH3), 102.4 (C-50), 109.1 (C-30), 115.7 (C-10), 123.3
(C-2), 124.7 (C-4), 130.5 (C-5), 131.0 (C-a), 132.2 (C-40),
134.3 (C-6), 136.4 (C-1), 140.9 (C-b), 148.4 (C-3), 157.0
(C-20), 158.3 (C-60), 194.0 (CvO). EI-MS: m/z (rel.
intensity) 299 (Mþz, 55), 298 (39), 282 (7), 252 (6), 224
(5), 210 (3), 177 (100), 162 (7), 151 (33), 136 (8), 107 (9),
102 (11). IR n 1635, 1583, 1529, 1475, 1436, 1353, 1238,
1209, 1087 cm21. Anal. calcd for C16H13NO5: C 64.21, H
4.35, N 4.68. Found: C 64.13, H 4.39, N 4.61.
4.2.5. 20-Hydroxy-40-methoxy-3-nitrochalcone (3f). Mp
177.6–178.3 8C (recrystallised from ethyl acetate, lit.52
1
172–1738C). H NMR: d 3.85 (s, 3H, OCH3), 6.52 (d, 1H,
H-30, J¼2.4 Hz), 6.58 (dd, 1H, H-50, J¼2.4, 9.0 Hz), 7.75 (t,
1H, H-5, J¼8.0 Hz), 7.91 (d, 1H, H-b, J¼15.7 Hz), 8.22 (d,
1H, H-a, J¼15.7 Hz), 8.27 (dd, 1H, H-60, J¼2.4, 9.0 Hz),
8.31–8.35 (m, 2H, H-4 and H-6), 8.80 (br s, 1H, H-2), 13.31
(s, 1H, 20-OH). 13C NMR: d 55.9 (OCH3), 100.9 (C-30),
107.7 (C-50), 113.9 (C-10), 1230.2 (C-2), 124.1 (C-a), 124.9
(C-6), 130.4 (C-5), 133.1 (C-6 ), 1350.4 (C-4), 136.3 (C-1),
141.6 (C-b), 148.5 (C-3), 165.9 (C-2 ), 166.3 (C-40), 191.7
(CvO). EI-MS: m/z (rel. intensity) 299 (Mþz, 100), 298
(38), 282 (8), 252 (6), 224 (10), 177 (97), 151 (53), 120 (9),
102 (9), 95 (7), 76 (5). IR n 1641, 1581, 1527, 1438, 1353,
1284, 1230, 1132 cm21. Anal. calcd for C16H13NO5: C
64.21, H 4.35, N 4.68. Found: C 63.88, H 4.33, N 4.61.
4.2.9. 20-Hydroxy-60-methoxy-4-nitrochalcone (3j). Mp
1
160.3–161.0 8C (recrystallised from acetone:ethanol). H
NMR: d 3.75 (s, 3H, OCH3), 6.55 (d, 1H, H-30, J¼8.3 Hz),
6.59 (d, 1H, H-50, J¼8.3 Hz), 7.28 (t, 1H, H-40, J¼8.3 Hz),
7.35 (d, 1H, H-a, J¼16.2 Hz), 7.45 (d, 1H, H-b,
J¼16.2 Hz), 8.00 (d, 2H, H-2,6, J¼8.7 Hz), 8.23 (d, 2H,
H-3,5, J¼8.7 Hz), 10.41 (s, 1H, 20-OH). 13C NMR: d 55.8
(OCH3), 102.4 (C-50), 109.0 (C-30), 115.5 (C-10), 124.0
(C-3,5), 129.6 (C-2,6), 132.0 (C-a), 132.2 (C-40), 1400.3
(C-b), 141.0 (C-1), 148.0 (C-4), 157.1 (C-20), 158.2 (C-6 ),
194.0 (CvO). EI-MS: m/z (rel. intensity) 299 (Mþz, 70), 298
(56), 282 (7), 252 (9), 177 (100), 162 (6) 151 (40), 136 (10),
130 (5), 122 (7), 107 (8), 102 (12). IR n 1633, 1581, 1515,
1440, 1344, 1226, 1133 cm21. Anal. calcd for C16H13NO5:
C 64.21, H 4.35, N 4.68. Found: C 64.22, H 4.33, N 4.77.
4.2.6. 20-Hydroxy-40-methoxy-4-nitrochalcone (3g). Mp
191.8–192.78C (recrystallised from ethyl acetate, lit.52
1
194–195 8C). H NMR: d 3.86 (s, 3H, OCH3), 6.54 (d,
1H, H-30, J¼2.4 Hz), 6.59 (dd, 1H, H-50, J¼2.4, 9.0 Hz),
7.88 (d, 1H, H-b, J¼15.6 Hz), 8.18 (d, 2H, H-2,6, J¼
8.7 Hz), 8.20 (d, 1H, H-a, J¼15.5 Hz), 8.29 (d, 2H, H-3,5,
J¼8.7 Hz), 8.30 (d, 1H, H-60, J¼9.0 Hz), 13.23 (s, 1H,
20-OH). 13C NMR: d 55.9 (OCH3), 101.0 (C-30), 107.7
(C-50), 114.0 (C-10), 124.0 (C-3,5), 125.5 (C-a), 130.1
(C-2,6), 133.0 (C-60), 141.0 (C-1), 141.1 (C-b), 148.1 (C-4),
165.8 (C-20), 166.4 (C-40), 191.4 (CvO). EI-MS: m/z (rel.
intensity) 299 (Mþz, 82), 298 (46), 282 (10), 271 (11), 252
(12), 224 (6), 210 (3), 177 (100), 165 (7), 151 (64), 130 (5),
102 (14), 95 (11), 76 (9). IR n 1637, 1589, 1509, 1340, 1287,
1224, 1209, 1132 cm21. Anal. calcd for C16H13NO5: C
64.21, H 4.35, N 4.68. Found: C 64.11, H 4.38, N 4.61.
4.2.10. 20-Hydroxy-40,60-dimethoxy-2-nitrochalcone (3k).
Mp 173.0–173.9 8C (recrystallised from acetone:ethanol).
1H NMR: d 3.86 (s, 3H, OCH3), 3.90 (s, 3H, OCH3), 6.16 (d,
1H, H-30, J¼2.2 Hz), 6.18 (d, 1H, H-50, J¼2.2 Hz), 7.66–
7.72 (m, 1H, H-4), 7.69 (d, 1H, H-a, J¼15.6 Hz), 7.81 (d,
1H, H-5, J¼7.5 Hz), 7.87 (d, 1H, H-b, J¼15.6 Hz), 7.95 (d,
1H, H-6, J¼7.50Hz), 8.10 (dt, 1H, H-3, J¼0.9, 8.1 Hz),
13.15 (s, 1H, 2 -OH). 13C NMR: d 55.9 (OCH3), 56.4
(OCH3), 91.3 (C-50), 94.0 (C-30), 106.3 (C-10), 124.9 (C-3),
129.3 (C-6), 130.0 (C-1), 131.0 (C-4), 131.8 (C-a), 1340.1
(C-5), 136.6 (C-b), 148.7 (C-2), 162.1 (C-60), 165.5 (C-2 ),
166.0 (C-40), 191.9 (CvO). EI-MS: m/z (rel. intensity) 329
(Mþz, 11), 312 (27), 282 (24), 253 (3), 207 (9), 194 (19), 181
(100), 166 (5), 138 (8), 102 (4), 95 (7), 69 (6). IR n 1631,
1581, 1531, 1438, 1347, 1270, 1155 cm21. Anal. calcd for
C17H15NO6: C 62.01, H 4.56, N 4.26. Found: C 62.32, H
4.56, N 4.19.
4.2.7. 20-Hydroxy-60-methoxy-2-nitrochalcone (3h). Mp
1
180.2–181.4 8C (recrystallised from acetone:ethanol). H
NMR: d 3.76 (s, 3H, OCH3), 6.55 (d, 1H, H-30, J¼8.3 Hz),
6.58 (d, 1H, H-50, J¼8.3 Hz), 7.15 (d, 1H, H-a, J¼15.9 Hz),
7.27 (t, 1H, H-40, J¼8.3 Hz), 7.64 (d, 1H, H-b, J¼15.9 Hz),
7.67 (ddd, 1H, H-4, J¼1.3, 7.6, 8.1 Hz), 7.78 (t, 1H, H-5,
J¼7.6 Hz), 7.97 (d, 1H, H-6, J¼7.6 Hz), 8.06 (dd, 1H, H-3,
J¼1.0, 8.1 Hz), 10.41 (s, 1H, 20-OH). 13C NMR: d 55.8
(OCH3), 102.3 (C-50), 109.0 (C-30), 115.2 (C-10), 124.8
(C-3), 129.2 (C-6), 129.6 (C-1), 131.0 (C-4), 132.3 (C-40
and C-a), 134.0 (C-5), 138.2 (C-b), 148.5 (C-2), 157.2
(C-20), 158.3 (C-60), 194.0 (CvO). EI-MS: m/z (rel.
intensity) 299 (Mþz, 100), 282 (80), 252 (58), 177 (10),
164 (11), 136 (21), 108 (20), 77 (10), 65 (16). IR n 1633,
4.2.11. 20-Hydroxy-40,60-dimethoxy-3-nitrochalcone (3l).
1
Mp 169.1–170.0 8C (recrystallised from ethyl acetate). H
NMR: d 3.82 (s, 3H, OCH3), 3.89 (s, 3H, OCH3), 6.14 (d,
1H, H-30, J¼2.1 Hz), 6.16 (d, 1H, H-50, J¼2.1 Hz), 7.71 (d,
1H, H-b, J¼15.6 Hz), 7.73 (t, 1H, H-5, J¼8.0 Hz), 7.85 (d,
1H, H-a, J¼15.6 Hz), 8.20 (d, 1H, H-6, J¼8.0 Hz), 8.25
(dd, 1H, H-4, J¼1.5, 8.0 Hz), 8.51 (br s, 1H, H-2), 13.22 (s,
1H, 2-OH). 13C NMR: d 55.7 (OCH3), 56.0 (OCH3), 91.2
(C-50), 94.0 (C-30), 106.4 (C-10), 123.1 (C-2), 124.5 (C-4),
130.4 (C-a), 130.6 (C-5), 134.0 (C-6), 136.8 (C-1), 1390.3
(C-b), 148.4 (C-3), 162.0 (C-60), 165.4 (C-20), 165.9 (C-4 ),
192.1 (CvO). EI-MS: m/z (rel. intensity) 329 (Mþz, 61), 328
(39), 312 (13), 301 (15), 282 (5), 254 (9), 207 (100), 181
(46), 166 (7), 138 (8), 102 (10), 95 (6), 69 (7). IR n 1635,
1581, 1531, 1438, 1347, 1270, 1218, 1159 cm21. Anal.
calcd for C17H15NO6: C 62.01, H 4.56, N 4.26. Found: C
62.18, H 4.51, N 4.13.
1583, 1529, 1473, 1454, 1351, 1236, 1205, 1085 cm21
.
Anal. calcd for C16H13NO5: C 64.21, H 4.35, N 4.68. Found:
C 64.17, H 4.29, N 4.70.
4.2.8. 20-Hydroxy-60-methoxy-3-nitrochalcone (3i). Mp
137.0–138.6 8C (recrystallised from ethyl acetate). 1H
NMR: d 3.74 (s, 3H, OCH3), 6.55 (d, 1H, H-30, J¼
8.3 Hz), 6.58 (d, 1H, H-50, J¼8.3 Hz), 7.27 (t, 1H, H-40,
J¼8.3 Hz), 7.34 (d, 1H, H-a, J¼16.1 Hz), 7.48 (d, 1H, H-b,
J¼16.1 Hz), 7.69 (t, 1H, H-5, J¼8.0 Hz), 8.19 (d, 1H, H-6,

6520
A. I. R. N. A. Barros et al. / Tetrahedron 60 (2004) 6513–6521
4.2.12. 20-Hydroxy-40,60-dimethoxy-4-nitrochalcone
(3m). Mp 235.0–236.4 8C (recrystallised from acetone:
4.2.16. 4,6-Dimethoxy-40-nitroaurone (4m). Mp 266.7–
261.9 8C (recrystallised from ethanol). H NMR: d 3.95
1
1
ethanol). H NMR: d 3.84 (s, 3H, OCH3), 3.91 (s, 3H,
(s, 3H, OCH3), 3.98 (s, 3H, OCH3), 6.17 (d, 1H, H-5,
J¼1.7 Hz), 6.43 (d, 1H, H-7, J¼1.7 Hz), 6.75 (s, 1H, H-a),
7.99 (d, 2H, H-20,60, J¼8.8 Hz), 8.26 (d, 2H, H-30,50,
J¼8.8 Hz). 13C NMR: d 56.3 (OCH3), 56.4 (OCH3), 89.6
(C-7), 94.4 0(C-5), 104.7 (C-9), 107.3 (C-a), 123.9 (C-30,50),
131.4 (C-2 ,60), 139.1 (C-10), 147.3 (C-40), 149.6 (C-2),
159.7 (C-4), 169.1 (C-8), 169.6 (C-6), 180.1 (CvO).
EI-MS: m/z (rel. intensity) 327 (Mþz, 100), 326 (25), 310
(7), 298 (38), 251 (16), 180 (8), 137 (9), 106 (12), 85 (11),
69 (20), 57 (22). IR n 1695, 1664, 1617, 1585, 1506, 1421,
1338, 1157, 1089, 827 cm21. Anal. calcd for C17H13NO6: C
62.39, H 3.98, N 4.28. Found: C 62.39, H 4.00, N 4.46.
OCH3), 6.17 (d, 1H, H-30, J¼1.9 Hz), 6.19 (d, 1H, H-50,
J¼1.9 Hz), 7.59 (d, 1H, H-b, J¼15.7 Hz), 7.70 (d, 1H, H-a,
J¼15.7 Hz), 8.02 (d, 2H, H-2,6, J¼8.6 Hz), 8.29 (d, 2H,
H-3,5, J¼8.6 Hz), 13.21 (s, 1H,0 20-OH). 13C NMR: d 550.8
(OCH3), 56.4 (OCH3), 91.3 (C-5 ), 93.9 (C-30), 106.4 (C-1 ),
124.1 (C-3,5), 129.5 (C-2,6), 131.7 (C-a), 139.0 (C-b),
141.4 (C-1), 148.0 (C-4), 162.0 (C-60), 165.4 (C-20), 166.0
(C-40), 192.0 (CvO). EI-MS: m/z (rel. intensity) 329 (Mþz,
69), 328 (32), 312 (8), 301 (20), 282 (5), 255 (3), 207 (100),
181 (53), 166 (9), 125 (10), 97 (21), 71 (25), 57 (35). IR n
1639, 1583, 1519, 1438, 1342, 1216, 1160 cm21. Anal.
calcd for C17H15NO6: C 62.01, H 4.56, N 4.26. Found: C
62.23, H 4.49, N 4.31.
1
4.2.17. 4-Nitrobenzyl alcohol. H NMR: d 4.84 (s, 2H,
CH2), 7.54 (d, 2H, H-2,6, J¼8.7 Hz), 8.22 (d, 2H, H-3,5,
J¼8.7 Hz). EI-MS: m/z (rel. intensity) 153 (Mþz, 54), 137
(100), 120 (45), 92 69), 83 (11), 71 (27), 57 (37).
4.2.13. 4-Methoxy-20-nitroaurone (4h). Mp 194.0–
195.0 8C (recrystallised from ethanol). H NMR: d 3.95 (s,
1
3H, OCH3), 6.87 (d, 1H, H-5, J¼8.3 Hz), 6.97 (d, 1H, H-7,
J¼8.3 Hz), 7.00 (s, 1H, H-a), 7.67 (t, 1H, H-40, J¼7.9 Hz),
7.72 (t, 1H, H-6, J¼8.3 Hz), 7.85 (t, 1H, H-500, J¼7.9 Hz),
8.10 (d, 1H, H-30, J¼7.9 Hz), 8.19 (d, 1H, H-6 , J¼7.9 Hz).
13C NMR: d 56.2 (OCH3), 104.0 (C-a), 104.4 (C-7), 106.7
(C-5), 109.04 (C-9), 124.8 (C-30), 125.9 (C-10), 130.1 (C-40),
131.9 (C-6 ), 133.3 (C-50), 139.7 (C-6), 147.7 (C-2), 148.7
(C-20), 158.2 (C-8), 166.3 (C-4), 180.4 (CvO). EI-MS: m/z
(rel. intensity) 297 (Mþz, 7), 280 (22), 267 (25), 251 (71),
236 (100), 221 (13), 208 (47), 180 (47), 165 (48). IR n 1708,
Acknowledgements
Thanks are due to the University of Aveiro, ‘Fundac¸a˜o para a
ˆ
Ciencia e Tecnologia‘ and FEDER for funding the Organic
Chemistry Research Unit (62/94). Financial support from
´
the University of Tras-os-Montes e Alto Douro is gratefully
acknowledged. This work has been partially supported by
the DGI of the Project Nos. BQU2003-01251.
1656, 1602, 1519, 1496, 1347, 1251, 1193, 1074, 794 cm21
.
Anal. calcd for C16H11NO5: C 64.65, H 3.70, N 4.71. Found:
C 64.45, H 3.67, N 4.62.
References and notes
4.2.14. 4-Methoxy-40-nitroaurone (4j). Mp 201.5–
202.3 8C (recrystallised from ethanol). H NMR: d 3.95 (s,
1
1. Dhar, D. N. The Chemistry of Chalcones and Related
Compounds; Wiley: New York, 1981.
3H, OCH3), 6.89 (s, 1H, H-a), 7.04 (d, 1H, H-7, J¼8.1 Hz),
7.74 (t, 1H, H-6, J¼8.1 Hz), 7.88 (d, 1H, H-5, J¼8.1 Hz),
8.16 (d, 2H, H-20,60, J¼8.8 Hz), 8.28 (d, 2H, H-30,50,
J¼8.8 Hz). 13C NMR: d 56.1 (OCH3), 104.4 (C-7), 106.7
(C-50), 107.4 (C-a), 109.3 (C-9), 123.6 (C-30,500), 131.5
(C-2 ,60), 138.5 (C-10), 139.5 (C-6), 146.9 (C-4 ), 147.8
(C-2), 158.1 (C-8), 166.2 (C-4), 180.5 (CvO). EI-MS: m/z
(rel. intensity) 297 (Mþz, 100), 298 (14), 280 (3), 268 (17),
236 (8), 221 (28), 165 (15), 139 (4), 107 (9), 89 (16), 76
(26), 63 (21). IR n 1704, 1654, 1604, 1494, 1336, 1255,
1078, 796 cm21. Anal. calcd for C16H11NO5: C 64.65, H
3.70, N 4.71. Found: C 64.46, H 3.66, N 4.71.
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222.0 8C (recrystallised from ethanol). H NMR: d 3.93 (s,
6H, OCH3), 6.40 (d, 1H, H-5, J¼1.5 Hz), 6.68 (d, 1H, H-7,
J¼1.5 Hz), 6.950 (s, 1H, H-a), 7.68 (t, 1H, H-400, J¼7.8 Hz),
7.86 (t, 1H, H-5 ,0J¼7.8 Hz), 8.13 (d, 1H, H-3 , J¼7.8 Hz),
8.19 (d, 1H, H-6 , J¼7.8 Hz). 13C NMR: d 56.4 (OCH3),
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