Synthesis of α-azido-2′-hydroxychalcones from chalcone dibromides with azide ion

Article abstract of DOI:10.1081/SCC-120006013

The reaction of the 2′-hydroxychalcone dibromides with azide ion was found to afford various products such as α-azido-2′-hydroxychalcones, flavones, aurones, isoxazoles or the parent chalcones depending on the substituent pattern of the substrate. Efficie

Full text of DOI:10.1081/SCC-120006013

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SYNTHESIS OF α-AZIDO-2′-HYDROXYCHALCONES FROM
CHALCONE DIBROMIDES WITH AZIDE ION
Tamás Patonay a , József Jekö b & Éva Rimán a
a Department of Organic Chemistry, University of Debrecen, Debrecen, H-4010, Hungary
b ICN Hungary, Tiszavasvári, H-4440, Hungary
Published online: 16 Aug 2006.
To cite this article: Tamás Patonay , József Jekö & Éva Rimán (2002): SYNTHESIS OF α-AZIDO-2′-HYDROXYCHALCONES FROM
CHALCONE DIBROMIDES WITH AZIDE ION, Synthetic Communications: An International Journal for Rapid Communication of
Synthetic Organic Chemistry, 32:15, 2403-2415
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SYNTHETIC COMMUNICATIONS
Vol. 32, No. 15, pp. 2403–2415, 2002
SYNTHESIS OF
a-AZIDO-20-HYDROXYCHALCONES
FROM CHALCONE DIBROMIDES
WITH AZIDE ION
00
Tamas Patonay,1, Jozsef Jeko,2 and Eva Riman1
*
1Department of Organic Chemistry,
University of Debrecen, H-4010 Debrecen, Hungary
2ICNHungary, H-4440 Tiszavasva ri, Hungary
Dedicated to Prof. Albert Levai on the occasion of his
60th birthday
ABSTRACT
The reaction of the 20-hydroxychalcone dibromides with azide
ion was found to afford various products such as a-azido-20-
hydroxychalcones, flavones, aurones, isoxazoles or the parent
chalcones depending on the substituent pattern of the sub-
strate. Efficient transformation of a-azido-20-hydroxy-
chalcones to 3-amino-2-substituted chromones was also
demonstrated.
Key Words: Azides; Chalcones dibromides; Flavones;
Isoxazoles; Substituent effect
*Corresponding author. E-mail: tpatonay@tigris.klte.hu
2403
DOI: 10.1081/SCC-120006013
Copyright & 2002 by Marcel Dekker, Inc.
0039-7911 (Print); 1532-2432 (Online)
www.dekker.com

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00
PATONAY, JEKO, AND RIMAN
2404
INTRODUCTION
20-Hydroxychalcone dibromides have been studied very thoroughly
due to their synthetic importance in the preparation of 2-aryl-4H-1-benzo-
pyran-4-ones (flavones), 2-arylmethylenbenzo[b]furan-3(2H)-ones (aurones)
and related derivatives.[1–3] It was also pointed out that the reaction of 20-
hydroxychalcone dibromide and its 4-substituted derivatives with azide ion
resulted in the formation a-azido-20-hydroxychalcone.[4,5] The reaction was
found to depend strongly on the electronic character of the substituent in
position 4. In the presence of electron-withdrawing group other reactions
such as the formation of aurones, 3-(2-hydroxyphenyl)-5-(4-substituted
phenyl)isoxazoles and 3(5)-(2-hydroxybenzoyl)-5(3)-(4-substituted phenyl)-
1,2,3-triazoles dominated and a-azides were only minor products. The prod-
uct distribution was interpreted on the basis of mechanistic considerations [5]
but no studies were performed on the effect of the substituents in ring A or
the change of ring B for heteroaromatic moiety. As a part of an on-going
project we were interested in the synthesis of various 3-aminoflavones and -
chromones and investigated the reaction of chalcone dibromides with the
above-mentioned substituent pattern and azide ion. Some selected and char-
acteristic results are presented in this contribution.
RESULTS AND DISCUSSION
Starting material dibromides 2a–e were synthesized in good yields
(60–79%) by the reaction of the corresponding 1-(2-hydroxyphenyl)-3-phe-
nyl/hetaryl-2-propen-1-ones 1a–e with pyridinium tribromide (PTB) in
acetic acid[6] at room temperature (Scheme 1). The erythro relative config-
3
uration was proven by the large Ja,b coupling constants (11.0–11.7 Hz)
1
observed in their H NMR spectra. Surprisingly, no chalcone dibromide
2f but a diastereomeric mixture of cis -and trans-3-bromo-2-(3-methyl-2-
thienyl)chromanone (3) with a ratio of 58 : 42 was obtained from chalcone
1f under similar conditions. The structure of 3 was supported by spectro-
scopic evidences and its easy transformation into chromone 5f upon treat-
ment by triethyl amine. The desired erythro-2f was prepared by using
bromine in diethyl ether as brominating reagent.
The reaction of dibromides 2a–f with sodium azide in DMF solution
at room temperature[5] afforded various products such as Z-a-azidochal-
cones 4, flavones 5, aurones 6, isoxazoles 7 and parent chalcones 1 which
were separated by column chromatography. The product ratio depended
strongly on the substituents R1–R3 and Ar (Scheme 1, Table 1). The for-
mation of azides 4 took place with complete diastereoselectivity, the Z

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a-AZIDO-20-HYDROXYCHALCONES
2405
Scheme 1.
Table 1. Product Distribution in the Reaction of Dibromides 2 and NaN3
Yielda (%)
Starting
Mat’l
R1
R2
R3
Ar
1
4
5
6
7
2a
2b
2c
2d
2e
2f
Cl
Me
H
H
H
H
H
Me
Cl
H
Cl
H
H
H
H
H
Ph
Ph
Ph
0
0
0
0
2.5
0
93
0
1.5
27
0
30
0
0
0
3.8
5.0
0
0
75
73
50
5.2
1.7
2.5
3.8
2.3
51.2
0
Ph
2-benzofuryl
3-Me-2-thienyl
H
H
47
aYields refer to pure isolated products.

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00
PATONAY, JEKO, AND RIMAN
2406
relative configuration of the products was assigned on the basis of their
spectral data.[7] Structure elucidation of products 7 was crucial since both
isoxazoles and the isomeric oxazoles could be formed from the intermediate
b-azidochalcones 12 (vide infra) depending on their stereochemistry.
Z-b-azidovinyl ketones were reported to give isoxazoles by spontaneous
loss of nitrogen whereas E isomers were found more stable and yielded
[8–12]
oxazoles only at elevated temperature or under photolytic conditions
but it was unknown how structural changes in the substrate modified its
reactivity. Our products were unequivocally assigned as isoxazoles on the
basis of the measured 13C chemical shifts of the heteroring which fitted
excellently with the ranges reported by Baumstark and his coworkers for
3,5-diarylisoxazoles.[13] Consequently, the intermediates 12 should possess
of Z stereochemistry.
Analysis of product ratio data given in the Table 1 led us to some
conclusions which could be important in designing of syntheses. In the
presence of electron-attracting chloro substituent(s) the formation of
chromones 5 by b cyclization of intermediate 9 and the subsequent
HBr elimination from 3-bromochromanone 10 is preferred (Scheme 2),
the more acidic phenolate tends to add faster to the b carbon atom of
Scheme 2.

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a-AZIDO-20-HYDROXYCHALCONES
2407
the enone system and consequently the yield of azide 4 decreases. Data
collected in the Table 1 reveal that aurones 6 and isoxazoles 7 are only
minor products, if any. The only exception is the reaction of the 2-ben-
zofuryl derivative 2e. Compounds 6 and 7 were reported[5,8] to be formed
via b-azidochalcones 12 and the participation of this pathway (Scheme 2)
is usually smaller than of the route leading to azides 4 unless Ar group
exerts a marked stabilizing effect on the b-carbanions of E1cB steps.[5,8]
The extended delocalisation in the adjacent 2-benzofuryl unit clearly
provides this stabilization.
Surprisingly, azide ion-induced dehalogenation leading to the parent
chalcone 1f was the major route in the reaction of dibromide 2f (Scheme 2).
Similar dehalogenation have also been observed as a side reaction in the case
of 20-hydroxy-4-methoxychalcone dibromide[5] but it have been found to be
major pathway in the reaction of some a-arylidene benzo(hetera)cyclanone
dibromides [14]. The increasing stabilization of the benzylic type cation by
the b-aryl or heteroaryl group supports this dehalogenation. Noteworthy
that Donnelly and coworkers[15] have been published on the similarity of the
effects of 2-thienyl and 4-methoxyphenyl substituents in the chalcone series.
By comparing the product distribution of heteroaryl derivatives 2e and 2f
we can also conclude that there is no general rule for the reactivity of
dibromides 2 with heterocyles in their position b and the electronic character
of the group plays decisive role.
In accordance with our earlier observations,[4,5] the treatment of azides
4b–f with sodium hydroxide in methanol solution resulted in the formation
of 3-amino-2-substituted-chromones 8b–f in good-to-excellent yields
(62–93%) (Scheme 1) proving that this method is the more efficient
approach to these target compounds.
EXPERIMENTAL SECTION
General
Column chromatography was performed on Kieselgel 60 or Kieselgel
40.—Melting points: Boetius hot-stage, uncorrected values. – IR: Perkin
Elmer 16 PC-FT-IR; KBr pellets unless otherwise stated. – NMR: Varian
1
Gemini 200, Bruker WP 200 SY, Bruker AM 360 (200 or 360 MHz for H;
50 or 90 MHz for 13C), recorded in CDCl3 solution unless otherwise stated.
Chemical shifts are given in ꢀ relative to an internal standard TMS (ꢀ ¼ 0) or
1
to the residual CHCl3 (ꢀ ¼ 7.26 for H NMR and ꢀ ¼ 77.0 for 13C NMR).—
MS: VG Trio-2 (EI, 70 eV). – Elemental analysis: Carlo Erba EA 1106 CHN

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PATONAY, JEKO, AND RIMAN
2408
analyzer.—Starting chalcones 1a16, 1b17, 1c18, and 1d19 were synthesized
according to literature procedures.
Synthesis of trans-3-Hetaryl-1-(2-hydroxyphenyl)-2-propen-1-ones 1e,f.
General procedure: A mixture of 20-hydroxyacetophenone (14.4 mL,
0.1196 mol), the appropriate aldehyde (0.1175 mol), methanol (200 mL)
and 50% NaOH solution (2.8 mL) was allowed to stand at room tempera-
ture for 24 h then acidified with dil. hydrochloric acid and the precipitation
was filtered off. The crude product was purified by crystallization.
trans-3-(2-Benzofuryl)-1-(2-hydroxyphenyl)-2-propen-1-one(1e): Yield:
44%. M.p. 125–126ꢀC (methanol–ethyl acetate). IR: 1641 (C¼O), 1571,
1486, 1289, 1256, 1199, 947, 801, 745 cmꢁ1. H NMR: 6.97 (d, 1H, 50-H),
1
7.04 (dd, J ¼ 8.4, 1.6 Hz, 1H, 30-H), 7.09 (s, 1H, 300-H), 7.27 (m, 1H, 600-H),
7.41 (m, 1H, 500-H), 7.52 (m, 2H, 40, 700-H), 7.63 (dd, J ¼ 8.1, 1.7 Hz, 400-H),
7.79, 7.80 (AB q, J ¼ 16 Hz, 2H, Ha, Hb), 8.00 (dd, J ¼ 7.7, 2.0 Hz, 1H, 60-H),
12.84 (s, 1H, 20-OH). MS: 264 (Mꢂꢃ, 57), 247 (M–OH, 7), 236 (M–CO, 7), 221
(6), 171 (M–PhO, 11), 144 (RDA fragment, 100), 131 (benzopyrylium ion,
88), 120 (RDA fragment, 20), 115 (36), 89 (17), 77 (8), 65 (33). Anal. calcd for
C17H12O3 (264.28): C, 77.26; H, 4.58%. Found: C, 77.02; H, 4.74%.
trans-1-(2-Hydroxyphenyl)-3-(3-methyl-2-thienyl)-2-propen-1-one
(1f):
Yield: 59%. M.p. 77–78ꢀC (methanol). IR: 3434 (OH), 1632 (C¼O), 1560,
1440, 1336, 1302, 1264, 1246, 1200, 1152, 842, 760, 728 cmꢁ1. 1H NMR: 2.42
(s, 3H, 300-Me), 6.94 (m, 1H, 50-H), 6.93 (d, J ¼ 5.1 Hz, 1H, 400-H), 7.02 (dd,
J ¼ 8.4, 1.5 Hz, 1H, 30-H), 7.36 (d, J ꢄ 5.0 Hz, 1H, 500-H), 7.38 (d,
J ¼ 15.0 Hz, 1H, Ha), 7.49 (m, 1H, 40-H), 7.89 (dd, J ¼ 8.1, 2.0 Hz, 1H, 60-
H), 8.14 (dd, J ¼ 15.0, 0.9 Hz, 1H, Hb), 12.94 (s, 1H, 20-OH). Anal. calcd. for
C14H12O2S (244.30): C, 68.83; H, 4.95%. Found: C, 69.03; H, 5.11%.
Synthesis of erythro-20-hydroxychalcone dibromides 2. General
Procedure: To a stirred suspension of trans-20-hydroxychalcone 1 (5.50 mmol)
in acetic acid (15 mL), pyridinium tribromide (PTB) (2.110 g, 6.597 mmol)
was added in portions at room temperature in 1 h. After 24 h stirring
the mixture was poured into water, the precipitate was filtered off and
washed with water. The crude product was crystallized from hexane–
benzene (5 : 1).
erythro-30,50-Dichloro-20-hydroxychalcone dibromide (2a): Yield: 60%.
M.p. 151–152ꢀC. (Lit.[16] 115–116ꢀC). IR: 1647 (C¼O), 1430, 1322, 1238,
1226, 1160, 767, 740, 702, 692 cmꢁ1 1H NMR (DMSO-d6): 5.78 (d,
.
J ¼ 11.7 Hz, 1H, Ha), 6.79 (d, J ¼ 11.7 Hz, 1H, Hb), 7.46 (m, 3H, 3,4,5-H),
7.80 (dd, J ¼ 7.8, 1.9 Hz, 2H, 2,6-H), 8.05 (d, J ¼ 2.2 Hz, 1H, 40-H), 8.24 (d,
J ¼ 2.2 Hz, 1H, 60-H), 11.70 (s, 1H, 20-OH). Anal. calcd for C15H10Br2Cl2O2
(452.95): C, 39.78; H, 2.23%. Found: C, 40.02; H, 2.08%.
erythro-20-Hydroxy-50-methylchalcone dibromide (2b): Yield: 78%.
M.p. 146–148ꢀC. (Lit.[20] 146ꢀC, lit.[21] 151–152ꢀC).

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a-AZIDO-20-HYDROXYCHALCONES
2409
erythro-20-Hydroxy-40-methylchalcone dibromide (2c): Yield: 72%.
M.p. 158–159ꢀC. IR: 1639 (C¼O), 1338, 1302, 1255, 1236, 1213, 1136,
783, 693 cmꢁ1
.
1H NMR: 2.41 (s, 3H, 40-Me), 5.64 (d, J ¼ 11.3 Hz, 1H,
Ha), 5.87 (d, J ¼ 11.3 Hz, 1H, Hb), 6.83 (dd, J ¼ 7.5, 1.5 Hz, 1H, 50-H),
6.91 (br s, 1H, 30-H), 7.38–7.57 (m, 5H, Ph), 7.74 (d, J ¼ 8.2 Hz, 1H, 60-
H), 11.89 (s, 1H, 20-OH). Anal. calcd for C16H14Br2O2 (398.09): C, 48.27; H,
3.54%. Found: C, 48.07; H, 3.79%.
erythro-40-Chloro-20-hydroxychalcone dibromide (2d): Yield: 73%. M.p.
185–187ꢀC. (Lit.[22] 180ꢀC). IR: 1641 (C¼O), 1612, 1482, 1242, 1200, 1182,
1078, 979, 903, 773, 691 cmꢁ1. H NMR (DMSO-d6): 5.78 (d, J ¼ 11.4 Hz,
1
1H, Ha), 6.61 (d, J ¼ 11.4 Hz, 1H, Hb), 7.10–7.18 (m, 2H, 30,50-H), 7.34–7.48
(m, 3H, 3,4,5-H), 7.70 (dd, J ¼ 8.2, 2.0 Hz, 2H, 20,60-H), 8.10 (d, J ¼ 8.0 Hz,
1H, 60-H), 11.74 (s, 1H, 20-OH). Anal. calcd for C15H11Br2ClO2 (418.51): C,
43.05; H, 2.65%. Found: C, 42.97; H, 2.77%.
erythro-3-(2-Benzofuryl)-2,3-dibromo-1-(2-hydroxyphenyl)-1-propanone
(2e): Yield: 79%. M.p. 173–175ꢀC (hexane-ethyl acetate). IR: 1633 (C¼O),
1613, 1540, 1450, 1299, 1280, 1249, 1196, 751 cmꢁ1 1H NMR: 5.88 (d,
.
J ¼ 11.0 Hz, 1H, Ha), 6.15 (d, J ¼ 11.0 Hz, 1H, Hb), 6.96 (s, 1H, 300-H),
7.00–7.13 (m, 2H, 30,50-H), 7.31, 7.42 (2xm, 2H, 500,600-H), 7.57–7.66 (m,
3H, 40,400,700-H), 7.92 (dd, J ¼ 8.1, 1.3 Hz, 1H, 60-H), 11.80 (s, 1H, 20-OH).
Anal. calcd for C17H12Br2O3 (424.08): C, 48.15; H, 2.85%. Found: C, 47.99;
H, 2.96%.
erythro-2,3-Dibromo-1-(2-hydroxyphenyl)-3-(3-methyl-2-thienyl)-1-pro-
panone (2f): To a solution of 1-(2-hydroxyphenyl)-3-(3-methyl-2-thienyl)-2-
propene-1-one (1f) (1.8 g, 7.368 mmol) in diethyl ether (40 mL), bromine
(0.6 mL, 11.646 mmol) was dropped under stirring at 0ꢀC. The precipitate
was filtered off, washed with diisopropyl ether and recrystallized from
diethyl ether to give 2.193 g (74%) of pure 2f. M.p. 119–121ꢀC. IR: 1636
(C¼O), 1574, 1486, 1448, 1304, 1248, 1200, 752, 724 cmꢁ1. 1H NMR: 2.33 (s,
3H, 300-Me), 5.86 (d, J ¼ 11.0 Hz, 1H, Ha), 6.06 (dd, J ¼ 11.0, 0.9 Hz, 1H,
Hb), 6.83 (d, J ¼ 5.1 Hz, 1H, 400-H), 6.96–7.18 (m, 2H, 30,50-H), 7.39 (d,
J ¼ 5.1 Hz, 1H, 500-H), 7.57 (m, 1H, 40-H), 7.84 (dd, J ¼ 8.4, 1.6 Hz, 1H,
60-H), 11.78 (s, 1H, 20-OH). MS: 244 (Mꢂꢃ– Br2, 50), 243 (19), 236 (M-
Br2 – H2O, 29), 151 (12), 124 (3-Me-2-vinylthiophene, 100), 120 (M—Br2
– 3-Me-2-vinylthiophene, 62), 111 (35), 97 (23), 78 (31), 77 (31). Anal. calcd
for C14H12Br2O2S (404.11): C, 41.61; H, 2.99%. Found: C, 41.88; H, 3.12%.
Synthesis of 2-(3-Methyl-2-thienyl)chromone (5f) via 3-bromo-2-(3-
methyl-2-thienyl)chromanone (3): To a stirred solution of trans-1-(2-hydroxy-
phenyl)-3-(3-methyl-2-thienyl)-2-propen-1-one (1f) (2.443 g, 10.000 mmol) in
acetic acid (25 mL), PTB (3.520 g, 11.055 mmol) was added at room tempera-
ture. After 18 h the mixture was poured into water, extracted with chloroform
(3 ꢅ 60 mL), the extract was washed with NaHCO3 solution, dried (Na2SO4)

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00
PATONAY, JEKO, AND RIMAN
2410
and concentrated under reduced pressure. Column chromatography separa-
tion (1,2-dichloroethane–hexane ¼ 2 : 1) of the residue afforded 2.567 g (79%)
oily 3 product.
3. IR (neat): 1694 (C¼O), 1606, 1580, 1472, 1462, 1338, 1300, 1222 (C–
1
O–C), 1150, 1114, 1020, 764, 718 cmꢁ1. H NMR: 2.27, 2.32 (2 ꢅ s, 2 ꢅ 3H,
30-Me), 4.54 (d, J ¼ 1.5 Hz, 1H, 3-H, cis-3), 4.95 (d, J ¼ 9.1 Hz, 1H, 3-H,
trans-3), 5.69 (d, J ¼ 1.5 Hz, 1H, 2-H, cis-3), 5.85 (d, J ¼ 9.1 Hz, 1H, 2-H,
trans-3), 6.87, 6.90 (2 ꢅ d, J ¼ 5.1 Hz, 2 ꢅ 1H, 40-H), 7.03–7.19 (m, 2H, 6,8-H),
7.27, 7.35 (2 ꢅ d, J ¼ 5.1 Hz, 2 ꢅ 1H, 50-H), 7.52-7.59 (m, 1H, 7-H),
7.96–8.04 (m, 1H, 5-H). Diastereomeric ratio trans-3/cis-3 ¼ 42 : 58 was
1
determined by H NMR spectroscopy.
A mixture of 3 (2.301 g, 7.119 mmol), triethyl amine (1.3 mL,
9.366 mmol) and DMF (15 mL) was stirred for 3 d, then poured into
water, extracted with chloroform (3 ꢅ 40 mL), the extract was washed
with water, dried (CaCl2) and the solvent was removed under reduced press-
ure. The oily residue solidified on standing. Hexane–abs. ethanol (10 : 1)
mixture was added, the crude product was filtered off and recrystallized
from hexane–ethyl acetate (5 : 1) mixture to give 651 mg (38%) pure 5f pro-
duct. M.p. 77–78ꢀC. IR 1640 (C¼O), 1596, 1569, 1466, 1414, 1362, 1128,
778 cmꢁ1 1H NMR: 2.58 (s, 3H, 30-Me), 6.64 (s, 1H, 3-H), 6.99 (d,
.
J ¼ 5.2 Hz, 40-H), 7.39 (m, 1H, 6-H), 7.44 (d, J ¼ 5.2 Hz, 50-H), 7.51 (dd,
J ¼ 8.4 Hz, 1H, 8-H), 7.70 (m, 1H, 7-H), 8.23 (dd, J ¼ 8.0, 1.9 Hz, 1H, 5-H).
Anal. calcd for C14H10O2S (242.29): C, 69.40; H, 4.16%. Found: C, 69.57;
H, 4.02%.
Treatment of 20-hydroxychalcone dibromides 2 with sodium azide.
General procedure:
A mixture of the corresponding dibromide 2
(10.000 mmol), NaN3 (2.423 g, 37.271 mmol) and DMF (45 mL) was stirred
at room temperature for 3 h then poured into water and extracted with
dichloromethane (4 ꢅ 40 mL). The dried (MgSO4) extract was concentrated
under reduced pressure and the residue was submitted to column chroma-
tography (hexane–ethyl acetate ¼ 4 : 1 or 1,2-dichloroethane–toluene ¼ 3 : 1).
The mixed fractions of lower Rf value were re-chromatographed (tolue-
ne–ethyl acetate ¼ 4 : 1 and/or hexane–acetone ¼ 6 : 1) to give pure products.
Yields of isolated products are shown in the Table 1, physical and spectral
characteristics of products are listed below.
Z-a-Azido-20-hydroxy-50-methylchalcone (4b): M.p. 82–85ꢀC (dec.). IR:
2116 (N3), 1630 (C¼O), 1586, 1482, 1448, 1340, 1292, 1238, 1192,
840, 692 cm1. 1H NMR: 2.30 (s, 3H, 50-Me), 6.36 (s, 1H, Hb), 6.99
(d, J ¼ 8.3 Hz, 1H, 30-H), 7.25–7.46 (m, 4H, 3,4,5,40-H), 7.56
(d, J ¼ 1.7 Hz, 1H, 60-H), 7.83 (dd, J ¼ 8.1, 1.8 Hz, 2H, 2,6-H), 10.94 (s,
1H, 20-OH). 13C NMR: 20.4 (50-Me), 118.1 (Ca), 118.4 (C-30), 127.7 (C-4),
128.2 (C-10), 128.6 (C-2,6), 129.6 (Cb), 130.4 (C-3,5), 131.8 (C-60), 132.5,

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a-AZIDO-20-HYDROXYCHALCONES
2411
133.0 (C-1,50), 137.8 (C-40), 160.8 (C-20), 184.6 (C¼O). Anal. calcd for
C16H13N3O2 (279.29): C, 68.81; H, 4.69; N, 15.04%. Found: C,
69.02; H, 4.55; N, 14.89%.
Z-a-Azido-20-hydroxy-40-methylchalcone (4c): M.p. 82–85ꢀC (metha-
nol). IR: 2118 (N3), 1628 (C¼O), 1610, 1502, 1449, 1382, 1345, 1296,
1244, 910, 772 cmꢁ1. H NMR: 2.40 (s, 3H, 50-Me), 6.32 (s, 1H, Hb), 6.76
1
(d, J ¼ 8.1 Hz, 1H, 50-H), 6.89 (br s, 1H, 30-H), 7.31–7.44 (m, 3H, 3,4,5-H),
7.69 (d, J ¼ 8.1 Hz, 1H, 60-H), 7.81 (dd, J ¼ 7.9, 1.7 Hz, 2H, 2,6-H), 11.28 (s,
1H, 20-OH). Anal. calcd for C16H13N3O2 (279.29): C, 68.81; H, 4.69; N,
15.04. Found: C, 69.04; H, 4.65; N, 14.99.
Z-a-Azido-40-chloro-20-hydroxychalcone (4d): M.p. 90–94ꢀC (dec.)
(methanol). IR: 2118 (N3), 1620 (C¼O), 1485, 1447, 1377, 1331, 1203,
1
1060, 945, 775 cmꢁ1. H NMR: 6.33 (s, 1H, Hb), 6.92 (dd, J ¼ 8.2, 2.1 Hz,
1H, 50-H), 7.11 (d, J ¼ 2.1 Hz, 1H, 30-H), 7.33–7.50 (m, 3H, 3,4,5-H), 7.74 (d,
J ¼ 8.2 Hz, 1H, 60-H), 7.83 (m, 2H, 2,60-H), 11.29 (s, 1H, 20-OH). Anal. calcd
for C15H10ClN3O2 (299.71): C, 60.11; H, 3.36; N, 14.02%. Found: C, 59.89;
H, 3.35; N, 13.72%.
Z-2-Azido-3-(2-benzofuryl)-1-(2-hydroxyphenyl)-2-propene-1-one (4e):
M.p. 108–109ꢀC (methanol). IR: 2122 (N3), 1622 (C¼O), 1598, 1584,
1
1544, 1484, 1370, 1340, 1278, 1208, 740 cmꢁ1. H NMR: 6.49 (s, 1H, Hb),
6.96 (m, 1H, 50-H), 7.09 (dd, J ¼ 8.4, 0.9 Hz, 1H, 30-H), 7.28, 7.34 (2 ꢅ m,
2 ꢅ 1H, 500,600-H), 7.45 (dd, J ¼ 8.2, 0.7 Hz, 1H, 700-H), 7.55 (m, 2H, 40,300-H),
7.64 (dd, J ¼ 7.0, 1.2 Hz, 1H, 400-H), 7.77 (dd, J ¼ 8.0, 1.6 Hz, 1H, 60-H),
10.97 (s, 1H, 20-OH). 13C NMR: 111.2, 111.5 (C-300,700), 116.4 (C-30), 118.2
(Ca), 118.8, 119.2, 122.0, 123.4, 126.2 (Cb, C-50,400,500,600), 128.7 (C-100), 131.9
(C-60), 133.0 (C-3a00), 136.8 (C-40), 150.3 (C-7a00), 154.9 (C-200), 162.7 (C-20),
193.1 (C-1). Anal. calcd for C17H11N3O3 (305.29): C, 66.88; H, 3.63; N,
13.76%. Found: C, 66.98; H, 3.42; N, 13.57%.
Z-2-Azido-1-(2-hydroxyphenyl)-3-(3-methyl-2-thienyl)-2-propene-1-one
(4f): Orange oil. IR (neat): 3070, 2922 (OH), 2112 (N3), 1628 (C¼O), 1558,
1330, 1260, 1218, 1176, 1030, 1010, 964, 944, 772 cmꢁ1 1H NMR: 2.35
.
(s, 3H, 300-Me), 6.79 (s, 1H, Hb), 6.80 (d, J ꢄ 5.0 Hz, 1H, 400-H), 7.07–7.21
(m, 2H, 30,50-H), 7.56 (d, J ¼ 5.0 Hz, 1H, 500-H), 7.75 (m, 1H, 40-H), 7.92
(dd, J ¼ 8.7, 2.2 Hz, 1H, 60-H), 10.97 (s, 1H, 20-OH). Anal. calcd for
C14H11N3O2S (285.32): C, 58.94; H, 3.89; N, 14.73%. Found: C, 59.11;
H, 3.51; N, 14.48%.
6,8-Dichloroflavone (5a): M.p. 165–167ꢀC (ethyl methyl ketone).
(Lit.[23] 154ꢀC). IR: 3072 (C-H), 1665 (C¼O), 1640 (C¼C), 1562, 1461,
1
1440, 1350, 1302, 872, 769 cmꢁ1. H NMR: 6.88 (s, 1H, 3-H), 7.53–7.60
(m, 3H, 30,40,50-H), 7.75 (d, J ¼ 2.5 Hz, 1H, 7-H), 7.97–8.02 (m, 2H, 20,60-
H), 8.11 (d, J ¼ 2.5 Hz, 1H, 5-H). Anal. calcd for C15H8Cl2O2 (291.13): C,
61.88; H, 2.77%. Found: C, 61.69; H, 2.58%.

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PATONAY, JEKO, AND RIMAN
2412
7-Methylflavone (5c): M.p. 116–120ꢀC (hexane). (Lit.[24] 123ꢀC).
1H NMR: 2.51 (s, 3H, 7-Me), 6.88 (s, 1H, 3-H), 7.27 (dd, J ¼ 8.0, 1.4 Hz,
1H, 6-H), 7.38 (br s, 1H, 8-H), 7.51 (m, 3H, 30,40,50-H), 7.92 (m, 2H, 20,60-H),
8.12 (d, J ¼ 8.0 Hz, 1H, 5-H).
7-Chloroflavone (5d): M.p. 153–154ꢀC (hexane–abs. ethanol). (Lit.[19]
156–157ꢀC) 1H NMR: 6.83 (s, 1H, 3-H), 7.38 (dd, J ¼ 8.6, 1.8 Hz, 1H, 6-H),
7.51–7.56 (m, 3H, 30,40,50-H), 7.59 (d, J ¼ 1.8 Hz, 1H, 8-H), 7.90 (m, 2H,
20,60-H), 8.16 (d, J ¼ 8.6 Hz, 1H, 50-H).
6-Chloroaurone (6d): M.p. 140–142ꢀC (benzene–hexane). (Lit.[22]
195ꢀC). IR: 1712 (C¼O), 1658 (C¼C), 1605, 1429, 1126, 1057, 919,
1
768 cmꢁ1. H NMR: 6.90 (s, 1H, Ha), 7.21 (dd, J ¼ 8.1, 1.9 Hz, 1H, 5-H),
7.38 (d, J ¼ 1.9 Hz, 7-H), 7.45 (m, 3H, 30,40,50-H), 7.75 (d, J ¼ 8.1 Hz, 1H, 4-H),
7.89 (dd, J ¼ 7.9, 2.3 Hz, 2H, 20,60-H). Anal. calcd for C15H9ClO2 (256.68):
C, 70.19; H, 3.53%. Found: C, 70.17; H, 3.47%.
2-[(2-Benzofuryl)methylene]coumaranone (6e): M.p. 152–154ꢀC (metha-
nol). IR: 1697 (C¼O), 1641 (C¼C), 1595, 1458, 1298, 1185, 1097, 873,
738 cmꢁ1. H NMR: 6.93 (s, 1H, Ha), 7.04–7.39 (m, 4H, 5,7,50,60-H), 7.43
1
(s, 1H, 30-H), 7.52 (d, J ¼ 8.1 Hz, 1H, 70-H), 7.65 (m, 2H, 6,40-H), 7.77 (d,
J ¼ 7.6 Hz, 1H, 4-H). 13C NMR: 101.4 (C-30), 111.5, 112.9 (C-7, C-70, Ca),
121.7, 123.4, 123.7, 124.6, 126.3 (C-4,5,40,50,60), 128.7 (C-3a,30a), 136.9 (C-6),
146.8 (C-2), 150.1 (C-70a), 150.6 (C-20), 165.8 (C-7a), 183.7 (C-3).
Anal. calcd for C17H10O3 (262.26): C, 77.86; H, 3.84%. Found: C, 78.04;
H, 3.89%.
5-(2-Hydroxy-5-methylphenyl)-3-phenylisoxazole (7b): M.p. 207–210ꢀC
(DMSO). (Lit.[25] 209–211ꢀC, Lit.[26] 214–216ꢀC). IR: 3114 br (OH), 1624
(C¼N, isoxazole), 1470 (isoxazole skeleton), 1406, 1280, 1246, 800,
766 cmꢁ1. H NMR (DMSO-d6): 2.33 (s, 3H, 50-Me), 7.01 (d, J ¼ 8.7 Hz,
1
1H, 30-H), 7.20 (dd, J ¼ 8.4, 2.3 Hz, 1H, 40-H), 7.34 (s, 1H, 4-H),
7.56–7.59 (m, 3H, 300,400,500-H), 7.67 (d, J ¼ 2.3 Hz, 1H, 60-H), 7.96–7.98
(m, 2H, 200,600-H), 10.44 (s, 1H, 20-OH).
5-(2-Hydroxy-4-methylphenyl)-3-phenylisoxazole (7c): M.p. 232–235ꢀC
(DMSO). (Lit.[26] 240–242ꢀC). IR: 3126 br (OH), 2922, 1622 (C¼N, isoxa-
1
zole), 1574, 1472 (isoxazole skeleton), 1410, 1256, 814, 766 cmꢁ1. H N MR
(DMSO-d6): 2.33 (s, 3H, 40-Me), 6.84 (d, J ¼ 8.0 Hz, 1H, 50-H), 6.92 (br s,
1H, 30-H), 7.29 (s, 1H, 4-H), 7.55 (m, 3H, 300,400,500-H), 7.74 (d, J ¼ 8.0 Hz,
1H, 60-H), 7.94–7.97 (m, 2H, 200,600-H), 10.57 (s, 1H, 20-OH).
5-(4-Chloro-2-hydroxyphenyl)-3-phenylisoxazole (7d): M.p. 268–271ꢀC
(DMSO). IR: 3050 br (OH), 1616 (C¼N, isoxazole), 1472 (isoxazole skele-
ton), 1420, 1262, 850, 796, 766 cmꢁ1 1H NMR (DMSO-d6): 7.06 (dd,
.
J ¼ 8.4, 1.9 Hz, 1H, 50-H), 7.12 (d, J ¼ 1.9 Hz, 1H, 30-H), 7.35 (s, 1H, 40-
H), 7.52–7.56 (m, 3H, 300,400,500-H), 7.85 (d, J ¼ 8.4 Hz, 1H, 60-H), 7.92–7.97
(m, 2H, 200,600-H), 11.22 (br s, 1H, 20-OH). 13C NMR (DMSO-d6): 101.3 (C-

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a-AZIDO-20-HYDROXYCHALCONES
2413
4), 108.4 (C-30), 119.8 (C-50), 126.9 (C-300,500), 128.4 (C-60), 128.9 (C-100),
129.3 (C-200,600), 130.4 (C-400), 135.6 (C-40), 155.9 (C-200), 162.7 (C-3), 166.0
(C-5). Anal. calcd for C15H10ClNO2 (271.70): C, 66.31; H, 3.71; N, 5.16%.
Found: C, 66.21; H, 3.99; N, 4.98%.
3-(2-Benzofuryl)-5-(2-hydroxyphenyl)isoxazole (7e): M.p. 248–249ꢀC
(acetone-methanol). IR: 3080 br (OH), 1614 (C¼N, isoxazole), 1572, 1446
1
(isoxazole skeleton), 1387, 1262, 807, 753 cmꢁ1. H NMR (DMSO-d6): 7.00
(m, 1H, 50-H), 7.11 (d, J ¼ 8.2 Hz, 1H, 30-H), 7.31–7.49 (m, 4H, 4,500,600,700-
H), 7.73–7.79 (m, 3H, 40-300,400-H), 7.87 (d, J ¼ 7.8 Hz, 1H, 60-H), 10.81
(s, 1H, 20-OH).). 13C NMR (DMSO-d6): 101.0 (C-4), 107.9 (C-300), 111.8
(C-700), 113.6 (C-10), 116.7 (C-30), 119.7 (C-50), 122.9, 123.9, 126.3, 127.1
(C-60,400,500,600), 127.9 (C-300a), 132.1 (C-40), 146.0 (C-3), 154.9, 155.2 (C-20,
C-200,700a), 167.1 (C-5). Anal. calcd for C17H11NO3 (277.27): C, 73.64; H,
4.00; N, 5.05%. Found: C, 73.82; H, 3.89; N, 5.22%.
Synthesis 3-aminoflavones 8. General procedure: To the stirred solution
of a-azido-20-hydroxychalcone 4 (4.000 mmol) in methanol (20 mL) 1%
sodium hydroxide solution (4 mL) was added dropwise at room tempera-
ture. The solution turned immediately red and gas evolution started. The
stirring was maintained for 18 h then the precipitate was filtered off.
Addition of water (5 mL) to the mother liquor resulted in the precipitation
of a next crop of crystals. The combined crude products were purified by
crystallization from methanol.
3-Amino-6-methylflavone (8b): Yield: 86%. M.p. 122.5–125ꢀC. IR:
3398, 3319 (NH2), 1633 (C¼O), 1586, 1563, 1487, 1449, 1397, 1188,
764 cmꢁ1. H NMR: 2.48 (s, 3H, 6-Me), 7.37–7.62 (m, 5H, 7,8,30,40,50-H),
1
7.94 (m, 2H, 20,60-H), 8.06 (d, J ¼ 1.7 Hz, 1H, 5-H). 13C NMR: 20.7 (6-Me),
117.8 (C-8), 120.8 (C-4a), 124.9 (C-5), 127.7 (C-20,60), 128.2 (C-10), 129.0 (C-
30,50), 129.7 (C-40), 133.1 (C-3), 134.4 (C-6), 134.4 (C-7), 144.4 (C-2), 154.0
(C-8a), 173.7 (C-4). Anal. calcd for C16H13NO2 (251.28): C, 76.48; H, 5.21;
N, 5.57%. Found: C, 76.41; H, 5.02; N, 5.74%.
3-Amino-7-methylflavone (8c): Yield: 93%. M.p. 113–115ꢀC. IR: 3384,
3304 (NH2), 1638 (C¼O), 1614 (C¼C), 1590, 1448, 1188, 766 cmꢁ1
.
1H NMR: 2.49 (s, 3H, 7-Me), 4.02 (s, 2H, NH2), 7.18 (dd, J ¼ 8.1, 1.9 Hz,
1H, 6-H), 7.26 (d, J ¼ 1.9 Hz, 1H, 8-H), 7.41–7.59 (m, 3H, 30,40,50-H), 7.91
(dd, J ¼ 8.4, 2.0 Hz, 2H, 20,60-H), 8.15 (d, J ¼ 8.1 Hz, 1H, 5-H). 13C NMR:
21.8 (7-Me), 117.6 (C-8), 120.2 (C-4a), 125.4, 125.7 (C-5,6), 127.5 (C-20,60),
128.9 (C-30,50), 129.5 (C-40), 132.9 (C-3), 139.7, 144.0 (C-2,7), 155.6 (C-8a),
173.4 (C-4). Anal. calcd for C16H13NO2 (251.28): C, 76.48; H, 5.21; N,
5.57%. Found: C, 76.37; H, 5.39; N, 5.42%.
3-Amino-7-chloroflavone (8d): Yield: 77%. M.p. 167–168.5ꢀC. IR:
3391, 3307 (NH2), 1643 (C¼O), 1612 (C¼C), 1593, 1561, 1450, 1439,
1
1183, 1078 (Ar–Cl), 759 cmꢁ1. H NMR: 3.95 (vbr s, 2H, NH2), 7.33 (dd,

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PATONAY, JEKO, AND RIMAN
2414
J ¼ 8.1, 2.0 Hz, 1H, 6-H), 7.43–7.61 (m, 4H, 8,30,40,50-H), 7.89 (m, 2H, 20,60-
H), 8.20 (d, J ¼ 8.1 Hz, 1H, 5-H). 13C NMR: 119.8 (C-8), 121.9 (C-4a), 125.0
(C-5,6), 127.6 (C-20,60), 128.4 (C-10), 129.1 (C-30,50), 130.0, 132.5 (C-3), 133.1
(C-7), 144.5 (C-2), 153.9 (C-8a), 172.5 (C-4). Anal. calcd for C15H10ClNO2
(271.70): C, 66.31; H, 3.71; N, 5.16%. Found: C, 66.48; H, 3.86; N, 4.99%.
3-Amino-2-(2-benzofuryl)chromone (8e): Yield: 79%. M.p. 147–148ꢀC.
IR: 3446, 3348 (NH2), 1644 (C¼O), 1614 (C¼C), 1566, 1478, 1430, 1322,
1
1196, 1162, 800, 742 cmꢁ1. H NMR: 4.7 (vbr s, 2H, NH2), 7.27–7.42 (m,
4H, 6,8,50,70-H), 7.48–7.57 (overlapping dd’s, 2H, 40,70-H), 7.66 (overlapping
s and ddd, 2H, 7,30-H), 8.26 (dd, J ¼ 8.0, 1.8 Hz, 1H, 5-H). 13C NMR: 106.3
(C-30), 111.5 (C-70), 117.9 (C-8), 120.9 (C-4a), 121.6, 124.0, 124.1, 125.7,
125.9 (C-5,6,40,50,60-H), 127.9, 128.6 (C-2,30a), 133.3 (C-7), 134.7 (C-3),
150.6, 155.3, 155.4 (C-8a, 20,70a), 173.4 (C-4). Anal. calcd for C17H11NO3
(277.27): C, 73.64; H, 4.00; N, 5.05%. Found: C, 73.79; H, 3.79; N, 4.99%.
3-Amino-2-(3-methyl-2-thienyl)chromone (8f ): Yield: 62%. M.p.
152–155ꢀC. IR: 3430, 3322 (NH2), 2924, 2852, 1632 (C¼O), 1608 (C¼C),
1554, 1468, 1428, 1300, 1186, 754 cmꢁ1. H NMR: 2.38 (s, 3H, 30-Me), 2.72
1
(br s, 2H, NH2), 7.02 (d, J ¼ 5.1 Hz, 40-H), 7.38 (m, 1H, 6-H), 7.46 (d,
J ¼ 8.5 Hz, 1H, 8-H), 7.51 (d, J ¼ 5.1 Hz, 1H, 50-H), 7.65 (m, 1H, 7-H),
8.28 (dd, J ¼ 8.0, 1.4 Hz, 1H, 5-H). Anal. calcd for C14H11NO2S (257.30):
C, 65.35; H, 4.31; N, 5.44%. Found: C, 65.11; H, 4.55; N, 5.12%.
ACKNOWLEDGMENTS
This work was financially supported by Hungarian Scientific Research
Found (OTKA T22290).
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a-AZIDO-20-HYDROXYCHALCONES
2415
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Received in the USA August 8, 2001

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