Novel and convenient one-pot synthesis of 3-aroyl-7-hydroxy-6-nitroflavones

Article abstract of DOI:10.1081/SCC-200048471

A novel and conveient one-pot synthesis of 3-aroyl-7-hydroxy-6- nitroflavones from 2′,4′-dihydroxy-5′-nitroacetophenone and (substituted)benzoyl chlorides in refluxing dry acetone in the presence of anhydrous potassium carbonate was developed. The structu

Full text of DOI:10.1081/SCC-200048471

This article was downloaded by: [Stony Brook University]
On: 21 October 2014, At: 19:35
Publisher: Taylor & Francis
Informa Ltd Registered in England and Wales Registered Number: 1072954
Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH,
UK
Synthetic Communications: An
International Journal for Rapid
Communication of Synthetic
Organic Chemistry
Publication details, including instructions for
authors and subscription information:
http://www.tandfonline.com/loi/lsyc20
Novel and Convenient
One‐Pot Synthesis of
3‐Aroyl‐7‐Hydroxy‐6‐Nitroflavones
Lijun Tang a b , Shufen Zhang a b , Jinzong Yang a ,
Wentao Gao b , Jian Cui a & Tianyu Zhuang a
a State Key Laboratory of Fine Chemicals , Dalian
University of Technology , Zhongshan Road 158‐40,
Dalian, 116012, P.R. China
b College of Chemistry and Chemical Engineering ,
Bohai University , Jinzhou, P.R. China
Published online: 28 Jul 2007.
To cite this article: Lijun Tang , Shufen Zhang , Jinzong Yang , Wentao Gao ,
Jian Cui & Tianyu Zhuang (2005) Novel and Convenient One‐Pot Synthesis of
3‐Aroyl‐7‐Hydroxy‐6‐Nitroflavones, Synthetic Communications: An International
Journal for Rapid Communication of Synthetic Organic Chemistry, 35:2, 315-323, DOI:
10.1081/SCC-200048471
To link to this article: http://dx.doi.org/10.1081/SCC-200048471
PLEASE SCROLL DOWN FOR ARTICLE
Taylor & Francis makes every effort to ensure the accuracy of all the
information (the “Content”) contained in the publications on our platform.
However, Taylor & Francis, our agents, and our licensors make no
representations or warranties whatsoever as to the accuracy, completeness,
or suitability for any purpose of the Content. Any opinions and views

expressed in this publication are the opinions and views of the authors, and
are not the views of or endorsed by Taylor & Francis. The accuracy of the
Content should not be relied upon and should be independently verified with
primary sources of information. Taylor and Francis shall not be liable for any
losses, actions, claims, proceedings, demands, costs, expenses, damages,
and other liabilities whatsoever or howsoever caused arising directly or
indirectly in connection with, in relation to or arising out of the use of the
Content.
This article may be used for research, teaching, and private study purposes.
Any substantial or systematic reproduction, redistribution, reselling, loan,
sub-licensing, systematic supply, or distribution in any form to anyone is
expressly forbidden. Terms & Conditions of access and use can be found at
http://www.tandfonline.com/page/terms-and-conditions

Synthetic Communicationsw, 35: 315–323, 2005
Copyright # Taylor & Francis, Inc.
ISSN 0039-7911 print/1532-2432 online
DOI: 10.1081/SCC-200048471
Novel and Convenient One-Pot Synthesis of
3-Aroyl-7-Hydroxy-6-Nitroflavones
Lijun Tang
State Key Laboratory of Fine Chemicals, Dalian University of
Technology, Dalian, P.R. China and College of Chemistry and Chemical
Engineering, Bohai University, Jinzhou, P.R. China
Shufen Zhang and Jinzong Yang
State Key Laboratory of Fine Chemicals, Dalian University of
Technology, Dalian, P.R. China
Wentao Gao
College of Chemistry and Chemical Engineering, Bohai University,
Jinzhou, P.R. China
Jian Cui and Tianyu Zhuang
State Key Laboratory of Fine Chemicals, Dalian University of
Technology, Dalian, P.R. China
Abstract: A novel and conveient one-pot synthesis of 3-aroyl-7-hydroxy-6-
nitroflavones from 20,40-dihydroxy-50-nitroacetophenone and (substituted)benzoyl
chlorides in refluxing dry acetone in the presence of anhydrous potassium carbonate
was developed. The structures of the prepared compounds were characterized by IR,
1H NMR, and MS spectroscopy.
Keywords: 3-Aroylflavone, one-pot synthesis, flavone, 4H-1-benzopyran-4-one,
chromone
Received in the UK June 2, 2004
Address correspondence to Shufen Zhang, State Key Laboratory of Fine Chemicals,
Dalian University of Technology, Zhongshan Road 158-40, Dalian 116012, P.R. China
and College of Chemistry and Chemical Engineering, Bohai University, Jinzhou, P.R.
China. E-mail: zhangshf@chem.dlut.edu.cn

316
L. Tang et al.
INTRODUCTION
Flavones are one of the most common classes of natural flavonoids for which
significant biocidal,[1–3] pharmaceutical,[4–7] and antioxidant[8–10] activities
have been described. It has been shown that some flavones containing an
amino group on their A-ring have potent pharmaceutical activities,[11,12] and
a nitro group, as the precursor of amino group, can be converted conveniently
into amino group by treatment with many reductants. Many biological studies
have shown that the existence of hydroxyl groups at positions of 7 and/or 5 of
the flavone ring is necessary for biological activity. Thus, flavones bearing
nitro and hydroxyl groups on the A-ring, serving as the precursor for
aminoflavone, aroused our interest and promoted us to synthesize this kind
of compound.
Among the methods for the synthesis of flavones, the modified Baker–
Venkataraman rearrangement approach is widely used; this method
can perform esterification and intramolecular Claisen condensation (Baker–
Venkataraman rearrangement) in one pot. Thus, the modified Baker–
Venkataraman rearrangement approach was selected as the first-reaction
step in our initial experiments. We tried to synthesize 1-(4-benzoyloxy-2-
hydroxy-5-nitrophenyl)-3-phenyl-1,3-propanedione from the reaction of
20,40-dihydroxy-50-nitroacetophenone (1) and 2.0 equivalents of benzoyl
chloride (2) in dry acetone, which was heated to reflux in the presence of
anhydrous potassium carbonate. However, none of the desired 1,3-diketone
was obtained. The major product in the obtained mixture was purified by
recrystallization from acetic acid and was identified as 3-benzoyl-7-
hydroxy-6-nitroflavone (3a). When other substituted benzoyl chlorides were
used in the process, the corresponding 3-aroylflavones (3c–3d) were also
obtained. Thus, it provided a new approach to 3-aroylflavones. We report
Scheme 1. One-pot synthesis of 3-aroylflavones.

One-Pot Synthesis of 3-Aroyl-7-Hydroxy-6-Nitroflavones
317
herein a novel and convenient one-pot synthesis of 3-aroyl-7-hydroxy-6-
nitroflavones (3a–3d) from 20,40-dihydroxy-50-nitroacetophenone (1), and
the adopted synthetic route is depicted in Scheme 1.
It is worth mentioning that significant antibacterial and antifungal activi-
ties for flavones bearing a 3-aroyl group have been reported.[13] Despite
the important biocidal applications of 3-aroylflavones, synthetic strategies
affording these compounds have not been widely explored. There are three
main synthetic routes: 1) Baker–Venkataraman rearrangement of 20,60-di-
hydroxyacetophenones;[14–17] 2) oxidation of benzylideneflavanones with a
number of oxidants;[18–20] and 3) condensation of diaroylmethane derivatives
with aromatic aldehydes, followed by oxidation of the formed products.[13,21]
In the latter two methods, the preparation of the precursors of target 3-aroyl-
flavone is relatively time-consuming and troublesome. In the first synthetic
route, researches were limited to the use of 20,60-dihydroxyacetophenone
as starting material. The two hydroxyl groups in the starting acetophenone
are all adjacent to the carbonyl group; thus, the required twice and con-
secutively intramolecular Claisen condensation could occur smoothly.
However, reports on the synthesis of 3-aroylflavones using other types of
dihydroxyacetophenones were rare. In our study, the reaction of compound
1 with benzoyl chloride was carried out in acetone heated to reflux in the
presence of anhydrous potassium carbonate for 24 hr; after the solvent was
evaporated, the residue mixture was diluted and acidified with dilute
hydrochloric acid to weak acidity. The formed precipitate was collected by
filtration, dried, and recrystallized from acetic acid afforded 3a as offwhite
needles. Compounds 3c–3d were also prepared following the same
procedure as described for 3a.
Infrared spectrum (KBr pellet) of 3a shows bands at 1671 and 1637 cm21
corresponding to PhC55O and benzopyranone C55O stretches, respectively.
1
The H NMR (CDCl3) spectrum of 3a shows a single peak at 10.92 ppm;
this strongly deshielded peak disappears when D2O is added to the sample,
and thus it can be assigned to the OH proton. The lack of the characteristic
single peak at approximately 6.8 ppm owing to C3-H of flavone indicates
that the benzoyl group is attached to the 3-C, and the mass spectrum is in
agreement with the assigned structure. Structures of 3b–3d were also
confirmed by the similar method.
The experimental result indicates that the hydroxyl group adjacent to nitro
group in compound 1 is less reactive to the reaction conditions. Thus, the
formation of 3 may be interpreted by the following proposed mechanism
(Scheme 2; the formation of 3a is selected for convenience). This approach
involves the O-acylation of 20,40-dihydroxy-50-nitroacetophenone with the
first equivalent of benzoyl chloride to give the monoester 4, and in the
process the hydroxyl group neighboring to acetyl group takes the priority to
be acylated. This can be attributed to the strong intramolecular hydrogen
bonding between nitro, and hydroxyl groups, which possibly retards the

318
L. Tang et al.
Scheme 2. Proposed mechanism for the formation of 3-aroylflavone.
acylation of the corresponding hydroxyl group. In compound 4, the acetyl,
nitro, and benzoyloxy groups exhibit together a highly electron-withdrawing
effect, which combined with the above-mentioned intramolecular hydrogen
bonding, decreases remarkably the reactivity of the hydroxyl group. Then
compound 4 undergoes a carbanion benzoylation with the second equivalent
of benzoyl chloride to afford 1-(2-benzoyloxy-4-hydroxy-5-nitrophenyl)-3-
phenyl-1,3-propanedione (5), which may adopt the more stable form 6,[22]
and then compound 6 undergoes in situ cyclodehydration via intermediates
7, 8, and 9 to give product 3a. In the second step, formation of 5 is prior
to intramolecular Claisen condensation, which leads to the formation of

One-Pot Synthesis of 3-Aroyl-7-Hydroxy-6-Nitroflavones
319
1-(2,4-dihydroxy-5-nitrophenyl)-3-phenyl-1,3-propanedione (10), because
benzoyl chloride is more activated than its ester.
To verify the proposed mechanism, HPLC/MS analysis was selected as a
simple and powerful tool, and the synthesis of 3a was tested as a typical
process. To obtain the comparable compounds, we endeavored to prepare
the assigned intermediates 4 and 6 as standard samples. Compound 4 can be
easily synthesized by the reaction of 1 and benzoyl chloride in acetone in
the presence of potassium carbonate. Treatment of 3a with potassium
hydroxide in ethanol can give compounds 6 and 10; they were synthesized
and structurally characterized. Thus, the reaction was monitored with
HPLC/MS analysis as follows: portions of the reaction mixture were
sampled and were worked up, the qualitative analysis was performed by
HPLC/MS, and the retention time and molecular weight of each component
were compared with those of authentic samples. The results revealed that
compounds 4 and 10 all existed during the reaction process and there were
no dibenzoates of 1 observed during the course of the reaction according to
mass spectroscopic detection.
In summary, a mild and convenient one-pot synthesis of 3-aroyl-7-
hydroxy-6-nitroflavones has been developed. The procedure offered several
advantages including mild reaction conditions, simple experimental and
product isolation procedures, which make it a useful and attractive
methodology.
EXPERIMENTAL
Melting points were measured on an X-6 micromelting point apparatus and
are uncorrected. NMR spectra were recorded by using a Varian INOVA 400
NMR spectrometer at 400 MHz (1H NMR) and 100 MHz (13C NMR), and
chemical shifts are expressed in ppm relative to TMS used as an internal
standard. Infrared spectra were measured as KBr pellets with an FT/IR-430
spectrophotometer. HPLC/MS analysis and mass spectra were performed
on a HP1100 system HPLC/MS spectrometer. High-resolution mass spectra
were recorded on Mariner System 5303. 20,40-dihydroxy-50-nitroacetophenone
was prepared according to literature method;[12] other reagents were commer-
cial analytical grade and used as such. Acetone was dried over anhydrous
K2CO3 and distilled before use.
Synthesis of Compounds 3a–3d: General Procedure
To a stirred solution of 20,40-dihydroxy-50-nitroacetophenone (5.30 g, 0.027 mol)
in dry acetone (300 mL) was added anhydrous potassium carbonate (27 g,
0.196 mol). The mixture was stirred at room temperature for 10 min, and the

320
L. Tang et al.
corresponding benzoyl chloride (0.054 mol) was added dropwise; then the
mixture was stirred at room temperature for another 0.5 hr. After heating
to reflux for 24 hr the acetone was evaporated under reduced pressure.
The residue mixture was diluted with cooled water and acidified with dilute
hydrochloric acid in a beaker to acidity. The precipitate formed was
collected by filtration and dried, recrystallized form acetic acid affording
3a–3d.
Compound 3a
1
Yield: 36%; offwhite needles; mp 279–2818C (lit[23] mp 272–2738C). H
NMR (400 MHz, CDCl3): d ¼ 10.92 (s, 1H), 9.066 (s, 1H), 7.89 (d, 2H,
J ¼ 7.6 Hz), 7.63 (d, 2H, J ¼ 7.6 Hz), 7.55 (m, 1H), 7.35–7.47 (m, 5H),
7.27 (s, 1H). 13C NMR (100 MHz, DMSO-d6): d ¼ 192.1, 174.1, 161.8,
158.4, 156.7, 136.2, 136.0, 133.6, 131.3, 130.7, 128.8, 128.5, 128.4, 128.0,
123.6, 121.4, 114.7, 106.2. IR (KBr): 3170, 1671, 1637, 1614, 1577, 1556,
1529, 1367 cm21. API-ES-MS (negative): m/z (%) ¼ 386 (100) [M 2 H]2,
387 (25) [M]2.
Compound 3b
1
Yield: 38%; brown plates; mp 175–1778C. H NMR (400 MHz, CDCl3):
d ¼ 10.95 (s, 1H), 9.06 (s, 1H), 7.85 (m, 1H), 7.75 (dd, 1H, J ¼ 0.8 Hz,
8.0 Hz), 7.67 (m, 1H), 7.55 (dd, 1H, J ¼ 0.8 Hz, 8.0 Hz), 7.37–7.47
(m, 3H), 7.29–7.33 (m, 2H). 13C NMR (100 MHz, CDCl3): d ¼ 190.9,
174.5, 161.7, 160.2, 158.6, 138.1, 135.4, 134.3, 132.8, 132.4, 130.4, 129.2,
128.5, 127.6, 126.9, 126.0, 122.3, 116.6, 107.7. IR (KBr): 3191, 1677,
1635, 1608, 1581, 1556, 1527, 1462, 1427, 1360, 1317, 1267 cm21. API-
ES-MS (positive): m/z (%) ¼ 456 (100) [M þ H]þ, 458 (65) [M þ 2 þ H]þ,
460 (12) [M þ 4 þ H]þ. HRMS (ESI, positive): m/z cacld. for
C22H12Cl2NO6 [M þ H]þ: 456.0042; found: 456.0051.
Compound 3c
Yield: 46%; offwhite needles; mp 229–2318C. 1H NMR (400 MHz, CDCl3):
d ¼ 10.93 (s, 1H), 9.05 (s, 1H), 7.81 (d, 2H, J ¼ 8.4 Hz), 7.54 (d, 2H,
J ¼ 8.4 Hz), 7.22 (d, 2H, J ¼ 8.4 Hz), 7.18 (d, 2H, J ¼ 8.4 Hz), 2.39
(s, 3H), 2.35 (s, 3H). 13C NMR (100 MHz, DMSO-d6): d ¼ 192.2, 174.4,
161.6, 158.4, 156.4, 144.8, 141.9, 136.5, 134.1, 129.5, 129.4, 128.2, 123.4,
121.2, 114.7, 106.1, 21.2, 20.9. IR (KBr): 3442, 1675, 1632, 1612, 1529,
1359 cm21. API-ES-MS (negative): m/z (%) ¼ 414 (100) [M 2 H]2, 415
(29) [M]2. HRMS (ESI, negative): cacld. for C24H16NO6 [M 2 H]2:
414.0978; found: 414.0974.

One-Pot Synthesis of 3-Aroyl-7-Hydroxy-6-Nitroflavones
321
Compound 3d
1
Yield: 35%; yellow prisms; mp 173–1758C. H NMR (400 MHz, CDCl3):
d ¼ 10.91 (s, 1H), 9.03 (s, 1H), 7.88 (d, 2H, J ¼ 8.8 Hz), 7.62 (d, 2H,
J ¼ 8.4 Hz), 7.25 (s, 1H), 6.88 (d, 2H, J ¼ 8.8 Hz), 6.86 (d, 2H,
J ¼ 8.8 Hz), 3.84 (s, 3H), 3.80 (s, 3H). 13C NMR (100 MHz, DMSO-d6):
d ¼ 190.7, 174.1, 163.6, 161.7, 161.1, 158.4, 156.6, 135.2, 131.1,
129.7, 129.3, 123.7, 122.6, 120.3, 114.8, 112.8, 113.7, 106.2, 55.0, 54.9.
IR (KBr): 3432, 2935, 1674, 1645, 1629, 1600, 1543, 1365, 1298, 1259,
1182 cm21. API-ES-MS (positive): m/z (%) ¼ 448 (100) [M þ H]þ, 449
(27) [M þ 2H]þ. HRMS (ESI, positive): cacld. for C24H18NO8 [M þ H]þ:
448.1032; found: 448.1032.
Synthesis of Compounds 6 and 10
Compound 3a (1.50 g, 3.88 mmol) was added to 5% ethanolic KOH (50 mL) at
room temperature, and the mixture was stirred and heated to reflux for 1 hr.
After cooling to room temperature, the mixture was diluted with ice-cold
water and acidified. The precipitated products were filtered, washed with
water, dried, and then purified by preparative thin-layer chromatographic
plates (ethyl acetate/petroleum ether ¼ 1 : 7) to afford compounds 6 and 10
in 64% and 32% yields, respectively. And the latter was obtained in 97%
yield when the reaction time was increased to 24 hr.
Compound 6
1
mp 180–1828C (yellow needles, recrystallization from acetone); H NMR
(CDCl3) d: 16.54 (s, 1H), 10.90 (s, 1H), 8.81 (s, 1H), 8.24 (d, 2H,
J ¼ 8.4 Hz), 7.65–7.72 (m, 3H), 7.47–7.56 (m, 3H), 7.30–7.34 (m, 2H),
7.16 (s, 1H), 6.72 (s, 1H); 13C NMR (100 MHz, CDCl3): d ¼ 185.6, 182.2,
163.9, 157.8, 155.8, 134.7, 132.9, 131.7, 130.7, 129.1, 128.8, 128.4, 128.0,
127.3, 123.2, 115.1, 96.5. IR (KBr pellet) cm21: 3444, 1745, 1633, 1242,
1157, 1054; HRMS (ESI) for C22H14NO7 ([M 2 H]2): calcd. 404.0770;
found 404.0754.
Compound 10
1
mp 220–2228C (yellow needles, recrystallization from acetone); H NMR
(CDCl3) d: 15.12 (s, 1H), 12.94 (s, 1H), 10.99 (s, 1H), 8.68 (s, 1H), 7.97
(d, 2H, J ¼ 7.6 Hz), 7.53–7.60 (m, 3H), 6.77 (s, 1H), 6.626 (s, 1H) (this
species exists completely in the enolic form); 13C NMR (100 MHz, CDCl3):
d ¼ 193.6, 182.7, 179.2, 169.7, 160.5, 133.3, 129.2, 128.1, 127.3, 113.8,
106.7, 91.9. IR (KBr pellet) cm21: 1604, 1560, 1492, 1297, 1220, 1196,

322
L. Tang et al.
1078; HRMS (ESI) for C15H10NO6 ([M 2 H]2): calcd. 300.0508; found
300.0508.
ACKNOWLEDGMENT
Sincere thanks are expressed to the National Natural Science Foundation of
China for financial support (No. 20276009).
REFERENCES
1. Rao, K. V.; Chattopadhyay, S. K.; Reddy, G. C. Flavonoids with mosquito larval
toxicity. J. Agric. Food. Chem. 1990, 38, 1427–1430.
¨
2. Silva, A. M.; Weidenborner, M.; Cavaleiro, J. A. S. Growth control of different
fusarium species by selected flavones and flavonoid mixtures. Mycol. Res. 1998,
102, 638–640.
3. Weidenborner, M.; Jha, H. C. Antifungal activity of flavonoids and their mixtures
against different fungi occurring on grain. Pestic. Sci. 1993, 38, 347–351.
4. Akama, T.; Ishida, H.; Kimura, U.; Gomi, K.; Saito, H.; Fuse, E.; Kobayashi, S.;
Yoda, N.; Kasai, M. Design and synthesis of potent antitumor 5,40-diaminoflavone
derivatives based on metabolic considerations. J. Med. Chem. 1997, 40,
1894–1900.
5. Gee, J. M.; Johnson, I. T. Polyphenolic compounds: interactions with the gut and
implications for human health. Curr. Med. Chem. 2001, 8, 1245–1255.
6. Wolfman, C.; Viola, H.; Marder, M.; Wasowski, C.; Ardenghi, P.; Izquierdo, I.;
Paladini, A. C.; Medina, J. H. Anxioselective properties of 6,30-dinitroflavone,
a high-affinity benzodiazepine receptor ligand. Eur. J. Pharmacol. 1996, 318,
23–30.
7. Wu, E. S. C.; Loch, J. T.; Toder, B. H.; Borrelli, A. R.; Gawlak, D.; Radov, L. A.;
Gensmantel, N. P. Flavones. 3. Synthesis, biological activities, and conformational
analysis of isoflavone derivatives and related compounds. J. Med. Chem. 1992, 35,
3519–3525.
8. Pietta, P. G. Flavonoids as antioxidant. J. Nat. Prod. 2000, 63, 1035–1042.
9. Rice-Evans, C. Flavonoid antioxidants. Curr. Med. Chem. 2001, 8, 797–807.
10. Rice-Evans, C. A.; Miller, N. J.; Paganga, G. Structure antioxidant activity
relationships of flavonoids and phenolic acids. Free. Rad. Biol. Med. 1996, 20,
933–956.
11. Akama, T.; Ishida, H.; Kimura, U.; Gomi, K.; Saito, H. Structure-activity
relationships of the 7-substituents of 5,40-diamino-6,8,30-trifluoroflavone, a
potent antitumor agent. J. Med. Chem. 1998, 41, 2056–2067.
12. Cushman, M.; Zhu, H.; Geahlen, R. L.; Kraker, A. J. Synthesis and biochemical
evaluation of a series of aminoflavones as potential inhibitors of protein-tyrosine
kinases p56lck, EGFr, and p60v-src. J. Med. Chem. 1994, 37, 3353–3362.
13. Hogale, M. B.; Pawar, B. N.; Nikam, B. P. Synthesis and biological activity of
some new flavones. J. Indian. Chem. Soc. 1987, 64, 486–487.

One-Pot Synthesis of 3-Aroyl-7-Hydroxy-6-Nitroflavones
323
14. Cardoso, A. M.; Silva, A. M. S.; Barros, C. M. F.; Almeida, L. M. P. M.; Ferrer-
Correia, A. J.; Cavaleiro, J. A. S. 3-Aroyl-5-hydroxyflavones: synthesis and
mechanistic studies by mass spectrometry. J. Mass. Spectrom. 1997, 32, 930–939.
´
´
`
15. Gaydon, E. M.; Bianchini, J.-P. Etudes de composes flavoniques. I. Synthesis et
´ ´
proprietes (Uv, RMN du 13C) de quelques flavones. Bull. Soc. Chim. Fr. 1978,
II, 43–47.
16. Looker, J. H.; Hanneman, W. W. Physical and chemical properties of hydroxy-
flavones. II. 3-Aroyl-5-hydroxyflavones. Synthetic and infrared spectral studies.
J. Org. Chem. 1962, 27, 3261–3263.
17. Looker, J. H.; Edman, J. R.; Dappen, I. A high-yield modification of the Baker-
Venkataraman rearrangement. Application to the synthesis of 5-hydroxyflavone
and 6,8-dichloro-5-hydroxyflavone. J. Heterocycl. Chem. 1964, 1, 141–144.
18. Chawla, H. M.; Sharma, S. K. Novel one-pot photochemical synthesis of
3-C-aroyl-2-aryl-4H-1-benzopyran-4-ones. Synth. Commun. 1990, 20, 301–306.
19. Dhara, M. G.; De, S. K.; Mallik, A. K. A Facile transformation of E-3-benzyl-
ideneflavanones to 3-(a-hydroxybenzyl)flavones. Tetrahedron Lett. 1996, 37,
8001–8002.
´
´
´
20. Nemes, C.; Levai, A.; Patonay, T.; Toth, G.; Boros, S.; Halasz, J.; Adam, W.;
Golsch, D. Dioxirane oxidation of 3-arylideneflavanones: diastereoselective
formation of trans, trans spiroepoxides from the E isomers. J. Org. Chem. 1994,
59, 900–905.
21. Ganvir, J. T.; Ingle, V. N. Synthesis of 4-benzoyl-3,5-diarylisoxazoles. J. Indian.
Chem. Soc. 1988, 65, 878–879.
22. Bois, F.; Beney, C.; Mariotte, A.-M.; Boumendjel, A. A one-step synthesis of
5-hydroxyflavone. Synlett 1999, 9, 1480–1482.
23. Naik, R. M.; Thakor, V. M. Chromones. III. Kostanecki-Robinson acylation of
some o-hydroxyacetophenones. Proc. Indian Acad. Sci. 1953, 37A, 774–783.