A simple and rapid entry to 5-alkyl (aryl)-5-hydroxy-3,4-diarylfuranones and 3a-hydroxy-1-aryl-2,3a,4,5-tetrahydronaphthofuranones via a tandem esterification and oxidative cyclization process

Article abstract of DOI:10.1016/S0040-4039(02)02144-5

A synthesis of 5-hydroxy-3,4-diarylfuranones and related derivatives is accomplished by the reaction of arylacetic acid with α-bromoketone in the presence of base and atmospheric oxygen. A variety of compounds were synthesized in good to excellent yield and many are of potential biological interest.

Full text of DOI:10.1016/S0040-4039(02)02144-5

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 43 (2002) 8715–8719
A simple and rapid entry to 5-alkyl
(aryl)-5-hydroxy-3,4-diarylfuranones and
3a-hydroxy-1-aryl-2,3a,4,5-tetrahydronaphthofuranones via a
tandem esterification and oxidative cyclization process†
Srinivas Padakanti, Venugopal Rao Veeramaneni, Vijaya Raghavan Pattabiraman, Manojit Pal* and
Koteswar Rao Yeleswarapu*
Chemistry-Discovery Research, Dr. Reddy’s Laboratories Ltd, Bollaram Road, Miyapur, Hyderabad 500050, India
Received 12 August 2002; revised 19 September 2002; accepted 26 September 2002
Abstract—A synthesis of 5-hydroxy-3,4-diarylfuranones and related derivatives is accomplished by the reaction of arylacetic acid
with a-bromoketone in the presence of base and atmospheric oxygen. A variety of compounds were synthesized in good to
excellent yield and many are of potential biological interest. © 2002 Elsevier Science Ltd. All rights reserved.
5-Hydroxyfuranones 1 (Fig. 1) are an integral part of
many natural1 and unnatural products,2 including anal-
gesic as well as the anti-inflammatory agent
manoalide,3a,b endothelin-A (ETA), the selective recep-
tor antagonist PD-1567073c and a strong mutagen4 in
drinking water. They are valuable precursors for hete-
rocycle synthesis as exemplified by the use of muco-
bromic acid 2 in pyrimidine synthesis. They are also
useful as synthetic intermediates in the preparation of
and the treatment of diaryl-2(5H)-furanones with
benzoylperoxide16 or atmospheric oxygen in the pres-
ence of charcoal.9b
In connection with our studies on sulfonyl-substituted
diarylheterocycles, the most widely used pharma-
cophore for the development of selective COX-2
inhibitors, we have reported the synthesis of 3,4-diaryl
furanones,8,17 3,4-diarylmaleic anhydrides18 and
diphenyl-1,2,3-thiadiazole.19 In pursuance of our
research under the new drug discovery program we
needed a wide variety of appropriately functionalized
5-hydroxy-3,4-diaryl furanones in order to generate a
combinatorial library for a high throughput screen. We
therefore required a rapid synthetic procedure for the
synthesis of such compounds. The existing methods,
however, were unattractive due to the lengthy synthetic
procedures.3c,10–15 We now wish to present here our
exploratory work on the development of a general and
convenient one-pot synthesis of 5-alkyl/aryl substituted
physiologically
active
compounds5,6
such
as
pheromones, and selective COX-2 inhibitors7,8 such as
3 (Fig. 1). 5-Hydroxyfuranone 4 (Fig. 1) has been
detected as one of the major metabolites during the
metabolism of rofecoxib.9
Because of their enormous importance in chemical as
well as pharmaceutical research, a number of methods
have been reported for the synthesis of 1 in the litera-
ture. Among the existing methods, the most useful
routes involve photosensitized oxygenation of furans
bearing a hydrogen or trialkylsilyl group at the a-posi-
tion,10,11 the oxidative cleavage of silyloxyfurans in the
presence of dimethyldioxirane,12 Sn[Co(CO)4]4-cata-
lyzed double carbonylation of (2-bromoethyl)benzene,13
the reaction of 5-halofuranones with water14 or the
reaction of maleic anhydride with Grignard reagents15
Keywords: 5-hydroxyfuranone; esterification; oxidative cyclization;
phenylacetic acid; a-bromoketone.
* Corresponding authors. Fax: 91-40-3045438/3045007; e-mail:
manojitpal@drreddys.com; koteswarraoy@drreddys.com
† DRF Publication No. 226.
Figure 1. Examples of some 5-hydroxyfuranones.
0040-4039/02/$ - see front matter © 2002 Elsevier Science Ltd. All rights reserved.
PII: S0040-4039(02)02144-5

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S. Padakanti et al. / Tetrahedron Letters 43 (2002) 8715–8719
5-hydroxy-3,4-diarylfuranones starting from readily
available starting materials.
presence of atmospheric oxygen and then poured into
an ice-cold 3N HCl solution (30 mL) with stirring. The
solid separated was filtered off and washed with water
(2×15 mL) followed by petroleum ether (2×10 mL). The
solid product was then analyzed.20
The esterification of an arylacetic acid with an a-bro-
moketone in the presence of base under an inert atmo-
sphere has been documented as the easiest protocol for
accessing phenacyl esters III. The maximum yield of
product was achieved when the reaction was carried out
in the presence of 0.9–1.0 equiv. of base at 10–15°C for
20–25 min (Method A, Scheme 1). However, we
observed that 5-hydroxy-3,4-diarylfuranones IV (R"
H) were formed as the major product when the same
reaction (when R"H for I) was performed in the
presence of 3 equiv. of base (with respect to the aryl-
acetic acid) under an oxygen atmosphere at 25–30°C
for a longer reaction time (Method B, Scheme 1). Our
results are summarized in Table 1.
As can be seen from Table 1, a variety of a-bromo-
ketones21 I (R"H) and arylacetic acids II (obtained
from the corresponding ketones via a Willgerodt reac-
tion)17a were reacted to generate a number of 5-hydroxy-
furanones IV (5–15) in good to excellent yields.
The reactions were usually carried out in the presence
of potassium hydroxide or DBU. However, the use of
other bases such as diisopropylamine and triethylamine
was also investigated when phenacyl ester III was iso-
lated as the sole product. In all the cases (entries 1–12,
Table 1), the reaction proceeded well at 25–30°C lead-
ing to the formation of IV as the major product.
However, another side product, i.e. 4-hydroxy-3,4-
diaryltetrahydro-2-furanone V has been isolated as a
minor product in many cases. Therefore, the effect of
temperature and concentration of base (KOH) on
product distribution has been investigated and is shown
in Table 2.
In a typical experiment, 4-methoxyphenylacetic acid
(1.1 g, 6.61 mmol) in N,N-dimethyl formamide (DMF)
(10 mL) was stirred along with potassium hydroxide
(1.13 g, 20.17 mmol) and water (2 mL) for 0.5 h at 25°C
to which was added a solution of 2-bromo-1-(4-methyl-
sulfanylphenyl)-1-butanone (1.8 g, 6.59 mmol) in DMF
(10 mL). The mixture was stirred for 6 h at 25°C in the
Scheme 1. Reaction of arylacetic acid with an a-bromoketone.
Table 1. Synthesis of 5-hydroxy-3,4-diarylfuranones IVa

S. Padakanti et al. / Tetrahedron Letters 43 (2002) 8715–8719
8717
Table 2. Effect of reaction conditions on product distributiona
A mixture of furanone 18, 5-hydroxyfuranone 8 along
with 4-hydroxyfuranone 17 was isolated when the reac-
tion was carried out at a lower temperature in the
presence of 3 equiv. of KOH (entry 7, Table 2). On the
other hand decomposition of the products was
observed when the reaction temperature was increased.
It is evident from Table 2 that the base has a crucial
role in the formation of product 8. Phenacyl ester 16
was isolated as the sole product even when the reaction
was carried out in the presence of oxygen using a lesser
amount of KOH (entries 1 and 2, Table 2). Indeed,
ester 16 was isolated as the major product in most of
the cases (entries 3–6, Table 2). However, 4-hydroxy-
furanone 17 was detected along with the furanone 18 in
appreciable quantity when the reaction time was
restricted to 2 h instead of 6 h (entry 8 versus 9, Table
2). All these observations indicated that the ester, 4-
hydroxyfuranone and furanone are possible sequential
intermediates formed during the course of the reac-
tion,22 whereas the most effective molar ratio of aryl-
acetic acid II to base was found to be 1:3 to give a high
yield of product IV. Thus, the temperature, base and
oxygen have combined influences on the nature of the
product formed in this tandem esterification–oxidative
cyclization reaction.
5-Hydroxy-3,4-diarylfuranones 5–10 and 3a-hydroxy-
2,3a,4,5-tetrahydronaphthofuranones 11–15 have been
synthesized using a single-step operational procedure in
the presence of atmospheric oxygen. Many of these
compounds showed biological activity23 when tested in
vitro24 against the cyclooxygenase (COX) enzyme. A
few of them showed strong inhibition23b against both of
its isoforms (COX-1 and COX-2). Compound 5 was
dehydrated (using p-toluene sulfonic acid in benzene)
and then oxidized (using oxone in acetone) to the
corresponding 5-alkylidenefuranone 20 which has
potential biological interest (Scheme 2).8
In conclusion, we have demonstrated a distinctly mild
and efficient one-pot procedure (a single-step opera-
tion) for the synthesis of 5-alkyl/aryl substituted 5-
hydroxyfuranones starting from readily available
starting materials. We have also described the first
synthesis of 3a-hydroxy-1-aryl-2,3a,4,5-tetrahydro-
naphthofuranones using this two-component coupling
process. The present protocol certainly has distinct
advantages over the existing methods in terms of time,
operational simplicity and environmental drawbacks.
As 5-hydroxyfuranones are of great interest due to their
interesting biological activities, the present protocol will
Scheme 2. Synthesis of a compound of potential biological importance.

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S. Padakanti et al. / Tetrahedron Letters 43 (2002) 8715–8719
find wide usage both in organic and medicinal chem-
istry.
13. Monflier, E.; Pellegrini, S.; Mortreux, A.; Petit, F. Tetra-
hedron Lett. 1991, 32, 4703–4704.
14. Takabe, K.; Yoda, H.; Tanaka, M.; Sugimoto, M.; Ish-
ioka, T.; Miyazaki, A. Jpn. Kokai Tokkyo Koho JP
02218672, 31 Aug 1990, 5 pp. Chem. Abstr. 114:42558.
15. Lardelli, G.; Dijkstra, P.; Harkes, D.; Boldingh, J. Rec.
Trav. Chim. 1966, 85, 43.
Acknowledgements
16. Black, C.; Grimm, E.; Wang, Z.; Leger, S. World Patent
WO 9636623, 21 Nov 1996, 109 pp., Chem. Abstr.
126:89250.
The authors would like to thank Dr. A. Venkateswarlu,
Dr. R. Rajagopalan and Professor J. Iqbal for their
constant encouragement and the Analytical Depart-
ment for spectral support.
17. (a) Pal, M.; Rao, V. V.; Srinivas, P.; Murali, N.; Akhila,
V.; Premkumar, M.; Rao, C. S.; Misra, P.; Ramesh, M.;
Rao, Y. K. Indian J. Chem. 2002, in press; (b) Srinivas,
P.; Pal, M.; Rao, Y. K. Synth. Commun., submitted.
18. Pattabiraman, V. R.; Padakanti, P. S.; Veeramaneni, V.
R.; Pal, M.; Yeleswarapu, K. R. Synlett 2002, 947–951.
19. Pal, M.; Rao, V. V.; Rao, Y. K. Presented at the sympo-
sium on Current Perspectives in Organic Chemistry
(CPOC-2002), Indian Association for the Cultivation of
Science, Kolkata, India, 24–25 January, 2002; Paper
number 6.
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1
20. All new compounds were characterized by H NMR, IR,
Mass and C, H, N microanalyses; some selected analyti-
cal data are listed below: Spectral data for 6: mp 94–95°C
(1:9 EtOAc–hexane); 1H NMR (200 MHz, CDCl3) l
7.50–7.26 (m, 10H, ArH), 2.09–2.02 (m, 2H, CH
6
2CH3),
0.87 (t, J=7.4 Hz, 3H, CH2CH3
6
); IR (KBr, cm−1) 3319
(bs, OH), 1739 (CꢀO). Mass (EI) m/z 280 (M+, 11), 262
(93), 178 (100). Elemental analysis found: C, 77.24; H,
5.73; C18H16O3 requires C, 77.13; H, 5.75%.
Spectral data for 7: mp 121–122°C (2:8 EtOAc–hexane);
1H NMR (200 MHz, CDCl3) l 7.56–7.0 (m, 8H, ArH),
2.48 (s, 3H, SCH
J=7.3 Hz, 3H, CH2CH3
6
3), 2.05–1.86 (m, 2H, CH2
6
CH3), 0.87 (t,
6
); IR (KBr, cm−1) 3455 (bs, OH),
1741 (CꢀO). Mass (EI) m/z 344 (M+, 6), 326 (100).
Elemental analysis found: C, 66.30; H, 4.97; C19H17FO3S
requires C, 66.26; H, 4.98%.
1
Spectral data for 12: mp: 227–229°C (MeOH); H NMR
(200 MHz, CDCl3) l 7.41–7.25 (m, 5H, ArH), 7.08 (s,
1H, ArH), 6.89 (d, J=7.89 Hz, 1H, ArH), 3.31–2.90 (m,
3H, one is D2O exchangeable, OH and CH2), 2.80–2.60
(m, 1H, H
2.25–2.10 (m, 1H, H
6 -CH-), 2.55 (s, 3H, SCH3), 2.35 (s, 3H, CH3),
6
-CH-); IR (KBr, cm−1) 3329, 1742.
Mass (CI, i-butane) m/z 339 (M+, 43), 321 (100). Elemen-
tal analysis found: C, 70.89; H, 5.37; C20H18O3S requires
C, 70.98; H, 5.36%.
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S. Padakanti et al. / Tetrahedron Letters 43 (2002) 8715–8719
8719
23. (a) A separate account of the biological activities of the
compounds described here will be communicated soon; (b)
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COX-2 inhibition over COX-1 when tested against recom-
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baculovirus) and COX-1 (Ram Seminal vesicles) enzyme
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