Regioselective monobromination of (E)-1-(2′-hydroxy-4′, 6′-dimethoxyphenyl)-3-aryl-2-propen-1-ones using bromodimethylsulfonium bromide and synthesis of 8-bromoflavones and 7-bromoaurones

Article abstract of DOI:10.1016/j.tetlet.2012.06.122

A wide variety of monobrominated compounds 2a-l have been prepared in good yields from (E)-1-(2′-hydroxy-4′,6′-dimethoxyphenyl)-3-aryl-2- propen-1-ones (1a-l) through regioselective ring bromination using 1.5 equiv of bromodimethylsulfonium bromide (BDMS)

Full text of DOI:10.1016/j.tetlet.2012.06.122

Tetrahedron Letters 53 (2012) 4852–4857
Contents lists available at SciVerse ScienceDirect
Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Regioselective monobromination of (E)-1-(20-hydroxy-40,60-dimethoxyphenyl)-
3-aryl-2-propen-1-ones using bromodimethylsulfonium bromide and synthesis
of 8-bromoflavones and 7-bromoaurones
Abu T. Khan a, , Abhik Choudhury a, Shahzad Ali a, Md. Musawwer Khan b
⇑
a Department of Chemistry, Indian Institute of Technology Guwahati, Guwahati 781 039, Assam, India
b Department of Chemistry, Aligarh Muslim University, Aligarh 202 002, Uttar Pradesh, India
a r t i c l e i n f o
a b s t r a c t
A wide variety of monobrominated compounds 2a–l have been prepared in good yields from (E)-1-(20-
hydroxy-40,60-dimethoxyphenyl)-3-aryl-2-propen-1-ones (1a–l) through regioselective ring bromination
using 1.5 equiv of bromodimethylsulfonium bromide (BDMS) at room temperature. Similarly, some of the
20-hydroxychalcones can be converted directly into tribromides 3 or dibromides 4 by employing
4.0 equiv of BDMS under different reaction conditions which in turn can be transformed into 8-bromof-
lavones and 7-bromoaurones on treatment with 0.2 M ethanolic KOH solution. Mild reaction conditions,
good yields and no chromatographic separation are some of the salient features of the present protocol.
Ó 2012 Elsevier Ltd. All rights reserved.
Article history:
Received 30 May 2012
Revised 25 June 2012
Accepted 27 June 2012
Available online 3 July 2012
Keywords:
Bromodimethylsulfonium bromide (BDMS)
(E)-1-(20-Hydroxy-40,60-dimethoxy phenyl)-
3-aryl-2-propen-1-ones
(20-hydroxychalcone)
8-Bromoflavones
7-Bromoaurones
20-Hydroxychalcones are essential intermediates for biosynthe-
sis of flavonoids in plants and many of them are found as such in
nature.1 In addition, they display a wide range of biological activi-
ties such as antitumoral,2–4 anti-inflammatory,5 antibacterial,6
antiulcerogenic,7 antioxidant,6,8,9 antimalarial10 and antileishman-
iosis activities.10,11 Link and Sorensen reported12 that 20,40,60,4-tet-
rahydroxychalcone is a key precursor for phlorizin (Fig 1) which is
used for inhibition of the sodium/glucose cotransporters (SGLTs)
and thereby lowering the blood glucose levels in diabetic animals.
A few years ago, Rossi-Bergmann and co-workers have shown11
that 20-hydroxychalcone containing bromine atom in ring A of flav-
ones moiety exhibits better antileishmanial activity as compared
to 20-hydroxychalcone itself. Moreover, these brominated com-
pounds might be converted easily into 8-bromoflavones and 7-bro-
moaurones which are key building blocks for the synthesis of
naturally occurring flavonoids such as vitexin, phlorizin, orientin,
and cupressuflavone as shown in Figure 1. Therefore, the synthesis
of brominated 20-hydroxychalcones is highly desirable from bio-
logical point of view.
viewed15 in 2009. It is easier to handle as compared to hazardous
molecular bromine. Recently we have further shown its usefulness
in multicomponent reactions for the synthesis of heterocyclic com-
pounds16 as well as in carbohydrate chemistry.17 Due to its unique
reactivity and properties, we have perceived that it can be explored
further for regioselective ring bromination over enone double bond
of 20-hydroxychalcones. Though numerous methods for bromina-
tion are known in the literature, the regioselective bromination
in the aromatic ring remains a challenging task particularly for
phenols and amines.18 In this Letter, we wish to report regioselec-
tive mono bromination of (E)-1-(20-hydroxy-40,60-dimethoxy-
phenyl)-3-aryl-2-propen-1-ones as depicted in Scheme 1.
For the present study, the brominating reagent, bro-
modimethylsulfonium bromide (BDMS)19 and (E)-1-(20-hydroxy-
40,60-dimethoxyphenyl)-3-aryl-2-propen-1-ones11(1) were pre-
pared by following the literature procedures. Subsequently, the
substrate 1a, (E)-1-(20-hydroxy-40,60-dimethoxyphenyl)-3-aryl-2-
propen-1-ones (0.5 mmol), in 2 mL of dichloromethane (DCM)
was treated with 1.0 equiv amount of BDMS at room temperature.
The brominated compound 2a was isolated in 67% yield within
5 min and it was characterized from 1H and 13C NMR spectra and
elemental analysis. After getting the desired product, the reaction
condition was optimized by carrying out the experiment with dif-
ferent amounts of BDMS under various solvent systems. The best
result obtained in terms of yield, time and selectivity is mentioned
in Table 1. It was noted that the best yield of the mono brominated
In the past few years, our research group13 as well as others14
have demonstrated that bromodimethylsulfonium bromide
(BDMS) can serve as a useful brominating reagent and an effective
catalyst in various organic transformations, which has been re-
⇑
Corresponding author. Tel.: +91 361 2582305; fax: +91 361 2582349.
E-mail address: atk@iitg.ernet.in (A.T. Khan).
0040-4039/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tetlet.2012.06.122

A. T. Khan et al. / Tetrahedron Letters 53 (2012) 4852–4857
4853
HO
OH
HO
OH
OH
O
O
O
HO
OH
HO
OH
OH
O
HO
O
OH
OH
O
O
HO
HO
OH
HO
OH
O
OH
O
OH
OH
Phlorizin
Orientin
Vitexin
O
OH
OH
O
OH
O
HO
HO
OH
O
Cupressuflavone
Figure 1. Some naturally occurring flavonoids.
l) were also examined with 1.5 equiv amount of BDMS under sim-
ilar reaction conditions20 and the desired regioselective monobro-
minated products 2c–l were obtained in excellent yields as shown
in Table 2.
Br
MeO
OH Ar
MeO
OH
Ar
1.5 equiv. BDMS
DCM/rt/5 min
The products were characterized by usual spectroscopic meth-
ods and also by single crystal XRD data. The XRD data reveal that
regioselective monobromination occurs at the position adjacent
to the OH group as shown in Figure 2.21
OMe O
OMe O
1
2
Ar=aryl/furyl/naphthyl
It is a well-known fact that (E)-1-(20-hydroxy-40,60-dimethoxy-
phenyl)-3-aryl-2-propen-1-ones are key starting materials for the
synthesis of flavones and aurones. We conceived that 8-bromoflav-
ones and 7-bromoaurones can be synthesized easily from (E)-1-(20-
Scheme 1. Synthesis of (E)-1-(30-bromo-20-hydroxy-40,60-dimethoxyphenyl)-3-
aryl-2-propen-1-ones using BDMS.
hydroxy-40,60-dimethoxyphenyl)-3-aryl-2-propen-1-ones
since
Table 1
there still exists a further possibility for bromination. Conse-
quently, the scope and generality of the reaction were also exam-
ined with excess amount of BDMS. It was noted that compound
1a on treatment with 4.0 equiv of BDMS in DCM provided the tri-
brominated product 3a in 84% yield which was smoothly con-
verted into 8-bromoflavone (5a) on treatment with 0.2 M
ethanolic KOH solution as shown in Scheme 2. The structure was
also confirmed by usual spectroscopic techniques and from single
crystal XRD data. It is clear that the cyclization took place at the
b-position with respect to carbonyl group. Likewise, other sub-
strates 1b and 1l were also converted into desired 8-bromoflavone
derivatives 5b and 5l by following the two-step procedure.22
It is well-established in the literature that the bromination of al-
kene can give methoxy brominated compound on treatment with
molecular Br2 in MeOH.23 We thought that methoxy group can
be incorporated at the b-position of the (E)-1-(20-hydroxy-40,60-
dimethoxyphenyl)-3-aryl-2-propen-1-ones if the reaction is car-
ried out with DCM-MeOH system. Subsequently, the substrate 1a
was treated with 4 equiv of BDMS in DCM/MeOH (5:2) and the
product 4a was isolated in 80% yield. Then, the compound 4a
was further transformed into 7-bromoaurone (6a) on treatment
with 0.2 M ethanolic KOH solution as depicted in Scheme 3. Like-
wise, the substrate 1b was converted into the corresponding 7-bro-
moaurone derivative 6b by performing the similar sequence of
reactions.24
Optimization of the reaction conditionsa
OMe
OMe
Br
MeO
OH
MeO
OH
BDMS
OMe O
1a
OMe O
2a
S. No.
BDMS/equiv
Solvent
Time/min
Yieldb (/%)
1
2
3
4
5
1.0
1.5
2.0
1.5
1.5
DCM
DCM
DCM
MeCN
EtOAc
45
5
5
10
5
67
96
95
81
86
a
The reactions were carried out with 0.5 mmol of the substrate.
Isolated yields.
b
product, (E)-1-(30-bromo-20-hydroxy-40,60-dimethoxyphenyl)-3-
aryl-2-propen-1-ones (2a) was obtained using 1.5 equiv of BDMS
in dichloromethane.
After optimization, the reaction of (E)-1-(20-hydroxy-40,60-dime-
thoxyphenyl)-3-aryl-2-propen-1-one (1b) was carried out under
identical reaction conditions and the product 2b was isolated in
93% yield.
All the products were fully characterized from IR, 1H, and 13C
NMR spectra as well as by their elemental analysis. The structures
of 8-bromoflavone and 7-bromoaurone were further confirmed by
X-ray crystallography studies as shown in Fig 3a and 3b.21
Encouraged by these successful results, a wide range of (E)-1-
(20-hydroxy-40,60-dimethoxyphenyl)-3-aryl-2-propen-1-ones (1c–

4854
A. T. Khan et al. / Tetrahedron Letters 53 (2012) 4852–4857
Table 2
Regioselective bromination of (E)-1-(20-hydroxy-40,60-dimethoxyphenyl)-3-aryl-2-propen-1-ones by employing bromodimethylsulfonium bromidea
Entry
Substrate (1)
Product (2)
Yieldb (%)
OMe
OMe
Br
MeO
OH
MeO
OH
1
95
OMe O
OMe O
1a
2a
OMe
OMe
OMe
OMe
Br
MeO
OH
MeO
OH
2
3
4
93
98
94
OMe O
OMe O
1b
2b
OMe
OMe
OMe
OMe
OMe
OMe
Br
MeO
MeO
OH
MeO
OH
OMe O
OMe O
1c
2c
OMe
OMe
Br
OH
MeO
OH
OMe
OMe
OMe O
OMe O
2d
1d
Cl
Cl
Br
MeO
MeO
OH
MeO
OH
5
6
7
90
87
85
OMe O
OMe O
1e
2e
Br
OH
MeO
OH
OMe O
OMe O
1f
2f
Br
Br
Br
MeO
MeO
MeO
OH
MeO
MeO
MeO
OH
OMe O
OMe O
1g
2g
Me
Me
Br
OH
OH
8
9
94
97
OMe O
OMe O
1h
2h
Cl
Cl
Br
OH
OH
OMe O
OMe O
1i
2i

A. T. Khan et al. / Tetrahedron Letters 53 (2012) 4852–4857
4855
Table 2 (continued)
Entry
Substrate (1)
Product (2)
Yieldb (%)
Br
Br
OMe
OMe
Br
MeO
OH
MeO
MeO
OH
10
11
82
OMe O
OMe O
1j
2j
O
Br
O
MeO
OH
OH
95
85
OMe O
1k
OMe O
2k
Br
MeO
OH
MeO
OH
12
OMe O
OMe O
1l
2l
a
The reaction was carried out with 0.5 mmol of the substrate in each case using 1.5 equiv amount of BDMS in DCM.
Isolated yields.
b
Figure 2. X-ray crystal structure of (E)-1-(30-bromo-20-hydroxy-40,60-dimethoxyphenyl)-3-aryl-2-propen-1-one (2b).
Br
Br
MeO
OH Ar
Br
MeO
OH Ar
MeO
O
Ar
4 equiv.BDMS
DCM/ rt
0.2 M KOH
EtOH-H2O
Br
OMe O
OMe O
OMe O
3
5
1
5a: Ar= 4-Methoxyphenyl
5b: Ar= 3,4-Dimethoxyphenyl
5l:
Ar= Napthyl
Scheme 2. Synthesis of 8-bromoflavones.
In conclusion, we have achieved regioselective monobromina-
of vitexin, bisflavones, and aureusidin which is under progress and
will be reported in due course of time.
tion of (E)-1-(20-hydroxy-40,60-dimethoxyphenyl)-3-aryl-2-pro-
pen-1-ones using BDMS under mild reaction conditions. In
addition, 8-bromoflavones and 7-bromoaurones were also synthe-
sized by employing excess amount of BDMS followed by base cat-
alyzed cyclization using ethanolic KOH solution. The 7-
bromoaurone and 8-bromoflavone can be utilized for the synthesis
Acknowledgments
A.C. is thankful to CSIR, New Delhi for his research fellowship.
The authors acknowledge to the Director, IIT Guwahati for provid-

4856
A. T. Khan et al. / Tetrahedron Letters 53 (2012) 4852–4857
Br
Br
MeO
OH Ar
OMe
MeO
MeO
OH Ar
Ar
O
0.2 M KOH
EtOH-H2O
4 equiv.BDMS
DCM-MeOH/ rt
Br
O
OMe O
OMe O
OMe
1
4
6
6a: Ar= 4-Methoxyphenyl
6b: Ar= 3,4-Dimethoxyphenyl
Scheme 3. Synthesis of 7-bromoaurones.
Figure 3a. X-ray crystal structure of 8-bromoflavone 5a.
Figure 3b. X-ray crystal structure of 7-bromoaurone 6a.
2. Kobori, M.; Iwashita, K.; Shinmoto, H.; Tsushida, T. Biosci. Biotechnol. Biochem.
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Cerecetto, H.; Gonza´ lez, M. Bioorg. Med. Chem. 2007, 15, 3356.
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T. Plant. Med. 1992, 58, 389.
8. Zhan, C.; Yang, J. Pharmacol. Res. 2006, 53, 303.
9. Zhang, Y.; Jiao, J.; Liu, C.; Wu, X.; Zhang, Y. Food Chem. 2008, 107, 1326.
10. Liu, M.; Wilairat, P.; Croft, S. L.; Tan, A. L.; Go, M. L. Bioorg. Med. Chem. 2003, 11,
2729.
ing laboratory facilities and DST-FIST for financial support for cre-
ating single crystal XRD facility in the Department of Chemistry.
We are thankful to the referees for their valuable comments and
suggestions.
Supplementary data
Supplementary data (compounds 2b, 5a and 6a) associated with
this article can be found, in the online version, at http://dx.doi.org/
10.1016/j.tetlet.2012.06.122.
References and notes
11. Boeck, P.; Falca~o, C. A. B.; Leal, P. C.; Yunes, R. A.; Cechinel, V.; Torres-Santos, E.
C.; Rossi-Bergamann, B. Bioorg. Med. Chem. 2006, 14, 1538.
1. Ni, L.; Meng, C. Q.; Sikorski, J. A. Expert Opin. Ther. Pat. 2004, 14, 1669.

A. T. Khan et al. / Tetrahedron Letters 53 (2012) 4852–4857
4857
12. Link, J. T.; Sorensen, B. K. Tetrahedron Lett. 2000, 41, 9213.
22. Typical procedure for the preparation of tribromides (3) and synthesis of 8-
bromoflavones (5): To
well stirred solution of (E)-1-(20-hydroxy-40,60-
13. (a) Khan, A. T.; Ali, M. A.; Goswami, P.; Choudhury, L. H. J. Org. Chem. 2006, 71,
8961; (b) Khan, A. T.; Parvin, T.; Choudhury, L. H. J. Org. Chem. 2008, 73, 8398.
14. (a) Yadav, D. K.; Patel, R.; Srivastava, V. P.; Watal, G.; Yadav, L. D. S. Tetrahedron
Lett. 2010, 51, 5701; (b) Yadav, L. D. S.; Patel, R.; Srivastava, V. P. Tetrahedron
Lett. 2010, 51, 739.
15. Choudhury, L. H.; Parvin, T.; Khan, A. T. Tetrahedron 2009, 65, 9513. and
references therein.
16. (a) Khan, A. T.; Basha, R. S.; Lal, M. Tetrahedron Lett. 2012, 53, 2211; (b) Khan, A.
T.; Basha, R. S.; Lal, M.; Mir, M. H. RSC Adv. 2012, 2, 5506.
a
dimethoxyphenyl)-3-aryl-2-propen-1-one (0.5 mmol) in 5 mL of DCM was
added BDMS (0.444 g, 2 mmol) at room temperature. The reaction was
complete within 10 min. Then, it was quenched by adding 10% sodium
metabisulphite solution and the reaction mixture was extracted with DCM
(2 ꢀ 15 mL), washed with water, and dried over anhydrous sodium sulfate to
obtain the tribromo derivatives 3. The pure tribromide was obtained after
recrystallization in DCM-hexane. Then the tribrominated compounds 3 on
treatment with 0.2 M KOH (0.5 mL) in EtOH/H2O (4:1) yielded 8-
bromoflavones after usual work-up procedure. Compound 5a: Pale yellow
solid, mp 239–240 °C; 1H NMR (400 MHz, CDCl3): d 3.90 (s, 3H), 4.03 (s, 3H) ,
4.05 (s, 3H), 6.46 (s, 1H), 6.64 (s, 1H), 7.03 (d, 2H, J = 8.8 Hz), 7.96 (d, 2H,
J = 9.2 Hz); 13C NMR (100 MHz, CDCl3): d 55.6, 56.7 (2C), 91.2, 92.2, 106.9,
109.9, 114.6 (2C), 117.8, 123.5, 128.1 (2C), 160.3, 160.5, 161.0, 162.4, 177.5; IR
mmax (KBr): cmꢁ1 1639, 1593, 1341; Anal. Calcd for C18H15BrO5: C, 55.26; H,
3.86%; found C, 55.18; H, 3.81%. Compound 5b: Pale yellow solid, mp 229–
230 °C; 1H NMR (400 MHz, CDCl3): d 3.94 (s, 3H), 3.94 (s, 3H) , 3.98 (s, 3H), 3.99
(s, 3H), 6.05 (s, 1H), 6.90 (s, 1H), 7.21 (dd, 1H, J = 1.6, 8.0 Hz), 7.73 (d, 1H,
J = 15.2 Hz), 7.80 (d, 1H, J = 15.6 Hz); IR mmax (KBr): cmꢁ1 1610, 1516, 1219,
1111; Anal. Calcd for C19H17BrO6: C, 54.17; H, 4.07%; found C, 54.11; H, 4.01%.
Compound 5l: Pale yellow solid, mp 315–316 °C; 1H NMR (400 MHz, CDCl3): d
4.04 (s, 3H), 4.06 (s, 3H) , 6.48 (s, 1H), 6.86 (s, 1H), 7.57–7.59 (m, 2H), 7.96–8.01
(m, 4H), 8.60 (s, 1H); IR mmax (KBr): cmꢁ1 1641, 1592, 1324, 1212; Anal. Calcd
for C21H15BrO4: C, 61.33; H, 3.68%; found C, 61.27; H, 3.61%.
17. (a) Khan, A. T.; Khan, M. M. Carbohydr. Res. 2010, 345, 2139; (b) Khan, A. T.;
Khan, M. M. Carbohydr. Res. 2010, 345, 154. and references therein.
18. Gribble, G. W. Chem. Soc. Rev. 1999, 28, 335.
19. Olah, G. A.; Vankar, Y. D.; Arvanaghi, M.; Prakash, G. K. S. Synthesis 1979, 720.
20. General method for the regioselective synthesis of (E)-1-(30-bromo-20-hydroxy-
40,60-dimethoxyphenyl)-3-aryl-2-propen-1-ones (2): To a well stirred solution of
(E)-1-(20-hydroxy-40,60-dimethoxyphenyl)-3-aryl-2-propen-1-ones (0.5 mmol)
in 3 mL of DCM was added BDMS (0.167 g, 0.75 mmol) at room temperature.
The reaction was complete instantaneously and the excess bromine was
destroyed with 10% sodium metabisulphite solution. The reaction mixture was
extracted with DCM (2 ꢀ 15 mL), washed with water, and dried over
anhydrous sodium sulfate. After removal of solvent in rotary evaporator, the
pure product was obtained as yellow solid. Compound 2a: Yellow solid, mp
178–179 °C; 1H NMR (400 MHz, CDCl3): d 3.86 (s, 3H), 3.99 (s, 3H) , 4.00 (s, 3H),
6.08 (s, 1H), 6.94 (d, 2H, J = 8.8 Hz), 7.57 (d, 2H, J = 8.8 Hz), 7.76 (d, 1H,
J = 15.6 Hz), 7.84 (d, 1H, J = 15.6 Hz); 13C NMR (100 MHz, CDCl3): d 55.6, 56.3,
56.5, 87.3, 92.1, 107.1, 114.6 (2C), 124.7, 128.2, 130.5 (2C), 143.7, 161.8, 161.9,
23. Clayden, J.; Greeves, N.; Wothers, P. Organic Chemistry, 1st ed.; Oxford
University Press: Oxford, 2006. p 503.
162.4, 163.4, 192.8; IR
m
max(KBr): cmꢁ1 1622, 1551, 1219, 1171; Anal. Calcd for
24. Typical procedure for the preparation of dibromides (4) and synthesis of 7-
C
18H17BrO5: C, 54.98; H, 4.36%; found C, 54.72; H, 4.27%. Compound 2b: Yellow
bromoaurones (6): To a
well stirred solution of (E)-1-(20-hydroxy-40,60-
solid, mp 200–201 °C; 1H NMR (400 MHz, CDCl3): d 3.93 (s, 3H), 3.94 (s, 3H),
3.98 (s, 3H), 3.99 (s, 3H), 6.05 (s, 1H), 6.90 (d, 1H, J = 8.4 Hz), 7.11 (d, 1H,
J = 2.0 Hz), 7.21 (dd, 1H, J = 1.6, 8.0 Hz), 7.73 (d, 1H, J = 15.2 Hz), 7.80 (d, 1H,
J = 15.6 Hz); 13C NMR (100 MHz, DMSO): d 55.5, 55.7, 56.6, 56.8, 88.9, 90.6,
106.7, 110.9, 111.8, 123.2, 124.5, 127.5, 143.9, 149.0, 151.4, 161.3, 161.5, 161.9,
192.3; IR mmax (KBr): cmꢁ1 1627, 1557, 1518, 1261, 1218; Anal. Calcd for
dimethoxyphenyl)-3-aryl-2-propen-1-one (0.5 mmol) in DCM/MeOH (5:2),
BDMS (0.444 g, 2 mmol) was added at room temperature. The reaction was
over within 10 min and it was quenched by adding 10% sodium metabisulfite
solution. The reaction mixture was extracted with DCM (2 ꢀ 15 mL), washed
with water and dried over anhydrous sodium sulfate. The solvent was
evaporated in rotary evaporator and the crude product recrystallized in
DCM-hexane mixture to get the pure brominated product 4. The dibrominated
product 4 on treatment with 0.2 M KOH (0.5 mL) in EtOH/H2O (4:1) afforded 7-
bromoaurones. Compound 6a: Pale yellow solid, mp 250–251 °C; 1H NMR
(400 MHz, CDCl3): d 3.89 (s, 3H), 4.05 (s, 6H) , 6.21 (s, 1H), 6.84 (s, 1H), 7.01 (d,
2H, J = 8.4 Hz), 7.92 (d, 2H, J = 8.8 Hz); 13C NMR (100 MHz, CDCl3): d 55.6, 56.7,
57.2, 85.4, 90.8, 106.6, 112.5, 114.7 (2C), 125.2, 133.5 (2C), 146.6, 159.0, 161.1,
C
19H19BrO6: C, 53.92; H, 4.52; found C, 53.75; H, 4.48%. Compound 2k: Yellow
solid, mp 146–147 °C; 1H NMR (400 MHz, CDCl3): d 3.99 (s, 3H), 4.00 (s, 3H) ,
6.07 (s, 1H), 6.52 (dd, 1H, J = 2.0 Hz, 3.2 Hz), 6.70 (d, 1H, J = 3.2 Hz), 7.53 (d, 1H,
J = 1.6 Hz), 7.62 (d, 1H, J = 15.6 Hz), 7.76 (d, 1H, J = 15.2 Hz); 13C NMR
(100 MHz, DMSO): d 56.9, 57.1, 89.2, 90.6, 106.7, 113.7, 118.1, 123.6, 130.5,
146.9, 151.4, 161.8, 162.1, 162.3, 191.9; IR m
max (KBr): cmꢁ1 1633, 1604, 1424,
1317, 1225, 1136; Anal. Calcd for C15H13BrO5: C, 51.01; H, 3.71%; found C,
50.95; H, 3.62%.
163.9, 164.2, 180.6; IR m
max (KBr): cmꢁ1 1598, 1513, 1173, 1102; Anal. Calcd for
C
18H15BrO5: C, 55.26; H, 3.86%; found C, 55.19; H, 3.78%. Compound 6b: Pale
21. Complete crystallographic data of 2b, 5a, and 6a for the structural analysis
have been deposited with the Cambridge Crystallographic Data Centre, CCDC
No. 810812, 810814 and 810813, respectively. Copies of this information may
be obtained free of charge from the Director, Cambridge Crystallographic Data
Centre, 12 Union Road, Cambridge CB2 1EZ, UK, (fax: +44-1223-336033, e-
mail: deposit@ccdc.cam.ac.uk or via: www.ccdc.cam.ac.uk).
yellow solid, mp 207–208 °C; 1H NMR (400 MHz, CDCl3): d 3.92 (s, 3H), 4.01 (s,
9H) , 6.18 (s, 1H), 6.80 (s, 1H), 6.90 (d, 1H, J = 8.4 Hz), 7.31 (dd, 1H, J = 1.6,
8.4 Hz), 7.81 (d, 1H, J = 1.6 Hz); 13C NMR (100 MHz, DMSO): d 55.5, 55.7, 56.6,
56.8, 88.9, 90.6, 106.7, 110.9, 111.8, 123.2, 124.5, 127.5, 143.9, 149.0, 151.4,
161.3, 161.5, 161.9, 192.3; IR mmax (KBr): cmꢁ1 1609, 1517, 1247, 1111; Anal.
Calcd for C19H17BrO6: C, 54.17; H, 4.07%; found C, 54.11; H, 4.01%.