Synthesis of 5/-bromo-2/-hydroxy-4,4/,6/-trimethoxychalcone from Garcinia nervosa and of its isomer 3/-bromo-2/-hydroxy-4,4/,6-/trimethoxychalcone

Article abstract of DOI:10.3184/030823410X12754665381128

The unambiguous syntheses of the naturally occurring 5'-bromo-2'-hydroxy-4, 4',6'-trimethoxychalcone 1, a constituent of Garcinia nervosa, and its positional isomer 3'-bromo-2'-hydroxy-4,4',6'-trimethoxychalcone 6 are described.

Full text of DOI:10.3184/030823410X12754665381128

318 RESEARCH PAPER
JUNE, 318–321
JOURNAL OF CHEMICAL RESEARCH 2010
Synthesis of 5′-bromo-2′-hydroxy-4,4′,6′-trimethoxychalcone from
Garcinia nervosa and of its isomer 3′-bromo-2′-hydroxy-4,4′,6′-
trimethoxychalcone
Sulaksha J. Paraba, Shubhada G. Kapdia, Chandrakant G. Naikb, Shrivallabh P. Kamata*
aDepartment of Chemistry, Goa University, Goa 403 206, India
bBioorganic Chemistry Laboratory, National Institute of Oceanography, Goa 403 004, India
The unambiguous syntheses of the naturally occurring 5′-bromo-2′-hydroxy-4,4′,6′-trimethoxychalcone 1, a constitu-
ent of Garcinia nervosa, and its positional isomer 3′-bromo-2′-hydroxy-4,4′,6′-trimethoxychalcone 6 are described.
Keywords: Garcinia, bromochalcone, phloroacetophenone
Garcinia species have well known medicinal properties
such as antimicrobial,1 anti-inflammatory,2 and are used in
healing skin infections and wounds.3 Ilyas, et al.4 isolated
a new bromochalcone from the leaves of Garcinia nervosa
and assigned structure 5′-bromo-2′-hydroxy-4,4′,6′-trime-
thoxychalcone 1 on the basis of its spectral data. In its 1H NMR
data, the assignment of a two proton singlet at δ 7.89 for
the trans-α, β-olefinic protons appeared to be rather unusual
although such an observation has been made earlier for
2′-hydroxy-4,4′,6′-trimethoxychalcone5 and a bichalcone.6 The
Fig. 1 HMBC and NOE correlations of 5.
simple structure and lack of any report of its synthesis prompted
us to synthesise the bromochalcone 1. Our retrosynthesis of
1 is depicted in Scheme 1.
Condensation7 of 5 with 4-methoxybenzaldehyde in the
presence of 50% ethanolic KOH gave the expected chalcone
6 in quantitative yield (m.p. 180 °C; m.p. of natural4 1 is also
2′-Hydroxy-4′,6′-dimethoxyacetophenone 3 was prepared
from phloroglucinol using literature7,8 procedures. Bromina-
tion9 of 3 using KBrO3 and HBr in glacial AcOH gave yellow
1
180 °C) and was fully characterised on the basis of its H
1
needles, m.p. 200 °C, whose simple H and 13C NMR data
NMR, 13C NMR, COSY and HMBC data. Interestingly, the 1H
NMR spectrum of 6 did show the two characteristic 1H
doublets at δ 7.76 and 7.84 with J = 15.4 Hz for the trans-α, β
olefinic protons respectively as against the singlet observed4
for these protons in the natural chalcone 1.
were inadequate to establish conclusively that the mono-bromo
derivative of 3 had the structure 4 or 5. Hence the position of
the Br atom was determined by the study of its long-range
1H–13C HMBC (Heteronuclear Multiple Bond Coherence) data
in which the hydroxyl proton on C-2′ correlated to C-1′, C-2′
and C-3′ while the proton on C-5′ correlated to C-1′, C-3′, C-4′
and C-6′. The fact that the OH proton did not correlate to the
carbon (C-5′) which is directly attached to the lone aromatic
proton and the H-5′ also did not show correlation to C-2′ indi-
cated that the aromatic proton is at the p-position with respect
to the OH group (Fig. 1).
1
In the H–13C HMBC experiment on 6, the OH proton at
C-2′ showed correlations with C-1′, C-2′ and C-3′ while
the proton at C-5′ correlated to C-1′, C-3′, C-4′ and C-6′, thus
establishing the structure 6 of our synthetic chalcone (Fig. 2)
Thus the bromo derivative was assigned the structure 3′-
bromo-2′-hydroxy-4′,6′-dimethoxyacetophenone 5 which was
further supported by the study of its NOESY and high-resolu-
tion electrospray ionisation mass spectrometry (HRESIMS)
data. The equivalence of the NOE from H-5′ to both the
methoxy groups at C-4′ and C-6′ indicated that the lone
aromatic proton is indeed at the C-5′ (Fig. 1).
Fig. 2 Selected HMBC correlations of 6.
Scheme 1
* Correspondent. E-mail: shrivkamat@yahoo.com

JOURNAL OF CHEMICAL RESEARCH 2010 319
which was further supported by the presence of a pseudomo-
lecular ion peak [M + H]+ at m/z 395.0332 in its HRESIMS
data.
The chalcone 6 on acetylation4 using acetic anhydride
and pyridine furnished the acetate 7 (m.p. 178–180 °C; lit.4
m.p. of 2 is 120–122 °C). The presence of strong carbonyl
bands at 1770 and 1660 cm−1 in its IR spectrum and a 3H sin-
glet at δ 2.16 in its 1H NMR spectrum established the presence
of the acetate group and hence the structure 7 which was
further supported by the presence of a pseudomolecular ion
peak at m/z 457.0244 [M + Na]+ in its mass spectrum.Although
the melting points of the natural and synthetic chalcones
(1 and 6) were identical (180 °C), the melting points as well as
the NMR data of their respective acetates (2 and 7) differed
considerably.
Fig. 3 Selected HMBC correlations of 11.
NMR and MS data. Appearance of a 3H singlet at δ 3.72 due
1
to methoxy group in its H NMR spectrum supported its for-
mation. The position of Br at C-3′ in 11 was unambiguously
established from the 1H–13C HMBC correlation studies of H-5′
to C-3′, C-4′ and C-6′ (Fig.3).
Thus bromination9 of 3 using KBrO3 and HBr gave 5 and
did not give the desired bromo derivative 4. Several other
brominating reagents10–18 were tried under varying reaction
conditions but all gave exclusively 5. We then resorted to
an alternative route to 4 involving protection of the two OH
groups in phloroacetophenone 8 followed by bromination,
methylation and then deprotection. Of the various protecting
groups used, protection by tosyl19 group worked. This new
route is depicted in Scheme 2.
Alkaline hydrolysis19 of the bromo-di-p-tosylate 11 to the
required 5′-bromo-2′,4′-dihydroxy-6′-methoxyacetophenone
12 was indicated by the presence of two 1H singlets at δ 6.25
1
(C4′-OH) and δ 13.22 (chelated C2′-OH) in its H NMR spec-
trum. Selective methylation8 of the non-chelated hydroxyl
group at C-4′ gave the required 5′-bromo-2′-hydroxy-4′,6′-
dimethoxyacetophenone 4 as colourless solid having m.p.
102 °C and its structure was established by the study of
its NMR and MS data. Finally condensation20 of 4 with 4-
methoxybenzaldehyde gave the chalcone 1, identical in all
respects (mp and spectral data including the singlet for the
Selective esterification of 8 using two equivalents of p-TsCl
and anhydrous K2CO3 in dry acetone19 gave the di-p-tosylate 9.
In its 1H NMR spectrum, two ortho coupled doublets at δ 7.32
and 7.72 for 4H each and two (3H) singlets at δ 2.46 and 2.49
established the presence of two p-tosyl groups and hence the
structure 2′-hydroxy-4′,6′-di-p-tosyloxyacetophenone 9 which
was further supported by the presence of a pseudomolecular
ion peak at m/z 477.0675 [M + H]+ in its HRESIMS data.
Bromination9 of 9 using KBrO3 and HBr in glacial AcOH gave
lemon yellow crystals having m.p. 114 °C. The presence of
1
trans olefinic protons in the H NMR) with the natural 1.
Moreover, the data (m.p., 1H NMR) of the acetate of the syn-
thetic 1 also matched well with the acetate 2 of the natural 1.
This is the first report of the synthesis of the bromochalcone4 1
and its positional isomer 6.
Experimental
1
Melting points were determined in open capillary tubes and are uncor-
rected. IR spectra were recorded as KBr diluted pellets on a Shimadzu
a singlet at δ 6.63 (H-5′, 1H) in its H NMR spectrum estab-
lished nuclear monobromination. Its HRESIMS measurement
showed a pseudomolecular ion peak at m/z 556.9765 [M + H]+
(Calcd for C22H2081BrO8S2: 556.9763), supporting the forma-
tion of 3′-bromo-2′-hydroxy-4′,6′-di-p-tosyloxyacetophenone
10. Methylation8 of 10 with Me2SO4 and anhydrous K2CO3 in
dry acetone gave 3′-bromo-4′,6′-di-p-tosyloxy-2′-methoxyace-
tophenone 11 as colourless shiny crystals having m.p. 128 °C.
The structure of 11 was established by the study of its
1
(IR Prestige-21) FTIR spectrophotometer. H and 13C NMR spectra
were recorded at 300 and 75 MHz respectively on a Bruker WT 300
FT-NMR instrument with TMS as internal standard and chemical
shifts are recorded in δ values. High-resolution mass measurements of
all the new compounds except that for 4 were recorded on QSTARXL
MS/MS mass spectrometer, Applied Biosystems, Switzerland. All
yields refer to isolated products unless stated otherwise. All solvents
were distilled prior to use. Petroleum ether refers to hydrocarbon
Scheme 2 Reagents and conditions (i) p-TsCl (2 equiv.), K2CO3 (3 equiv.), acetone, reflux, 5 h, 71%; (ii) KBrO3, HBr, rt, 30 min,
97%; (iii) Me2SO4 (1 equiv.), K2CO3 (3 equiv.), acetone, reflux, 4 h, 85%; (iv) KOH (0.04 equiv.), MeOH, reflux, 4 h, 79%;
(v) Me2SO4 (1 equiv.), K2CO3 (3 equiv.), acetone, reflux, 3 h, 67%.

320 JOURNAL OF CHEMICAL RESEARCH 2010
fraction boiling in the range 60–80 °C and ether refers to diethyl ether.
Phloroacetophenone 8 and 2′-hydroxy-4′,6′-dimethoxyacetophenone
3 were prepared by using the procedures reported in literature.7,8
3′-Bromo-2′-hydroxy-4′,6′-dimethoxyacetophenone (5): To a stirred
solution of 3 (0.290 g, 1.48 mmol) and KBrO3 (0.085 g, 0.50 mmol)
in glacial acetic acid (2 mL) was added drop by drop HBr (48%,
2.6 mmol, 0.3 mL). The mixture was stirred at room temperature for
30 min, diluted with cold water (5 mL) and stirred for further 15 min.
Yellow solid separated was collected by filtration, washed with dilute
NaHSO3, water and dried at 100 °C to afford 5 (0.313 g, 83%). Recrys-
tallisation from benzene gave pale brown needles m.p. 186–188 °C
while recrystallisation from CHCl3-petroleum ether mixture afforded
pale yellow needles m.p. 200 °C. IR (cm−1): 1632 (C=O), 1581 (C=C).
1H NMR (CDCl3) δ: 2.63 (s, 3H, –COCH3), 3.93 (s, 3H, 6′-OCH3),
3.96 (s, 3H, 4′-OCH3), 6.0 (s, 1H, H-5′), 14.59 (s, 1H, OH). 13C NMR
(CDCl3) δ: 32.9 (–COCH3), 55.7 (6′-OCH3), 56.2 (4′-OCH3), 86.6
(C-5′), 91.5 (C-3′), 106.4 (C-1′), 161.8 (C-6′), 162.5 (C-2′), 162.6
(C-4′), 203.2 (CO). HRESIMS: m/z 274.9921 [M + H]+; Calcd for
C10H11O479Br, 274.9919.
CHCl3–petroleum ether mixture gave lemon yellow crystals m.p.
1
114 °C. IR (cm−1): 1627 (C=O), 1595 (C=C), 1387 (S=O). H NMR
(CDCl3) δ: 2.74 (s, 3H, –COCH3), 6.68 (s, 1H, H-5′), 13.6 (s, 1H,
–OH), For the tosyl group at C-4′: 2.50 (s, 3H, –CH3), 7.79 (dt, 4H,
J = 7.1 and 2.1 Hz), For the tosyl group at C-6′: 2.46 (s, 3H, –CH3),
7.34 (d, 2H, J = 8.4 Hz), 7.42 (d, 2H, J = 8.4 Hz),. 13C NMR (CDCl3)
δ: 32.4 (–COCH3), 105.2 (C-5′), 108.0 (C-3′), 113.8 (C-1′), 149.3
(C-6′), 151.1 (C-4′), 161.4 (C-2′), 203.3 (CO), For the tosyl group at
C-4′: 21.8, 129.9, 130.4, 132.1, 146.8, For the tosyl group at C-6′:
21.8, 128.6, 131.4, 146.3. HRESIMS: m/z 556.9765 [M + H]+; Calcd
for C22H2081BrO8S2: 556.9763.
3′-Bromo-4′,6′-di-p-tosyloxy-2′-methoxyacetophenone (11):
A
mixture of 10 (1.32 g, 2.378 mmol), anhydrous Me2SO4 (0.2996 g,
2.378 mmol) and anhydrous K2CO3 (0.984 g, 7.134 mmol) in dry
acetone (20 mL) was heated to reflux for 4 h. The reaction mixture
was cooled to room temperature, diluted with water and extracted
with ether. The combined organic extracts were washed with water,
dried over anhydrous Na2SO4 and concentrated to afford 11 as colour-
less solid (1.593 g, 85%). Recrystallisation from benzene-petroleum
ether mixture gave colourless shiny crystals m.p. 128 °C. IR (cm−1):
3′-Bromo-2′-hydroxy-4,4′,6′-trimethoxychalcone (6): A mixture
of 5 (0.115 g, 0.41 mmol) and 4-methoxybenzaldehyde (0.056 g,
0.4 mmol, 0.050 mL) in alcoholic KOH (50%, 2.5 mL) was kept at
room temperature for 72 h. The dark yellow mass was diluted with
water (3 mL) and acidified with aqueous HCl. Yellow solid separated
was filtered, washed with water and dried to afford 6 (0.142 g, quanti-
tative). Recrystallisation from CHCl3-MeOH mixture gave yellow
1
1710 (C=O), 1585 (C=C), 1377 (S=O). H NMR (CDCl3) δ: 2.56
(s, 3H, –COCH3), 3.72 (s, 3H, –OCH3), 7.00 (s, 1H, H-5′), For the
tosyl group at C-4′: 2.47 (s, 3H, –CH3), 7.74 (d, 2H, J = 8.1 Hz), 7.78
(d, 2H, J = 8.7 Hz), For the tosyl group at C-6′: 2.42 (s, 3H, –CH3),
7.36 (d, 4H, J = 6.6 Hz). 13C NMR (CDCl3) δ: 31.8 (–COCH3), 62.9
(–OCH3), 111.7 (C-3′), 114.1 (C-5′), 130.2 (C-1′), 146.4 (C-6′), 148.1
(C-4′), 155.6 (C-2′), 197.3 (CO), For the tosyl group at C-4′: 21.7,
129.9, 130.1, 132.1, 146.2, For the tosyl group at C-6′: 21.7, 128.5,
128.6, 131.5, 144.5. HRESIMS: m/z 570.9948 [M + H]+; Calcd for
C23H2281BrO8S2: 570.9919.
5′-Bromo-2′,4′-dihydroxy-6′-methoxyacetophenone (12): A mixture
of 11 (0.958 g, 1.683 mmol) and KOH (3.76 g, 0.0673 mmol) in a
mixture of ethanol (30 mL) and water (30 mL) was heated to reflux for
4 h, cooled, neutralised with acetic acid and extracted with ether. The
combined organic extracts were washed with saturated NaHCO3,
water, dried over anhydrous Na2SO4 and concentrated to afford resid-
ual oil which was chromatographed over silica gel with petroleum
ether-ethyl acetate (98:2) to afford 12 as colourless solid (0.3483 g,
79%). Recrystallisation from petroleum ether gave colourless flakes
m.p. 116 °C. IR (cm−1): 3302 (OH), 1581 (C=C). 1H NMR (CDCl3) δ:
2.70 (s, 3H, –COCH3), 3.89 (s, 3H, –OCH3), 6.25 (s, 1H, –OH), 6.45
(s, 1H, H-3′), 13.22 (s, 1H, –OH). 13CNMR (CDCl3) δ: 31.1 (–COCH3),
61.9 (–OCH3), 97.1 (C-5′), 100.6 (C-3′), 110.6 (C-1′), 158.8 (C-6′),
165.0 (C-2′), 166.4 (C-4′), 202.9 (CO). HRESIMS: m/z 262.9748
[M + H]+; Calcd for C9H1081BrO4: 262.9742.
5′-Bromo-2′-hydroxy-4′,6′-dimethoxyacetophenone (4): A mixture
of 12 (0.095 g, 0.362 mmol), anhydrous Me2SO4 (0.0456 g, 0.362
mmol) and anhydrous K2CO3 (0.15 g, 1.086 mmol) in dry acetone
(10 mL) was heated to reflux for 3 h. The reaction mixture was cooled
to room temperature, diluted with water and extracted with ether.
The combined organic extracts were washed with water, dried over
anhydrous Na2SO4 and concentrated to leave residual oil which was
chromatographed over silica gel with petroleum ether–ether (9:1) to
afford 4 as colourless solid (0.0665 g, 67%). Recrystallisation from
petroleum ether gave colourless needles m.p. 102 °C. IR (cm−1): 1627
(C=O), 1585 (C=C). 1H NMR (CDCl3) δ: 2.71 (s, 3H, –COCH3), 3.89
(s, 3H, 6′-OCH3), 3.91 (s, 3H, 4′-OCH3), 6.32 (s, 1H, H-3′), 13.49
(s, 1H, –OH). 13C NMR (CDCl3) δ: 31.2 (–COCH3), 51.0 (–OCH3),
56.6 (–OCH3), 97.2 (C-3′), 97.7 (C-5′), 110.1 (C-1′), 160.4 (C-6′),
162.2 (C-4′), 165.4 (C-2′), 203.1 (CO). HRMS: m/z 275.9816 [M]+
Calcd. for C10H1181BrO4: 275.9820.
1
flakes m.p. 180 °C. IR (cm−1): 3420 (OH), 1625 (C=O). H NMR
(CDCl3) δ: 3.86 (s, 3H, 2′-OCH3), 3.99 (s, 3H, 4′-OCH3), 4.0 (s, 3H,
4-OCH3), 6.07 (s, 1H, H-5′), 6.94 (d, 2H, H-3 and H-5, J = 9 Hz), 7.57
(d, 2H, H-2 and H-6, J = 9 Hz), 7.76 (d, 1H, H-α, J = 15.4 Hz), 7.84
(d, 1H, H-β, J = 15.4 Hz), 14.94 (s, 1H, –OH). 13C NMR (CDCl3)
δ: 55.4 (6′-OCH3), 56.0 (4′-OCH3), 56.3 (4-OCH3), 87.1 (C-5′), 91.9
(C-3′), 106.9 (C-1′), 114.4 (C-3, C-5), 124.5 (C-8), 128.0 (C-1), 130.2
(C-2, C-6), 143.5 (C-7), 161.6 (C-4′), 161.7 (C-4), 162.2 (C-6′), 163.2
(C-2′), 192.6 (C-9). HRESIMS: m/z 395.0332 [M + H]+; Calcd for
C18H17O581Br: 395.0317.
2′-Acetoxy-3′-bromo-4,4′,6′-trimethoxychalcone (7): Chalcone 6
(25 mg, 0.0636 mmol) in Ac2O (2 mL) and dry pyridine (1 mL) was
heated on a boiling water bath for 2 h. The reaction mixture was
cooled, poured over crushed ice containing few drops of conc. HCl
and the solid separated out was collected by filtration, washed with
water and dried in an oven at 100 °C to afford 7 (0.0161 g, 73%).
Recrystallisation from CHCl3–MeOH mixture gave greenish shiny
flakes m.p. 178–180 °C. IR (cm−1): 1770 (C=O), 1660 (C=O), 1597
(C=C). 1H NMR (CDCl3) δ: 2.16 (s, 3H, –OCOCH3), 3.79 (s, 6H, 2 ×
-OCH3), 3.92 (s, 3H, –OCH3), 6.40 (s, 1H, H-5′), 6.78 (d, 1H, H-α,
J = 16 Hz), 6.85 (d, 2H, H-3 and H-5, J = 9 Hz), 7.43 (d, 2H, H-2 and
H-6, J = 9 Hz), 7.37 (d, 1H, H-β, J = 16 Hz). HRESIMS: m/z 457.0244
[M + Na]+; Calcd for C20H19O679BrNa: 457.0263.
2′-Hydroxy-4′,6′-di-p-tosyloxyacetophenone (9): A mixture of 8
(1.008 g, 6 mmol), p-TsCl (2.286 g, 12 mmol) and anhydrous K2CO3
(2.484 g, 18 mmol) in dry acetone (25 mL) was heated to reflux for
5 h. The reaction mixture was cooled to room temperature, diluted
with water and extracted with ether. The combined organic extracts
were washed with water, dried over anhydrous Na2SO4 and concen-
trated to afford a residual solid which was chromatographed on silica
gel with petroleum ether/ethyl acetate (8:2) to afford 9 as colourless
solid (2.016 g, 71%). Recrystallisation from petroleum ether gave
colourless crystals m.p. 78 °C. IR (cm−1): 1634 (C=O), 1595 (C=C),
1377 (S=O). 1H NMR (CDCl3) δ: 2.67 (s, 3H, –COCH3), 6.35 (d, 1H,
H-3′, J = 2.4 Hz), 6.44 (d, 1H, H-5′, J = 2.4 Hz), 12.74 (s,1H, –OH),
For the tosyl group at C-4′: 2.49 (s, 3H, –CH3), 7.72 (d, 4H, J = 8.4
Hz), For the tosyl group at C-6′: 2.46 (s, 3H, –CH3), 7.37 (dt, 4H,
J = 8.1 Hz). 13C NMR (CDCl3) δ: 32.5 (–COCH3), 107.6 (C-3′), 110.2
(C-5′), 113.8 (C-1′), 150.6 (C-6′), 153.6 (C-4′), 164.5 (C-2′), 203.2
(CO), For the tosyl group at C-4′: 21.8, 128.6, 130.3, 131.9, 146.7, For
the tosyl group at C-6′: 21.8, 128.4, 130.1, 131.7, 146.2. HRESIMS:
m/z 477.0675 [M + H]+; Calcd for C22H21O8S2: 477.0678.
5′-Bromo-2′-hydroxy-4,4′,6′-trimethoxychalcone (1): To a mixture
of 4 (0.02 g, 0.0727 mmol) and 4-methoxybenzaldehyde (0.01 g,
0.073 mmol) in ethanol (1 mL), KOH (0.1 g) in water (1 mL) was
added drop-wise and the reaction mixture was stirred for 4 h at 45 °C.
The yellow-orange mixture was diluted with water (3 mL) and acidi-
fied with conc. HCl. Yellow solid separated was filtered, washed
with water and dried to afford 1 (0.02 g, 70%). Recrystallisation
from CHCl3-MeOH mixture gave yellow flakes m.p. 178 °C (lit.4 m.p.
3′-Bromo-2′-hydroxy-4′,6′-di-p-tosyloxyacetophenone (10): HBr
(48%, 0.2 mL, 1.84 mmol) was added to a mixture of 9 (0.5044 g, 1.05
mmol) and KBrO3 (0.06 g, 0.35 mmol) in glacial acetic acid (2 mL).
The reaction mixture was stirred for 30 min at room temperature,
diluted with cold water (5 mL) and stirred for further 15 min to afford
10 as yellow solid (0.57 g, 97%) which on recrystallisation from
1
180 °C). IR (cm−1): 2963 (OH), 1626 (C=O), 1605 (C=C). H NMR
(CDCl3) δ: 3.79 (s, 3H, –OCH3), 3.86 (s, 3H, –OCH3), 3.93 (s, 3H,
–OCH3), 6.36 (s, 1H, H-3′), 6.93 (d, 2H, H-3 and H-5, J = 8.1 Hz),
7.62 (d, 2H, H-2 and H-6, J = 8.1 Hz), 7.87 (s, 2H, H-α and H-β),
13.65 (s, 1H, –OH). 13C NMR (CDCl3) δ: 55.4 (6′-OCH3), 56.6

JOURNAL OF CHEMICAL RESEARCH 2010 321
References
(4′-OCH3), 62.3 (4-OCH3), 97.3 (C-3′), 114.0 (C-5′), 114.4 (C-3,
C-5), 123.2 (C-8), 127.7 (C-1′), 130.4 (C-2, C-6), 144.4 (C-7), 159.5
(C-4), 161.7 (C-2′), 161.8 (C-4′), 165.5 (C-6′), 192.5 (C-9). HRESIMS:
m/z 395.0323 [M + H]+; Calcd for C18H1881BrO5: 395.0317.
1
2
3
4
5
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2′-Acetoxy-5′-bromo -4,4′,6′-trimethoxychalcone (2): A mixture of
1 (7.5 mg, 0.019 mmol) inAc2O (1 mL) and dry pyridine (0.5 mL) was
heated on a boiling water bath for 2 h. The reaction mixture was
cooled, poured over crushed ice containing few drops of conc. HCl
and the solid separated out was collected by filtration, washed with
water and dried to afford 2 as yellow solid (0.006 g, 72%), m.p. 126–
28 °C (lit.4 m.p. 122–26 °C). IR (cm−1): 1766 (C=O), 1638 (C=O),
1599 (C=C). 1H NMR (CDCl3) δ: 2.17 (s, 3H, –OCOCH3), 3.80
(s, 3H, –OCH3), 3.83 (s, 3H, –OCH3), 3.93 (s, 3H, –OCH3), 6.54 (s,
1H, H-3′), 6.90 (d, 2H, H-3 and H-5, J = 8.7 Hz), 6.92 (d, 1H, H-α,
J = 16.0 Hz), 7.39 (d, 1H, H-β, J = 16.0 Hz), 7.49 (d, 2H, H-2 and
H-6, J = 8.7 Hz). HRESIMS: m/z 474.9940 [M + K]+; Calcd for
C20H19O681BrK: 474.9982.
6
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Received 27 February 2010; accepted 16 May 2010
Paper 101026 doi: 10.3184/030823410X12754665381128
Published online: 2 July 2010

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