A convenient and simple method for the synthesis of condensed γ-lactams and substituted xanthones from cyclic-1,3-diketones

Article abstract of DOI:10.1016/S0040-4020(00)00484-1

A systematic study of alkylation of cyclic-1,3-diones with 2-bromo-6-methoxybenzofuran-3-one was undertaken. Upon condensation in acetic acid with p-substituted aniline the O-alkylated product 3a gave condensed γ-lactam heterocycle 4. In contrast, the condensation of analogous O-alkylated derivatives 3b and 3c with p-substituted anilines furnished the substituted xanthone derivatives 6 and 7a. The probable mechanism of formation of 4, 6 and 7a was discussed. (C) 2000 Elsevier Science Ltd.

Full text of DOI:10.1016/S0040-4020(00)00484-1

TETRAHEDRON
Pergamon
Tetrahedron 56 (2000) 5947±5952
A Convenient and Simple Method for the Synthesis of Condensed
g-Lactams and Substituted Xanthones from Cyclic-1,3-diketones
²
*
B. Chandrasekhar, S. R. Ramadas and D. V. Ramana
Department of Chemistry, Indian Institute of Technology, Chennai 600 036, India
Dedicated to Professor K. K. Balasubramanian on the occasion of his 60th birthday
Received 23 March 2000; revised 11 May 2000; accepted 1 June 2000
AbstractÐA systematic study of alkylation of cyclic-1,3-diones with 2-bromo-6-methoxybenzofuran-3-one was undertaken. Upon conden-
sation in acetic acid with p-substituted aniline the O-alkylated product 3a gave condensed g-lactam heterocycle 4. In contrast, the condensa-
tion of analogous O-alkylated derivatives 3b and 3c with p-substituted anilines furnished the substituted xanthone derivatives 6 and 7a. The
probable mechanism of formation of 4, 6 and 7a was discussed. q 2000 Elsevier Science Ltd. All rights reserved.
Introduction
Results and Discussion
In the literature1±3 a considerable number of reports indicate
the exclusive formation of C-alkylation products during the
reaction of a-bromoketones with cyclic-1,3-diones. 1,4-di-
carbonyl compounds are most reactive and versatile
substrates for the general synthesis of pyrroles (Paal±
Knorr Pyrrole Synthesis), which can be derived from
a-bromoketones by C-alkylation of cyclic-1,3-diones. The
cyclization condensation of 1,4-dicarbonyl systems with
ammonia or primary amines has been well investigated
and synthetically exploited in the ®eld of pyrroles4±6
(Scheme 1), whereas reports on analogous studies invol-
ving O-alkylation are lacking. The reactivity of indan-
1,3-dione with phenacyl bromide has been investigated by
Ramadas and Padmanabhan7±10 with a view to synthesizing
condensed heterocycles using triones as building blocks.
Alkylation of cyclic-1,3-diones (1)
The 2-bromo-6-methoxy-2H-benzo[b]furan-3-one (2),
required for the study was prepared from 6-methoxyben-
zo[b]furan-3-one following the literature11 procedure and
characterized thoroughly. Alkylation of 1with 2 in presence
of K2CO3 in dry chloroform at room temperature gave a
dark brown solid identi®ed as the O-alkylated compound
as the major product. The NMR spectrum of the product
displayed a singlet at d 5.75 characteristic of O-alkylated
product 3. This was further con®rmed by the presence of a
doublet in the 13C NMR spectrum at d 105. Chromatograph-
ic puri®cation afforded 3 in 60±75% yield. Varying the
solvent, the temperature, or the base12±14 did not alter reac-
tion course. This was found to be a genuine, unique O-
alkylation, (Scheme 2).
However, there are no reports on the use of heterocyclic
a-bromoketo ethers as the alkylating agents. In this publica-
tion we wish to report a novel transformation encoun-
tered in an attempted condensation of the O-alkylated
product 3 derived from 2-bromo-6-methoxy-benzofuran-
3-one.
Condensation of O-alkylated product (3a)
The condensation of O-alkylated product with p-substituted
anilines gave very interesting results both from the mechan-
istic and synthetic point of view. The reaction was found to
Scheme 1.
Keywords: cyclic-1,3-diketones; O-alkylated derivatives; g-lactams; xanthones.
* Corresponding author. Present address: Dr. Reddy's Research Foundation, 7-1-27, Ameerpet, Hyderabad 500016, India. Tel.: 191-040-3045439; fax: 191-
040-3045438; e-mail: drf@hdl.vsnl.net.in
Emeritus Scientist, CSIR, India.
²
0040±4020/00/$ - see front matter q 2000 Elsevier Science Ltd. All rights reserved.
PII: S0040-4020(00)00484-1

5948
B. Chandrasekhar et al. / Tetrahedron 56 (2000) 5947±5952
Scheme 2.
be dependent upon acetic acid and p-substituted anilines.
Thus when 3a was condensed with p-anisidine in glacial
acetic acid at re¯ux temperature, instead of the expected
diamine derivative 5 (Scheme 3), the product was found
to be different, for the IR spectrum showed a carbonyl func-
tionality at 1720 cm21. The product obtained in 50% yield
after passing the crude mixture through a column of neutral
alumina showed a singlet at d 5.1 (1H) apart from the
aromatic signals in its NMR spectrum. Based on spectral
data and X-ray diffraction studies15 the product was identi-
®ed as g-lactam heterocycle 4 with cross conjugation. The
transformation was found to be a general one by extending the
same product to other p-substituted anilines 4b±d (Table 1).
O-alkylated derivative 3b wherein 6a was isolated in 30%
yield. Thus when 3b was condensed with p-anisidine in
glacial acetic acid at its re¯ux temperature, instead of the
expected g-lactam derivative, the product was found to be
different, for the IR spectrum showed carbonyl functionality
at 1630 cm21. The product obtained in 30% yield after
passing the crude mixture through a column of neutral
alumina showed a broad singlet at d 11 apart from the
aromatic signals in its NMR spectrum. Based on spectral
data and X-ray diffraction studies,16 the product was identi-
®ed as xanthone derivative 6a. Conversion of other O-alky-
lated derivatives 3b±c to the corresponding xanthones 6b±d
and 7a upon condensation in acetic acid revealed this trans-
formation to be a general one (Scheme 4) (Table 1).
The presence of a gem dimethyl group in the pyran ring
alters the course of reaction as evidenced in the case of
Probable mechanistic pathway

B. Chandrasekhar et al. / Tetrahedron 56 (2000) 5947±5952
5949
Scheme 3.
Table 1.
could lead to the species 12. This on dehydration may
furnish the more stable cross-conjugated ole®n 13. The
formation of g-lactam is assumed by intramolecular nucleo-
philic addition of -NH2 to the aldehydic function followed
by aerial oxidation of the resulting aminol during work up. It
is speculated that loss of carbon atom after the formation of
benzopyran ring either by decarbonylation or decarboxylation
Entry
R1
mp (8C) Yield of 4 (%) mp (8C) Yield of 6 (%)
a
b
c
OMe 206±208 50
Me
H
132±134 30
116±118 28
140±142 25
158±160 20
172±174 48
182±184 45
202±204 40
d
Cl
The structure assigned to 4 is supported by X-ray data.15 The
structure assigned to 6 is supported by X-ray data.16
with concomitant aerial oxidation at position 9 could lead to
the xanthone skeleton. The exact mechanistic implications
of the last step d are not very clear. This mechanism gains
some support from observations carried out by us.
Mechanistic investigations
The O-alkylated product 3 is recovered unchanged, even
after re¯uxing in glacial acetic acid without the addition
of a primary amine. This suggests that ring opening of fura-
none occurs perhaps only in presence of p-substituted
aniline in acid medium. The role of acetic acid (as a medium
and protonating agent) appears to be unique, as this conden-
sation failed to occur between the O-alkylated product
and p-substituted aniline either in re¯uxing toluene or in
The reaction involves initially the protonation of conjugated
carbonyl followed by Michael-type of addition of the p-
substituted aniline resulting in the formation of aminoenol
8, which could lead to the ring opening of the ®ve-
membered furanone furnishing ®ssion products namely
ketoaldehydes 9 and enamine derivative 10. The enamine
could attack the ketoaldehyde affording 11 which by intra-
molecular nucleophilic attack on the carbonyl function
Scheme 4.

5950
B. Chandrasekhar et al. / Tetrahedron 56 (2000) 5947±5952
re¯uxing toluene containing catalytic amount of PTS17 or
other protonic acids.
gave analytically pure sample of O-alkylated products
3a±c.
The atmospheric oxidation of aminol 14 to the g-lactam
could be visualized during the work up, since the conden-
sation of the O-alkylated product with aromatic amines gave
the same fused heterocycles 4 and 6 even under a dry nitro-
gen atmosphere.
O-Alkylated products
2-[5,5-Dimethyl-3-oxo-1-cyclohexen-1-yl)oxy]-6-methoxy-
3(2H)-benzofuranone (3a). Using the above procedure,
5,5-dimethyl-1,3-cyclohexanedione (1a) (7 g, 50 mmol) in
chloroform (150 ml) and 2-bromo-6-methoxybenzofuran-3-
one (2) (11.25 g, 46 mmol) in chloroform (50 ml) were
reacted in presence of K2CO3 (14 g, 100 mmol) for 24 h.
The crude mixture was puri®ed by column chromatography
(9:1 hexane/benzene) to afford 3a (11.32 g, 75%) as a light
yellow crystalline solid, mp 118±1208. IR (KBr): 1720,
Our serious attempts either to isolate or synthesize the
ketoaldehyde 9, one of the reactive intermediates proposed
in the above mechanism, have met with little success. Treat-
ment of 2-bromo-6-methoxycoumaran-3-one by sodium
carbonate in dioxane gave no such ketoaldehydes, on the
other hand, the attempted reaction gave some decomposed
products.
1640, 1620, 1480, 1440,1360 cm21; H NMR (400 MHz,
1
CDCl3): d 6.6±7.6 (m, 3H), 5.82 (s, 1H), 5.75 (s, 1H), 3.8
(s, 3H), 2.45 (d, Hb, Jˆ4 Hz), 2.35 (d, Ha, Jˆ4 Hz), 2.28 (s,
2H), 1.2 (s, 6H); 13C NMR (CDCl3) d 199.1, 190.0, 173.9,
169.3, 126.2, 112.6, 111.7, 105.0, 96.6, 96.1, 56.1, 50.6,
41.8, 32.4, 28.4, 27.9; MS (EI): m/z 302 (M1., 18), 287
(7), 243 (11), 241 (7.5), 163 (24), 135 (15); Anal.: Calcd
for C17H18O5: C, 67.54; H, 5.96. Found C, 67.72; H, 6.05.
Thus, the condensation of O-alkylated product is found to be
highly dependent on acetic acid and p-substituted aniline.
The preparation of condensed g-lactam and xanthone
derivatives from cyclic-1,3-diones is novel. It constitutes
entirely a new method for the synthesis of xanthones.18±30
6-Methoxy-2-[(3-oxo-1-cyclohexen-1-yl)oxy]-3(2H)-benzo-
furanone (3b). Using the above procedure 1,3-cyclo-
hexanedione (1b) (5.6 g, 50 mmol) in chloroform (150 ml)
and 2-bromo-6-methoxybenzofuran-3-one (2) (11.25 g,
46 mmol) in chloroform (50 ml) were reacted in presence
of K2CO3 (14 g, 100 mmol) for 24 h. The crude mixture was
puri®ed by column chromatography (9:1 hexane/benzene)
to afford 3b (9.5 g, 70%) as a light yellow crystalline solid,
mp 158±1608. IR (KBr): 1720, 1650, 1620, 1450,
Experimental
All experiments involving air or moisture sensitive reagents
were performed in an atmosphere of nitrogen. The glass-
ware was dried under vacuum and ¯ushed with nitrogen.
Chloroform was freshly distilled from calcium chloride.
Cyclic 1,3 diones, p-substituted anilines were obtained
from Aldrich Chemcal Co. Column chromatography was
performed on ACME neutral aluminum oxide activated,
Brockman grade II-III (70±230 mesh) and analytical TLC
on silica gel 60F-254 plates. Melting points are uncorrected.
Nuclear magnetic resonance spectra were recorded in
CDCl3, using either a Varian EM-390 or Bruker-400 spec-
trometer. Chemical shifts are given in parts per million
down®eld from tetramethylsilane. Infrared (IR) spectra
were recorded on a Perkin±Elmer Spectrum 1310 FT-IR
infrared spectrometer as KBr pellets. High-resolution mass
spectra were recorded using Varian MATCH-7 and
Finnigan MAT 8230 mass spectrometers. Elemental
analyses were performed by Department of Chemistry,
IIT, Chennai, India and analytical, spectroscopic division,
VSSC, Trivandrum, India.
1
1250 cm21; H NMR (CDCl3): d 6.5±7.5 (m, 3H), 5.75 (s,
1H), 5.6 (s, 1H), 3.8 (s, 3H), 1.9±2.5 (m, 6H); MS (EI) m/z
274 (M1, 8), 242 (16), 192 (2.5), 163 (66); Anal. Calcd for
C15H14O5: C, 65.69; H, 5.1. Found: C, 65.27; H, 4.92.
6-Methoxy-2-[(5-methyl-3-oxo-1-cyclohexen-1-yl)oxy]-3-
(2H)-benzofuranone (3c). Using the above procedure,
5-methyl-1,3-cyclohexanedione (1c) (6.3 g, 50 mmol) in
chloroform (150 ml) and 2-bromo-6-methoxybenzofuran-
3-one (2) (11.25 g, 46 mmol) in chloroform (50 ml) were
reacted in presence of K2CO3 (14 g, 100 mmol) for 24 h.
The crude mixture was puri®ed by column chromatography
(9:1 hexane/benzene) to afford 3c (8.46 g, 60%) as a light
yellow crystalline solid, mp 152±1548. IR (KBr): 1720,
1
1650, 1620, 1400, 1250 cm21; H NMR (CDCl3): d 6.5±
7.6 (m, 3H), 5.8 (s, 1H), 5.7 (s, 1H), 3.9 (s, 3H), 2.1±2.7 (m,
5H), 1.2 (d, 3H); MS (EI) m/z 288 (M1, 100), 273 (25), 255
(8), 219 (7), 190 (22), 163 (100); Anal. Calcd for C16H16O5:
C, 66.66; H, 5.58. Found: C, 66.41; H, 5.35.
General procedure for synthesis of O-alkylated products
(3a±c)
To a 250 ml round-bottom ¯ask, ®tted with a stir bar and
Nitrogen inlet was added CHCl3 (150 ml) and cyclic-1,3-
dione 1a±c (50 mmol). Freshly fused potassium carbonate
(14 g, 100 mmol) was added portionwise to the ¯ask over a
period of 10 min and the reaction was stirred for 10 min at
308C. A solution of 2-bromo-6-methoxybenzofuran-3-one
(2, 11.25 g, 46 mmol) in dry chloroform (50 ml) was
added dropwise over a period of 30 min. The reaction was
stirred for 24 h at 308C. The reaction mixture was ®ltered
and the solid was washed thoroughly with CHCl3. The
CHCl3 layer was dried over Na2SO4. The removal of chloro-
form in vacuo afforded a yellow orange gummy solid.
Repeated crystallization from hexane-benzene (9:1) mixture
Condensed g-lactams
General procedure for synthesis of g-lactams (4a±d) and
xanthones (6a±d). To a 100 ml round bottom ¯ask, ®tted
with a stirrer bar and nitrogen inlet was added glacial acetic
acid (50 ml) and O-alkylated product 3a±c (50 mmol).
p-Substituted anilines (52 mmol) were added portionwise
to the ¯ask over a period of 10 min and the reaction was
re¯uxed for 18 h with stirring. The reaction was quenched
with ice cold water. The resulting solid was ®ltered, washed
with water (2£50 ml2) and dried under vacuum. The crude

B. Chandrasekhar et al. / Tetrahedron 56 (2000) 5947±5952
5951
product was chromatographed over a column of neutral
alumina (100 g) (9:1 hexane/EtOAc) to obtain pure
g-lactam (4a±d) and xanthone (6a±d).
for C23H18ClNO3: C, 70.58; H, 4.60. Found: C, 70.12; H,
4.35.
Xanthone derivatives
2,4-Dihydro-8-methoxy-2-(4-methoxyphenyl)-4,4-dimethyl-
1H-[1]-benzopyrano[4,3,2-cd]-indol-1-one (4a). Using the
above procedure, O-alkylated 3a (1.51 g, 50 mmol) in acetic
acid (50 ml) and p-anisidine (0.65 g, 52 mmol) were
re¯uxed for 24 h. The crude mixture was puri®ed by column
chromatography (9:1 hexane/EtOAc) to afford 4a (0.97 g,
50%) as a light yellow solid, mp 206±2088. IR (KBr): 1700,
6-Methoxy-1[(4-methoxyphenyl)amino]-9H-xanthene-9-
one (6a). Using the above procedure, O-alkylated 3b
(1.37 g, 50 mmol) in acetic acid (50 ml) and p-anisidine
(0.65 g, 52 mmol) were re¯uxed for 18 h. The crude mixture
was puri®ed by column chromatography (9:1 hexane/
EtOAc) to afford 6a (0.52 g, 30%) as a light yellow solid,
mp 132±1348. IR (KBr): 3450±3300, 1630, 1600, 1450,
1
1590, 1450, 1250 cm21; H NMR (CDCl3): d 6.5±7.8 (m,
1
1260 cm21; H NMR: d 11.08 (s, 1H), 6.59±8.17 (m, 6H),
7H), 5.4 (s, 1H), 5.1 (s, 1H), 3.8 (s, 3H), 3.7 (s, 3H) 1.3 (s,
6H); 13C NMR (CDCl3) d 166.8, 160.6, 158.3, 155.3, 142.9,
132.9, 130.1, 127.5, 127.3, 124.7, 119.6, 114.4, 113.0,
111.8, 110.7, 108.3, 102.6, 55.4, 55.3, 41.6, 30.7; MS (EI)
m/z 387 (M1., 21), 372 (100), 359 (2), 329 (8), 301 (6), 286
(6), 258 (7), 238 (4). Anal. Calcd for C24H21NO4: C, 74.41;
H, 5.42. Found: C, 74.21; H, 5.36.
3.91 (s, 3H), 3.83 (s, 3H); 13C NMR (CDCl3): 179.4, 164.7,
158.0, 157.2, 156.9,150.3, 135.0, 133.1, 115.8, 114.7, 112.7,
107.0, 105.5, 103.5, 99.7, 55.7, 55.4; MS (EI): m/z 347 (M1,
97.5), 332 (100), 319 (2), 317 (6), 316 (5), 289 (21), 288
(22), 261 (5), 232 (2); Anal. Calcd for C21H17NO4: C, 72.62,
H, 4.89. Found: C, 72.41; H, 4.72.
2,4-Dihydro-8-methoxy-4,4-dimethyl-2-(4-methylphenyl)-
1H-[1]benzopyrano[4,3,2-cd]-indol-1-one (4b). Using the
above procedure, O-alkylated 3a (1.51 g, 50 mmol) in acetic
acid (50 ml) and p-toluidine (0.55 g, 52 mmol) were
re¯uxed for 24 h. The crude mixture was puri®ed by column
chromatography (9:1 hexane/EtOAc) to afford 4b (0.89 g,
48%) as a light yellow solid, mp 172±1748. IR (KBr): 1700,
6-Methoxy-1-[(4-methylphenyl)amino]-9H-xanthene-9-
one (6b). Using the above procedure, O-alkylated 3b
(1.37 g, 50 mmol) in acetic acid (50 ml) and p-toluidine
(0.55 g, 52 mmol) were re¯uxed for 18 h. The crude mixture
was puri®ed by column chromatography (9:1 hexane/
EtOAc) to afford 6b (0.46 g, 28%) as a light yellow solid,
mp 116±1188. IR (KBr): 1630, 1600, 1580, 1440, 1270,
1
1620, 1450, 1240 cm21; H NMR: d 6.54±7.80 (m, 7H),
1
1160 cm21; H NMR: d 10.4 (s, 1H), 6.61±8.18 (m, 10H),
3.93 (s, 3H), 2.36 (s, 3H); MS (EI) m/z 331 (M1, 100), 314
(3), 288 (1), 279 (5); Anal. Calcd for C21H17NO3: C, 76.13;
H, 5.13. Found: C, 75.89; H, 5.0.
5.56 (s, 1H), 5.17 (s, 1H), 3.79 (s, 3H), 2.39 (s, 3H), 1.29
(s, 6H); 13C NMR (CDCl3): d 166.7, 160.7, 155.3, 143.0,
136.7, 132.6, 132.3, 124.8, 119.8, 113.1, 111.8, 110.7,
108.4, 102.7, 55.4, 30.1, 21.1; MS (EI) m/z 371 (M1, 24),
356 (100), 327 (4), 313 (10), 284 (4); Anal. Calcd for
C24H21NO3, C, 77.62; H, 5.66. Found: C, 77.24; H, 5.35.
6-Methoxy-1-[(phenyl)amino]-9H-xanthen-9-one (6c).
Using the above procedure, O-alkylated 3b (1.37 g,
50 mmol) in acetic acid (50 ml) and freshly distilled aniline
(0.48 g, 52 mmol) were re¯uxed for 18 h. The crude mixture
was puri®ed by column chromatography (9:1 hexane/
EtOAc) to afford 6c (0.40 g, 25%) as a pale yellow solid,
mp 140±1428. IR (KBr): 1640, 1600, 1400, 1270 cm21; 1H
NMR: d 10.8 (s, 1H), 6.32±7.92 (m, 10H), 3.85 (s, 3H), MS
(EI) m/z 317 (M1, 100), 316 (22), 300 (22), 274 (8), 257
(12), 167 (11); Anal. Calcd for C20H15NO3: C, 75.7; H, 4.73.
Found: C, 75.52; H, 4.51.
2,4-Dihydro-8-methoxy-4,4-dimethyl-2-phenyl-1H-[1]-
benzopyrano[4,3,2-cd]-indol-1-one (4c). Using the above
procedure, O-alkylated 3a (1.51 g, 50 mmol) in acetic acid
(50 ml) and freshly distilled aniline (0.48 g, 52 mmol) were
re¯uxed for 24 h. The crude mixture was puri®ed by column
chromatography (9:1 hexane/EtOAc) to afford 4c (0.78 g,
45%) as a light yellow solid, mp 182±1848. IR (KBr): 1700,
1620, 1240 cm21; 1H NMR (CDCl3): d 6.5±7.8 (m, 8H), 5.6
(s, 1H), 5.2 (s, 1H), 3.8 (s, 3H), 1.3 (s, 6H); 13C NMR
(CDCl3): d 166.5, 160.7, 155.2, 142.9, 135.0, 132.4,
130.3, 129.1, 126.8, 125.8, 124.7, 119.0, 113.0, 111.9,
110.6, 55.4, 41.7, 30.1; MS (EI) m/z 357 (M1, 22), 342
(100), 299 (6), 270 (4); Anal. Calcd for C23H19NO3; C,
77.31; H, 5.32. Found: C, 77.18; H, 5.08.
6-Methoxy-1[(4-chlorophenyl)amino]-9H-xanthen-9-one
(6d). Using the above procedure, O-alkylated 3b (1.37 g,
50 mmol) in acetic acid (50 ml) and p-chloroaniline
(0.66 g, 52 mmol) were re¯uxed for 18 h. The crude mixture
was puri®ed by column chromatography (9:1 hexane/
EtOAc) to afford 6d (0.35 g, 20%) as a lemon yellow
solid, mp 158±1608. IR (KBr): 1640, 1600, 1400,
2-(4-Chlorophenyl)-2,4-dihydro-8-methoxy-4,4-dimethyl-
1H-[1]benzopyrano[4,3,2-cd]-indol-1-one (4d). Using the
above procedure, O-alkylated 3a (1.51 g, 50 mmol) in acetic
acid (50 ml) and p-chloroaniline (0.66 g, 52 mmol) were
re¯uxed for 24 h. The crude mixture was puri®ed by column
chromatography (9:1 hexane/EtOAc) to afford 4d (0.78 g,
40%) as a lemon-yellow solid, mp 202±2048. IR (KBr):
1
1270 cm21; H NMR: d 10.8 (s, 1H), 6.32±7.92 (m, 10H),
3.85 (s, 3H). MS (EI): m/z 351 (M1, 100), 350 (14), 334
(18), 315 (10), 308 (4), 273 (10), 263 (22); Anal. Calcd for
C20H14ClNO3: C, 68.37; H, 3.98. Found: C, 68.15; H, 3.75.
6-Methoxy-3-methyl-1-[(4-methoxyphenyl)amino]-9H-
xanthen-9-one (7a). Using the above procedure, O-alkyl-
ated 3c (1.44 g, 50 mmol) in acetic acid (50 ml) and p-anisi-
dine (0.65 g, 52 mmol) were re¯uxed for 18 h. The crude
mixture was puri®ed by column chromatography (9:1 hex-
ane/EtOAc) to afford 7a (0.36 g, 20%) as a pale yellow
solid, mp 145±1468. IR (KBr): 1630, 1600, 1400,
1
1700, 1600, 1420, 1240 cm21; H NMR (CDCl3): d 6.6±
7.8 (m, 7H), 5.6 (s, 1H), 5.2 (s, 1H), 3.8 (s, 3H), 1.3 (s, 6H);
13C NMR (CDCl3): 166.4, 160.7, 155.2, 142.9, 133.5, 132.3,
132.1, 130.5,129.3, 127.0, 124.7, 120.0, 113.0, 112.1,
110.4, 108.4, 102.7, 55.4, 41.7, 30.1; MS (EI) m/z 391
(M1, 12), 376 (100), 333 (14), 270 (8), 240 (4); Anal. Calcd

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B. Chandrasekhar et al. / Tetrahedron 56 (2000) 5947±5952
1260 cm21; NMR: d 11.02 (s, 1H), 6.49±8.15 (m, 9H), 3.91
(s, 3H), 3.84 (s, 3H), 2.77 (s, 3H); MS (EI): m/z 361 (M1,
100), 346 (78), 303 (20), 280 (24), 252 (10); Anal. Calcd for
C22H19NO4: C, 73.13; H, 5.26. Found: C, 72.85; H, 5.01.
13. Lenoble, N. J. Synthesis 1970, 1.
14. Zook, H. D.; Russo, T. J.; Ferrand, E. F.; Stolz, D. S. J. Org.
Chem. 1968, 33, 2222.
15. Sudarsana Kumar, C.; Srinivasan, S.; Chandra Sekhar, B.;
Ramadas, S. R. Acta Cryst. C 1990, 46, 1475.
16. Sudarsana Kumar, C.; Srinivasan, S.; Chandra Sekhar, B.;
Ramadas, S. R. Acta Cryst. C 1990, 46, 849.
17. Olah, G. D.; Iyer, P. S.; Surya Prakash, G. K. Synthesis 1981,
513.
Acknowledgements
We thank the Department of Science and Technology for
the ®nancial assistance; RSIC, IIT, Chennai; Prof. Jacobs,
Netherlands for spectral and analytical data of our
compounds. We are grateful to Dr S. Srinivasan, Depart-
ment of Physics, IIT, Chennai for X-ray diffraction studies.
Our thanks to Prof. C. N. Pillai and Prof. K. K.
Balasubramanian, IIT, Chennai for useful discussions.
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