Convenient synthesis of linear pyrano[3,2-g]-, [2,3-g]- and angular pyrano[3,2-f]coumarins from 4[(1,1-dimethyl-2-propynyl)oxy]phenol

Article abstract of DOI:10.1016/j.tet.2006.06.032

An easy preparation of new 4-alkoxycarbonyl angular and linear pyranocoumarins starting from 4-[(1,1-dimethyl-2-propynyl)oxy]phenol and their transformation to the known coumarins xanthyletin, 8,8-dimethylpyrano[3,2-f]chromen-3(8H)-one and 7,7-dimethylpyrano[2,3-g]chromen-2(7H)-one is described.

Full text of DOI:10.1016/j.tet.2006.06.032

Tetrahedron 62 (2006) 8016–8020
Convenient synthesis of linear pyrano[3,2-g]-, [2,3-g]-
and angular pyrano[3,2-f]coumarins from
4[(1,1-dimethyl-2-propynyl)oxy]phenol*
*
V. Baldoumi, D. R. Gautam, K. E. Litinas and D. N. Nicolaides
Laboratory of Organic Chemistry, Aristotle University of Thessaloniki, Thessaloniki 54124, Greece
Received 10 April 2006; revised 25 May 2006; accepted 8 June 2006
Available online 30 June 2006
Abstract—An easy preparation of new 4-alkoxycarbonyl angular and linear pyranocoumarins starting from 4-[(1,1-dimethyl-2-propynyl)-
oxy]phenol and their transformation to the known coumarins xanthyletin, 8,8-dimethylpyrano[3,2-f ]chromen-3(8H)-one and 7,7-dimethyl-
pyrano[2,3-g]chromen-2(7H)-one is described.
Ó 2006 Elsevier Ltd. All rights reserved.
1. Introduction
methyl-2-butene,10 while seselin and seselin derivatives
were conveniently prepared in a two-step approach from
2,4-dihydroxybenzaldehyde and 2,4-dihydroxyacetophe-
none, using Claisen rearrangement and Wittig reaction.5
6-Hydroxy-2,2-dimethyl-2H-chromen-7-carbaldehyde and
7-hydroxy-2,2-dimethyl-2H-chromen-6-carbaldehyde, pre-
pared earlier by the formylation of the corresponding
6-methoxy- and 7-methoxy-chromene derivatives and sub-
sequent demethylation, were effectively converted into the
corresponding linear pyranocoumarins by refluxing with
N,N-dimethylacetamide dimethylacetal.11
Several linear and angular pyranocoumarins, like xanthy-
letin (I) and seselin (II) have been isolated from natural
sources.1–5 These compounds are known to possess useful
biological activities.3–6 Thus, xanthyletin shows4 antifungal,
insecticidal, anticancer, and anti-HIV activities, while sese-
lin is used as a photoactive drug for skin disorders.5 For
the syntheses of these compounds various methods have
been developed.4–11
4-Alkoxycarbonylcoumarins have been prepared earlier,12,13
mainly by our group, from the reaction of o-quinones with
alkoxycarbonylmethylene(triphenyl)phosphoranes (Ph3P]
CHCOOR) via an initial Wittig monoolefination to the cor-
responding o-quinonemethide, which by further Michael
addition of a second ylide species followed by Hofmann
elimination of Ph3P, and finally by d-lactonization gives
rise to the corresponding coumarins. Recently Yavari and
co-workers reported14 that reactions of phenols with DMAD
in the presence of Ph3P lead to the corresponding 4-meth-
oxycarbonylcoumarins via an initial addition of Ph3P to the
acetylenic ester and a concominant protonation of the reac-
tive 1:1 adduct, followed by electrophilic attack of the vinyl-
triphenylphosphonium cation formed to the aromatic ring,
in the ortho position relative to the strongly activating
PhO-group.
O
O
O
O
O
O
II
I
Thus, the 7-(1,1-dimethyl-prop-2-ynyl)ethers of coumarins,
when heated, at reflux in N,N-dimethylaniline, gave the
angular pyranocoumarins with cyclization taking place at
the more reactive 8-position. If the 8-position is substituted
however, the corresponding 8-substituted linear pyrano-
coumarins are obtained.6–8 Thermal [3,3]-sigmatropic
rearrangement of 6-prop-2-ynyloxycoumarins also resulted
in the efficient synthesis of angular pyrano[3,2-f ]chromen-
2(7H)-ones.9 Angular pyranocoumarins were also obtained
from both 5- and 7-hydroxycoumarins and 1,1-diethoxy-3-
*
Preliminary communication presented at 20th Panhellenic Chemistry
Congress, September 20–23, 2005, University of Ioannina, Ioannina,
Greece, Abstract, p. 225.
Keywords: Pyranocoumarins; Xanthyletin; Phenols; DMAD; Ph3P; Wittig
reaction; d-Lactonization; Dealkoxycarbonylation.
* Corresponding author. Tel.: +302310997864; fax: +302310997679;
e-mail: klitinas@chem.auth.gr
Brown and co-workers in 1990 reported15 the synthesis of
4-[(1,1-dimethyl-2-propynyl)oxy]phenol 1 from hydroqui-
none, which by refluxing in o-xylene afforded 2,2-dimethyl-
chromen-6-ol 2. Oxidation of 2 with Fremy’s salt gave
2,2-dimethyl-2H-chromene-6,7-dione (3).
0040–4020/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2006.06.032

V. Baldoumi et al. / Tetrahedron 62 (2006) 8016–8020
8017
(iv)
CO2Me
C=CHCO2Me
CO2Me
CO2Me
O
O
O
O
+
(v)
OH
O
O
O
O
O
O
5 (48%)
6 (2%)
7 (38%)
4
(iii)
(iii)
O
OH
O
O
(i)
(ii)
OH
O
O
2
3
1
(iii)
(vi)
CO2Me
O
C=CHCO2Me
CH-CO2Me
O
OH
C-CO2Me
O
8
11
CO2Me
O
O
(v)
O
O
O
O
9 (40%)
10 (51%)
Scheme 1. Reagents and conditions: (i) Ref. 15, o-xylene, reflux, N2 (91%); (ii) Ref. 15, Fremy’s salt (68%); (iii) Ph3P, DCM, DMAD (at ꢀ5 ꢁC), reflux;
(iv) o-xylene, reflux (77%); (v) Cu, quinoline, N2, 175–180 ꢁC, 19 h and (vi) DMAD, ZnCl2, N2, 100 ꢁC, 1.5 h (23%).
O
O
O
I (43%)
for 14b
(ii)
CO2R
CH
CO2R
C=CHCO2R
CO2R
O
O
+
O
(i)
O
O
O
15a,b
O
OH
O
O
O
3
14a,b (41%,38%)
13a,b
(13%,33%)
13-15 a: R=Me
b: R=Et
Scheme 2. Reagents and conditions: (i) Ph3P]CHCOOR (12a: R¼Me, b: R¼Et), DCM, rt, N2, 30 min and (ii) Cu, quinoline, N2, 175–180 ꢁC, 19 h.
As a continuation of our investigation on the syntheses of
coumarin derivatives,13 we now report the easy preparation
of the new coumarin derivatives 6, 9, and 14a,b from the
compounds 1, 2, and 3, respectively. The reactions studied
and the products obtained are depicted in Schemes 1–2.
and 2% yields, respectively. Compound 5 by refluxing in
o-xylene for 20 h gave coumarin 6 in 77% yield (Scheme 1).
Obviously product 5 was obtained by d-lactonization of the
intermediate 4 and gave the angular coumarin 6 by further
cyclization.9
When compound 1 was previously cyclized to phenol 2
according to the lit. 15 and the latter was then subjected to
a similar treatment with Ph3P and DMAD in refluxing
DCM for five days, ethyl 7,7-dimethyl-2-oxo-2,7-dihydro-
pyrano[2,3-g]chromene-4-carboxylate (9) was obtained in
40% yield. The linear coumarin 9 was obviously produced
by further d-lactonization of the intermediate 8. Both key in-
termediates 4 and 8 are formed via an electrophilic attack of
the vinyltriphenylphosphonium cation14 on the aromatic
2. Results and discussion
Treatment of phenol 1 with DMAD in the presence of
Ph3P in refluxing DCM for two days, and separation of
the reaction mixture by column chromatography afforded
methyl 6-[(1,1-dimethyl-2-propynyl)oxy]-2-oxo-2H-chro-
mene-4-carboxylate (5) and methyl 8,8-dimethyl-3-oxo-
3,8-dihydropyrano[3,2-f]chromene-1-carboxylate (6) in 48%

8018
V. Baldoumi et al. / Tetrahedron 62 (2006) 8016–8020
ring ortho to the –OH substituent of 1 and 2, respectively. In
contrast to the formation of 4 from the symmetrically
substituted phenol 1, the formation of 8 can be attributed
to the attack of the vinyltriphenylphosphonium cation to
the less sterically hindered 7-position (in comparison to
the 5-position) of the non-symmetric phenol 2.
a VG-250 spectrometer at 70 eV under Electron Impact
(EI) conditions. High-resolution mass spectra (HRMS)
were recorded on an Ionspec mass spectrometer under
Matrix-Assisted Laser Desorption-Ionization Fourier
Transform Mass Spectrometer (MALDI-FTMS) conditions
with 2,5-dihydroxybenzoic acid (DHB) as the matrix.
Microanalyses were performed on a Perkin–Elmer 2400-II
Element analyzer. Silica gel no. 60, Merck A.G. has been
used for column chromatography. Compounds 1, 2, and 3
were prepared according to the lit. 15.
We considered as an alternative path for the preparation of
linear pyranocoumarins the initial transformation of phenol
2 to the known15 quinone 3 and the reaction12,13 of the latter
with the phosphoranes Ph3P]CHCOOR 12a,b (Scheme 2).
Treatment of quinone 3 with Ph3P]CHCOOCH3 (12a) at
room temperature afforded methyl 8,8-dimethyl-2-oxo-
2H,8H-pyrano[3,2-g]chromene-4-carboxylate (14a) (41%)
along with methyl 2-[7,7-dimethyl-2-oxo-7H-furo[3,2-g]-
chromen-3(2H)-ylidene]acetate (15a) (13%) via the d- and
g-lactonization, respectively, of the intermediate 13a. Simi-
larly, the reaction of 3 with Ph3P]CHCOOC2H5 (12b) gave
compounds 14b and 15b in 38% and 33% yield, respectively.
The formation of intermediate 13 instead of 8 can be pre-
dicted from the lower electrophilicity of the C-7 C]O,
due to the +R effect of the pyran ring O-atom, since this in-
termediate is formed by the initial Wittig monoolefination of
the C-6 C]O of 3, followed by Michael addition of a second
ylide and Hofmann elimination of Ph3P.11,12 The IR spectra
of compounds 15a,b exhibited the characteristic13a absorp-
tion at nmaxw1790 cmꢀ1 for a five-member lactone carbonyl.
3.1.1. Procedure for the synthesis of methyl 6-[(1,1-
dimethyl-2-propynyl)oxy]-2-oxo-2H-chromene-4-carb-
oxylate (5) and methyl 8,8-dimethyl-3-oxo-3,8-dihydro-
pyrano[3,2-f ]chromene-1-carboxylate
(6).
4-[(1,1-
Dimethyl-2-propynyl)oxy]phenol 1 (0.6 g, 3.41 mmol) and
Ph3P (0.893 g, 3.41 mmol) were dissolved in DCM (15 ml).
A solution of DMAD (0.484 g, 0.418 ml, 3.41 mmol) in
DCM (10 ml) was added dropwise over 10 min at ꢀ5 ꢁC
and the orange solution was heated under reflux for two
days. Evaporation of the solvent and separation by column
chromatography (hexane/DCM 1:1) followed by PTLC (sil-
ica gel, DCM) afforded 5 (0.465 g, 48%) and 6 (15 mg, 2%).
3.1.1.1. Methyl 6-[(1,1-dimethyl-2-propynyl)oxy]-2-
oxo-2H-chromene-4-carboxylate (5). Yellow crystals, mp
76–78 ꢁC (DCM/hexane); IR (Nujol) n (cmꢀ1): 3230, 1725,
1
1705, 1600, 1550; H NMR (CDCl3, 300 MHz) d: 1.67 (s,
We also studied the reaction of phenol 2 with DMAD in the
presence of ZnCl2, which resulted in the formation of di-
methyl 2-[(2,2-dimethyl-2H-chromen-6-yl)oxy]-2-butene-
dioate (11) in 23% yield, but no cyclization product was
isolated.
6H), 2.63 (s, 1H), 4.00 (s, 3H), 6.97 (s, 1H), 7.29
(d, J¼8.9 Hz, 1H), 7.43 (dd, J¼ 2.9 and 8.9 Hz, 1H), 8.18
(d, J¼2.9 Hz, 1H); 13C NMR (CDCl3, 75 MHz) d: 29.4,
53.1, 73.4, 74.7, 85.4, 117.4, 118.8, 119.7, 123.8, 126.7,
142.0, 150.1, 152.0, 160.1, 164.2; MS m/z: 286 (M+, 14),
271 (28), 221 (38), 220 (37), 219 (52), 192 (56), 160 (56),
134 (74), 67 (100). Anal. Calcd for C16H14O5: C, 67.11;
H, 4.93. Found: C, 66.92; H, 4.98.
The proposed structures of all the new pyranocoumarins 6, 9,
and 14a,b were in good agreement with their analytical
and spectral data (1H NMR, 13C NMR, IR, and MS) and
they are unequivocally proved via their transformation, by
heating in quinoline and Cu powder, into the known 8,8-
dimethylpyrano[3,2-f ]chromen-3(8H)-one9,10 (7) (38%),
7,7-dimethylpyrano[2,3-g]chromen-2(7H)-one11 (10) (51%),
and 8,8-dimethyl-2H,8H-pyrano[3,2-g]chromen-2-one11 (I)
[xanthyletin, 43% (from 14b)], respectively. The yields for
the preparation of these coumarins are comparable to the
yields of the earlier preparation.4–11
3.1.1.2. Methyl 8,8-dimethyl-3-oxo-3,8-dihydropyrano-
[3,2-f ]chromene-1-carboxylate (6). Yellow crystals, mp
98–100 ꢁC (DCM/hexane); IR (Nujol) n (cmꢀ1): 1720,
1
1705, 1600, 1555; H NMR (CDCl3, 300 MHz) d: 1.46 (s,
6H), 3.96 (s, 3H), 5.73 (d, J¼9.8 Hz, 1H), 6.22 (d, J¼
9.8 Hz, 1H), 6.52 (s, 1H), 7.06 (d, J¼8.9 Hz, 1H), 7.17 (d,
J¼8.9 Hz, 1H); 13C NMR (CDCl3, 75 Hz) d: 26.9, 53.2,
75.5, 111.6, 116.8, 117.1, 117.6, 118.9, 121.7, 131.5, 144.9,
149.2, 150.1, 159.5, 167.0; MS m/z: 286 (M+, 20), 271
(100), 243 (16), 211(10), 184(8), 156(4), 128(4). Anal. Calcd
for C16H14O5: C, 67.11; H, 4.93. Found: C, 67.35; H, 5.12.
The above mentioned synthetic approaches demonstrate
their utility for the synthesis of different linear and angular
pyranocoumarins, using the same starting material, depend-
ing on the reaction conditions.
3.1.2. Procedure for the preparation of methyl 8,8-
dimethyl-3-oxo-3,8-dihydropyrano[3,2-f ]chromene-1-
carboxylate (6). A degassed solution of coumarin 5
(0.209 g, 0.73 mmol) in o-xylene (40 ml) under an Argon
atmosphere was heated at reflux for 20 h. The solvent was
evaporated and the residue was separated by PTLC (silica
gel, DCM) and gave 6 (0.161 g, 77%).
3. Experimental
3.1. General
Melting points were determined on a Kofler hot-stage appa-
ratus and are uncorrected. IR spectra were obtained with
a Perkin–Elmer 1310 spectrophotometer as Nujol mulls.
NMR spectra were recorded on a Bruker AM 300
3.1.3. Procedure for the synthesis of methyl 7,7-dimethyl-
2-oxo-2,7-dihydropyrano[2,3-g]chromene-4-carboxylate
(9). 2,2-Dimethylchromen-6-ol (2) (0.35 g, 2 mmol) and
Ph3P (0.524 g, 2 mmol) were dissolved in DCM (10 ml). A
solution of DMAD (0.284 g, 0.246 ml, 2 mmol) in DCM
(5 ml) was added dropwise over 10 min period at ꢀ5 ꢁC
1
(300 MHz and 75 MHz for H and 13C, respectively) using
CDCl3 as solvent and TMS as an internal standard. J values
are reported in Hertz. Mass spectra were determined on

V. Baldoumi et al. / Tetrahedron 62 (2006) 8016–8020
8019
and the solution was heated under reflux for five days. Evapo-
ration of the solvent and separation by column chromato-
graphy (hexane/DCM 1:1) resulted to 9 (0.23 g, 40%);
yellow crystals, mp 181–182 ꢁC (DCM/hexane); IR (Nujol)
n (cmꢀ1): 1705, 1690, 1605, 1520; 1H NMR (CDCl3,
300 MHz) d: 1.46 (s, 6H), 3.99 (s, 3H), 5.87 (d, J¼9.8 Hz,
1H), 6.38 (d, J¼9.8 Hz, 1H), 6.87 (s, 1H), 6.97 (s, 1H),
7.61 (s, 1H); 13C NMR (CDCl3, 75 MHz) d: 27.9, 53.1,
77.7, 112.7, 113.8, 115.8, 118.7, 121.2, 125.8, 135.7, 142.1,
149.1, 149.5, 160.3, 164.3; MS m/z: 286 (M+, 15), 272 (11),
271 (100), 241 (18), 156 (10), 128 (12), 91 (10). Anal. Calcd
for C16H14O5: C, 67.11; H, 4.93. Found: C, 67.15; H, 4.96.
J¼10.2 Hz, 1H), 6.37 (d, J¼10.2 Hz, 1H), 6.55 (s, 1H),
6.70 (s, 1H), 8.30 (s, 1H); 13C NMR (CDCl3, 75 MHz) d:
28.4, 29.7, 52.2, 78.3, 99.8, 113.6, 117.1, 120.2, 121.6,
126.8, 129.4, 133.5, 157.7, 158.9, 166.0, 168.2; MS m/z:
286 (M+, 14), 272 (17), 271 (100), 243 (10), 184 (7), 156
(9), 128 (10), 115 (7). HRMS calcd for C16H15O5 [M+H]+
287.0914, found: 287.0910.
3.1.5.3. Ethyl 8,8-dimethyl-2-oxo-2H,8H-pyrano[3,2-g]-
chromene-4-carboxylate (14b). Yellow crystals (from
Et2O/hexane); mp 151–152 ꢁC; yield 38%; IR (Nujol)
n (cmꢀ1): 1720, 1690, 1605, 1550; 1H NMR (CDCl3,
300 MHz) d: 1.42 (t, J¼7.6 Hz, 3H), 1.47 (s, 6H), 4.44
(q, J¼7.6 Hz, 2H), 5.70 (d, J¼10.2 Hz, 1H), 6.37 (d,
J¼10.2 Hz, 1H), 6.74 (s, 2H), 7.88 (s, 1H); 13C NMR
(CDCl3, 75 MHz) d: 14.1, 28.4, 62.3, 77.9, 104.5, 109.6,
115.5, 118.7, 121.2, 124.0, 131.2, 142.4, 155.8, 157.2,
160.6, 164.1; MS m/z: 300 (M+, 46), 285 (100), 257 (49),
229 (8), 213 (8), 185 (42), 156 (12), 128 (16). Anal. Calcd
for C17H16O5: C, 67.99; H, 5.37. Found: C, 67.86; H, 5.34.
3.1.4. Procedure for the synthesis of dimethyl 2-[(2,2-di-
methyl-2H-chromen-6-yl)oxy]-2-butenodioate (11).
DMAD (0.69 g, 0.6 ml, 4.88 mmol) was added to a mixture
of 2,2-dimethylchromen-6-ol (2) (0.5 g, 2.84 mmol) and
anhydrous ZnCl2 (0.387 g, 2.84 mmol) and the mixture
was heated under an Argon atmosphere at 100 ꢁC for
90 min. After cooling the mixture was partitioned in ethyl
acetate (10 ml) and 10% HCl (10 ml). The organic layer
was separated, washed with H2O (10 ml), dried by an-
hydrous Na2SO4, separated by column chromatography
(hexane/DCM 1:2) and gave 11 (0.208 g, 23%); colorless
crystals, mp 65–66 ꢁC (ethyl acetate/hexane); IR (Nujol)
n (cmꢀ1): 1725, 1690, 1640, 1255, 1195; 1H NMR (CDCl3,
300 MHz) d: 1.41 (s, 6H), 3.72 (s, 3H), 3.73 (s, 3H), 5.64 (d,
J¼10.2 Hz, 1H), 6.25 (d, J¼10.2 Hz, 1H), 6.50 (s, 1H), 6.62
(d, J¼2.5 Hz, 1H), 6.69 (d, J¼8.9 Hz, 1H), 6.70 (dd,
J1¼2.5 Hz, J2¼8.9 Hz, 1H); 13C NMR (CDCl3, 75 MHz)
d: 27.7, 51.9, 52.9, 76.1, 113.9, 114.1, 116.6, 116.9, 121.9,
122.0, 131.9, 148.8, 150.3, 150.4, 162.8, 164.0; MS m/z:
316 (M+, 11), 304 (20), 303 (100), 161 (9), 144 (17), 132
(8), 115 (12), 91 (8). HRMS calcd for C17H18O6 [M]+
318.1097, found: 318.1094.
3.1.5.4. Ethyl 2-[7,7-dimethyl-2-oxo-7H-furo[3,2-g]-
chromen-3(2H)-ylidene]acetate (15b). Yellow crystals
(from EtOAc/hexane); mp 138–140 ꢁC; yield 33%; IR
(Nujol) n (cmꢀ1): 1788, 1705, 1600, 1575; 1H NMR
(CDCl3, 300 MHz) d: 1.37 (t, J¼7.6 Hz, 3H), 1.47 (s, 6H),
4.31 (q, J¼7.6 Hz, 2H), 5.61 (d, J¼10.2 Hz, 1H), 6.37 (d,
J¼10.2 Hz, 1H), 6.55 (s, 1H), 6.70 (s, 1H), 8.30 (s, 1H);
13C NMR (CDCl3, 75 MHz) d: 14.2, 28.4, 29.7, 61.2, 78.2,
99.7, 113.6, 117.7, 120.8, 121.6, 126.8, 129.4, 133.3,
157.6, 158.8, 165.6, 168.3; MS m/z: 300 (M+, 14), 285
(100), 259 (14), 258 (30), 257 (27), 229 (10), 213 (12),
185 (45), 156 (22), 128 (55), 115 (29), 69 (60). HRMS calcd
for C17H17O5 [M+H]+ 301.1070, found: 301.1060.
3.1.6. General procedure for the dealkoxycarbonylation
of the coumarin derivatives 6, 9, and 14b. A mixture of
coumarin derivative 6 or 9 or 14b (0.32 mmol) and copper
powder (0.66 mmol) in dry quinoline (5 ml) was heated under
an Argon atmosphere at 175–180 ꢁC for 19 h. After cooling,
ethyl acetate (50 ml) was added, the copper powder was fil-
tered and the residue was treated with 5% HCl (50 ml). The
water layer was washed with ethyl acetate (50 ml) and the
combined organic layers were washed with water (50 ml)
and dried over anhydrous Na2SO4. The solvent was evapo-
rated in a rotary evaporator and the residue was subjected to
column chromatography (silica gel, DCM) to give the couma-
rin derivatives 79,10 (38%), 1011 (51%), and I11 (43%).
3.1.5. General procedure for the preparation of the
coumarins 14a,b and the furanones 15a,b. A solution of
o-quinone 3 (1 mmol) and ylides 12a,b (2.2 mmol) in dry
DCM (50 ml) was stirred under an Argon atmosphere at
room temperature for 1 h. The solvent was evaporated in
a rotary evaporator and the residue was subjected to column
chromatography (silica gel, hexane/ethyl acetate 15:1) to
give products 15a,b and 14a,b.
3.1.5.1. Methyl 8,8-dimethyl-2-oxo-2H,8H-pyrano-
[3,2-g]chromene-4-carboxylate (14a). Yellow crystals
(from EtOAc/hexane); mp 186–187 ꢁC; yield 41%; IR
(Nujol) n (cmꢀ1): 1725, 1675, 1605, 1545; 1H NMR
(CDCl3, 300 MHz) d: 1.47 (s, 6H), 3.99 (s, 3H), 5.70 (d,
J¼10.2 Hz, 1H), 6.36 (d, J¼10.2 Hz, 1H), 6.74 (s, 2H),
7.87 (s, 1H); 13C NMR (CDCl3, 75 MHz) d: 28.2, 53.0,
77.9, 104.5, 109.5, 115.6, 118.7, 121.1, 123.9, 131.2,
142.0, 155.8, 157.2, 160.4, 164.6; MS m/z: 286 (M+, 10),
272 (17), 271 (81), 244 (10), 243 (11), 184 (7), 156 (11),
128 (14), 91 (100). HRMS calcd for C16H15O5 [M+H]+
287.0914, found: 287.0910.
Acknowledgements
D.R.G. thanks State Scholarships Foundation (IKY),
Greece, for financial support and Tribhuvan University,
Kathmandu, Nepal, for granting him the PhD study leave.
References and notes
1. Murray, R. D. H.; Mendez, J.; Brown, S. A. The Natural
Coumarins; Wiley: New York, NY, 1982.
2. Ceccherelli, P.; Curini, M.; Marcotullio, M. C.; Madruzza, G.;
Menghini, A. J. Nat. Prod. 1989, 52, 888–890.
3. Fylaktakidou, K. C.; Hadjipavlou-Litina, D. J.; Litinas, K. E.;
Nicolaides, D. N. Curr. Pharm. Des. 2004, 10, 3813–3833.
3.1.5.2. Methyl 2-[7,7-dimethyl-2-oxo-7H-furo[3,2-g]-
chromen-3(2H)-ylidene]acetate (15a). Yellow crystals
(from EtOAc/hexane); mp 129–131 ꢁC; yield 13%; IR
(Nujol) n (cmꢀ1): 1795, 1702, 1625, 1598; 1H NMR
(CDCl3, 300 MHz) d: 1.46 (s, 6H), 3.86 (s, 3H), 5.62 (d,

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V. Baldoumi et al. / Tetrahedron 62 (2006) 8016–8020
4. Mali, R. S.; Joshi, P. P.; Saudhu, P. K.; Manekar-Tilve, A.
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