Preparation and synthetic use of polymer-supported acetoacetate reagent

Article abstract of DOI:10.1055/s-2005-872142

Coumarin synthesis using polymer-supported acetoacetate reagent was carried out to produce various coumarin derivatives in excellent yield and purity with a facile work-up process. It was found that the polymer reagent could be recycled without any diminishment of the yield and purity. Georg Thieme Verlag Stuttgart.

Full text of DOI:10.1055/s-2005-872142

2664
PAPER
Preparation and Synthetic Use of Polymer-Supported Acetoacetate Reagent
P
olymer-Suppo
a
k
c
etate Reage
e
nt shi Hirai,a Hideo Togo*a,b
a
Graduate School of Science and Technology, Chiba University, Yayoi-cho 1-33, Inage-ku 263-8522, Chiba, Japan
Department of Chemistry, Faculty of Science, Chiba University, Yayoi-cho 1-33, Inage-ku 263-8522, Chiba, Japan
Fax +81(43)2902874; E-mail: togo@faculty.chiba-u.jp
b
Received 23 March 2005; revised 10 May 2005
acetoacetylation reagent of alcohol, to convert it into O-
Merrifield resin-bound 4-(2¢-acetoacetylethyl)phenol
(Polymer 1). In this reaction, excellent conversion to the
acetoacetate group was observed, and loading rate was de-
termined to be 1.27 mmol/g (nearly quantitative conver-
Abstract: Coumarin synthesis using polymer-supported acetoace-
tate reagent was carried out to produce various coumarin derivatives
in excellent yield and purity with a facile work-up process. It was
found that the polymer reagent could be recycled without any di-
minishment of the yield and purity.
Key words: polymer-supported acetoacetate, coumarin, Knoeve-
nagel condensation, von Pechmann reaction, green chemistry
K2CO3, 2
O
Cl
DMF, 60 °C
1.87 mmol/g
OH
1: 1.42 mmol/g
Among various synthetic methods for heterocycles,
acetoacetates are the important precursors for furans,
pyrroles, quinolines, quinolinones, coumarins, pyrimidi-
nones, etc., to which many trials and extensive efforts
have been devoted.1,2 Some of these accomplishments
have been accepted as name reactions and are widely used
for the synthesis of these heterocycles up to now.
O
O
O
(3)
O
O
O
DMF, reflux
O
Polymer 1: 1.27 mmol/g
: 1% cross-linked chloromethylated
styrene/divinylbenzene copolymer
On the other side, synthetic use of polymer-supported
reagents3,4 has become a popular and indispensable meth-
od for organic synthesis. Its universal acceptance comes
from the following features such as facile isolation of the
desired product from the reaction system, potential to re-
cycle, ability to use reagent which is dangerous, trouble-
some for handling or expensive by fixing on it, potential
to an automated process, etc., and these lead to organic
synthesis with savings in cost, time and environment.
Scheme 1
sion) (Scheme 1).
Next, we applied Polymer 1 to 3-acetylcoumarin synthe-
sis, which consists of the Knoevenagel condensation8a,b of
salicylaldehyde (4a) with the b-keto ester bound to the
polymer, and intramolecular transesterification by phenol
accompanied with elimination of the hydroxyl end of the
polymer. The reaction is catalyzed by weak bases, Lewis
acids,8c organic salts8d and heterogeneous catalysts.8e Sol-
id-phase syntheses of 3-alkoxycarbonylcoumarins5a and
3-acetylcoumarin synthesis utilizing the polymer
reagent5b were reported; however, they are not so effective
in terms of yield and purity of products or recyclability of
the polymer reagent. Here, we chose piperidine9 as cata-
lyst which was freshly distilled, for easy work-up owing
to its volatility. Among various solvents such as CHCl3, n-
C6H14, Et2O, toluene, and THF, EtOH showed the best re-
sult. Thus, salicylaldehyde (4a) was treated with various
amounts of Polymer 1 in the presence of piperidine catal-
ysis in EtOH. Table 1 shows excess amount of Polymer 1
is not required and reflux temperature is effective.
Now, we have prepared a polymer-supported acetoacetate
reagent5 and applied it to the synthesis of coumarins, one
of the most important chemicals in the cosmetics, agricul-
tural, pharmaceutical and material industries for its bioac-
tivity and photodynamic effect.6
First of all, we planned to synthesize a polymer-supported
acetoacetate reagent. O-Merrifield resin-bound 4-(2¢-hy-
droxyethyl)phenol 1 was prepared by the reaction of Mer-
rifield resin (chloromethylated styrene/divinylbenzene
copolymer) and 2-(4¢-hydroxyphenyl)ethanol (2) in the
presence of K2CO3 in DMF, based on the Williamson
ether synthesis. The conversion could be checked by 13
C
NMR and IR spectroscopy, and loading rate of the hy-
droxyethyl group was determined by elemental analysis to
be 1.42 mmol/g (88% conversion). Then, O-Merrifield
resin-bound 4-(2¢-hydroxyethyl)phenol 1 was treated with
2,2,6-trimethyl-4H-1,3-dioxin-4-one (3),7 a very useful
SYNTHESIS 2005, No. 16, pp 2664–2668
x
x.
x
x
.
2
0
0
5
Advanced online publication: 04.08.2005
DOI: 10.1055/s-2005-872142; Art ID: F05605SS
© Georg Thieme Verlag Stuttgart · New York

PAPER
Polymer-Supported Acetoacetate Reagent
2665
Table 1 Examination of Optimal Conditions for Synthesis of 5a
In addition, the recycling of Polymer 1 was investigated.
The recovered polymer, whose terminal functional group
was a mixture of hydroxyl and acetoacetyl groups, was re-
acted again with 2,2,6-trimethyl-4H-1,3-dioxin-4-one (3)
to regenerate Polymer 1 cleanly. We found that this could
react with salicylaldehyde (4a) without any trouble and
produce 3-acetylcoumarin (5a) keeping the quantitative
yield and excellent purity 1 to 5 times or more
(Scheme 2). From these results, it is clear that 3-acetyl-
coumarin synthesis utilizing Polymer 1 not only gives
high yield and purity but is a facile, speedy and environ-
mentally friendly method throughout the course of the re-
action.
CHO
Polymer 1
OH
Ac
O
piperidine
EtOH, ∆
O
4a
5a
Entry
Polymer 1 Piperidine Reaction
Yield of 5a
(mol%)
Conditions
(%)a
1
2
3
4
5
2.0 equiv
2.0 equiv
2.0 equiv
1.5 equiv
1.3 equiv
10
10
5
r.t., 3.5 h
37
89
60 °C, 3.5 h
reflux, 1.5 h
reflux, 2 h
reflux, 2.5 h
94
5
>99
>99
quantitative reaction
>99% purity
5
for 5 times
a Isolated yield.
4a
5a
O
O
OH
O
3 (1.45 equiv)
DMF, reflux
1
An optimal condition of the reaction was found to be entry
5, giving 3-acetylcoumarin (5a) in quantitative yield. Af-
ter the reaction, the polymer reagent was easily removed
Polymer 1
Scheme 2
1
by filtration and the filtrate was evaporated. H NMR
measurement of the crude residue indicated that it was al-
most in pure state, and there was no contamination such as
side products or dissolved polymer, and so on. Under the
same conditions, 2-hydroxy-5-methylbenzaldehyde (4b),
2-hydroxy-5-methoxybenzaldehyde (4c), 5-bromo-2-hy-
droxybenzaldehyde (4d), 5-acetyl-2-hydroxybenzalde-
hyde (4e) and 2-hydroxynaphthaldehyde (4f) were treated
with Polymer 1 to provide the corresponding coumarins
5b–f in nearly quantitative yields with excellent purity
(Table 2). 3-Acetylcoumarins synthesized here need no
extra purification such as column chromatography, re-
crystallization, etc. Thus, this method eliminates the fur-
ther use of the organic solvent, and saves time in a series
of the reaction.
Next, we applied polymer-supported acetoacetate reagent
to the von Pechmann reaction,10 condensation of b-keto
ester with phenols, which is one of the most simple and
straightforward methods to 4-substituted coumarins. Or-
dinarily, many Brønsted and Lewis acids like H2SO4,
POCl3, BF3·Et2O, MeSO3H, etc. have been used as a con-
densing reagent. Recently, improved methods have been
developed such as utilizing cation exchange resins,11a, sol-
id acid catalysis under microwave irradiation11b, and sol-
vent-free methods catalyzed by InCl3,11c sulfamic acid11d
or p-TsOH.9 Here, we chose p-TsOH as a condensing re-
agent.
Polymer 1 was treated with resorcinol (6a) in the presence
of a catalytic amount of p-TsOH in chlorobenzene at 60
°C, and then, the polymer reagent was removed by filtra-
tion. p-TsOH contaminated in the liquid phase was easily
separated by washing with water. From the NMR mea-
surement of the residue, it was found that perfect conver-
sion to 7-hydroxy-4-methylcoumarin (7a) was achieved.
However, about 10% of 2-(4¢-hydroxyphenyl)ethanol (2)
which was a cleaved spacer from the Polymer 1, was de-
tected as a contaminated side-product (Scheme 3).
Table 2 Synthesis of 3-Acetylcoumarins 5a–f Utilizing Polymer 1
CHO
OH
Y
Polymer 1 (1.3 equiv)
piperidine (5 mol%)
Y
X
X
Ac
O
O
EtOH, reflux
4a–f
5a–f
Substrate
X
Y
Time (h)
Purity (%)a Yield of
5a–f (%)b
4a
4b
4c
4d
4ec
4f
H
H
H
H
H
H
2
>99
>99
>99
>99
96
>99
>99
>99
>99
95
Me
Polymer 1 (1.5 equiv)
p-TsOH (0.1 equiv)
Me
MeO
Br
2.5
2.5
2.5
6
HO
OH
chlorobenzene
60 °C, 10 h
HO
O
O
6a
7a
Yield: 99%
2: 0.15 equiv
Ac
Scheme 3
benzo
2.5
>99
>99
The formation of 2-(4¢-hydroxyphenyl)ethanol (2) was
not inhibited by the reaction conditions. Then, we tried O-
Merrifield resin-bound 6-acetoacetylhexan-1-ol (Polymer
2), a modified polymer-supported acetoacetate reagent,
a Purity was determined by integration of 1H NMR spectra.
b Isolated yield.
c 1.5 equiv of Polymer 1 was used.
Synthesis 2005, No. 16, 2664–2668 © Thieme Stuttgart · New York

2666
T. Hirai, H. Togo
PAPER
since it has an alkyl ether moiety as a spacer, which was excellent yield, purity and recyclability of the polymer re-
expected to be tolerant to acidic conditions. Merrifield agent, as compared with the previously reported polymer-
resin (1.56 mmol/g) and 6-(tetrahydro-2H-pyranyl- supported reagents.5
oxy)hexan-1-ol (8) were combined under the condition of
Williamson ether synthesis to generate O-Merrifield
Merrifield Resin: 1% cross-linked chloromethylated styrene/divi-
resin-bound
6-(tetrahydro-2H-pyranyloxy)hexan-1-ol
nylbenzene copolymer, purchased from Argonaut Technologies,
loading rate of chloromethyl: 1.87 mmol/g and 1.56 mmol/g, mean
bead size: 75–150 microns; measured: 103 and 105 microns.
(9). The terminal THP group of 9 was deprotected by a
standard method, and the same operation was repeated for
perfect deprotection to convert O-Merrifield resin-bound
hexane-1,6-diol 10. Then, the hydroxyl end of 10 was
acetoacetylated to generate the desired Polymer 2 whose
loading rate was determined to be 0.94 mmol/g
(Scheme 4).
O-Merrifield Resin-Bound 4-(2¢-Hydroxyethyl)phenol 1
To a suspension of Merrifield resin (21.4 g, 40 mmol) in anhyd
DMF (200 mL) at r.t. under argon were added 2 (11.0 g, 80 mmol)
and K2CO3 (19.3 g, 140 mmol). The mixture was allowed to warm
to 60 °C and stirred for 2 d. The mixture was cooled to r.t. and the
polymer species were collected on a glass filter. The polymer spe-
cies were washed with H2O, MeOH, acetone and CH2Cl2 to remove
salts and contaminated species, and then dried under reduced pres-
sure.
NaH, KI, 8
OTHP
Cl
O
3
DMF, 60 °C
9
1.56 mmol/g
IR (KBr): 3420, 1510, 1230, 1010, 820, 755, 695 cm–1.
13C NMR (125 MHz, CDCl3): d = 38.4, 63.9, 70.1, 115.1, 130.1;
and polystyrene part (d = 40–47, 120–135, 146, all broad).
1. p-TsOH
MeOH, reflux
OH
O
3
2. same as above
Anal. Calcd: loading rate, 1.42 mmol/g (– OH). Found: C, 87.04; H,
7.33; Cl, 0.70.
10: 1.07 mmol/g
O
O-Merrifield Resin-Bound 4-(2¢-Acetoacetylethyl)phenol
(Polymer 1)
3
O
3
O
O
DMF, reflux
A suspension of 1 (9.48 g, 13.5 mmol) in DMF (80 mL) was heated
at refluxing temperature in a flask equipped with a dropping funnel
under argon. 2,2,6-Trimethyl-4H-1,3-dioxin-4-one (3; 3.27 g, 19.5
mmol) was added to the solution over a period of 7 h and then the
mixture was refluxed for 1 h. The mixture was cooled to r.t. and the
Polymer 2: 0.94 mmol/g
Scheme 4
Surprisingly even for Polymer 2, spacer scission occurred polymer species were collected on a glass filter. The polymer spe-
cies were washed with MeOH, acetone and CH2Cl2 to remove con-
taminated species, and then dried under reduced pressure.
at the alkyl ether group to provide a contaminated side-
product, hexane-1,6-diol. When 6-benzyloxyhexyl ace-
IR (KBr): 1740, 1710, 1510, 1310, 1240, 1160, 1010, 815, 755, 700
cm–1.
13C NMR (125 MHz, CDCl3): d (keto form) = 30.1, 34.1, 50.0, 66.0,
70.1, 114.9, 129.9, 137.1, 157.7, 167.0, 200.5; d (enol form) = 20.9,
89.7.
toacetate was used instead of Polymer 2, the correspond-
ing bond cleavage was not observed. So, this problem
seems to arise from a kind of ‘polymer effect’ due to its
unique higher-order structure. However, the amount of
side product was fortunately decreased to 1% based on the
used polymer, and the desired compound was obtained in Anal. Calcd: loading rate, 1.27 mmol/g (– acetylacetate). Found: C,
83.64; H, 7.06; Cl, 0.00.
90% yield. In phloroglucinol (6b), the same operation was
carried out to give the corresponding coumarins 7b in
6-(Tetrahydro-2H-pyranyloxy)hexan-1-ol (8)12
94% yield (Table 3).
A mixture of hexane-1,6-diol (23.6 g, 200 mmol), aq 5 M NaHSO4
(40 mL), and 3,4-dihydro-2H-pyran (DHP)–toluene solution [5:95
(v/v), 1.2 L] was stirred at r.t. for 5 h. After removal of the aqueous
Table 3 Synthesis of 4-Methylcoumarins 7a,b Utilizing Polymer 2
Polymer 2 (2 equiv)
p-TsOH (0.3 equiv)
X
X
Me
O
layer and addition of a small amount of K2CO3, the solvent was
evaporated and the residue was purified by vacuum distillation [bp
90–100 °C/2 mmHg (Lit.12 bp 150 °C/0.5 mmHg)] to give 38.2 g
(94%) of the title compound as a colorless oil (1–2% of di-THP
ether was present).
HO
OH
HO
O
chlorobenzene, 60 °C
Substrate
X
Time (h) Purity (%)a Yield of 7a,b (%)b
6a
6b
H
10
9
87
91
90
94
O-Merrifield Resin-Bound Hexane-1,6-diol 10
To a suspension of Merrifield resin (15.0 g, 23.4 mmol), 8 (14.2 g,
70.2 mmol) and KI (0.78 g, 4.7 mmol) in DMF (200 mL), was added
NaH (60% in paraffin oil, 2.9 g, 72.5 mmol) at 0 °C. The mixture
was stirred for 2 d at 60 °C. The mixture was cooled to r.t. and the
polymer species were collected on a glass filter. The polymer spe-
cies were washed with H2O, MeOH, acetone and then CH2Cl2 to re-
move contaminated species, and dried under reduced pressure. The
same reaction operation was done again to make the ether chain at-
tach completely. Next, the polymer species were suspended in
OH
a Purity was determined by integration of 1H NMR spectra.
b Isolated yield.
In conclusion, the present polymer-supported acetoace-
tate reagent was found to be a useful reagent for the prep-
aration of 3-acetylcoumarins and 4-methylcoumarins.
Especially for 3-acetylcoumarin (5a), we realized a facile, MeOH (400 mL), and p-TsOH (catalytic amount) was added. The
solution was stirred at reflux for 12 h. The polymer species were
speedy, environmentally friendly synthetic method with
Synthesis 2005, No. 16, 2664–2668 © Thieme Stuttgart · New York

PAPER
Polymer-Supported Acetoacetate Reagent
2667
collected on a glass filter, and washed with water, MeOH, acetone
and then CH2Cl2. In this deprotection, the same operation was re-
peated. Finally, the polymer species were dried under reduced pres-
sure.
1H NMR (400 MHz, CDCl3): d = 2.73 (s, 3 H), 3.87 (s, 3 H), 7.04
(d, J = 2.9 Hz, 1 H), 7.24 (dd, J = 9.2, 2.9 Hz, 1 H), 7.31 (d, J = 9.2
Hz, 1 H), 8.46 (s, 1 H).
MS (FAB): m/z (%) = 219 (55, [M + H]+).
IR (neat): 3440, 2925, 2850, 1600, 1490, 1450, 1360, 1095, 1030,
755, 695 cm–1.
13C NMR (125 MHz, CDCl3): d = 25.7, 26.2, 29.8, 32.8, 62.8, 70.2,
72.8.
3-Acetyl-6-bromocoumarin (5d)
Mp 220–221 °C (Lit. 13 mp 216-217 °C).
IR (KBr): 1735, 1675, 1610, 1550, 1410, 1355, 1235, 1205, 1070,
980, 970, 835, 770, 660, 560 cm–1.
1H NMR (400 MHz, CDCl3): d = 2.73 (s, 3 H), 7.28 (d, J = 8.0 Hz,
1 H), 7.74 (dd, J = 8.0, 2.2 Hz, 1 H), 7.79 (d, J = 2.2 Hz, 1 H), 8.41
(s, 1 H).
Anal. Calcd: loading rate, 1.07 mmol/g (– OH). Found: C, 87.25; H,
7.76; Cl, 1.29.
O-Merrifield Resin-Bound 6-Acetoacetylhexan-1-ol (Polymer
2)
A suspension of 10 (18.7 g, 20.0 mmol) in DMF (200 mL) was heat-
ed at refluxing temperature in a flask equipped with a dropping fun-
nel under argon. 2,2,6-Trimethyl-4H-1,3-dioxin-4-one (3; 6.44 g,
38.5 mmol) was added to the solution over a period of 4.5 h and
then, the mixture was refluxed for 2 h. The mixture was cooled to
r.t. and the polymer species were collected on a glass filter. The
polymer species were washed with MeOH, acetone and then
CH2Cl2 to remove contaminated species, and dried under reduced
pressure.
3,6-Diacetylcoumarin (5e)
Mp 169–170 °C.
IR (KBr): 1745, 1685, 1610, 1570, 1430, 1355, 1240, 1200, 975,
830, 770, 555 cm–1.
1H NMR (400 MHz, CDCl3): d = 2.67 (s, 3 H), 2.74 (s, 3 H), 7.45
(d, J = 8.5 Hz, 1 H), 8.25 (dd, J = 8.5, 1.9 Hz, 1 H), 8.27 (d, J = 1.9
Hz, 1 H), 8.56 (s, 1 H).
13C NMR (100 MHz, CDCl3): d = 26.5, 30.5, 117.2, 118.0, 125.3,
130.9, 133.8, 133.9, 147.1, 157.9, 158.5, 194.8, 195.5.
IR (neat): 2925, 2855, 1745, 1720, 1495, 1455, 1360, 1315, 1240,
1150, 1095, 1030, 755, 695 cm–1.
HRMS-FAB: m/z [M + H]+ calcd for C13H11O4: 231.0657; found:
13C NMR (125 MHz, CDCl3): d (keto form) = 25.8, 25.9, 28.5, 29.6,
30.2, 50.1, 65.4, 70.2, 72.9, 167.2, 200.6; d (enol form) = 21.2, 89.9.
203.0661.
3-Acetylbenzo[f]coumarin (5f)
Anal. Calcd: loading rate, 0.94 mmol/g (– acetoacetate). Found: C,
84.87; H, 7.79; Cl, 1.10.
Mp 188–189 °C (Lit.15 mp 190 °C).
IR (KBr): 1730, 1675, 1560, 1245, 1215, 975, 815, 750 cm–1.
1H NMR (400 MHz, CDCl3): d = 2.78 (s, 3 H), 7.43 (d, J = 9.0 Hz,
1 H), 7.60 (ddd, J = 8.0, 7.0, 1.0 Hz, 1 H), 7.73 (ddd, J = 8.5, 7.0,
1.2 Hz, 1 H), 7.90 (d, J = 8.0 Hz, 1 H), 8.07 (d, J = 9.0 Hz, 1 H),
8.31 (d, J = 8.5 Hz, 1 H), 9.24 (s, 1 H).
3-Acetylcoumarin (5a); Typical Procedure
To a refluxing mixture of Polymer 1 (1.3 mmol) and salicylalde-
hyde (4a; 122 mg, 1 mmol) in EtOH (5 mL) was added freshly dis-
tilled piperidine (5 mol%). The reaction was monitored by TLC
until the starting 4a was consumed completely (2.5 h). After com-
pletion of the reaction, the mixture was filtered through a glass filter
and washed with MeOH, acetone and then CHCl3. The filtrate was
evaporated under reduced pressure to give 5a in quantitative yield
with excellent purity (over 99%); mp 119–120 °C (Lit.13 mp 122–
123 °C).
IR (KBr): 1730, 1685, 1605, 1560, 1230, 1205, 970, 770 cm–1.
1H NMR (400 MHz, CDCl3): d = 2.73 (s, 3 H), 7.33–7.39 (m, 2 H),
7.64–7.69 (m, 2 H), 8.52 (s, 1 H).
MS (FAB): m/z (%) = 239 (90, [M + H]+).
7-Hydroxy-4-methylcoumarin (7a); Typical Procedure
A mixture of resorcinol (6a; 1 mmol), Polymer 2 (1.5 mmol) and p-
TsOH (0.3 mol%) in chlorobenzene (13 mL) was heated at 60 °C
until the starting material had disappeared. After completion of the
reaction, aq K2CO3 (0.15 mmol) was added to the solution. The
mixture was filtered through a glass filter and washed with H2O,
MeOH, acetone and then CHCl3. After evaporation of the filtrate,
H2O was added to the residue, and extracted with EtOAc. The or-
ganic layer was evaporated to give 7a in 90% yield with good purity
(>87%); mp 189–191 °C (Lit.16 mp 190–192 °C).
MS (FAB): m/z (%) = 189 (100) [M + H]+
3-Acetyl-6-methylcoumarin (5b)
1H NMR (400 MHz, acetone-d6): d = 2.39 (d, J = 1.2 Hz, 3 H), 6.06
(q, J = 1.2 Hz, 1 H), 6.72 (d, J = 2.4 Hz, 1 H), 6.84 (dd, J = 8.7, 2.4
Hz, 1 H), 7.58 (d, J = 8.7 Hz, 1 H), 9.49 (s, 1 H).
Mp 127.5–128.3 °C (Lit.14 mp 121 °C).
IR (KBr): 1730, 1685, 1620, 1565, 1360, 1235, 1215, 980, 830, 770
cm–1.
1H NMR (500 MHz, acetone-d6): d = 2.39 (s, 3 H), 2.59 (s, 3 H),
7.24 (d, J = 8.2 Hz, 1 H), 7.53 (dd, J = 8.2, 1.5 Hz, 1 H), 7.63 (d,
J = 1.5 Hz, 1 H), 8.42 (s, 1 H).
13C NMR (125 MHz, acetone-d6): d = 20.7, 30.1, 116.9, 119.2,
125.8, 131.1, 135.6, 136.2, 147.5, 154.4, 159.8, 195.6.
5,7-Dihydroxy-4-methylcoumarin (7b)
Mp 232–233 °C (Lit.17 mp 231 °C).
1H NMR (400 MHz, acetone-d6): d = 2.39 (d, J = 1.1 Hz, 3 H), 6.05
(q, J = 1.1 Hz, 1 H), 6.85 (d, J = 8.6 Hz, 1 H), 7.13 (d, J = 8.6 Hz, 1
H), 8.58 (s, 1 H), 8.70 (s, 1 H).
HRMS-FAB: m/z [M + H]+ calcd for C12H11O3: 203.0708; found:
203.0715.
Acknowledgment
3-Acetyl-6-methoxycoumarin (5c)
Financial support from a Grant-in-Aid for Scientific Research
(16655012) by the Ministry of Education, Science, Sports and
Culture is gratefully acknowledged.
Mp 180–181 °C (Lit.13 mp 182–183 °C).
IR (KBr): 1730, 1680, 1560, 1470, 1350, 1270, 1230, 1200, 1025,
975, 850, 770, 610, 570 cm–1.
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T. Hirai, H. Togo
PAPER
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Synthesis 2005, No. 16, 2664–2668 © Thieme Stuttgart · New York