Trimethylamine catalyzed stereoselective reaction between dimethyl acetylenedicarboxylate and phenols

Article abstract of DOI:10.1007/s00706-008-0919-z

Stereoselective reaction of various substituted phenols with dimethyl acetylenedicarboxylate in the presence of a catalytic amount of aqueous trimethylamine solution in dichloromethane leads to dimethyl 2-phenoxymaleates in good to excellent yields under mild condition.

Full text of DOI:10.1007/s00706-008-0919-z

Monatsh Chem 139, 1223–1227 (2008)
DOI 10.1007/s00706-008-0919-z
Printed in The Netherlands
Trimethylamine catalyzed stereoselective reaction between dimethyl
acetylenedicarboxylate and phenols
Farough Nasiri, Bahareh Atashkar
Department of Chemistry, Faculty of Sciences, University of Kurdistan, Sanandaj, Iran
Received 8 February 2008; Accepted 27 February 2008; Published online 9 May 2008
# Springer-Verlag 2008
Abstract Stereoselective reaction of various substi-
tuted phenols with dimethyl acetylenedicarboxylate
in the presence of a catalytic amount of aqueous tri-
methylamine solution in dichloromethane leads to
dimethyl 2-phenoxymaleates in good to excellent
yields under mild condition.
studies, usually the fumarate isomer is the major
product. On the other hand, the addition of phenols
to dimethyl acetylenedicarboxylate adsorbed onto
alumina has been reported to be stereoselective, pro-
ducing only maleate adducts, although only simple
cresol and 4-bromophenol have been examined in
that study [9]. Stoermer and Fairlie have described
[10] the addition reaction of various phenols to
dimethyl acetylenedicarboxylate in the presence of
an excess amount of triethylamine in dry diethyl
ether to produce a mixture of fumarate and maleate
adducts. The time of the reactions was long and in
some cases the yields of the products were poor.
Also no considerable stereoselectivity was encoun-
tered in that study. In the current work we wish to
report a facile synthesis of dimethyl 2-phenoxymale-
ates from the reaction of a wide range of functional-
ized phenols and dimethyl acetylenedicarboxylate
in the presence of a catalytic amount of aqueous
trimethylamine solution in dichloromethane.
Keywords Dimethyl phenoxymaleates; Acetylenic esters;
Trialkylamines.
Introduction
Vinyl ethers of alcohols and phenols are well
established monomers, building blocks, and auxili-
aries in organic synthesis, steadily expanding their
scope of application [1]. There are many studies on
the reaction between acetylenic esters and phenols to
produce these compounds [2–5]. In general, phe-
nols react with acetylenic esters to give a mixture
of phenoxymaleates and phenoxyfumarates, arising
through a cis or trans – mode of addition [6–10].
Recently, silica-gel powder has been found [8] to
catalyze the stereoselective conversion of phosphor-
anes obtained from the reaction of 2-nitrophenol
and dialkyl acetylenedicarboxylates in the presence
of triphenylphosphine to dialkyl 2-(2-nitro-phenoxy)-
2-butenedioates under solvent-free conditions and un-
der microwave and thermal conditions. In the above
Results and discussion
Reaction of substituted phenols with dimethyl ace-
tylenedicarboxylate (1, R ¼ Me) in the presence of
a catalytic amount of aqueous trimethylamine in
dichloromethane at room temperature for 2 h, gives
the maleate isomer of 3 in good to excellent yields
1
(see Scheme 1 and Table 1). The H and 13C NMR
Correspondence: Farough Nasiri, Department of Chemistry,
Faculty of Sciences, University of Kurdistan, P.O. Box 66315-
416, Sanandaj, Iran. E-mail: fnasiri@uok.ac.ir
spectra of the crude products clearly indicated the
formation of compounds 3. The ratio of fumarate:

1224
F. Nasiri, B. Atashkar
Scheme 1
Table 1 Stereoselectivity in addition of phenols to dimethyl
acetylenedicarboxylate in the presence of trimethylamine in
CH2Cl2 at room temperaturea
Ar
Isomer=%
Fumarate
Maleate
3a
3b
3c
3d
3e
3f
3g
3h
3i
Phenyl
16
6
3
6
4
3
3
8
7
84
94
97
94
96
97
97
92
93
96
87
91
4-Chlorophenyl
2,4-Dichlorophenyl
2-Acetylphenyl
2-Formylphenyl
2-Methoxyphenyl
2-Methoxy-4-formylphenyl
1-Naphthyl
2-Naphthyl
2-Nitrophenyl
3-Nitrophenyl
4-Nitrophenyl
3j
3k
3l
4
13
9
Scheme 2
a All of the reactions have quantitative yields except for 3i
which is about 85%
reaction is outlined in Scheme 2 based on the previ-
ous reports [11–16]. Initially, trialkylamine reacts
with the electron-deficient acetylenic esters to gen-
erate the zwitterionic intermediate 6, which deproto-
nates the nucleophile to give the corresponding
intermediates 7 and 8. Subsequent Michael addition
of 8 to 7 forms the 1,3-dipolar ion 9, which then
eliminates trialkylamine to afford the final product
[13, 17].
From the reaction of 2-naphthol with dimethyl
acetylenedicarboxylate in the presence of trimethyl-
amine, in addition to the derivative 3i, addition prod-
ucts 5 (15%) were isolated (Scheme 3).
maleate isomers were detected by 1H NMR spectros-
copy. The vinylic proton positions for maleate iso-
mers of 3 at ꢀ ¼ 5.00–5.78 ppm compare favorably
with the reported values for the proton positions in
dimethyl 2-phenoxymaleates [6, 10]. Table 1 shows
that this addition reaction tolerates a wide range of
functional groups on the phenol including alkoxyls,
ketones, aldehydes, halides, and nitro groups.
Although the mechanistic details of the above re-
action are unknown, a proposed mechanism for this
Scheme 3

Trimethylamine catalyzed stereoselective reaction
1225
Table 2 Stereoselectivity in addition of phenols to dialkyl acetylenedicarboxylates in the presence of trialkylamines in CH2Cl2 at
room temperature
Ar
R
R0
Yield=%a
of 3 or 4
Isomer=%
Fumarate
Maleate
2-Acetylphenyl
4-Chlorophenyl
4-Chlorophenyl
4-Chlorophenyl
4-Chlorophenyl
2-t-Butylphenyl
2,6-Dimethylphenyl
2,6-Dimethylphenyl
Me
Me
Me
Et
t-Bu
Me
Me
t-Bu
Et
Et
n-Bu
Me
Me
Me
Me
n-Bu
3d (>98)
3b (>98)
3b (>98)
4a (>98)
4b (>98)
3m (47)
64
57
52
13
42
82
59
71
36
43
48
87
58
18
41
29
3n (87)
4c (>98)
a
Isolated yields
O-Rapid analyzer. These results agreed favorably with
the calculated values. IR spectra were measured with a
Shimadzu IR-460 spectrometer. NMR spectra were re-
corded with a Bruker DRX-250 AVANCE instrument
(250.1 MHz for 1H and 62.9 MHz for 13C) with CDCl3
as solvent. Chemical shifts are given in ppm (ꢀ) relative
to internal TMS, and coupling constant (J) are reported in
Hertz (Hz).
The maleate:fumarate isomer ratio (84:16) obtained
from the reaction of 4-chlorophenol with dimethyl
acetylenedicarboxylate in chloroform at room temper-
ature was approximately similar to the ratio obtained
from its reaction in dichloromethane. When this reac-
tion was carried out in refluxing chloroform, the iso-
mer ratio of maleate:fumarate is changed to 61:39.
This result clearly shows that the reaction is under
kinetic control at room temperature. Also, when the
reactions were carried out in the presence of bulky
trialkylamines, bulky acetylenic esters, or with phe-
nols containing bulky groups on ortho position, the
stereoselectivity of the reaction was reduced or even
inverted (see Table 2). In these cases, the reactions
give products as a pair of inseparable (E)- and (Z)-
isomers. It may be assumed that steric effects play a
significant role in the stereoselectivity of these reac-
tions. Maleate isomers are the major products when
the alkyl groups on the ester moieties, amines, and on
the ortho position of aryl groups are small.
General procedure for the preparation of 3
To a stirred solution of 0.28 g dimethyl acetylenedicarbox-
ylate (2 mmol) and 0.05 g trimethylamine solution (0.05 g,
45% in water, 0.4 mmol) in 8 cm3 CH2Cl2 was added drop-
wise a mixture of 0.19 g phenol (2 mmol) in 4 cm3 CH2Cl2
at 0ꢀC over 5 min. The reaction mixture was then allowed to
warm to room temperature and stirred for 2 h. The mixture
was washed with dilute HCl and then cold H2O. The organ-
ic phase was dried (Na2SO4) and the solvent was removed
under reduced pressure to give 3a as pale yellow oil. It
should be noted that in some cases (3i, 3m, and 3n), the
mixture of (E)- and (Z)-isomers were separated and purified
by flash chromatography on a silica gel (Merck 230–400
mesh) column using n-hexane=EtOAc mixture as eluent.
Compounds 3a and 3b [10], 3e [6], and 3f, 3g, and 3l
[10] are known compounds.
In conclusion, the stereoselective reaction be-
tween dimethyl acetylenedicarboxylate and phenols
in the presence of a catalytic amount of trimethyla-
mine provides a simple entry to the synthesis of
dimethyl 2-phenoxymaleates in good to excellent
yields. This procedure has advantages of high yields,
mild reaction conditions, and simple experimental
and easy work-up conditions.
Dimethyl 2-(2,4-dichlorophenyl)-2-butenedioate
(3c, C12H10Cl2O5)
Pale yellow oil; IR (KBr): ꢁꢀ¼ 1748, 1717, 1637cmꢁ1; Major
isomer (E)-3c: 97%; 1H NMR (250.1MHz, CDCl3): ꢀ ¼ 3.69,
3
3.94 (2s, 2OCH3), 5.04 (s, ¼CH), 7.14 (d, JHH ¼ 8.8 Hz, H–
3
4
Ar), 7.30 (dd, JHH ¼ 8.8, JHH ¼ 2.5 Hz, H–Ar), 7.49 (d,
4JHH ¼ 2.5 Hz, H–Ar) ppm; 13C NMR (62.9 MHz, CDCl3):
ꢀ ¼ 51.9, 53.3 (2OMe), 99.6 (C¼CH), 123.7 (CH), 127.7
(CCl), 128.7, 130.1 (CH), 132.6, (CCl), 147.2, 158.7 (2C),
162.5, 165.3 (2C¼O, ester) ppm.
Experimental
Acetylenic esters, phenols, and trialkylamines were ob-
tained from Fluka (Buchs, Switzerland) and were used
without further purification. Melting points were measured
with an Electrothermal 9100 apparatus. Elemental analy-
ses (C, H, and N) were performed using a Heraeus CHN-
Dimethyl 2-(2-acetylphenoxy)-2-butenedioate
(3d, C14H14O6)
Yellow oil; IR (KBr): ꢁꢀ¼ 1746, 1715, 1693, 1632cmꢁ1
;
Major isomer (E)-3d: 94%; H NMR (250.1MHz, CDCl3):
1

1226
F. Nasiri, B. Atashkar
ꢀ ¼ 2.58 (s, CH3), 3.65, 3.90 (2s, 2OCH3), 5.14 (s, ¼CH), 7.12
(d, 3JHH ¼ 8.0 Hz, H–Ar), 7.31 (t, 3JHH ¼ 8.0 Hz, H–Ar), 7.53
(t, 3JHH ¼ 8.0 Hz, H–Ar), 7.84 (d, 3JHH ¼ 8.0 Hz, H–Ar) ppm;
13C NMR (62.9MHz, CDCl3): ꢀ ¼ 30.8 (CH3), 51.9, 53.3
(2OCH3), 100.4 (C¼CH), 121.9, 126.7, 131.0 (3CH), 131.2
(C), 134.0 (CH), 151.6, 159.7 (2C), 162.8, 165.4 (2C¼O,
ester), 197.3 (C¼O) ppm.
131.1 (4CH), 149.2, 153.7, 158.2 (3C), 162.4, 165.0 (2C¼O,
Minor isomer (Z)-3k: 13%; 1H NMR (250.1 MHz, CDCl3):
ester) ppm.
3
ꢀ ¼ 3.77, 3.79 (2s, 2OCH3), 6.73 (s, ¼CH), 7.24 (d, JHH
¼
8.3 Hz, H–Ar), 7.73 (t, 3JHH ¼ 8.3 Hz, H–Ar), 7.82 (s, H–Ar),
8.12 (d, JHH ¼ 8.3 Hz, H–Ar) ppm; 13C NMR (62.9 MHz,
3
CDCl3): ꢀ ¼ 52.2, 53.3 (2OCH3), 111.0 (C¼CH), 118.2,
122.4, 126.6, 130.4 (4CH), 148.4, 153.7, 157.0 (3C), 161.8,
163.2 (2C¼O, ester) ppm.
1
Minor isomer (Z)-3d: 6%; H NMR (250.1 MHz, CDCl3):
ꢀ ¼ 2.67 (s, CH3), 3.67, 3.72 (2s, 2OCH3), 6.65 (s, ¼CH),
7.10–7.84 (m, H–Ar) ppm.
Dimethyl 2-(2-(tert-butyl)phenoxy)-2-butenedioate
(3m, C16H20O5)
Dimethyl 2-(1-naphthyloxy)-2-butenedioate (3h, C16H14O5)
Yellow oil, IR (KBr): ꢁꢀ¼ 1745, 1716, 1634cmꢁ1; Major iso-
Pale yellow oil; IR (KBr): ꢁꢀ¼ 1732, 1706, 1647cmꢁ1; Major
isomer (Z)-3m: 82%; 1H NMR (250.1MHz, CDCl3): ꢀ ¼ 1.53
(s, CMe3), 3.73, 3.75 (2s, 2OCH3), 6.61 (s, ¼CH), 6.63–7.45
(m, H–Ar) ppm; 13C NMR (62.9 MHz, CDCl3): ꢀ ¼ 29.5
(CMe3), 34.8 (CMe3), 51.9, 52.9 (2OCH3), 114.1 (C¼CH),
116.5, 120.5, 123.2, 127.0 (4CH), 138.1, 149.5, 154.2 (3C),
162.8, 164.2 (2C¼O, ester) ppm.
1
mer (E)-3h: 92%; H NMR (250.1 MHz, CDCl3): ꢀ ¼ 3.63,
4.00 (2s, 2OCH3), 5.00 (s, ¼CH), 7.26–8.22 (m, H–Ar) ppm;
13C NMR (62.9MHz, CDCl3): ꢀ ¼ 52.0, 53.3 (2OCH3), 101.8
(C¼CH), 117.5, 119.3, 121.6, 126.9, 127.7, 129.3, 130.7
(7CH), 130.8, 136.1, 155.1, 159.7 (4C), 162.6, 165.2 (2C¼O,
ester) ppm.
1
Minor isomer (Z)-3h: 8%; H NMR (250.1 MHz, CDCl3):
ꢀ ¼ 3.66, 3.69 (2s, 2OCH3), 6.68 (s, ¼CH), 7.10–7.84 (m, H–
Minor isomer (E)-3m: 18%; 1H NMR (250.1 MHz, CDCl3):
ꢀ ¼ 1.42 (s, CMe3), 3.97, 3.99 (2s, 2OCH3), 5.23 (s, ¼CH),
6.63–7.45 (m, H–Ar); 13C NMR (62.9 MHz, CDCl3): ꢀ ¼ 29.8
(CMe3), 34.5(CMe3), 51.9, 53.5 (2OCH3), 98.1 (C¼CH),
116.5, 120.5, 123.2, 127.4 (4CH), 136.1, 149.5, 155.2 (3C),
162.8, 165.2 (2C¼O, ester) ppm.
Ar) ppm.
Dimethyl 2-(2-naphthyloxy)-2-butenedioate (3i, C16H14O5)
Yellow oil; IR (KBr): ꢁꢀ¼ 1747, 1716, 1633cmꢁ1; Major iso-
1
mer (E)-3i: 93%; H NMR (250.1MHz, CDCl3): ꢀ ¼ 3.67,
Dimethyl 2-(2,6-dimethylphenoxy)-2-butenedioate
(3n, C14H16O5)
3.95 (2s, 2OCH3), 5.19 (s, ¼CH), 7.19–7.92 (m, H–Ar)
ppm; 13C NMR (62.9 MHz, CDCl3): ꢀ ¼ 51.8, 53.2 (2OCH3),
99.3 (C¼CH), 117.9, 120.0, 126.2, 127.0, 127.6, 127.9, 130.5
(7CH), 131.5, 134.0, 150.5, 160.9 (4C), 162.0, 165.9 (2C¼O,
ester) ppm.
Pale yellow oil; IR (KBr): ꢁꢀ¼ 1738, 1707, 1646cmꢁ1; Major
1
isomer (Z)-3n: 59%; H NMR (250.1MHz, CDCl3): ꢀ ¼ 2.24
(s, 2CH3), 3.52, 3.72 (2s, 2OCH3), 6.10 (s, ¼CH), 6.90–7.01
(m, H–Ar) ppm; 13C NMR (62.9 MHz, CDCl3): ꢀ ¼ 15.6
(2CH3), 53.0, 53.5 (2OCH3), 105.2 (C¼CH), 125.1 (CH),
128.8 (2CH), 129.9 (2C), 149.0, 150.8 (2C), 162.6, 165.1
(2C¼O, ester) ppm.
1
Minor isomer (Z)-3i: 7%; H NMR (250.1MHz, CDCl3):
ꢀ ¼ 3.71, 3.72 (2s, 2OCH3), 6.69 (s, ¼CH), 7.19–7.92 (m,
H–Ar) ppm.
Minor isomer (E)-3n: 41%; 1H NMR (250.1MHz, CDCl3):
ꢀ ¼ 2.21 (s, 2CH3), 3.65, 3.97 (2s, 2OCH3), 4.82 (s, ¼CH),
7.02–7.07 (m, H–Ar) ppm; 13C NMR (62.9MHz, CDCl3):
ꢀ ¼ 16.5 (2CH3), 51.6, 53.1 (2OCH3), 95.4 (C¼CH), 126.5
(CH), 129.3 (2CH), 130.2 (2C), 152.1, 160.2 (2C), 164.5,
166.1 (2C¼O, ester) ppm.
Dimethyl 2-(2-nitrophenoxy)-2-butenedioate
(3j, C12H11NO7)
Yellow oil; IR (KBr): ꢁꢀ¼ 1746, 1714, 1634cmꢁ1; Major iso-
1
mer (E)-3j: 96%; H NMR (250.1MHz, CDCl3): ꢀ ¼ 3.70,
3
3.93 (2s, 2OCH3), 5.24 (s, ¼CH), 7.32 (dd, JHH ¼ 8.3,
4JHH ¼ 1.0 Hz, H–Ar), 7.44 (m, H–Ar), 7.69 (m, H–Ar),
3
4
8.08 (dd, JHH ¼ 8.3, JHH ¼ 1.5 Hz, H–Ar) ppm; 13C NMR
(62.9MHz, CDCl3): ꢀ ¼ 52.2, 53.4 (2OCH3), 102.2 (C¼CH),
123.9, 126.5, 127.3, 135.3 (4CH), 141.8, 146.1, 158.4 (3C),
162.4, 165.2 (2C¼O, ester) ppm.
Diethyl 2-(4-chlorophenoxy)-2-butenedioate
(4a, C14H15ClO5)
Yellow oil; IR (KBr): ꢁꢀ¼ 1741, 1716, 1633cmꢁ1; Major iso-
1
1
mer (E)-4a: 87%; H NMR (250.1 MHz, CDCl3): ꢀ ¼ 1.16,
Minor isomer (Z)-3j: 4%; H NMR (250.1MHz, CDCl3):
3
3
1.28 (2t, JHH ¼ 7.0 Hz, 2OCH2CH3), 4.09, 4.29 (2q, JHH
¼
ꢀ ¼ 3.85, 3.89 (2s, 2OCH3), 6.72 (s, ¼CH), 7.30–8.10 (m,
3
7.0 Hz, 2OCH2CH3), 5.09 (s, ¼CH), 7.01 (d, JHH ¼ 8.7 Hz,
H–Ar) ppm.
3
H–Ar), 7.31 (d, JHH ¼ 8.7 Hz, H–Ar) ppm; 13C NMR
(62.9 MHz, CDCl3): ꢀ ¼ 13.8, 14.0 (2OCH2CH3), 60.6, 62.4
(2OCH2CH3), 99.9 (C¼CH), 122.2, 130.2 (4CH), 131.6
(CCl), 151.5, 160.2 (2C), 162.5, 165.0 (2C¼O, ester) ppm.
Minor isomer (Z)-4a: 13%; 1H NMR (250.1MHz, CDCl3):
Dimethyl 2-(3-nitrophenoxy)-2-butenedioate
(3k, C12H11NO7)
Pale yellow oil; IR (KBr): ꢁꢀ¼ 1744, 1718, 1633 cmꢁ1; Major
3
isomer (E)-3k: 87%; 1H NMR (250.1 MHz, CDCl3): ꢀ ¼ 3.71,
ꢀ ¼ 1.16, 1.28 (2t, JHH ¼ 7.0 Hz, 2OCH2CH3), 4.09, 4.29
3
3
3.90 (2s, 2OCH3), 5.33 (s, ¼CH), 7.43 (d, JHH ¼ 8.3 Hz,
(2q, JHH ¼ 7.0 Hz, 2OCH2CH3), 6.55 (s, ¼CH), 6.85 (d,
3JHH ¼ 8.7 Hz, H–Ar), 7.19 (d, JHH ¼ 8.7 Hz, H–Ar) ppm;
3
3
H–Ar), 7.61 (t, JHH ¼ 8.3 Hz, H–Ar), 7.89 (s, H–Ar), 8.12
13C NMR (62.9 MHz, CDCl3): ꢀ ¼ 13.8, 14.0 (2OCH2CH3),
(d, 3JHH ¼ 8.3 Hz, H–Ar) ppm; 13C NMR (62.9 MHz, CDCl3):
ꢀ ¼ 52.0, 53.2 (2OCH3), 102.6 (C¼CH), 115.8, 121.0, 126.6,
61.0, 62.3 (2OCH2CH3), 115.9 (C¼CH), 117.4 (2CH), 128.3

Trimethylamine catalyzed stereoselective reaction
1227
(CCl), 129.5 (2CH), 149.4, 155.3 (2C), 161.7, 163.2 (2C¼O,
ꢀ ¼ 3.71, 3.99 (2s, 2OCH3), 5.26 (s, ¼CH), 6.23 (bs, OH),
7.11–7.92 (m, H–Ar) ppm.
1
Minor isomer (E)-5: 16%; H NMR (250.1MHz, CDCl3):
ester)ppm.
ꢀ ¼ 3.73, 3.75 (2s, 2OCH3), 6.23 (bs, OH), 6.74 (s, ¼CH),
Di(tert-butyl)-2-(4-chlorophenoxy)-2-butenedioate
(4b, C18H23ClO5)
7.11–7.92 (m, H–Ar) ppm.
Yellow oil; IR (KBr): ꢁꢀ¼ 1715, 1714, 1632cmꢁ1; Major iso-
1
mer (E)-4b: 58%; H NMR (250.1MHz, CDCl3): ꢀ ¼ 1.43,
3
Acknowledgements
1.49 (2s, 2CMe3), 5.13 (s, ¼CH), 7.03 (d, JHH ¼ 9.0 Hz,
3
H–Ar), 7.32 (d, JHH ¼ 9.0 Hz, H–Ar) ppm; 13C NMR
We are thankful to the University of Kurdistan Research
Council for the partial support of this work.
(62.9MHz, CDCl3): ꢀ ¼ 27.8, 28.1 (2CMe3), 81.0, 83.7
(2CMe3), 102.6 (C¼CH), 122.0, 130.0 (4CH), 131.0 (CCl),
152.2, 155.5 (2C), 160.9, 164.3 (2C¼O, ester) ppm.
Minor isomer (Z)-4b: 42%; 1H NMR (250.1MHz, CDCl3):
References
3
ꢀ ¼ 1.34, 1.39 (2s, 2CMe3), 6.44 (s, ¼CH), 6.88 (d, JHH
¼
9.0 Hz, H–Ar), 7.24 (d, 3JHH ¼ 9.0 Hz, H–Ar) ppm; 13C NMR
(62.9MHz, CDCl3): ꢀ ¼ 27.7, 28.0 (2CMe3), 81.9, 83.5
(2CMe3), 117.0 (C¼CH), 117.4 (2CH), 128.0 (CCl), 129.4
(2CH), 149.5, 159.11 (2C), 161.4, 162.9 (2C¼O, ester) ppm.
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Di(tert-butyl)-2-(2,6-dimethylphenoxy)-2-butenedioate
(4c, C20H28O5)
Yellow oil; IR (KBr): ꢁꢀ¼ 1728, 1713, 1633cmꢁ1; Major iso-
1
mer (Z)-4c: 71%; H NMR (250.1MHz, CDCl3): ꢀ ¼ 1.20,
1.45 (2s, 2CMe3), 2.25 (s, 2CH3), 5.81 (s, ¼CH), 6.90–7.00
(m, H–Ar) ppm; 13C NMR (62.9 MHz, CDCl3): ꢀ ¼ 15.8
(2CH3), 27.4, 28.1 (2CMe3), 80.9, 83.3 (2CMe3), 105.9
(C¼CH), 124.6 (CH), 128.8 (2CH), 129.7 (2C), 153.0,
154.3 (2C), 161.8, 163.7 (2C¼O, ester) ppm.
Minor isomer (E)-4c: 29%; 1H NMR (250.1MHz, CDCl3):
ꢀ ¼ 1.41, 1.56 (2s, 2CMe3), 2.21 (s, 2CH3), 4.71 (s, ¼CH),
7.02–7.06 (m, H–Ar) ppm; 13C NMR (62.9 MHz, CDCl3):
ꢀ ¼ 16.7 (2CH3), 27.4, 27.8 (2CMe3), 80.5, 83.3 (2CMe3),
97.0 (C¼CH), 126.0 (CH), 129.0 (2CH), 130.6 (2C), 149.5,
159.8 (2C), 162.1, 164.9 (2C¼O, ester) ppm.
Dimethyl 2-(2-hydroxy-1-naphthyl)-2-butenedioate
15. Huisgen R, Herbig K (1965) Liebigs Ann Chem 688:98
16. Winterfeldt E (1965) Chem Ber 98:3537
17. Nasiri F, Pourdavaie K, Yosefdad S, Atashkar B (2007)
Mendeleev Commun 17:352
(5, C16H14O5)
Pale yellow oil; IR (KBr): ꢁꢀ¼ 3420, 1747, 1716, 1633 cmꢁ1
;
Major isomer (Z)-5: 84%; 1H NMR (250.1MHz, CDCl3):