An efficient solid-phase synthesis of substituted isoxazole, triazole, and cycloalkadiene derivatives using supported selenium resin

Article abstract of DOI:10.1055/s-2006-950366

We have developed efficient methods for the syntheses of 3,5-disubstituted isoxazoles and 1,2,3-triazoles, and 1,3- and 1,4-cycloalkadiene derivatives using polymer-supported selenium resin. The advantages of these methods include straightforward operation, lack of odor, good stability, and high purity of the products. Georg Thieme Verlag Stuttgart.

Full text of DOI:10.1055/s-2006-950366

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28
PAPER
An Efficient Solid-Phase Synthesis of Substituted Isoxazole, Triazole, and
Cycloalkadiene Derivatives Using Supported Selenium Resin
Isoxazoles,
Triazo
u
les, and Cycl
-
oalkadie
G
nes Using Support
u
e
d
Selenium
a
Resin ng Wang,a Wei-Ming Xu,a Xian Huang*a,b
a
Department of Chemistry, Zhejiang University (Xixi Campus), Hangzhou 310028, P. R. of China
State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences,
Shanghai 200032, P. R. of China
b
Fax +86(571)88807077; E-mail: huangx@mail.hz.zj.cn
Received 2 August 2006; revised 20 September 2006
changed to pale yellow after stirring for two hours at room
temperature. The FT-IR spectrum showed a strong peak
for the carbonyl absorptions at 1734–1738 cm–1 and pro-
longing the reaction time did not increase the carbonyl
peak further. Resin 2 then reacted with sodium tert-butox-
ide to give the corresponding yellow resin 3 almost quan-
titatively (Br was undetectable by elemental analyses).
Resin 3 was hydrolyzed in the presence of lithium hydrox-
ide and from this hydrolyzed resin the minimum loading
of carboxy groups in the resin 3 was determined to be 1.08
mmol/g by acid–base titration9 (Scheme 1).
Abstract: We have developed efficient methods for the syntheses
of 3,5-disubstituted isoxazoles and 1,2,3-triazoles, and 1,3- and 1,4-
cycloalkadiene derivatives using polymer-supported selenium res-
in. The advantages of these methods include straightforward opera-
tion, lack of odor, good stability, and high purity of the products.
Keywords: 1,3-dipolar cycloaddition, Diels–Alder reaction, poly-
mer-supported selenium resin, solid-phase synthesis, heterocycles
The preparation of diverse libraries of organic compounds
is an important facet of modern drug discovery programs.
One of the most commonly employed methods in library
production is solid-phase organic synthesis (SPOS).1 As
efficient and important methods for the preparation of het-
erocycles and carbocycles, 1,3-dipolar cycloadditions2
and Diels–Alder reactions3 are widely used in solid-phase
organic synthesis.
a
b
Se
Se
SeBr
COOEt
Br
COOEt
COOEt
3
1
2
Scheme 1 Reagents and conditions: (a) ZnCl2 (0.2 equiv), CH2Cl2,
r.t., 2 h; (b) t-BuONa, Et2O, r.t., 10 h.
Isoxazole and triazole moieties are found in various bio-
logically active compounds, since they are readily trans-
formed into various biodynamic agents, including those
with antithrombotic, PAF antagonist, and hypolipidemic
properties.4 While 1,3- and 1,4-cycloalkadiene deriva-
tives, as the products of the Diels–Alder reaction, have
also been widely used in natural product synthesis.5
Therefore, they are all interesting targets that, potentially,
can be made via solid-phase chemistry.
1,3-Dipolar cycloadditions2 of nitrile oxides in solution
are known to suffer from many side reactions, including
dimerization, as a result of the high reactivity of nitrile ox-
ides. Therefore, it is synthetically interesting to perform
these reactions using solid-phase synthesis, which makes
isolation of the product easier. Resin 3 reacted with nitrile
oxides to give resins 4. In this process, we found that it
was necessary for triethylamine to be slowly added drop-
wise over 24 hours to avoid the dimerization of the nitrile
oxides. 3,5-Disubstituted isoxazoles were obtained with
good yield and purity through syn-elimination of selenox-
ide from resin 4 (Scheme 2). The results are given in
Table 1.
Since the first organoselenium resin was reported in
1976,6 several groups have developed organoselenium
resins as convenient linkers.7 Recently, our research
group has been interested in the application of organic se-
lenium resins in organic synthesis.8 Herein we wish to
present our investigation of solid-phase organic synthesis
methodology for the preparation of 3,5-disubstituted isox-
azoles and 1,2,3-triazoles and 1,3- and 1,4-cycloalkadiene
derivatives with the advantages of straightforward opera-
tion, lack of odor, good stability, and high purity of the
products.
Se
O
COOEt
a
b
Se
COOEt
SeOOH
O
COOEt
R
R
N
N
3
4
5
We began our efforts from polystyrene-supported selen-
enyl bromide 17a (Br: 1.18 mmol/g), which was treated
with zinc chloride and acrylic ester to give the corre-
sponding pale-yellow resin 2; the dark-red resin 1 was
Scheme 2 Reagents and conditions: (a) RCH=NOH, NCS, CH2Cl2,
Et3N, r.t., 24 h; (b) H2O2, THF, 0 °C, 30 min, then r.t., 30 min.
Besides nitrile oxides, azides were also found to undergo
readily 1,3-dipolar cycloadditions. In the presence of cop-
per(I) iodide and proline, resin 3 reacted smoothly with
aryl halides and sodium azide in a one-pot 1,3-dipolar
SYNTHESIS 2007, No. 1, pp 0028–0032
x
x
.
x
x
.2
0
0
6
Advanced online publication: 13.11.2006
DOI: 10.1055/s-2006-950366; Art ID: F11906SS
© Georg Thieme Verlag Stuttgart · New York

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PAPER
Isoxazoles, Triazoles, and Cycloalkadienes Using Supported Selenium Resin
29
Table 1 Synthesis of 3,5-Disubstituted Isoxazoles
Due to the presence of the carboxy group as an electron-
withdrawing group, resin 3 can undergo Diels–Alder
reactions11 with dienes smoothly, which greatly expanded
the diversity of this method from heterocycles to carbocy-
cles.
Product
5a
R
Yielda (%)
Purityb (%)
CO2Et
Cy
86
89
86
81
80
95
96
93
92
93
5b
In the presence of zinc iodide, resin 3 reacted smoothly
with cyclopentadiene and furan through the Diels–Alder
reaction to furnish resins 8. These were then treated with
hydrogen peroxide to give the substituted products 9 in
good yield and high purity (Scheme 4).
5c
4-MeC6H4
3-BrC6H4
4-ClC6H4
5d
5e
a Yield of the crude product based on the loading of resin 1.
Besides cyclic dienes, acyclic dienes can also perform the
same reaction. The use of isoprene in place of cyclopenta-
diene as the diene gave the product 11 using the same pro-
cedure (Scheme 5).
b Determined by HPLC.
cycloaddition10 to give resin 6, which was followed by
syn-elimination of selenoxide to afford 3,5-disubstituted
1,2,3-triazoles 7 (Scheme 3). The results are given in
Table 2.
It is noteworthy that, although the same Diels–Alder reac-
tion and selenoxide syn-elimination are performed, the re-
gioselectivities of the products 9 and 11 are completely
different. In product 9, the 1,4-diene was formed due to
steric effects, while the 1,3-diene was formed due to the
conjugative effect in product 11.12
Se
N
COOEt
a
b
Se
COOEt
The polystyrene-supported benzeneseleninic acid reacted
with potassium iodide/sodium thiosulfate followed by
bromine13 to regenerate polystyrene-supported selenenyl
bromide 1 (Scheme 6), which could be reused as starting
material and recycled in the same reaction for several
times without the loss of purity of the products but with a
slight decrease in yield. For example, ethyl 4-methylcy-
clohexa-1,3-dienecarboxylate (11) was obtained in 76%
yield under the same reaction conditions using the recov-
ered selenenyl bromide resin 1 (second run), and in 72%
yield after being recycled for a second time (third run).
SeOOH
N
N
N
R
COOEt
R
N
N
7
6
3
Scheme 3 Reagents and conditions: (a) NaN3, RI, CuI, proline,
LiOH, DMSO, 65 °C, 12 h; (b) H2O2, THF, 0 °C, 30 min, then r.t., 30
min.
Table 2 Synthesis of 3,5-Disubstituted 1,2,3-Triazoles
Product
7a
R
Yielda (%)
Purityb (%)
Ph
79
77
74
73
61
94
92
90
92
86
a
7b
4-MeC6H4
2-MeC6H4
4-ClC6H4
i-Pr
SeOOH
SeBr
1
7c
Scheme 6 Reagents and conditions: (a) (1) KI, Na2S2O3, DMF,
H2O, 24 h; (2) Br2, CHCl3, r.t., 30 min.
7d
7e
a Yield of the crude product based on the loading of resin 1.
In summary, we have developed an efficient method for
the synthesis of 3,5-disubstituted isoxazoles and 1,2,3-tri-
b Determined by HPLC.
X
X
Se
a
b
Se
SeOOH
COOEt
COOEt
COOEt
9
3
8
9a: X = CH2, 89% yield, 92% purity
9b: X = O, 74% yield, 88% purity
Scheme 4 Reagents and conditions: (a) dienes, ZnI2, CH2Cl2, r.t., 8 h (for cyclopentadiene) or 45 °C, 96 h (for furan); (b) H2O2, THF, 0 °C,
30 min, then r.t., 40 min.
Se
a
Se
b
COOEt
11 79% yield, 93% purity
SeOOH
COOEt
COOEt
10
3
Scheme 5 Reagents and conditions: (a) isoprene, ZnI2, CH2Cl2, r.t., 48 h; (b) H2O2, THF, 0 °C, 30 min, then r.t., 40 min.
Synthesis 2007, No. 1, 28–32 © Thieme Stuttgart · New York

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30
Y.-G. Wang et al.
PAPER
Anal. Calcd for C9H11NO5: C, 50.70; H, 5.20; N, 6.57. Found: C,
50.62; H, 5.29; N, 6.55.
azoles, and 1,3- and 1,4-cycloalkadiene derivatives using
polymer-supported selenium resin. The advantages of this
method include straightforward operation, lack of odor,
good stability, and high purity of the products.
Ethyl 3-Cyclohexylisoxazole-5-carboxylate (5b)
Low-melting solid.
IR: 2931, 2850, 1729, 1604, 1451, 1425, 1112, 865, 757 cm–1.
1H NMR (CDCl3): d = 6.86 (s, 1 H), 4.44–4.41 (m, 2 H), 2.83–2.80
(m, 1 H), 2.00–1.29 (m, 13 H).
13C NMR (CDCl3): d = 168.3, 159.4, 156.3, 107.2, 61.4, 35.2, 31.3,
25.3, 25.2, 13.5.
Starting materials were obtained from commercial suppliers and
used without further purification. Et2O and THF were distilled from
Na/benzophenone immediately prior to use. Polystyrene (H 1000,
100–200 mesh, cross-linked with 1% divinylbenzene) was pur-
1
chased from commercial sources (Nankai University). H NMR
(400 MHz) and 13C NMR (100 MHz) spectra were recorded on a
Bruker Avance (400 MHz) spectrometer, using CDCl3 as the sol-
vent and TMS as internal standard. MS spectra (EI, 70eV) were re-
corded on a HP5989B mass spectrometer. IR spectra were recorded
on a Shimadzu IR-408 spectrophotometer. Elemental analyses were
performed on a Flash EA1112 instrument. HPLC was performed on
an Agilent 1100 HPLC. The samples were further purified by TLC
for 13C NMR and microanalyses.
MS: m/z = 223 (M+).
Anal. Calcd for C12H17NO3: C, 64.55; H, 7.67; N, 6.27. Found: C,
64.49; H, 7.76; N, 6.30.
Ethyl 3-(4-Tolyl)isoxazole-5-carboxylate (5c)
White solid; mp 50–52 °C.
IR: 3131, 2986, 1729, 1600, 1449, 1428, 1281, 1245, 1089, 1024,
927, 765, 510 cm–1.
Polystyrene-Supported 2-Selanylpropanoic Ester Resin 3
To a suspension of the swollen polystyrene-supported selenenyl
bromide resin 1 (1.0 g, 1.18 mmol Br/g) in CH2Cl2 (10 mL) was
added ZnCl2 (0.20 mmol). The mixture was stirred at r.t. for 10 min
and then ethyl acrylate (5 mmol) was added and the mixture was
stirred for 2 h. The resin was collected on a filter and washed suc-
cessively with H2O (2 × 20 mL), THF (2 × 10 mL), acetone (2 × 10
mL), THF–H2O (2:1. 2 × 10 mL), THF (2 × 10 mL), and CH2Cl2 (2
× 10 mL), and then dried under vacuum overnight to afford resin 2.
1H NMR (CDCl3): d = 7.73 (d, J = 8.0 Hz, 2 H), 7.29 (d, J = 8.0 Hz,
2 H), 7.23 (s, 1 H), 4.45 (q, J = 7.2 Hz, 2 H), 2.41 (s, 3 H), 1.44 (t,
J = 7.2 Hz, 3 H).
13C NMR (CDCl3): d = 162.3, 160.1, 156.5, 141.1, 129.8, 127.3,
124.4, 107.7, 61.6, 21.4, 14.2.
MS: m/z = 231 (M+).
Anal. Calcd for C13H13NO3: C, 67.52; H, 5.67; N, 6.06. Found: C,
67.45; H, 5.73; N, 6.10.
t-BuONa (4.0 mmol) was added to a suspension of the swollen resin
2 in anhyd Et2O (20 mL), and the mixture was stirred at r.t. for 10
h. Resin was collected by filtration, washed with H2O (2 × 20 mL),
THF–H2O (2:1, 2 × 10 mL), THF (2 × 10 mL), and CH2Cl2 (2 × 10
mL), and then dried in a vacuum overnight to afford resin 3.
Ethyl 3-(4-Bromophenyl)isoxazole-5-carboxylate (5d)
Low-melting solid.
IR: 3131, 2985, 1729, 1599, 1448, 1428, 1282, 1245, 1088, 1022,
926, 764, 509 cm–1.
1H NMR (CDCl3): d = 7.99–7.98 (m, 1 H), 7.76–7.74 (m, 1 H),
7.61–7.58 (m, 1 H), 7.37–7.33 (m, 1 H), 7.23 (s, 1 H), 4.46 (q,
J = 7.2 Hz, 2 H), 1.44 (t, J = 7.2 Hz, 3 H).
13C NMR (CDCl3): d = 161.7, 161.2, 156.5, 133.4, 130.6, 129.9,
129.7, 125.3, 123.1, 107.1, 62.4, 14.1.
3,5-Disubstituted Isoxazoles 5a–e; General Procedure
To a suspension of the swollen resin 3 (0.5 g) in CH2Cl2 (15 mL)
was added a soln of hydroximoyl halide (1.6 mmol) in CH2Cl2 [pre-
pared from aldoxime (1.6 mmol) and NCS (1.6 mmol) in CH2Cl2
(15 mL) stirring at r.t. for 4 h before use]. A soln of Et3N (4 mmol)
in CH2Cl2 (15 mL) was slowly added dropwise in three portions ev-
ery 8 h [each portion consisted of Et3N (1.3 mmol) in anhyd CH2Cl2
(5 mL)]. The mixture was stirred at r.t. for 2 h and then resin 4 was
collected by filtration, washed with DMF (3 × 10 mL), THF (2 × 10
mL), Et2O (2 × 10 mL), THF–H2O (2:1, 2 × 10 mL), H2O (2 × 10
mL), THF (2 × 10 mL), benzene (2 × 10 mL), and CH2Cl2 (2 × 10
mL).
MS: m/z = 295 (M+), 297 (M + 2).
Anal. Calcd for C12H10BrNO3: C, 48.67; H, 3.40; N, 4.73. Found: C,
48.76; H, 3.44; N, 4.70.
Ethyl 3-(4-Chlorophenyl)isoxazole-5-carboxylate (5e)
White solid.; mp 136–138 °C.
The washed resin 5 was suspended in THF (15 mL), 30% aq H2O2
(0.5 mL) was added, and the mixture was stirred at 30 °C for 30 min
and then at r.t. for 30 min. The mixture was filtered, and the resin
was washed with CH2Cl2 (2 × 15 mL). The filtrate was washed with
H2O (2 × 30 mL), dried (MgSO4), and evaporated to dryness under
vacuum to give the crude products 5. Further purification was via
flash chromatography (hexanes–EtOAc, 8:1) for 13C NMR and mi-
croanalyses.
IR: 3132, 2986, 1728, 1600, 1449, 1428, 1281, 1245, 1089, 1023,
927, 764, 510 cm–1.
1H NMR (CDCl3): d = 7.78 (d, J = 8.4 Hz, 2 H), 7.46 (d, J = 8.4 Hz,
2 H), 7.23 (s, 1 H), 4.46 (q, J = 7.2 Hz, 2 H), 1.44 (t, J = 7.2 Hz, 3
H).
13C NMR (CDCl3): d = 162.0, 161.2, 156.6, 136.6, 129.3, 128.1,
126.4, 107.1, 62.4, 14.1.
MS: m/z = 251 (M+).
Diethyl Isoxazole-3,5-dicarboxylate (5a)
Anal. Calcd for C12H10ClNO3: C, 57.27; H, 4.01; N, 5.57. Found: C,
57.20; H, 4.11; N, 5.54.
Oil.
IR: 3138, 2987, 1741, 1456, 1242, 1188, 1078, 1017, 842, 771 cm–1.
1H NMR (CDCl3): d = 7.22 (s, 1 H), 4.41–4.36 (m, 4 H), 1.37–1.33
3,5-Disubstituted 1,2,3-Triazoles 7a–e; General Procedure
Under a positive pressure of N2, to a suspension of the swollen resin
3 (0.5 g) in DMSO (10 mL) was added NaN3 (2.2 mmol), ArI (2.2
mmol), proline (0.27 mmol), CuI (0.27 mmol), and Et3N (0.27
mmol). The mixture was stirred at 65 °C for 15 h. The resin 6 was
collected by filtration, washed with DMF (3 × 10 mL), sat. NaHCO3
(m, 6 H).
13C NMR (CDCl3): d = 161.7, 158.7, 156.7, 155.8, 109.3, 62.5, 62.4,
13.8, 13.7.
MS: m/z = 213 (M+).
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Isoxazoles, Triazoles, and Cycloalkadienes Using Supported Selenium Resin
31
(2 × 10 mL), sat. Na2S2O3 (2 × 10 mL), H2O (3 × 10 mL), and THF
(3 × 10 mL).
MS: m/z = 251 (M+).
Anal. Calcd for C11H10ClN3O2: C, 52.50; H, 4.01; N, 16.70. Found:
C, 52.41; H, 4.12; N, 16.63.
The washed resin 6 was suspended in THF (15 mL), 30% aq H2O2
(0.5 mL) was added, and the mixture was stirred at 0 °C for 30 min
and then at r.t. for 30 min. The mixture was filtered, and the resin
was washed with CH2Cl2 (2 × 15 mL). The filtrate was washed with
H2O (2 × 30 mL), dried (MgSO4), and evaporated to dryness under
vacuum to give the crude products 7. Further purification was via
flash chromatography (hexanes–EtOAc, 6:1) for 13C NMR and mi-
croanalyses.
Ethyl 1-Isopropyl-1H-1,2,3-triazole-4-carboxylate (7e)
Oil.
IR: 3150, 2980, 1721, 1500, 1267, 1163, 1037, 837, 769, 516, 465
cm–1.
1H NMR (CDCl3): d = 7.60 (d, J = 13.2 Hz, 1 H), 5.04 (m, 1 H),
4.12 (q, J = 7.2 Hz, 2 H), 1.28–1.23 (m, 9 H).
13C NMR (CDCl3): d = 171.4, 169.1, 147.9, 68.9, 58.8, 21.6, 21.5,
14.4.
Ethyl 1-Phenyl-1H-1,2,3-triazole-4-carboxylate (7a)
White solid; mp 84–86 °C.
MS: m/z = 183 (M+).
IR: 3140, 1712, 1597, 1548, 1508, 1469, 1375, 1269, 1170, 1039,
869, 839, 765, 688, 507 cm–1.
1H NMR (CDCl3): d = 8.51 (s, 1 H), 7.75–7.73 (m, 2 H), 7.54–7.47
(m, 3 H), 4.44 (q, J = 7.2 Hz, 2 H), 1.42 (t, J = 7.2 Hz, 3 H).
Anal. Calcd for C8H13N3O2: C, 52.45; H, 7.15; N, 22.94. Found: C,
52.36; H, 7.23; N, 23.01.
13C NMR (CDCl3): d = 160.1, 139.7, 136.0, 129.8, 129.2, 127.1,
120.5, 60.7, 14.1.
Ethyl Bicyclo[2.2.1]hepta-2,5-diene-2-carboxylates 9a,b; Gen-
eral Procedure
Under a positive pressure of N2, to a suspension of the swollen resin
3 (0.5 g) in CH2Cl2 (15 mL) was added ZnI2 (0.6 mmol). The mix-
ture was stirred for 10 min and cyclopentadiene (2.2 mmol) was
added. The mixture was stirred at r.t. for 8 h (for cyclopentadiene)
or at 45 °C for 96 h in a sealed tube (for furan). Resin 8 was collect-
ed by filtration, washed with sat. aq NaHCO3 (2 × 20 mL), sat.
Na2S2O3 (2 × 10 mL), THF (2 × 10 mL), H2O (2 × 10 mL), THF–
H2O (2:1, 2 × 10 mL), THF (2 × 10 mL), CH2Cl2 (2 × 10 mL), and
THF (2 × 10 mL).
MS: m/z = 217 (M+).
Anal. Calcd for C11H11N3O2: C, 60.82; H, 5.10; N, 19.34. Found: C,
60.75; H, 5.18; N, 19.29.
Ethyl 1-(4-Tolyl)-1H-1,2,3-triazole-4-carboxylate (7b)
White solid; mp 179–181 °C.
IR: 3146, 3085, 2982, 1718, 1552, 1519, 1473, 1410, 1369, 1344,
1309, 1292, 1269, 1192, 1161, 1128, 1042, 1017, 990, 951, 827,
771, 696 cm–1.
1H NMR (CDCl3): d = 8.49 (s, 1 H), 7.64 (d, J = 8.4 Hz, 2 H), 7.35
(d, J = 8.4 Hz, 2 H), 4.46 (q, J = 7.2 Hz, 2 H), 2.43 (s, 3 H), 1.43 (t,
J = 7.2 Hz, 3 H).
13C NMR (CDCl3): d = 160.6, 140.6, 139.7, 134.0, 130.3, 125.4,
120.6, 61.3, 21.0, 14.2.
MS: m/z = 231 (M+).
The washed resin 8 was suspended in THF (15 mL), 30% aq H2O2
(0.5 mL) was added, and the mixture was stirred at 0 °C for 30 min
and then at r.t. for 40 min. The mixture was filtered, and the resin
was washed with CH2Cl2 (2 × 15 mL). The filtrate was washed with
H2O (2 × 30 mL), dried (MgSO4), and evaporated to dryness under
vacuum to give the crude products 9. Further purification was via
flash chromatography (hexanes–EtOAc, 19:1) for 13C NMR and mi-
croanalyses.
Anal. Calcd for C12H13N3O2: C, 62.33; H, 5.67; N, 18.17. Found: C,
62.43; H, 5.70; N, 18.24.
Ethyl Bicyclo[2.2.1]hepta-2,5-diene-2-carboxylate (9a)
Oil.
IR: 2932, 1732, 1492, 1355, 1153, 1069, 925, 765 cm–1.
Ethyl 1-(2-Tolyl)-1H-1,2,3-triazole-4-carboxylate (7c)
1H NMR (CDCl3): d = 7.64 (d, J = 3.2 Hz, 1 H), 6.92–6.90 (m, 1 H),
6.73–6.71 (m, 1 H), 4.25 (q, J = 7.2 Hz, 2 H), 3.88 (s, 1 H), 3.69 (s,
1 H), 2.14–2.12 (m, 2 H), 1.33 (t, J = 7.2 Hz, 3 H).
Oil.
IR: 3143, 3084, 2980, 1718, 1551, 1473, 1409, 1369, 1344, 1309,
1293, 1269, 1161, 1128, 1042, 1016, 990, 951, 828, 772, 696 cm–1.
13C NMR (CDCl3): d = 165.4, 155.5, 149.0, 143.3, 141.1, 59.2, 51.3,
1H NMR (CDCl3): d = 8.29 (s, 1 H), 7.46–7.35 (m, 4 H), 4.47 (q,
J = 7.2 Hz, 2 H), 2.23 (s, 3 H), 1.44 (t, J = 7.2 Hz, 3 H).
13C NMR (CDCl3): d = 160.6, 140.0, 135.6, 133.5, 131.5, 130.3,
128.8, 126.9, 125.8, 61.3, 17.6, 14.2.
51.0, 49.9, 14.1.
MS: m/z = 164 (M+).
Anal. Calcd for C10H12O2: C, 73.15; H, 7.37. Found: C, 73.21; H,
7.40.
MS: m/z = 231 (M+).
Anal. Calcd for C12H13N3O2: C, 62.33; H, 5.67; N, 18.17. Found: C,
62.24; H, 5.78; N, 18.10.
Ethyl 7-Oxabicyclo[2.2.1]hepta-2,5-diene-2-carboxylate (9b)
Oil.
IR: 2934, 1730, 1447, 1089, 1022, 926, 761 cm–1.
Ethyl 1-(4-Chlorophenyl)-1H-1,2,3-triazole-4-carboxylate (7d)
1H NMR (CDCl3): d = 7.68 (d, J = 3.6 Hz, 1 H), 7.47 (d, J = 1.2 Hz,
1 H), 6.80 (d, J = 12.8 Hz, 1 H), 6.51–6.50 (m, 1 H), 5.75 (d,
J = 12.8 Hz, 1 H), 4.24 (q, J = 7.2 Hz, 2 H), 1.32 (t, J = 7.2 Hz, 3
H).
13C NMR (CDCl3): d = 166.0, 150.8, 143.9, 130.3, 117.0, 114.4,
112.6, 60.1, 14.3.
Pale yellow solid; mp 170–172 °C.
IR: 3151, 2980, 1720, 1552, 1500, 1369, 1342, 1267, 1163, 1091,
1039, 837, 769, 516, 459 cm–1.
1H NMR (CDCl3): d = 8.50 (s, 1 H), 7.74 (d, J = 8.8 Hz, 2 H), 7.55
(d, J = 8.8 Hz, 2 H), 4.47 (q, J = 7.2 Hz, 2 H), 1.44 (t, J = 7.2 Hz,
3 H).
13C NMR (CDCl3): d = 160.4, 141.1, 135.5, 134.8, 130.2, 125.4,
122.0, 61.6, 14.3.
MS: m/z = 166 (M+).
Anal. Calcd for C9H10O3: C, 65.05; H, 6.07. Found: C, 64.94; H,
6.17.
Synthesis 2007, No. 1, 28–32 © Thieme Stuttgart · New York