3
08 J. Chin. Chem. Soc., Vol. 57, No. 3A, 2010
Li and Peng
1
tion of carboxylic acids. The key advantages of this method
are the simplicity of work-up (simple filtration), ease and
safety of reagent handling, cheapness of dehydrating re-
agent, and no organic byproducts which must be isolated
from products after reactions. Today it is regularly used in
our laboratory for the preparation of methyl esters and has
proven to be efficient in parallel solution phase synthesis
for the construction of combinatorial libraries. Investiga-
tions on the further application of methoxyl silica gel are
currently in progress.
ble 1, entry 5): Colorless liquid. H NMR (CDCl
MHz): d 3.93 (s, 3H, OCH ), 2.95 (s, 3H, CH ) ppm;
NMR (100 MHz, CDCl ): d 162.43, 160.21, 138.99, 53.13,
3
, 400
1
3
H
3
3
C
3
C
+
13.90 ppm. GC-MS: 158 [M ].
ACKNOWLEDGEMENTS
Financial support for this work from the Shanghai
Commission of Science and Technology (08431901800)
and the Shanghai Leading Academic Discipline Project
(B507) are gratefully acknowledged.
EXPERIMENTAL SECTION
Received December 31, 2009.
Reagents and solvents are purchased from commer-
cial resources expect 4-methyl-1,2,3-thiadiazole-5-carbox-
ylic acid, which was prepared previously in our laboratory
REFERENCES
1
. Benz, G. In Comprehensive Organic Synthesis; Trost, B. M.;
Fleming, I., Eds.; Pergamon: Oxford, UK, 1991; Vol. 6, p
323.
1
7
for pesticide research. All products are known and gave
1
spectral ( H NMR and MS) data consistent with the as-
2
. Neises, B.; Steglich, W. Org. Synth. 1985, 63, 183.
. Keck, G. E.; Sanchez, C.; Wager, C. A. Tetrahedron Lett.
1
signed structures. H NMR spectra were recorded on
3
Bruker AV 400 spectrometer in CDCl
nal standard. GC-MS data were recorded on a HP 6890-
973 apparatus.
3
with TMS as inter-
2
000, 41, 8673.
4
. (a) Crosignani, S.; Gonzalez, J.; Swinnen, D. Org. Lett.
2004, 6, 4579. (b) Convers, E.; Tye, H.; Whittaker, M. Tetra-
hedron Lett. 2004, 45, 3401.
5
Preparation of methoxyl silica gel
5
. Disadee, W.; Watanabe, T.; Ishikawa, T. Synlett 2003, 115.
. Rademann, J.; Smerdka, J.; Jung, G.; Grosche, P.; Schmid, D.
Angew. Chem. Int. Ed. 2001, 40, 381.
A stirred slurry of 20 g of well-dried fine powders of
6
silica gel (G60, ~400 mesh) in SOCl
for about 24 h in a flask charged with CaCl
The excess SOCl was removed by distillation. 20 mL of
2
(25 mL) was refluxed
2
drying tube.
7
. (a) Elson, K. E.; Jenkins, I. D.; Loughlin, W. A. Tetrahedron
Lett. 2004, 45, 2491. (b) Elson, K. E.; Jenkins, I. D.;
Loughlin, W. A. Org. Bioorg. Chem. 2004, 2, 1979.
2
anhydrous methanol was then mixed with the obtained
white powders and stirred at 0 °C for further 12 h. The solid
was collected by filtration, washed thoroughly with anhy-
drous methanol, and dried under vacuum to afford meth-
oxyl silica gel (26.6 g) as a free-flowing white powder.
Methoxyl silica gel should be stored in a desiccator.
Methyl esterification using methoxyl silica gel as de-
hydrating reagent
8. (a) Crosignani, S.; White, P. D.; Linclau, B. Org. Lett. 2002,
, 1035. (b) Crosignani, S.; White, P. D.; Linclau, B. J. Org.
4
Chem. 2004, 69, 5897.
9. Srinivas, K. V. N. S.; Mahender, I.; Das, B. Synthesis 2003,
2
479.
0. Sathe, M.; Gupta, A. K.; Kaushik, M. P. Tetrahedron Lett.
006, 47, 3107.
1. Odlyha, M.; Scott, R. P. W.; Simpson, C. F. J. Thermal Anal.
1
2
1
To a suspension of methoxyl silica gel (2.5 g, 20
mmol of MeO) in 10 mL of methanol was added 10 mmol
1993, 40, 1197.
1
2. (a) Locke, D. C.; Schmermund, J. T.; Banner, B. Anal.
Chem. 1972, 44, 90. (b) Saunders, D. H.; Barford, R. A.;
Magidman, P.; Olszewski, L. T.; Rothbart, H. L. Anal.
Chem. 1974, 46, 834.
3 40
of carboxylic acid and 0.29 g (0.1 mmol) of H PW12O .
The reaction mixture was then stirred under refluxing for
reaction times indicated in Table 1. On completion of the
reaction as monitored by TLC, the resulting mixture was
filtered and the excess methanol in filtrate was then removed
by a rotary evaporator. The crude product was purified by
column chromatography to afford the corresponding
methyl ester.
1
1
1
1
1
3. Knyzaev, V. N.; Borbulevich, O. Ya.; Shishkin, O. V. Russ.
J. Org. Chem. 2000, 36, 1634.
4. Hecht, S. M.; Kozarich, J. W. Tetrahedron Lett. 1973, 14,
1397.
5. Hirai, Y.; Aida, T.; Inoue, S. J. Am. Chem. Soc. 1989, 111,
3
062.
6. Chakraborti, A. K.; Basak, A.; Grover, V. J. Org. Chem.
999, 64, 8014.
7. Raap, R.; Micetich, R. G. Can. J. Chem. 1968, 46, 1057.
Selected characterization data
1
Methyl 4-methyl-1,2,3-thiadiazole-5-carboxylate (Ta-