1658
A. K. Gupta et al. / Tetrahedron Letters 49 (2008) 1656–1659
Table 1 (continued)
Entry Substrate
a
b
31
c
Product
Bp/mmHg
122–124/1
Yield (%)
Reaction time (min)
P NMR (ppm)
O
P
O
OH
OC H
3
7
1
3
4
C3H7i
C3H7i
81
55
38.23
39.82
P
OH
OH
OH
n
O
P
O
P
O C H
4
9
1
C3H7i
C3H7i
Oil
Oil
87
88
60
70
OH
OH
OH
O
P
O
P
OC H
5
11
15
C3H7i
C3H7i
41.68
OH
OH
a
b
c
Isolated yield.
Reactions in entries 4, 5, 8, 9, and 15 were performed at 50–60 °C.
31
3
P NMR spectra were recorded in CD OD at 162 MHz.
products were obtained in short reaction times (30–
0 min), Table 1. The structures of the monoesters were
References and notes
6
1
31
1
. (a) Sikorski, J. A.; Logusch, E. W. Aliphatic Carbon–phosphorus
Compounds as Herbicides. In Handbook of Organophosphorus
Chemistry; Engel, R., Ed.; Marcel Dekker: New York, 1992; p 739;
confirmed by their spectral data ( H NMR, P NMR,
2
0
and MS). To find an effective combination of the solid
support with condensing agent, various reactions were per-
formed using a variety of reagents such as alumina (acidic,
basic, and neutral), silica, clay (Symctone, Montmorillo-
nite, and KSF), Kieselgel, ZnO–SiO , H PO –Silica,
(
b) Eto, M. Phosphorus-containing Insecticides. In Handbook of
Organophosphorus Chemistry; Engel, R., Ed.; Marcel Dekker: New
York, 1992; p 807; (c) Hinkle, P. C.; McCarty, R. E. Sci. Am. 1978,
2
38, 104.
2
3
3
2
. (a) Eto, M. Organophosphorus Pesticides. In Organic and Biological
Chemistry; CRC Press: Ohio, USA, 1974; p 18; (b) Van Wazer John,
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Hildebrand, R. The Role of Phosphonates in Living Systems; CRC
Press: Boca Raton, 1983.
P O –Celite, p-TsOH, TiCl , and DCC–Celite. The best
2
5
4
results were obtained with DCC–Celite.
To optimize further the reaction conditions with DCC–
Celite, reactions were carried out using different mole ratios
and amounts of the solid support. The maximum yield of
the alkyl hydrogen alkylphosphonate was obtained when
the reactions were carried out using 1:1:2 molar ratios
of the alkyl phosphonic acid, the alcohol, and DCC–Celite,
respectively. The process involves mixing the alkylphos-
phonic acid and the alcohol in the presence of the immobil-
ized DCC–Celite in a mortar and grinding the mixture at
room temperature for 30–60 min, Table 1. The method
was found to be fast with purification of the products
achieved simply by washing the reaction mixture with
ether. In most cases, the isolated products required no fur-
ther purification.
Mono-esterification with alicyclic and primary alcohols
was complete within 30–45 min, while secondary alcohols
took longer (45–60 min). Tertiary alcohols did not react
with the alkyl phosphonic acids under these conditions.
The advantages of using DCC–Celite are that it is com-
mercially available and the only by-product dicyclohexyl-
urea is removed by filtration. To summarize, we have
described a general and efficient procedure for the rapid
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3
4
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7
8
. (a) Norlin, R.; Juhlin, L.; Lind, P.; Trogen, L. Synthesis 2005, 1765;
(
4
b) Cherbuliez, E.; Weber, G.; Rabinowitz, J. Helv. Chim. Acta 1963,
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Acknowledgment
We thank Dr. R. Vijayaraghavan, Director DRDE,
Gwalior, for his keen interest and encouragement.
1
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