S. Rostamizadeh, S. A. G. Housaini / Tetrahedron Letters 45 (2004) 8753–8756
8755
20. (a) Chiba, T.; Okimoto, M. J. Org. Chem. 1992, 57, 1375;
(b) Yang, R.; Dai, L. J. Org. Chem. 1993, 58, 3381.
21. Reddy, P. S. N.; Reddy, P. R. Indian J. Chem. 1987, 26B,
890.
22. (a) Tandon, V. K.; Chhor, R. B. Synth. Commun. 2001, 31,
1727; (b) Mashraqui, S. H.; Ghadigaonkar, Sh. G.;
Kenny, R. S. Synth. Commun. 2003, 33, 2541.
As indicated in Table 4, the reaction time is shortened
in this solvent under microwave irradiation and also
in comparison to solvent-free conditions (Table 3).
The higher yields in a solvent, are due to an easier
work-up.
In conclusion, we have developed an efficient method for
the synthesis of 1,3,4-oxadiazoles on the surface of
montmorillonite K10 and in a mixture of acetone/water
under microwave irradiation. The reaction was more
efficient in the solvent.
23. Bentiss, F.; Lagrenee, M.; Barbry, D. Synth. Commun.
2001, 31, 935.
24. Brown, B. J.; Clemens, I. R.; Neesom, J. K. Synlett 2000,
131.
25. Brain, C. T.; Brunton, Sh. A. Synlett 2001, 382.
26. (a) Brain, C. T.; Paul, J. M.; Loong, Y.; Oakley, P. J.
Tetrahedron Lett. 1999, 40, 3275; (b) Wipf, P.; Venkatr-
aman, S. Tetrahedron Lett. 1996, 37, 4659.
27. Microwave irradiation was carried out using a commercial
Moulinex AET 5 microwave oven.
Acknowledgements
The authors gratefully acknowledge Dr. S. Balalaie for
helpful consultations.
28. (a) Generalprocedure for the synthesis of 1-aroy-2l -
arylidene hydrazines on the surface of silica gel: a mixture
of the acid hydrazide (6mmol), aldehyde (6mmol), and
silica gel (12g) was thoroughly ground in a mortar with
addition of three drops of phosphoric acid. The mixture
was then subjected to microwave irradiation in an open
Pyrex beaker for the appropriate time and power (Table
2). After complete conversion as indicated by TLC, the
mixture was extracted with ethylacetate (5 · 40mL),
washed with saturated sodium bicarbonate solution, and
then water (3 · 50mL). The ethylacetate alyer was dried
over MgSO4 and evaporated in vacuo. The precipitated
solids were crystallized from ethanol; (b) General proce-
dure for the synthesis of 1-aroyl-2-arylidene hydrazines in
ethanol: a mixture of the acid hydrazide (6mmol) and
aldehyde (6mmol) was dissolved in ethanol (25mL). Then,
three drops of phosphoric acid was added and the mixture
placed in a Teflon vessel. The mixture was then subjected
to microwave irradiation at 150W. After complete con-
version as indicated by TLC, the reaction mixture was
cooled and the precipitated solids were filtered off. All the
products were then recrystallized from ethanol.
References and notes
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29. All the 1,3,4-oxadiazoles prepared are known compounds
and were characterized by comparison of their spectral
and physicaldata with those of known sampels.
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30. (a) Generalprocedure for the synthesis of 2,5-disubsti-
tuted 1,3,4-oxadiazoles (on the surface of silica gel): a
mixture of 1-aroyl-2-arylidene hydrazines (3mmol), potas-
sium permanganate (15mmol), and silica gel (10g) was
thoroughly ground in a mortar. The mixture was then
subjected to microwave irradiation in an open Pyrex
beaker for the appropriate time at 350W (Table 2). After
complete conversion as indicated by TLC, the mixture was
extracted with chloroform and the products were identi-
fied by comparison with known samples. The same
procedure was used in the case of other solid supports;
(b) Generalprocedure for the synthesis of 2,5-disubsti-
tuted 1,3,4-oxadiazoles (in solvent): a mixture of 1-aroyl-
2-arylidene hydrazines (3mmol) and potassium perman-
ganate (9mmol) was dissolved in a mixtures of acetone/
water (20/5), and then transferred to a Teflon vessel. The
mixture was then subjected to irradiation at 150W. After
complete conversion as indicated by TLC, the solvent was
removed in vacuo and the aqueous residue was extracted
with chloroform (5 · 40mL), washed with water
(3 · 50mL), and dried over MgSO4. The solvent was
evaporated in vacuo and the precipitated solids were
recrystallized directly from an appropriate solvent.
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