9
60
ZHOU, TU, AND FENG
4
5
as chromium trioxide-silica gel and Ni(II)-complex catalyst . However,
these methods were performed in liquid phase and require stoichiometric
or excess amounts of organic solvents. In some cases, reaction time is long
6
(
12 ꢀ 94 h) and the yield obtained very low.
Microwave irradiation in organic synthesis is a useful technique.
7
Dry media using microwave heating have attracted much attention.
A number of deoximation methods has been developed in dry media under
8
microwave irradiation, such as silica supported ammonium persulfate, silica
9
10
11,12
supported sodium periodate, pyridinium chloro-chromate and clayfen.
In our laboratory, HCOOH/SiO was used as a solid support catalyst for
synthesis of nitriles in dry media under microwave irradiation.
HCOOH/SiO was also used for synthesis of amides from ketones and
hydroxylamine in dry media under microwave irradiation, but further
investigation revealed that most ketones cannot be converted to amides
under these conditions. We found that the deoximation of ketoximes using
2
1
3
2
1
4
HCOOH/SiO as solid support catalyst in dry media under microwave
2
irradiation was easy. Here we report a new and efficient method to regenerate
ketones from oximes in dry media under microwave irradiation. The reactions
are generally complete in 2–4 min with excellent yield.
The results obtained are shown in Table 1.
EXPERIMENTAL
All reagents were commercially available and used without further
1
purification. HCOOH/SiO2 was prepared from literature procedure.
4
Melting points were determined in open capillaries and uncorrected. IR
spectra were recorded on a Nicolet FT-IR 5DX instrument. The reactions
were carried out under atmospheric pressure with a modified commercial
microwave oven (Sanle WP650D 650 W). All oximes were prepared by the
standard procedures from commercially available ketones.
GENERAL PROCEDURE
Oxime (10 mmol) and HCOOH/SiO (5 g) were thoroughly mixed in a
2
flask (50 ml), connected to refluxing equipment. After irradiation by micro-
wave for 2 ꢀ 4 min (as indicated by TLC), the mixture was cooled to room
temperature, dichloromethane was added, the mixture filtered and the fil-
trate washed with water and dried with anhydrous magnesium sulfate. The
solvent was evaporated to give crude product, which was further purified by
recrystallization or distillation.