Amberlyst-15(H+)-NaBH4-LiCl: An effective reductor for oximes and hydrazones

Article abstract of DOI:10.1055/s-1999-2637

A simple and mild procedure reduces oximes and hydrazones on amberlyst 15(H⁺) support with LiCl-NaBH₄ to the corresponding amines and hydrazines respectively in high yield and purity.

Full text of DOI:10.1055/s-1999-2637

LETTER
409
+
Amberlyst-15(H )-NaBH -LiCl: An Effective Reductor for Oximes and
4
Hydrazones
Bipul Baruah, Manu P. Dutta, Anima Boruah, Dipak Prajapati, Jagir S. Sandhu*
Regional Research Laboratory, Jorhat-785006, India
Fax + 91 (376) 321158
Received 15 January 1999
Abstract: A simple and mild procedure reduces oximes and
+
hydrazones on amberlyst 15(H ) support with LiCl-NaBH to the
4
corresponding amines and hydrazines respectively in high yield and
purity.
Key words: Amberlyst, sodium borohydride, lithium chloride,
oximes, hydrazone, amines
and NaBH (25.5 mmol, 1g) were added to the reaction
4
The reduction of oximes and subsequent cleavage of the
N-O bond to afford primary amines is an important syn-
thetic operation. Literature methods involve either ex-
mixture and the stirring is continued at room temperature
for 2 hr. After completion of the reaction (monitored vide
TLC), it was filtered and the residue was washed with
ether (20ml x 2). The combined organic layer was washed
with brine solution (20ml x 2) and dried over anhydrous
sodium sulfate. The solvent was then removed on a rotary
evaporator and the residue was recrystallised from petrol-
1
pensive complex metal hydrides or sodium borohydride in
combination with a variety of transition metal salts includ-
2
3
4
4
ing TiCl , ZrCl , NiCl and MoO . But careful scrutiny
3
4
2
3
of the reaction procedures reveals some shortcomings in
most of these procedures, e.g. LiAlH can reduce oximes,
4
o
eum ether (60-80 C) to afford α-aminodiphenylmethane
but affords amines in low yields, Beckman-type rear-
in 90% yield exclusively without the formation of any ob-
5
rangement products or aziridines are obtained as side
servable Beckman reduction product (i.e.PhCH NHPh
6
2
products in some cases . Diborane reduction of oximes
from benzophenone oxime). In contrast the reaction gives
Beckman reduction product in about 10% yield together
with α-aminodiphenylmethane(75%) when carried out
with 1M solution of diborane in THF and amberlyst at am-
bient temperature. Similar treatment of other oximes (en-
try 2 - 7) gave the corresponding amines in 75-86% yields
and the results are summerised in the table. This reduction
procedure is fairly general and several functionalities in-
cluding nitro, methoxy, olefinic bond and cyclopropyl
do survive during the course of the reaction. Similarly
hydrazones were reacted and the corresponding hydra-
zines were obtained in 80-85% yields(see entries 8-10 in
the table). Attempts to perform this reduction using sodi-
um borohydride in methanol were fruitless even when a
large excess of hydride was used. Also the reaction did not
usually affords hydroxylamines. In order to obtain the
corresponding primary amines high temperature is
required . Treatment of oximes with lithium aluminium
7
hydride in HMPA does not afford the expected amine
products, but rather gives ketones from ketoximes and ni-
8
triles and/or aldehydes from aldoximes . These results are
attributed to the formation of imine intermediates which
are hydrolysed to carbonyls or undergo elimination to ni-
triles. On the other hand the catalytic hydrogenation of α-
phenyl ketoximes, such as acetophenone oxime and benz-
ophenone oxime, gave the correesponding amines, while
the reduction of alkyl and aryl aldoximes afforded N,N-
9
disubstituted hydroxylamines . Therefore, there is merit
in developing a selective reduction procedure of oximes
using inexpensive reagents. Herein we wish to report the
simple and high yielding reduction of various oximes in
+
proceed either in the absence of LiCl or amberlyst-15(H ).
But the reaction proceeds less effectively when LiBH4
+
THF to primary amines using amberlyst-15(H )-LiCl-
was used in place of LiCl and NaBH with the reduced
4
NaBH a new combination system. Although borohydride
4
product being obtained in 30% yield (entry 1). The system
1
0
exchanged-ion resin and acid-sodium borohydride
+
amberlyst-15(H )-LiCl-NaBH in THF is found to be an
1
1
4
systems have been used for the reduction of a variety of
organic functions, this is the first use of an exchanged-
acid resin in the reduction of oximes by sodium borohy-
dride in an aprotic solvent. This novel system is also
found to be effective for the reduction of a variety of hy-
drazones 1 (X = NHPh) to hydrazines 3.
exceptionally active reductor, and able to undergo this
transformation smoothly in high yield. It is also interest-
ing to note that with NiCl /NaBH , conjugated oximes af-
2
4
+
ford saturated amines, while ambarlyst-15(H ) gives
exclusively the allylic amine. All the compounds obtained
were characterised by infrared and H NMR spectroscopy
1
In a typical case, a solution of benzophenone oxime (8.5
mmol, 1.67g) in THF (40ml) containing amberlyst-15
and finally by comparision with authentic samples.
In conclusion, the present method for the reduction of
oximes and hydrazones using a novel reduction system
(10g) was stirred for 15 minutes. LiCl (25.5 mmol, 1.1g)
Synlett 1999, No. 4, 409–410 ISSN 0936-5214 © Thieme Stuttgart · New York

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10
B. Baruah et al.
LETTER
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i.e. amberlyst-15(H )-LiCl-NaBH has some advantages References and Notes
4
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(
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Synlett 1999, No. 4, 409–410 ISSN 0936-5214 © Thieme Stuttgart · New York