1196
Chemistry Letters 2000
Indium-Mediated Facile Dehydration and Beckmann Rearrangement of Oximes
Dhiren C. Barman, Ashim J. Thakur, Dipak Prajapati, and Jagir S. Sandhu*
Regional Research Laboratory, Jorhat 785006, Assam, India
(Received July 18, 2000; CL-000682)
Indium chloride has been developed as an efficient reagent
for the conversion of aldoximes to nitriles and the Beckmann
rearrangement of ketoximes to anilides.
(monitored vide tlc) the solvent was removed and the residue
was treated with dichloromethane, washed with water (15 mL)
and the organic layer was dried over anhydrous sodium sulfate.
Removal of solvent under reduced pressure gave the correspon-
ding benzonitrile in 98% yield. Similarly substituted arylal-
doximes and aliphatic oximes afforded corresponding nitriles
(entries 2–11) in high yields (Table 1). When benzophenone
oxime reacted with indium chloride under the same reaction
conditions in dry acetonitrile, interestingly the Beckmann
rearrangement occurred within 15 min to give the correspon-
ding benzanilide (entry 12) in 95% yield (Scheme 2).
Acetophenone oxime (entry 14) also reacted with InCl3 to
The synthesis of nitriles from aldoximes is an important
functional group transformation in organic synthesis.1 In recent
reports, it was demonstrated that nitriles could be converted to
thiazole derivatives as inhibitors of superoxide,2 condensed
with β-amino alcohol in the presence of catalyst to give new
chiral 2-oxazolines as FLC dopants3 or used as a starting mate-
rial for synthesizing triazolo[1,5-c]pyrimidines with potential
antiasthma activity.4 Numerous methods have been developed
for the conversion of aldoximes into nitriles such as 4,6-
diphenyl-2-methylthiopyrylium tetrafluoroborate, phenyl
chlorosulfite, sulfuryl chloride fluoride, chlorosulfonyl iso-
cyanate, trifluoroacetic anhydride, triflic anhydride, iodotri-
ethoxy phosphoranes, cyanuric chloride, trichloroacetyl chlo-
ride,5 2,4-dinitrophenylhydroxylamine6 (expensive), hydroxyl-
amine o-sulfonic acid,7 aluminum iodide,8 selenium dioxide9
(hazardous) or formic acid10 (corrosive) reagents. Also very
recently peroxymonosulfate on alumina,11 carbomethoxy N,N-
dimethylhydrazonium salts12 and phthalic anhydride13 have
been reported. Some of these methods require the use of
strong bases, acids, or oxidizing agents and may thus lead to
the formation of side products. Further, the practical applica-
tion of these methods in organic synthesis may suffer from dis-
advantages such as the use of expensive or less easily available
reagents, vigorous reaction conditions prolonged standing or
heating at moderately high temperatures, tedious manipulations
in the isolation of the pure products, and limited adaptability
both to aryl and alkyl substitution of aldoximes. Consequently
there is a need for the development of protocol using readily
available and safer reagents which lead to high yields of nitrile
compounds. The difficulties associated with these reagents can
be overcome by the use of indium chloride as a dehydrating
agent. In continuation to our studies on indium metals14 we
report herein the novel utility of indium15 chloride as an effi-
cient reagent for the conversion of aldoximes to nitriles and the
Beckmann rearrangement of ketoximes to anilides. The method
is applicable to aliphatic, aromatic, and heterocyclic aldoximes.
In a typical case, benzaldoxime (0.12 g, 1 mmol, R=Ph)
was taken in dry acetonitrile (10 mL) and stirred for 2 min to
dissolve the aldoxime. Then catalytic amount of anhydrous
indium chloride (0.13 mmol 0.03 g) was added to it and the
resulting mixture was refluxed for 1.5 h. After completion
Copyright © 2000 The Chemical Society of Japan
Barman, Dhiren C.
