JOURNAL OF CHEMICAL RESEARCH 2012
RESEARCH PAPER 363
JUNE, 363–364
Synthesis of N-sulfonylimines using CeCl3 under neutral conditions
Xun Zhua,b and Yunyang Weia*
aSchool of Chemical Engineering, Nanjing University of Science andTechnology, 210094, Nanjing, P. R. China
bDepartment of Chemical Engineering, YanchengTextile VocationalTechnology College, 224005, Yancheng, P. R. China
An efficient and environmentally benign method for the synthesis of N-sulfonylimines is reported. Condensation of
aryl sulfonamides with different aromatic aldehydes and ketones gave N-sulfonylimines in good to excellent yields
in the presence of 10 mol% CeCl3 as catalyst. This method can be used with both aldehydes and ketones.
Keywords: N-sulfonylimines, aldehydes, cerium(III) chloride, condensation
N-Sulfonylimines are important precursors for the preparation
of synthetic intermediates. because they are one of the electron
deficient imines that are stable enough to be isolated but
sufficiently reactive to be useful intermediates.1 They have
been used in numerous reactions such as Diels–Alder,2 nucleo-
philic addition,3 ene,4 and radical reactions.5 In addition,
they are important precursors for the preparation of reactive
aziridines6,7 imidazolines,8 and N-sulfonyloxaziridines.9
Recently, attention has been paid to the development of
efficient methods for the preparation of N-sulfonylimines. A
number of methods for the synthesis of N-sulfonylimines have
been reported. These have involved catalysis with Lewis acid,10
titanium tetrachloride,11 tellurium,12 ruthenium,13 Montmoril-
lonite K-10,14 oxidation with m-CPBA,15 catalysis with
zeolite,16 DBU,17 Pd,18 Tf2O,19 and rearrangements of sulfinate
esters of oximes,20 imine-transfer reaction,21,22 and microwave
facilitated acid catalysis.23 However, these methods suffer from
some limitations, such as a poor scope, unsatisfactory yields,
expensive reagents and difficult scale-up. The requirements for
environmentally benign and efficient chemical processes in
recent years have led to the search for clean, high-yielding, and
economical reduction methods.
According to Table 1, aromatic aldehydes with electron-
donating groups such as the methyl group were converted to
the corresponding N-tosylaldimines in good yields (Table1,
entry 4). Substrates with electron-withdrawing groups such as
nitro, chloro and bromo had a reduced yield (Table 1, entries 1,
2, 3 and 6). 3-Phenyl-propenal also gave the desired product in
high yield ( Table 1, entry 7). When 2-furaldehyde was used,
low yield was obtained in 65% ( Table 1, entry 8).
We have also studied the reaction of sulfonamide with
ketones which were converted to the corresponding N-sulfony-
limines. In these reactions, the overall yields were not as high
as those obtained from the aldehydes ( Table 1, entries 9 and
10).
We observed that the reaction of 4-toluenesulfonamide with
aldehydes was better than the other sulfonamides, due to the
difference of nucleophilicity of the amino groups (Table 1,
entries 5, 11 and 12).
It turned out that CeCl3 catalysed condensation could be
adapted for use with various aromatic aldehydes.
In conclusion, we have developed a new procedure for the
synthesis of N-sulfonylimines of aromatic aldehydes in the
presence of catalytic amounts of 10 mol% of CeCl3 which
has less environmental impact and is an easier method. The
process is suitable for synthesis of a range of N-sulfonylimines
and is amenable to larger scale preparations.
Cerium(III) chloride has become an attractive candidate for
use as a Lewis acid in organic chemistry since it is inexpen-
sive, environmentally friendly and readily available, and
involves simple reaction conditions.24 We now describe a very
simple, general and highly efficient synthesis method for the
preparation of N-sulfonylimines in the presence of CeCl3 in
relatively high yields.
Experimental
All chemicals (AR grade) were obtained from commercial resources
and used without further purification. Gas chromatography (GC) anal-
ysis was performed on an Agilent GC-6820 chromatograph equipped
with a 30m×0.32mm×0.5µm HP-Innowax capillary column and a
flame ionisation detector. GC-MS spectra were recorded on Thermo
Trace DSQ GC-MS spectrometer using TRB-5MS (30m × 0.25mm ×
0.25µm) column. Progress of the reactions was followed by TLC
using silica-gel polygrams SIL G/UV 254 plates. Column chromato-
Results and discussion
We initially attempted to synthesise N-sulfonylimine using a
CeCl3 catalysed procedure as a new and efficient method for
the preparation of sulfonylimines. The reaction of the benzal-
dehyde with 4-toluenesulfonamide was chosen as a model.
Our catalytic system consisted of commercially available
metallic salts. Among the different salt precursors tested, the
best result was achieved when the reaction was performed in
presence of 10 mol% CeCl3. GC showed that the yield obtained
was 93%. Interestingly, the conversion was 81% when
CeCl3.7H2O was used, which shows the Lewis acid ability of
CeCl3 was far better. Control experiments in the absence of
CeCl3 showed that the reaction of benzaldehyde and 4-toluene-
sulfonamide did not occur. In general, the optimised condi-
tions for the synthesis of N-tosylaldimines were 1 equiv. of
aldehyde and 1 equiv. of N-tosylamide in the presence of
10 mol% of CeCl3 in ethyl acetate at 50 °C for 6h.
1
graphy was performed using Silicycle (0.2–0.3mm) silica gel. H
NMR spectra were obtained using a Bruker DRX 500 (500 MHz)
spectrometer in CDCl3 with TMS as the internal standard. All prod-
ucts are known. Products were also identified by melting point which
were determined using XT-4 apparatus and are not corrected.
General procedure: 4-Toluenesulfonamide (1 mmol) and benzalde-
hyde (1 mmol) in ethyl acetate (5 mL) and CeCl3 (0.0246 g, 0.1 mmol)
was then added and the mixture was stirred at 50 °C for 6h. The aque-
ous solution was extracted with ethyl acetate (3×10 mL) and the prod-
uct was purified on a small silica gel column with EtOAc: petroleum
ether (1:10) as eluent.
We are grateful to Nanjing University of Science and Technol-
ogy and Yancheng Textile Vocational Technology College for
financial support.
A variety of aldehydes and N-sulfonylamides were tested
under the optimised conditions using 10 mol% CeCl3 as cata-
lyst (Table 1). In general, all the reactions were successful.
Received 14 February 2012; accepted 31 March 2012
Paper 1201164 doi: 10.3184/174751912X13360669852266
Published online: 4 June 2012
* Correspondent. E-mail: ywei@mail.njust.edu.cn
Zhu, Xun
