A Solvent-Free Procedure for Synthesis of N-Sulfonylimines Using Microwave Irradiation Catalyzed by ZrO2/S2O2- 8 Solid Superacid

Article abstract of DOI:10.1081/SCC-120030315

A solvent-free synthesis of N-sulfonylimines from aldehydes with sulfonamides is described using ZrO₂/S₂O^2- ₈ as catalyst under microwave irradiation. This method is fast and high yielding for a range of substrates.

Full text of DOI:10.1081/SCC-120030315

SYNTHETIC COMMUNICATIONSw
Vol. 34, No. 7, pp. 1277–1283, 2004
A Solvent-Free Procedure for Synthesis of
N-Sulfonylimines Using Microwave
Irradiation Catalyzed by ZrO2/S2O822
Solid Superacid
*
Tongshou Jin, Guoliang Feng, Mina Yang, and
Tongshuang Li
Department of Chemistry, College of Chemistry and Environmental
Science, Hebei University, Baoding, P.R. China
ABSTRACT
A solvent-free synthesis of N-sulfonylimines from aldehydes with sulfo-
namides is described using ZrO2/S2O282 as catalyst under microwave
irradiation. This method is fast and high yielding for a range of substrates.
Key Words: N-Sulfonylimines; Microwave irradiation; Solvent-free
method; Sulfonamides.
*
Correspondence: Tongshou Jin, Department of Chemistry, College of Chemistry and
Environmental Science, Hebei University, Baoding 071002, P.R. China; E-mail:
orgsyn@mail.hbu.edu.cn.
1277
DOI: 10.1081/SCC-120030315
0039-7911 (Print); 1532-2432 (Online)
www.dekker.com
Copyright # 2004 by Marcel Dekker, Inc.

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INTRODUCTION
N-Sulfonylimines are powerful synthetic intermediates[1,2] in organic
synthesis and industrial application. They are used in numerous reactions
such as inverse electron-demand Diels–Alder reactions,[3,4] addition reactions
as carbonyl equivalents,[5] and in ene reactions.[6] Several synthetic methods for
the preparation of N-sulfonylimines have been found in the literature.[7–14]
Some of the reported methods suffer from drawbacks like long reaction
times, unsatisfactory yields, expensive and hazardous reagents, and cumber-
some experimental.
Recently, microwave irradiation in organic synthesis is a useful technique.
Dry method using microwave heating have attracted much more attention[15–17]
because avoiding organic solvents during the reactions leads to clean, efficient,
and economical technology. Solid superacid has been used as efficient catalyst
for a variety of organic reaction. Recently, we have developed easy and
efficient procedures for preparation of some organic products catalyzed by
ZrO2/SO422 [18,19]
in continuation of our interest on solid superacid catalysts.
,
Herein, we now describe a facile and solvent-free method for the synthesis
of N-sulfonylimines from aldehydes with sulfonamides catalyzed by ZrO2/
S2O282 solid superacid under microwave irradiation (Sch. 1).
Some of results that we have obtained for the preparation of N-sulfonylimines
are summarized in Table 1. We were pleased to find that aromatic
and aliphatic aldehydes in the presence of ZrO2/S2O282 were irradiated
with sulfonamide in microwave, the corresponding N-sulfonylimines were
obtained in good yield. The reaction proceeds cleanly and work-up is simple,
involving only filtration of the catalyst and removing of solvent to obtain
the product in high purity.
It should be noted that the efficacy of this dry synthetic method was evalu-
ated by comparison with the same reaction in refluxing toluene, for example
the later method required 70min for complete conversion of p-tolualdehyde
with p-CH3C6H4SO2NH2. We investigated the effect of ZrO2/S2O282 under
microwave irradiation and found that in the absence of catalyst lower product
was observed even with prolonged irradiating reaction time. For example, entry
3 without catalyst after 15 min only 60% yield of product was obtained, whereas
94% yield was obtained with catalyst for 3 min in microwave irradiation.
Scheme 1.

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Mention must be made here that the conversion rate of p-toluenesulfonamide
with aldehydes was a little higher than benzene sulfonamide and that the alde-
hydes with electron-withdrawing group (1k–1n) need longer reaction time
than the aldehydes with donate group (1c–1h, 1p, and 1q), this indicates that
electron-donating groups have increased the reaction speed as well as reaction
yields. On the other hand electron-withdrawing groups have decreased yields
and increased reaction time. We had studied the reaction of sulfonamide
with ketones and found that the yield was lower than the reaction of
sulfonamide with aldehydes. For example, the yield of acetophenone treated
with p-CH3C6H4SO2NH2 was 46% after irradiation 20 min and there was no
product for the reaction of diphenyl ketone with p-CH3C6H4SO2NH2.
In conclusion, we have described a novel and rapid procedure for the
synthesis of various N-sulfonylimine using ZrO2/S2O282 under microwave
irradiation in solvent-free conditions. This method possesses these advantages
of easy work-up, short reaction time, solvent-free reaction conditions, non-
polluting, and high yields.
EXPERIMENTAL
Melting points were determined with a digital electrothermal apparatus
1
without further correction. H NMR spectra were determinded on a Varian
VXP-400s spectrometer using CDCl3 as solvent and tetramethylsilane
(TMS) as internal reference. The products were also characterized by com-
parison of their melting point with literature values. The catalyst ZrO2/
S2O282 solid superacid was prepared as follows. Zr(OH)4 was immerged in
(NH4)2S2O8 liquor (1 mol/L) for 4 hr and the filtered off was dehydrated at
1108C for 2 hr, smashed over 150 mesh, dried calcined in furnace at 6008C
for 4 hr, and finally stored in a desiccator until use.
General Procedure for the Preparation of N-Sulfonylimines
A mixture of aldehyde (2.00mmol), sulfonamide (2.00 mmol), and ZrO2/
S2O282 (150mg) was well ground with a pestle and introduced to microwave
irradiation at 650 W in an open Pyrex beaker for the length of time indicated
in Table 1. The reaction was monitored by TLC. After completion of the reac-
tion, the reaction mixture was cooled to room temperature and mixed thoroughly
with ethylacetate (10 mL). ZrO2/S2O282 was filtered off with ethylacetate
washing. The solvent was evaporated under reduced pressure to afford the
residue which was recrystallized from hexane–ethyl acetate mixtures or chro-
matographed on silica gel (Et2O–hexane as eluent) to give the pure product.

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Scheme 2.
1H NMR (400MHz, CDCl3) data of some of the products are given below:
The number of carbon atom in aryl like Sch. 2.
3a: dH 9.03 (1H, s, HC55N), 7.92 (2H, d, J ¼ 7.6 Hz, 20,60-ArH), 7.89 (2H,
d, J ¼ 8.0 Hz, 2,6-SO2ArH), 7.60 (1H, t, J ¼ 7.6 Hz, 4-ArH), 7.48 (2H, t,
J ¼ 7.6 Hz, 30,50-ArH), 7.34 (2H, d, J ¼ 8.0 Hz, 3,5-SO2ArH), 2.43 (3H, s, CH3).
3c: dH 9.00 (1H, s, HC55N), 7.90 (2H, d, J ¼ 8.0 Hz, 2,6-SO2ArH), 7.83
(2H, d, J ¼ 7.6 Hz, 20,60-ArH), 7.35 (2H, d, J ¼ 8.0 Hz, 3,5-SO2ArH), 7.30
(2H, d, J ¼ 7.6 Hz, 30,50-ArH), 2.45 (6H, s, CH3).
3d: dH 9.04 (1H, s, HC55N), 8.02 (2H, d, J ¼ 7.6 Hz, 2,6-SO2ArH), 7.84
(2H, d, J ¼ 8.0 Hz, 20,60-ArH), 7.65 (1H, t, J ¼ 7.6 Hz, and J ¼ 7.6 Hz,
4-SO2ArH), 7.57 (2H, t, J ¼ 7.6 Hz and J ¼ 7.6 Hz, 3,5-SO2ArH), 7.31
(2H, d, J ¼ 8.0 Hz, 30,50-ArH), 2.45 (3H, s, CH3).
3e: dH 8.95 (1H, s, HC55N), 7.91 (2H, d, J ¼ 8.0 Hz, 2,6-SO2ArH), 7.88
(2H, d, J ¼ 7.6 Hz, 20,60-ArH), 7.34 (2H, d, J ¼ 8.0 Hz, 3,5-SO2ArH), 6.98
(2H, d, J ¼ 7.6 Hz, 30,50-ArH), 3.92 (3H, s, OCH3), 2.45 (3H, s, CH3).
3f: dH 8.98 (1H, s, HC55N), 8.01 (2H, d, J ¼ 7.6 Hz, 2,6-SO2ArH), 7.91
(2H, d, J ¼ 8.8 Hz, 20,60-ArH), 7.63 (1H, t, J ¼ 7.2 Hz and J ¼ 7.2 Hz,
4-SO2ArH), 7.55 (2H, dd, J ¼ 7.6 Hz and J ¼ 7.2 Hz, 3,5-SO2ArH), 6.98
(2H, d, J ¼ 8.8 Hz, 30,50-ArH), 3.93 (3H, s, OCH3).
3g: dH 10.84 (1H, s, –OH), 9.10 (1H, s, HC55N), 7.87 (2H, d, J ¼ 8.0 Hz,
2,6-SO2ArH), 7.52 (2H, m, 40,60-ArH), 7.36 (2H, d, J ¼ 8.0 Hz, 3,5-SO2ArH),
7.01 (2H, m, 30,50-ArH), 2.45 (3H, s, CH3).
3h: dH 10.83 (1H, s, –OH), 9.14 (1H, s, HC55N), 8.01 (2H, d, J ¼ 8.0 Hz,
2,6-SO2ArH), 7.68 (1H, t, J ¼ 8.0 Hz, 4-SO2ArH), 7.59 (2H, m, 40,60-ArH),
7.54 (2H, dd, J ¼ 8.0 Hz and J ¼ 8.0 Hz, 3,5-SO2ArH), 7.03 (2H, m, 30,50-ArH).
3j: dH 8.83 (1H, d, J ¼ 9.2 Hz, HC55N), 8.00 (2H, d, J ¼ 7.2 Hz,
2,6-SO2ArH), 7.65 (1H, d, J ¼ 14.8 Hz, PhCH55), 7.57 (5H, m, 20,60-ArH),
7.47 (3H, m, 3,5-SO2ArH), 7.02 (1H, dd, J ¼ 14.8 Hz and J ¼ 9.2 Hz,
HC55CHN).
3k: dH 9.01 (1H, s, HC55N), 7.90 (2H, d, J ¼ 7.6 Hz, 2,6-SO2ArH), 7.87
(2H, d, J ¼ 8.0 Hz, 20,60-ArH), 7.48 (2H, d, J ¼ 8.0 Hz, 30,50-ArH), 7.37 (2H,
d, J ¼ 7.6 Hz, 3,5-SO2ArH), 2.46 (3H, s, CH3).
3m: dH 9.44 (1H, s, HC55N), 8.12 (1H, d, J ¼ 8.4 Hz, 60-ArH), 7.91 (2H,
d, J ¼ 8.0 Hz, 2,6-SO2ArH), 7.51 (1H, s, 30-ArH), 7.38 (2H, d, J ¼ 8.0 Hz,
3,5-SO2ArH), 7.34 (1H, d, J ¼ 8.4 Hz, 50-ArH), 2.47 (3H, s, CH3).

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ACKNOWLEDGMENT
The project was supported by National Natural Science Foundation of
China (29872011 and 29572039), Educational Ministry of China, Educational
Department of Hebei Province (990104), Science and Technology Commis-
sion of Hebei province.
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Received in Japan August 18, 2003

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