Cyanuric chloride-catalyzed synthesis of N-sulfonyl imines

Article abstract of DOI:10.1080/17415993.2010.521940

Cyanuric chloride is an inexpensive, efficient, and mild catalyst for the synthesis of N-sulfonyl imines by the reaction of sulfonamides with aryl aldehydes at 110°C under solvent-free conditions. This method affords the N-sulfonyl imines in short reactio

Full text of DOI:10.1080/17415993.2010.521940

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Cyanuric chloride-catalyzed synthesis
of N-sulfonyl imines
Liqiang Wu a , Xiaojuan Yang b , Xiao Wang a & Fulin Yan a
a School of Pharmacy, Xinxiang Medical University, Xinxiang,
Henan, 453003, People's Republic of China
b College of Chemistry and Chemical Engineering, Xinxiang
University, Xinxiang, Henan, 453003, People's Republic of China
Published online: 22 Oct 2010.
To cite this article: Liqiang Wu , Xiaojuan Yang , Xiao Wang & Fulin Yan (2010): Cyanuric chloride-
catalyzed synthesis of N-sulfonyl imines, Journal of Sulfur Chemistry, 31:6, 509-513
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Journal of Sulfur Chemistry
Vol. 31, No. 6, December 2010, 509–513
Cyanuric chloride-catalyzed synthesis of N-sulfonyl imines
Liqiang Wua*, Xiaojuan Yangb, Xiao Wanga and Fulin Yana
aSchool of Pharmacy, Xinxiang Medical University, Xinxiang, Henan 453003, People’s Republic of China;
bCollege of Chemistry and Chemical Engineering, Xinxiang University, Xinxiang, Henan 453003,
People’s Republic of China
(Received 19 July 2010; final version received 4 September 2010)
Cyanuric chloride is an inexpensive, efficient, and mild catalyst for the synthesis of N-sulfonyl imines
by the reaction of sulfonamides with aryl aldehydes at 110 ◦C under solvent-free conditions. This method
affords the N-sulfonyl imines in short reaction times, under solvent-free conditions, and in high yields.
Keywords: N-sulfonyl imines; sulfonamides; cyanuric chloride; solvent-free; synthesis
1. Introduction
N-Sulfonyl imines are versatile synthetic intermediates in organic synthesis (1, 2). They are used
in numerous reactions such as inverse electron-demand Diels–Alder reactions (3–5), in addition
reactions as carbonyl equivalents (6), and in ene reactions (7, 8). There are several methods avail-
able for the preparation of N-sulfonyl imines including the rearrangement of oxime O-sulfinates
(9), Lewis acid- or solid acid-catalyzed reactions of sulfonamides with aldehydes or acetals
(10–21), utilization of tellurium metal and chloramines T (22), halogen-mediated conversion of
N-(trimethylsilyl) imines in the presence of the corresponding sulfonyl chloride (23), or two-step
synthesis using sulfamic acid (24). However, many of the methods utilizing these reagents suffer
from various drawbacks such as long reaction times, unsatisfactory yields, expensive and haz-
ardous reagents, and cumbersome experimental conditions. Therefore, it seems highly desirable
to find a simple and efficient protocol for synthesis of N-sulfonyl imines.
Cyanuric chloride (TCT, Figure 1), an inexpensive, easily available reagent of low toxicity and
less corrosiveness than other similar reactants, has been widely used in organic reactions (25–28),
but it has not been carefully studied as a catalyst in the synthesis of N-sulfonyl imines until now.
In continuation of our work to bring in and develop some new synthetic methodologies (29–31),
we report that a new and simple TCT-promoted synthesis of N-sulfonyl imines by the reaction of
sulfonamides with aryl aldehydes under mild conditions (Scheme 1).
*Corresponding author. Email: wliq870@163.com
ISSN 1741-5993 print/ISSN 1741-6000 online
© 2010 Taylor & Francis
DOI: 10.1080/17415993.2010.521940
http://www.informaworld.com

510 L. Wu et al.
Cl
N
Cl
N
N
Cl
Figure 1. Structure of cyanuric chloride.
O
O
TCT
neat, 110°C
R2CHO
R1
S NH2
O
R1
S N
O
+
R2
1
3
2
Scheme 1. Cyanuric chloride-catalyzed synthesis of N-sulfonyl imines.
2. Results and discussion
In order to optimize the reaction conditions, we first examined the amount of catalyst and the
reaction temperature, the reaction of benzenesulfonamide with benzaldehyde to the corresponding
(E)-N-benzylidenebenzenesulfonamide was studied under solvent-free conditions in the presence
of TCT at different temperatures. The results are summarized in Table 1. As shown in Table 1,
the reaction using 15 mmol% TCT at 110 ◦C proceeded in highest yield.
With these results in hand, we turned our attention to the scope of the aromatic aldehydes in the
reaction. The results are summarized in Table 2.Aromatic aldehydes containing electron-donating
as well as electron-withdrawing groups smoothly underwent the conversion. The reaction pro-
ceeded at 110 ◦C within 3.5 h in excellent yields after the addition of the catalyst TCT (15 mol%)
(Table 2). The structures of the products were established from their spectral properties (IR,
1H-NMR, and elemental analysis) and also by comparison with the available literature data.
The plausible mechanism of the reaction is shown in Scheme 2. The adventitious moisture
reacts with TCT to release 3 mol of HCl and cyanuric acid (removable by water washing) as a
Table 1. Synthesis of (E)-N-benzylidenebenzenesulfonamide under various conditions.a
Entry
TCT (mol%)
Temperature (◦C)
Time (h)
Yield (%)b
1
2
3
4
5
6
7
8
9
10
11
12
13
14
0
5
110
110
100
110
rt
6
3
3
3
6
6
4
2
2
2
2
2
2
2
12
61
74
79
49
62
71
89
93
92
90
88
90
87
10
10
15
15
15
15
15
15
15
20
20
25
50
90
100
110
120
130
100
110
110
Notes: aReaction conditions: benzenesulfonamide (1 mmol); benzaldehyde (1 mmol); neat. bIsolated yield.

Journal of Sulfur Chemistry 511
Table 2. Preparation of N-sulfonyl imines catalyzed by TCT.a
Entry
R1
R2
Time (h)
Product
Melting point (literature)
Yield (%)b
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
H
H
H
H
H
H
H
H
H
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
C6H5
4-Cl-C6H4
2
2.5
2.5
2.5
3
4a
4b
4c
4d
4e
4f
4g
4h
4i
4j
4k
4l
4m
4n
4o
4p
4q
4r
4s
75–77 (77–78) (17)
132–133 (131–133) (20)
204–205 (206–208) (17)
132–133 (130–132) (17)
112–114 (114–116) (20)
115–116 (113–114) (15)
162–164 (161–163) (17)
121–124
121–122 (123–124) (17)
109–110 (108–109) (17)
169–170 (171–173) (17)
125–126 (127–129) (20)
113–115 (112–114) (17)
159–160 (163–164) (20)
128–130 (128–129) (17)
122–123 (124–126) (17)
118–120
90
86
88
82
85
79
75
82
86
92
88
84
82
80
88
76
82
89
92
80
4-Br-C6H4
4-MeO-C6H4
4-Me-C6H4
3-NO2-C6H4
4-NO2-C6H4
2-F-C6H4
2,4-Cl2-C6H3
C6H5
4-Cl-C6H4
4-MeO-C6H4
4-Me-C6H4
4-NO2-C6H4
2-Cl-C6H4
2,5-MeO-C6H3
2,4-Br-C6H3
2-Furyl
3
3.5
2.5
2
2
2
2
2
2.5
3
3.5
3.5
3
99–100 (100–101) (17)
124–126 (127–129) (17)
138–139 (136–137) (20)
3-Thiophenyl
CH3(CH2)5CH2
3
2.5
4t
Notes: aReaction conditions: sulfonamide (1 mmol); aldehyde (1 mmol); TCT (0.15 mmol); 110 ◦C; neat. bIsolated yield.
H
N
H
N
Cl
N
OH
O
N
Cl
H2O
N
N
N
N
+ 3HCl
OH
Cl
Cl
HO
N
Cl
Cl
Scheme 2. Proposed reaction pathway.
by-product. The in situ-generated HCl acts as a protic acid to activate the carbonyl oxygen to
form the N-sulfonyl imines.
To recognize the capability of the present method in comparison with the reported methods
for the preparation of N-sulfonyl imines from sulfonamides and aldehydes, the model reaction
between benzenesulfonamide with benzaldehyde is described (Table 3). The results show that this
method is superior to some previously reported methods in terms of yields and reaction times.
Table 3. Effect of catalyst on the reaction of benzenesulfonamide with benzaldehyde.
Entry
Reagent and conditions
Time (min)
Yield (%)
Reference
1
2
3
4
5
6
7
8
9
Silica chloride, solvent-free, 120 ◦C
Si(OEt)4, 160 ◦C
CaCO3, K10 Clay, CH(OMe)3, microwave
TiCl4, NEt3, 0 ◦C, CH2Cl2
P2O5/SiO2, solvent-free, 110 ◦C
ZrO2, S2O82−, microwave
180
360
6
25
120
9
8
240
120
75
68
69
58
88
89
87
90
90
(10)
(11)
(12)
(13)
(14)
(20)
(15)
(16)
This work
MgO, solvent-free, microwave
ZnO, solvent-free, 110 ◦C
TCT, solvent-free, 110 ◦C

512 L. Wu et al.
3. Conclusion
In summary, a new catalytic protocol to synthesize N-sulfonyl imines has been developed.
Compared with previous reported methodologies, the present protocol features simple work-up,
easy and quick isolation of the products, cheap and a catalytic amount of catalyst. This protocol
avoids the use of hazardous solvent and toxic metallic catalysts and is of low cost.
4. Experimental
4.1. General
IR Spectra were determined on FTS-40 infrared spectrometer; NMR spectra were recorded on a
Bruker AV-400 spectrometer at room temperature using TMS as an internal standard. Coupling
constants (J) were measured in hertz; elemental analyses were performed by aVario-III elemental
analyzer; and melting points were determined on a XT-4 binocular microscope and were uncor-
rected. Commercially available reagents were used throughout without further purification unless
otherwise stated.
4.2. General procedure for the preparation of N-sulfonyl imines
A mixture of the aldehyde (1 mmol), sulfonamide (1 mmol), and TCT (0.15 mmol) was stirred at
110 ◦C for appropriate time (Table 2). Completion of the reaction was monitored by thin layer
chromatography. The material was cooled to 25 ◦C, and, after addition of water, the mixture was
stirred for 5 min. The solid so obtained was filtered off and recrystallized from hexane–ethyl
acetate mixture. The structure of the products was confirmed by NMR, IR, and comparison with
authentic samples obtained commercially or prepared by reported methods. The spectral data of
some new N-sulfonyl imines are given below.
(E)-N-(2-Fluoro-benzylidene)benzenesulfonamide (4h): White crystals, IR (KBr): v 1648
(C = N), 1325 (S = O) cm−1
;
1H NMR (CDCl3, 400 MHz) δ 9.41 (s, 1H), 8.08 (d, 1H,
J = 8.0 Hz), 7.91 (d, 2H, J = 8.4 Hz), 7.60–7.48 (m, 3H), 7.35 (t, 2H, J = 7.6 Hz), 7.22 (t,
1H, J = 7.6 Hz); Anal. calcd for C13H10FNO2S: C 59.30, H 3.83, N 5.32, S 12.18; found: C
59.42, H 3.90, N 5.26, S 12.09.
(E)-N-(2,4-Dibromobenzylidene)-4-methylbenzenesulfonamide (4q): White crystals, IR
1
(KBr): v 1652 (C = N), 1312 (S = O) cm−1; H NMR (CDCl3, 400 MHz) δ 9.42 (s, 1H), 8.10
(d, 1H, J = 8.44 Hz), 7.89 (d, 1H, J = 8.0 Hz), 7.46 (s, 1H), 7.40 (d, 2H, J = 8.4 Hz), 7.31 (d,
2H, J = 8.0 Hz), 2.44 (s, 3H); Anal. calcd for C14H11Br2NO2S: C 40.31, H 2.66, N 3.36, S 7.69;
found: C 40.26, H 2.49, N 3.41, S 7.72.
Acknowledgement
We are pleased to acknowledge the financial support from Xinxiang Medical University.
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