Air-Induced One-Pot Synthesis of N-Sulfonylformamidines from Sulfonyl Chlorides, NaN3, and Tertiary/Secondary Amines

Article abstract of DOI:10.1002/ejoc.201901048

An efficient and practical one-pot strategy for the synthesis of N-sulfonylformamidines was developed by directly using easily available sulfonyl chlorides, sodium azide and tertiary/secondary amines in the presence of 5 mol-% CuBr₂ under aerob

Full text of DOI:10.1002/ejoc.201901048

A Journal of
Accepted Article
Title: Air-induced one-pot synthesis of N-sulfonylformamidines from
sulfonyl chlorides, NaN3 and tertiary/secondary amines
Authors: Wenzhu Bi, Wen-Jie Zhang, Zi-Jie Li, Xiao-Yi Xia, Xiao-Lan
Chen, Ling-Bo Qu, and Yu-Fen Zhao
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To be cited as: Eur. J. Org. Chem. 10.1002/ejoc.201901048
Link to VoR: http://dx.doi.org/10.1002/ejoc.201901048
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10.1002/ejoc.201901048
European Journal of Organic Chemistry
COMMUNICATION
Air-induced one-pot synthesis of N-sulfonylformamidines from
sulfonyl chlorides, NaN3 and tertiary/secondary amines
Wen-Zhu Bi,*[a] Wen-Jie Zhang,[a] Zi-Jie Li,[a] Xiao-Yi Xia,[b] Xiao-Lan Chen,[b] Ling-Bo Qu,[b] and Yu-Fen
Zhao[b,c]
Dedication ((optional))
Abstract: An efficient and practical one-pot strategy for the synthesis
of N-sulfonylformamidines was developed by directly using easily
available sulfonyl chlorides, sodium azide and tertiary/secondary
amines in the presence of 5 mol% CuBr2 under aerobic oxidative
conditions.
Introduction
Due to the unique structural features, N-sulfonylformamidines
exhibit a variety of biological properties,1 and are widely used as
synthetic intermediates for drugs2 and metal ligand for catalyst.3
As to the synthesis of these important compounds, the first
approach in the literature is the Hinsberg reaction, through which
N-sulfonylformamidines can be directly formed by reaction of
sulfonyl chlorides with amidines under basic conditions.4 However,
Hinsberg reaction generally suffers from several drawbacks, such
as narrow reaction scopes, unsatisfactory yields and unavailable
starting materials (Scheme 1a). In recent years, Cu-catalyzed
three-component coupling reactions of sulfonyl azides, alkynes
and secondary amines have been well explored and applied for
the synthesis of N-sulfonylamidines.5-11 In this kind of reactions,
some by-products are easily formed, such as alkyne-alkyne
coupling products and triazole, which significantly decrease the
yield of N-sulfonylamidines. Besides, the secondary amines used
Scheme 1. Comparison of previous works with this work.
in these reactions are also limited (Scheme 1b). Through
oxidative dehydration of tertiary amines and the consequent 1,3-
dipolar tandem reaction with sulfonyl azides, Weng et al,12 Zheng
et al,13 He et al,14 Li et al,15 Odell et al16 and Wusiman et al17 have
synthesis of N-sulfonylformamidines in moderate to good yield
(Scheme 1c). By the use of direct electrochemical synthetic
developed several approaches for the synthesis of N-
sulfonylformamidine derivatives (Scheme 1c). Very recently,
Zeng et al18a and Pan et al18b developed two photoinduced
cascade reaction of tertiary amines and sulfonyl azides for the
strategy, Wang et al19 broadened the tertiary amines to secondary
and primary amines (Scheme 1c). Even through, this type of
reactions still suffer from drawbacks, such as the requirement of
previously prepared sulfonyl azides and large amount of catalyst.
Theoretically, the most straightforward and atom-economic
method for the synthesis of N-sulfonylformamidine derivatives are
direct condensation of sulfonamides and formamides. Numerous
strategies of this type have been developed (Scheme 1d).20-26
However, in order to achieve these goals, some harsh and toxic
reagents, such as TBHP (tert-butyl hydroperoxide),20 NBS (N-
[a]
W. Z. Bi, W. J. Zhang, Z. J. Li
College of Pharmacy
Henan University of Chinese Medicine
Henan Province, Zhengzhou, 450046, (P. R. China)
E-mail: biwenzhu2018@hactcm.edu.cn
Homepage: http://en.hactcm.edu.cn/
X. Y. Xia, X. L. Chen, L. B. Qu, Y. F. Zhao
College of Chemistry and Molecular Engineering
Zhengzhou University
23
bromosuccinimide),22 (CO)2Cl2 and SOCl2,26 are employed,
[b]
[c]
which greatly limit the further application of this kind of reactions.
In spite of the significant previous works, the pursuit of newly and
practical method for the synthesis of N-sulfonylformamidine
derivatives is untiring.27-34
Herein, we would like to disclose an efficient and practical one-
pot strategy to synthesize N-sulfonylformamidines, via three-
component coupling reaction of sulfuryl chloride, sodium azide
and tertiary/secondary amines in the presence of 5 mol% CuBr2
under aerobic oxidative conditions at 70 °C (Scheme 1e).
Henan Province, Zhengzhou, 450052, (P. R. China)
Y. F. Zhao
The Key Laboratory for Chemical Biology of Fujian Province
Xiamen University
Fujian Province, Xiamen, 361005, (P. R. China)
Supporting information for this article is given via a link at the end of
the document.((Please delete this text if not appropriate))
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10.1002/ejoc.201901048
European Journal of Organic Chemistry
COMMUNICATION
Compared with previous synthetic methods, the advantages of
this work include short reaction time, inexpensive and less
amount of catalyst and step-economy.
An increased yield of 4a (75%, entry 12) was obtained in 1,2-
dichloroethane (DCE) in contrast with the decreased yields in
DMF (47%), DMSO (31%), THF (58%) and CHCl3 (61%) (entries
10-11, 13-14). In the following steps, the influence of the amount
of CuBr2 (entries 12, 15-18), NaN3 (entries 15, 19-21) and NEt3
(entries 19, 22-24) were investigated, respectively. Those
investigation results showed that very small amount of CuBr2 (5
mol%) could well catalyze the reaction process and a slightly
excess amount of NaN3 (1.2 eq.) and equal amount of NEt3 were
efficient to provide 4a with excellent yield (79%) as shown in entry
19. Finally, a general investigation of reaction temperature
(entries 19, 25-29) and time (entries 27, 30-33) showed that 70 °C
and 3 h were the best reaction temperature and time (entry 27). It
worth mentioning here that the yield of 4a was low at 40 °C even
for 12 h (entry 25) and higher temperature than 70 °C or longer
time than 3 h could cause a decrease of the yield. Therefore, the
optimal reaction conditions were 0.5 mmol of TsCl together with
NaN3 (1.2 eq.), NEt3 (1.0 eq.) and CuBr2 (5 mol%) in DCE at 70 °C
for 3 h as shown in entry 27.
Results and Discussion
We initiated our study by screening for the optimal reaction
conditions using the model reaction of TsCl (1a), NaN3 (2) and
triethylamine (3a) in CH3CN at 80 °C for 3 h under open-air
conditions. As shown in Table 1, the metal catalysis were firstly
investigated (entries 1-9) and the results showed that the model
reaction could be catalyzed by 20 mol% of the following transition
metal salts or oxides with different yields CuI (43%), CuCl (35%),
CuBr (39%), Cu2O (30%), CuCN (38%), CuBr2 (63%), FeSO4
(51%), CoCl2 (47%) and NiCl2 (41%). Among those tested metal
catalysis, CuBr2 provided the satisfied yield of N,N-diethyl-N'-
tosylformimidamide (4a, 63%, entry 6). Subsequently, the
investigation of solvents on the model reaction were performed.
Table 1. Optimization of reaction conditions [a]
Entry
Cat. (mol%)
NaN3 (eq.)
NEt3 (eq.)
Solvent
Temp. (°C)
Time (h)
Yield[b] (%)
1
2
3
4
5
6
7
8
CuI (20)
CuCl (20)
CuBr (20)
Cu2O (20)
CuCN (20)
CuBr2 (20)
FeSO4 (20)
CoCl2 (20)
NiCl2 (20)
CuBr2 (20)
CuBr2 (20)
CuBr2 (20)
CuBr2 (20)
CuBr2 (20)
CuBr2 (5)
CuBr2 (10)
CuBr2 (15)
CuBr2 (25)
CuBr2 (5)
CuBr2 (5)
CuBr2 (5)
CuBr2 (5)
CuBr2 (5)
CuBr2 (5)
CuBr2 (5)
CuBr2 (5)
CuBr2 (5)
CuBr2 (5)
CuBr2 (5)
CuBr2 (5)
CuBr2 (5)
CuBr2 (5)
CuBr2 (5)
1.2
1.2
1.2
1.2
1.2
1.2
1.2
1.2
1.2
1.2
1.2
1.2
1.2
1.2
1.2
1.2
1.2
1.2
1.2
1.2
1.2
2.0
3.0
4.0
1.2
1.2
1.2
1.2
1.2
1.2
1.2
1.2
1.2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
1
3
4
1
1
1
1
1
1
1
1
1
1
1
1
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
DMF
DMSO
DCE
THF
CHCl3
DCE
DCE
DCE
DCE
DCE
DCE
DCE
DCE
DCE
DCE
80
80
80
80
80
80
80
80
80
80
80
80
80
80
80
80
80
80
80
80
80
80
80
80
40
60
70
90
100
70
70
70
70
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
43
35
39
30
38
63
51
47
41
47
31
75
58
61
78
76
76
75
79
76
75
68
68
70
30, 38[c]
74
83
78
68
40
60
76
75
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
DCE
DCE
DCE
DCE
DCE
DCE
DCE
DCE
3, 12
3
3
3
3
1
2
4
5
DCE
[a] Reaction conditions: 1a (0.5 mmol), 2 (1.2-4.0 eq.), 3a (1-4 eq.), Cat. (5-25 mol%) in 5 mL solvent in a 25 mL round-bottom
flask at 60-100 °C for 1-5 h under open-air conditions. [b] Isolated yields were provided. [c] 12 h was used.
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With the promising reaction conditions in hand, the substrates
scope were examined as illustrated in Scheme 2. As it can be
seen, a series of sulfonyl chlorides bearing electron donating
groups (4-Me) or electron withdrawing groups (4-Cl, 4-NO2, 3-NO2
and 2-NO2) reacted smoothly with triethylamine, affording the
corresponding N-sulfonylformamidines in moderate to good yields
(4a-g, 66-83%) without obvious electronic effects. It worth
mentioning that heteroatom-containing sulfonyl chloride,
thiophene-2-sulfonyl chloride, could also react well with
triethylamine, giving the target compound in 73% yield (4h).
Subsequently, different tertiary amines, including tripropylamine,
tributylamine and triisopropylamine, were employed to react with
the above-mentioned sulfonyl chlorides, providing the
corresponding compounds in good yields (4i-p). Meanwhile, two
sulfonyl chlorides (0.5 mmol) and NaN3 (1.0 mmol), secondary
amines (1.25 mmol) and CuBr2 (5 mol% based on the sulfonyl
chloride) were separately mixed and stirred in 5 mL DCE at 70 °C
for 1 h. Then, the amine/coper solution were slowly dropwised into
the solution of sulfonyl chlorides and NaN3. Then the reaction
mixture was continuously stirred at 70 °C for 2 h. Through this
procedure, a series of sulfonyl chlorides were used to react with
diethylamine to provide the same products as found for the tertiary
amines (Scheme 3, 4a-d, 4g) with good yields. Besides, a wide
array of secondary amine derivatives were employed to react with
TsCl. As it can be seen, dipropylamine, dibutylamine, N-
ethylcyclohexanamine as well as piperidine were transformed into
their corresponding N-sulfonylformamidine 4i-j and 4w-x in
moderate to good yield respectively. However, other secondary
cyclic tertiary amines, N-methylpyrrolidine and N-methylpiperidine, amines,
such
as
diisopropylamine,
N-methyl-1-
were also employed to react with sulfonyl chlorides under our
optimal conditions. As expected, the predominantly products were
obtained as a result of the hydrogen abstraction of the cyclic α-
carbon (4q-v).15 The yields of the products from the reaction of
cyclic tertiary amines were lower than that of trialkylamines
probably because of the steric hindrance.
phenylmethanamine and N-ethylaniline were not tolerated this
transformation.
In order to further extend the reaction scope, diethylamine was
attempted to be employed in this reaction under standard
conditions. Interestingly, the same product was obtained as found
for the triethylamine. However, the isolated yield was relatively
low (38%, Table S1, entry 1 in Supporting Information). After a
series of investigations of the reaction conditions, we obtained the
optimal conditions for the reaction of sulfonyl chlorides, NaN3 and
secondary amines (Table S1). In this new reaction system,
Scheme 3. Scope of the reaction with secondary amines. Reaction condition:
0.5 mmol of 1, 1.0 mmol of 2, 1.25 mmol of 5, CuBr2 ( 5 mol%) in 25 mL round-
bottom flask at 70 °C . Isolated yield were provided. a Detected by TLC.
A series of control experiments were carried out to gain further
insight into the mechanism of the reaction (Scheme 4). Firstly, p-
tolylsulfonyl chloride and NaN3 were reacted under the standard
reaction conditions. As can be seen, p-tolylsulfonyl chloride was
almost completely converted to sulfonyl azide (Scheme 4a).
When the reaction was performed under 1 atm of O2, the yield of
the corresponding product was 85%, which was only slightly
higher than that under air (83%). Considering the economy and
safety of the reaction, the use of air as oxidant was still the best
choice (Scheme 4b). When the reaction were performed without
CuBr2 both in the present of air and just O2, the yields of the
product were relatively low (17% (air), 21% (O2)), which indicated
that CuBr2 were necessary in the reaction system (Scheme 4c).
Furthermore, no product was obtained when the reaction was
performed under N2 atmosphere, indicating that the O2 in the air
had an important role in the reaction process (Scheme 4d). Finally,
2,2,6,6-tetramethylpiperidineoxide (TEMPO) as
scavenger was added to the reaction mixture. When 2.0 eq. of
TEMPO was used, the reaction proceeded smoothly and provided
a
radical
Scheme 2. Scope of the reaction with tertiary amines. Reaction condition: 0.5
mmol of 1, 0.6 mmol of 2, 0.5 mmol of 3, CuBr2 (5 mol%) and 5 mL of DCE in
25 mL round-bottom flask at 70 °C for 3 h under open-air. Isolated yield were
provided.
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10.1002/ejoc.201901048
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COMMUNICATION
4a with a yield of 75% (Scheme 4e), suggesting that no radical Conclusions
pathway was involved in the reaction process.
In summary, we developed an efficient and practical one-pot
strategy for the synthesis of N-sulfonylformamidines, by directly
using easily available sulfonyl chlorides, sodium azide and
tertiary/secondary amines in the presence of 5 mol% CuBr2 under
aerobic oxidative conditions in DCE at 70 °C for 3 h. The reaction
conditions for tertiary amines and secondary amines were
carefully screened and established, respectively. The exploration
of the mechanism showed that the O2 in the air was essential in
the oxidative dehydration of tertiary/secondary amines. Multiple
remarkable merits of this method include one-pot procedure,
short reaction time, inexpensive and less amount of catalyst and
great step-economy, which provided a preferable alternative for
the synthesis of the biologically and chemically significant N-
sulfonylformamidines.
Experimental Section
Scheme 4. Control experiments.
General procedure for the reaction with tertiary amines: 0.5 mmol of
sulfonyl chloride, 0.6 mmol of sodium azide, 1.0 mmol of tertiary amines
and 5 mol% of CuBr2 were mixed and stirred in 5 mL of DCE at 70 °C for
3 h under open-air condition. Then the mixture was cooled to room
temperature, washed with brine and extracted with CH2Cl2 (3 × 5 mL). The
organic layers were collected and dried over Na2SO4. After filtration and
evaporation of the solvent, the target compounds were obtained by silica
gel chromatography.
Referencing to known literature12,35 and control experimental
results, a general possible mechanism for the two methods were
postulated in Scheme 5. Initially, sulfonyl chloride 1 reacted with
sodium azide to from sulfonyl azide 2 (Scheme 5a). For the
tertiary amines employed in this reaction system, iminium ion 4
was first generated through the general accepted mechanism:
oxidative dehydration of C-H bond adjacent to a nitrogen atom of
tertiary amines.36 4 was further dehydrogenated to the key
intermediate enamine 5, which reacted with sulfonyl azide 2
through 1,3-dipolar addition and gave the unstable triazoline 6.
Triazoline 6 released one molecule of CH2N2 to afford target
product 7 (Scheme 5b). When secondary amines were employed,
the corresponding enamine 10 was formed through the same
route as tertiary amines. Then the α unsaturated carbon in 10 was
attacked by the nucleophilic nitrogen atom in another molecule of
diethylamine, resulting in the leaving of one molecule of
ethylamine and the formation of the key intermediate enamine 5
(Scheme 5c).37 Then the same product for secondary amines
were produced as that of tertiary amines by 1,3-dipolar addition
with 2.
General procedure for the reaction with secondary amines: 0.5 mmol
of sulfonyl chloride and 1.0 mmol of sodium azide, 1.25 mmol of secondary
amines and CuBr2 (5 mol% based on the sulfonyl chloride) were separately
mixed and stirred in 5 mL DCE at 70 °C for 1 h. Then, the amine/coper
solution were slowly dropwised into the solution of sulfonyl chlorides and
NaN3. The reaction mixture were continuously stirred at 70 °C for 2 h. Then
the mixture was processed with the same procedure as that of tertiary
amines to provide the corresponding compounds.
Acknowledgments
This work was supported by the Zhongjing Scholars Research
Funding of Henan University of Chinese Medicine (No. 00104311-
2019-28).
Keywords: N-sulfonylformamidines • tertiary/secondary amines
• oxidative dehydration reaction • air-induced • step-economy
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European Journal of Organic Chemistry
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Entry for the Table of Contents (Please choose one layout)
Layout 2:
COMMUNICATION
Key Topic*
Wen-Zhu Bi,* Wen-Jie Zhang, Zi-Jie Li,
Xiao-Yi Xia, Xiao-Lan Chen, Ling-Bo Qu,
Yu-Fen Zhao
Page No. – Page No.
Through directly using easily available sulfonyl chlorides, sodium azide and
tertiary/secondary amines, several of N-sulfonylformamidines were synthesized in
one-pot in the presence of 5 mol% CuBr2 in DCE under aerobic oxidative
conditions.
Air-induced one-pot synthesis of N-
sulfonylformamidines from sulfonyl
chlorides, NaN3 and
tertiary/secondary amines
* Oxidative dehydrogenation reaction
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