Guanidinium-based sulfonic acid as a new Bronsted acid organocatalyst in organic synthesis in water

Article abstract of DOI:10.1007/s11164-015-2181-4

Guanidinium-based sulfonic acid as a new Bronsted acid organocatalyst has been synthesized, characterized, and applied for the synthesis of 3,4-dihydroquinoxalin-2-amine, 1,6-dihydropyrazine-2,3-dicarbonitrile, triazolo[1,2-a]indazole-trione, and spiro tr

Full text of DOI:10.1007/s11164-015-2181-4

Res Chem Intermed
DOI 10.1007/s11164-015-2181-4
Guanidinium-based sulfonic acid as a new Brønsted
acid organocatalyst in organic synthesis in water
Mozhdeh Seyyedhamzeh1 Shabnam Shaabani1
•
•
Mona Hamidzad Sangachin1 Ahmad Shaabani1
•
Received: 8 June 2015 / Accepted: 17 July 2015
Ó Springer Science+Business Media Dordrecht 2015
Abstract Guanidinium-based sulfonic acid as a new Brønsted acid organocatalyst has
been synthesized, characterized, and applied for the synthesis of 3,4-dihydroquinoxalin-
2-amine, 1,6-dihydropyrazine-2,3-dicarbonitrile, triazolo[1,2-a]indazole-trione, and
spiro triazolo[1,2-a]indazole-tetraone derivatives in an aqueous medium. The catalytic
system, reported here, possesses the advantages of both homogeneous and heterogeneous
catalysts and can be repetitively used in water.
Graphical Abstract
&
Ahmad Shaabani
a-shaabani@sbu.ac.ir
1
Faculty of Chemistry, Shahid Beheshti University, G. C., P. O. Box 19396-4716, Tehran, Iran
123

M. Seyyedhamzeh et al.
Keywords Tetramethylguanidine Á Chlorosulfonic acid Á Organocatalyst Á
Dihydroquinoxalin Á Dihydropyrazine Á Triazolo[1,2-a]indazole
Introduction
Strong mineral acids are efficient catalysts; however, they can corrode equipment, and
they are noxious to the environment to some extent. Solid catalysts as non-volatile
materials are considered less noxious than traditional liquid ones [1]. These systems
do not reach the high activities of homogeneous catalysts and often suffer from
shortcomings such as accessibility of the matrix-bound acidic sites, high molecular
weight/active-site ratios, and rapid deactivation from coking [2, 3]. For these reasons,
the discovery of systems that contain both Brønsted acid with the solid non-volatile
support would result in reduced equipment corrosion, ease of product separation, less
potential contamination, and benign environmental properties.
Guanidines and their corresponding guanidinium salts have been known to
chemists because of widespread use as strong and weak Brønsted base catalysts in
useful chemical transformations, respectively [4]. Recently, a number of excellent
reviews on guanidine organocatalysis exist because of their high charge dispersion
and excellent thermal and chemical stabilities owing to their special structures [5–
11]. Despite this wealth of functionality present in guanidine, the synthesis of
guanidinium-based Brønsted acid has not been reported previously. Bearing in mind
the organocatalysis applications of guanidines [12], functional guanidinium-based
sulfonic acid as a solid Brønsted acid organocatalyst is designed to replace
traditional mineral liquid acids in organic transformations.
Heterocyclic systems are common structural motifs in many biologically active
substances and natural products. In view of this, multi-component reactions (MCRs)
have emerged as a valuable asset in order to create complex and diversity-oriented
libraries of scaffolds with interesting biological activities [13–15].
Therefore, the combination of synthetic potentialities of MCRs with a solid
Brønsted acid organocatalyst has resulted in the development of promising eco-
compatible synthetic methodologies. It is important to note that the synthetic
potentialities of MCRs with SO3H-functionalized Brønsted acid as environmentally
benign and a recyclable catalyst have been combined to prepare quinoxalines [16]
and pyrazines [17–22], which are seen in some important marketed drugs (I–III)
[23–25], and urazole derivatives which also exhibit biological activities (IV–VII)
[26–29] (Fig. 1).
Many biological processes and organic compound synthesis in nature occur very
efficiently in water. The diversity of reactants seen in vivo promotes chemists in
discovering the potential power of water as a solvent [30]. Therefore, to develop
cost-effective and environmentally benign catalytic systems [31], herein we wish to
report the synthesis of sulfonic acid functionalized 1,1,3,3-tetramethylguanidine
(TMG) as a water recyclable acidic organocatalyst for the synthesis of 3,4-
dihydroquinoxalin-2-amines 4, 1,6-dihydropyrazine-2,3-dicarbonitriles 6, tria-
zolo[1,2-a]indazole-triones 10, and spiro triazolo[1,2-a]indazole-tetraones 12 in
good to excellent yields in water (Scheme 1).
123

Guanidinium-based sulfonic acid as a new Brønsted acid…
N
NH
Cl
Cl
N
O
N
S
O
N
N
NH
H
O
N
HN
O
O
N
H
N
I (Varenicline)
II (Zibotentan)
III (WAY-161503)
N
O
H
N
O
O
N
BzHN
RO
O
N
N
N
N
O
H2N
O
N
N
O
O
N
O
O
N
CH3
CH3
H
O
O
N
H
OH
N
N
O
O
H
Ph
N
MeO
N
NH2
H
IV
V
VI
VII
Fig. 1 Quinoxaline and pyrazine moieties in drugs and biological active molecules of urazole
Scheme 1 Synthesis of 3,4-dihydroquinoxalin-2-amines 4, 1,6-dihydropyrazine-2,3-dicarbonitriles 6,
triazolo[1,2-a]indazole-triones 10, and spiro triazolo[1,2-a]indazole-tetraones 12
Results and discussion
First, we disclose herein a simple procedure for the preparation of -SO3H
functionalized organocatalyst. The catalyst is simply prepared by dropwise addition
of chlorosulfonic acid to a n-hexane mixture of TMG at 0 °C (Scheme 2).
After the preparation of acid-based organocatalyst, its structure was identified by
IR, 1H NMR, 13C NMR, and mass spectra analysis. The presence of chloride ion in
the new acidic organocatalyst’s structure was indicated by precipitation of AgCl
123

M. Seyyedhamzeh et al.
Scheme 2 Preparation of
catalyst
Fig. 2 The effect of the amount of the catalyst on reaction yield of synthesis of 3,4-dihydroquinoxalin-2-
amine derivative 4a (Reaction conditions: 1,2-phenylenediamine (1 mmol), acetone (1 mmol), and
cyclohexyl isocyanide (1 mmol); water (3 ml), r.t., 50 min)
when a solution of AgNO3 in distilled water was added to a solution of the reagent
in distilled water. Furthermore, the H? content of it was tested and pH = 2 was seen
for the 0.01 M solution of the catalyst. Also, acid–base titration of an aqueous
solution of prepared catalyst with NaOH indicated high acidic character of this new
acidic organocatalyst. The procedure in detail is as follows: 1 mmol (0.196 g) of
sample was weighed accurately and placed in a 50 ml Erlenmeyer flask, and 10 ml
of distilled water was added to the Erlenmeyer. Then the mixture was neutralized
with 9.8 ml of 0.1 N sodium hydroxide using phenolphthalein as an indicator.
Then, we investigated the performance of the new organocatalyst in the synthetic
reactions. In a pilot experiment, 1,2-phenylenediamine, acetone, and cyclohexyl
isocyanide in water were stirred at room temperature using a catalytic amount of the
prepared catalyst. The reaction turned out to be clean and simple, giving the N-
cyclohexyl-3,4-dihydro-3,3-dimethylquinoxalin-2-amine 4a in high yield.
To evaluate the catalytic property of this catalyst, the reaction mixture was stirred
in the absence of catalyst but no product was formed. The effect of the amount of
the catalyst on the synthesis of dihydroquinoxalin-2-amines is presented in Fig. 2.
The results obtained here indicate that the efficiency of the reaction (higher yield)
increased when a higher amount of the catalyst is used. The yield of the final
product increases from 69 to 91 % with increasing the amount of the catalyst.
Among the various amounts of the catalyst studied, 5 mol% was found to be highly
effective.
In order to obtain the best media, among the various solvents, water was found to
be the excellent solvent for this transformation and the results are shown in Table 1.
It is well known that water is a non-flammable, non-hazardous, non-toxic, and
inexpensive green solvent; therefore, using water as the reaction medium has gained
considerable interest [31]. It is interesting to note, the precipitation of the product in
water could assist the reaction to proceed.
123

Guanidinium-based sulfonic acid as a new Brønsted acid…
Table 1 The effect of solvent on the synthesis of 3,4-dihydroquinoxalin-2-amine derivative 4a (Reaction
conditions: 1,2-phenylenediamine, acetone, and cyclohexyl isocyanide; r.t., 5 mol% catalyst)
Entry
Solvent
Time
Yielda (%)
1
2
3
4
5
a
Water
50 min
24
91
Ethanol
Trace
Trace
–
Acetone
24
Acetonitrile
Tetrahydrofuran
24
24
–
Isolated yield
To evaluate the use of this interesting approach, a variety of alkyl, aryl, benzyl
and alicyclic isocyanides, aliphatic, alicyclic, and aromatic ketones or aromatic
aldehydes with ADs were reacted under similar circumstances. The results are
summarized in Table 2 (Table 2, entries 1–12).
In order to investigate the scope and limitations of this reaction, we decided to
extend it to DAMN instead of ADs. In this regard, DAMN, acetone, and cyclohexyl
isocyanide were stirred in the presence of guanidinium-based sulfonic acid as an
acidic organocatalyst in water to lead to the synthesis of 5-(cyclohexylamino)-1,6-
dihydro-6,6-dimethylpyrazine-2,3-dicarbonitrile 6a in 90 % yield. As indicated in
Table 2 (entries 13–17), to evaluate the use of this approach, a variety of aliphatic
and aromatic ketones and various isocyanides with DAMN were condensed under
similar circumstances. The reactions proceeded very cleanly, and no undesirable
side reactions were observed.
In these experiments the product was precipitated and isolated easily by filtration
and the catalyst in the filtrate was separated from the unreacted starting materials by
extracting the filtrate with ethyl acetate, then, the water layer containing catalyst
was vacuum-dried to remove water, and it was reused in further reactions (Table 2,
entry 1). Apparently, recycling of the catalyst is possible for four successive times
without significant loss of activity (Fig. 3).
The results of our catalyst with respect to the yields, solvents, temperature, and
reaction times have been compared with previously reported catalysts in the
synthesis of dihydroquinoxaline derivatives [32–39]. As shown in Table 3, in the
case of the present work, a shorter reaction time at room temperature and minimal
environmental impact are notable features of this procedure.
In order to explore the application of the new organocatalyst, the synthesis of
compound 10a was selected as a model reaction and the results carried out under
different reaction conditions are summarized in Table 4. Under the optimized
conditions, the reactions proceeded smoothly and a variety of the desired
triazolo[1,2-a]indazole-trione derivatives were obtained in good yields (Table 5).
The reusability of the new prepared organocatalyst, considering the commercial
point of view, was examined by using benzaldehyde, dimedone, and urazole as
substrates. It was found that the catalyst could be reused five times with slightly
decreasing catalytic activity: 87, 86, 84, 82, and 81 % (Fig. 4).
123

M. Seyyedhamzeh et al.
123

Guanidinium-based sulfonic acid as a new Brønsted acid…
Fig. 3 Recycle of the catalyst
for the synthesis of 4a
Table 3 Comparison of efficiency of various catalysts in the synthesis of dihydroquinoxalines
Entry Catalyst
Conditions
Yielda (%) Time
Ref.
1
2
3
4
5
6
7
8
9
a
Guanidinium-based sulfonic acid H2O/rt
73–91
90
50–90 min This work
p-TSA
EtOH/rt
4 h
[32]
[33]
[34]
[35]
[36]
[37]
[38]
[39]
Fe(ClO4)3
CAN
CH3CN/reflux
EtOH/rt
91–93
62–96
2 h
3 h
EDTA
H2O/80 °C or rt 20–95
1–12 h
2–4 h
2–3 h
2–4 h
2 h
AlKIT-51
Amberlyst-15
EtOH/rt
85–98
85–98
85–98
90
EtOH/rt
Silica gel supported sulfuric acid EtOH/rt
CSA
EtOH/rt
Isolated yield
Table 4 The optimization of
condensation of dimedone
(1 mmol), benzaldehyde
(1 mmol), 4-phenylurazole
(1 mmol)
Entry
Conditions
H2O/r.t.
Time (h)
Yielda(%)
1
24
24
24
24
–
2
H2O/r.t./10 mol% catalyst
–
3
H2O/r.t./20 mol% catalyst
–
4
H2O/80 °C/10 mol% catalyst
H2O/reflux/10 mol% catalyst
H2O/reflux/7 mol% catalyst
H2O/reflux/5 mol% catalyst
H2O/reflux/3 mol% catalyst
EtOH/reflux/10 mol% catalyst
CH3CN/reflux/10 mol% catalyst
CHCl3/reflux/10 mol% catalyst
–
5
2.5
87
88
87
56
65
71
49
6
2.5
2.5
7
8
24
9
24
24
24
10
11
a
Isolated yield
To further expand the scope of the present method, we investigated one-pot
reactions involving substituted isatin, urazole, and dimedone (Scheme 1). The
results of the reactions are summarized in Table 6.
The efficiency of SO3H-functionalized tetramethylguanidin was compared with
other catalysts used in the synthesis of triazolo[1,2-a]indazole-triones [40–45] and
123

M. Seyyedhamzeh et al.
Table 5 One-pot three-
component synthesis of
triazolo[1,2-a]indazole-triones
10
Entry Aldehyde
Product Time (h) Yielda(%)
1
2
3
4
5
6
7
8
Benzaldehyde
10a
10b
10c
10d
10e
10f
2.5
2
87
88
89
86
89
87
81
79
2-Chlorobenzaldehyde
3-Nitrobenzaldehyde
4-Methylbenzaldehyde
4-Bromobenzaldehyde
4-Chlorobenzaldehyde
2.5
3
3
2.5
5
3-Methoxybenzaldehyde 10g
2-Naphthaldehyde 10h
6
a
Isolated yield
Fig. 4 Recycling of catalyst in
the synthesis of a model
compound 10a
Table 6 One-pot three-
component synthesis of spiro
triazolo[1,2-a]indazole-tetraones
12
Entry
1
Isatin
Product
Time (h)
3
Yielda (%)
82
12a
2
3
4
12b
12c
12d
3
3
3
84
81
84
a
Isolated yield
spiro triazolo[1,2-a] indazole-tetraones [41, 45]. As can be seen from Table 7, this
method was chemically simpler and employs a cheap and organic-based catalyst.
Conclusions
In summary, guanidine-based sulfonic acid as an efficient and environmentally
friendly proton source organocatalyst was prepared, characterized and employed for
the synthesis of structurally diverse 3,4-dihydroquinoxalin-2-amines, 1,6-dihy-
dropyrazine-2,3-dicarbonitriles, triazolo[1,2-a]indazole-triones, and spiro tria-
zolo[1,2-a]indazole-tetraones using readily available starting materials in water
media. Our method will potentially find its application in organic synthesis or even
in the pharmaceutical industry because of the advantages such as simple product
123

Guanidinium-based sulfonic acid as a new Brønsted acid…
Table 7 The efficiency of various catalysts in the synthesis of triazolo[1,2-a]indazole-triones and spiro
triazolo[1,2-a]indazole-tetraones
Entry
Catalyst
Conditions
Yielda
(%)
Time
Ref.
1
Guanidinium-based sulfonic
acid
H2O/reflux
79–89
2–6 h
This
work
2
3
4
5
6
7
p-TSA
SF/80 °C
SF/80 °C
CH3CN/reflux
78–90
88–92
80–96
80–90
*80
15–30 min
30–65 min
30–60 min
20–35 min
0.5 h
29
30
31
32
33
34
PEG-SO3H
AlKIT-5
Nano SiO2–OSO3H
[Cu(CH3CN)4]PF6
Camphor-10-sulfonic acid
SF/80 °C
SF/100 °C
H2O:EtOH (80:20)/
reflux
78–86
20–35 min
8
Guanidinium-based sulfonic
acid
H2O/reflux
81–84
3 h
This
work
9
PEG-SO3H
SF/80 °C
H2O:EtOH (80:20)/
reflux
86–92
80–89
5–8 h
30
34
10
Camphor-10-sulfonic acid
3–4.5 h
a
Isolated yield
isolation, lack of problems connected with conventional solvent use, and
satisfactory yields of products. In addition, the sulfonated guanidine shows
desirable catalytic activity in water and can be used several times without an
obvious decrease in its catalytic activity.
Experimental
General
Melting points were measured on an Electrothermal 9200 apparatus and are
1
uncorrected. IR spectra were recorded on a Shimadzu IR-470 spectrometer. H
NMR Spectra were recorded on a Bruker DRX-300 Avance spectrometer
300.13 MHz with TMS as internal standards. The chemicals used in this work
were purchased from the Merck and Fluka chemical companies. All the products are
known compounds and were characterized by IR and NMR spectroscopic data, and
their melting points are compared with reported values [32–45].
123

M. Seyyedhamzeh et al.
Synthesis of guanidinium-based sulfonic acid
To a magnetically stirred mixture of 1,1,3,3-tetramethyl guanidine (0.23 g, 2 mmol)
in 10 ml of n-hexane, chlorosulfonic acid (0.23 g, 2 mmol) was added dropwise at
0 °C during 1 h. After the addition was completed, the mixture was stirred for 2 h.
Then, the precipitate was filtered off and washed with methanol (20 ml) and dried at
`
room temperature to obtain acid-based organocatalyst as a creme powder. This solid
`
acid is very stable and is not affected by air, water, heat, and light. Creme powder
(0.22 g, 96 %): mp 139 °C. IR (KBr) cm-1: 3000–3500 (broad band), 2892, 1647,
1607, 1562, 1487, 1421, 1315, 1190. 1H NMR (300.13 MHz, DMSO) d: 2.89 (12H,
s, CH3), 7.77 (br s, NH, SO3H). 13C NMR (75.47 MHz, DMSO) d: 39.5, 161.0. MS
m/z: 196 (M-Cl, 100), 115 (23), 71 (52), 44 (80), 37 (62), 35 (7). Anal. Calcd for
C5H14ClN3O3S: C, 25.92; H, 6.09; N, 18.14; S, 13.84; Found: C, 25.72; H, 5.99; N,
18.20; S, 13.75.
General procedure for the preparation of products 4a–l and 6a–e
The catalyst (0.01 g, 5 mol%) was added to a solution of diamines (1 mmol),
carbonyl compounds (1 mmol), and isocyanides (1 mmol) in 3 ml of water. The
reaction mixture was allowed to stir for an appropriate time until the precipitate
appeared. After completion of the reaction, as indicated by TLC (EtOAc:n-hexane,
1:2), the reaction mixture was filtered off and the residue was washed with water
and then crystallized from ethanol or acetone to give pure products.
General procedure for the preparation of 10a–h and 12a–d
A mixture of dimedone (1 mmol), aldehyde or isatin (1 mmol) and 4-phenylurazole
(1 mmol), and catalyst (0.01 g, 5 mol%) in water (5 mL) was refluxed. After
completion of the reaction that was monitored by TLC (EtOAc:n-hexane, 1:3), the
reaction mixture was cooled to room temperature. Then, the precipitated product
was filtered and washed with water and cooled with ethanol to afford the pure
product.
Acknowledgments We gratefully acknowledge financial support from the Iran National Elites
Foundation (INEF) and the Research Council of Shahid Beheshti University.
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