A novel D-glucosamine-derived pyridyltriazole@ palladium catalyst for solvent-free Mizoroki-Heck reactions and its application in the synthesis of Axitinib

Article abstract of DOI:10.1039/c4gc01606h

A green method for the synthesis of a D-glucosamine-derived triazole@ palladium catalyst is described. The synthesized catalyst containing a 2-pyridyl-1,2,3-triazole ligand was prepared via a click route in high yields and was explored in Heck cross-coupling reactions between different aryl halides and olefins under solventfree conditions. The catalyst can be separated from the reaction mixture and reused at least six times with superior activity. In addition, using this protocol, the marketed drug Axitinib (antitumor) could be synthesized easily.

Full text of DOI:10.1039/c4gc01606h

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DOI: 10.1039/C4GC01606H
Novel -glucosamine-derived pyridyl-triazole@palladium catalyst for
D
solvent-free Mizoroki-Heck reactions and its application in the
synthesis of Axitinib
Chao Shen, a Hongyun Shen,b Ming Yang,b Chengcai Xiab and Pengfei Zhang*b
Novel D-glucosamine-derived pyridyl-triazole@palladium catalyst for solvent-free
Mizoroki-Heck reaction and the synthesis of Axitinib .

Green Chemistry
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DOI: 10.1039/C4GC01606H
Novel -glucosamine-derived pyridyl-triazole@palladium catalyst for solvent-free
D
Mizoroki-Heck reactions and its application in the synthesis of Axitinib
Chao Shen, a,b Hongyun Shen,b Ming Yang,b Chengcai Xiab and Pengfei Zhang*b
Received (in XXX, XXX) Xth XXXXXXXXX 20XX, Accepted Xth XXXXXXXXX 20XX
DOI: 10.1039/b000000x
5
A green method for the synthesis of Dꢀglucosamineꢀderived triazole@palladium catalyst has been
described. The synthesized catalyst containing a 2ꢀpyridylꢀ1,2,3ꢀtriazole ligand was prepared via a click
route in high yields and was explored in Heck crossꢀcoupling reactions between different aryl halides and
olefins under solventꢀfree conditions. The catalyst can be separated from the reaction mixture and reused
10 at least six times with superior activity. In addition, by using this protocol, the marketed drug Axitinib
(antitumor) could be synthesized easily.
Introduction
50 have been made to design novel ligands/catalysts to promote
Palladiumꢀcatalyzed MizorokiꢀHeck coupling reaction is one of
the most powerful synthetic methods for the formation of CꢀC
15 bonds between alkenes and aryl or alkyl halides.1 The
MizorokiꢀHeck coupling products find good applications as
intermediates in the preparation of materials, natural products,
and bioactive compounds.2 However, drawbacks like the high
cost of palladium catalysts, harsh reaction conditions and low
20 yields greatly hamper its largeꢀscale practical applications,
especially in the pharmaceutical industry.3 Attempts to overcome
these boundaries include attempted syntheses of more efficient
catalysts,4 performing coupling reactions in ionic liquids or
water,5 the utilization of solventꢀfree reaction conditions and the
25 application of nonꢀclassical energy sources such as microwave
irradiation, ultrasonication or high pressure and mechanchemical
techniques.6 Recently, interest in the exploration of catalytic
reactions in solventꢀfree conditions is increasing dramatically due
to the solventꢀfree organic syntheses are generally faster,
30 selective, higher yielding with cleaner products, environmentally
benign and involve simple operational procedure as compared to
the classical reaction.7 Hence during the past years, many efforts
transformations under solventꢀfree conditions.8 While how to
keep the activity of catalyst in solventꢀfree catalytic reaction was
still a real challenge.
To data, numerous attempts have been made to prepare new
55 heterogeneous metal catalysts for the coupling reactions, because
of their reusability compared to homogeneous catalysts.9 The
advantages of heterogeneous processes, ease of separation of
product, reusability of catalyst and better steric control of the
reaction intermediate, prompted researchers to immobilize a
60 homogeneous catalytic site on various supports such as silica,10
zeolites,11 magneticꢀmaterials,12 and polymers.13 And from the
published literatures, we also can know most of these catalysts
are in nanoꢀsize. Among these heterogeneous metal catalysts, the
biopolymers (such as starch, cellulose, chitosan or pectin) offers a
65 unique set of environmentally benign properties such as
biodegradability to harmless products, biocompatibility,
stability to air and moisture, and cheapness.14 However, extensive
progress in designing more sustainable chemical processes takes
place if biopolymers themselves without any postꢀmodification.
70 On the other hand, one of the major reasons for poor recyclability
is the aggregation and agglomeration of metal naonoparticles into
less active large particles during the reaction due to the high
surface energy of nanoparticles. Even for these systems using
molecular catalysts, the aggregation and agglomeration still
75 occurred because metal nanoclusters were formed as the reaction
proceeded and all of these lead to the drastic decrease in activity
of the reused catalysts. In this context, the development of highly
active and easily recoverable catalysts which can be used not only
in academic fieldis but also in industrial applications are full of
80 significance.
aCollege of Biology and Environmental Engineering, Zhejiang Shuren
35 University, Hangzhou 310015, China
bCollege of Material, Chemistry and Chemical Engineering, Hangzhou
Normal University, Hangzhou 310036 China
Fax: +86-571-28862867; Tel: +86-571-28862867;
E-mail: zpf100@163.com
40 † Electronic Supplementary Information (ESI) available: 1H NMR
spectra, 13C NMR spectrum, GC/MS profile, HRMS profile. See
DOI: 10.1039/b000000x/
Following our interesting in carbohydrates as a source of
highly efficient catalysts,15 we have recently reviewed that
Dꢀglucosamine as a cheap and readily available chiral scaffold for
the synthesis of a series of novel ligands and organocatalysts.16
85 And our previous investigation and other groups’ work revealed
that support structure and functional groups grafted on the
support played an important role in preventing the aggregation of
metal nanoparticles into the less active large particles.14a,17 The
‡ Footnotes should appear here. These might include comments relevant
to but not central to the matter under discussion, limited experimental and
45 spectral data, and crystallographic data.
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hydrogen bonding interaction and special structure of the sugar
ring may inhibit the motion of metal nanoparticles, thereby
preventing the undesired aggregation and agglomeration.
Herein, we report an effecient method for the synthesis of
5
Dꢀglucosamineꢀderived triazole@palladium catalyst. The
synthesized catalyst containing a 2ꢀpyridylꢀ1,2,3ꢀtriazole ligand
was prepared via a click route and was explored in Heck
crossꢀcoupling reactions between different aryl halides and
olefins under solventꢀfree conditions. The catalyst can be
10 separated from the reaction mixture and reused at least six times
with superior activity. In addition, by using this protocol, the
marketed drug Axitinib (antitumor) could be synthesized easily.
Figure 1. Partial 1H NMR spectra (400 MHz, DMSOꢀd6, 298 K) of (a) the
50 ligand DꢀGlucosamineꢀderived triazoles 4, (b) the palladium complex
Pd@triazoles 5.
15 Results and discussion
spectra of PdL(OAc)2 showed two sets of proton signals, the ratio
of which was around 1:5. Hence the formation of sixꢀmembered
55 chelate rings by binding with the N3 atom and the nitrogen atom
of pyridine is considered to be the predominant structure.Then a
twoꢀdimensional ROESY NMR experiment was conducted, with
the aim of examining the potential spatial proximities among the
different protons of catalyst 5 (Figure S4, ESI†). From the
60 spectrum, it turned out that no contacts were observed among the
aromatic protons of triazoleꢀpyridine and the sugar ring protons,
implying that the functional group was not embraced in the
hydrophobic cavity of the Dꢀglucosamine.
Catalyst synthesis and characterization
20
Scheme 1 Synthesis of
DꢀGlucosamineꢀderived triazole@ Pd catalyst 5.
Reaction conditions: (a) AcONa/(AcO)2O, 12 h; (b) TMSN3, SnCl4,
CH2Cl2, rt; (c) 2ꢀethynylpyridine, CuSO4/NaASc, MeOH/H2O, rt, 12 h; (d)
Pd(OAc)2, toluene, rt, 6h.
25
The synthetic pathway for chelating palladium complexes is
depicted in Scheme 1. Acetylation of the free Dꢀglucosamine
using AcONa/(AcO)2O to afford sugar substrate (2) and the azide
group was introduced into 2 through a simple procedure and
65 Figure 2 TEM images of (a) catalyst 5, (b) recovered catalyst 5 after the
sixth run.
30 verified by the appearance of the N3 band at 2118 cmꢀ1 in FTꢀIR
spectra (Figure S1, ESI†). Then azide (3) underwent a click
process with commercially available 2ꢀethynylpyridine in the
presence of copper sulfate and sodium ascorbate in tertꢀbutanol.
The resulting Dꢀglucosamineꢀderived triazole (4) was further
35 treated with Pd(OAc)2 in toluene to provide the desired solid
catalyst (5).
The surface morphology of the synthesized catalyst 5 was also
characterized by TEM. The TEM analysis showed that the
70 average diameter of the catalysts’ diameter was about 3ꢀ7 nm and
the dispersion of the Pd particles was very well (Figure 1a). The
TEM images also suggested that no palladium clusters were
formed during the preparation.
Complex 5 is stable in air and moisture. They can be stored in
1
air for a long period of time. They are characterized by H, 13C
NMR, 2D ROESY NMR spectrum, Infraꢀred analyses (FTꢀIR),
40 Thermogravimetric analysis (TG) and inductively coupled
plasmaꢀatomic emission spectrometry (ICPꢀAES). It was clear
that the proton signals on pyridine and triazole rings of Pd(OAc)2
in general were shifted downfield apparently (Fig. 1), which
indicated that the palladium ion was coordinated with both units
45 of the ligand and the triazole unit worked as a part of the
bidentate chelator. Meanwhile, because the triazole ligand could
bind with the palladium metal through either N2 or N3 atom, the
.
75 Figure 3. Thermogravimetric plots of
Pd catalyst 5.
Dꢀglucosamineꢀderived triazoles@
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Entry
Solvent
Base
Catalyst
(mol %)
Time
(h)
6
Yieldb
(%)
and 4). With H2O as the solvent, no target product was obtained
(Table 1, entry 5). Excellent yield was achieved under
solventꢀfree conditions (Table 1, entry 6). In order to find a
30 suitable base that would effect the desired reaction, we also
screened several bases such as NaOH, KOAc, K2CO3, and K3PO4.
All the reactions examined led to some conversion, albeit with
quite different efficiencies (Table 1, entries 7ꢀ11), with Et3N
being the most reactive, allowing the reaction to be completed in
35 6 h. However the coupling reactions did not proceed in the
absence of base (Table 1, entry 12). Lowering the reaction
temperature to 60 oC decreased the yield to 77% even with a
prolonged reaction time (Table 1, entry 13). When the amount of
1
2
DMSO
DMF
Toluene
Dioxane
H2O
Et3N
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.05
97
80
Et3N
Et3N
Et3N
Et3N
Et3N
NaOH
KOAc
K2CO3
Cs2CO3
K3PO4
ꢀ
6
3
6
55
4
6
61
5
6
trace
99(95)c
35
6
Neat
Neat
6
40 Table 1 Optimization of reaction conditions.a
7
12
12
12
12
12
6
8
Neat
35
9
Neat
45
aReaction conditions: iodobenzene (1 mmol), styrene (2 mmol), 0.1 mol%
b
of 5, base (3 mmol), solvent (3 mL) under air. Determined by GCꢀMS.
10
11
12
13
14
Neat
61
cIsolated yield in parentheses. dUnder 60 oC.
Neat
23
45 catalyst was reduced to 0.05 mol%, the yields decreased
obviously (Table 1, entry 14). Thus, we gained the optimal
conditions: 1.0 mmol iodobenzene, 2.0 mmol styrene, 0.1 mol%
catalyst 5, 3.0 mmol Et3N, at 80 °C under solventꢀfree conditions.
With optimal conditions determined, the scope of Heck
50 coupling reactions of iodobenzene, bromobenzene and
chlorobenzene with various olefins was investigated and the
results are summarized in Table 2. Many valuable functional
groups such as hydroxylꢀ, chloroꢀ, acetyl and trifluoromethyl
groups were well tolerated. We found substrate with
55 electronꢀwithdrawing group on the benzene ring performed better
than those with electronꢀdonating group. Furthermore,
substituents at meta-, or orthoꢀpositions of the benzene ring do
not affect the efficiency of this transformation (Table 2, entries
10ꢀ12). This catalytic system was also applied for the
60 bromobenzene and chlorobenzene. It is clear from Table 2 that
aryl bromides containing electron donating, electron withdrawing,
or electron neutral substituents are coupled in good yields (Table
2, entries 13ꢀ18). However, aryl chloride coupled with olefins in
moderate yields within 24 h reaction times and also much higher
65 temperature were needed (Table 2, entries 19ꢀ21).
Neat
0
Neat
Et3N
Et3N
12
6
77 d
81
Neat
The catalysts was also characterized by TG to study its thermal
behavior and stability at elevated temperatures and the TG shows
that the catalyst 5 are stable up to 230.9 oC (Figure 3), suggesting
that its high thermal stability allows it to be compatible with most
organic reactions. The palladium amount of which measured by
inductively coupled plasma atomic emission spectrometry (ICPꢀ
5
10 MS) was 1.41 mmol/ gꢀ1.
The optimized conditions were also applied to Heck reactions
between methyl acrylate and tꢀbutyl acrylate with iodobenzene
and bromobenzene, two olefins can give the products in excellent
yield and the tꢀbutyl acrylate acrylate substrate was the best
70 (Table 2, entries 22ꢀ25).
Catalytic studies
15 To evaluate the catalytic performance of catalyst, the model
coupling reaction between iodobenzene 6a and styrene 7a in the
presence of catalyst 5 was conducted to screen the optimal
reaction conditions, including solvents, bases, temperature and
catalyst loadings. Initially, considering that the solvent always
20 plays important roles in Heck coupling reaction. Thus, we have
studied the solvent effect, and the results were shown in Table 1.
After much experimentation on optimizing solvent, it was found
that the use of a high polar solvent like DMF and DMSO afforded
product 3a in high yields (Table 1, entries 1 and 2). In stark
25 contrast, the coupling reaction proceeded less efficiently in
nonpolar solvent such as dioxane and toluene (Table 1, entries 3
Table 2 Heck reaction in the presence of catalyst 5a
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aUnless otherwise stated, the reaction were carried out using 1.0 mmol
Entry
R1
X
R2
Time
(h)
6
Yieldb (%)
aryl halid, 2 mmol olefin, 3.0 mmol Et3N, 0.1 mol% of 5, at 80 oC under
air. bIsolated yield. cUnder 120 oC.
1
H
I
I
I
I
I
I
I
I
I
I
I
I
Ph
95(8a)
83(8b)
86(8c)
95(8d)
94(8e)
82(8f)
71c(8g)
84(8h)
85(8i)
Further experiments were performed to verify the catalyst
recyclability using the reaction of iodobenzene with styrene as a
model system. After the first use, the catalyst was recovered by
simple filtration and reused in the next run after a simple workup.
We were pleased to find that the recovered catalyst was
successfully reused in the subsequent six cycles with a consistent
10 catalytic activity, giving the products in excellent yields
(84ꢀ94%). No Pd metal was detected in the solution by ICP
analysis. Furthermore, the TEM image of the catalyst taken after
the sixth cycle of the reaction does not show significant change in
the morphology and the size of the catalyst (5ꢀ9 nm) (Figure 1b),
15 which indicates the retention of the catalytic activity after
recycling.
2
4ꢀCH3O
4ꢀCH3
4ꢀNO2
4ꢀCF3
4ꢀCl
Ph
6
5
3
Ph
6
4
Ph
6
5
Ph
6
6
Ph
6
7
4ꢀOH
4ꢀCH3CO
4ꢀPh
Ph
12
6
8
Ph
9
Ph
6
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
3ꢀNO2
3ꢀNO2
2ꢀCH3
H
Ph
6
96(8j)
92(8k)
81(8l)
Run
1
2
3
4
5
6
Pyridine
Ph
6
Yield(%)b
94
90
90
88
85
84
12
12
12
12
12
12
12
24
24
24
6
Table 3. Catalyst recycling for solventꢀfree MizorokiꢀHeck reactions.a
Br
Br
Br
Br
Br
Br
Cl
Cl
Cl
I
Ph
82(8a)
80(8b)
83(8c)
92(8d)
90(8e)
80(8i)
aReaction conditions: see Table 1, entry 6. The catalyst was recovered by
20 simple filtration after reaction. b Isolated yield.
4ꢀCH3O
4ꢀCH3
4ꢀNO2
4ꢀCF3
4ꢀPh
Ph
Ph
Ph
With this methodology in hand, we turned our attention to the
synthesis of Axitinib, an important anticancer agent of the vascuꢀ
lar endothelial growth factor (VEGF)(Scheme 3).18 Axitinib has
25 exhibited a tendency to retain palladium, a fact that likely is due
to the indazole ring that may enable formation of a relatively
stable complex with the metal. As a result, the separation of the
Axitinib API from residual palladium has been a challenging
task.19,20 So we planned to enable the palladium removal process
30 using our system to reduce the residual Pd content. Firstly, a
Pd2(dba)3ꢀcatalyzed Migita coupling reaction between
commercially available 6ꢀiodoindazole 9 and 2ꢀmercaptoꢀNꢀ
methylbenzamide 10 and iodination reactions afforded the
iodoindazole intermediate 11 in 90% yield. Then the intermediate
35 11 was treated with 2ꢀvinylpyridine 7e (2 mmol) in the presence
of 0.1 mol% of catalyst 5 and Et3N (3.0 mmo) at 100 oC for 24 h,
Axitinib was isolated in 70% yield.
Ph
Ph
H
Ph
70c(8a)
62c(8b)
73c(8k)
93(8m)
85(8n)
95(8m)
83(8n)
4ꢀCH3O
4ꢀNO2
H
Ph
Ph
CO2Me
CO2Me
CO2t-Bu
CO2t-Bu
H
Br
I
6
H
6
H
Br
6
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m = multiplet and br = broad), coupling constant (J values, Hz).
45 Mass spectra (EIꢀMS) were acquired on an Agilent 5975
spectrometer. Analytical thin layer chromatography (TLC) was
performed on Merk precoated TLC (silica gel 60 F254) plates.
The sugar substrates were prepared according to our previous
reports.15 All compounds were characterized by 1H NMR and
50 mass spectroscopy, which are consistent with those reported in
the literature.1ꢀ3
General procedure for solvent-free Mizoroki-Heck reaction.
55 To a flask, a mixture of Dꢀglucosamineꢀderived triazole @
palladium catalyst 5 (0.1 mol%), aryl halide (1 mmol), olefins (2
mmol) and Et3N (3 mmol) were added and heated at 80 oC under
solventꢀfree conditions. After completion of the reaction,
ethylacetate (10 mL) was added to the flask. The catalyst was
60 separated by simple filtration. Water (3×15 mL) was added to
the ethylacetate phase and decanted. The organic layer was dried
over anhydrous Na2SO4. After evaporation of the solvent, the
resulted crude products was purified by column chromatography
(hexane/ethylacetate) giving the pure products in excellent yields.
65
Scheme 2 Application of the catalyst 5 in the synthesis of Axitini.
Such a heterogeneous catalysts not only gave the product in
satisfying yield but also provided an effficient method for
removal of residual palladium from Axitinib drug substance
material. Residual Pd content in system was determined to be not
more than 20 ppm by atomic absorption spectroscopy. Nextly the
method was also successfully applied to the synthesis of novel
5
10 fluoroquinolone derivatives (Scheme S1, ESI†).
General procedure for recycling of the catalyst in solvent-free
Mizoroki-Heck reaction.
Conclusions
In conclusion, we have prepared a new Dꢀglucosamineꢀderived
After completion of the reaction at the first run, the reaction
70 mixture was cooled down to room temperature and ethylacetate
(5 mL) was added to the reaction mixture to extract organics. The
ethylacetate phase was sucked from the vial by a syringe and the
catalyst was dried under vacuum. After complete drying, the
catalyst was reused for the similar reaction. This process was
75 repeated for six runs.
triazole@palladium catalyst via a “click” route and was explored
15 in Heck crossꢀcoupling reactions between different aryl halides
and olefins under solventꢀfree conditions. The catalyst was very
stable and could be easily separated from the products and reused
at least six times with superior activity. The significantly
enhanced recyclability may be attributed to the catalyst which
20 could efficiently prevent the aggregation and agglomeration of Pd
particles formed during the catalytic reaction into the less active
large particles, as evidenced by TEM. In addition, by using this
protocol, the marketed drug Axitinib(antitumor) could be
synthesized easily and such an efficient process for removal of
25 residual palladium from Axitinib drug was well provided. The
General procedure for synthesis of Axitini under solvent-free
condition.
80 To
a
flask,
a
mixture of intermediate 11 (1 mmol),
ꢀglucosamineꢀ
2ꢀvinylpyridine 7e (2 mmol), Et3N (3 mmol) and
D
derived triazole @palladium catalyst 5 (0.1 mol%) were added
and heated at 100 C under solventꢀfree conditions. The reaction
applicability of the
catalyst in other fields of organic transformation is underway in
our laboratory.
Dꢀglucosamineꢀderived triazole@palladium
o
progress was monitored by TLC. After completion of the reaction,
85 the mixture was allowed to cool to room temperature,
ethylacetate (10 mL) was added to the flask. The catalyst was
separated by simple filtration and the aqueous phase was
extracted with CH2Cl2 for 3 times (3×2 mL). Then the combined
organic layers were dried over anhydrous Na2SO4, concentrated
90 under vacuum and purified by column chromatography
(hexane/ethyl acetate 10:1) to afford the desired product.
Residual Pd content in solvent was determined to be not more
than 20 ppm by atomic absorption spectroscopy.
30
Experimental section
The starting materials were commercially available and were
used without further purification except solvents. The products
35 were isolated by column chromatography on silica gel (200ꢀ300
mesh) using petroleum ether (60ꢀ90oC) and ethyl acetate. Melting
points were determined on an Xꢀ5 Data microscopic melting
point apparatus. 1H NMR and 13C NMR spectra were recorded on
a Bruker Advance 400 spectrometer at ambient temperature with
40 CDCl3 or DMSOꢀd6 as solvent unless otherwise noted and
95
1
Acknowledgments
tetramethylsilane (TMS) as the internal standard. H NMR data
were reported as follows: chemical shift (δ ppm), multiplicity (s =
singlet, d = doublet, t = triplet, q = quartet, dd = doubleꢀdoublet,
This work was supported by the National Natural Science
100 Foundation of China (No. 21376058, 21302171), Zhejiang
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