Combining ethylenediamine and ionic liquid functionalities within SBA-15: A promising catalytic pair for tandem Cu–AAC reaction

Article abstract of DOI:10.1016/j.apcata.2017.07.006

This paper discloses the assembly and characterization of an advanced heterogeneous catalyst formulated as CuI@SBA-15/PrEn/ImPF₆. It is based on a mesoporous silica SBA-15 skeleton which bears a supported ethylenediamine/CuI complex and covalently anchored imidazolium/PF₆ ionic liquid. This catalyst was successfully applied in tandem methods for triazole synthesis starting from different substrate pairs: aryl halides and aryl acetylenes (method A), arylboronic acids and aryl acetylenes (method B). The CuI@SBA-15/PrEn/ImPF₆ catalyst showed high activity (up to 90% yields of triazole products under optimized reaction conditions), high stability and no appreciable leaching of CuI owing to its strong binding via the coordination with PrEn functionality. Therefore, the catalyst can be recycled for several consecutive runs (7–14 cycles) in this new synthetic method. For both methods A and B, specific types of green approaches were developed and the favorable products were produced in high yields.

Full text of DOI:10.1016/j.apcata.2017.07.006

Accepted Manuscript
Title: Combining Ethylenediamine and Ionic Liquid
Functionalities within SBA-15: A Promising Catalytic Pair for
Tandem Cu–AAC Reaction
Authors: Habib Golchin Hosseini, Esmail Doustkhah, Marina
V. Kirillova, Sadegh Rostamnia, Ghodrat Mahmoudi,
Alexander M. Kirillov
PII:
S0926-860X(17)30306-X
DOI:
Reference:
http://dx.doi.org/doi:10.1016/j.apcata.2017.07.006
APCATA 16311
To appear in:
Applied Catalysis A: General
Received date:
Revised date:
Accepted date:
14-5-2017
29-6-2017
5-7-2017
Please cite this article as: Habib Golchin Hosseini, Esmail Doustkhah, Marina
V.Kirillova, Sadegh Rostamnia, Ghodrat Mahmoudi, Alexander M.Kirillov,
Combining Ethylenediamine and Ionic Liquid Functionalities within SBA-15: A
Promising Catalytic Pair for Tandem Cu–AAC Reaction, Applied Catalysis A,
Generalhttp://dx.doi.org/10.1016/j.apcata.2017.07.006
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Combining Ethylenediamine and Ionic Liquid Functionalities within SBA-15: A Promising
Catalytic Pair for Tandem Cu–AAC Reaction1
Habib Golchin Hosseini,a Esmail Doustkhah,a Marina V. Kirillova,b Sadegh Rostamnia,*,a Ghodrat
Mahmoudi,c,*, Alexander M. Kirillov*,b
aOrganic and Nano Group (ONG), Department of Chemistry, University of Maragheh, P.O. Box. 55181-
83111, Maragheh, Iran. Fax: +98 (421) 2276066. E-mail: srostamnia@gmail.com;
rostamnia@maragheh.ac.ir
bCentro de Química Estrutural, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais,
Lisbon, Portugal. E-mail: kirillov@tecnico.ulisboa.pt
cDepartment of Chemistry, University of Maragheh, P.O. Box. 55181-83111, Maragheh, Iran. Fax: +98
(421) 2276066. E-mail:mahmoudi_ghodrat@yahoo.co.uk
1This article is dedicated to Prof. Martin Schmal on the occasion of his 80th birthday and for his
important contribution to catalysis science.
Graphical Abstract
Research highlights:





New heterogeneous SBA-15 based catalyst was assembled and fully characterized;
This CuI@SBA-15/PrEn/ImPF6 material bears ethylenediamine and ionic liquid functionalities;
Catalyst was successfully applied in triazole synthesis in aqueous medium;
Two different reaction protocols were developed and optimized;
High product yields and catalyst recyclability were achieved.
1

Abstract
This paper discloses the assembly and characterization of an advanced heterogeneous catalyst
formulated as CuI@SBA-15/PrEn/ImPF6. It is based on a mesoporous silica SBA-15 skeleton
which bears a supported ethylenediamine/CuI complex and covalently anchored imidazolium/PF6
ionic liquid. This catalyst was successfully applied in tandem methods for triazole synthesis starting
from different substrate pairs: aryl halides and aryl acetylenes (method A), arylboronic acids and
aryl acetylenes (method B). The CuI@SBA-15/PrEn/ImPF6 catalyst showed high activity (up to
90% yields of triazole products under optimized reaction conditions), high stability and no
appreciable leaching of CuI owing to its strong binding via the coordination with PrEn
functionality. Therefore, the catalyst can be recycled for several consecutive runs (7–14 cycles) in
this new synthetic method. For both methods A and B, specific types of green approaches were
developed and the favorable products were produced in high yields.
Keywords: Click chemistry; Triazole synthesis; Cu–AAC; Green chemistry; Heterogeneous
catalysis; Aqueous medium.
1. Introduction
Copper compounds are present in a wide diversity of catalytic systems owing to versatile redox
characteristics of this metal, its low cost, biological relevance, and rich chemistry [1–7]. In
particular, copper catalysts are also used in click chemistry that plays a significant role in strategic
organic synthesis owing to its advantages such as high yields, regioselectivity, and atom economy
[7–9]. Copper-catalyzed 1,3-dipolar azide-acetylene cycloaddition (Cu–AAC) can be assumed as
a click reaction which leads to a regioselective synthesis of triazoles [9–14]. Among various copper
species, derivatives of Cu(I) represent the most common type of catalysts in this reaction [7–10].
2

Besides, Cu(II) species can also be applied in the presence of sodium ascorbate or hydrazine as a
reducing agent [11]. Copper ferrite [12], metallic Cu or CuO nanoparticles [13,15], and Cu-BDC
[14] (BDC = 1,4-benzene dicarboxylate) are some examples of copper species which are applied
in the Cu–AAC reactions. In addition, the role of ligand on the efficiency of copper catalysis is
inevitable. Various types of ligands were suggested and developed for Cu species [7–9]. The
individual use of diamine-based blocks [16] and imidazolium derivatives [15,17] as ligands for
copper was also reported. In comparison to homogeneous protocols, the application of
heterogeneous copper (e.g., CuO nanostructures or CuFe2O4) catalysts is somehow a prevailing
approach [18] to achieve catalyst recycling with an easier operation protocol in typical three-
component (3-CRs) Cu–AAC reactions. The use of recyclable and stable heterogeneous catalysts
can have a drastic impact on the development of green and sustainable synthetic protocols
[7,19,20].
In the present paper, we have used two methods for the in situ synthesis of phenyl azides to react
with phenylacetylene (or derivatives) via tandem procedure (Scheme 1) under aqueous conditions,
as a green medium for organic synthesis [21]. Typical starting materials for the in situ synthesis of
azides are iodobenzene (method A) and phenylboronic acid (method B), along with
phenylacetylene and sodium azide. Both of the reactions were developed under the specific reaction
conditions with the same catalyst. The catalyst which is designed for this series of syntheses, has
been developed based on our previous background and following the principles of green chemistry
[22-24]. The catalyst is based on a mesoporous silica (SBA-15) support with supported active CuI
species, that are covalently bonded via ethylenediamine functionality present on the surface of
-
SBA-15. Moreover, an imidazolium-based ionic liquid with a PF6 counter ion, as a hydrophobic
anion, was also anchored to the surface of SBA-15 to balance hydrophobicity and hydrophilicity
within the pores in order to increase the diffusability of the substrate and product molecules.
3

2. Experimental
2.1. Materials and methods
All reagents were obtained from commercial sources and were used without further purification.
1H and 13C NMR spectra were measured (CDCl3) on a Bruker DRX-500 AVANCE spectrometer
at 500.13 and 125.7 MHz, respectively. IR spectra were recorded on Shimadzu IR-460
spectrometer (KBr pellets). Scanning electron microscopy (SEM) images were obtained on Zeiss-
DSM 960A microscope. Transmission electron microscopy (TEM) images were recorded on Zeiss
EM 900 electron microscope. Additional NMR and TGA data are available as Supplementary
Material.
2.2. Synthetic procedure for SBA-15/ImCl
For the preparation of SBA-15/ImCl, SBA-15 was first synthesized according to a previously
reported procedure [24]. The obtained solid was used for functionalization with 3-
chloropropyltrimethoxysilane (CPTMS) and then reacted with N-methylimidazole to form SBA-
15/ImCl. Typically, 1 g of SBA-15 was activated at 70 oC for 60 min and then dispersed in 15 mL
of toluene at room temperature for 30 min. To the obtained mixture, 2 mmol of CPTMS was added
o
and the temperature was raised to 110 C under reflux conditions for 12 h. Then the final white
solid, named as SBA-15/PrCl, was obtained by filtration, washed with methanol, and dried in oven
at 70 oC for 2 h. The obtained solid in this step was dispersed in toluene (15 mL) and then 4 mmol
o
of N-methylimidazole was added. The reaction mixture was allowed to stir at 80 C for 24 h.
Finally, the SBA-15/ImCl solid was isolated by filtration and dried at 70 oC in vacuum for 4 h.
4

2.3. Synthesis of CuI@SBA-15/PrEn/ImPF6
The SBA-15/ImCl solid (1 g) was dispersed in toluene (10 mL) to react with (MeO)3SiPrEn (4
mmol) under reflux conditions for 18 h to obtain ethylenediamine functionality on the surface of
SBA-15/ImCl (this was named SBA-15/PrEn/ImCl). Chloride anions of the obtained solid were
-
ion exchanged with PF6 . Typically, SBA-15/PrEn/ImCl (0.5 g) was dispersed in 15 mL solution
of 0.02 M KPF6 in acetone at room temperature for 6 h. Finally, the solid was filtered and dried in
o
oven for 3 h at 70 C. The resulted solid (0.5 g) in this step was dispersed in the solution of CuI
(0.15 g) in acetonitrile (10 mL) and allowed to stir vigorously for 20 h at room temperature. The
final solid (CuI@SBA-15/PrEn/ImPF6) was isolated by filtration, washed with acetone, and dried
in oven at 70 oC for 2 h under reduced pressure. The amount of copper loading (2.3 wt% of Cu) on
SBA-15/PrEn/ImPF6 was determined by atomic absorption spectroscopy (AAS).
2.4. Typical synthetic pathway for triazoles via method A
For the synthesis of triazoles from iodobenzenes and phenylacetylenes via the in-situ generated
azides [25], in a typical reaction, iodobenzene (1 mmol) was reacted with NaN3 (1.5 mmol) in 0.5
mL H2O/DMSO (1:2) at room temperature under inert atmosphere in the presence of CuI@SBA-
15/PrEn/ImPF6 (4.1 mol% of Cu) and L-proline (10 mol%) under vigorous stirring. After 8 h,
phenylacetylene (1 mmol) was added to the reaction mixture and allowed to react for further 8 h at
80 oC. Finally, the reaction mixture was centrifuged to separate the catalyst to reuse in next runs.
The product was extracted from solution by adding ethyl acetate. The extracted organic residue
was allowed to evaporate to generate a solid. The solid was purified by n-hexane without any
column chromatography. Total isolated yield was calculated.
5

2.5. Typical synthesis pathway of triazoles via method B
For the synthesis of triazoles from phenylboronic acids and phenylacetylenes, in a typical reaction,
phenylboronic acid (1 mmol) was reacted with NaN3 (1.2 mmol) in 0.5 mL H2O at room
temperature under inert atmosphere in the presence of CuI@SBA-15/PrEn/ImPF6 (3.8 mol% of
Cu) under vigorous stirring. After 4 h, phenylacetylene (1 mmol) was added to the reaction mixture
and allowed to react for further 4 h at room temperature. Finally, the reaction mixture was
centrifuged to separate the catalyst to reuse in next runs. The product was extracted from solution
by adding ethyl acetate. The extracted organic residue was allowed to evaporate to generate a solid.
The solid was purified by n-hexane without any column chromatography. Total isolated yield was
calculated.
3. Results and discussion
3.1. Synthesis and characterization of catalyst
In this paper, we designed a new heterogeneous catalyst based on mesoporous silica SBA-15 as a
support for CuI. The aim of this work was to obtain a recyclable material that could stabilize CuI
by incorporating it into the SBA-15 functionalized with PrEn and an ionic liquid (IL). In fact, the
-
presence of N-methylimidazolium/PF6 functionality in the material can increase the mass transfer
regarding to its ionic liquid and hydrophobic nature. In general, for the synthesis of the catalyst,
SBA-15 was first functionalized by 3-chloropropyltrimethoxysilane (CPTMS) to obtain SBA-
15/PrCl with propylchloride chains. Then, N-methylimidazole reacted with SBA-15/PrCl to
produce an ionic liquid functionality. In the next step, this material was post-modified again by
PrEn allowing an additional functionalization of the surface of SBA-15 via residual silanol groups.
-
A Cl- anion of N-methylimidazolium chloride in SBA-15/ImCl was also exchanged with PF6 anion
6

-
to obtain a final version of support (SBA-15/PrEn/ImPF6). Ion exchange of Cl- with PF6 could
cause a remarkable effect on the hydrophobicity/hydrophilicity and, therefore, on the mass transfer
of reactants [26,27]. Finally, CuI as a recognized catalyst for Cu–AAC and related reactions [7-
9,28], was supported onto SBA-15/PrEn/ImPF6 by coordination with ethylenediamine
functionality to produce a supported CuI@SBA-15/PrEn/ImPF6 catalyst (Cu content 2.3 wt%).
A general six-step synthetic pathway for this catalyst was applied. In our previous reports, we
showed that ethylenediamine (PrEn) can be an excellent bidentate ligand to support metal ions such
as Pd2+ and Cu2+ [29]. Apart from the ligand functionality, by confining or immobilizing an ionic
liquid functionality within a heterogeneous catalyst, we can potentially improve the mass transfer
and diffusion rate of reactants [30].
Hence, in the present work, we functionalized the SBA-15 matrix with both imidazolium/PF6 and
PrEn moieties to enhance the catalytic activity of the resulting material. TEM image of CuI@SBA-
15/PrEn/ImPF6 (Figure 1a) shows that the morphology is related to mesochannels of SBA-15,
which is maintained after several steps of post-modification. Besides, the absence of any small dots
suggests that CuI is converted neither to copper oxide nor metallic nanoparticles, but is present as
a copper(I) iodide complex with PrEn. SEM image of CuI@SBA-15/PrEn/ImPF6 indicates the
morphology of this mesostructure. The rod-like morphology also originally refers to SBA-15
structure (Figure 1b).
3.2. Catalytic activity of CuI@SBA-15/PrEn/ImPF6 in triazole synthesis by method A
In order to obtain a diversity of triazole derivatives, we attempted the in situ synthesis of aryl azides
starting from aryl halides. In fact, the formation of aryl azides from the reaction between an aryl
7

halide and azide anion is an important step in synthetic organic chemistry [31]. Therefore, the use
of aryl halides for the in situ synthesis of phenyl azides and subsequently their application in the
Cu–AAC reaction was designed in this work as a method A tandem reaction (Table 2). As a model
reaction, the CuI@SBA-15/PrEn/ImPF6 catalyst was evaluated for tandem coupling of
iodobenzene, sodium azide, and phenylacetylene to give 1,4-diphenyl-1H-1,2,3-triazole. Addition
of L-proline as an additive (organobase) was effective in raising the efficiency of the reaction by
producing higher product yields [25]. Several solvents were tested at various temperatures and
different reaction times (Table 1). Among the tested solvents, the mixture of DMSO/H2O (2:1) led
to the best results. Besides, the reactions are more efficient at higher temperatures and 80 oC was
found to be an optimum one. At temperatures above 80 oC, a side reaction can occur to some extent,
namely a homocoupling that lowers the yield of the principal triazole product. No formation of
regio-isomers was detected. Effect of the reaction time was also investigated (Table 1). Therefore,
o
the optimized reaction conditions were set to 16 h of the reaction at 80 C in DMSO/H2O (2:1),
resulting in the maximum 93% product yield of 1,4-diphenyl-1H-1,2,3-triazole. Besides, an effect
of catalyst loading was also studied, revealing that 4.1 mol% Cu (relatively to substrate) is an
optimum catalyst amount.
After finding proper reaction conditions for the one-pot tandem synthesis of 1,4-diphenyl-1H-
1,2,3-triazole (model substrate), other types of aryl iodides and aryl acetylenes were applied for the
synthesis of triazole derivatives. In this study, phenyl bromides were relatively less active than
phenyl iodides (Table 2, entries 1 and 2), and thus the latter were used as preferable substrates. The
data given in Table 2 demonstrate that 4-iodoanisole and 4-iodotoluene along with phenylacetylene
or p-tolylacetylene can also be used as substrates, leading to a successful synthesis of the
8

corresponding triazole derivatives in 90–93% total isolated yields.
The recyclability of the catalyst was also tested under typical reaction conditions. The CuI@SBA-
15/PrEn/ImPF6 catalyst essentially maintains the activity for at least for 14 consecutive runs
(Figure 2). In fact, only a slight reduction of the product yield from 93 to 83% was observed after
fourteen cycles. This observation supports the stability of the catalyst. A slight decrease of the total
product yield can be explained by a minor reduction of the amount of catalyst during its
isolation/centrifugation procedure after each reaction run; it can also be associated with a partial
surface deactivation. The CuI@SBA-15/PrEn/ImPF6 catalyst showed high activity (up to 90%
yields of triazole products under optimized reaction conditions), high stability and no appreciable
leaching of CuI owing to its strong binding via the coordination with PrEn functionality. The AAS
analysis of the recovered catalyst after 14 reaction cycles reveals a comparable Cu loading (2.3
wt% of Cu) to that of the parent sample. Besides, the TEM image of the catalyst recovered after 14
runs shows that the main backbone and mesochannels remain intact (Fig. S5, Supplementary
Material).
3.3. Catalytic activity of CuI@SBA-15/PrEn/ImPF6 in triazole synthesis by method B
In the present work, we developed a tandem synthesis pathway for various triazoles, by replacing
aryl halides with arylboronic acids [32] (method B). This method represents an alternative synthetic
pathway for the in situ production of aryl azides, which is also efficiently catalyzed by CuI@SBA-
9

15/PrEn/ImPF6. Other related catalytic systems were evaluated for comparative purposes in the
tandem synthesis of 1,4-diphenyl-1H-1,2,3-triazole (Table 3) as a model substrate. On this
comparison, the CuI@SBA-15/PrEn/ImPF6 catalyst showed a superior activity (88–92% yield) to
those of simple CuI or CuCl salts (45% yields) or supported IL-free CuI@SBA-15/PrEn catalyst
(50% yield, Table 3). Method B in comparison with method A has some advantages such as shorter
reaction time and lower temperature. Moreover, the use of the DMSO/H2O mixture can be avoided
in method B since the reaction efficiently proceeds in sole H2O as a solvent.
In method B, the type of the solvent also plays an important role (Fig. 3a). Likewise in method A,
protic solvents are more efficient than the aprotic ones in method B, with H2O and MeOH being
more favorable to attain high product yields. Given green character of H2O, it was selected for
further studies. The CuI@SBA-15/PrEn/ImPF6 catalyst is essentially stable and maintains an
almost original level of activity even after 10 reaction cycles (Fig. 3b).
Beyond these studies, we explored some other substrates in the method B and synthesized different
derivatives of triazoles (Table 4). In fact, p-tolyl- or m-tolylboronic acids along with
phenylacetylene or p-tolylacetylene are also suitable substrates, resulting in high (92–93%) yields
of the respective triazole derivatives. These syntheses can be performed using shorter reaction
times and lower temperatures if compared to the protocols based on the aryl halide substrates.
10

4. Conclusions
In the present study, we designed a stable and recyclable heterogeneous catalyst formulated as
CuI@SBA-15/PrEn/ImPF6. It is based on CuI supported on SBA-15 that additionally contains an
ethylene diamine (PrEn) and an ionic liquid (ImPF6) functionalities. The pores of the catalyst were
functionalized by an ionic liquid, allowing to remarkably alter its efficiency by affecting the
-
diffusion and mass transfer characteristics. The hydrophobic nature of IL anion (PF6 ) is also
important in the reaction progress by affecting the hydrophobicity of the mesochannels.
The obtained CuI@SBA-15/PrEn/ImPF6 material was applied as an efficient and recyclable
catalyst for the copper-catalyzed azide–alkyne cycloaddition (Cu–AAC) synthesis of various
triazole derivatives via two different reaction methods. The effects of various reaction parameters,
namely catalyst loading, solvent, temperature and time, and catalyst recycling were investigated in
the tandem synthesis of 1,4-diphenyl-1H-1,2,3-triazole by two different methods as a model
reaction, resulting in very high yields (>90%) of this product. Substrate scope was also studied by
exploring some other aryl halide and aryl acetylene substrates. A notable feature of the present
catalyst concerns its bifunctional activity [33], suitable for both the in situ synthesis of aryl azides
from aryl halides or arylboronic acids (step 1) and in the conventional Cu–AAC reactions (step 2).
Between methods A and B, the latter was more efficient and advantageous owing to lower reaction
times and temperatures, as well as the use of sole water as a green reaction medium. The study thus
also contributes to the design of catalysts and catalytic processes that proceed efficiently in aqueous
medium [21,34–36].
Acknowledgements
We are grateful to the University of Maragheh for the financial support of this research. We also
acknowledge the FCT (IF/01395/2013/CP1163/CT005, UID/QUI/00100/2013), Portugal.
11

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13

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14

Figure 1. SEM (a) and TEM (b) images and schematic synthesis (c) of CuI@SBA-15/PrEn/ImPF6.
Figure 2. Effect of catalyst recycling in the synthesis of 1,4-diphenyl-1H-1,2,3-triazole by method A
(reaction conditions are those of Table 2).
15

Figure 3. 1,4-Diphenyl-1H-1,2,3-triazole synthesis by method B catalyzed by CuI@SBA-15/PrEn/ImPF6:
(a) effect of different solvents and (b) effect of catalyst recycling (solvent H2O). Reaction conditions are
those of Table 3.
Scheme 1. A glimpse at the present work.
16

Table 1. Optimization of the reaction conditions in tandem synthesis of 1,4-diphenyl-1H-1,2,3-
triazole by method A catalyzed by CuI@SBA-15/PrEn/ImPF6.a
Entry
Solvent
t (h) T (oC) Yield (%)b
1
2
3
4
5
6
7
8
H2O
19
16
16
16
16
16
24
20
80
80
80
80
80
100
80
80
88
88
55
90
93
91
20
24
MeOH
EtOH
DMSO
DMSO/H2O (2:1)
DMSO/H2O (2:1)
Toluene
Dioxane
aReaction conditions: iodobenzene (1 mmol), phenylacetylene (1.1 mmol), NaN3 (1.5 mmol), catalyst (4.1 mol% Cu
vs. substrate), DMSO/H2O (2:1) (0.5 mL), L-proline (10 mol%); bTotal isolated yield.
17

Table 2. Substrate scope in tandem synthesis of triazoles from aryl halides and aryl acetylenes by
method A catalyzed by CuI@SBA-15/PrEn/ImPF6.a
Entry Aryl halide
1
Product
Yield (%)b
93
2
85
3
4
5
6
91
93
93
92
a Reaction conditions: aryl halide (1 mmol), aryl acetylene (1.1 mmol; phenylacetylene: entries 1–4; p-tolylacetylene:
entries 5 and 6), NaN3 (1.5 mmol), L-proline (10 mol%), and DMSO/H2O (2:1) (0.5 mL), catalyst (4.1 mol% Cu vs.
substrate), 80 oC, 16 h; b Total isolated yield.
18

Table 3. Catalyst optimization in tandem synthesis of 1,4-diphenyl-1H-1,2,3-triazole by method
B.a
Catalyst
Yieldb
Entrya Catalyst
loading
t (h) T (oC)
)%(
(mol% Cu)
1
2
3
4
5
6
7
8
–
–
8
8
8
8
12
8
8
50
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
–
CuCl
CuI
10
10
3.8
5
3.8
3.5
4.0
40
45
50
85
92
88
92
CuI@SBA-15/PrEn
CuI@SBA-15/PrEn/ImCl
CuI@SBA-15/PrEn/ImPF6
CuI@SBA-15/PrEn/ImPF6
CuI@SBA-15/PrEn/ImPF6
8
aReaction conditions: phenylboronic acid (1 mmol), phenylacetylene (1 mmol), NaN3 (1.2 mmol), different Cu(I)-
based catalysts (3.5-10 mol% Cu vs. substrate), H2O (1 mL). bTotal isolated yield.
19

Table 4. Substrate scope in tandem synthesis of triazoles from arylboronic acids and aryl
acetylenes by method B catalyzed by CuI@SBA-15/PrEn/ImPF6.a
Entry
Boronic acid
Product Yield )%(b
1
2
92
93
92
3
4
93
aReaction conditions: arylboronic acid (1 mmol), aryl acetylene (1 mmol; phenylacetylene: entries 1–3; p-
tolylacetylene: entry 4), NaN3 (1.2 mmol), catalyst (3.8 mol% Cu vs. substrate), H2O solvent (0.5 mL), r.t., 8 h. b Total
isolated yield.
20