The synthesis and structural characterization of furanyl-1,2,3-triazole Gold(I) and its application in synthesis of enones from propargylic esters and alcohols

Article abstract of DOI:10.1016/j.jorganchem.2019.120944

Furanyl-1,2,3-triazole gold(I) was designed, synthesized and characterized by X-ray crystallography, and was found to exhibit high catalytic activity for the synthesis of enones in good to high yields through a propargylic ester rearrangement and subsequent hydration. Notably, excellent E/Z selectivity was observed in these transformations. This catalyst was also effective in catalyzing the rearrangement of propargylic alcohols and hydration of alkynes. Compared to triazole acetyl gold(III) and other gold complexes, the furanyl-1,2,3-triazole gold(I) is able to promote these transformations smoothly at a low temperature with the E isomer of enones as the only product.

Full text of DOI:10.1016/j.jorganchem.2019.120944

Journal of Organometallic Chemistry 901 (2019) 120944
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
The synthesis and structural characterization of furanyl-1,2,3-triazole
Gold(I) and its application in synthesis of enones from propargylic
esters and alcohols
,
,
, *
Wei Yao a b, Yilin Zhang c, Xiaqing Xu d, Yongchun Yang a, Wei Zeng b **, Dawei Wang a
a Key Laboratory of Synthetic and Biological Colloid, Ministry of Education, School of Chemical and Material Engineering, Jiangnan University, Wuxi, 214122,
China
b Dalian Wondersun Biochemical Technology Co. LTD, Double D4 street, Development zone, Dalian, 116600, Liaoning Province, China
c C. Eugene Bennett Department of Chemistry, West Virginia University, Morgantown, WV, 26506, United States
d Department of Chemistry and Biochemistry, Suffolk University, Boston, MA, 02108, United States
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 8 July 2019
Received in revised form
16 September 2019
Accepted 18 September 2019
Available online 19 September 2019
Furanyl-1,2,3-triazole gold(I) was designed, synthesized and characterized by X-ray crystallography, and
was found to exhibit high catalytic activity for the synthesis of enones in good to high yields through a
propargylic ester rearrangement and subsequent hydration. Notably, excellent E/Z selectivity was
observed in these transformations. This catalyst was also effective in catalyzing the rearrangement of
propargylic alcohols and hydration of alkynes. Compared to triazole acetyl gold(III) and other gold
complexes, the furanyl-1,2,3-triazole gold(I) is able to promote these transformations smoothly at a low
temperature with the E isomer of enones as the only product.
Keywords:
Gold
© 2019 Elsevier B.V. All rights reserved.
Enones
Propargylic alcohols
Propargylic ester
Alkynes
1. Introduction
improved stability and activity (Scheme 1) [7]. For example, we
have synthesized the pyridyltriazole gold(III) complex (TA-Py-Au)
In past several decades, gold catalysis has attracted great
attention in organic synthesis for its potential in delivering highly
desirable derivatives from relatively accessible unsaturated com-
pounds [1]. However, gold catalysis remains a highly challenging
field and has received limited development, because of poor sta-
bility and easy decomposition at high temperatures, which usually
yields gold nanoparticles or gold mirrors [2]. To address this limi-
tation, scientists have developed ligands of strong coordination
ability aiming to improve the stability of the gold catalyst [3]. In
particular, Shi et al. found that triazole is able to enhance the sta-
bility [4] and thereby improve the catalytic efficiency of gold(I)
complexes [5], which have found important applications in a va-
riety of organic transformations [6]. Recently, we have developed a
series of triazole coordinated gold catalysts which have exhibited
which exhibits high catalytic activity to produce a-haloenones. We
have also used the high efficiency of triazole to promote hydrogen
borrowing reactions [8]. However, development of innovative li-
gands is highly desirable for the next generation gold catalysts. In
this work, we designed and synthesized a novel triazole gold(I)
complex, which revealed high catalytic activity for the synthesis of
enones in good to high yields through a propargylic ester rear-
rangement and subsequent hydration.
2. Results and discussion
The novel Au complex (FTA-Au) was prepared as follows. First,
2-formylofuran was mixed with MeOH and KOH and stirred
vigorously for 1 h in an ice bath to achieve 2-(2-nitrovinyl)furan L1.
Next, furanyl-1,2,3-triazole L2 was synthesized from L1 and NaN3 in
DMSO using anhydrous aluminum chloride as catalyst (Scheme 2).
Finally, the Au complex was successfully prepared in high yield by
mixing AuPPh3Cl, AgSbF6 and corresponding triazole ligand L2 in a
1:1.1:1.04 M ratio in DCM at RT for 4 h. The exact structure of the
* Corresponding author.
** Corresponding author.
E-mail addresses: wzengdicp@163.com (W. Zeng), wangdw@jiangnan.edu.cn
(D. Wang).
https://doi.org/10.1016/j.jorganchem.2019.120944
0022-328X/© 2019 Elsevier B.V. All rights reserved.

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W. Yao et al. / Journal of Organometallic Chemistry 901 (2019) 120944
Scheme 1. Several gold complexes.
enone was seen in the aforementioned allene synthesis, we next
focused on improving enone selectivity of this propargylic ester
rearrangement. After screening several reaction conditions
(Table 1), a mild condition was found to produce enone in high yield
using 1,4-dioxane as the solvent (Table 1, entry 7). It should be
noted that no reaction was found when AuCl3 was employed as the
catalyst. The following conditions revealed that the best result was
obtained under 40 ꢀC, while high temperature produced lower
yields, which might be caused by the decomposition of gold
catalysts.
With optimal reaction conditions in hand, the substrate scope of
this Au catalyzed propargylic ester rearrangement was assessed
and the substituent effect on the aryl moiety was investigated
(Table 2). Several useful functional groups were found to be well
tolerated in this reaction, including nitro, methyl, fluoro, methoxyl
and chloro substituents. When a sterically hindered ortho substit-
uent was used, a slightly lower yield was obtained. Furthermore,
the diaryl substituents were also employed and found to be effi-
cient to afford the desired product by this methodology. Overall, the
highest yield was achieved when a methoxyl substituent was used
in this transformation.
Since FTA-Au exhibited excellent catalytic efficiency and high
stability, we next explored whether this FTA-Au could also be
effective in promoting the MeyereSchuster arrangement of prop-
argylic alcohols. So we conducted the rearrangement of propargylic
alcohols using FTA-Au as a catalyst and gladly found the enone
product can be efficiently generated in good yield. Further
Scheme 2. Synthesis and X-ray of FTA-Au.
resulting gold complex FTA-Au was confirmed by a single-crystal X-
ray diffraction analysis (CCDC number 1909674).
As illustrated in Fig. 1, complex FTA-Au adopted the general
linear structure, with the triphenylphosphine chelating ligand
occupying one coordination position, the furanyl-1,2,3-triazole ring
acting as another ligand. In addition, the Au-P and Au-N1 distances
were 2.2443(6) Å and 2.0715(19) Å, respectively. Notably, the AueP
bond length was longer than AueN1 so the combination of gold and
nitrogen may be stronger.
The catalytic activity of the FTA-gold(I) complex was found in
the propargylic ester rearrangement to achieve allenes and enones
[9,10]. The common propargyl ester 1a was selected as the starting
material in the model reaction with 2 mol% FTA-Au loaded. Initially,
the allene product 2a was obtained in 36% yield. Meanwhile, the
starting material and enone (3a) were also found in 21% and 29%
yield, respectively. A series of reaction conditions were attempted
in order to improve the selectivity of allenes in this reaction.
However, these attempts remained unsuccessful revealing the low
activity nature of the FTA-Au in producing allenes. Since 29% of
Table 1
Optimization of reaction conditionsa.
Entry
Solvent
T (oC)
Convn.
2a[%]b
3a[%]b
1
2
3
4
5
6
7
8
CH2Cl2
1,4-dioxane
acetone
CHCl3
MeOH
rt
rt
rt
rt
rt
rt
rt
rt
rt
rt
40
50
60
70
79
85
43
36
65
58
93
84
36
8
7
29
61
16
12
54
51
86
72
16c
<5d
88
88
87
79
5
<5
<5
<5
<5
5
<5
<5
<5
<5
<5
EtOH
1,4-dioxane/H2O
MeOH/H2O
1,4-dioxane/H2O
1,4-dioxane/H2O
1,4-dioxane/H2O
1,4-dioxane/H2O
1,4-dioxane/H2O
1,4-dioxane/H2O
9
37
10
11
12
13
15
<5
>95
>95
>95
>95
a
Fig. 1. X-ray crystal structure of FTA-Au with the thermal ellipsoids drawn at the 50%
probability level. Hydrogen atoms have been omitted for clarity. Selected bond lengths
(Å) and angles (deg): Au-P ¼ 2.2443(6), Au-N1 ¼ 2.0715(19), C4-C5 ¼1.448(3), P-Ir-
N1 ¼177.18(5), N1-C5-C4 ¼123.7(2).
Conditions: 1a (1.0 mmol), FTA-Au (2 mol%), solvent (4 mL), 24 h.
b
c
Isolated yields.
AuCl3 was used.
No [Au].
d

W. Yao et al. / Journal of Organometallic Chemistry 901 (2019) 120944
3
Table 2
Substrate experiments of propargylic estera,b
.
a
b
Conditions: 1 (1.0 mmol), FTA-Au (2 mol%), 1,4-dioxane (10% H2O, 4 mL), 40 ꢀC, 24 h Isolated yields based on 1.
experiments revealed that the reaction could tolerate a large vari-
ety of substituted substrates, while also achieving good to excellent
yields with the use of FTA-Au catalyst (Table 3).
this reaction to produce acetophenone in 86% yield in the presence
of FTA-Au. In general, a wide range of substrates can be converted
into the desired products in moderate to good yields through this
reaction (Table 4).
At last, we attempted the hydration of alkynes to understand
whether our novel gold(I) complex could promote this challenging
reaction. To date, an example of this type of reaction was reported
which was promoted by the complex formed in situ between
alanine triazole ligand (ATA) and gold(III) salt [7a]. However, the
exact structure was not very clear. To our delight, it was found that
the FTA-Au also showed good catalytic activity for this trans-
formation. For example, the simple phenylacetylene was used in
3. Conclusions
In conclusion, we synthesized the triazole gold(I) complex FTA-
Au with furanyl-1,2,3-triazole and obtained a single crystal struc-
tural analysis of it. We described FTA-Au catalyzed rearrangement
reactions of propargylic esters and propargylic alcohols to afford
Table 3
Substrate experiments of propargylic alcoholsa,b
.
aConditions: 4 (1.0 mmol), FTA-Au (2 mol%), MeOH (10% H2O) (4 mL), 40 ꢀC, 24 h bIsolated yields.
Table 4
a,b
FTA-Au-catalyzed hydration of alkynes.
.
a
Conditions: 5 (1.0 mmol), HOAc/H2O (10:1 ¼ v:v, 4 mL), 12 h, 100 ꢀC. b Isolated yields based on 5.

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Beltran, O.R. Suarez-Castillo, A. Alvarez-Hernandez, R. Santillan, Organome-
tallics 34 (2015) 4529.
enones with moderate to good yields. These transformations
further revealed the fact that the catalytic activity and stability of
FTA-Au can be improved with the help of triazole. We anticipate
that this new complex may find industrial applications through
further developments in the near future.
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We gratefully acknowledge financial support of this work by the
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21776111), the Fundamental Research Funds for the Central Uni-
versities (JUSRP 51627B) and MOE & SAFEA for the 111 Project
(B13025).
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