Heterogeneous gold(I)-catalyzed three-component reaction of aldehydes, alkynes, and orthoformates toward propargyl ethers

Article abstract of DOI:10.1080/00397911.2020.1761391

A novel and efficient heterogeneous gold(I)-catalyzed three-component reaction of aldehydes, alkynes, and orthoformates has been developed that proceeds smoothly in dichloroethane (DCE) at 83 °C in the presence of 5 mol% magnetic nanoparticles-anchored phosphine gold(I) complex (Fe₃O₄@SiO₂-P-AuOTf) and offers a general and practical approach for the preparation of a variety of propargyl ethers with good yields. This heterogeneous gold(I) catalyst can be facilely recovered by simply applying an external magnetic field and recycled at least eight times without any apparent decrease in the catalytic efficiency.

Full text of DOI:10.1080/00397911.2020.1761391

Synthetic Communications
An International Journal for Rapid Communication of Synthetic Organic
Chemistry
ISSN: 0039-7911 (Print) 1532-2432 (Online) Journal homepage: https://www.tandfonline.com/loi/lsyc20
Heterogeneous gold(I)-catalyzed three-component
reaction of aldehydes, alkynes, and orthoformates
toward propargyl ethers
Jiajun Zeng, Feiyan Yi & Mingzhong Cai
To cite this article: Jiajun Zeng, Feiyan Yi & Mingzhong Cai (2020): Heterogeneous gold(I)-
catalyzed three-component reaction of aldehydes, alkynes, and orthoformates toward propargyl
ethers, Synthetic Communications, DOI: 10.1080/00397911.2020.1761391
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https://doi.org/10.1080/00397911.2020.1761391
Heterogeneous gold(I)-catalyzed three-component reaction
of aldehydes, alkynes, and orthoformates toward
propargyl ethers
Jiajun Zeng, Feiyan Yi, and Mingzhong Cai
Key Laboratory of Functional Small Organic Molecule, Ministry of Education and College of Chemistry
and Chemical Engineering, Jiangxi Normal University, Nanchang, China
ABSTRACT
ARTICLE HISTORY
Received 9 November 2019
A novel and efficient heterogeneous gold(I)-catalyzed three-compo-
nent reaction of aldehydes, alkynes, and orthoformates has been
developed that proceeds smoothly in dichloroethane (DCE) at 83 ꢀC
in the presence of 5 mol% magnetic nanoparticles-anchored phos-
phine gold(I) complex (Fe3O4@SiO2-P-AuOTf) and offers a general
and practical approach for the preparation of a variety of propargyl
ethers with good yields. This heterogeneous gold(I) catalyst can be
facilely recovered by simply applying an external magnetic field and
recycled at least eight times without any apparent decrease in the
catalytic efficiency.
KEYWORDS
Gold; heterogeneous
catalysis; magnetic
nanoparticles; propargyl
ether; three-
component reaction
GRAPHICAL ABSTRACT
Introduction
Development of catalytic carbon–carbon bond-forming reactions by additions to C¼O
or C¼N is of great importance in modern organic synthesis. In this context, metal alky-
nilides are a class of versatile nucleophiles that can react with a wide range of electro-
philes.[1] The traditional methods for the generation of metal alkynilides involve the
reaction of terminal alkynes with organolithium or organomagnesium reagents.[2] The
alkyne deprotonation for the formation of metal alkynilides must be carried out as a
separate step owing to the strong nucleophilicity of organolithium or organomagnesium
reagents. Therefore, development of catalytic processes that can lead to the generation
of reactive transition-metal alkynilides from the corresponding terminal alkynes in situ
CONTACT Mingzhong Cai
caimzhong@163.com
Key Laboratory of Functional Small Organic Molecule, Ministry of
Education and College of Chemistry and Chemical Engineering, Jiangxi Normal University, Nanchang, China.
Supplemental data for this article can be accessed on the publisher’s website.
ß 2020 Taylor & Francis Group, LLC

2
J. ZENG ET AL.
under conditions that are compatible with electrophiles are highly desirable. Carreira
et al. reported an efficient addition of terminal alkynes to nitrones in the presence of
10 mol% Zn(OTf)2 and 25 mol% i-Pr2NEt which involving a catalytic in situ generation
of Zn(II)-alkynilides intermediates.[3] Subsequently, a variety of addition reactions of
terminal alkynes to various electrophiles have been reported with In,[4] Ru,[5] Rh,[6]
Ir,[7] Cu,[8] Fe,[9] Ag,[10] and Hg[11] complexes as catalysts. Recently, gold-catalyzed A3
coupling reaction of aldehydes, alkynes, and amines has provided a convenient and effi-
cient route to propargylamines.[12] In almost all the reactions, metalated terminal
alkynes are considered as reactive intermediates.
In the past decades, homogeneous Au(I) or Au(III) complexes have proven to be
highly efficient catalysts for a wide variety of organic transformations involving alkynes,
allenes, and alkenes.[13] The majority of these reactions are based on the propensity of
gold to serve as a soft and carbophilic Lewis acid in the activation of carbon–carbon p
bonds,[14] thus allowing for the construction of carbon–carbon and carbon–heteroatom
bonds by nucleophilic attack on these activated multiple bonds. In contrast, the reac-
tions involving gold-alkyne species as nucleophiles have received less attention. Li et al.
have developed a gold(I)-catalyzed cascade addition/cyclization of terminal alkynes with
ortho-alkynylaryl aldehydes leading to 1-alkynyl-1H-isochromenes. A gold alkynilide
species is suggested as the reactive intermediate which adds to C¼O bond of alde-
hyde.[15] Wang et al. reported a AuCl3/CuBr-catalyzed three-component reaction of
aldehydes, alkynes, and amines toward quinoline derivatives through a sequential cata-
lytic process, which involving initial formation of propargylamine via nucleophilic add-
ition of gold acetylide species to C¼N bond.[16] Zhang and coworkers reported a
Au(III)-catalyzed acyl migration of propargylic esters in which the intramolecular attack
of nuceleophilic Au(III)–C(sp2) to C¼O bond is proposed as the key step.[17] These
results demonstrate that the nucleophilicity of Au–C bond can be utilized in the con-
struction of C–C bond. In addition, gold-catalyzed reaction of terminal alkynes with
benzyl trichloroacetimidates and the three-component reaction of aldehydes, alkynes,
and triethyl orthoformate have been reported by Wang and coworkers.[18]
However, in almost all cases, homogeneous gold(I) or gold(III) catalysts were used in
the reactions involving gold-alkyne species. The non-recyclability of expensive homoge-
neous gold catalysts and the decay of cationic gold greatly restrict their application in
large-scale synthesis.[19] Therefore, development of highly efficient and recyclable het-
erogeneous gold catalysts for use in such transformations is highly desirable. In this
regard, magnetic nanoparticles-supported catalysts are a better choice because of their
facile magnetic separation which efficiently prevents loss of the catalyst and improves
the reusability.[20] Recently, we reported the synthesis of a magnetic nanoparticles-anch-
ored phosphine gold(I) complex [Fe3O4@SiO2-P-AuOTf] and its successful application
to ring expansion of unactivated alkynylcyclo-propanes.[21] In order to expand the
application range of this heterogeneous gold(I) catalyst, herein, we wish to report an
efficient heterogeneous gold(I)-catalyzed three-component reaction of aldehydes,
alkynes, and orthoformates using the Fe3O4@SiO2-P-AuOTf complex as a recyclable
gold(I) catalyst (Scheme 1), providing a novel and practical route to propargyl ethers
which are important structural motifs that can serve as intermediates in many organic
transformations.[22]

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Scheme 1. Heterogeneous gold(I)-catalyzed three-component reaction of aldehydes, alkynes, and
orthoformates.
Scheme 2. Preparation of the Fe3O4@SiO2-P-AuOTf catalyst.
Results and discussion
The Fe3O4@SiO2-P-AuOTf catalyst was easily prepared by a simple procedure from
commercially easily available starting materials according to our previously reported
method,[21] as illustrated in Scheme 2. The content of gold was found to be 0.38 mmol
gꢁ1 based on ICP-AES analysis. The oxidation states of gold in the fresh Fe3O4@SiO2-
P-AuOTf complex and the used catalyst were determined by X-ray photoelectron spec-
troscopy (XPS). The XPS of the fresh Fe3O4@SiO2-P-AuOTf (Figure 1a) showed that
the pair at 85.0 and 88.7 eV can be assigned as the spin orbit coupling of Au 4f7/2 and
Au 4f5/2, respectively, of Au(I).[23]
The magnetically separable nanocomposite Fe3O4@SiO2-P-AuOTf was then used as
catalyst for the three-component reaction of aldehydes, alkynes, and orthoformates.
Initial experiments with benzaldehyde (1a), triethyl orthoformate (2a) and phenylacety-
lene (3a) were performed to optimize the reaction conditions, and the results are sum-
marized in Table 1. At first, the effect of reaction temperature on the model reaction
was examined in the presence of 5 mol% Fe3O4@SiO2-P-AuOTf with DCE as the solvent
(entries 1–5). The reaction did not occur at room temperature or 40 ꢀC. When the reac-
tion was carried out at reflux temperature, the desired product 4a was isolated in 85%
yield (entry 4), whilst other temperatures such as 65 or 100 ꢀC were substantially less
effective. The use of Fe3O4@SiO2-P-AuCl as catalyst did not give the desired 4a, which
indicating the important role of the counterion (ˉOTf) (entry 6). When homogeneous
Ph3PAuCl/AgOTf system was used as catalyst, the desired product 4a was also isolated
in 87% yield (entry 7), while the use of AgOTf alone as catalyst was ineffective (entry
8). These results indicated that the catalytic efficiency of Fe3O4@SiO2-P-AuOTf was
comparable to that of Ph3PAuCl/AgOTf system. We next checked the effect of solvents
on the reaction (entries 9–12). When the reaction was performed in benzene or toluene,
the product 4a was also obtained in good yields (entries 9 and 10), however,

4
J. ZENG ET AL.
Figure 1. XPS of the fresh Fe3O4@SiO2-P-AuOTf complex (a) and the recovered gold catalyst after the
8th run (b).
Table 1. Optimization of the reaction conditions.a
Entry
Catalyst (mol%)
Solvent
Temp (ꢀC)
Time (h)
Yield (%)b
1
2
3
4
5
6
7
8
Fe3O4@SiO2-P-AuOTf (5)
Fe3O4@SiO2-P-AuOTf (5)
Fe3O4@SiO2-P-AuOTf (5)
Fe3O4@SiO2-P-AuOTf (5)
Fe3O4@SiO2-P-AuOTf (5)
Fe3O4@SiO2-P-AuCl (5)
Ph3PAuCl (5)/AgOTf (5)
AgOTf (5)
Fe3O4@SiO2-P-AuOTf (5)
Fe3O4@SiO2-P-AuOTf (5)
Fe3O4@SiO2-P-AuOTf (5)
Fe3O4@SiO2-P-AuOTf (5)
Fe3O4@SiO2-P-AuOTf (5)
Fe3O4@SiO2-P-AuOTf (2)
Fe3O4@SiO2-P-AuOTf (10)
Fe3O4@SiO2-P-AuOTf (5)
DCE
DCE
DCE
DCE
DCE
DCE
DCE
DCE
Benzene
Toluene
MeCN
THF
H2O
DCE
25
40
65
83
100
83
83
83
80
83
80
65
83
83
83
83
24
24
24
12
12
24
12
24
12
12
24
24
24
24
6
0
Trace
46
85
73
0
87
Trace
82
78
56
52
0
9
10
11
12
13
14
15
16c
61
86
80
c
DCE
DCE
12
aReaction conditions: 1a (0.5 mmol), 2a (0.6 mmol), 3a (0.6 mmol) and solvent (3 mL) under Ar. bIsolated yield. The reac-
tion was carried out under air.
replacement of DCE with MeCN or THF resulted in lower yields (entries 11 and 12).
The reaction in water did not occur at all (entry 13). Reducing the amount of the cata-
lyst to 2 mol% led to a decreased yield and required a longer reaction time (entry 14),
while increasing the amount of the catalyst to 10 mol% did not improve the yield sig-
nificantly (entry 15). When the reaction was carried out under air, the desired 4a was
produced in a slightly lower yield of 80% (entry 16). Hence, the optimal reaction

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Table 2. Heterogeneous gold(I)-catalyzed synthesis of propargyl ethers.a,b
Entry
R1
R
R2
t (h)
Yield (%)
TON
TOF (hꢁ1
)
1
2
3
4
5
6
7
8
C6H5 (1a)
C6H5 (1a)
Et (2a)
Me (2b)
Et (2a)
Me (2b)
Et (2a)
Me (2b)
Me (2b)
Et (2a)
Me (2b)
Et (2a)
Me (2b)
Et (2a)
Et (2a)
Me (2b)
Et (2a)
Me (2b)
Me (2b)
Et (2a)
Me (2b)
Et (2a)
Et (2a)
Me (2b)
Et (2a)
Me (2b)
Et (2a)
C6H5 (3a)
C6H5 (3a)
C6H5 (3a)
C6H5 (3a)
C6H5 (3a)
C6H5 (3a)
C6H5 (3a)
C6H5 (3a)
C6H5 (3a)
C6H5 (3a)
C6H5 (3a)
C6H5 (3a)
C6H5 (3a)
C6H5 (3a)
C6H5 (3a)
C6H5 (3a)
C6H5 (3a)
12
12
12
18
18
18
12
12
12
12
12
12
12
18
18
18
24
24
12
12
12
12
12
24
24
4a, 85
4b, 87
4c, 81
4d, 48
4e, 83
4f, 79
4g, 86
4h, 84
4i, 87
17.0
17.4
16.2
9.6
1.4
1.5
1.4
0.5
0.9
0.9
1.4
1.4
1.5
1.4
1.4
1.3
1.3
0.9
1.0
0.9
0.7
0.6
1.3
1.2
1.1
1.3
1.4
0.5
0.5
4-MeC6H4 (1b)
4-MeOC6H4 (1c)
3-MeOC6H4 (1d)
3,4-CH2O2C6H3 (1e)
4-ClC6H4 (1f)
4-ClC6H4 (1f)
4-BrC6H4 (1g)
4-BrC6H4 (1g)
3-BrC6H4 (1h)
3-BrC6H4 (1h)
4-CF3C6H4 (1i)
2-BrC6H4 (1j)
2-MeC6H4 (1k)
1-Naphthyl (1l)
2-Naphthyl (1m)
2-Naphthyl (1m)
C6H5 (1a)
16.6
15.8
17.2
16.8
17.4
16.6
16.4
15.8
15.4
15.8
17.6
16.4
15.6
14.8
15.0
14.4
13.4
15.6
16.4
12.0
11.2
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
4j, 83
4k, 82
4l, 79
4m, 77
4n, 79
4o, 88
4p, 82
4q, 78
4r, 74
4s, 75
4t, 72
4u, 67
4v, 78
4w, 82
4x, 60
4y, 56
C6H5 (3a)
4-ClC6H4 (3b)
4-ClC6H4 (3b)
4-MeOC6H4 (3c)
4-MeC6H4 (3d)
4-ClC6H4 (3b)
4-ClC6H4 (3b)
4-ClC6H4 (3b)
C6H5 (1a)
C6H5 (1a)
4-BrC6H4 (1g)
4-BrC6H4 (1g)
C6H11 (1n)
C6H11 (1n)
aReaction conditions: 1 (0.5 mmol), 2 (0.6 mmol), 3 (0.6 mmol), Fe3O4@SiO2-P-AuOTf (5 mol%), and DCE (3 mL) at 83 ꢀC
under Ar. bIsolated yield.
conditions for this transformation are the use of 5 mol% Fe3O4@SiO2-P-AuOTf in DCE
as solvent at 83 ꢀC under Ar for 12 h (entry 4).
With the optimal reaction conditions in hand, we started to examine the scope of
this heterogeneous gold(I)-catalyzed three-component reaction by using a series of alde-
hydes and terminal alkynes as substrates. The results are summarized in Table 2. For a
wide range of 3- or 4-substituted benzaldehydes bearing either electron-donating or
electron-withdrawing groups 1b and 1d–i, the reactions with phenylacetylene 3a and
orthoformates 2a or 2b proceeded smoothly to give the corres-ponding propargylation
products 4c and 4e–m in good to high yields (entries 3 and 5–13). In the case of 4-
methoxybenzaldehyde 1c as substrate, the desired product 4d was obtained in only 48%
yield and 1,5-diphenyl-3-(4-methoxyphenyl)pent-1,4-diyne as by-product was also
isolated in 39% yield (entry 4). When aromatic aldehydes with a strong electron-with-
drawing group such as 4-nitrobenzaldehyde and 4-cyanobenzaldehyde were used as sub-
strates, the formation of a complex mixture was observed. The sterically hindered 2-
substituted benzaldehydes 1j and 1k were also suitable substrates and afforded the
desired addition products 4n and 4o in 79 and 88% yield, respectively (entries 14 and
15). Besides, bulky 1-naphthaldehyde 1l and 2-naphthaldehyde 1m were compatible

6
J. ZENG ET AL.
with the standard conditions and gave the expected products 4p–r in 74–82% yields
(entries 16–18). However, when aliphatic aldehydes such as butyraldehyde and heptanal
were used as substrates, no desired addition products were detected. We also checked
the possibility of reaction using ketones as substrates, but ketones such as acetone and
acetophenone were not reactive in this transformation, and the reaction did not occur
at all. In addition to phenylacetylene, electron-deficient or electron-rich arylacetylenes
3b–d also proven to be good substrates and underwent the three-component reaction
effectively with various aromatic aldehydes and orthoformates to furnish the corre-
sponding propargylation products 4s–w in good yields (entries 19–23). Unfortunately,
aliphatic terminal alkynes such as 1-hexyne and ethynylcyclohexane were not suitable
substrates and no reaction was observed. Notably, secondary cyclohexanecarbaldehyde
1n could react with 4-chlorophenylacetylene 3b effectively and afforded the expected
products 4x–y in 56–60% yields (entries 24 and 25).
To verify that the high activity of Fe3O4@SiO2-P-AuOTf results from the gold sites
on the surface of the magnetic nanoparticles and not from the soluble Pd species
leached from Fe3O4@SiO2-P-AuOTf, the heterogeneity of the catalyst was confirmed by
hot filtration test. For this, the three-component reaction of benzaldehyde (1a), triethyl
orthoformate (2a) and phenylacetylene (3a) was carried out until an approximately 40%
conversion of 1a. Then the Fe3O4@SiO2-P-AuOTf catalyst was separated magnetically
from the solution at 83 ꢀC and the solution was transferred to another reaction tube
and stirred again at 83 ꢀC for 12 h. It was found that no increase in conversion of ben-
zaldehyde (1a) was observed in the clear solution, demonstrating that the observed high
activity was not related to the soluble Au species leached from Fe3O4@SiO2-P-AuOTf.
Besides, no Au species could be detected in the clear solution based on ICP-AES ana-
lysis. The above results confirm the fact that the Fe3O4@SiO2-P-AuOTf catalyst is stable
during the reaction and supports heterogeneous nature of the three-compo-
nent reaction.
A possible mechanism for this heterogeneous gold(I)-catalyzed three-component reac-
tion of aldehydes, alkynes, and orthoformates is illustrated in Scheme 3.[18b] First,
coordination of the Fe3O4@SiO2-P-AuOTf complex to phenylacetylene 3a produces an
Fe3O4@SiO2-bound gold(I)–alkyne–p complex intermediate A, which is further trans-
formed into an Fe3O4@SiO2-bound gold(I)–alkynilide intermediate B with the aid of a
base. Under the catalysis of Fe3O4@SiO2-P-AuOTf as a Lewis acid, triethyl orthoformate
2a can form a reactive intermediate C, which reacts with benzaldehyde 1a to generate
the oxocarbenium ion intermediate D. Subsequent nucleophilic addition of
gold(I)–alkynilide intermediate B to the C¼O bond of oxocarbenium ion intermediate
D affords the desired product 4a and regenerates the gold(I) catalyst to complete the
catalytic cycle.
For investigation on the reusability of the catalyst, it was recovered by magnetic sep-
aration, washed with ethyl acetate and ethanol, dried in air and reused in the next cycle.
More than 99% of the catalyst could be recovered by simply fixing a magnetic field
near to the reaction tube. For the reaction of 2-methylbenzaldehyde 1k with phenylace-
tylene 3a and triethyl orthoformate 2a, the supported gold catalyst Fe3O4@SiO2-P-
AuOTf could be recycled up to eight times without apparent loss of activity, and the
yield of 4o in eight consecutive runs was found to be 88, 87, 85, 86, 85, 85, 84, and

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7
Scheme 3. Proposed catalytic cycle.
83%, respectively. In addition, the content of gold for the recovered gold catalyst after
eight consecutive cycles was determined to be 0.37 mmol gꢁ1 based on ICP-AES ana-
lysis. After the first cycle, the amount of residual gold species in the crude reaction
product 4o was also measured to be 0.4 ppm by ICP-AES analysis, compared with
14.5 ppm for Ph3PAuCl/AgOTf catalytic system. Thus, gold species leaching into the
crude product was not completely eliminated, but appeared to be negligible. Figure 1b
shows the XPS of the recycled gold catalyst. The binding energies of Au 4f7/2 and Au
4f5/2 of the recovered Fe3O4@SiO2-P-AuOTf (after 8th run) are 84.8 and 88.4 eV,
respectively, indicating that the oxidation state of gold in the recovered catalyst is
still Au(I).
Conclusions
In summary, we have developed an efficient and practical heterogeneous gold(I)-cata-
lyzed three-component reaction of aldehydes, terminal alkynes, and orthoformates lead-
ing to propargyl ethers which are important building blocks in organic synthesis. The
developed methodology has some attractive advantages such as easily available starting
materials, straightforward and simple procedure, mild reaction conditions, good yields,
and easy recyclability of the expensive gold catalyst, thus providing an attractive alterna-
tive to prepare propargyl ethers.
Experimental
All chemicals were obtained from different commercial sources and used as received
without further purification. All solvents were dried and distilled before use.
Fe3O4@SiO2-P-AuOTf was prepared according to our previously reported method.[21]
The products were purified by flash column chromatography on silica gel with a mix-
1
ture of light petroleum ether and ethyl acetate as eluent. H NMR and 13C NMR spectra

8
J. ZENG ET AL.
were recorded on a Bruker Avance 400 NMR spectrometer (400 MHz or 100 MHz,
respectively) in CDCl3 as solvent with TMS as internal reference. HRMS spectra were
recorded on a Q-Tof spectrometer with micromass MS software using electrospray ion-
ization (ESI). Gold content was determined with inductively coupled plasma atom emis-
sion Atomscan16 (ICP-AES, TJA Corporation).
[21]
Preparation of Fe3O4@SiO2-P-AuOTf
A mixture of Fe3O4@SiO2 (0.75 g) and 2-(diphenylphosphino)ethyltriethoxysilane
(0.57 g) in 40 mL of dry toluene was stirred at reflux under Ar for 24 h. Then the result-
ing nanoparticles were magnetically separated, washed repeatedly with toluene and
CH2Cl2 and dried at 90 ꢀC in vacuo for 6 h to give 0.85 g of the diphenyl-phosphine-
modified Fe3O4@SiO2 (Fe3O4@SiO2-P) as brown nanoparticles. The content of phos-
phorus was determined to be 0.44 mmol gꢁ1 by elemental analysis.
A mixture of AuCl (80 mg, 0.34 mmol) and 0.82 g of Fe3O4@SiO2-P in MeOH
(50 mL) was stirred at 65 ꢀC under Ar for 12 h. The solid product was magnetically sep-
arated, washed with MeOH, and dried in vacuo at 80 ꢀC for 3 h. The resulting
Fe3O4@SiO2-P-AuCl catalyst was then reacted with AgOTf (0.4 mmol) in DCM (50 mL)
at room temperature for 2 h. The product was magnetically separated, washed with
DCM, and dried in vacuo at 80 ꢀC for 2 h to provide 0.86 g of Fe3O4@SiO2-P-AuOTf as
brown nanoparticles. The content of gold was determined to be 0.38 mmol gꢁ1 by ICP-
AES analysis.
General procedure for heterogeneous Au(I)-catalyzed three-component reaction of
aldehydes, alkynes, and orthoformates
A mixture of aldehyde 1 (0.5 mmol), HC(OR)3 2 (0.6 mmol), terminal alkyne 3
(0.6 mmol), and Fe3O4@SiO2-P-AuOTf (66 mg, 0.025 mmol) in DCE (3 mL) was stirred
at 83 ꢀC under Ar for 12–24 h (TLC monitored). After the reaction mixture was cooled
to room temperature, the gold catalyst was magnetically separated and the reaction mix-
ture was concentrated under reduced pressure and then purified by flash column chro-
matography on silica gel (petroleum ether: ethyl acetate ¼ 100:1) to afford the
corresponding propargyl ether 4. The recovered gold catalyst was washed with DCE
(2 ꢂ 2 mL), air-dried, and reused directly in the next run.
Supporting Information: Full experimental detail, characterization data of all com-
pounds. This material can be found via the “Supplementary Content” section of this
article’s webpage.
Funding
We thank the National Natural Science Foundation of China [No. 21462021], the Natural
Science Foundation of Jiangxi Province of China [No. 20161BAB203086] and Key Laboratory of
Functional Small Organic Molecule, Ministry of Education [No. KLFS-KF-201704] for finan-
cial support.

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