Heterogeneous gold-catalyzed oxidative cross-coupling of propargylic acetates with arylboronic acids leading to (E)-α-arylenones

Article abstract of DOI:10.1016/j.tetlet.2018.11.053

An efficient heterogeneous gold-catalyzed oxidative cross-coupling of propargylic acetates with arylboronic acids has been developed that proceeds smoothly in the presence of Selectfluor and provides a general and powerful tool for the preparation of various valuable α-arylenones with moderate to good yields, excellent E-selectivity, and recyclability of the gold catalyst. The reaction is the first example of heterogeneous gold-catalyzed arylative rearrangement of propargylic acetates for construction of complex enones.

Full text of DOI:10.1016/j.tetlet.2018.11.053

Accepted Manuscript
Heterogeneous gold-catalyzed oxidative cross-coupling of propargylic acetates
with arylboronic acids leading to (E)-α-arylenones
Dayi Liu, Quan Nie, Rongli Zhang, Mingzhong Cai
PII:
S0040-4039(18)31400-X
https://doi.org/10.1016/j.tetlet.2018.11.053
TETL 50438
DOI:
Reference:
Tetrahedron Letters
To appear in:
Received Date:
Revised Date:
Accepted Date:
26 September 2018
18 November 2018
20 November 2018
Please cite this article as: Liu, D., Nie, Q., Zhang, R., Cai, M., Heterogeneous gold-catalyzed oxidative cross-
coupling of propargylic acetates with arylboronic acids leading to (E)-α-arylenones, Tetrahedron Letters (2018),
doi: https://doi.org/10.1016/j.tetlet.2018.11.053
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Heterogeneous gold-catalyzed oxidative cross-coupling of
propargylic acetates with arylboronic acids leading to (E)-α-
arylenones
Dayi Liu, Quan Nie, Rongli Zhang and Mingzhong Cai*
Key Laboratory of Functional Small Organic Molecule, Ministry of Education and
College of Chemistry & Chemical Engineering, Jiangxi Normal University, Nanchang
330022, China
E-mail: caimzhong@163.com
ABSTRACT
An efficient heterogeneous gold-catalyzed oxidative cross-coupling of propargylic
acetates with arylboronic acids has been developed that proceeds smoothly in the
presence of Selectfluor and provides a general and powerful tool for the preparation
of various valuable α-arylenones with moderate to good yields, excellent E-
selectivity, and recyclability of the gold catalyst. The reaction is the first example of
hetero- geneous gold-catalyzed arylative rearrangement of propargylic acetates for
construc- tion of complex enones.
Keywords: Gold; Oxidative cross-coupling; Propargylic acetate; α-Arylenone;
Heterogeneous catalysis
Introduction
The development of efficient synthetic routes to α,β-enone structural motif is of
great importance as this bifunctional unit is one of the main structural components in
a large number of biologically active natural products [1]. α,β-Enones are versatile
intermediates in the synthesis of natural products, pharmaceuticals, agrochemicals,
and other useful materials. Traditionally, α,β-enones are prepared via aldol conden-
sation or via a Wittig, Horner-Wadsworth-Emmons or Peterson olefination reaction
1

[2]. The Meyer-Schuster rearrangement of readily available propargylic alcohols is a
potentially useful alternative strategy for the construction of α,β-enones due to its high
atom economy [3]. The classical Meyer-Schuster rearrangement reaction involves
heating the propargylic alcohol in the presence of a strong acid which is not tolerant
of many functional groups, thereby having rather limited usage due to narrow
substrate scope [3a].
Recently, extensive efforts have been devoted to the development of highly
effective transition metal-catalyzed Meyer-Schuster rearrangement reactions and a
wide variety of transition metals including V [4], Mo [5], Cu [6], Ag [7], Re [8], Ru
[9], Rh [10], In [11], and Hg [12] have been reported to be used as efficient catalysts
for this transformation. During the past two decades, homogeneous gold-catalyzed
organic reactions have been developed into a highly efficient and powerful tool for
the synthesis of valuable building blocks [13]. Recently, gold-catalyzed Meyer-
Schuster reaction of propargylic alcohols [14] or rearrangement of propargylic esters
[15] have attracted much attention owing to their high efficiency and mild conditions,
and greatly enriched the synthetic methodologies of α,β-unsaturated carbonyl
compounds. Besides, gold(I)-catalyzed arylative rearrangement of propargylic
acetates and arylative Meyer-Schuster rearrangement of propargylic alcohols under
dual gold/ photoredox catalytic conditions have also been reported for the preparation
of α-arylenones [16], which are highly useful intermediates in the synthesis of organic
materials since they possess an extended conjugation. Although these gold-catalyzed
rearrangement reactions of propargylic alcohols or esters are highly efficient for
2

construction of α,β-unsaturated carbonyl compounds, the non-recyclability of expen-
sive homogeneous gold catalysts and the decay of cationic gold greatly restrict their
application in large-scale synthesis or multistep syntheses. Recycle of homogeneous
metal catalysts is a task of great economic and environmental importance, especially
when expensive and/or toxic heavy metal catalysts are used in chemical and
pharmaceutical industries [17]. Immobilization of the existing homogeneous gold
complexes on various solid supports appears to be an attractive solution to this
problem [18].
Recently, mesoporous MCM-41 material has proven to be an ideal heterogeneous
support for immobilization of homogeneous metal catalysts because of its outstanding
advantages including ultrahigh surface area, large and defined pore size, big pore
volume, high thermal stability and the existence of a large number of Si–OH groups
on the inner surface, in comparison with other solid supports [19]. In recent years,
functionalized MCM-41-supported Au(I) or Au(III) complexes have been
successfully used in a variety of organic reactions as highly efficient and recyclable
catalysts [20]. Very recently, we reported the synthesis of diphenylphosphine-
functionalized MCM- 41-supported gold(I) complex [Ph2P-MCM-41-AuCl] and its
successful application to the regiospecific hydroamination of electron-rich or
electron-poor internal alkynes with anilines [21]. In order to further expand our Au(I)-
MCM-41 chemistry toolbox [20g, h, 21], herein we report the heterogeneous gold-
catalyzed oxidative cross- coupling of propargylic acetates and arylboronic acids with
Ph2P-MCM-41-AuCl as a recyclable gold(I) catalyst leading to (E)-α-arylenones
3

(Scheme 1).
O
Ph2P-MCM-41-AuCl (5 mol%)
Selectfluor (2 equiv)
OAc
Ar
R
+
Ar-B(OH)2
R1
MeCN/H2O = 20:1, 80 oC, 30 min
R
R1
2
1
3
Scheme 1. Heterogeneous gold-catalyzed synthesis of (E)-α-arylenones.
Results and discussions
The Ph2P-MCM-41-AuCl complex could be easily prepared via a simple two-step
procedure as illustrated in Scheme 2 [21]. First, diphenylphosphine-functionalized
MCM-41 material (Ph2P-MCM-41) was obtained by the condensation reaction of the
mesoporous MCM-41 with commercially available 2-(diphenylphosphino)ethyltri-
ethoxysilane in toluene at 100 ºC for 24 h, followed by the treatment with Me3SiCl in
toluene at room temperature for 24 h. Then Ph2P-MCM-41 reacted with Me2SAuCl in
dichloromethane (DCM) at room temperature for 8 h to provide the Ph2P-MCM-41 -
AuCl complex as a gray powder. The gold content of the heterogeneous gold(I)
complex was determined to be 0.35 mmol g-1 according to the ICP-AES analysis.
OH
OH
OSiMe3
1. (EtO)3Si(CH2)2PPh2
Toluene, 100 oC, 24 h
PPh2
O
Si
OH
O
OEt
2. Me3SiCl, r.t., 24 h
MCM-41
Ph2P-MCM-41
OSiMe3
Ph2PAuCl
O
Me2SAuCl
DCM, r.t., 8 h
Si
O
OEt
Ph2P-MCM-41-AuCl
4

Scheme 2. Preparation of Ph2P-MCM-41-AuCl.
The Ph2P-MCM-41-AuCl complex was then used as the catalyst for the oxidative
cross-coupling of propargylic acetates and organometallic reagents with Selectfluor as
the oxidant. In our initial screening experiments, arylboronates/arylboronic acids were
chosen as the external arylmetallic reagents due to their stability and easy availability.
Oct-3-yn-2-yl acetate 1a was selected as a model substrate to optimize the reaction
conditions and the results are listed in Table 1. When PhBF3K was used as the
arylmetal reagent in anhydrous MeCN as solvent at 80 ºC for 2 h, the formation of the
desired 3a was not observed (entry 1). The use of various phenylboronates such as
PhB(OCH2)2, PhB(pin) and PhB[O(CH2)3O] as coupling partners afforded cross-
coupling product 3a in moderate yields (entries 2-4). To our delight, a commercially
readily available and inexpensive PhB(OH)2 also gave the desired product 3a in 48%
yield (entry 5). In order to further improve the yield, we next examined the effect of
H2O on the reaction with PhB(OH)2 as coupling partner. Gratifyingly, the yield of 3a
could be improved to 59% by using a MeCN/H2O (100:1) mixed solvent (entry 6).
When a MeCN/H2O (20:1) solvent mixture was used, the reaction afforded the
desired 3a in 71% yield (entry 7), but further increasing water concentration in MeCN
resulted in a decreased yield (entry 8). When 1.5 equiv of Selectfluor and 3.0 equiv of
PhB(OH)2 were used, the yield of 3a was decreased to 49% (entry 9). Finally, the
amount of the gold(I) catalyst was also screened. Reducing the amount of the catalyst
to 2.5 mol% also resulted in a decreased yield and required a longer reaction time
(entry 10), Increasing the amount of the catalyst could shorten the reaction time, but
5

did not improve the yield significantly (entry 11). When a homogeneous Ph3PAuCl (5
mol%) was used as the catalyst, the desired 3a was also isolated in 71% yield (entry
12), which indicating that the catalytic activity of Ph2P-MCM-41-AuCl was com-
parable to that of Ph3PAuCl. Thus, the optimized conditions for this transformation
are the use of Ph2P-MCM-41-AuCl (5 mol%), PhB(OH)2 (4.0 equiv), Selectfluor (2.0
equiv) in MeCN/H2O (20:1) as solvent at 80 ºC under Ar for 30 min (entry 7).
Table 1 Optimization of reaction conditions.a
O
OAc
Ph
Ph2P-MCM-41-AuCl (5 mol%)
+ Ph-BXn
(4.0 equiv)
n-Bu
Selectfluor (2.0 equiv), solvent, 80 oC
Me
n-Bu
Me
3a
2
1a
Entry
1
Ph-BXn
PhBF3K
Solvent
Time (min) Yield (%)b
MeCN
120
60
60
60
60
30
30
30
60
60
15
15
0
2
PhB(OCH2)2
PhB(pin)
MeCN
45
37
46
48
59
71
55
49
51
72
71
3
MeCN
4
PhB[O(CH2)3O]
PhB(OH)2
PhB(OH)2
PhB(OH)2
PhB(OH)2
PhB(OH)2
PhB(OH)2
PhB(OH)2
PhB(OH)2
MeCN
5
MeCN
6
MeCN/H2O (100:1)
MeCN/H2O (20:1)
MeCN/H2O (5:1)
MeCN/H2O (20:1)
MeCN/H2O (20:1)
MeCN/H2O (20:1)
MeCN/H2O (20:1)
7
8
9c
10d
11e
12f
a Reaction conditions: 1a (0.6 mmol), 2 (2.4 mmol), Selectfluor (1.2 mmol), Ph2P-MCM-41-AuCl
(5 mol%) in solvent (6.0 mL) at 80 ºC under Ar. b Isolated yield. c 1.5 equiv of Selectfluor and 3.0
equiv of PhB(OH)2 were used. d 2.5 mol% of Ph2P-MCM-41-AuCl was used. e 10 mol% of Ph2P-
MCM-41-AuCl was used. f 5 mol% of Ph3PAuCl was used as the catalyst.
6

With the optimized reaction conditions in hand, we started to study the scope of
this heterogeneous gold-catalyzed oxidative cross-coupling reactions by using a wide
range of propargylic acetates and various arylboronic acids as substrates and the
results are summarized in Table 2. A variety of propargylic acetates 1a-1e bearing
various alkyl or cycloalkyl groups on both ends of the propargyl moiety underwent
the oxidative cross-coupling with PhB(OH)2 2a smoothly to give the corresponding
(E)-α-phenylenones 3a-3e in good yields (entries 1-5). Similarly, a wide variety of
propargylic acetates 1f-1t having various aryl groups at either end of the propargyl
moiety reacted well in this transformation, thus providing a variety of (E)-α-phenyl-
enones 3f-3t in 54-67% yields (entries 6-20). In addition, acetate 1u having two
phenyl groups on both ends of the propargyl moiety also proved to be a suitable
substrate and produced the expected 3u in moderate yield (entry 21). Notably, the
reaction also worked well with a substrate without substitution at the propargylic
position, yielding a β-unsubstituted (E)-α-phenylenone 3v in 61% yield (entry 22).
We next examined the scope of arylboronic acids. Electron-rich arylboronic acids
such as p-tolylboronic acid 2b or m-tolylboronic acid 2c displayed a similar reactivity
with PhB(OH)2 2a and the reactions with propargylic acetate 1d afforded the target
products 3w and 3x in 71-72% yields (entries 23 and 24). However, 4-methoxy-
phenylboronic acid with a strong electron-donating group did not furnish the desired
product, which may be due to the incompatibility of the anisole ring with strongly
oxidative Selectfluor. Electron-deficient arylboronic acids such as 4-chlorophenyl-
boronic acid 2d and 4-(methoxycarbonyl)phenylboronic acid 2e showed a relatively
7

lower reactivity than PhB(OH)2 2a and the reactions with propargylic acetate 1d gave
the desired products 3y and 3z in acceptable yields (entries 25 and 26). In addition,
the oxidative cross-coupling reactions of various propargylic acetates with substituted
phenylboronic acids also proceeded effectively to provide the corresponding (E)-α-
arylenones 3a'-3d' in respectful yields (entries 27-30). It is noteworthy that all the
oxidative cross-coupling reactions proceeded with 100% E-selectivity and the forma-
tion of Z-isomers was not observed.
Table 2 Synthesis of (E)-α-arylenones by heterogeneous gold-catalyzed oxidative
cross-coupling reaction.a
O
Ph2P-MCM-41-AuCl (5 mol%)
Selectfluor (2 equiv)
OAc
Ar
R
+
Ar-B(OH)2
R1
MeCN/H2O = 20:1, 80 oC, 30 min
R
R1
2
1
3
Entry
1
R
R1
Ar
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Product Yield (%)b
Me
Me
n-Bu
3a
3b
3c
3d
3e
3f
71
69
70
68
68
62
58
59
61
61
65
60
62
2
cyclohexyl
cyclohexyl
n-Bu
3
cyclohexyl
cyclohexyl
PhCH2
Ph
4
5
n-Bu
6
n-Bu
7
4-BrC6H4
Me
n-Bu
3g
3h
3i
8
Ph
9
Me
4-MeOC6H4
cyclohexyl
Ph
10
11
12
13
Ph
3j
cyclohexyl
3-BrC6H4
Ph
3k
3l
n-Bu
t-Bu
3m
8

14
15
16
17
18
19
20
21
22
23
24
25
26c
27
28
29
30
n-Pr
Ph
Ph
Ph
Ph
Ph
Ph
3n
3o
3p
3q
3r
3s
54
64
67
63
62
63
65
53
61
72
71
58
55
67
60
68
59
4-AcOC6H4 n-Bu
4-BrC6H4
4-MeC6H4
Me
cyclohexyl
n-Bu
4-MeC6H4
Ph
ClCH2CH2CH2 Ph
Me
4-ClC6H4
Ph
Ph
3t
Ph
Ph
3u
3v
3w
3x
3y
H
Ph
Ph
cyclohexyl
cyclohexyl
cyclohexyl
cyclohexyl
4-BrC6H4
Me
n-Bu
4-MeC6H4
3-MeC6H4
4-ClC6H4
n-Bu
n-Bu
n-Bu
4-MeOCOC6H4 3z
n-Bu
4-MeC6H4
4-MeC6H4
3-MeC6H4
4-ClC6H4
3a'
4-MeOC6H4
n-Bu
3b'
3c'
3d'
PhCH2
PhCH2
n-Bu
a Reaction conditions: 1 (0.6 mmol), 2 (2.4 mmol), Selectfluor (1.2 mmol), Ph2P-MCM-41-AuCl
b
c
(5 mol%) in MeCN/H2O = 20:1 (6.0 mL) at 80 ºC under Ar for 30 min. Isolated yield.
MeCN/H2O = 100:1
In order to further expand the application field of Ph2P-MCM-41-AuCl, we also
conducted heterogeneous gold(I)-catalyzed hydroamination reaction of phenylacety-
lene with 2-iodoaniline and hydration reaction of (bromoethynyl)benzene with Ph2P-
MCM-41-AuCl as catalyst (Scheme 3). In the presence of Ph2P-MCM-41-AuCl (2
mol%) and AgNTf2 (2 mol%), the hydroamination of phenylacetylene with 2-iodo-
aniline (1.1 equiv) in DCM proceeded effectively at room temperature to give the
Markovnikov addition product (E)-2-iodo-N-(1-phenylethylidene)aniline (4) in 90%
9

yield after 5 h. The hydration reaction of (bromoethynyl)benzene also worked well in
DCE at room temperature with the same catalysts, thereby affording the desired 2-
bromo-1-phenylethanone (5) in 92% yield.
NH2
I
Ph2P-MCM-41-AuCl (2 mol%)
AgNTf2 (2 mol%)
N
I
+
DCM, r.t., 5 h
(1.1 equiv)
4
, 90%
O
Ph2P-MCM-41-AuCl (3 mol%)
AgNTf2 (3 mol%)
Br
+
Br
H2O
DCE, r.t., 14 h
5
, 92%
Scheme 3. Heterogeneous gold(I)-catalyzed hydroamination of phenylacetylene and
hydration of (bromoethynyl)benzene.
To verify whether Ph2P-MCM-41-AuCl is actually functioning in a heterogeneous
manner, or whether it is merely a reservoir for more active soluble forms of Au, the
hot-filtration test was performed [22]. For this, the oxidative cross-coupling reaction
of oct-3-yn-2-yl acetate 1a with PhB(OH)2 2a was conducted until a conversion of
approximately 30%. Then the gold(I) catalyst was removed from the reaction mixture
by filtration at the reaction temperature (80 ºC), and the filtrate was again stirred at 80
ºC for 30 min. It was found that the filtered solution did not exhibit any further
reactivity, and no gold species could be detected in the solution by ICP-AES analysis.
These results exclude the possibility of a contribution to the observed conversion from
the leached gold species, indicating that the gold(I) catalyst was stable during the
oxidative cross-coupling reaction and actually functioning in a heterogeneous manner.
A plausible reaction mechanism for this heterogeneous gold-catalyzed oxidative
cross-coupling reaction is shown in Scheme 4 [16a]. Firstly, the tandem reactions of
10

propargylic acetate 1 catalyzed by Ph2P-MCM-41-AuCl provide an MCM-41-bound
vinyl-Au(I) intermediate A upon hydrolysis, which is then oxidized by Selectfluor to
form an MCM-41-bound vinyl-Au+(III)F intermediate B. Subsequent transmetalation
between intermediate B and ArB(OH)2 2 leads to the formation of an MCM-41-bound
vinyl-Au(III)F-Ar intermediate C. Finally, intermediate C could undergo reductive
elimination to afford the desired α-arylenone 3 and regenerate the gold(I) catalyst.
F
OAc
[LAu]
L = Ph2P-MCM-41
O
R
R1
Ar
R
1
[LAu]F
R1
Au-catalyzed
tandem process
3
reductive
elimination
Ar
L
Au
O
OAc
L
Au
R1
R1
F
R
C
( )
R
hydrolysis
H2O
O
L
O
L
Ar-B(OH)2
Au
R
Au
R1
R1
2
F
H, HOAc
R
B
( )
A
( )
oxidation
F
N
N
N
NH
Cl
Cl
2 BF4
2 BF4
Scheme 4. Proposed catalytic cycle.
A long catalyst lifetime and the easy recyclability of the catalyst are highly
desirable for the practical application of a supported precious metal catalyst. The
recycle efficiency of Ph2P-MCM-41-AuCl was investigated in the oxidative cross-
coupling reaction of 1-cyclohexylhept-2-ynyl acetate 1d with p-tolylboronic acid 2b.
After completion of the reaction, the gold catalyst was recovered by a simple filtration
of the reaction mixture, and washed with distilled water and acetone. After being
11

dried at 80 ºC under vacuum for 1 h, it can be reused directly without further
purification. The recovered gold catalyst was used in the next run, and almost the
same yield of 3w was observed for seven consecutive cycles (Table 3). However, a
slower reaction kinetic was observed after three cycles, which may be due to loss of
the catalyst during the recovery process by filtration. To determine if the phosphine
ligand was oxidized to the phosphine oxide during the reaction under the strongly
oxidative conditions, the recovered gold catalyst after seven consecutive cycles was
subjected to hydrolysis under basic conditions. 31P NMR spectrum of the silyl
attachment obtained showed a strong signal at δ 39.1 ppm, which indicating that gold
is strongly coordinated with the phosphine [23], and the oxidation of the phosphine
ligand to the phosphine oxide did not occur. The structure of the recovered gold(I)
catalyst after the first catalytic cycle was also investigated by X-ray photoelectron
spectroscopy (XPS). As shown in Fig. 1, the XPS spectrum demonstrated that all the
gold species in the recovered gold(I) catalyst were present in Au(I) oxidation state
[24], corresponding to the bonding energies around at 84.9 eV (Au 4f7/2) and 88.6 eV
(Au 4f5/2), which indicating that the catalyst recycle is attributed by the Au(I)
complex, not the gold nanoparticles formed by the decomposition of the Au(I)
complex. In addition, ICP-AES analysis was performed on the recovered catalyst after
seven consecutive runs, the gold content was found to be 0.34 mmol g-1, which
revealing almost the same gold content as the fresh one.
Table 3 Recycle of the Ph2P-MCM-41-AuCl catalyst.a
12

Me
O
Ph2P-MCM-41-AuCl (5 mol%)
Selectfluor (2 equiv)
OAc
+
Me
B(OH)2
n-Bu
MeCN/H2O = 20:1, 80 oC
n-Bu
1d
2b
3w
Catalyst
cycle
Time
(min)
Yield b
(%)
Catalyst
Entry
Time
(min)
Yield b
(%)
71
Entry
cycle
1
2
3
4
1st (fresh)
2nd
30
72
71
72
70
5
6
7
5th
6th
7th
60
30
30
40
90
70
69
3rd
120
4th
a
Reaction conditions: 1d (0.6 mmol), 2b (2.4 mmol), Selectfluor (1.2 mmol), Ph2P-MCM-41-
AuCl (5 mol%) in MeCN/H2O = 20:1 (6.0 mL) at 80 ºC under Ar. b Isolated yield.
Fig. 1. XPS spectrum of the recovered gold(I) catalyst.
Conclusions
In conclusion, we have developed a highly efficient heterogeneous gold-catalyzed
oxidative cross-coupling of propargylic acetates with arylboronic acids, leading to a
one-step synthesis of (E)-α-arylenones. The reactions generated a wide variety of (E)-
α-arylenones in moderate to good yields with excellent E-selectivity and were
13

applicable to a wide range of propargylic acetates and various arylboronic acids.
Importantly, this heterogeneous gold(I) catalyst can easily be prepared via a simple
procedure from commercially available reagents, and recovered by filtration of the
reaction solution and recycled up to seven times with almost consistent activity. The
present method provides a novel, efficient and practical route for the synthesis of a
wide variety of (E)-α-arylenones.
Acknowledgements
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 financial support.
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Research Highlights
► The Ph2P-MCM-41-AuCl complex can be easily prepared by a simple procedure.
► Heterogeneous gold-catalyzed oxidative cross-coupling reaction is first reported.
► The reaction generates a variety of (E)-α-arylenones in moderate to good yields.
► The Au(I) catalyst can be recycled up to 7 times with almost consistent activity.
► Our catalytic system provides a novel and practical route to (E)-α-arylenones.
17

Graphical Abstract
Heterogeneous gold-catalyzed oxidative cross-coupling of
propargylic acetates with arylboronic acids leading to (E)-α-
arylenones
Dayi Liu, Quan Nie, Rongli Zhang, Mingzhong Cai*
O
Ph2P-MCM-41-AuCl (5 mol%)
Selectfluor (2 equiv)
OAc
Ar
R
+
Ar-B(OH)2
R1
MeCN/H2O = 20:1, 80 oC, 30 min
R
R1
2
1
3
OSiMe3
Ph2PAuCl
O
O
Si
Ph2P-MCM-41-AuCl =
OEt
18