Gold-catalyzed hydroarylation of alkynes

Article abstract of DOI:10.1002/ejoc.200300260

The hydroarylation of aryl-substituted alkynes by substituted electron-rich arenes is catalyzed by AuCl₃ activated by such silver salts as AgSbF₆. In the case of terminal alkynes, complete regioselectivity in favor of the 1,1-disubstituted olefin is observed. In the case of electron-poor alkynes such as acetylenecarboxylic acid ester, gold(I) complexes such as [Ph₃PAuCl] activated by Ag salts or BF ₃·OEt₂ are the best catalysts, resulting in opposite regioselectivity and high degrees of (Z)-selectivity. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003.

Full text of DOI:10.1002/ejoc.200300260

FULL PAPER
Gold-Catalyzed Hydroarylation of Alkynes
Manfred T. Reetz*[a] and Knut Sommer[a]
Dedicated to Professor Gernot Boche on the occasion of his 65th birthday
Keywords: Homogeneous catalysis / Gold / Alkynes / Aromatic substitution / CϪH Activation
The hydroarylation of aryl-substituted alkynes by substituted
electron-rich arenes is catalyzed by AuCl3 activated by such
[Ph3PAuCl] activated by Ag salts or BF3·OEt2 are the best
catalysts, resulting in opposite regioselectivity and high de-
silver salts as AgSbF6. In the case of terminal alkynes, com- grees of (Z)-selectivity.
plete regioselectivity in favor of the 1,1-disubstituted olefin
is observed. In the case of electron-poor alkynes such as acet-
( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2003)
ylenecarboxylic acid ester, gold(
I)
complexes such as
Introduction
tentially useful synthetic transformation, the lutidine ad-
ducts 4 were shown to undergo stoichiometric coupling
with phenylacetylene (5), product 6 being formed in nearly
quantitative yield (Scheme 2).[6d]
Activation of aromatic CϪH bonds followed by CϪC
bond formation constitutes a conceptionally attractive and
potentially environmentally benign methodology because it
avoids the otherwise necessary prefunctionalization by me-
ans of aromatic halogenation. Although a number of stoi-
chiometric reactions of this kind are known, catalytic sys-
tems are rare. Two mechanistically distinct processes have
evolved. One is based on chelation-assisted reactions of
low-valent metals, prominent examples being Ru0 or RhI
insertion into CϪH bonds of arenes followed by addition
to alkenes.[1] The other type of process is initiated by elec-
trophilic metalation (e.g., palladation) of arenes with for-
mation of arylmetal species which then undergo coupling
reactions (e.g., Heck type).[2Ϫ4] Moreover, electrophilic met-
alation may also be involved in some FriedelϪCrafts reac-
tions catalyzed by certain metal salts.[5]
Scheme 2. The reaction of lutidine-stabilized arylgold complexes 4
with phenylacetylene 5
Although the mechanism of the reaction was not eluci-
dated, the formation of alkynyl-arylgold() intermediates
is likely, which then undergo reductive elimination. This
would generate AuI species, which would have to be re-oxid-
ized to AuIII in order for a catalytic overall process starting
from the arene to be possible. Our original goal was to de-
vise such a catalytic cycle by employing appropriate oxi-
dants.[7] However, upon screening several oxidants, appreci-
able amounts of the desired coupling products were never
obtained. Rather, low yields of hydroarylated products 7
were observed in a catalytic reaction (Scheme 3).
We were attracted by old and new reports concerning the
ready auration of aromatic compounds 1 by gold() salts
such as AuCl3 (2) with formation of arylgold compounds
3 (Scheme 1).[6]
Scheme 1. Auration of arenes by AuCl3
Scheme 3. Hydroarylation of phenylacetylene 5
Compounds 3 are actually dimeric in nature and tend to
decompose, although isolation in ligand-stabilized mono-
meric form of the type [ArAuCl2(L)] (L ϭ PPh3, SR2, luti-
This type of transformation, which can be viewed as re-
dine, etc.) poses no problems. In what appears to be a po- gioselective hydroarylation of alkynes or FriedelϪCrafts al-
kenylation, had previously been reported to be catalyzed by
[a]
palladium salts,[8] and more recently by Zr, In and Sc tri-
Max-Planck-Institut für Kohlenforschung,
Kaiser-Wilhelm-Platz 1, 45470 Mülheim/Ruhr, Germany
flates.[9] Furthermore, heterogeneous catalysis by zeolites
Fax: (internat.) ϩ49-(0)208-306-2985
E-mail: reetz@mpi-muelheim.mpg.de
was reported.[10] The yields vary widely according to the
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M. T. Reetz, K. Sommer
FULL PAPER
nature of the arene and alkyne. Whereas in the case of PdII- tected. Although the precise structure was not cleared up,
catalysis arylpalladium species were postulated, the metal GC-MS analysis showed that the product 9 had undergone
triflates were believed to induce a FriedelϪCrafts alkenyl- a second hydroarylation. Of the four Ag salts tested,
ation. Whatever the mechanism of these reactions may be, AgSbF6 seems to be most efficient. For example, using 5
a change in valence of the metal is not involved. Therefore, mol % of AuCl3 in combination with three parts of AgSbF6
re-oxidation is not relevant.
at 60 °C for 1 h results in an 88% yield of 9 (Table 1, Entry
The aim of the present study was to optimize the Au- 8). Further optimization showed that lower amounts of
catalyzed reaction and to test its scope, which includes the catalyst and co-catalyst can be used, e.g., only 1 mol % of
problem of regio- and stereoselectivity as well as the ques- AuCl3 and two parts of AgSbF6 as an activator suffice
tion whether AuI or AuIII salts should be used. It should (Table 1, Entry 12). Interestingly, the use of AgClO4 as a
be noted that other types of Au-catalyzed reactions have co-catalyst essentially shuts down the reaction (Table 1, En-
previously been reported by Ito, Hashmi and others.[11Ϫ13] try 4). Silver salts alone do not catalyze the reaction. In
Moreover, Fürstner has described a phenanthrene synthesis further experiments AuI salts of the type Ph3PAuCl/AgBF4
by Pt- and Au-catalyzed cycloisomerization reactions.[14a]
turned out to be completely ineffective.
In order to test the scope of the reaction, the arene and
alkyne were varied under ‘‘standard’’ conditions employing
1.5 mol % of AuCl3 activated by 3.0 mol % AgSbF6 (10
equiv. arene) at 50 °C for 4 h. Excess arene can be easily
recovered after the reaction by distillation or sublimation.
The products together with their GC and isolated yields
are shown in Scheme 5, the bold-faced bonds indicating the
CϪC bond formed in the reaction. It can be seen that a
variety of arenes react with variously substituted alkynes.
The yields appear to be best in the case of alkynes with
electron-rich aryl-substituents. In all cases regioselectivity
in favor of the 1,1-product was complete.
Results and Discussion
Terminal Aryl-Substituted Alkynes
Preliminary experiments directed towards optimizing the
conditions of the AuIII-catalyzed hydroarylation were car-
ried out with mesitylene (8) and phenylacetylene (5) in
nitromethane (Scheme 4). Nitromethane was the solvent of
choice because it dissolves AuCl3 and most silver salts.
With electron-rich arenes good to excellent yields are ob-
tained in most cases (e.g., 70% 9 or 95% 23). Less activated
arenes (e.g., bromomesitylene) give acceptable yields in
combination with electron rich alkynes (e.g., 61% 17). Ani-
sole turned out to be a poor substrate (13), resulting in the
formation of isomer mixtures and low yields. In this case
several side products were observed which could not be
identified. In most cases small amounts (ca. 5Ϫ10%) of a
side product were formed, corresponding to compounds
Scheme 4. Test reaction for the optimization of the hydroarylation
of aryl-substituted alkynes
Table 1 shows some remarkable trends. AuCl3 itself leads containing two alkenyl moieties as indicated by GC-MS
to poor yields of the desired product 9 (Entry 1). In con- analysis. Furthermore, traces (Ͻ 5%) of the corresponding
trast, activation of AuCl3 via cationization induced by treat- acetophenone derivative were observed in most cases due
ment with appropriate silver salts, results in excellent yields. to reaction of the alkyne with traces of water present in the
In most cases a small amount of a side product was de- reaction mixture.
Table 1. Au-catalyzed hydroarylation of phenylacetylene 5 by mesitylene 8 in CH3NO2
Entry
AuCl3 [mol %]
Co-catalyst (Ag:Au)
Equiv. 8
Temp. [°C]
Reaction time [h]
Yield 9 [%][a]
Side products [%][a]
1
2
3
4
5
6
7
8
9
10
11
12
13
5
5
5
5
5
5
5
5
5
1.5
1
1
1.5
Ϫ
2
2
2
2
2
4
2
3
4
10
10
10
10
60
60
60
60
60
60
60
60
60
50
50
50
50
16
16
16
16
16
1
1
1
1
4
20
56
85
5
85
84
81
88
88
86
69
84
50
4
5
15
0
15
9
16
10
8
13
19
16
Ͻ5
AgOTf (3)
AgBF4 (3)
AgClO4 (3)
AgSbF6 (3)
AgBF4 (3)
AgSbF6 (3)
AgSbF6 (3)
AgSbF6 (3)
AgSbF6 (2)
AgSbF6 (1)
AgSbF6 (2)
AgBF4 (2)
4
4
4
[a]
Determined by GC using n-hexadecane as an internal standard.
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Gold-Catalyzed Hydroarylation of Alkynes
FULL PAPER
Table 2. Hydroarylation of internal aryl-substituted alkynes with
mesitylene 8[a]
.
[a]
Conditions (unless otherwise stated): 1.5 mol % AuCl3, 3.0
mol % AgSbF6, 50 °C, CH3NO2, 10 equiv. mesitylene 8. [b] Isolated
yield. Values in parentheses refer to GC-yields, determined with
[c]
n-hexadecane as an internal standard.
4.5 mol % AgSbF6 em-
ployed. [d] Determinded by GC and/or NMR spectroscopy. Isomers
were assigned by comparison with literature NMR spectroscopic
data.[25]
Obviously regioselectivity of hydroarylation has been
completely reversed. The same was observed by Fujiwara
using PdII-catalysts.[8] Since this reaction appeared to be
different from the previous ones, we studied it more closely
using a variety of gold catalysts under different conditions.
It soon became apparent that AuI salts complexed with ap-
propriate ligands are in fact superior to the use of AuIII
salts. Therefore, optimization focused on AuI-catalysts
(Table 3).
Table 3 shows that several AuI complexes are effective in
catalyzing the regioselective hydroarylation of 29 by mes-
itylene 8. Typically, Et3PAuCl and Ph3PAuCl function well,
nitromethane and 1,2-dichloroethane being the best sol-
vents (Table 3, Entries 3, 4 and 7). In all cases activation by
a co-catalyst such as AgSbF6 or the cheaper BF3·OEt2 is
necessary. High degrees of (Z)-selectivity are observed in
almost all cases. Remarkably, the gold() complex can be
prepared in situ simply by mixing AuCl and equimolar
amounts of a phosphorus ligand in nitromethane (Table 3,
Scheme 5. Scope of the hydroarylation reactions with aryl-substi-
tuted alkynes. Conditions: 1.5 mol % AuCl3, 3.0 mol % AgSbF6,
10 equiv. arene, CH3NO2, 50 °C, 4 h. (GC yield/isolated yield);
nd ϭ not determined
Internal Aryl-Substituted Alkynes
We tested the reaction of mesitylene 8 with diphenyl-
acetylene 25 and 1-phenyl-1-propyne (26). The latter alkyne
gave the desired product 28 in good yield as a (79:21)-mix-
ture of (Z)/(E)-isomers (Table 2, Entry 3). Diphenylacety-
lene 25 showed only very low reactivity, perhaps due to
steric hindrance.
Entries
15Ϫ18).
2-(Dicyclohexylphosphanyl)biphenyl
turned out to be the best ligand (Table 3, Entry 17), whereas
phosphane ligands with electron-withdrawing groups re-
sulted in low yields (Table 3, Entry 16). Phosphite ligands
were also employed successfully (Table 3, Entry 18). Under
such conditions product yields of 60Ϫ70% are achieved,
(Z)-selectivity again being the rule. If a large excess of mes-
Electron-Poor Terminal Alkynes
The results obtained with the terminal aryl-substituted itylene 8 is used, yields of 84Ϫ95% are reached (Table 3,
alkynes suggest that electron-donating groups in the para Entries 19Ϫ22). The amount of the gold catalyst can then
position of the phenylalkyne exert a positive effect, the be lowered to 1 mol %, but BF3·OEt2 must be used in excess
yields being consistently higher in these cases. On this basis (a BF3:Au ratio of 5:1 turned out to be best). However, due
we expected acetylenecarboxylic acid ester 29 to be a poor to the low price of BF3·OEt2 this is no significant disadvan-
substrate. However, in an initial experiment using mesityl- tage. Control experiments have shown that BF3·OEt2 itself
ene 8 as the arene and 5 mol % of AuCl3/3AgBF4 at 60 °C does not catalyze the hydroarylation of 29 by 8. This obser-
(16 h), product 30 was obtained in 60% yield (GC) as a vation makes proton catalysis under our reaction con-
3.6:1 Z/E mixture (Table 3, Entry 1). Under these con- ditions unlikely.
ditions small amounts of a second alkyne addition product
31 was observed (Scheme 6).
On the basis of these promising results other arenes were
also tested, although complete optimization was not strived
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M. T. Reetz, K. Sommer
FULL PAPER
Table 3. Regioselective hydroarylation of 29 by 8 catalyzed by various gold catalysts
Entry Au cat. (mol %)
Co cat. (mol %) Equiv. 8 Solvent
Temp. [°C] Time [h] Yield 30 [%][a] (Z:E)
Yield 31 [%][a][b]
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
AuCl3 (5)
AgBF4 (15)
AgBF4 (5)
AgBF4 (5)
AgBF4 (5)
AgBF4 (5)
AgBF4 (5)
AgBF4 (5)
AgSbF6 (5)
AgClO4 (5)
AgOTf (5)
BF3·OEt2 (5)
BF3·OEt2 (3)
BF3·OEt2 (3)
BF3·OEt2 (3)
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
CH3NO2 60
CH3NO2 60
CH3NO2 60
1,2-DCE 60
16
16
4
4
4
60 (78:22)
57 (Ͼ99:1)
57 (100:0)
56 (100:0)
0
10
17
16
25
0
Ph3PAuCl (5)
Ph3PAuCl (5)
Ph3PAuCl (5)
Ph3PAuCl (5)
Ph3PAuCl (5)
Et3PAuCl (5)
Et3PAuCl (5)
Et3PAuCl (5)
Et3PAuCl (5)
Et3PAuCl (5)
Et3PAuCl (3)
Ph3PAuCl (3)
AuCl (3)
THF
60
CH3CN 60
4
0
0
CH3NO2 room temp. 16
CH3NO2 room temp. 16
CH3NO2 room temp. 16
CH3NO2 room temp. 16
CH3NO2 room temp. 16
CH3NO2 50
CH3NO2 50
CH3NO2 50
CH3NO2 50
CH3NO2 50
CH3NO2 50
CH3NO2 50
CH3NO2 50
CH3NO2 50
CH3NO2 50
CH3NO2 50
65 (100:0)
67 (Ͼ99:1)
27 (100:0)
67 (Ͼ99:1)
69 (100:0)
66 (100:0)
62 (100:0)
14 (100:0)
57 (100:0)
10 (100:0)
71 (100:0)
62 (99:1)
84 (100:0)
90 (100:0)
88 (100:0)
95 (100:0)
20
20
3
22
21
18
19
0
16
0
20
19
12
9
14
14
14
14
14
14
14
14
14
14
14
AuCl (3)/TPMP[c] (3)[d] BF3·OEt2 (3)
AuCl (3)/TPTP[e] (3)[d] BF3·OEt2 (3)
AuCl (3)/DCPB[f] (3)[d] BF3·OEt2 (3)
AuCl (3)/(MeO)3P (3)[d] BF3·OEt2 (3)
3
Ph3PAuCl (1)
Et3PAuCl (1)
BF3·OEt2 (5)
BF3·OEt2 (5)
10
10
10
30
AuCl (1)/DCPB[f] (1)[d] BF3·OEt2 (5)
9
5
Ph3PAuCl (1)
BF3·OEt2 (5)
[a]
[b]
Determined by GC using n-hexadecane as an internal standard.
In some cases small amounts (Յ 5%) of a second side product
[c]
[d]
which according to GC-MS analysis contains three alkenyl moieties were formed. TPMP ϭ tris(p-methoxyphenyl)phosphane.
gold complex was prepared in situ by mixing AuCl and equimolar amounts of the phosphorus ligand. TPTP ϭ tris(p-trifluoromethyl-
phenyl)phosphane. DCPB ϭ 2-(dicyclohexylphosphanyl)biphenyl.
The
[e]
[f]
changed from 83:17 to 97:3 upon subjecting the isolated
product mixture to the reaction conditions (1 mol %
Ph3PAuCl/5 mol % BF3·OEt2/50 °C/14 h).
Internal Electron-Poor Alkynes
Scheme 6. Test reaction for the optimization of the hydroarylation
of electron poor alkynes
Unfortunately, internal electron-poor alkynes show es-
sentially no reactivity with the described catalyst system (1
mol % Ph3PAuCl/5 mol % BF3·OEt2). For example, the re-
action of mesitylene (8) with acetylene dicarboxylic acid di-
methyl ester failed to provide the desired product.
for in each case. In all cases an excess of the arene was used.
Excess arene can be easily recovered after the reaction.
Table 4 shows that the best results are obtained in the case
of electron-rich arenes, which are highly substituted. In con-
trast such substrates as toluene or phenol hardly participate
in the hydroarylation reaction (Table 4, Entries 4 and 6).
Mechanism
The synthetic results regarding the hydroarylation de-
Noteworthy are the smooth reactions of furan and 2-meth- scribed herein need to be viewed within the context of other
ylfuran (Table 4, Entries 7 and 8). Alternative reactions gold-catalyzed nucleophilic addition reactions of
(e.g., Wittig type) give the product 37 mainly as the (E)- alkynes.[17,18] Although cationization of AuCl3 or AuCl
isomer.[15] The reaction of 2-methylfuran and acetylenecar- complexes by Agϩ or other Lewis acids is required, aur-
boxylic acid ester 29 was reported previously to proceed ation of the arene as part of the hydroarylation seems un-
predominantly in a DielsϪAlder like manner when using likely in view of the known stoichiometric reaction of aryl-
AlCl3 as the Lewis acid.[16] Unfortunately, an inseparable gold compounds with alkynes, which yields diarylace-
mixture of isomers was obtained with our catalyst system. tylenes.[6d] Thus, we believe that activation of the alkyne by
As a final example of a terminal electron-poor alkyne, 3- Au-π complexation is involved, as has been postulated for
butyne-2-one (39) was reacted with various arenes using other nucleophilic addition reactions.[17,18] In the case of
Ph3PAuCl/BF3·OEt2 as the catalyst system (Scheme 7). Sur- phenylacetylene (5), the π complex undergoes a type of elec-
prisingly, (E)-selectivity was observed in all cases (Table 5). trophilic aromatic substitution with the electron-rich arene
The opposite (E)/(Z)-selectivity is not due to a change in to form an intermediate vinyl-Au species. The simul-
mechanism. Rather, it is likely that the primary products taneously released Hϩ protonates this intermediate, setting
are in fact (Z)-configured but undergo isomerization to the free the product 7 as well as re-generating the catalyst
(E)-form under the reaction conditions. This was supported (Scheme 8). Regioselectivity is determined by electronic fac-
by the observation that the (E):(Z) ratio of product 40 tors.
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Gold-Catalyzed Hydroarylation of Alkynes
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Table 4. Hydroarylation of acetylenecarboxylic acid ester 29 by various arenes[a]
[a] Conditions: 1 mol % Ph3PAuCl, 1 mol % AgSbF6 or 5 mol % BF3·OEt2, CH3NO2, excess arene. [b] Isolated yields of purified products.
GC Yields (determined with n-hexadecane as an internal standard) in parentheses[c] Determined by GC or NMR spectroscopy. [d] GC of
the crudes product shows minor amounts of two other isomers and side products (according to GC-MS analysis hydroarylation products
containing two furyl moieties or (analog to 31) two alkenyl moieties, respectively). [e] The product consists of 82% (Z)-2-isomer 38a, 15%
(Z)-4-isomer 38b, and 3% of a third isomer 38c, probably the (Z)-3-isomer (this isomer was characterized only by GC-MS). Traces of a
side product which according to GC-MS analysis contains two methylfuryl moieties are formed.
Scheme 8. Proposed mechanism for the hydroarylation of phenyl-
Scheme 7. Hydroarylation of 3-butyn-2-one 39
acetylene 5
Table 5. Hydroarylation of 3-butyne-2-one 39 by various arenes[a]
In the case of AuCl3 as the gold compound the exact
nature of the catalytic active species is not clear, although
it is obviously cationic. However, the reaction of AuCl3 with
two equivalents of AgX does not necessarily lead to the
formation of ‘‘[AuCl]2ϩ 2XϪ’’ as one might expect. For ex-
ample, upon reacting AuCl3 with three equivalents of Ag-
OTf, the desired Au(OTf)3 was not formed. It needs to be
pointed out that Au(OTf)3 was prepared previously by a
different route.[19] Since this procedure is rather complicated
(the required starting material Au(O3SF)3 is prepared in a
two step synthesis starting from F2 and SO3), we did not
test Au(OTf)3 in our reaction. Our own attempts to prepare
Au(OTf)3 by reacting AuCl3 with AgOTf failed. Therefore,
we examined the precipitate which formed during the reac-
tion more closely (Scheme 9). Instead of the expected for-
mation of AgCl, an orange precipitate was observed, the
composition of which was shown by elemental analysis to
be ‘‘Au9Ag11Cl28’’ (44). Formally, this is a mixture of AuI
and AuIII (‘‘4AuCl3·5AuCl·11AgCl’’). In the filtrate triflate
ions could be detected by means of IR spectroscopy. In the
case of AgSbF6 as the silver compound an orange precipi-
tate was also observed, so that similar processes as in the
[a] Conditions: 1 mol % Ph3PAuCl, 5 mol % BF3·OEt2, CH3NO2, 50
[b]
°C, excess arene. Isolated yields of purified products. GC yields
(determined with n-hexadecane as an internal standard) in paren-
theses. Side products analog to 31 were not formed (due to the
stronger electron-withdrawing effect of a keto- compared to
an ester group a second alkenylation of the product does not
[c]
[d]
occur). Determined by GC. After recrystallization
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M. T. Reetz, K. Sommer
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triflate case may be involved. Thus, the oxidation state of reactive enough to remove the chloride ligand in amounts
the active catalyst is not clear. Further attempts to charac- sufficient to be detected. The situation changes in the pres-
terize the catalyst failed. However, we do not believe the ence of acetylenecarboxylic acid ester 29, which as a soft
precipitate formed to be responsible for the catalysis. nucleophile is able to displace the hard chloride in the pres-
Rather, cationic gold species [Au]nϩ in solution are likely to ence of BF3·OEt2: A sample of Ph3PAuCl, five equivalents
be the catalytically active species.[20]
of BF3·OEt2 and five equivalents of 29 in CD3NO2 shows
at 50 °C a broad signal at δ ϭ 31.4 ppm, probably due to
the formation of [Ph3P-Au-(29)]ϩ [ClBF3]Ϫ.[21] In the corre-
1
sponding H NMR spectrum, the slow formation of ethyl
(Z)-3-chloroprop-2-enoate (47) is observed. The proton
which is necessary for the formation of this product orig-
inates probably from traces of water that are present in the
reaction mixture. Unfortunately, we were not able to detect
the intermediate vinyl-Au species by NMR spectroscopy.
Obviously, when no other nucleophile is present, the gold-
alkyne-π complex reacts with a chloride ion, which orig-
inates either from [ClϪBF3]Ϫ or unchanged Ph3PAuϪCl
(Scheme 11).
Scheme 9. The reaction of AuCl3 with AgOTf
The described mechanism should lead to the preferential
formation of the (Z)-isomer in the case of 28, which is in
fact observed. The formation of a mixture of isomers can
be explained by isomerization of the initially formed (Z)-
compound just as it was observed with 40. An alternative
explanation involves the formation of a vinyl-Au cation as
an intermediate which could be attacked by an arene from
both sides and would thus lead to the formation of a mix-
ture of isomers. However, due to the low stability of vinyl
cations this seems rather unlikely.
In the case of the gold()-catalyzed reactions of electron-
poor alkynes such as 29, we believe the catalytic active spec-
ies to be a cationic ligand-stabilized gold() complex -Auϩ
45 as in the previously reported[18] additions of oxygen nu-
cleophiles to alkynes. Gold catalysts are very soft and thus
carbophilic rather than oxophilic. On the basis of this as-
sumption a plausible mechanism for the reaction of acety-
lenecarboxylic acid ester 29 with arenes can be formulated
as shown in Scheme 10.
Scheme 11. The formation of 47 in absence of arenes 1
Activation by silver salts was also examined by means of
NMR spectroscopy: A sample of Ph3PAuCl and one equiv-
alent of AgSbF6 in CD3NO2 shows at room temperature a
broad peak at δ ϭ 29.8 ppm in the 31P NMR spectrum
(Ph3PAuCl: sharp signal at δ ϭ 32.4 ppm). When five equiv-
alents of the alkyne 29 are added to the same sample, one
observes a very small and extremely broad peak at
30Ϫ40 ppm, probably due to the formation of [Ph3P-Au-
(29)]ϩ [SbF6]Ϫ. After addition of 15 equivalents of mesityl-
ene (8), a broad peak at δ ϭ 31.3 ppm is observed. In the
corresponding 1H NMR spectrum the signals of the hy-
droarylation product 30 are visible. These results are fully
consistent with our proposed mechanism.
Conclusions
Scheme 10. Proposed mechanism for the hydroarylation of acety-
lenecarboxylic acid ester 29
The present study shows that cationic forms of AuIII- and
The cationic gold complex coordinates to the alkyne, and AuI complexes catalyze the hydroarylation of aryl-substi-
nucleophilic attack of the arene from the opposite side leads tuted terminal alkynes[22] and of electron-poor alkynes of
to the formation of a vinylgold intermediate which is stereo- the type acetylenecarboxylic acid ester, respectively. With
specifically protonated with final formation of the (Z)-ole- electron rich arenes good to excellent yields are obtained in
fin. Regioselectivity is dominated by electronic factors in a most cases at low catalyst loadings under mild conditions.
type of gold-catalyzed Michael addition. As mentioned Previous work[8,9] has shown that other metal catalysts such
above, the formation of (E)-double bonds in case of the as Pd-, Pt-, Zr- and Sc salts are also active and in some
ketone is due to isomerization of the initially produced cases more effective. For example, Sc(OTf)3 catalyzes the
(Z)-isomer.
addition of benzene to phenylacetylene 5,[9] whereas Au-
Several NMR experiments were conducted to test these catalysis gives a lower yield even with p-xylene. However, it
mechanistic assumptions. The 31P NMR spectrum of a should be noted that in the case of the Sc-catalysis much
sample of Ph3PAuCl and five equivalents of BF3·OEt2 in higher catalyst loadings (10 mol %) are necessary. Diphenyl-
CD3NO2 shows at 50 °C a sharp signal at δ ϭ 32.4 ppm acetylene 25 shows almost no reactivity with our catalyst
which is essentially identical to the 31P NMR shift of the system. In this case, Pd-catalysis is superior.[8a] In the case
pure gold complex. BF3·OEt2 alone thus seems to be not of the electron-poor alkynes 29 and 39 our results are simi-
3490
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Eur. J. Org. Chem. 2003, 3485Ϫ3496

Gold-Catalyzed Hydroarylation of Alkynes
FULL PAPER
flask under argon. An orange precipitate was observed. 9.0 mmol
arene and 0.90 mmol alkyne (solid alkynes as a concentrated solu-
tion in nitromethane) were then added using syringes. The reaction
mixture was stirred for 4 h at 50 °C. After cooling, 100 µL of n-
hexadecane and 2 mL of ethyl acetate were added. An aliquot (ca.
0.5 mL) was taken and filtered through a small plug of silica gel
(elution with ethyl acetate). The yield of hydroarylation product
was determined by GC. The double bond structure was determined
lar to or better than the corresponding Pd-/Pt-catalysis. For
example, product 32 was obtained in similar yield as in the
case of the Pt-catalysis,[8a] but at lower catalyst loadings
(1 mol % Au vs. 5 mol % Pt). Moreover, the Pd- and Pt-
catalysis needs to be conducted in trifluoroacetic acid,
whereas the Au-catalyzed reactions occur under neutral
conditions. Aqueous workup and neutralization are not
necessary in our protocols. In the case of product 33, Au-
catalysis leads to much better selectivities (Z):(E) ϭ
95:5 [Au] vs. 67:33 [Pd][8a]). The fact that internal electron
poor alkynes such as dimethyl acetylenedicarboxylate fail
to give the desired product is a disadvantage of our proto-
col. In this case, Pd-catalysis is superior, albeit higher cata-
lyst loadings (5 mol %) are necessary.[8a]
Our study shows that cationic gold complexes are ex-
tremely useful soft and thus carbophilic Lewis acids,
whereas most ‘‘classical’’ Lewis acids such as AlCl3 or TiCl4
are hard (and thus oxophilic) electrophiles.[5] This interesting
property of gold complexes should lead to new and useful
applications in catalysis, which is currently under investi-
gation.
1
by H NMR of the crude product after all volatiles were removed
in vacuo.
Solid Arenes: Solid arenes (9.0 mmol) were weighed into the reac-
tion flask with exposure to air. The flask was then evacuated for
several minutes and charged with argon (3 ϫ). 2 mL of nitrometh-
ane was added. The Au and Ag solutions and the alkyne
(0.90 mmol) were added rapidly, and the reaction mixture was
stirred at 50 °C for 4 h. Workup was conducted as described above.
General Procedure for the Hydroarylation of Aryl-Substituted
Alkynes (Large-Scale Experiments). Liquid Arenes: 45.5 mg AuCl3
(0.150 mmol) and 103 mg AgSbF6 (0.300 mmol) were weighed into
a 100-mL Schlenk flask under argon. 20 mL of nitromethane was
added. The arene (100 mmol) and the alkyne (10 mmol; solid
alkynes as a concentrated solution in nitromethane) were added,
and the reaction mixture was stirred for 4 h at 50 °C. After cooling,
the solvent and excess arene were removed in vacuo. The residue
was purified by column chromatography (silica gel, hexanes/ethyl
acetate). After all volatiles were removed, an oil remained which
was further purified by distillation in diffusion pump vacuum
(Ͻ 10Ϫ3 mbar).
Experimental Section
General Remarks: All gold and silver compounds are commercially
available (Aldrich, Lancaster) and were handled under argon but
used without further purification. Liquid arenes were distilled from
CaH2 prior to use. Commercially available alkynes (Aldrich,
ACROS, Lancaster) were dried (CaH2 or molecular sieves) and dis-
tilled. p-Chlorophenylacetylene[23] and p-methoxyphenylacety-
lene[24] were prepared according to literature procedures. All phos-
phorus ligands are commercially available (Aldrich, STREM) and
were used as received. BorontrifluorideϪdiethyl ether (Aldrich) was
distilled in vacuo. Nitromethane (Aldrich, H2O Ͻ 0.03%) was
handled under argon but used without further purification. All re-
actions were conducted in an atmosphere of dry argon. Experi-
ments on a small scale (typically 0.90 mmol) were conducted in
rapid parallel screening reactors, and yields were determined by
GC using the internal standard method (usually n-hexadecane was
employed as standard). Larger scale experiments (5.0 or 10 mmol)
were conducted in Schlenk flasks, and isolated yields were deter-
mined. Isolated compounds were fully characterized (NMR, IR,
MS, HRMS and in the cases of new compounds also by elemen-
tal analysis).
Solid Arenes (2,4,6-Trimethylphenol): 2,4,6-Trimethylphenol
(13.62 g, 100.0 mmol) was weighed into a 100-mL Schlenk flask
with exposure to air. The flask was then evacuated for several mi-
nutes and charged with argon (3 ϫ). 20 mL of nitromethane was
added. Solutions of 45.5 mg AuCl3 (0.150 mmol) and 103 mg
AgSbF6 (0.300 mmol) in 8.0 mL of nitromethane and the alkyne
(10 mmol, solid alkynes as a concentrated solution in nitrometh-
ane) were added rapidly. The reaction mixture was stirred at 50 °C
for 4 h. After cooling, the solvent was removed in vacuo. Excess
2,4,6-trimethylphenol was removed by sublimation in vacuo (ca.
10Ϫ2 mbar) at 80 °C. The further workup procedure was the same
as described above.
Analytical Data: Yields are given in Scheme 5 and Table 2.
1-Mesityl-1-phenylethene (9): Slightly yellow oil; b.p. 66 °C (dif-
fusion pump). NMR (CDCl3, TMS as internal standard): 1H NMR
(300.13 MHz): δ ϭ 7.28 Ϫ7.19 (m, 5 H, Ph), 6.90 (s, 2 H, mesityl-
H), 5.95 (d, J ϭ 1.4 Hz, 1 H, vinyl-H), 5.09 (d, J ϭ 1.4 Hz, vinyl-
H), 2.31 (s, 3 H, Me), 2.11 (s, 6 H, 2 ϫ Me) ppm. 13C NMR
(75.48 MHz): δ ϭ 146.9, 139.6, 138.2, 136.4, 136.1, 128.4, 128.1,
127.5, 125.8, 114.5, 21.1, 20.1 ppm. IR [vs ϭ very strong; s ϭ
strong; m ϭ medium; w ϭ weak]: ν˜ ϭ 3081 (s), 3056 (s), 3022 (s),
An inert atmosphere is advisable in order to minimize ketone for-
mation which was observed in the cases of aryl-substituted
alkynes.[7] Furthermore, AuCl3 and silver salts are hygroscopic and
therefore should be handled under exclusion of moisture. Ph3PAuCl
is perfectly air-stable. However, several experiments showed that an 2948 (s), 2917 (s), 1614 (s), 1574 (m), 1493 (vs), 1482 (s), 1445 (vs),
increasing amount of water diminishes the yield in the case of the
catalyst system Ph3PAuCl/BF3·OEt2, probably due to the hydrolysis
of the BF3·OEt2. The influence of oxygen was not systematically
investigated, but oxygen does not appear to cause any harm. If the
reactions are conducted with exposure to air, the yields may be
slightly lower due to the above mentioned issues.
1377 (m), 1028 (s), 902 (vs), 851 (vs), 782 (vs), 710 (vs), 691 (m),
597 (s) 535 (w) cmϪ1. MS: m/z (rel. int.) ϭ 222 (48), 207 (100), 192
(59). C17H18 (222.33): calcd. 222.140850; found 222.140771
(HRMS).
1-(2,5-Dimethylphenyl)-1-phenylethene (10): Slightly yellow oil; b.p.
55 °C (diffusion pump). NMR (CDCl3, TMS as internal standard):
1H NMR (300.13 MHz): δ ϭ 7.28Ϫ7.23 (m, 5 H, Ph), 7.09Ϫ7.05
(m, 2 H, p-xylyl-H), 7.05Ϫ7.02 (m, 1 H, p-xylyl-H), 5.75 (d, J ϭ
1.4 Hz, 1 H, vinyl-H), 5.18 (d, J ϭ 1.4 Hz, 1 H, vinyl-H), 2.33 (s,
3 H, Me), 2.01 (s, 3 H, Me) ppm. 13C NMR (75.48 MHz): δ ϭ
General Procedure for the Hydroarylation of Aryl-Substituted
Alkynes (Small Scale Experiments). Liquid Arenes: Stock solutions
of AuCl3 (c ϭ 0.015 ) and AgSbF6 (c ϭ 0.030 ) in nitromethane
were prepared. 0.90 mL of each solution was added to a reaction
Eur. J. Org. Chem. 2003, 3485Ϫ3496
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3491

M. T. Reetz, K. Sommer
FULL PAPER
149.6, 141.5, 140.7, 135.1, 133.0, 130.7, 130.0, 128.3, 128.1, 127.5, 1018 (m), 899 (s), 851 (vs), 826 (vs), 754 (w), 736 (m), 587 (m)
126.5, 114.7, 20.9, 19.6 ppm. IR: ν˜ ϭ 3082 (s), 3018 (s), 2971 (s),
2948 (s), 2921 (s), 2864 (m), 1613 (s), 1574 (m), 1493 (vs), 1445 (vs),
1379 (m), 1322 (m), 1028 (s), 900 (vs), 813 (vs), 780 (vs), 703 (vs),
606 (m), 495 (m), 470 (w) cmϪ1. MS: m/z (rel. int.) ϭ 208 (44), 193
(100), 178 (51). C16H16 (208.30): calcd. 208.125200; found
208.125370 (HRMS).
cmϪ1. MS: m/z (rel. int.) ϭ 236 (42), 221 (100), 206 (65). HRMS:
calcd. 236.156500; found 236.156732. C18H20 (236.36): calcd. C
91.47, H 8.53; found C 91.35, H 8.47.
1-(3-Hydroxy-2,4,6-trimethylphenyl)-1-(p-tolyl)ethene (16): New
compound. Highly viscous orange oil; b.p. 110 °C (diffusion
pump). NMR (CDCl3, TMS as standard): 1H NMR (300.13 MHz):
δ ϭ 7.17 (pd, J ϭ 8.3 Hz, 2 H, p-tolyl-H), 7.07 (pd, J ϭ 8.3 Hz, 2
H, p-tolyl-H), 6.87 (s, 1 H, Ar-H), 5.93 (d, J ϭ 1.2 Hz, 1 H, vinyl-
H), 5.01 (d, J ϭ 1.2 Hz, 1 H, vinyl-H), 4.51 (br. s, 1 H, OH), 2.32
(s, 3 H, Me); 2.26 (s, 3 H, Me), 2.05 (s, 3 H, Me), 2.04 (s, 3 H, Me)
ppm. 13C NMR (75.48 MHz): δ ϭ 150.0, 146.7, 140.0, 137.4, 136.6,
129.4, 129.2, 127.8, 125.8, 121.5, 121.4, 113.6, 21.1, 19.5, 15.9,
13.0 ppm. IR: ν˜ ϭ 3575 (vs, br), 3083 (s), 3008 (s), 2920 (vs), 1618
(s), 1568 (m), 1511 (vs), 1479 (vs), 1461 (vs), 1416 (s), 1378 (s), 1319
(s), 1295 (vs), 1240 (vs), 1190 (vs), 1120 (m), 1103 (s), 1040 (vs),
1018 (vs), 938 (w), 901 (vs), 866 (m), 847 (m), 828 (vs), 737 (m),
656 (m), 558 (m), 455 (w) cmϪ1. MS: m/z (rel. int.) ϭ 252 (64),
237 (100), 222 (67). HRMS: calcd. 252.151415; found 252.151676.
C18H20O (252.36): calcd. C 85.67, H 7.99; found C 85.70, H 8.10.
1-(3-Hydroxy-2,4,6-trimethylphenyl)-1-phenylethene (11): New com-
pound. Yellow oil; b.p. 93 °C (diffusion pump). NMR (CDCl3,
1
TMS as standard): H NMR (300.13 MHz): δ ϭ 7.29Ϫ7.22 (m, 5
H, Ph), 6.88 (s, 1 H, Ar-H), 5.97 (d, J ϭ 1.5 Hz, vinyl-H), 5.08 (d,
J ϭ 1.5 Hz, 1 H, vinyl-H), 4.50 (s, 1 H, OH), 2.62 (s, 3 H, Me),
2.06 (s, 3 H, Me), 2.04 (s, 3 H, Me) ppm. 13C NMR (75.48 MHz):
δ ϭ 150.1, 147.0, 139.8, 139.5, 129.4, 128.4, 127.8, 127.6, 125.9,
121.6, 121.5, 114.6, 19.5, 15.9, 13.0 ppm. IR: ν˜ ϭ 3576 (br.,vs),
3082 (s), 3056 (s), 2921 (vs), 2860 (s), 1614 (s), 1599 (m), 1574 (s),
1492 (vs), 1480 (vs), 1462 (vs), 1444 (vs), 1414 (s), 1379 (s), 1296
(s), 1240 (vs), 1187 (vs), 1108 (s), 1077 (w), 1040 (s), 1026 (vs), 904
(vs), 869 (m), 843 (m), 787 (vs), 710 (vs), 689 (s), 664 (m), 568 (m),
536 (w) cmϪ1. MS: m/z (rel. int.) ϭ 238 (81), 223 (100), 208 (55).
HRMS: calcd. 238.135765; found 238.135648. C17H18O (238.33):
calcd. C 85.67, H 7.61; found C 85.75, H 7.69.
1-(3-Bromo-2,4,6-trimethylphenyl)-1-(p-tolyl)ethene (17): New com-
pound. Yellow oil; b.p. 104 °C (diffusion pump). NMR (CDCl3,
TMS as standard): 1H NMR (300.13 MHz): δ ϭ 7.15 (d, J ϭ
8.4 Hz, 2 H, p-tolyl-H), 7.07 (d, J ϭ 8.4 Hz, 2 H, p-tolyl-H), 6.99
(s, 1 H, Ar-H), 5.93 (d, J ϭ 1.2 Hz, 1 H, vinyl-H), 5.00 (d, J ϭ
1.2 Hz, 1 H, vinyl-H), 2.42 (s, 3 H, Me); 2.32 (s, 3 H, Me), 2.26 (s,
3 H, Me), 2.01 (s, 3 H, Me) ppm. 13C NMR (75.48 MHz): δ ϭ
146.9, 140.2, 137.7, 136.7, 136.1, 134.9, 129.6, 129.2, 125.7, 125.4,
113.8, 24.0, 21.4, 21.1, 19.9 ppm. In CDCl3 one signal could not
be resolved. Therefore, a 13C NMR in [D6]acetone was measured,
too: 13C NMR (75.48 MHz) in [D6]acetone (δ[(CD3)2CO] ϭ 29.3):
δ ϭ 147.3, 140.7, 138.0, 136.9, 136.3, 135.9, 135.2, 130.1, 129.6,
125.9, 125.4, 113.8, 23.5, 21.1, 20.6, 19.5 ppm. IR: ν˜ ϭ 3084 (w),
3023 (s), 2949 (s), 2921 (vs), 2859 (m), 1621 (w), 1608 (w), 1566
(w), 1512 (vs), 1451 (vs), 1379 (s), 1316 (w), 1291 (w), 1215 (w),
1186 (m), 1131 (m), 1120 (w), 1071 (m), 1018 (s), 975 (vs), 901 (s),
864 (m), 826 (vs), 736 (w), 563 (w) cmϪ1. MS: m/z (rel. int.) ϭ
316 (24), 314 (24), 301 (35), 299 (36), 220 (100). HRMS: calcd.
314.067025; found 314.067310. C18H19Br (315.25): calcd. C 68.58,
H 6.08; found C 68.78, H 6.15.
1-(3-Bromo-2,4,6-trimethylphenyl)-1-phenylethene (12, not isolated):
[Not all products were isolated in pure form. In the cases where
only GC yields were determined, the structure of the double bond
was determined by 1H NMR of the crude product. Only the vinyl-
H
resonances are given.] 1H NMR of the crude product
(300.13 MHz, CDCl3, TMS as standard) [p ϭ pseudo]: δ(vinyl-
H) ϭ 5.93 (pd, J ϭ 1.2 Hz), 5.02 (pd, 1.2 Hz) ppm. MS (GC/MS):
m/z (rel. int.) ϭ 302 (12), 300 (15), 287 (18), 285 (20), 220 (10), 206
(100). C17H17Br (301.23).
1-(4-Methoxyphenyl)-1-phenylethene and 1-(2-Methoxyphenyl)-1-
phenylethene (13a,b not isolated): 1H NMR of the crude product
(300.13 MHz, CDCl3, TMS as standard): δ(vinyl-H) ϭ 5.69 (d, J ϭ
1.5 Hz), 5.36 (d, 1.5 Hz), 5.32 (d, 1.5 Hz), 5.29 (d, 1.5 Hz) ppm. MS
(GC/MS): ortho-Isomer: m/z (rel. int.) ϭ 210 (17), 195 (100), 167
(67), 165 (33), 152 (18). para-Isomer: m/z (rel. int.) ϭ 210 (100),
195 (69), 167 (19), 165 (22), 152 (17). C15H14O (210.28).
1-(2,5-Dimethylphenyl)-1-(p-tolyl)ethene (14): New compound.
Slightly yellow oil; b.p. 58 °C (diffusion pump). NMR (CDCl3,
1-(4-Chlorophenyl)-1-(2,5-dimethylphenyl)ethene (18, not isolated):
1H NMR of the crude product (300.13 MHz, CDCl3, TMS as
standard): δ(vinyl-H) ϭ 5.69, (d, J ϭ 1.5 Hz), 5.17 (d, 1.5 Hz) ppm.
MS (GC-MS): m/z (rel. int.) ϭ 242 (15), 227 (25), 207 (45), 192
(100). C16H15Cl (242.75).
1
TMS as standard): H NMR (300.13 MHz): δ ϭ 7.19Ϫ7.14 (m, 2
H, Ar-H), 7.10Ϫ7.02 (m, 5 H, Ar-H), 5.71 (pd, J ϭ 1.5 Hz, 1 H,
vinyl-H), 5.11 (pd, J ϭ 1.5 Hz, 1 H, vinyl-H), 2.32 (s, 6 H, 2 ϫ
Me), 2.01 (s, 3 H, Me) ppm. 13C NMR (75.48 MHz): δ ϭ 149.3,
141.6, 137.8, 137.3, 135.0, 132.9, 130.6, 129.9, 129.0, 128.1, 126.4,
113.7, 21.1, 20.9, 19.6 ppm. IR: ν˜ ϭ 3085 (m), 3022 (s), 2921 (vs),
1612 (s), 1567 (w), 1511 (vs), 1498 (s), 1450 (s), 1322 (m), 1305 (m),
1185 (m), 1119 (m), 1039 (m), 1019 (m), 896 (vs), 827 (vs), 811 (vs),
736 (m), 604 (m): 482 (s) cmϪ1. MS: m/z (rel. int.) ϭ 222 (39), 207
(100), 192 (66). HRMS: calcd. 222.14085; found 222.140697.
C17H18 (222.23): calcd. C 91.84, H 8.16; found C 91.69, H 8.24.
1-(4-Chlorophenyl)-1-mesitylethene (19): New compound. Slightly
yellow oil; b.p. 82 °C (diffusion pump). NMR (CDCl3, TMS as
1
standard): H NMR (300.13 MHz): δ ϭ 7.24Ϫ7.17 (m, 4 H, ArCl-
H), 6.90 (s, 2 H, mesityl-H), 5.93 (d, J ϭ 1.2 Hz, 1 H, vinyl-H),
5.10 (d, J ϭ 1.2 Hz, 1 H, vinyl-H), 2.31 (s, 3 H, Me), 2.09 (s, 6 H,
2 ϫ Me) ppm. 13C NMR (75.48 MHz): δ ϭ 145.8, 138.0, 137.6,
136.7, 136.0, 133.4, 128.6, 128.2, 127.1, 115.0, 21.0, 20.0 ppm. IR:
ν˜ ϭ 3084 (m), 2948 (vs), 2918 (vs), 2857 (s), 1615 (vs), 1590 (m),
1665 (m), 1490 (vs), 1438 (s), 1395 (s), 1377 (s), 1311 (m), 1291 (m),
1177 (m), 1112 (m), 1093 (vs), 1066 (m), 1032 (w), 1012 (vs), 905
(vs), 852 (vs), 838 (vs), 823 (vs), 755 (m), 738 (m), 721 (m), 615
(w), 564 (m), 460 (m) cmϪ1. MS: m/z (rel. int.) ϭ 258 (13), 256
(38), 243 (17), 241 (50), 221 (37), 206 (100). HRMS: calcd.
256.101878; found 256.101935. C17H17Cl (256.77): calcd. C 79.52,
H 6.67; found C 79.39, H 6.78.
1-Mesityl-1-(p-tolyl)ethene (15): New compound. Slightly yellow
oil; b.p. 79 °C (diffusion pump). NMR (CDCl3, TMS as standard):
1H NMR (300.13 MHz): δ ϭ 7.16 (d, J ϭ 8.2 Hz, 2 H, p-tolyl-H),
7.06 (d, J ϭ 8.2 Hz, 2 H, p-tolyl-H), 6.90 (s, 2 H, mesityl-H), 5.91
(d, J ϭ 1.4 Hz, 1 H, vinyl-H), 5.03 (d, J ϭ 1.4 Hz, 1 H, vinyl-H),
2.31 (s, 6 H, 2 ϫ Me), 2.11 (s, 6 H, 2 ϫ Me) ppm. 13C NMR
(75.48 MHz): δ ϭ 146.6, 138.3, 137.3, 136.7, 136.3, 136.1, 135.8,
129.1, 128.1, 125.7, 21.1, 21.0, 20.1 ppm. IR: ν˜ ϭ 3083 (m), 3028
(s), 2947 (s), 2918 (vs), 2859 (m), 1619 (s), 1611 (s), 1568 (m), 1511 1-(4-Chlorophenyl)-1-(3-hydroxy-2,4,6-trimethylphenyl)ethene (20):
(vs), 1482 (s), 1439 (s), 1377 (s), 1303 (m), 1176 (m), 1068 (m), New compound. Viscous orange oil; b.p. 114 °C (diffusion pump).
3492
 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Eur. J. Org. Chem. 2003, 3485Ϫ3496

Gold-Catalyzed Hydroarylation of Alkynes
FULL PAPER
NMR (CDCl3, TMS as standard): 1H NMR (300.13 MHz): δ ϭ
12.9 ppm. IR: ν˜ ϭ 3504 (s, br), 3003 (s), 2921 (s), 2836 (m),1605
7.25Ϫ6.87 (m, 4 H, ArCl-H), 6.87 (s, 1 H, Ar-H), 5.95 (d, J ϭ (vs), 1574 (s), 1510 (vs), 1479 (vs), 1462 (vs), 1442 (vs), 1419 (s),
1.2 Hz, 1 H, vinyl-H), 5.09 (d, J ϭ 1.2 Hz, 1 H, vinyl-H), 4.52 (s, 1378 (m), 1300 (vs), 1278 (vs), 1248 (vs), 1177 (vs), 1118 (m), 1104
1 H, OH), 2.26 (s, 3 H, Me), 2.04 (s, 3 H, Me), 2.02 (s, 3 H, Me) (s), 1033 (vs), 897 (s), 837 (vs), 810 (s), 762 (m), 749 (m), 643 (m),
ppm. 13C NMR (75.48 MHz): δ ϭ 150.2, 145.9, 139.3, 138.0, 133.4, 563 (m), 535 (m) cmϪ1. MS: m/z (rel. int.) ϭ 268 (58), 253 (100),
129.5, 128.6, 127.7, 127.2, 121.8, 121.4, 115.1, 19.5, 15.9, 13.0 ppm. 238 (41), 222 (18). HRMS: calcd. 268.146330; found 268.146394.
IR: ν˜ ϭ 3588 (vs, br), 3084 (m), 2920 (s), 2860 (m), 1615 (m), 1588 C18H20O2 (268.36): calcd. C 80.56, H 7.51; found C 80.66, H 7.60.
(m), 1490 (vs), 1461 (s), 1396 (s), 1379 (s), 1292 (s), 1243 (s), 1186
1-Mesityl-1,2-diphenylethene (27, not isolated): Due to the very low
yield, the structure of the double bond was not determined. MS
(GC-MS): m/z (rel. int.) ϭ 298 (100), 283 (30), 268 (15), 207 (45),
192 (50). C23H22 (298.43).
(vs), 1114 (s), 1089 (vs), 1040 (s), 1011 (s), 907 (s), 870 (m), 837
(vs), 755 (m), 739 (m), 711 (m), 652 (w), 546 (w), 524 (w), 460 (m)
cmϪ1. MS (DE): m/z (rel. int.) ϭ 274 (23), 272 (66), 259 (17), 257
(48), 424 (17), 237 (35), 222 (100). HRMS: calcd. 272.096793;
found 272.097012. C17H17ClO (272.77): calcd. C 74.86, H 6.28;
found C 74.68, H 6.35.
(Z)- and (E)-1-Mesityl-1-phenyl-1-propene (28a,b): Colourless oil.
This product was pure after column chromatography; distillation
was not necessary. NMR (CDCl3, TMS as standard, Z:E mixture,
3.7:1).1H NMR (300.13 MHz; integral intensities are given relative
to the (E)-vinyl-H (ϭ 1 H); isomers were assigned by comparison
with literature NMR spectroscopic data):[25] δ ϭ 7.15 Ϫ7.26 [m, 24
H, (E,Z)-Ph], 6.91 [s, 7.4 H, (Z)-mes-H], 6.85 [s, 2 H, (E)-mes-H],
6.35 [q, J ϭ 6.8 Hz, 3.7 H, (Z)-vinyl-H], 5.62 [q, J ϭ 7.2 Hz, 1 H,
1-(3-Bromo-2,4,6-trimethylphenyl)-1-(4-chlorophenyl)ethene (21, not
isolated): 1H NMR of the crude product (300.13 MHz, CDCl3,
TMS as standard): δ(vinyl-H) ϭ 5.86 (br. s), 5.00 (br. s) ppm. MS
(GC/MS): m/z (rel. int.) ϭ 336 (25), 334 (20), 286 (25), 284 (25),
242 (30), 240 (100), 220 (70). C17H16BrCl (335.67).
1-(3-Bromo-2,4,6-trimethylphenyl)-1-(4-methoxyphenyl)ethene (22): (E)-vinyl-H], 2.31 [s, 11 H, mes-Me, (Z)-isomer], 2.27 [s, 3 H, mes-
New compound. Yellow oil (this product was pure after column
chromatography; distillation was not necessary). NMR (CDCl3,
Me, (E)-isomer], 2.15 [s, 6 H, 2 ϫ mes-Me, (E)-isomer], 2.04 [s, 22
H, 2 ϫ mes-Me, (Z)-isomer], 1.97 [d, J ϭ 7.2 Hz, 3 H, (E)-vinylic-
TMS as standard): 1H NMR (300.13 MHz): δ ϭ 7.18 (m, 2 H, Me], 1.52 [d, J ϭ 6.8 Hz, 11 H, (Z)-vinylic-Me] ppm. 13C NMR
ArOMe-H), 6.99 (s, 1 H, ArBr-H), 6.80 (m, 2 H, ArOMe-H), 5.85 (d, (100.61 MHz): δ ϭ 140.9, 140.5, 139.9, 139.5, 139.4, 136.4, 136.3,
J ϭ 1.1 Hz, 1 H, vinyl-H), 4.94 (d, J ϭ 1.1 Hz, 1 H, vinyl-H), 3.78 136.2, 136.0, 135.6, 129.1, 128.3, 128.2, 128.1, 127.8, 126.6, 126.4,
(s, 3 H, OMe), 2.42 (s, 3 H, Me), 2.67 (s, 3 H, Me), 2.07 (s, 3 H,
126.2, 125.5, 123.3, 21.1, 21.0, 20.5, 19.7, 15.4, 15.0 ppm. IR: ν˜ ϭ
3021 (s), 2969 (s), 2915 (vs), 2855 (s), 1611 (m), 1597 (m), 1493 (s),
Me) ppm. 13C NMR (75.48 MHz): δ ϭ 159.4, 146.4, 140.2, 136.7,
136.1, 134.9, 131.6, 129.6, 127.0, 125.4, 113.8, 112.7, 55.2, 24.0, 1442 (vs), 1376 (s), 1179 (w), 1077 (w), 1031 (m), 966 (w), 881 (m),
21.4, 19.9 ppm. IR: ν˜ ϭ 3083 (m), 2999 (s), 2952 (s), 2922 (s), 2834
850 (s), 759 (vs), 695 (vs), 618 (m) cmϪ1. MS (GC-MS): m/z (rel.
(s), 1605 (vs), 1573 (m), 1511 (vs), 1462 (vs), 1453 (vs), 1441 (vs), int.) ϭ 236 (60), 207 (100), 192 (63), 115 (15). [(Z)-isomer; the MS
1379 (m), 1301 (s), 1250 (vs), 1179 (vs), 1132 (m), 1117 (m), 1035 of the (E)-isomer is virtually identical.]. C18H20 (236.36): calcd.
(vs), 975 (s), 897 (m), 83 (vs), 778 (m), 565 (m) cmϪ1. MS: m/z (rel. 236.15650; found 236.156389 (HRMS).
int.) ϭ 332 (29), 330 (29), 317 (44), 315 (45), 236 (100), 220 (14),
General Procedure for the Hydroarylation of 29 by 8 with in situ
Prepared Gold Complexes: 6.28 mg AuCl (0.027 mmol) and
0.027 mmol of a (solid) phosphorus ligand were weighed into a
193 (16), 118 (21). HRMS: calcd. 330.061940; found 330.061640.
C18H19OBr (331.25): calcd. C 65.27, H 5.78; found C 65.76, H 5.85.
1-Mesityl-1-(4-methoxyphenyl)ethene (23): New compound. Yellow
reaction flask in air. The flask was evacuated several minutes and
oil (this product was pure after column chromatography; distil-
charged with argon (3 ϫ). 2 mL of nitromethane were added.
lation was not necessary). NMR (CDCl3, TMS as standard): 1H Liquid phosphorus ligands (0.027 mmol) were now added (either
NMR (300.13 MHz): δ ϭ 7.22Ϫ7.20 (m, 2 H, Ar-H), 6.89 (br. s, 2 with microliter syringes or as stock solutions in nitromethane). Yel-
H, mesityl-H), 6.81Ϫ6.77 (m, 2 H, Ar-H), 5.83 (d, J ϭ 1.4 Hz, 1
H, vinyl-H), 4.97 (d, J ϭ 1.4 Hz, 1 H, vinyl-H), 3.76 (s, 3 H, MeO), tions within a few minutes of stirring. 1.0 mL of a stock solution
2.31 (s, 3 H, Me), 2.11 (s, 6 H, 2 ϫ Me) ppm. 13C NMR
of BF3·OEt2 in nitromethane (c ϭ 0.027 ) were added. Finally,
(75.48 MHz): δ ϭ 159.2, 146.2, 138.4, 136.3, 136.1, 132.2, 128.2, 0.38 mL (2.7 mmol) mesitylene 8 and 92 µL (0.90 mmol) acety-
127.0, 114.2, 112.4, 55.2, 21.0, 20.0 ppm. IR: ν˜ ϭ 3082 (m), 2998 lenecarboxylic acid ester 29 were added rapidly. The reaction mix-
(s), 2952 (vs), 2917 (vs), 2857 (m), 2835 (s), 1605 (vs), 1573 (s), ture was stirred for 14 h at 50 °C. After cooling, 100 µL of n-
low suspensions were obtained which became clear colourless solu-
1510 (vs), 1460 (s), 1441 (s), 1376 (s), 1319 (s), 1298 (s), 1287 (s),
1249 (vs), 1183 (s), 1174 (vs), 1128 (m), 1117 (m), 1068 (w), 1035
hexadecane and 2 mL ethyl acetate were added. An aliquot (ca.
0.5 mL) was taken and filtered through a small plug of silica gel
(vs), 865 (s), 851 (s), 837 (vs), 771 (w), 652 (w), 588 (s), 537 (w) (elution with ethyl acetate). The yields of 30 and 31 were deter-
cmϪ1. MS: m/z (rel. int.) ϭ 252 (49), 237 (100), 222 (38), 206 (21).
HRMS: calcd. 252.151415; found 252.151643 . C18H20O (252.36):
calcd. C 85.67, H 7.99; found C 85.52, H 7.84.
mined by GC.
General Procedure for the Hydroarylation of Alkynes 29 and 39 by
various Arenes with Ph3PAuCl under Optimized Conditions (Small-
Scale Experiments). Liquid Arenes: 4.45 mg (0.00900 mmol)
Ph3PAuCl were weighed into a reaction flask in air. The flask was
then evacuated for several minutes and charged with argon (3 ϫ).
2.0 mL of nitromethane were added. Now the co-catalyst (either
1.5 mL of a 0.030  solution of BF3·OEt2 in nitromethane or
1-(3-Hydroxy-2,4,6-trimethylphenyl)-1-(4-methoxyphenyl)ethene
(24): New compound. Viscous orange oil (this product was pure
after column chromatography; distillation was not necessary).
NMR (CDCl3, TMS as standard): 1H NMR (300.13 MHz): δ ϭ
7.22Ϫ7.19 (m, 2 H, ArOMe-H), 6.87 (br. s, 1 H, Ar-H), 6.82Ϫ6.78
(m, 2 H, ArOMe-H), 5.85 (d, J ϭ 1.3 Hz, 1 H, vinyl-H), 4.96 (d, 0.90 mL of a 0.010  solution of AgSbF6 in the same solvent) was
J ϭ 1.3 Hz, 1 H, vinyl-H), 4.51 (br. s, 1 H, OH), 3.78 (s, 3 H,
added. Finally, the flask was charged with the arene (excess) and
the alkyne (0.90 mmol). The reaction mixture was stirred at the
OMe), 2.26 (s, 3 H, Me), 2.06 (s, 3 H, Me), 2.04 (s, 3 H, Me)
ppm. 13C NMR (75.48 MHz): δ ϭ 159.2, 150.1, 146.3, 140.1, 132.1, temperature and for the time given in Table 4 and 5. Workup was
129.4, 127.7, 127.1, 121.5, 121.4, 113.8, 112.5, 55.2, 19.4, 15.9, conducted as described above.
Eur. J. Org. Chem. 2003, 3485Ϫ3496
www.eurjoc.org
 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
3493

M. T. Reetz, K. Sommer
FULL PAPER
Solid Arenes: Solid arenes were weighed into the flask in air as well
as the gold catalyst. The flask was then evacuated for several mi-
nutes and charged with argon (3 ϫ). 2.0 mL of nitromethane were
added. A solution of the co-catalyst and the alkyne was then added.
The further procedure was the same as described above for liquid
arenes.
115 (12), 105 (5), 91 (8), 77 (8), 29 (10). C16H22O2 (246.35): calcd.
246.161980; found 246.162055 (HRMS).
Ethyl (Z)-3-(2,5-Dimethylphenyl)propenoate (33): Colourless oil.
NMR (CDCl3, TMS as standard, (17:1)-Z:E mixture): 1H NMR
(400.13 MHz; integral intensities are given relative to (E)-vinyl-H
(ϭ 1 H]): δ ϭ 7.95 [d, J ϭ 15.6 Hz, 1 H, (E)-vinyl-H], 7.36 [s, 1 H,
(E)-ArϪH], 7.12 [s, 17 H, (Z)-ArϪH], 6.98Ϫ7.10 [m, 53 H, (E,Z)-
Ar-H ϩ (Z)-vinyl-H], 7.07 [d, J ϭ 12.3 Hz, 17 H, (Z)-vinyl-H], 6.35
[d, J ϭ 15.6 Hz, 1 H, (E)-vinyl-H], 5.99 [d, J ϭ 12.3 Hz, 17 H, (Z)-
vinyl-H], 4.26 [q, J ϭ 7.1 Hz, 2 H, (E)-OCH2] 4.08 [q, J ϭ 7.1 Hz,
34 H, (Z)-OCH2], 2.38 [s, 3 H, (E)-Me], 2.31 [s, 3 H, (E)-Me], 2.29
[s, 51 H, (Z)-Me], 2.22 [s, 51 H, (Z)-Me], 1.33 [t, J ϭ 7.1 Hz, 3 H,
General Procedure for the Hydroarylation of Alkynes 29 and 39 by
various Arenes with Ph3PAuCl under Optimized Conditions (Large-
Scale Experiments). Liquid Arenes: 24.7 mg Ph3PAuCl
(0.0500 mmol) and (where applicable, see Table 4) 17.2 mg AgSbF6
(0.0500 mmol) were weighed in a 100-mL Schlenk flask under ar-
gon. 5.0 mL of nitromethane and (where applicable, see Table 4) 32
µL (0.25 mmol) BF3·OEt2 were added. Now the arene (excess) and
alkyne (5.0 mmol) were added rapidly. The reaction mixture was
stirred for the time and at the temperature given in the Table 4 and
5. After cooling, the solvent was removed at reduced pressure, and
the remaining residue was purified by column chromatography (sil-
ica gel, hexanes/ethyl acetate).
(E)-OCH2CH3] 1.13 [t, J ϭ 7.1 Hz, 51 H, (Z)-OCH2CH3] ppm. 13
C
NMR (100.61 MHz): δ ϭ 167.1, 166.0, 142.9, 142.4, 135.7, 134.9,
134.6, 134.5, 133.2, 132.6, 130.8, 130.7, 129.6, 129.3, 129.1, 127.0,
121.0, 119.0, 60.4, 60.1, 20.9 (br., 2 ϫ Me), 19.4, 19.3, 14.3,
14.0 ppm. IR: ν˜ ϭ 2980 (s), 2923 (m), 1227 (vs), 1716 (vs), 1633
(m), 1496 (m), 1446 (m), 1384 (m), 1274 (m), 1177 (vs), 1108 (m),
1240 (m), 1033 (s), 830 (s), 811 (m) cmϪ1. MS (GC-MS): m/z (rel.
int.) ϭ 204 (27), 189 (13), 161 (21), 160 (12), 159 (100), 131 (44),
130 (60), 115 (40), 91 (22), 29 (9). [(Z)-isomer; the MS of the (E)-
compound is virtually identical]. C13H16O2 (204.27): calcd.
204.115030; found 204.115336 (HRMS).
Solid Arenes: Solid arenes were weighed into a 100-mL Schlenk
flask in air as well as 24.7 mg (0.0500 mmol) of Ph3PAuCl. The
flask was then evacuated for several minutes and charged with ar-
gon (3 ϫ). 20Ϫ35 mL nitromethane were added. Finally, 32 µL
(0.25 mmol) BF3·OEt2 and the alkyne (5.0 mmol) were added. The
reaction mixture was stirred for the time and at the temperature
given in the Table 4 and 5. The workup procedure was the same as
described above for liquid arenes.
Ethyl (Z)-3-(4-Tolyl)propenoate and Ethyl (Z)-3-(2-Tolyl)propenoate
(34a,b, not isolated): 1H NMR of the crude product, ortho/para
mixture (1.5:1) [300.13 MHz, CDCl3, TMS as standard, integral
intensities are given relative to para vinyl-H (ϭ 1 H)]: δ ϭ 7.51 (d,
J ϭ 7.7 Hz, 2 H, Ar-H para-isomer), 7.30 (d, J ϭ 7.7 Hz, 2 H, Ar-
H para-isomer), 7.14Ϫ7.24 (m, 6 H, Ar-H ortho-isomer), 7.11 (d,
J ϭ 12.6 Hz, 1.5 H, vinyl-H ortho-isomer), 6.88 (d, J ϭ 12.9 Hz, 1
H, vinyl-H para-isomer), 6.02 (d, J ϭ 12.6 Hz, 1.5 H, vinyl-H ortho-
isomer); 5.88 (d, J ϭ 12.9 Hz, 1 H, vinyl-H para-isomer), 4.12 (q,
J ϭ 7.2 Hz, 2 H, OCH2 para-isomer), 4.07 (q, J ϭ 7.2 Hz, 3 H,
OCH2 ortho-isomer), 2.34 (s, 3 H, Me para-isomer), 2.27 (s, 4.5 H,
Me ortho-isomer), 1.30 (t, J ϭ 7.2 Hz, 3 H, OCH2CH3 para-iso-
mer), 1.14 (t, J ϭ 7.2 Hz, 4.5 H, OCH2CH3 ortho-isomer) ppm.
MS (GC-MS): ortho-Isomer: m/z (rel. int.) ϭ 190 (10), 175 (10),
145 (100), 115 (95), 91 (30), 65 (20), 29 (15). para-Isomer: m/z (rel.
int.) ϭ 190 (50), 175 (5), 162 (15), 145 (100), 115 (65), 91 (25), 65
(20), 29 (10). C12H14O2 (190.24).
Analytical Data: Yields are given in Table 4 and 5.
Ethyl (Z)-3-Mesitylprop-2-enoate (30): Colourless liquid. NMR
1
(CDCl3, TMS as standard): H NMR (300.13 MHz): δ ϭ 7.00 (d,
J ϭ 11.9 Hz, 1 H, vinyl-H), 6.83 (s, 2 H, Ar-H), 6.10 (d, J ϭ
11.9 Hz, 1 H, vinyl-H), 4.01 (q, J ϭ 7.1 Hz, 2 H, OCH2), 2.25 (s,
3 H, CH3), 2.15 (s, 6 H, 2 ϫ CH3), 1.08 (t, J ϭ 7.1 Hz, 3 H,
OCH2CH3) ppm. 13C NMR (75.48 MHz): δ ϭ 165.4, 144.1, 136.7,
134.5, 133.1, 127.8, 122.8, 59.9; 21.0, 20.1, 14.0 ppm. IR: ν˜ ϭ 2980
(m), 1919 (m), 1729 (s), 1715 (vs), 1636 (w), 1612 (w), 1479 (w),
1445 (w), 1384 (w), 1287 (m), 1196 (s), 1172 (s), 1130 (w), 1032
(m), 851 (m), 595 (w) cmϪ1. MS: m/z (rel. int.) ϭ 218 (40), 203
(15), 173 (100), 144 (60), 129 (55), 115 (25), 105 (9), 91 (10), 29 (10).
C14H18O2 (218.30): calcd. 218.130680; found 218.130913 (HRMS).
Ethyl (Z)-3-(3-Hydroxy-2,4,6-trimethylphenyl)propenoate (35):
Slightly yellow powder. NMR (CDCl3, TMS as standard): 1H
NMR (300.13 MHz): δ ϭ 7.00 (d, J ϭ 11.9 Hz, 1 H, vinyl-H), 6.80
(s, 1 H, Ar-H), 6.13 (d, J ϭ 11.9 Hz, 1 H, vinyl-H), 4.54 (s, 1 H,
OH), 4.04 (q, J ϭ 7.1 Hz, 2 H, OCH2), 2.20 (s, 3 H, CH3); 2.09 (s,
Diethyl (Z)-3,3Ј-(2,3,6-Trimethyl-1,3-phenylene)bis(prop-2-enoate)
(31): 1H NMR (300.13 MHz): δ ϭ 7.01 (d, J ϭ 11.9 Hz, 2 H, vinyl-
H), 6.88 (s, 1 H, Ar-H), 6.10 (d, J ϭ 11.9 Hz, 2 H, vinyl-H), 4.03
(q, J ϭ 7.2 Hz, 4 H, 2 ϫ OCH2), 2.15 (s, 6 H, 2 ϫ Ar-CH3), 2.05
(s, 3 H, Ar-CH3), 1.12 (t, J ϭ 7.2 Hz, 6 H, 2 ϫ OCH2CH3) ppm.
13C NMR (75.48 MHz): δ ϭ 165.4, 144.4, 133.5, 133.0, 131.0,
128.4, 122.7, 59.9, 20.2, 17.7, 14.0 ppm. MS (GC-MS): m/z (rel.
int.) ϭ 316 (7), 301 (14), 298 (14), 271 (29), 225 (62), 197 (100),
169 (28), 153 (34), 128 (19). C19H24O4 (316.40).
br., 6 H, 2 ϫ CH3), 1.11 (t, J ϭ 7.1 Hz, 3 H, OCH2CH3) ppm. 13
C
NMR (75.48 MHz): δ ϭ 165.4, 149.8, 144.0, 134.3, 129.2, 126.1,
122.8, 121.9, 120.2, 60.0, 19.6, 15.9, 14.0, 13.0 ppm. IR: ν˜ ϭ 3480
(s), 2980 (m), 2924 (m), 2867 (w), 1713 (vs), 1636 (m), 1479 (m),
1384 (m), 1299 (m), 1203 (s), 1181 (vs), 1082 (m), 1028 (m), 866
(w), 831 (w) cmϪ1. MS (DE): m/z (rel. int.) ϭ 234 (96), 189 (100),
160 (91), 145 (48), 115 (16), 91 (16). C14H18O3 (234.30): calcd.
234.125595; found 234.125419 (HRMS).
Ethyl (Z)-3-(Pentamethylphenyl)propenoate (32): White powder.
NMR (CDCl3, TMS as standard): 1H NMR (300.13 MHz): δ ϭ
7.13 (d, J ϭ 11.9 Hz, 1 H, vinyl-H), 6.13 (d, 1 H J ϭ 11.9 Hz,
vinyl-H), 4.02 (q, J ϭ 7.1 Hz, 2 H, OCH2), 2.23 (s, 3 H, CH3), 2.20
(s, 6 H, 2 ϫ CH3), 2.14 (s, 6 H, 2 ϫ CH3), 1.10 (t, J ϭ 7.1 Hz, 3
Ethyl (Z)-3-(2-Furyl)propenoate (37): Colourless liquid which be-
H, OCH2CH3) ppm. 13C NMR (75.48 MHz): δ ϭ 165.4, 146.5, comes yellow rapidly. NMR (CDCl3, TMS as standard) [The struc-
134.0, 133.2, 131.9, 129.8, 122.1, 59.8, 17.6, 16.8, 16.4, 14.0 ppm.
ture of 37 was unequivocally confirmed by COSY and HSQC
IR: ν˜ ϭ 2981 (m), 2920 (m), 2870 (m), 1721 (vs), 1632 (s), 1458 experiments]: 1H NMR (400.13 MHz): δ ϭ 7.68 (d, 3J3,4 ϭ 3.6 Hz,
3
(m), 1445 (m), 1383 (m), 1297 (w), 1226 (s), 1184 (vs), 1093 (m),
1 H, furyl-H3), 7.47 (d, J5,4 ϭ 1.7 Hz, 1 H, furyl-H5), 6.78 (d,
1059 (w), 1021 (m), 935 (w), 847 (m), 828 (w), 812 (m), 762 (w), 3Jβ,α ϭ 12.9 Hz, 1 H, vinyl-Hβ), 6.50 (pdd, 1 H, 3J4,3 ϭ 3.6, 3J4,5 ϭ
718 (w), 626 (w) cmϪ1. MS: m/z (rel. int.) ϭ 246 (88), 231 (69), 203 1.7 Hz, furyl-H4), 5.73 (d, 1 H, 3Jα, β ϭ 12.9 Hz, vinyl-Hα), 4.22 (q,
(57), 201 (100), 186 (23), 172 (70), 157 (64), 143 (31), 128 (19), J ϭ 7.1 Hz, 2 H, CH2), 1.31 (t, J ϭ 7.1 Hz, 3 H, CH3) ppm. 13C
3494
 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
Eur. J. Org. Chem. 2003, 3485Ϫ3496

Gold-Catalyzed Hydroarylation of Alkynes
FULL PAPER
(100.62 MHz): δ ϭ 166.0 (CO2Et), 150.9 (furyl-C2), 143.9 (furyl-
(vs), 1567 (m), 1481 (m), 1458 (m), 1380 (w), 1354 (m), 1313 (m),
1290 (m), 1253 (m), 1178 (m), 1145 (w), 1035 (w), 1003 (m), 974
C5), 130.4 (vinyl-Cβ), 117.0 (furyl-C3), 114.4 (vinyl-Cα), 112.6 (fu-
ryl-C4), 60.2 (CH2), 14.3 (CH3) ppm. IR: ν˜ ϭ 3147 (w), 2982 (w), (m), 906 (w), 858 (m), 722 (w), 600 (m), 577 (m), 514 (w) cmϪ1
.
1716 (vs), 1626 (s), 1479 (m), 1430 (s), 1374 (m), 1215 (s), 1182
(vs), 1090 (m), 1020 (m), 835 (w), 752 (m), 595 (w) cmϪ1. MS (GC-
MS): m/z (rel. int.) ϭ 166 (60), 138 (35), 121 (100), 110 (10), 94
(30), 65 (35), 39 (23). C9H10O3 (166.18): calcd. 166.062995; found
166.062842 (HRMS).
MS: m/z (rel. int.) ϭ 188 (10), 173 (100), 145 (10), 129 (12).
C13H16O (188.27): calcd. 188.120115; found 188.120003 (HRMS).
(E)-4-(2,5-Dimethylphenyl)-3-buten-2-one (42, not isolated): 1H
NMR of the crude product (300.13 MHz, CDCl3, TMS as stand-
ard): δ ϭ 7.78 (d, J ϭ 16.2 Hz, 1 H, vinyl-H), 7.06Ϫ7.12 (m, 3 H,
Ar-H), 6.63 (d, J ϭ 16.2 Hz, 1 H, vinyl-H), 2.38 (s, 3 H, Me), 2.35
(s, 3 H, Me), 2.31 (s, 3 H, Me) ppm. MS (GC-MS): m/z (rel. int.) ϭ
174 (15), 159 (100), 131 (15), 91 (10), 43 (5). C12H14O (174.24).
Ethyl (Z)-3-[2-(5-Methylfuryl)]propenoate (38a): The different iso-
mers of 38 could not be separated by colomn chromatography, but
it was possible to interpret the NMR spectra and thus to assign
the different isomers to the GC peaks (except for 38c). NMR
(CDCl3, TMS as standard, assignments were confirmed by means
(E)-4-(3-Hydroxy-2,4,6-trimethylphenyl)-3-buten-2-one (43): New
compound. Dark yellow needles; m.p. (hexanes/chloroform)
141Ϫ142 °C. NMR (CDCl3, TMS as standard): 1H NMR
(300.13 MHz): δ ϭ 7.64 (d, J ϭ 16.6 Hz, 1 H, vinyl-H), 6.86 (s, 1
H, Ar-H), 6.26 (d, J ϭ 16.6 Hz, 1 H, vinyl-H), 4.78 (s, 1 H, OH),
2.39 (s, 3 H, CH3), 2.24 (s, 9 H, 3 ϫ CH3) ppm. 13C NMR
(75.48 MHz): δ ϭ 198.6, 150.5, 142.5, 133.1, 132.8, 130.1, 128.1,
123.6, 121.8, 27.4, 20.3, 16.0, 13.3 ppm. IR: ν˜ ϭ 3386 (s), 2964 (w),
2923 (w), 1655 (s), 1634 (s), 1618 (s), 1477 (w), 1458 (w), 1410 (m),
1384 (w), 1366 (m), 1266 (s), 1225 (s), 1203 (m), 1108 (m), 1025
(w), 1009 (m), 994 (m), 867 (w), 742 (w) cmϪ1. MS: m/z (rel. int.) ϭ
204 (32), 189 (100), 174 (11), 160 (17), 145 (20). HRMS: calcd.
204.115030; found 204.115259. C13H16O2 (204.27): calcd. C 76.44,
H 7.90; found C 76.32, H 7.82.
1
of HSQC): H NMR (400.13 MHz): δ ϭ 7.60 (d, J ϭ 3.3 Hz, 1 H,
furyl-H3), 6.71 (d, J ϭ 12.8 Hz, 1 H, vinyl-Hβ), 6.11 (pd, J ϭ
3.3 Hz, 1 H, furyl-H4), 5.64 (d, J ϭ 12.8 Hz, 1 H, vinyl-Hα), 4.21
(q, J ϭ 7.1 Hz, 2 H, OCH2), 2.32 (s, 3 H, furyl-CH3), 1.31 (t, J ϭ
7.1 Hz, 3 H, OCH2CH3) ppm. 13C NMR (100.62 MHz): δ ϭ 166.2
(CO2Et), 154.4 (furyl-C2 or C5), 149.6 (furyl-C5 or C2), 130.5 (vi-
nyl-Cβ), 118.7 (furyl-C3), 112.6 (vinyl-Cα), 109.3 (furyl-C4), 60.0
(OCH2CH3), 14.3 (OCH2CH3), furyl-CH3) ppm. MS (GC-MS): m/
z (rel. int.) ϭ 180 (57), 152 (23), 135 (100), 108 (19), 77 (24), 43 (53).
C10H12O3 (180.20): calcd. 180.078645; found 180.078799 (HRMS).
Ethyl (Z)-3-[4-(5-Methylfuryl)]propenoate (38b): 1H NMR
(400.13 MHz): δ ϭ 7.24 (d, J ϭ 2.0 Hz, 1 H, furyl-H), 7.22 (d, J ϭ
2.0 Hz, 1 H, furyl-H), 6.67 (d, J ϭ 12.5 Hz, 1 H, vinyl-Hβ), 5.71
(d, J ϭ 12.5 Hz, 1 H, vinyl-Hα), 4.20 (q, J ϭ 7.1 Hz, 2 H, OCH2),
2.34 (s, 3 H, furyl-CH3), 1.30 (t, J ϭ 7.1 Hz, 3 H, OCH2CH3) ppm.
It was not possible to assign all 13C NMR peaks undoubtedly to
certain isomers, thus only the 1H NMR spectroscopic data are
given. MS (GC-MS): m/z (rel. int.) ϭ 180 (93), 151 (31), 135 (100),
77 (66), 43 (85). C10H12O3 (180.20).
Reaction of AuCl3 with AgOTf to give ‘‘Au9Ag11Cl28’’ (44): 200 mg
AuCl3 (0.659 mmol) were dissolved in 6.0 mL CH3NO2 under Ar
to give a yellow solution. A solution of 169 mg (0.659 mmol) Ag-
OTf in 14 mL CH3NO2 was added all at once. An orange precipi-
tate formed immediately. The suspension was stirred 14 h under
exclusion of light. The precipitate was filtered under Ar and washed
with 5 mL CH3NO2 and 3 ϫ with 5 mL pentane. The product was
dried in vacuo (14 h) to give 102.3 mg of an orange powder (44).
A cloudy filtrate was obtained. All volatiles were removed, and the
remaining residue was dried in vacuo (14 h). A light brown oily
product was obtained, the IR spectrum of which indicated the pres-
ence of triflate, but showed a band structure different from that
of AgOTf.
Ethyl (Z)-3-[3-(5-Methylfuryl)]propenoate (38c): Since only traces
of this isomer were formed, we were not able to obtain NMR spec-
troscopic data for 38c. Thus, it was not possible to determine the
structure of 38c beyond doubt. However, in view of the structures
of 38a and 38b, it is likely that this compound is the isomer Ethyl
(Z)-[3-(5-methylfuryl)]propenoate. MS (GC-MS): m/z (rel. int.) ϭ
180 (56), 136 (35), 107 (100), 77 (30). C10H12O3 (180.20).
Ag11Au9Cl28 (3951.90): calcd. Au 44.86, Ag 30.03, Cl 25.12; found
Au 44.98, Ag 29.72, Cl 25.06.
(E)-4-(Pentamethylphenyl)-3-buten-2-one (40): Slightly yellow pow-
der. NMR (CDCl3, TMS as standard): 1H NMR (300.13 MHz):
δ ϭ 7.73 (d, J ϭ 16.6 Hz, 1 H, vinyl-H), 6.15 (d, 1 H J ϭ 16.6 Hz,
vinyl-H), 2.40 (s, 3 H, CH3), 2.26 (s, 3 H, CH3), 2.28 (s, 6 H, 2 ϫ
CH3), 2.22 (s, 6 H, 2 ϫ CH3) ppm. 13C NMR (75.48 MHz): δ ϭ
198.4, 145.1, 135.4, 133.9, 132.9, 132.7, 131.1, 27.4, 18.0, 16.9,
Ethyl (Z)-3-Chloropropenoate (47): An authentic sample of 47 was
prepared by esterification of the corresponding carboxylic acid
with ethanol according to a standard protocol.[26] The authentic
sample showed identical NMR shifts, the same GC retention time
and mass spectrum as the compound observed in the described
mechanistic experiment. NMR (CDCl3, TMS as standard): 1H
NMR (300.13 MHz): δ ϭ 6.71 (d, J ϭ 8.2 Hz, 1 H, vinyl-H), 6.19
(d, J ϭ 8.2 Hz, 1 H, vinyl-H), 4.24 (q, J ϭ 7.1 Hz, 2 H, OCH2),
1.31 (t, J ϭ 7.1 Hz, 3 H, CH3) ppm. 13C NMR (75.48 MHz): δ ϭ
163.5, 132.4, 121.5, 60.7, 14.2 ppm. MS (GC-MS): m/z (rel. int.) ϭ
134 (0.1), 119 (2), 109 (2), 99 (42), 91 (35), 89 (100), 61 (16).
C5H7ClO2 (134.56).
1
16.5 ppm. H NMR (300.13 MHz, (Z)-Isomer): (The vinyl-H sig-
nals are given only): δ ϭ 7.19 (d, J ϭ 12.5 Hz, 1 H, vinyl-H), 6.30
(d, J ϭ 12.5 Hz, 1 H, vinyl-H) ppm. IR: ν˜ ϭ 3033 (w), 1297 (w),
2921 (m), 1670 (s), 1617 (s), 1444 (m), 1360 (s), 1253 (s), 1231 (m),
1062 (w), 981 (s), 602 (w), 531 (m) cmϪ1. MS: m/z (rel. int.) ϭ 216
(13), 201 (100), 186 (7), 157 (13), 43 (9). C15H20O (216.32): calcd.
216.151415; found 216.151587 (HRMS).
(E)-4-(Mesityl)-3-buten-2-one (41): Yellow powder. NMR (CDCl3,
TMS as standard): 1H NMR (300.13 MHz): δ ϭ 7.67 (d, J ϭ
16.6 Hz, 1 H, vinyl-H), 6.90 (s, 1 H, Ar-H), 6.33 (d, J ϭ 16.6 Hz,
1 H, vinyl-H), 2.38 (s, 3 H, CH3), 2.33 (s, 6 H, 2 ϫ CH3), 2.29 (s,
3 H, CH3) ppm. 13C NMR (75.48 MHz): δ ϭ 198.5, 142.0, 138.5,
136.8, 132.4, 130.9, 129.3, 27.4, 21.1, 21.0 ppm. 1H NMR
(300.13 MHz, (Z)-isomer): δ ϭ 7.05 (d, J ϭ 12.5 Hz, 1 H, vinyl-
H), 6.27 (d, J ϭ 12.5 Hz, 1 H, vinyl-H) ppm. IR: ν˜ ϭ 3006 (w),
2966 (w), 2918 (w), 2861 (w), 1682 (s), 1661 (w), 1628 (m), 1611
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3496
 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
Eur. J. Org. Chem. 2003, 3485Ϫ3496