On homogeneous gold/palladium catalytic systems

Article abstract of DOI:10.1002/adsc.201000044

Two substrates containing an aryl iodide and an allenoate ester were prepared and the goldinduced cycloisomerisation to vinylgold(I) species and their proto-deauration as well as the intramolecular palladium-catalysed cross-coupling reactions were investigated. Switching to catalytic amounts of gold and palladium and stoichiometric amounts of silver did indeed furnish the product of a cycloisomerisation/ intramolecular cross-coupling. Control experiments revealed that silver cannot substitute for gold or palladium in these reactions, but a different palladium catalyst in a different oxidation state also afforded the cycloisomerisation/intramolecular crosscoupling products in only slightly reduced yields. By ICP analysis the palladium was shown to contain gold only at the sub-ppm level. This shows how carefully results obtained with such systems have to be interpreted. Then a series of allylic and benzylic o-alkynylbenzoates were investigated in gold-and palladium-catalysed reactions. For esters of benzyl alcohol and cinnamyl alcohol no palladium co-catalyst was needed for the conversion. All reagents were thoroughly checked for palladium traces by ICP analysis in order to thoroughly exclude a gold/palladium cocatalysis. Optimisation of the gold complex, counter ion and solvent showed that gold(I) isonitrile precatalysts and silver triflate as activator in dioxane are suitable to convert a number of substrates with aryl, alkyl and even cyclopropyl substituents. Crossover experiments proved an intermolecular allyl transfer.

Full text of DOI:10.1002/adsc.201000044

FULL PAPERS
DOI: 10.1002/adsc.201000044
On Homogeneous Gold/Palladium Catalytic Systems
A. Stephen K. Hashmi,a,* Christian Lothschꢀtz,a Renꢁ Dçpp,a
Martin Ackermann,a Janosc De Buck Becker,a Matthias Rudolph,a
Christian Scholz,b and Frank Romingera
a
Organisch-Chemisches Institut, Ruprecht-Karls-Universitꢂt Heidelberg, Im Neuenheimer Feld 270, 69120 Heidelberg,
Germany
Fax : (+49)-(0)6221-54-4205; phone: (+49)-(0)6221-54-8413; e-mail: hashmi@hashmi.de
Institut fꢀr Geowissenschaften, Ruprecht-Karls-Universitꢂt Heidelberg, Im Neuenheimer Feld 236, 69120 Heidelberg,
b
Germany
Received: January 18, 2010; Revised: September 25, 2011; Published online: January 12, 2012
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/adsc.201000044.
Abstract: Two substrates containing an aryl iodide interpreted. Then a series of allylic and benzylic o-al-
and an allenoate ester were prepared and the gold- kynylbenzoates were investigated in gold- and palla-
induced cycloisomerisation to vinylgold(I) species dium-catalysed reactions. For esters of benzyl alcohol
and their proto-deauration as well as the intramolec- and cinnamyl alcohol no palladium co-catalyst was
ular palladium-catalysed cross-coupling reactions needed for the conversion. All reagents were thor-
were investigated. Switching to catalytic amounts of oughly checked for palladium traces by ICP analysis
gold and palladium and stoichiometric amounts of in order to thoroughly exclude a gold/palladium co-
silver did indeed furnish the product of a cycloiso- catalysis. Optimisation of the gold complex, counter
merisation/intramolecular cross-coupling. Control ex- ion and solvent showed that gold(I) isonitrile pre-
periments revealed that silver cannot substitute for catalysts and silver triflate as activator in dioxane are
gold or palladium in these reactions, but a different suitable to convert a number of substrates with aryl,
palladium catalyst in a different oxidation state also alkyl and even cyclopropyl substituents. Crossover
afforded the cycloisomerisation/intramolecular cross- experiments proved an intermolecular allyl transfer.
coupling products in only slightly reduced yields. By
ICP analysis the palladium was shown to contain
gold only at the sub-ppm level. This shows how care- Keywords: allenes; allylic esters; aryl halides; gold;
fully results obtained with such systems have to be heterocycles; palladium
Introduction
idising reagent.[6] The latter method provides access
to unsymmetrical products.
In the last decade, homogeneous gold catalysis[1] has
A very efficient access would be the transmetalla-
proven to be a very successful tool for organic synthe- tion from a vinylgold(I) species to a palladium(II)
sis.[2] Recently, even gold-catalysed cross-coupling species B. There are only a few reports on stoichio-
methodology has been reported.[3] Another interesting metric transmetallation reactions from gold to palladi-
development is the use of intermediate vinylgold spe- um in the literature.[7] We have recently investigated
ꢀ
cies A in C C bond forming reactions. This can be ac- cross-coupling reactions in detail which were stoichio-
complished by the use of external stoichiometric oxi- metric in the vinylgold compound A and the aryl
dants[4] instead of oxidation by the catalyst or stoi- halide ArX but catalytic in palladium.[8] These cross-
chiometric amounts of gold.[5] But these reactions coupling reactions efficiently deliver vinylarenes 3
always deliver symmetrical products 1 by an oxidative and thus prove that an efficient catalytic transmetalla-
homo-dimerisation of the vinylgold intermediates A tion from gold to palladium is possible, but reactions
(Scheme 1). Zhang and co-workers reported an im- catalytic in both gold and palladium did not give satis-
pressive oxidative cross-coupling reaction to 2 with factory results.
stoichiometric amounts of boronic acid derivatives
Now Blum et al. have reported a reaction specific
RB(OR’)2 using Selectfluor as a stoichiometric reox- to allylic esters 4 as substrates, which is catalytic in
ACHTUNGTRENNUNG
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Scheme 1. Conversions of vinylgold species A.
Scheme 2. Reaction catalytic in both gold and palladium.
both gold and palladium (Scheme 2).[9] The reaction is Results and Discussion
a special case, as the intermediate C is related to
Hammondꢄs[10] vinylgold intermediates and thus, The two substrate types 4 and 6 lead to two very dif-
unlike other vinylgold intermediates, is stable (not ferent vinylgold intermediates: 4 gives the electron-
sensitive to protodeauration like most other vinylgold poor vinylgold system D with a carbonyl substituent,
species from catalytic cycles). So there is no compet- while 6 leads to an electron-rich oxy-substituted vinyl-
ing reaction and C is waiting for the palladium cata- gold unit F. Thus, in fact, one would expect a quite
lyst to form the product 5 via intermediate D. These different reactivity of these two species, which indeed
reactions in a very clever way exploit the activity of was confirmed by this investigation. Thus the two dif-
allylic oxonium intermediates as allyl-transfer re- ferent reactions are discussed in two separate sections
agents and at the same time avoid the presence of below.
protons usually going along with gold-catalysed nucle-
ophilic additions.
In their publication, Blum et al.[9] also reported a Reactions of Allenoates
second related reaction, involving allylic o-alkynyl-
benzoates 6 (Scheme 3). As above, an activated allylic This investigation was initiated by our previous find-
species E is formed (equivalent to species C), but in ing that the conversions catalysed by both gold and
this case the vinylgold intermediate F would be more palladium were not efficient, but when using one
sensitive than the species D discussed above. The for- equivalent of a vinylgold or arylgold compound and
ꢀ
mation of a new C C bond delivers 7.
catalytic amounts of palladium, the transmetallation
This recent report prompted us to disclose our find- step proceeded without any problem.[8] Since both in-
ings from the investigation of such systems catalytic dividual cycles, the gold-catalysed cycloisomerisation
in both gold and palladium, which show that the and the palladium-catalysed cross-coupling are fast,
mechanistic interpretation of the results has to be the transmetallation must be the critical step. This
done extremely carefully. The recent discussion of might be due to the low concentration of the species
this point in the literature stresses the need for such a involved in the catalytic cycles, which makes collisions
thorough investigation.[11]
of the vinylgold species A and the palladium(II) spe-
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On Homogeneous Gold/Palladium Catalytic Systems
Scheme 3. Reaction catalytic in both gold and palladium.
cies B rare, and the competing protodeauration might
outrun the desired transmetallation. In order to in-
crease the local concentration of both species, one
could switch to an intramolecular transmetallation
step by using a hetero-dinuclear catalyst with both
metal centres at a distance suitable for the transmetal-
lation. This work is being continued in our group but,
due to the difficult synthesis of these complexes, will
still need some time to complete. The other option
would be to switch to an intramolecular transmetalla-
tion by using a substrate combining both reacting
functional groups in one molecule. This was syntheti-
cally easier to accomplish and is the basis for this part
of our investigation.
We designed a four-step synthesis for the substrates
8 and 9, both combining an aryl iodide and an alle-
noate ester unit in the same molecule.
Figure 1. Solid state molecular structure of the vinylgold(I)
species 10.
Using Hammondꢄs conditions,[10] stoichiometric
Ph3PAu(I)OTf and 8 or 9 delivered the expected vi-
nylgold(I) complexes 10 or 11 as stable compounds
(Scheme 4). The structure of 10 could even be con-
firmed by a X-ray structure analysis, unambiguously ditions the direct cross-coupling by gold only does not
showing the vinylgold(I) species and the aryl iodide in occur, mononuclear organogold(I) species do not un-
the same molecule (Figure 1).[12]
dergo the crucial oxidative addition step (which steri-
In the context of the recent discussion,[11] the stabil- cally could proceed readily by a six-membered transi-
ity of 10 and 11 proves that under these reaction con- tion state in the case of 10). This stresses that with
Scheme 4. Investigation of the first part, the cycloisomerisation.
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A. Stephen K. Hashmi et al.
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Scheme 5. Catalytic cycloisomerisation in the presence of a
strong acid.
Figure 2. Molecular structure of the coupling product 14 in
the solid state.
Scheme 6. Investigation of the second part, the palladium-
catalysed cyclisation of the vinylgold compounds 10 and 11.
these homogeneous mononuclear catalysts a direct
cross-coupling is not feasible.
With a catalytic amount of 10 mol% of the gold
catalyst and p-TsOH as a proton source at 808C the
cycloisomerisation to the lactones 12 or 13 was
achieved (Scheme 5), which is in full agreement with
the slow protodeauration of the allenoate-derived vi-
nylgold species reported by Hammond.[10,13] These ex-
periments clearly show that gold catalysts alone
ꢀ
cannot induce the C C bond formation. Control ex-
periments with silver(I) salts and with p-TsOH gave tained from DFT calculation.
no cycloisomerisation products.
Figure 3. Molecular structure of the coupling product 16 ob-
The vinylgold(I) species 10 or 11 with catalytic
amounts of Pd
isomerisation/cross-coupling products 14 or 15 but only a 12% yield was obtained, which at least
(Scheme 6). An X-ray crystal structure analysis of 14 meant more than two turnovers.
ACHTUNGTRENNUNG(dppf)Cl2 at 508C delivered the cyclo- the reaction mixture the product could be detected,
ACHTUNGTRENNUNG
clearly showed that the double bond at the annelation
In control experiments without either the palladium
of the two five-membered rings is highly strained or the gold catalyst, no conversion was observed. This
(Figure 2).[12] The double bond is twisted by 198, a at the same time indicates that silver(I) under these
pyramidalisation at the carbon atoms of the olefin is conditions cannot substitute for gold or palladium.
not observed (sum of the bond angles at these carbon
atoms: 357.58). No crystal structure of 15 could be ob- these reactions 1 equiv. 8, 1.1 equiv. AgOTf, 5 equiv
tained but computational chemistry (Figure 3) did H2O, 5 mol% of the palladium catalyst PdCl2A(dppf)
Then we investigated different factors, in all of
CHTUNGTRENNUNG
show that the product is much less strained, there is and 2.5 mol% of the gold catalyst Ph3PAuCl were
no twisting of the olefin, no pyramidalisation (sum of used.
the bond angles at the carbon atoms: 359.88), but the
olefin is not in full conjugation to the arene any more While with methanol (entry 1) the yield of 14 was the
(rotated by 48.18). best, the reaction mixtures quickly showed a metal
Next we investigated the reaction catalytic in both precipitate. Acetonitrile (entry 2) gave no 14, only
metals. Initially we tried 5 mol% PdCl2A(dppf), some proto-deauration product 12 and the conversion
For the solvent, the results are shown in Table 1.
CTHUNGTRENNUNG
5 mol% Ph3PAuCl, 5 equiv. H2O, THF as solvent and of 8 was low. In DMF (entry 3) the conversion was
1 equiv. AgOTf for removing the iodide and thus pre- significantly higher, but still not complete and the
venting the gold(I) complex from being deactivated yield of 14 was only 10%. In DCM (entry 4), THF
by the iodide produced in the cross-coupling step. In (entry 5) and toluene (entry 6) full conversion of the
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On Homogeneous Gold/Palladium Catalytic Systems
Table 1. Influence of the solvent on the catalytic gold/palla-
cient for the formation of 14 (Table 2, entry 2), deliv-
ering a yield of 52% (TON of 10 with respect to pal-
dium system (2.5 mol% Ph3PAuCl/2.5 mol% PdCl
2ACHTUNGTRNE(NUNG dppf)/
1.1 equiv. AgOTf).
ladium). With PdACHTNUTRGNE(NUG dppf)Cl2 only 11% of 14 and signifi-
cantly more 12 were obtained (entry 1). Catalyst 16[14]
also gave a good yield of 14, 45% of the proto-deau-
ration product was isolated, here oligomerisation/
polymerisation was a minor pathway.
Entry Solvent Conversion of 8 Yield of 14 Yield of 12
1
2
3
4
5
6
MeOH 100%
MeCN 33%
22%
0%
10%
16%
16%
14%
22%
6%
34%
36%
33%
25%
DMF
DCM
THF
79%
100%
100%
Finally, screening different gold catalysts revealed a
low dependency on the gold catalyst (Table 3, en-
tries 1–6). In all these cases a full conversion of the
substrate was detected, 14 was obtained in 39–45%
yield, proto-deauration was a minor side-reaction.
So far, one could have considered the reaction to
toluene 100%
substrate was observed and quite similar yields of 14 be catalysed by both gold and palladium. But the cru-
could be obtained. In these entries the proto-deaura- cial control experiment using 8 without gold [with
tion to 12 was between 25% and 36%. The major re- only palladium(0) and silver(I)] gave 14 in 38-44%
action was the formation of oligomeric/polymeric ma- yield. The difference to the control experiment men-
terial. For the further reactions we chose DCM, as in tioned above is the use of a palladium(0) catalyst
this solvent the most selective conversion and no pre- rather than a palladium(II) catalyst. We repeated the
cipitate of metal were observed.
experiment three times (entry 7) in different equip-
The next step was a screening of different palladi- ment to exclude impurities. We also investigated the
um catalysts. In this combination with Ph3PAuCl/ purity of the palladium catalyst, ICP indicated that
1.1 equiv. AgOTf the PdACHTUGNTRENNNUG
is true for the palladium catalyst alone (entry 9).
Basing on these findings, it is most probable that
with palladium(0) alone after an initial oxidative addi-
tion the silver is needed to abstract a halide from the
palladium(II) centre. Then the cationic, coordinatively
unsaturated species cyclises the allenic ester in an in-
Table 2. Influence of the palladium catalyst on the catalytic
gold/palladium system (using 2.5 mol% Ph3PAuCl/2.5 mol%
palladium catalyst/1.1 equiv. AgOTf).
Entry Catalyst
Conver- Yield Yield
sion
of 14 of 12
of 8
ꢀ
tramolecular reaction and ultimately forms the C C
bond by reductive elimination.[15] The failure of the
1
2
Pd
Pd
N
100%
100%
16% 36%
52% 10%
palladium(II) catalyst PdACHTNUGRTENUNG(dppf)Cl2 in the absence of
gold can be explained by the need of reduction of the
palladium(II) which is induced by the vinylgold com-
pound forming the bisACTHUNGTRENNG(U vinyl)palladium(II) compound
by transmetallation and subsequent reductive elimina-
tion.[8] The failure of palladium(0) alone can be ex-
plained by the coordinatively saturated neutral palla-
dium(II) species formed after oxidative addition not
being electrophilic enough to induce the cyclisation of
the allene part, while the cationic palladium(II) spe-
3
100%
45% 45%
Table 3. Influence of the gold catalyst on the catalytic gold/palladium system [using 2.5 mol% gold catalyst/2.5 mol% Pd-
ACHTUNGTRENNUNG(PPh3)4/1.1 equiv. AgOTf].
Entry
Catalyst
Conversion of 8
Yield of 14
Yield of 12
1
2
3
4
5
6
7
8
9
Ph3PAuCl
AHCTUNGRTENN(GUN PhO)3PAuCl
100%
100%
100%
100%
100%
100%
100%
18%
52%
39%
41%
39%
43%
40%
38–44%
1%
10%
13%
8%
9%
6%
11%
7%
15%
0%
XPhosAuCl
IPr-AuCl
NCAC-AuCl
t-BuNC-AuCl
without Au
only AgOTf
only Pd
N
50%
0%
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A. Stephen K. Hashmi et al.
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cies formed in the presence of the silver salt can
induce the cyclisation.
The first experiment was the use of Asaoꢄs condi-
tions (7.5 mol% Ph3PAuCl, 7.5 mol% AgOTf, ben-
With either palladium or gold catalysts 68% of sub- zene, room temperature),[17b] product 17a was ob-
strate 9 was converted, but only 13% of the cyclisa- tained selectively, but only 30% yield and 50% con-
tion/proto-deauration product 12 was obtained, 15 version were reached (Scheme 7). There was no evi-
could not be detected. With the palladium(0) catalyst dence in the GC-MS of the crude material for the al-
substrate 9 also gave no product 15. This failure can lylation product 7a. Asao had used alcohols as
be explained by a geometrically quite unfavourable nucleophiles, his focus was the allylation of the nucle-
ꢀ
interaction of the arylpalladium(II) with the allene, ophile and not C C bond formation by allyl transfer.
not facilitating ring closure.
Blumꢄs conditions (7.5 mol% Ph3PAuCl, 7.5 mol%
AgOTf, 7.5 mol% Pd2dba3, DCM, room temperature)
of “catalysed catalysis” indeed delivered an excellent
98% of the 6-endo-dig cyclization product 7a
(Table 4, entry 1; column 6a). And our experiments
Allylic o-Alkynylbenzoates
The use of these allylic esters in gold catalysis is not with
without precedence. Even with non-allylic esters the Pd2dba3 alone gave no conversion (Table 4, entry 3;
reaction is known to be catalysed by different transi- column 6a), completely confirming Blumꢄs results.
tion metals, usually a perfect 6-endo-dig selectivity is
But switching to another oxidation state of the pal-
ladium pre-catalyst, using Maꢄs conditions (10 mol%
observed,[16] this includes gold-catalysed versions.[17]
The allylic esters were known to give products of a PdCl2, DMA, 508C) with PdCl2 as catalyst also deliv-
[18]
ꢀ
C C bond formation, too. Again, highly related re- ered 7a in 37% yield, no gold catalyst was needed in
actions have been described before by Ma et al., this case (Table 4, entry 2; column 6a)!
Toste et al. and Fꢀrstner et al.[19] Only an efficient
In order to test whether Pd(II) allyl complexes
ꢀ
gold-catalysed C C bond forming cyclisation/allyla- could also initiate the cyclisation, we investigated the
tion was unknown.
reaction of 6a with a Pd2dba3/allyl tosylate mixture.
The test substrate 6a is identical to the one which But no conversion was observed, even when heating
was also used by Blum et al.[9]
to 508C overnight (Table 4, entry 4; column 6a).
Scheme 7. Reaction of 6a under Asaoꢄs conditions.
Table 4. Catalytic conversions of the o-alkynylbenzoate esters.
Entry Conditions
Yields of products obtained from
Substrate 6a
Substrate 18a
Substrate 18b
Substrate 18c
1
2
3
4
5
6
7
7.5 mol% Ph3PAuCl, 7.5 mol% AgOTf,
7.5 mol% Pd2dba3, DCM, r.t.
10 mol% PdCl2, DMA, 508C
0% 6a, <2%
17a, 98% 7a
34% 6a, 0%
17a, 37% 7a
100% 6a, 0%
17a, 0% 7a
100% 6a, 0%
17a, 0% 7a
70% 6a, 0%
17a, 30% 7a
100% 6a, 0%
17a, 0% 7a
0% 18a, 46%
17a, 0% 19a
0% 18a, 100%
17a, 0% 19a
0% 18b, 16%
17a, 22% 19b
100% 18b, 0%
17a, 0% 19b
0% 18c, 17%
17a, 83% 19c
100% 18c, 0%
17a, 0% 19b
Pd2dba3, allyl tosylate, DMA, r.t.
Pd2dba3, allyl tosylate, DMA, 508C
7.5 mol% Ph3PAuCl, 7.5 mol% AgOTf,
benzene, r.t.
7.5 mol% Ph3PAuCl, 7.5 mol% AgOTf,
DCM, r.t.
0% 18a, 100%
17a, 0% 19a
75% 18a, 25%
17a, 0% 19a
0% 18b, 26%
17a, 64% 19b
0% 18b, 26%
17a, 70% 19b
0% 18c, 19%
17a, 81% 19c
0% 18c, 25%
17a, 75% 19c
100% 18c, 0%
17a, 0% 19c
10 mol% AgOTf, benzene, r.t.
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On Homogeneous Gold/Palladium Catalytic Systems
ꢀ
Scheme 8. Cyclisation/C C bond formation with different substrates 6.
Scheme 9. Products 21 and 22 are obtained from 20.
In the context of bimetallic catalysis, it is of crucial (entries 1, 2, 5 and 6; column 18a). Different amounts
importance to verify the purity of the gold, silver and of the cyclisation product 17a were obtained.
palladium complexes used. By ICP analysis we
For the benzyl ester 18b the Au(I)/Pd2dba3 condi-
checked the authentic catalyst samples, no significant tions delivered some product (entry 1; column 18b),
amounts of gold were found in palladium, the same is PdCl2 alone failed (entry 2; column 18b), but most
true for palladium in gold and palladium in silver. successful were the conditions with the silver-activat-
Both values were at sub-ppm levels, only PdCl2 con- ed gold catalyst only (entries 5, 6; column 18b). This
tained 8 ppm of gold – when the ten-fold amount of means that in the case of substrate 18b the palladium-
gold was added externally, no increase of rate or yield free conditions were more successful than the “bimet-
was observed in the reaction mentioned above, using allic” catalysis, raising some questions about the bi-
Maꢄs conditions. Since the synthesis of substrate 6a in- metallic character of the catalysis reactions. This is a
cluded a palladium-catalyzed Sonogashira coupling clear confirmation of Asaoꢄs conditions reported for
(two steps and three purifications before the catalytic other substrates previously.[17b]
experiments with 6a), the content of palladium in the
Thus the next substrate 18c, combining a benzylic
substrate was also investigated. Palladium levels of and an allylic system, was interesting. Again a quite
less than 2 ppm were detected. It is interesting to similar behaviour was observed, a good yield with the
note that after the Sonogashira coupling and only one Au(I)/Pd2dba3 catalyst (entry 1; column 18c), failure
column chromatography on silica gel the substrate of PdCl2 alone (entry 2; column 18c), and yields
still contains about 500 ppm palladium![20] It is impor- better than for 18b with the silver-activated gold cata-
tant to verify the scope of a method. Therefore, we lyst only (entries 5, 6; column 18c). A final control ex-
first prepared three more substrates, the propargyl periment with silver triflate proved that the silver salt
ester 18a, the benzyl ester 18b and the cinnamyl ester alone lacks catalytic activity (entry 7; column 18c).
18c (Scheme 8). The substrates contained 2 ppm of
palladium, only 18c contained 6 ppm palladium.
This success of the cationic gold(I) catalyst encour-
aged us to test it with a range of other substrates, too.
The results of the catalytic conversions are also Before that, we first wanted to optimise the reaction
listed in Table 4. Again always the 6-endo-dig cyclisa- conditions. This screening started with an investiga-
tion products were formed. This could easily be as- tion of a series of different catalysts. Since the prod-
signed by the comparison with the known spectro- ucts with the 4-methoxyphenyl substituent which were
scopic data of the related compounds of Asao[17b] or obtained from 6a and 18a–c are not volatile enough
Blum.[9] The propargylic ester 18a did not deliver for an analysis by gas chromatography, we switched to
product 19a under the different conditions applied substrate 20 with a butyl substituent (Scheme 9). The
results are shown in Table 5. In comparison to the
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A. Stephen K. Hashmi et al.
FULL PAPERS
Table 5. Screening of different catalysts for the conversion of 20.[a]
Entry
1
Gold pre-catalyst
Ph3PAuCl
Conversion after 3 h (after 16 h)[b]
100%
GC yield of the products 21 and 22 after 16 h[b]
21 (33%)+22 (63%)
2
100%
21 (48%)+22 (38%)
3
100%
21 (46%)+22 (32%)
4
5
100%
100%
21 (54%)+22 (38%)
21 (50%)+22 (30%)
6
7
8
9
IPr-AuCl
100%
100%
21 (42%)+22 (57%)
21 (17%)+22 (83%)
21 (32%)+22 (7%)
n-PentNC-AuCl
[c]
–
<15% (ꢁ40%)
TsOH[d]
<20%
–
[e]
[a]
200-mmol scale, 7.5 mol% of pre-catalyst, 7.5 mol% AgOTf, room temperature, 16 h, 2 mL solvent.
Determined by GC-MS and corrected by the response factors, 200 mmol dodecane was used as internal standard.
Only AgOTf.
No AgOTf was added.
[b]
[c]
[d]
[e]
Traces of both products detectable by GC-MS.
Table 6. Screening of different counter ions for the gold(I) catalysed conversion of 20.[a]
Entry Silver salt used for the activation of the gold(I) chloride pre- Conversion after
GC yield of 21 and 22 after
catalyst
16 h[b]
16 h[b]
1
2
3
4
5
6
7
8
9
chloride
acetate
trifluoroacetate
tosylate
<5%
<5%
<10%
<10%
ꢁ25%
100%
100%
100%
100%
n.d.
n.d.
n.d.
n.d.
binolphosphate
triflaꢀte
21 (5%)+22 (20%)
21 (24%)+22 (75%)
21 (12%)+22 (87%)
21 (22%)+22 (77%)
21 (30%)+22 (69%)
NTf2
ꢀ
PF6
ꢀ
SbF6
[a]
[b]
200-mmol scale, 7.5 mol% n-PentNC-AuCl, 7.5 mol% silver salt, room temperature, 16 h, 2 mL solvent.
Determined by GC-MS and corrected by the response factors, 200 mmol dodecane were used as internal standard.
Ph3PAu+ catalyst (entry 1), the gold(I) complexes gands (entries 5 and 6) gave inferior yields of 12.
with an acyclic carbene ligand (entry 2), biaryl ligand Most remarkably, the pentyl isonitrile ligand deliv-
(entry 3), phosphite ligand (entry 4) and two NHC li- ered the best yield (entry 7). Again, the control ex-
140
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On Homogeneous Gold/Palladium Catalytic Systems
Table 7. Screening of different solvents for the gold(I) cata-
lysed conversion of 20.[a]
Entry Solvent[b] Conversion
after 16 h[c]
GC yield of 21 and 22
after 16 h[c]
1
2
3
4
5
6
7
8
9
toluene 100%
benzene 100%
21 (41%)+22 (57%)
21 (25%)+22 (74%)
21 (35%)+22 (64%)
21 (47%)+22 (52%)
21 (40%)+22 (60%)
n.d.
21 (9%)+22 (26%)
n.d.
21 (25%)+22 (74%)
DCM
THF
Et2O
DMA
100%
100%
100%
<20%
CH3CN ꢁ35%
pyridine <10%
dioxane 100%
[a]
200-mmol scale, 7.5 mol% n-PentNC-AuCl, 7.5 mol%
AgOTf, room temperature, 16 h, 2 mL solvent.
Absolute solvents were used.
Determined by GC-MS and corrected by the response
factors, 200 mmol dodecane were used as internal stan-
dard.
[b]
[c]
periment with the silver salt gave no satisfactory yield
of the product 20 (entry 8). With p-TsOH a slow de-
composition of the substrate was observed, only
traces of the products 21 and 22 could be detected
(entry 9).
The next screening concerned the counter ion of
the cationic gold(I) catalyst derived from n-PentNC-
AuCl (Table 6). The strongly coordinating anions
chloride (entry 1), acetate (entry 2), trifluoroacetate
(entry 3) and tosylate (entry 4) gave conversions
under 10%. Slightly more promising was binolphos-
phate (entry 5), but full conversions wꢀere obtained
Scheme 10. First crossover experiment with 23a and 23b.
only with triflate (entry 6), NTf2
(entry 7),
hexafluoro
G
In order to gain some mechanistic insight, under
nate (entry 9). The best yield of 22 was achieved with the conditions of the gold catalysis, crossover experi-
AgNTf2, but with some substrates used later (Table 8) ments with the substrates 23a and 23b were conduct-
AgOTf gave better results, thus the latter was used in ed (Scheme 10). As expected, besides 24 (33% by
ꢀ
the subsequent experiments shown here.
GC) and 21 (20% by GC) also the products of a C C
Finally, different solvents were investigated bond formation [25 (not detectable by GC) and 26
(Table 7). Low conversions were only observed with (30% by GC)] as well as the crossover products 27
the coordinating solvents DMA, acetonitrile and pyri- (7% by GC) and 28 (2% by GC) could be detected
dine (entries 6–8). In all other solvents complete con- by GC/MS analysis of the reaction mixture. Due to
versions of the substrate 20 were detected (entries 1–5 the different electronic properties of the substituents
and 8), the best yields of 22 we obtained from ben- at the alkyne and quite different response factors in
zene and dioxane.
the detector, the quantitative interpretation of the
The optimised conditions used in the next reactions data is difficult, but qualitatively the crossover prod-
were 5 mol% n-PentNC-AuCl, 5 mol% AgOTf in di- ucts prove an intermolecular exchange of the migrating
oxane at room temperature for 16 h. Still several reac- groups.
tions were finished within minutes. In the screening
Thus we switched to the substrates 23c and 23d,
described above, the reactions were all conducted which bear electronically quite similar substituents on
under an atmosphere of dinitrogen. While investigat- the alkyne and quite similar migrating groups
ing a range of other substrates (see below, Table 8), (Scheme 11). Again in addition to 24 (22% by GC),
experiments showed that this is not necessary. Identi- 28 (23% by GC), 27 (22% by GC) and 29 (22% by
cal yields were obtained without a protective atmos- GC) a clear crossover to 30 (7% by GC) and 31 (4%
phere.
by GC) could be detected, indicating an intermolecu-
Adv. Synth. Catal. 2012, 354, 133 – 147
ꢃ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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141

A. Stephen K. Hashmi et al.
FULL PAPERS
Table 8. Conversion of the substrates 23e–n under the optimised conditions.[a]
Entry
Starting Material
Product
Yield[b]
93%
1
23e
23f
32
31
2
64%
3
4
23g
23h
26
33
70%
30%
5
23i
25
98%
6
7
23j
27
34
80%
88%
23k
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On Homogeneous Gold/Palladium Catalytic Systems
Table 8. (Continued)
Entry
8
Starting Material
Product
Yield[b]
20%
23l
35
9
23m
23n
36
37
7%
10
16%
[a]
All reactions were conducted in dioxane at room temperature for 16 h using 5 mol% n-PentylNC-AuCl as pre-catalyst
and 5 mol% AgOTf as activator.
Amount of product isolated.
[b]
lar migration of the groups. But still, the GC detector
had quite different response factors.[21]
Finally, a number of different substrates was tested
under the optimised conditions (Table 8). While most
yields are good, the furfuryl ester 23h did not convert
well, only 30% of 33 were obtained (entry 4). The
same is true for 23l (entry 8). Aryl and alkyl groups
on the alkyne as well as benzyl and cinnamyl groups
on the esters give satisfactory results (entries 1–3, 5,
6). A cyclopropyl group on the alkyne is also tolerat-
ed, neither in the alkynylcyclopropane substructure of
the substrate nor in the vinylcyclopropane substucture
of the product is a ring-opening of the activated prop-
ꢀ
argylic or allylic C C bonds of the monosubstituted
cyclopropane observed (entry 7). This indicates that
the low yield obtained for 35 is caused by the furfuryl
group. Terminal alkynes give very low yields, remark-
able is the change of regioselectivity in this case (en-
tries 9 and 10). Now instead of the usual 6-endo-dig a
5-exo-dig cyclisation is observed.
Conclusions
The sequences 8!10!14 and 9!11!15 show the
feasibility of a pathway catalytic in gold and palladi-
um. On the other hand palladium(0) alone can also
catalyse the same reaction for the sequence 8!14,
which shows how important control experiments and
control of the purity of the metals are in this field.
Different palladium catalysts or intermediates of the Scheme 11. Second crossover experiment with 23c and 23d.
Adv. Synth. Catal. 2012, 354, 133 – 147
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143

A. Stephen K. Hashmi et al.
1277, 1228, 1200, 1110, 1090, 1048, 993, 763, 744 cmꢀ1
FULL PAPERS
;
palladium cycle might be active for the part of the re-
action which is assumed to be catalysed by gold.
While our experiments for the transfer of the un-
substituted allyl group in the allylic o-alkynylben-
zoates confirm the necessity of a gold(I)/palladium(0)
co-catalysis reported by Blum et al., our results also
confirm the finding of Ma et al. of a palladium(II)-
catalysed conversion of the same substrates in the ab-
sence of any gold catalyst. But lower yields are ob-
tained with the palladium(II) catalysts. On the other
hand, allylic esters with stabilising substituents on the
allyl group and benzyl esters readily were converted
to the same product type with gold(I) catalysts only.
Gold(I) isonitrile complexes are simple and very effi-
cient catalysts for these conversions. Thus the gold/
palladium catalysis is of limited scope, the palladium
is only needed for certain substrates. The crossover
experiments show an intermolecular allyl transfer.
Comparing the different outcomes for the two dif-
ferent substrate types, allenoates and o-alkynylben-
zoates, the assumption that the corresponding vinyl-
gold intermediates show a significant difference in the
electronic structure, is confirmed. The intermediate F
derived from the o-alkynylbenzoates with an oxy sub-
stituent is electron-rich and in an intermolecular
manner can be attacked by the activated allylic
system in intermediate E directly. Thus the reaction
also proceeds in the absence of a palladium catalyst
with a gold catalyst only. The intermediate F generat-
ed from the allenoates with the carbonyl substituent
is electron-deficient and thus the intermediate F
cannot attack there. Then a transmetallation to palla-
dium is necessary.
1H NMR (300 MHz, C6D6): d=2.37 (s, 3H, CH3), 3.08 (dd,
J=14.1, 8.3 Hz, 1H, CH2), 3.52 (dd, J=14.2, 4.8 Hz, 1H,
CH2), 5.35 (m, 1H, CH), 6.36 (m, 1H, ArH), 6.80 (m, 1H,
ArH), 6.96 (m, 9H, ArH), 7.31 (m, 7H, ArH), 7.53 (dd, J=
7.9, 1.8 Hz, 1H, ArH); 13C NMR (75 MHz, C6D6): d=15.53
(q), 47.29 (t), 89.59 [d, J=6.7 Hz, (d)], 102.19 (s), 129.29 [d,
J=10.8 Hz, (d)[, 130.73 [d, J=52.7 Hz, (s)], 131.77 (d),
132.72 (d), 133.70 (s), 134.86 [d, J=14.1 Hz, (d)], 139.57 (d),
142.26 (d), 175.69 (s), 198.37 [d, J=114.5 Hz, (s)], no further
signals observed; 31P NMR (101 MHz, C6D6): d=45.29.
Synthesis of gold complex (11): The synthesis was accom-
plished according to the procedure described by Hammond
et al.[2] Under an atmosphere of nitrogen
9 (150mg,
420 mmol) was dissolved in absolute DCM (6mL). Ph3PAuCl
(189mg, 380 mmol) and AgOTf (98mg, 380 mmol) were
added consecutively. The mixture was stirred for 2h under
exclusion of light at room temperature. During this period
the initially white precipitate turned dark violet. Water
(2mL) was added and stirring was continued for 15min.
After this, the mixture was extracted with DCM (3ꢅ15mL),
the organic layer was dried over MgSO4 and the solvent was
removed under reduced pressure at ambient temperature.
The solid residue was purified by column chromatography
(SiO2, PE:ethyl acetate/10:1!1:1) to yield the title com-
pound as a colourless solid; yield: 189 mg (248 mmol, 57%);
˜
Rf (PE:ethyl acetate/1:1)=0.43. IR (benzene): n=3060,
3029, 3010, 2985, 2926, 1738, 1482, 1435, 1374, 1281, 1240,
1101, 1048, 1028, 1009, 996, 748, 712, 695 cmꢀ1 1H NMR
;
(500 MHz, C6D6): d=2.13 (m, 1H, CH2), 2.38 (m, 4H, CH2,
CH3), 3.02 (m, 2H, CH2), 5.14 (m, 1H, CH), 6.43 (td, J=
7.6, 1.8 Hz, 1H, ArH), 6.84 (td, J=7.5, 1.5 Hz, 1H, ArH),
6.92 (dd, J=7.7, 1.9 Hz, 1H, ArH), 6.98 (m, 9H, ArH), 7.36
(m, 6H, ArH), 7.58 (dd, J=7.9, 1.0 Hz, 1H, ArH);
13C NMR (125 MHz, C6D6, P-decoupled): d=15.49 (q),
36.18 (t), 37.06 (t), 88.94 (d), 101.16 (s), 128.68 (d), 128.95
(d), 129.76 (d), 130.91 (d), 130.97 (s), 131.86 (d), 133.51 (s),
134.81 (d), 139.84 (d), 145.67 (s), 176.21 (s), 198.90 (s);
31P NMR (101 MHz, C6D6): d=45.46; HR-MS (FAB+):
m/z=787.0524, calcd. for C31H27O2I [M+H]+: 787.0537.
Synthesis of 5-(2-iodobenzyl)-3-methylfuran-2(5H)-one
(12) and 5-(2-iodophenethyl)-3-methylfuran-2(5H)-one (13):
Under an atmosphere of nitrogen compound 8 (65mg,
190 mmol) or 9 (68mg, 190 mmol) was dissolved in absolute
toluene (3mL). Ph3PAuCl (9.5mg, 19 mmol), AgOTf (4.9mg,
19 mmol) and p-toluenesulfonic acid (6.5mg, 38 mmol) were
added and the mixture was heated to 808C for 2 d. After
this the volatiles were removed and crude products were pu-
rified by column chromatography (SiO2, PE:ethyl acetate/
4:1) to yield the title compounds as colourless oils.
Further investigations will address the nature of the
allyl transfer step in more detail, including the elec-
tronic influence of substituents.
Experimental Section
Reactions of Allenoates
Synthesis of gold complex (10): The synthesis was accom-
plished according to the procedure described by Hammond
et al.[2] Under an atmosphere of nitrogen
8 (279mg,
815 mmol) was dissolved in absolute DCM (6mL). Ph3PAuCl
(366mg, 740 mmol) and AgOTf (190mg, 740 mmol) were
added consecutively. The mixture was stirred for 2h under
exclusion of light at room temperature. During this period
the initially white precipitate turned dark violet. Water
(4mL) was added and stirring was continued for 15min.
After this, the mixture was extracted with DCM (3ꢅ30mL),
the organic layer was dried over MgSO4 and the solvent was
removed under reduced pressure at ambient temperature.
The solid residue was purified by column chromatography
(SiO2, PE:ethyl acetate/20:1!1:1) to yield the title com-
pound as a colourless solid; yield: 390 mg (505 mmol, 68%);
12; yield: 28 mg (84 mmol, 44%); Rf (PE:EA 4:1)=0.32.
˜
IR (neat): n=3059, 2924, 1759, 1468, 1436, 1095, 1057,
758 cmꢀ1 1H NMR (300 MHz, CDCl3): d=1.90 (t, J=
;
1.8 Hz, 3H, -CH3), 3.05–3.22 (m, 2H, -CH2-), 5.09–5.19 (m,
1H, -OCH-), 6.91–7.01 (m, 1H), 7.07–7.12 (m, 1H), 7.27–
7.36 (m, 2H), 7.82–7.87 (m, 1H); 13C NMR (75 MHz,
CDCl3): d=10.62 (q), 44.38 (t), 80.01 (d), 100.74 (s), 128.59
(d), 129.01 (d), 130.50 (s), 130.98 (d), 138.27 (s), 139.68 (d),
147.67 (d), 173.77 (s); MS (EI+, 70 eV): m/z (%)=314 (22)
[M]+, 217 (100) [C7H6I]+, 90 (16) [C7H6]+; HR-MS (EI+): m/
z=313.9805, calcd. for C12H11IO2: 313.9804.
˜
Rf (PE:ethyl acetate/1:1)=0.34. IR (benzene): n=3015,
2936, 2884, 2873, 1739, 1593, 1567, 1493, 1429, 1403, 1359,
144
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On Homogeneous Gold/Palladium Catalytic Systems
13; yield: 27 mg (80 mmol, 42%); Rf (PE:EA 4:1)=0.30.
3.86 (s, 3H), 6.40 (dd, 3JH,H =16.1 Hz, 4JH,H =1.5 Hz, 1H),
3 3 3
˜
IR (film): n=2925, 1761, 1659, 1562, 1466, 1436, 1343, 1206,
6.52 (dt, JH,H =16.1 Hz, JH,H =4.7 Hz, 1H), 6.96 (d, JH,H =
1169, 1098, 1058, 1011, 975, 922, 860, 754, 648, 611, 553,
8.9 Hz, 2H), 7.20–7.36 (m, 5H), 7.52 (td, 3JH,H =7.6 Hz,
1
3
439 cmꢀ1; H NMR (300 MHz, C6D6): d=1.34 (m, 1H, CH2),
4JH,H =1.1 Hz, 1H), 7.60–7.66 (m, 3H), 7.73 (td, JH,H
=
=
4
1.58 (t, J=1.8 Hz, 3H, CH3), 1.58 (m, 1H, CH2), 4.21 (ddm,
J=8.2, 4.4, 1.9 Hz, 1H, CH), 5.95 (m, J=1.7 Hz, 1H, CH-
olefin), 6.49 (td, J=7.6, 1.9 Hz, 1H, ArH), 6.81 (dd, J=7.7,
1.9 Hz, 1H, ArH), 6.9 (td, J=7.1, 1.4 Hz, 1H, ArH), 7.63
(dd; J=7.9, 1.1 Hz, 1H, ArH); 13C NMR (75 MHz, C6D6):
d=10.96 (q), 34.18 (t), 36.81 (t), 79.65 (d), 100.97 (s), 128.64
(d), 128.97 (d), 130.38 (s), 130.45 (d), 140.2 (d), 144.01 (s),
147.94 (d), 173.52 (s); HR-MS (FAB+): m/z=329.0027,
calcd. for C13H14IO2 [M+H]+: 329.0038.
7.6 Hz, 4JH,H =1.3 Hz, 1H), 8.39 (dd, 3JH,H =7.9 Hz, JH,H
1.3 Hz, 1H); 13C NMR (CDCl3, 75 MHz): d=30.8 (t), 55.3
(q), 110.1 (s), 113.7 (d, 2C), 120.9 (s), 124.1 (d), 125.4 (s),
126.1 (d, 2C), 127.5 (d), 127.6 (d), 127.7 (d), 128.6 (d, 2C),
129.8 (d), 130.2 (d, 2C), 131.8 (d), 134.8 (d), 137.0 (s), 138.2
(s), 152.6 (s), 160.6 (s), 162.5 (s); HR-MS [ESI (+)]: m/z=
369.14827, calcd. for C25H21O3: 369.14852.
Synthesis of 4-benzyl-3-butyl-1H-isochromen-1-one: Ac-
cording to the general procedure, n-pentylNC-AuCl
(16.5 mg, 50.0 mmol, 5 mol%) was stirred with AgOTf
(12.8 mg, 50.0 mmol, 5 moll%) in dioxane. After addition of
the substrate 23g (292 mg, 1.00 mmol) the mixture was
stirred overnight. Purification on silica gel (petroleum ether/
ethyl acetate 100:1) afforded clean product 26 as a yellow
oil; yield: 205 mg (700 mmol, 70%); Rf (petroleum ether/
Synthesis
b]furan-2-one (14) and 1-methyl-4,5-dihydronaphtho
b]furan-2(3aH)-one (15): Under an atmosphere of nitrogen
compound 10 (147mg, 190 mmol) or 11 (150mg, 190 mmol)
was dissolved in absolute CH3CN (0.9mL). [PdCl2ACHTUNTGREG(NNUN dppf)]
of
3-methyl-8,8a-dihydro-2H-indenoACHUTNGTRENNUNG
AHCTUNGTRENNUNG
ACHTUNGTRENNUNG
(1mL, 1 mol%, 2.10ꢀ3 M in absolute CH3CN) was added and
the mixture stirred at 508C for 12h. After this, the precipi-
tate (Ph3PAuI) was filtered off, the solvent was removed and
the crude products were purified by column chromatogra-
phy (basic alumina, PE:ethyl acetate/3:1!1:1).
˜
ethyl acetate 2:1)=0.70. IR (film): n=2958, 2929, 2871,
1730, 1643, 1604, 1486, 1454, 1318, 1290, 1243, 1180, 1103,
1088, 1049, 1031, 768, 737, 710, 693 cmꢀ1
;
1H NMR
(300 MHz, CDCl3): d=0.93 (m, 3H), 1.40 (m, 2H), 1.64–
In the case of compound 14, we observed partial isomeri-
sation of the double bond using SiO2 as stationary phase.
All spectroscopic data are in good agreement with previous-
ly reported values.[a] 14; yield: 31mg (169 mmol, 89%).
1H NMR (250 MHz, CDCl3): d=2.05 (d, J=2.1 Hz, 3H,
CH3), 2.78 (dd, J=14.7, 7.4 Hz, 1H, CH2), 3.39 (dd, J=14.7,
7.5 Hz, 1H, CH2), 5.36 (tq, J=7.5, 2.1 Hz, 1H, CH), 7.38
(m, 3H, ArH), 7.58 (m, 1H, ArH).
1.74 (m, 2H), 2.50–2.67 (m, 2H), 4.04 (s, 2H), 7.16–7.62 (m,
3
4
8H), 8.31 (dd, JH,H =7.9 Hz, JH,H =1.0 Hz, 1H); 13C NMR
(75 MHz, CDCl3): d=13.8 (q), 22.5 (t), 29.9 (t), 30.9 (t),
31.9 (t), 102.8 (s), 109.9 (s), 123.4 (d), 125.0 (s), 126.5 (d),
127.2 (d), 127.7 (d, 2C), 128.7 (d, 2C), 129.7 (d), 134.6 (d),
138.0 (s), 138.6 (s), 156.1 (s); MS-EI (+): m/z (%)=292
(100) [M]+, 208 (21), 207 (61), 202 (29), 179 (11), 178 (31),
160 (15), 131 (13), 118 (53), 91 (57), 89 (13); HR-MS [EI
(+), 70 eV]: m/z=292.1450, calcd. for C20H20O2: 292.1463.
15; yield: 30mg (152 mmol, 80%). 1H NMR (300 MHz,
CD2Cl2): d=1.66 (m, 1H, CH2), 2.04 (d, J=1.9 Hz, 3H,
CH3), 2.51 (m, 1H, CH2), 3.00 (m, 2H, CH2), 7.24 (m, 3H,
ArH), 7.59 (dd, J=6.9, 2.4 Hz, 1H, ArH).
Acknowledgements
Reactions of Allylic o-Alkynylbenzoates
This work was supported by the Chinesisch-Deutsches Zen-
trum (GZ 419 (362/3)) and the Deutsche Forschungsgemein-
schaft (HA 1932/11-1); we thank Umicore AG & Co. KG for
the generous donation of noble metal salts; C.L. is thankful
for financial support by the Studienstiftung des dt. Volkes e.V.
General procedure for catalytic conversion of substrates: In
the specified solvent 5 mol% of the gold pre-catalyst was ac-
tivated with 5 mol% of the specified silver salt. After stir-
ring for 10 min at room temperature the substrate was
added and stirring was continued until monitoring by TLC
or GC-MS indicated complete conversion. The solvent was
removed under reduced pressure and the residue was ad- References
sorbed on celiteꢆ. Depending on the substrate and the item-
ised conditions, purification by column chromatography on
silica gel afforded the product in combination with smaller
amounts of the “cyclisation-only” byproduct.
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mann-Rçder, Org. Biomol. Chem. 2005, 3, 387–391;
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119, 3478–3519, Angew. Chem. Int. Ed. 2007, 46, 3410–
3449; h) D. J. Gorin, B. D. Sherry, F. D. Toste, Chem.
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Synthesis of 3-(4-methoxyphenyl)-4-[(2 E)-3-phenylprop-
2-en-1-yl]-1H-isochromen-1-one: According to the general
procedure, Ph3PAuCl (7.42 mg, 15.0 mmol, 7.5 mol%) was
stirred with AgOTf (3.85 mg, 15.0 mmol, 7.5 mol%) in dry
benzene. After addition of the substrate 18c (73.7 mg,
200 mmol) the mixture was stirred overnight. Purification on
silica gel (petroleum ether/ethyl acetate 10:1) afforded clean
product 19c as a yellow oil; yield: 59.7 mg (162 mmol, 81%);
˜
Rf (petroleum ether/ethyl acetate 2:1)=0.54. IR (film): n=
3060, 3027, 2958, 2838, 3551, 2250, 1722, 1628, 1604, 1511,
1485, 1461, 1443, 1323, 1293, 1255, 1179, 1097, 1063, 1031,
969, 909, 840, 773, 743, 692 cmꢀ1
;
1H NMR (CDCl3,
300 MHz): d=3.64 (dd, 3JH,H =4.7 Hz, 4JH,H =1.5 Hz, 2H),
Adv. Synth. Catal. 2012, 354, 133 – 147
ꢃ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
asc.wiley-vch.de
145

A. Stephen K. Hashmi et al.
FULL PAPERS
[2] For a recent summary of the application in total syn-
thesis, see: A. S. K. Hashmi, M. Rudolph, Chem. Soc.
Rev. 2008, 37, 1766–1775.
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this paper. These data can be obtained free of charge
from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif (or from the Cam-
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asc.wiley-vch.de
ꢃ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Synth. Catal. 2012, 354, 133 – 147

On Homogeneous Gold/Palladium Catalytic Systems
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ꢀ
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ꢀ
and in studies on gold-catalysed C C bond formation
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ꢀ
[18] The C C bond formation was observed as a side-prod-
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ꢃ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
asc.wiley-vch.de
147