Gold-catalyzed allyl-allyl coupling

Article abstract of DOI:10.1002/anie.200704500

(Chemical Equation Presented) Gold rings: Cationic gold(I) complexes efficiently catalyze the intramolecular allyl-allyl coupling of allyl acetates with allylstannanes with excellent stereoselectivity (see scheme). This reaction is mechanistically very di

Full text of DOI:10.1002/anie.200704500

Angewandte
Chemie
DOI: 10.1002/anie.200704500
Allyl–Allyl Coupling
Gold-Catalyzed Allyl–Allyl Coupling**
Susana Porcel, Verónica López-Carrillo, Cristina García-Yebra, and Antonio M. Echavarren*
Table 1: Cyclization of 1a–d with metal catalysts.[a]
The palladium(0)-catalyzed cyclization of allylstannanes with
allyl acetates in substrates of type 1 gives the five- or six-
membered rings 2.[1] This cross-coupling reaction proceeds by
oxidative addition of the allyl acetate to Pd0 followed by
transmetalation and an allyl/allyl reductive elimination. After
a search for other metal complexes that might promote the
cyclization of substrates 1 to give 2 more efficiently and with
Entry
1
[M] (mol%)
T [8C]
t [h]
Yield [%]
(2a/2b)
better stereoselectivity, we found that cationic AuI complexes
outperform all other catalysts for this process (Scheme 1).
1
2
3
4
5
6
7
8
9
1a
1b
1c
1d
1a
1b
1c
1d
1d
1c
1d
[RhCl(PPh3)3] (10)
[RhCl(PPh3)3] (10)
[RhCl(PPh3)3] (10)
[RhCl(PPh3)3] (10)
3 (3)
3 (3)
3 (3)
3 (3)
3 (3)
4/AgSbF6 (5)
[AuCl(PPh3)]/
AgSbF6 (10)
AuCl (20)
[AuClCO] (17)
[AuCl(SMe2)] (18)
AuCl3 (18)
5 (10)
80
80
80
80
80
80
50
50
23
80
50
14
14
14
14
19
19
1.25
0.25
14
63 (73:27)
62 (81:19)
55 (58:42)
73 (87:13)
40 (56:44)[b]
47 (56:44)[b]
92 (100:0)
95 (100:0)
88 (100:0)
Scheme 1.
[c]
10
11
22
0.6
–
92 (100:0)
Whereas a variety of transformations have been developed
based on the selective activation of alkynes, allenes, and
alkenes with AuI catalysts,[2–5] the use of AuI as a catalyst to
couple two allyl fragments is unprecedented. Significantly,
although it has been suggested recently that d10 AuI might act
similarly to Pd0 in cross-coupling reactions,[6] there is no
definitive mechanistic evidence for this process.
12
13
14
15
16
1c
1c
1c
1c
1d
50
50
50
50
50
5
5
5
1
11 (100:0)
<5
[c]
–
36 (100:0)[d]
44 (100:0)
7.5
[a] The reactions with RhI were performed in DMF containing 5 equiv-
alents of LiCl and those with AuI or AgI in DCE. [b] The destannylated
products were isolated in 17–18% yield. [c] The starting material was
recovered. [d] The destannylated product was isolated in 43% yield.
We first assayed RhI complexes as catalysts for the
cyclization of 1. Thus, stereoisomers 1a–d were treated with
[RhCl(PPh3)3]as catalyst in the presence of five equivalents
of LiCl to give 2a/b in 55–73% yield (Table 1, entries 1–4). A
lower yield and stereoselectivity were obtained with 1c
(Table 1, entry 3). Similar results were obtained with
[{RhCl(CO)2}2]and PCy 2(2-biphenyl) in the presence of
[*] S. Porcel, V. López-Carrillo, Dr. C. García-Yebra,
Prof. Dr. A. M. Echavarren
Institute of Chemical Research of Catalonia (ICIQ)
Av. Països Catalans 16, 43007 Tarragona (Spain)
and
Departamento de Química Orgµnica
Universidad Autónoma de Madrid (UAM)
Cantoblanco, 28049 Madrid (Spain)
Fax: (+34)97-792-0225
E-mail: aechavarren@iciq.es
Homepage: http://www.iciq.es/english/research/grups_eng/
echavarren/entrada.htm
iPr2NH (3 equiv).[7] Lower yields were obtained with
[RhCl(CO)(PPh3)2]as the catalyst, whereas no reaction was
observed with [{Rh(cod)}2]BF4 (cod = cyclooctadiene). The
RuII complexes [CpRu(PPh3)2Cl](Cp = C5H5), [CpRu-
(PPh3)2Cl]/AgSbF6, and [RuCl2(CO)2(PPh3)2]also proved to
be unable to catalyze this cyclization.The cyclization also
takes place in the presence of the cationic gold complex 3[8] in
1,2-dichloroethane (DCE; Table 1, entries 5–9), and the
reaction is considerably faster and more stereoselective with
substrates 1c and 1d (Table 1, entries 7–9). The reaction in
the presence of less-electrophilic catalysts formed from
complex 4[8] was not effective (Table 1, entry 10), whereas
AuCl3 and the cationic AgI complex 5[4c] gave 2a in only low
yields (Table 1, entries 15 and 16, respectively). Lewis acids,
[**] We thank the MEC (projects CTQ2007-60745/BQU, Consolider
Ingenio 2010 Grant CSD2006-0003, and a predoctoral fellowship to
V.L.-C.), the UAM (predoctoral fellowship to S.P.), the CAM
(postdoctoral fellowship to C.G.-Y.), the AGAUR (2005 SGR 00993),
and the ICIQ Foundation. Dr. C. García-Yebra is a recipient of a
Ramón y Cajal contract at the Departamento de Química Inorgµn-
ica, Universidad de Zaragoza.
Supporting information for this article is available on the WWW
under http://www.angewandte.org or from the author.
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such as AlCl3 or SnCl4, failed to cyclize 1a or 1c (DCE, 808C,
tion of 11 to give cis-decalin 12 took place with total
stereoselectivity and good yield (Table 2, entry 9), and
excellent yields and stereoselectivities were also obtained
for the cyclization of 13a–c, which afforded cis-hydrindane 14
exclusively (Table 2, entries 10–12, respectively).
Cyclization of the trimethylsilyl analogue of 1e gave only
traces of 2a even under forcing conditions, whereas the
intermolecular reaction of 1,5-enyne 15 with allyltrimethylsi-
lane afforded dienyne 16 in a rare reaction in which an allyl
acetate reacts with AuI in the presence of an alkyne
(Scheme 2). Indeed, 1,5-enynes similar to 15 have been
12 h) and gave only mixtures of destannylated products.
Similar negative results were obtained with AgSbF6 or IrCl3.
In comparison with the gold-catalyzed reaction, the Pd-
catalyzed cyclization of 1c under the optimum conditions
requires larger catalyst loadings and harsher conditions
(10 mol% at 808C in DMF/H2O for 17 h) and proceeds less
stereoselectively to give a 2/1 mixture of 2a and 2b.[1a]
The reaction with other substrates proceeded satisfacto-
rily with catalyst 3 in DCE (Table 2). Allyl alcohol 1e and
carbonates 1 f and 1g also provided 2a (Table 2, entries 1–3,
respectively). Acetate 1h and methyl ether 1i afforded 2c
(Table 2, entries 4 and 5, respectively), whereas the TBS-
protected analogue was recovered unchanged. The cycliza-
Table 2: Gold-catalyzed intramolecular allyl–allyl coupling.[a]
Entry Substrate
T [8C] t [h] Product
(yield [%])
1
50
1
2a (63)[b]
2
3
1 f: Z=C(SO2Ph)2, R=CO2E
t
50
8 2a (88)
2a (95)
1g: Z=C(SO2Ph)2, R=TROC[c] 50
1
4
5
1h: Z=C(CO2Me)2, R=Ac
1i: Z=C(CO2Me)2, R=Me
80
80
0.5
3.5 6 (62; 88:12)[d]
Scheme 2.
6
80
1
shown to act as nucleophiles and to react with water or
alcohols by 5-endo hydroxy- and alkoxycyclization in the
presence of AuI to give selective activation of the alkyne.[9]
The reaction of 17a with allyltrimethylsilane and catalyst 3
proceeds under microwave irradiation to give 18 and rear-
ranged acetates 19.[3a] None of the product allylated at C-3
was observed. The same reaction catalyzed by Sc(OTf)3
(5 mol%) gave a 1:1 mixture of 18 and the C-3 allylated
isomer. Alcohol 17b also gave 18, although the yield was
lower.[10] Interestingly, when substrate 17a was heated at 808C
(microwave irradiation, 50 min) with catalyst 3 (5 mol%) in
MeOH, the rearranged acetates 19 (75:25 E/Z) were obtained
quantitatively.
7
8
50
80
0.5
1
9[g]
80
50
0.5
0.5
Significantly, in contrast to AuI, the Pd0-catalyzed reaction
of substrate 13a (10 mol% Pd0) did not provide any cycliza-
tion product and a 1:1 mixture of destannylated products was
obtained quantitatively. Substrate 13b gave 14 in only 38%
yield along with products of destannylation (1:1 mixture,
61%). The result obtained in the Pd0-catalyzed reaction of 13
is consistent with the known mechanism for this reaction,[1]
since the (h3-allyl)palladium complex 20a, which is obtained
upon oxidative addition of Pd0 to 13a, cannot undergo
intramolecular transmetalation with the allylstannane
(Scheme 3). Complex 20b, however, which is derived from
13b, has the correct relative configuration to give 14. The
reaction of 13a with [RhCl(PPh3)3](20 mol%, 80 8C, 20 h) in
the presence of iPr2NH (3 equiv) and LiCl (5 equiv), on the
10
11
12
13b: 1’,4’-trans, 3Z
13c: 1’,4’-trans, 3E
50
50
0.5 14 (94)
0.5 14 (94)
[a] 3 mol% of 3 in DCE. [b] Along with 27% of the destannylated product.
[c] TROC=2,2,2-trichloroethoxycarbonyl. [d] Along with 15% of the
destannylated product. [e] Ts=p-Toluenesulfonyl. [f] Along with 59% of
the destannylated product. [g] 5 mol% of 3.
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formation of an allyl cation from the allyl acetate, which then
reacts with the allylstannane or allylsilane.[18]
In summary, we have found that cationic AuI complexes
are the most efficient catalysts for the intramolecular coupling
of allyl acetates with allylstannanes. This process is mecha-
nistically very different from that catalyzed by Pd0 or RhI.
Additional synthetic applications and mechanistic studies of
this new coupling reaction are underway.
Received: September 30, 2007
Revised: November 11, 2007
Published online: January 29, 2008
Keywords: cross-coupling · cyclization · gold · palladium ·
.
rhodium
Scheme 3.
[1]a) M. MØndez, J. M. Cuerva, E. Gómez-Bengoa, D. J. Cµrdenas,
A. M. Echavarren, Chem. Eur. J. 2002, 8, 3620 – 3628; b) M.
MØndez, A. M. Echavarren, Eur. J. Org. Chem. 2002, 15 – 28.
[2]a) A. S. K. Hashmi, Chem. Rev. 2007, 107, 3180 – 3211; b) A.
Fürstner, P. W. Davies, Angew. Chem. 2007, 119, 3478 – 3519;
Angew. Chem. Int. Ed. 2007, 46, 3410 – 3449; c) D. J. Gorin, F. D.
Toste, Nature 2007, 446, 395 – 403; d) E. JimØnez-Nfflæez, A. M.
Echavarren, Chem. Commun. 2006, 333 – 346.
[3]a) N. Marion, R. Gealageas, S. P. Nolan, Org. Lett. 2007, 9, 2653 –
2656, and references therein. For a discussion of the role of AuI
in the activation of alkenes, see: b) Z. Li, J. Zhang, C. Brouwer,
C.-G. Yang, N. W. Reich, C. He, Org. Lett. 2006, 8, 4175 – 4178;
c) D. C. Rosenfeld, S. Shekhar, A. Takemiya, M. Utsunomiya,
J. F. Hartwig, Org. Lett. 2006, 8, 4179 – 4182.
[4]For the reaction of allylsilanes or allylstannanes with alkynes in
the presence of electrophilic metal catalysts to form hetero- or
carbocycles, see: a) C. Fernµndez-Rivas, M. MØndez, A. M.
Echavarren, J. Am. Chem. Soc. 2000, 122, 1221 – 1222; b) C.
Fernµndez-Rivas, M. MØndez, C. Nieto-Oberhuber, A. M.
Echavarren, J. Org. Chem. 2002, 67, 5197 – 5201; c) S. Porcel,
A. M. Echavarren, Angew. Chem. 2007, 119, 2726 – 2730; Angew.
Chem. Int. Ed. 2007, 46, 2672 – 2676.
other hand, gave 14 (48%) and destannylation products (1:1
mixture, 46%), whereas 13b gave only a 1:1 mixture of
destannylated products (92%).[11] These results show that the
processes catalyzed by AuI, Pd0, and RhI are mechanistically
distinct.
Additional reactions were performed to determine the
role played by the cationic AuI complex in this cyclization.
Thus, the reaction of 13b in the presence of AuCl3 (5 mol%,
DCE, 808C, 15 h) gave a 2:1 mixture of destannylated
products quantitatively.[12] Similarly, the reaction of this
substrate in the presence of Yb(OTf)3 (5 mol%, DCE,
808C, 15 h) gave a 67% yield of destannylated product.
None of the cyclized product 14 was detected in these
experiments.
We also considered the possible formation of an allyl-
gold(I) species by a transmetalation-type process.[13,14] 1H and
31P NMR spectroscopic monitoring of the reaction between
complex 3 and allyltriphenylstannane or allyltributylstannane
in CD2Cl2 shows that complexation of AuI to the alkene
occurs at low temperature (À78 to À208C)[15] and that
propene is formed at about 08C. Similar results were obtained
with crotyl- and cinnamyltributylstannane, which gave 1-
butene and allylbenzene, respectively. The reaction between 3
and allyltrimethylsilane also led to the formation of propene
at around À408C. Complex 3 gave the aquo complex [Au{(o-
PhC6H4)PtBu2}H2O]SbF6 in the presence of a stoichiometric
amount of water,[16] and formation of propene from allyltri-
butylstannane or allyltrimethylsilane was observed at the
same temperatures.
Although cleavage of the allylsilane and allylstannanes
was observed in these experiments, direct evidence for the
formation of allylgold(I) species could not be obtained. In
addition, we were unable to observe oxidative addition of the
allyl acetate to AuI in a series of experiments carried out with
17a and complex 3 in CD2Cl2.[17] The fact that, in contrast to
Pd0 and RhI, the cationic catalyst 3 leads to similar high yields
of 14 from 13a and 13b (Table 2, entries 10 and 11) suggests
that AuI acts as a mild and selective Lewis acid that promotes
[5]Allylstannanes also react with alkynes in the presence of Pd 0 in a
process that involves an oxidative addition of the allylstannane
to Pd0: a) B. Martín-Matute, E. Buæuel, D. J. Cµrdenas, M.
MØndez, C. Nieto-Oberhuber, A. M. Echavarren, J. Organomet.
Chem. 2003, 687, 410 – 419; b) S. Shin, T. V. RajanBabu, J. Am.
Chem. Soc. 2001, 123, 8416 – 8417.
[6]a) C. Gonzµlez-Arellano, A. Corma, M. Iglesias, F. Sµnchez, J.
Catal. 2006, 238, 497 – 501; b) C. Gonzµlez-Arellano, A. Abad,
A. Corma, H. García, M. Iglesias, F. Sµnchez, Angew. Chem.
2007, 119, 1558 – 1560; Angew. Chem. Int. Ed. 2007, 46, 1536 –
1538.
[7]See the Supporting Information for additional results.
[8]C. Nieto-Oberhuber, S. López, A. M. Echavarren, J. Am. Chem.
Soc. 2005, 127, 6178 – 6179.
[9]a) A. Buzas, F. M. Istrate, F. Gagosz, Angew. Chem. 2007, 119,
1159 – 1162; Angew. Chem. Int. Ed. 2007, 46, 1141 – 1144. For the
selective activation of the alkyne moiety of 1-phenylprop-2-ynyl
acetate with gold(I) and Lewis acids, such as Sc(OTf)3, see:
C. H. M. Amijs, V. López-Carrillo, A. M. Echavarren, Org. Lett.
2007, 9, 4021 – 4024.
[10]However, alcohols are more reactive than acetates with allylsi-
lanes in the presence of InCl3/Me3SiBr: T. Saito, Y. Nishimoto,
M. Yasuda, A. Baba, J. Org. Chem. 2006, 71, 8516 – 8522.
[11]The rhodium(I)-catalyzed reaction probably starts with a trans-
metalation of the allylstannane by RhI: a) E. W. Abel, S.
Moorhouse, Angew. Chem. 1971, 83, 360 – 361; Angew. Chem.
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Communications
Int. Ed. Engl. 1971, 10, 339 – 340; b) E. W. Abel, S. Moorhouse, J.
[15]The 1H NMR spectrum (CD2Cl2, À808C) of a 1:1 mixture of 3
=
and allyltriphenylstannane shows an upfield shift of the CH2
Chem. Soc. Dalton Trans. 1973, 1706 – 1711; c) S. Oi, M. Moro,
H. Ito, Y. Honma, S. Miyano, Y. Inoue, Tetrahedron 2002, 58, 91 –
97. d) For a transmetalation from boron to RhI, see: P. Zhao,
C. D. Incarvito, J. F. Hartwig, J. Am. Chem. Soc. 2007, 129, 1876 –
1877.
signals. A well-characterized ethylene–gold(I) complex shows
the ethylene hydrogen atoms at d = 3.56 ppm (a shift of
À1.70 ppm with respect to free ethylene): H. V. Rasika Dias, J.
Wu, Angew. Chem. 2007, 119, 7960 – 7962; Angew. Chem. Int.
Ed. 2007, 46, 7814 – 7816. A styrene–gold(I) complex shows
upfield shifts of the CH and CH2 resonances: M. A. Cinellu, G.
Minghetti, S. Stoccoro, A. Zucca, M. Manassero, Chem.
Commun. 2004, 1618 – 1619.
[12]The substitution of benzylic-propargylic alcohols by allylsilane is
more efficiently catalyzed by AuIII: M. Georgy, V. Boucard, J.-M.
Campagne, J. Am. Chem. Soc. 2005, 127, 14180 – 14181.
[13]Allylgold(I) complexes are not known, although a few allylgold-
(III) complexes have been shown to react as nucleophiles with
carbonyl compounds at the g carbon: T. Sone, S. Ozaki, N. C.
Kasuga, A. Fukuoka, S. Komiya, Bull. Chem. Soc. Jpn. 1995, 68,
1523 – 1533.
[14]Transmetalation of allyltrimethylstannane has been observed
with pincer PdII complexes and the resulting allylpalldium(II)
intermediate undergoes protonolysis to form propene: a) N.
Solin, J. Kjellgren, K. Szabó, Angew. Chem. 2003, 115, 3784 –
3786; Angew. Chem. Int. Ed. 2003, 42, 3656 – 3658; b) N. Solin, J.
Kjellgren, K. Szabó, J. Am. Chem. Soc. 2004, 126, 7026 – 7033.
[16]E. Herrero-Gómez, C. Nieto-Oberhuber, S. López, J. Benet
Buchholz, A. M. Echavarren, Angew. Chem. 2006, 118, 5581 –
5585; Angew. Chem. Int. Ed. 2006, 45, 5455 – 5459.
[17]a) A. Tamaki, J. K. Kochi, J. Organomet. Chem. 1972, 40, C81 –
C84; b) A. Tamaki, J. K. Kochi, J. Chem. Soc. Dalton Trans. 1973,
2620 – 2626; c) A. Tamaki, J. K. Kochi, J. Organomet. Chem.
1973, 64, 411 – 425; d) A. Tamaki, S. A. Magennis, J. K. Kochi, J.
Am. Chem. Soc. 1974, 96, 6140 – 6148.
[18]For the reaction of allylsilanes with allyl cations formed in a
gold-catalyzed reaction, see: C.-C. Lin, T.-M. Teng, A. Odedra,
R.-S. Liu, J. Am. Chem. Soc. 2007, 129, 3798 – 3799.
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