Au(PPh3)OPOF2-catalyzed intramolecular [4+2] cycloaddition reaction of dienynes

Article abstract of DOI:10.1039/c1cc11127b

Solvolysis of Au(PPh₃)PF₆ afforded Au(PPh ₃)OPOF₂ which is an effective catalyst in the intramolecular [4+2] cycloaddition of unactivated dienynes bearing a terminal alkyne.

Full text of DOI:10.1039/c1cc11127b

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COMMUNICATION
Au(PPh3)OPOF2-catalyzed intramolecular [4+2] cycloaddition reaction
of dienynesw
Soo Min Kim, Ji Hoon Park and Young Keun Chung*
Received 25th February 2011, Accepted 18th April 2011
DOI: 10.1039/c1cc11127b
Solvolysis of Au(PPh3)PF6 afforded Au(PPh3)OPOF2 which is
an effective catalyst in the intramolecular [4+2] cycloaddition of
unactivated dienynes bearing a terminal alkyne.
However, to the best of our knowledge, Au(PPh3)OPOF2 is
first reported in this study (eqn (1)).6
ð1Þ
The development of effective cyclization reactions for the
synthesis of carbocycles and heterocycles has been the subject
of many extensive studies because of their relevance to
biologically important and other functional materials. Among
them, gold-catalyzed cyclization is one of the most popular
branches of research in the formation of functionalized cyclic
structures.1,2 In particular, the cycloisomerization of enynes,
which produces novel intermediates is one of the most studied
fields.3 In our continuous efforts to develop efficient catalytic
reactions using gold complexes,4 we have also been studying
the use of gold complexes in the catalytic cycloaddition of
dienynes. In our attempt to make a cationic gold(I) complex
[Au(PPh3)PF6] to use as the catalyst in the cycloisomerization
of dienyne 1, we isolated Au(PPh3)OPOF2 as the sole product.
The formation of Au(PPh3)OPOF2 was confirmed by a
combustion analysis and a X-ray diffraction study (Fig. 1).
The anion PF6ꢀ was found to be hydrolyzed to OPOF2ꢀ. Thꢀe
solvolysis of the PF6ꢀ anion and the formation of the OPOF2
anion have already been reported for other systems.5
In relation to gold-catalyzed [4+2] cycloaddition, Furstner
¨
and Stimson have reported7 the [Au(PPh3)Cl]/AgSbF6-
catalyzed cycloaddition of unactivated alkynes and Echavarren
group have reported8 the scope and mechanism of
gold(I)-catalyzed intramolecular [4+2] cycloadditions of
arylalkynes or 1,3-enynes with alkenes. Bohringer and Gagosz
¨
also used a gold(I)-catalyzed [4+2] reaction in the synthesis of
functionalized bicyclo[4.3.0]nonenes.9 Very recently, we found
that Au(PPh3)OPOF2 was also quite effective in the intra-
moleulcar [4+2] cycloaddition of dienynes. Herein, we
report the Au(PPh3)OPOF2-catalyzed intramolecular [4+2]
cycloaddition reaction of dienynes under very mild reaction
conditions.
We investigated the gold(I)-catalyzed intramolecular [4+2]
cycloaddition of a dienyne (1) bearing an N-Ts group
(Table 1). We first screened neutral gold compounds, such as
Table 1 Screening the reaction conditionsa
Yieldb (%)
1a 1b 1c
Entry Catalyst
Additive Solvent t/h
1
2
Au(PPh3)Cl
Au(IPr)Cl
—
—
CH2Cl2 24
CH2Cl2 24
13
15
—
—
7
—
3
Au(PPh3)Cl
Au(PPh3)Cl
Au(PPh3)Cl
Au(PPh3)Cl
Au(PPh3)Cl
Au(PPh3)OPOF2
Au(PPh3)OPOF2
Au(PPh3)OPOF2
Au(PPh3)OPOF2
AgSbF6 CH2Cl2
AgSbF6 CH2Cl2
0.5 25 20 29
0.5
1.5 14 23 27
AgNTf2 CH2Cl2 24 29 17 18
Fig. 1 X-Ray structure of Au(PPh3)OPOF2. Hydrogen atoms are
4c
5
8
—
7
AgBF4
CH2Cl2
omitted for clarity.
6
7
8
9
10
11d
AgPF6
—
—
CH2Cl2
CH2Cl2
THF
3
74 21
—
—
—
—
—
0.5 97
0.5 99
—
—
—
—
Intelligent Textile System Research Center, and Department of
Chemistry, College of Natural Sciences, Seoul National University,
Seoul 151-747, Korea. E-mail: ykchung@snu.ac.kr;
—
—
Toluene 12
THF 48
91
93
Fax: +82 (2)889 0310; Tel: +82 (2) 880 6662
a
w Electronic supplementary information (ESI) available: Detailed
experimental procedure and properties of compounds. CCDC
740934–740936. For ESI and crystallographic data in CIF or other
electronic format see DOI: 10.1039/c1cc11127b
0.5 mmol of 1 was reacted with 5 mol% catalyst and 5 mol% of
b
additive at room temperature. Isolated yield. 10 mol% AgSbF6
c
d
was used. 0.3 mol% catalyst used.
c
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Chem. Commun., 2011, 47, 6719–6721 6719

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[Au(PPh3)Cl] and [Au(IPr)Cl], as catalysts (entries 1 and 2).
The reaction of 1 with [Au(PPh3)Cl] in dichloromethane
afforded 1a and 1c in 13% and 7% yields, respectively. The
use of [Au(IPr)Cl] as a catalyst gave 1a in 15% yield. In both
of these reactions, 80% of 1 was recovered. Apparently, it is
concluded that a neutral gold compound was not active
enough as a catalyst for the [4+2] cycloaddition of 1.
Table
2
Au(PPh3)OPOF2-catalyzed intramolecular [4+2] cyclo-
addition reaction of dienynesa
Entry Reactant
t/h
Product
Yieldb (%)
99
1
1
2
3
4
5
6
0.5
0.5
1.5
1
1a
2a
3a
4a
5a
We next screened an in situ generated cationic gold(I) species
2
3
4
5
6
97
99
98
90c
derived from Au(PPh3)Cl/AgSbF6. When
5 mol% of
Au(PPh3)Cl and 5 mol% of AgSbF6 were used, a mixture of
1a, 1b, and 1c was obtained in 25%, 20%, and 29% yields,
respectively (entry 3). The formation of the cycloisomerization
products, 1b and 1c, was confirmed by a X-ray diffraction
study.10 The silver salt is very hydroscopic, making it difficult
to weigh. Thus, when the amount of AgSbF6 was doubled
(entry 4), most of the substrates were decomposed and 1a and
1c were obtained in 8% and 7% yields, respectively. Whꢀen we
screened a different counter anion, such as BF4ꢀ, NTf2 and
PF6ꢀ, a similar distribution of products was observed in all
three cases (entries 5–7). However, when Au(PPh3)OPOF2 was
used as a catalyst, the yield dramatically increased to 97%
(entry 8). In solvents such as dichloromethane, toluene, and
THF, a high yield (91–99%) of 1a was obtained. Moreover,
the amount of the catalyst used could be reduced to 0.3 mol%
in compensation for the long reaction time (48 h) (entry 11).
Considering the reaction time and yield, Au(PPh3)OPOF2 was
chosen as the catalyst in other reactions.
2
2
6a 100
7
7
4
2
7a
86
8d
8
8a
9a
96
97
Next, we studied the Au(PPh3)OPOF2-catalyzed intra-
molecular [4+2] cycloaddition of various dienynes in THF
(Table 2). All the terminal dienynes (entries 1–4) were good
substrates. They gave the expected products in quantitative
yields. The reaction was not affected by tethers. Dienynes
(entries 5–10) with substituent(s) on a diene moiety were still
good substrates. Interestingly, when an alkene or diene was a
part of a cyclic moiety, i.e., a cyclohexenyl or cyclohexadienyl
group (entries 11 and 12), a quite different result was observed.
When a dienyne bearing a cyclohexenyl group was used as the
substrate, a mixture of two tricyclic compounds, a [4+2]
cycloaddition product 11a and the respective aromatized
product, was obtained in 45% and 5% yields. However, when
a diene was part of a cyclohexadienyl group, the yield was
97%. The catalytic [4+2] cycloaddition was also effective for
1,7-dienynes (entries 13 and 14) although they needed a long
reaction time. When the chain length between an alkyne and
N-Ts increased, the yield after 72 h of reaction time was 66%.
A dienyne with a longer tether chain between a diene and N-Ts
was a good substrate, yielding 92% yield of the product after
24 h of reaction time.
9
9
24
10
10
6
10a 96
11
12
11 24
11a 45e
12 0.5
12a 97
13
13 72
14 24
13a 66
14a 92
14
a
However, the introduction of a substituent to the alkyne
moiety was detrimental (Scheme 1). Thus, a dienyne (15) with
a TMS-substituted internal alkyne gave the desilylated [4+2]
cycloaddition product, 1a, in 64% yield after 24 h of reaction
time with a 25% recovery of 15. Similarly, 16 also gave a
desilylated [4+2] cycloaddition product, 2a, in 35% yield.
Treatment of a dienyne (17) with a Me-substituted internal
alkyne gave the cyclopropanated product, 17b, in 15% yield
after 24 h of reaction time with a 51% recovery of the reactant.
Based on the reactivity difference of terminal, silyl-substituted,
and methyl-substituted alkynes, it seems that a desilyation
0.5 mmol of the substrate was reacted with 5 mol% of Au(PPh3)-
b
OPOF2 in THF at room temperature. Yield of the isolated product.
c
d
A trace amount of an aromatized product was included. The E/Z
e
isomeric ratio 3 : 7 in 8 was retained in 8a. In addition, an aromatized
product was isolated in 5% yield.
may happen slowly to generate a terminal alkyne under these
reaction conditions and the resulting terminal alkyne under-
goes a [4+2] cycloaddition reaction.
On the basis of the above results and previous reports,7,11
a
plausible reaction mechanism was proposed (Scheme 2).
c
6720 Chem. Commun., 2011, 47, 6719–6721
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(d) E. Jimenez-Nu´ nez and A. M. Echavarren, Chem. Rev., 2008,
´
108, 3326; (e) L. Zhang, J. Sun and S. A. Kozmin, Adv. Synth.
Catal., 2006, 348, 2271; (f) C. Nieto-Oberhuber, S. Lo
E. Jimenez-Nu
12, 5916.
2 For recent gold-catalyzed reactions, see: (a) H. Faustino, F. Lo
´
pez,
´
´
nez and A. M. Echavarren, Chem.–Eur. J., 2006,
´
pez,
L. Castedo and J. L. Mascarenas, Chem. Sci., 2011, 2, 633;
(b) C. Li, Y. Zeng, H. Zhang, J. Feng, Y. Zhang and J. Wang,
Angew. Chem., Int. Ed., 2010, 49, 6413; (c) H. J. Bae, W. Jeong,
J. H. Lee and Y. H. Rhee, Chem.–Eur. J., 2011, 17, 1433;
(d) A. Escribano-Cuesta, V. Lo
A. M. Echavarren, Chem.–Eur. J., 2009, 15, 5646;
(e) P. Mauleon, R. M. Zeldin, A. Z. Gonzalez and F. D. Toste,
´
pez-Carrillo, D. Janssen and
´
´
J. Am. Chem. Soc., 2009, 131, 6348; (f) R. A. Widenhoefer,
Chem.–Eur. J., 2008, 14, 5382.
Scheme 1 Au(PPh3)OPOF2-catalyzed [4+2] cycloaddition of internal
3 For recent papers, see: (a) H. Kusama, Y. Karibe, Y. Onizawa and
N. Iwasawa, Angew. Chem., Int. Ed., 2010, 49, 4269;
(b) Y. Matsumoto, K. B. Selim, H. Nakanishi, K.-I. Yamada,
Y. Yamamoto and K. Tomioka, Tetrahedron Lett., 2010, 51, 404;
(c) I. D. G. Watson, S. Ritter and F. D. Toste, J. Am. Chem. Soc.,
2009, 131, 2056; (d) Y. Odabachian and F. Gagosz, Adv. Synth.
Catal., 2009, 351, 379; (e) F.-D. Boyer, X. L. Goff and I. Hanna,
J. Org. Chem., 2008, 73, 5163.
alkynes.
4 (a) S. M. Kim, J. H. Park, Y. K. Kang and Y. K. Chung, Angew.
Chem., Int. Ed., 2009, 48, 4532; (b) S. M. Kim, J. H. Park,
S. Y. Choi and Y. K. Chung, Angew. Chem., Int. Ed., 2007, 46,
6172; (c) S. I. Lee, S. M. Kim, M. R. Choi, S. Y. Kim and
Y. K. Chung, J. Org. Chem., 2006, 71, 9366.
5 (a) F. L. Wimmer and M. R. Snow, Aust. J. Chem., 1978, 31, 267;
(b) M. A. Bennett, T. W. Matheson, G. B. Robertson,
W. L. Steffen and T. W. Turney, J. Chem. Soc., Chem. Commun.,
1979, 32; (c) G. Smith, D. J. Cole-Hamilton, A. C. Gregory and
N. G. Gooden, Polyhedron, 1982, 1, 97; (d) R. Fernandez-Galan,
B. R. Manzano, A. Otero, M. Lanfranchi and M. A. Pellinghelli,
Inorg. Chem., 1994, 33, 2309.
6 We took H and 31P NMR spectra of Au(PPh3)PF6 prepared in a
1
Scheme 2 Proposed mechanism.
glove box. Initially, we only observed the peak due to the phenyl
group and no water peak in the H NMR spectrum. However, as
1
We have demonstrated that Au(PPh3)OPOF2 is an effective
catalyst in the intramolecular [4+2] cycloaddition of terminal
dienynes. Further studies are needed to delineate the intimate
mechanistic steps, and the origin of the high activity of
Au(PPh3)OPOF2 is currently under investigation in our
laboratory.
time passed, we could see the transformation of PF6 into PF2O2 in
31P NMR spectra. The result of NMR experiments is deposited in
ESIw.
7 A. Furstner and C. C. Stimson, Angew. Chem., Int. Ed., 2007, 46,
¨
8845.
8 (a) C. Nieto-Oberhuber, P. Pe
T. Lauterbach, C. Rodrıguez, S. Lo
D. J. Cardenas and A. M. Echavarren, J. Am. Chem. Soc., 2008,
130, 269; (b) C. Nieto-Oberhuber, S. Lopez and A. M. Echavarren,
J. Am. Chem. Soc., 2005, 127, 6178.
´
rez-Gala
´
n, E. Herrero-Go
´
mez,
´
´
pez, C. Bour, A. Rosello
´
n,
´
This work was supported by the National Research
Foundation of Korea (NRF) (2010-0029663) and the Basic
Science Research Program through the NRF funded by the
Ministry of Education, Science and Technology (R11-2005-065).
´
9 S. Bohringer and F. Gagosz, Adv. Synth. Catal., 2008, 350,
2617.
¨
10 ESIw.
11 (a) N. Cabello, E. Jime
A. M. Echavarren, Eur. J. Org. Chem., 2007, 4217; (b) C. Nieto-
Oberhuber, M. P. Munoz, S. Lopez, E. Jimenez-Nunez,
C. Nevado, E. Herrero-Gomez, M. Raducan and
A. M. Echavarren, Chem.–Eur. J., 2006, 12, 1677.
nez-Nu´ nez, E. Bunuel, D. J. Cardenas and
´ ´
Notes and references
´
´
´
1 For reviews, see: (a) N. Krause and C. Winter, Chem. Rev., 2011,
111, 1994; (b) M. Bandini, Chem. Soc. Rev., 2011, 40, 1358; (c) A.
S. K. Hashmi, Angew. Chem., Int. Ed., 2010, 49, 5232;
´
c
This journal is The Royal Society of Chemistry 2011
Chem. Commun., 2011, 47, 6719–6721 6721