Catalytic cycloisomerisation of 1,6-dienes in ionic liquids

Article abstract of DOI:10.1016/j.tet.2008.02.016

The ruthenium and palladium catalysed cycloisomerisation of 1,6-dienes in [bdmim][PF₆], a room temperature ionic liquid (RTIL), is presented. The catalytic system comprising of [RuCl₂(COD)]_n in the presence of ⁱ

Full text of DOI:10.1016/j.tet.2008.02.016

Available online at www.sciencedirect.com
Tetrahedron 64 (2008) 3687e3690
www.elsevier.com/locate/tet
Catalytic cycloisomerisation of 1,6-dienes in ionic liquids
a
Xiaowei Miao , Joanna Feder-Kubis , Cedric Fischmeister
b
a,
*
,
´
Juliusz Pernak b, Pierre H. Dixneuf a,
*
a UMR 6226-CNRS-Universite´ de Rennes 1, Institut Sciences Chimiques de Rennes, Catalyse et Organome´talliques, Campus de Beaulieu,
Av. du ge´ne´ral Leclerc, 35042 Rennes Cedex, France
b
´
Poznan University of Technology, Poznan, Poland
´
Received 9 January 2008; received in revised form 6 February 2008; accepted 7 February 2008
Available online 9 February 2008
Abstract
The ruthenium and palladium catalysed cycloisomerisation of 1,6-dienes in [bdmim][PF6], a room temperature ionic liquid (RTIL), is pre-
i
sented. The catalytic system comprising of [RuCl2(COD)]n in the presence of PrOH was found to be particularly efficient and selective for the
cycloisomerisation of the N,N-diallyltosylamide. This system can be reused several times without loss of performances and displays catalytic
activity after a long storage period in the IL.
Ó 2008 Elsevier Ltd. All rights reserved.
Keywords: Cycloisomerisation; 1,6-Dienes; Ionic liquids; Ruthenium; Palladium; Recycling
1. Introduction
Room temperature ionic liquids (RTILs)8 are now commonly
used as medium to perform homogeneous organometallic cataly-
sis9,10 especiallybecausewhenthecatalystsshowastrongaffinity
for the ionic liquid it is possible to extract very easily the reaction
products and to reuse the catalysts. This strategy was reported for
the cycloisomerisation of 2,2-diallylmalonates using palladium
catalysts in [bmim][PF6] (1-butyl-2-methyl imidazolium hexa-
fluorophosphate) allowing catalyst recycling over several runs
but with significant variations in the product distribution.11
Herein we report the cycloisomerisation of two 1,6-dienes
in [bdmim][PF6] (1-butyl-2,3-dimethyl imidazolium hexa-
fluorophosphate) using ruthenium and palladium precatalysts.
We show that the ruthenium catalyst can be reused several
times with very high efficiency and selectivity for the cyclo-
isomerisation of N,N-diallyltosylamide in this ionic liquid,
whereas chiral ionic liquids (CILs), if they allow efficient
cycloisomerisation, do not induce enantioselectivity.
Transition metal catalysed cycloisomerisation of 1,6-dienes
constitutes a powerful and atom economic route for the syn-
thesis of carbo- and heterocyclic compounds (Scheme 1).1
Several organometallic complexes based on Ti,2 Rh,3 Ru,4
Ni5 and Pd6 have already been described as efficient catalysts
for this transformation. Until recently, high catalyst activity
and regioselectivity for the five-membered products
(a, b and c, Scheme 1) were the major concerns but asymmet-
ric versions of this transformation are now reported with enan-
tiomeric excess up to 80%.5,7
Catalyst
+
+
X
X
X
X
a
b
c
Scheme 1. Catalytic cycloisomerisation of 1,6-dienes.
2. Results and discussion
Several rhodium, ruthenium and palladium complexes have
been tested in the ionic liquid [bdmim][PF6] (1-butyl-2,3-di-
methylimidazoliumhexafluorophosphate)aimingattheselective
* Corresponding authors. Tel.: þ33 (0)2 23235998; fax: þ33 (0)2 23236939.
E-mail addresses: cedric.fischmeister@univ-rennes1.fr (C. Fischmeister),
pierre.dixneuf@univ-rennes1.fr (P.H. Dixneuf).
0040-4020/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2008.02.016

3688
X. Miao et al. / Tetrahedron 64 (2008) 3687e3690
preparation of the exo-methylenecyclopentane 1a (Scheme 2,
Table 1).
run). Thus, when the first run was completed, the organic prod-
ucts were extracted with toluene and the medium was reloaded
with fresh substrate only. The second run showed an important
loss of conversion but the regioselectivity remained very high
for 1a (Table 2). The next two runs did not show a drop in con-
version as we could expect and the activity seemed to be some-
Catalyst
+
+
TsN
TsN
TsN
TsN
[bdmim][PF6]
1a
1b
1c
1
i
how constant. At this point it became obvious that PrOH is
necessary to ensure high conversions. Indeed addition of iPrOH
in a fifth run allowed restoring a high conversion of 99% with
a selectivity remaining fairly high for the desired product 1a
(run 5, Table 2).
Scheme 2. Catalytic cycloisomerisation of N,N-diallyltosylamide in
[bdmim][PF6].
Among the complexes tested, RhCl3$3H2O, RuCl3$H2O
and RuCl(Cp*)(COD) showed very poor activity. On the
other hand, the Wilkinson catalyst RhCl(PPh3)3 afforded
very good conversion but the selectivity was in favour of the
endocyclic product 1c and the isomerised starting material
CH3CH]CHeN(Ts)eCH2CH]CH2 1d was also detected
(entry 2). The ruthenium polymer [Ru(O2CH)(CO)2]n with
iPrOH also afforded high conversion with a selectivity in
favour of the product 1b (entry 6). [RuCl2(COD)]n in pure
iPrOH was reported by Itoh to be an efficient catalyst for the
cycloisomerisation of 1,6-dienes to five-membered cycles
with a good selectivity for the exo-methylenecyclopentane de-
rivatives.4d We have evaluated this catalytic system by adding
iPrOH (120 equiv/Ru, optimised conditions) to the ruthenium
complex dissolved in the ionic liquid resulting in the selective
formation of 1a that was obtained in 95% isolated yield (entry
5).12 No conversion was observed in a blank test without
iPrOH under the same experimental conditions. It must be
noted that under conventional conditions ([RuCl2(COD)]n in
Table 2
Ruthenium catalyst recycling in [bdmim][PF6]a
Run
iPrOHb
Conv.c
1ac
1cc
1
2
3
4
5
a
120
0
>99
24
>95
21
2
2
0
33
36
30
32
0
120
>99
85
9
[RuCl2(COD)]n 5 mol %, 90 ꢀC for 16 h.
equiv/Ru.
Conversions and selectivity (%) determined by GC.
b
c
The above results suggested that only a portion of the
initially introduced [RuCl2(COD)]n complex was activated
i
by PrOH during the first run. Thus, the recycling test was
i
repeated by adding PrOH along with fresh substrate after
completion and workup of each run. As foreseen, this resulted
in a second run with a high conversion and selectivity for 1a.
This procedure was repeated and finally allowed to perform
seven consecutive runs with very good yields and full selectiv-
ity for 1a (Table 3).
i
pure PrOH) the product 1a is obtained in 65% yield and
86% purity4a demonstrating the benefit of using an ionic liquid
as the reaction media.
7b
The ionic palladium complex [Pd(MeCN)4](BF4)2 was
found to be more efficient than the ruthenium based system since
it afforded very good activity and selectivity for 1a under milder
conditions (40 ꢀC) using a lower catalyst loading (entry 7).
This initial catalyst screening led us to focus our efforts on the
recyclability of [RuCl2(COD)]n/iPrOH and [Pd(MeCN)4](BF4)2
in [bdmim][PF6]. With the [RuCl2(COD)]n/iPrOH system,
iPrOH acts as a hydride source allowing the formation of
a RueH species.4d We reasoned that addition of iPrOH should
be necessary only at the beginning of the recycling test (i.e., first
Table 3
Catalyst recycling in the cycloisomerisation of 1 with [RuCl2(COD)]n/iPrOH
in [bdmim][PF6]a
Run
Conv.b (selectivity)
Isolated yield
of 1a (%)
1
2
3
4
5
6
7
8
9c
a
>99 (100)
>99 (100)
>99 (100)
>99 (100)
>99 (100)
>99 (100)
98 (100)
92
97
94
93
96
98
93
96
90
56
Table 1
Catalyst screening for the cycloisomerisation of 1 in [bdmim][PF6]a
Entry Catalyst (mol %)
Conv.b Yield (%) Selectivityb
60
i
[RuCl2(COD)]n 5 mol %, PrOH 120 equiv/Ru, 90 ꢀC for 16 h.
Conversions and selectivity (%) determined by GC.
After 45 days.
1a
1b 1c
b
c
1
2
3
4
5
6
7
RhCl3$3H2O (5)
RhCl(PPh3)3 (5)
RuCl3$H2O (5)
5
d
d
d
d
96
93d
90
5
>99
0
87
RuClCp*(COD) (5)
20
>99
20
>98
After the eighth run was completed and the workup proce-
[RuCl2(COD)]n (5)þ PrOHc
i
dure was performed as described earlier, the resulting ionic
liquid was stored for 45 days under an inert atmosphere. It is
noteworthy that this solution showed catalytic activity upon
[Ru(O2CH)(CO)2]n (2.5)þ PrOHc >99
86 14
i
e
[Pd(MeCN)4](BF4)2 (2.5)
>99
>98
a
b
c
d
e
All reactions were carried out at 90 ꢀC for 16 h.
Conversions and selectivity (%) determined by GC.
120 equiv/Ru.
i
addition of fresh substrate and PrOH. These results demon-
strate that although the catalytic activity over the consecutive
runs is partially due to catalyst recycling, the ionic liquid phase
acts essentially as a reservoir of ruthenium catalyst precursor.
Isolated yield of (1bþ1c), 14 h.
40 ꢀC.

X. Miao et al. / Tetrahedron 64 (2008) 3687e3690
3689
The recyclability of [Pd(MeCN)4](BF4)2 was also evaluated
for the cycloisomerisation of 1 using the above mentioned
procedure except that no iPrOH is required with this complex.
In this case two consecutive runs were possible with good
conversions and selectivity. The third and fourth runs showed
a drop in conversion and selectivity for the exo-methylene-
cyclopentane 1a was strongly affected (Table 4).
interest in the domain of enantioselective transformations14
and very promising results have been reported.15 Having dem-
onstrated the possibility to use [RuCl2(COD)]n/iPrOH and
[Pd(MeCN)4](BF4)2 in IL, we have performed the cycloiso-
merisation of 1 using those catalysts in a series of (CILs)
chiral ionic liquids 3e7 (Fig. 1).
With [RuCl2(COD)]n/iPrOH at 90 ꢀC, as it was the case with
[bdmim][PF6], the menthol based ammonium or imidazol-
ium chiral ionic liquids 3e6 provided very good conversion
and selectivity for 1a (full conversion, isolated yields
ꢁ75%), however, no enantioselectivity could be observed.
CIL 7 bearing a chiral anion totally inhibited the reaction.
The palladium catalyst [Pd(MeCN)4](BF4)2 was also tested
in CILs for the cycloisomerisation of 1. The higher reactivity
of this catalyst allowed running the reaction at much lower
temperature than with the ruthenium based system. Using
the chiral IL 3 at 20 or 0 ꢀC, the reaction proceeded in 90
and 80% conversions, respectively,16 but the product 1a was
again obtained as a racemic mixture. As shown in a recent
example, the understanding of the interaction between the
solvent and the solute or reaction intermediate, leading to the
Table 4
Cycloisomerisation of 1 with [Pd(MeCN)4](BF4)2: catalyst recyclinga
Run
Conv.b
Selectivity for 1ab
Isolated yield
of 1a (%)
1
2
3
4
a
>99
>99
95
97
93
72
71
90
90
68
60
95
[Pd(MeCN)4](BF4)2, 2.5 mol %, 40 ꢀC for 16 h.
Conversions and selectivity (%) determined by GC.
b
The transformation of compound 2 was attempted using
[RuCl2(COD)]n/iPrOH and [Pd(MeCN)4](BF4)2 catalysts in
[bdmim][PF6] (Scheme 3).
EtO2C
EtO2C
EtO2C
EtO2C
EtO2C
EtO2C
EtO2C
EtO2C
Catalyst
+
+
[bdmim][PF6]
2c
2
2b
2a
Scheme 3. Catalytic cycloisomerisation of diethyl diallylmalonate in [bdmim][PF6].
N
N
C7H15
nBu
O
NTf2
N
O
NTf2
N
O
N
O
N
-
-
-
N
CH3CHCOO-
-N
NTf2
NTf2
nPr
OH
7
5
6
3
4
Figure 1. Chiral ionic liquids tested for the cycloisomerisation of 1.
[RuCl2(COD)]n/iPrOH afforded 99% conversion with a
52:47 ratio of 2a and isomerised starting material CH3CH]
CHeC(CO2Et)2eCH2CH]CH2 2d. [Pd(MeCN)4](BF4)2 led
also to 99% conversion but the reaction mixture was composed
of the three products 2a/2b/2c in a ratio 24:40:26. These results
constituteanotherexampleof thedependence ofthistransforma-
tion to the experimental conditions and to the substrate. Indeed,
it is generally observed that under conventional reaction condi-
synthesis of tailor-made functional chiral ionic liquids, is a pre-
requisite for a high asymmetric induction by the reaction
medium.15a
3. Conclusion
Two catalysts have been used for the cycloisomerisation of
N,N-diallyltosylamide 1 in IL [bdmim][PF6] allowing the effi-
cient and selective formation of the exo-methylenecyclo
pentane product 1a. The catalytic system resulting from [Ru
i
tion (pure PrOH), compound such as 2 usually leads to high
selectivity whereas lower selectivity is obtained with compound
1.4a
i
(COD)Cl2]n and PrOH in [bdmim][PF6] was found to be
Having reached two important objectives (efficiency and
selectivity) for the cycloisomerisation of compound 1 in IL,
we were interested in the enantioselective version of this reac-
tion for which examples remain scarce.5b,c,7 Recently, ee’s up
to 80% have been reported for the cycloisomerisation of 2 with
cationic nickel complexes [Ni(allyl)(COD)][Y] and chiral
monodentate phosphoramidite ligands.5b,c Due to their diver-
sity and easy access,13 chiral ionic liquids (CILs) are attracting
more efficient and selective in the ionic liquid media than in
pure iPrOH. This catalytic system can be reused for seven runs
without decrease in conversion and selectivity provided iPrOH
was added for each run. [Pd(MeCN)4](BF4)2 was also found
to be efficient under milder experimental conditions and af-
forded the exo-methylenecyclopentane 1a with a high selectiv-
ity. The challenging use of CILs as stereoselectivity promoters
was attempted but no enantioselectivity could be obtained.

3690
X. Miao et al. / Tetrahedron 64 (2008) 3687e3690
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4. Experimental
4.1. General
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All the solvents were dried and distilled prior to use.
RhCl3$xH2O, RuCl3$xH2O, were purchased from Jonhson Mat-
they and used as received. [Pd(MeCN)4](BF4)2 was purchased
from Alfa Aesar and stored under argon. [RuCl2(COD)]n,17
[Ru(O2CH)(CO)2]n,18 RuClCp*(COD)19 were obtained ac-
cording to literature procedures. [bdmim][PF6]10d and CILs15a
were prepared according to reported procedures. Flash chroma-
tography purifications were performed on silica gel column
(Merck Silica gel 60) using mixtures of heptane and diethyl-
ether as the eluant.
¨
Boing, C.; Francio, G.; Leitner, W. Chem. Commun. 2005, 1456.
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~
6. (a) Bray, K. L.; Lloyd-Jones, G. C.; Paz-Munoz, M.; Slatford, P. A.; Tan,
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7. (a) Heumann, A.; Moukhliss, M. Synlett 1999, 268; (b) Heumann, A.;
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1H NMRspectrawererecordedona BRUKERDPX 200 spec-
trometer. Gas chromatography analyses were performed on
aHewlett5890PackardSeriesII. HPLCanalyseswereperformed
on a Waters 1515 apparatus equipped with a Waters 2495 UV
detector. 3-Methyl-4-methylene-1-tosylpyrrolidine 1a: Daicel
column Chiralpak AD, 0.46ꢂ25 cm, hexane/iPrOH¼95:5,
0.5 ml/min, l¼230 nm, 29 and 35 min.
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heptadienes
ˆ
Parvulescu, V. I.; Hardacre, C. Chem. Rev. 2007, 6, 2615.
The ionic liquid (1.5 ml) was first dried for 1 h at 90 ꢀC
under vacuum. Catalyst (5 mol % for [RuCl2(COD)]n and
2.5 mol % for [Pd(MeCN)4](BF4)2), degassed iPrOH
(120 equiv/Ru) and diene (0.5 mmol) were then added under
argon and the reaction mixture was stirred at 90 ꢀC. The
organic products were extracted with toluene (4ꢂ3 ml) and
purified by flash column chromatography on silica gel (hep-
tane/diethyl/ether, 8:2 (v/v)).
´
10. (a) Semeril, D.; Olivier-Bourbigou, H.; Bruneau, C.; Dixneuf, P. H. Chem.
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Horvath, I. T.; Dixneuf, P. H. New J. Chem. 2002, 26, 1667; (c) Thurier,
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13. (a) Pernak, J.; Feder-Kubis, J. Chem.dEur. J. 2005, 11, 4441; (b) Pernak,
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1H NMR for products 1a4b and 2a3a were consistent with
reported data.
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S. J. C.; Parmar, V. S.; Malhorta, S. V. Org. Lett. 2007, 9, 3905.
¨
Acknowledgements
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The authors are grateful to the CNRS, to the Ministere de la
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