Asymmetric catalysis of planar-chiral cyclopentadienylruthenium complexes in allylic amination and alkylation [10]

Full text of DOI:10.1021/ja016334l

J. Am. Chem. Soc. 2001, 123, 10405-10406
Asymmetric Catalysis of Planar-Chiral
10405
Cyclopentadienylruthenium Complexes in Allylic
Amination and Alkylation
Yuji Matsushima,† Kiyotaka Onitsuka,† Teruyuki Kondo,‡
Take-aki Mitsudo,‡ and Shigetoshi Takahashi*,†
The Institute of Scientific and Industrial Research
Osaka UniVersity, Ibaraki, Osaka 567-0047, Japan
Department of Energy and Hydrocarbon Chemistry
Graduate School of Engineering, Kyoto UniVersity
Sakyo-ku, Kyoto 606-8501, Japan
Enantioselective allylic substitutions catalyzed by transition
metal complexes provide a powerful method for constructing
complex organic molecules.11 Palladium-based catalysts have
often given excellent results. To expand the scope of the reaction,
however, extensive studies on alternative metal catalysts have been
performed.12 Although some ruthenium complexes show high
catalytic activity for allylic substitutions,13 an asymmetric version
of such catalysis is still unknown. We describe here new
enantioselective allylic amination and alkylation catalyzed by
planar-chiral ruthenium complexes 1.
ReceiVed June 2, 2001
ReVised Manuscript ReceiVed September 2, 2001
A great deal of effort has been directed toward the molecular
design of chiral organometallic complexes, which are key to the
development of transition metal-catalyzed asymmetric reactions.1
Organometallic complexes bearing various chiral ligands such as
chiral phosphines and amines are recognized as effective asym-
metric catalysts.2 In addition, increasing attention has been paid
to other types of optically active complexes.3,4 Planar-chiral
complexes formed by π-coordination of prochiral unsaturated
hydrocarbons fall in this latter category. The efficiency of planar
chirality in asymmetric catalysis has been demonstrated by using
early transition-metal complexes such as ansa-metallocenes.5
There has been only one report, which showed low enantio-
selectivity, on the use of planar-chiral complexes of late transition
metals as catalysts (type A).6 Hayashi7 and recently Fu8 have
studied asymmetric catalysis using planar-chiral ferrocene deriva-
tives. In their system, metal species other than stable metal
moieties that generate planar chirality, which simply serve as a
bulky substituent, act as a reactive center of the catalyst (type
B). Recently, we prepared novel planar-chiral cyclopentadienyl-
ruthenium complexes,9 and found that ruthenium complexes (1)
with an anchor phosphine ligand can control metal-centered
chirality with high selectivity.10 These results prompted us to
develop a novel asymmetric reaction using complexes 1 as Type
A catalyst.
Our initial experiments focused on the allylic amination with
complex 1 as a catalyst. Representative results are shown in Table
1. Thus, the reaction of 1,3-diphenyl-2-propenyl ethyl carbonate
(2) with 1.1 equiv of di-n-propylamine in the presence of 5 mol
% of (S)-1 proceeded smoothly at 20 °C to give the allylic
aminated product (3) in a quantitative yield with 35% ee (Entry
1). Although the reaction with complex (S)-1b in place of (S)-1a
gave similar results (90% yield, 20% ee), the product had a
specific rotation with a sign opposite that obtained by (S)-1a
(Entry 2). A bulkier substituent at the 4-position of the cyclo-
pentadienyl ring increased the enantioselectivity to 64% ee (Entry
3), while a longer tether slightly decreased the enantioselectivity
(Entry 4). The reaction catalyzed by 1g which has no tether
between the cyclopentadienyl and phosphine ligands, also pro-
ceeded with high enantioselectivity (Entry 7). The enantioselec-
tivity was improved by using (S)-1f , which has 3,5-dimethyl-
phenyl groups on the anchor phosphorus atom (Entry 6). In the
† Osaka University.
‡ Kyoto University.
(1) ComprehensiVe Asymmetric Catalysis I-III; Jacobsen, E. N., Pflatz,
A., Yamamoto, H., Eds.; Springer-Verlag: Berlin, Germany, 1999.
(2) For recent reviews, see: (a) Ghosh, A. K.; Mathivanan, P.; Cappiello,
J. Tetrahedron: Asymmetry 1998, 9, 1. (b) Helmchen, G.; Pfaltz, A. Acc.
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Fache, F.; Schulz, E.; Tommasino, M. L.; Lemaire, M. Chem. ReV. 2000,
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(3) For reviews of planar-chiral complexes, see: (a) Halterman, R. L. Chem.
ReV. 1992, 92, 965. (b) Iwata, C.; Takemoto, Y. Chem. Commun. 1996, 2797.
(c) Schmalz, H.-G.; Siegel, S. In Transition Metals for Organic Synthesis:
Building Blocks and Fine Chemicals; Beller, M., Bolm, C., Eds.; Wiley-
VCH: Weinheim, Germany, 1998; Vol. 1, p 550.
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760. (b) Onitsuka, K.; Dodo, N.; Matsushima, Y.; Takahashi, S. Chem.
Commun. 2001, 521. (c) Onitsuka, K.; Ajioka, Y.; Matsushima, Y.; Takahashi,
S. Organometallics 2001, 20, 3274.
(4) For reviews of metal-centered chiral complexes, see: (a) Brunner, H.
Angew. Chem., Int. Ed. 1999, 38, 1194. (b) Brunner, H. Eur. J. Inorg. Chem.
2001, 905.
(5) For reviews, see: (a) Hoveyda, A. H.; Morken, J. P. Angew. Chem.,
Int. Ed. Engl. 1996, 35, 1262. (b) Hoveyda, A. H.; Morken, J. P. In
Metallocenes: Synthesis‚ReactiVity‚Applications; Togni, A., Halterman, R.
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(6) Trost, B. M.; Vidal, B.; Thommen, M. Chem. Eur. J. 1999, 5, 1055.
(7) For reviews, see: Hayashi, T. In Ferrocenes: Homogeneous Catalysis,
Organic Synthesis, Materials Science; Togni, A., Hayashi, T., Eds.; Wiley-
VCH: Weinheim, Germany, 1995; p 105. (b) Togni, A. In Metallocenes:
Synthesis‚ReactiVity‚Applications; Togni, A., Halterman, R. L., Eds.; Wiley-
VCH: Weinheim, Germany, 1998; Vol. 2, p 685.
(8) For a review and recent references, see: (a) Fu, G. C. Acc. Chem. Res.
2000, 33, 412. (b) Shintani, R.; Lo, M. M. C.; Fu, G. C. Org. Lett. 2000, 2,
3695. (c) Tao, B.; Lo, M. M. C.; Fu, G. C. J. Am. Chem. Soc. 2001, 123, 353.
(9) (a) Dodo, N.; Matsushima, Y.; Uno, M.; Onitsuka, K.; Takahashi, S. J.
Chem. Soc., Dalton Trans. 2000, 35. (b) Matsushima, Y.; Komatsuzaki, N.;
Ajioka, Y.; Yamamoto, M.; Kikuchi, H.; Takata, Y.; Dodo, N.; Onitsuka, K.;
Uno, M.; Takahashi, S. Bull. Chem. Soc. Jpn. 2001, 74, 527.
(11) For reviews, see: (a) Hayashi, T. In Catalytic Asymmetric Synthesis;
Ojima, I., Ed.; VCH: New York, 1993; p 325. (b) Reiser, O. Angew. Chem.,
Int. Ed. Engl. 1993, 32, 547. (c) Trost, B. M.; Van Vranken, D. L. Chem.
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Angew. Chem., Int. Ed. Engl. 1993, 32, 547. (b) Trost, B. M.; Hachiya, I. J.
Am. Chem. Soc. 1998, 120, 1104. (c) Glorius, F.; Pfaltz, A. Org. Lett. 1999,
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10.1021/ja016334l CCC: $20.00 © 2001 American Chemical Society
Published on Web 09/27/2001

10406 J. Am. Chem. Soc., Vol. 123, No. 42, 2001
Communications to the Editor
Table 1. Ruthenium-Catalyzed Asymmetric Allylic Amination
Table 2. Ruthenium-Catalyzed Asymmetric Allylic Alkylation
entry
catalyst
conversion (%)a
yield (%)a,b
ee (%)c,d
conversion
(%)a
yield
ee
entry catalyst nucleophile
product (%)a,b (%)c,d
1
2
3
4
5
6
7
(S)-1a
(S)-1b
(S)-1c
(S)-1d
(S)-1e
(S)-1f
(S)-1g
100
98
100
100
100
100
93
97
90
99
94
93
98(89)
86
35(-)
20(+)
64(+)
56(+)
57(+)
74(+)
65(+)
1
2
(S)-1a
(S)-1b
(S)-1c
(S)-1d
(S)-1e
(S)-1f
(S)-1g
(S)-1a
(S)-1f
(S)-1a
(S)-1c
(S)-1f
4a
4a
4a
4a
4a
4a
4a
4b
4b
4c
4c
4c
98
97
99
5a
5a
5a
5a
5a
5a
5a
5b
5b
5c
5c
5c
96
91
97
14
98
80(R)
91(S)
96(S)
10(S)
97(S)
3
4
5
6
7
8
9
10
11
12
19
100
100
10
100
87
91
88
99(79) 96(S)
3
96(88) 94(R)
85(77) 96(S)
82
75
a Conversion and yield were determined by HPLC on the basis of
allyl carbonate (2). b The number in parentheses indicates an isolated
yield. c The ee values were determined by HPLC equipped with a chiral
column (Daicel Chiralcel OJ, hexane/i-PrOH/HNEt2 1000/1/1). d The
sign of specific rotation of the products is given in parentheses.
63(S)
82(R)
88
80(68) 83(R)
a Conversion and yield were determined by HPLC on the basis of
allyl carbonate (2). b The number in parentheses indicates an isolated
yield. c The ee values were determined by HPLC equipped with a chiral
column (5a, Daicel Chiralcel OD, hexane/i-PrOH 99/1; 5b, Daicel
reactions of Entries 3-7, the signs of the specific rotation of the
products were the same as that of the product obtained with
(S)-1b.
Since allylamines tend to react with ruthenium complexes to
give π-allyl complexes, the possibility of the racemization of
product 3 should be considered.13b,14 A trace experiment of the
reaction with (S)-1f, however, showed that the enantioselectivity
stays constant independent of the conversion of 2. When the
reaction with (S)-1f was performed in the presence of an equimolar
amount of racemic 3, the enantioselectivity of the total product 3
was 34% ee, indicating that the enantioselectivity of the total
product 3 was not affected by the addition of racemic 3. These
results clearly show that the 3 does not undergo racemization in
the present reaction at all and that the enantioselectivity is
determined by kinetic factors.
1
Chiralcel OJ, hexane/i-PrOH 19/1) and/or by H NMR spectroscopy
using a chiral shift reagent Eu(hfc)3 in CDCl3. d Configuration of the
products was assigned on the basis of the sign of specific rotation
according to the literature (5a, ref 15; 5b, see Supporting Information;
5c, ref 16).
nucleophile, approximately the same results were obtained (Entries
8 and 9). However, the reaction with sodium dimethyl methyl-
malonate (4c) led to a slight decrease in both yield and
enantioselectivity relative to those with 4a (Entries 10-12). In
all cases, the configuration of the products with (S)-1a was
opposite those obtained with other complexes, indicating that the
substituents at the 4-position of the cyclopentadienyl ring play
an extremely important role in controlling stereochemistry in the
present reactions.
In summary, we have developed asymmetric allylic substitu-
tions catalyzed by planar-chiral cyclopentadienyl-ruthenium com-
plexes, in which we achieved enantioselectivities of up to 74%
ee for amination and 97% ee for alkylation. To the best of our
knowledge, this is not only the first successful ruthenium-
catalyzed asymmetric allylic amination and alkylation, it is also
the first asymmetric catalysis of planar-chiral complexes of late
transition metals. Further studies on the reaction mechanism to
understand the origin of the enantioselectivity and on the
application of planar-chiral ruthenium catalysts to other asym-
metric reactions are in progress.
Ruthenium complexes 1 also catalyzed allylic alkylation with
high enantioselectivity and high yields (Table 2). The reaction
of allylic carbonate with sodium dimethyl malonate (4a) in the
presence of 5 mol % of (S)-1a at 20 °C in THF resulted in the
formation of the alkylated product (5a) in 96% yield with 80%
ee (Entry 1). Although complexes (S)-1b and (S)-1c also showed
high catalytic activity with excellent enantioselectivity to give
5a (Entries 2 and 3), the absolute configuration of the product
5a was opposite that obtained by (S)-1a, as noted above for the
amination. The tether dramatically affects not only the enantio-
selectivity of the product but also the reactivity of the catalyst.
Thus, the reaction with (S)-1d afforded 5a in 14% yield with
10% ee (Entry 4), while complex (S)-1g hardly catalyzed the
allylic alkylation at all (Entry 7). In contrast to amination, the
substituents on the aromatic rings on the anchor phosphine had
little influence on the enantioselectivity in alkylation (Entries 5
and 6). When sodium diethyl malonate (4b) was used as a
Acknowledgment. This work was supported in part by Grant-in-Aid
for Scientific Research from the Ministry of Education, Science, Sports
and Culture, Japan. The author (Y.M.) gratefully acknowledges a JSPS
Fellowship for Japan Junior Scientists. We thank the technical staff at
The Material Analysis Center, ISIR, Osaka University, for their assistance
with spectral measurements and elemental analysis.
Supporting Information Available: Experimental details, spectro-
scopic data for complexes 1d-1f, and characterization of 1,3-diphenyl-
2-propenyl-di-n-propylamine (4) (PDF). This material is available free
of charge via the Internet at http://pubs.acs.org.
(14) Hiraki, K.; Matsunaga, T.; Kawano, H. Organometallics 1994, 13,
1878.
(15) Hayashi, T.; Yamamoto, A.; Hagihara, T.; Ito, Y. Tetrahedron Lett.
1986, 27, 191.
(16) Vyskocˇil, Sˇ.; Smrcˇina, M.; Hanusˇ, V.; Pola´sˇek, M.; Kocovsˇky´, P. J.
Org. Chem. 1998, 63, 7738.
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