J . Org. Chem. 1998, 63, 9425-9426
9425
Hyd r ogen a tion of th e Ca r bon yl Gr ou p in r-Ketoester s a n d
r-Ketoa m id es Ca ta lyzed by Ru th en iu m Cla y
Raluca Aldea and Howard Alper*
Department of Chemistry, University of Ottawa 10 Marie Curie, Ottawa, Ontario, Canada, K1N 6N5
Received J uly 23, 1998
Ruthenium clay, prepared by reaction of RuCl
3
2
‚H O with the 3-phosphinopropyl ligand anchored
on Fluka K10 montmorillonite, is an effective catalyst for the reduction of the R-carbonyl group of
R-ketoesters and R-ketoamides (50-89% yield).
In tr od u ction
catalyst can be chirally modified with cinchona alkaloids
or other simple nitrogen-containing compounds, and this
allows the synthesis of the R-hydroxyesters and R-hy-
droxyamides with enantiomeric excess values of up to
Early work on the homogeneous catalytic hydrogena-
tion of carbonyl compounds involved mainly rhodium-
1
phosphine complexes. Cationic rhodium complexes
4% and 60%, respectively.7
8
+
+
-
[RhH
2
L
2
S
2
] ClO
4
j or [RhH
2
L
2
S
2
] PF
6
(S ) solvent, L )
phosphine ligand) were found to be effective for the
reduction of simple ketones.2 The first homogeneous
asymmetric catalytic hydrogenation of ketones was per-
formed in the presence of a rhodium complex with (R)-
Resu lts a n d Discu ssion
Previous studies in our laboratory showed that the
heterogeneous system consisting of ruthenium anchored
on several clays is a useful catalyst for the selective
reduction of the carbon-carbon double bond of unsatur-
ated esters, sulfones, and vinyl oxiranes.8 We now wish
to report that ruthenium clay is an effective catalyst for
the reduction of the carbonyl group of R-ketoesters and
R-ketoamides.
(
+)-benzylmethylphenylphosphine as a ligand. Rhodium
phosphine systems with a neutral phosphine ligand
BPPM, CyDIOP) were found to be effective for the
(
3
4
reduction of R-ketocarboxylic esters, R-ketoamides, and
ketopantolactone.5
Ruthenium complexes have been used for the hydro-
genation of olefins, and recently ruthenium-based com-
plexes were found to be highly selective for the hydro-
genation of carbonyl compounds (aromatic ketones,
â-ketoesters, R-diketones, R-aminoketones, R,â-acetylenic
ketones) in homogeneous catalysis.6 For heterogeneous
hydrogenation, which is still a very convenient synthetic
method both on a micro and macro scale, the most
popular catalysts are based on platinum, palladium, and
nickel.1
Ruthenium clay was prepared by a three-step pro-
cess: reaction of Fluka K10 montmorillonite with (3-
chloropropyl)trimethoxysilane, followed by treatment
8
with KPPh
2
, and then by reaction with RuCl
3
‚H
2
O. The
ruthenium content varies from 0.13 to 0.17 mmol Ru/g
clay for different batches of catalyst (determined by
atomic absorption or ICP analysis). The reaction of
R-ketoesters with hydrogen in the presence of Ru clay
2
proceeded at 500 or 600 psi H and 75 °C, affording the
The reduction of R-ketoesters and R-ketoamides has
attracted considerable attention in recent years.7 The
catalytic hydrogenation of R-ketoacids and R-ketoamides
corresponding hydroxyesters in 60-100% conversion and
80-89% isolated yields (eq 1). For methyl pyruvate, an
were carried out using Pt/Al
2
O
3
,7
, PtO
2
, Pd/C, Pd/CaCO
, or Raney nickel.1 A platinum-supported
4
3
,
Pd/BaSO
(
1) Harada, K.; Munguni, T. In Comprehensive Organic Synthesis;
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970, 567.
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977, 428.
4) (a) Tani, K.; Suwa, K.; Tanigawa, E.; Yoshida, Y.; Okano, T.;
(
1
1
(
increase in hydrogen pressure from 500 to 600 psi results
in complete conversion of the starting material to the
hydroxyester (Table 1, entries 1, 2). The keto group
connected to a longer alkyl chain, like in ethyl 3-methyl-
(
Otsuka, S. Chem. Lett. 1982, 261. (b) Tani, K.; Tanigawa, E.; Tatsuno,
Y.; Otsuka, S. J . Organomet. Chem. 1985, 279, 87.
(
5) (a) Ojima, I.; Kogure, T.; Terasaki, T. J . Org. Chem. 1978, 43,
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Commun. 1984, 1641.
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3
2-oxobutyrate, can be reduced completely at 500 psi H
Table 1, entry 3). The reduction of substrates containing
2
(
(
M.; Welch, A. J . New J . Chem. 1997, 21, 1161. (b) Matsumura, K.;
Hashiguchi, S.; Ikariya, T.; Noyori, R. J . Am. Chem. Soc. 1997, 119,
(7) (a) Blaser, H.-U.; J alett, H.-P.; Garland, M.; Studer, M.; Thies,
8
738. (c) Ohta, T.; Tonomura, Y.; Nozaki, K.; Takaya, H. Organome-
H.; Wirthtijani, A. J . Catal. 1998, 173, 282. (b) Sch u¨ rch, M.; Schwalm,
O.; Mallat, T.; Weber, J .; Baiker, A. J . Catal. 1997, 169, 275 and
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dron: Asymmetry 1997, 8, 2133. (d) Blaser, H.-U.; J alett, H.-P.;
Spindler, F. J . Mol. Catal. 1996, 107, 85. (e) Niwa, S.; Imai, S.; Orito,
Y. Nippon Kagaku Kaishi 1982, 137 (Chem. Abstr. 1982, 96, 68117f).
(f) Orito, Y.; Imai, S.; Niwa, S. Nippon Kagaku Kaishi 1980, 670 (Chem.
Abstr. 1980, 93, 113912n).
tallics 1996, 15, 1521. (d) Fujii, A.; Hashiguchi, S.; Uematsu, N.;
Ikariya, T.; Noyori R. J . Am. Chem. Soc. 1996, 118, 2521. (e)
Hashiguchi, S.; Fujii, A.; Takehara, J .; Ikariya, T.; Noyori, R. J . Am.
Chem. Soc. 1995, 117, 7562. (f) Kitamura, M.; Ohkuma, T.; Inoue, S.;
Sayo, N.; Kumbayashi, H.; Akutagawa, S.; Ohta, T.; Takaya, H.;
Noyori, R. J . Am. Chem. Soc. 1988, 110, 629. (g) Ohta, T.; Takaya, H.;
Noyori, R. Inorg. Chem. 1988, 27, 566. (h) Noyori, R.; Ohkuma, T.;
Kitamura, M. J . Am. Chem. Soc. 1987, 109, 5856.
(8) Aldea, R.; Alper, H. J . Organomet. Chem. 1998, 551, 349.
1
0.1021/jo981447h CCC: $15.00 © 1998 American Chemical Society
Published on Web 11/12/1998