Asymmetric transfer hydrogenation of ketones catalyzed by rhodium and iridium complexes with chiral bidentate Schiff's bases

Article abstract of DOI:10.1023/A:1011393702787

Rhodium and iridium complexes of Schiff's bases derived from (1R,2R)-and (1S,2S)-diaminocyclohexane catalyze asymmetric transfer hydrogenation of alkyl aryl ketones in PrⁱOH at room temperature to give chiral secondary alcohols (up to 65% ee).

Full text of DOI:10.1023/A:1011393702787

7
34
Russian Chemical Bulletin, International Edition, Vol. 50, No. 4, pp. 734—735, April, 2001
Asymmetric transfer hydrogenation of ketones catalyzed by
rhodium and iridium complexes with chiral bidentate Schiff 's bases
a
a«
a
a
V. A. Pavlov, M. G. Vinogradov,
a
E. V. Starodubtseva, G. V. Chel´tsova,
b
a
V. A. Ferapontov, O. R. Malyshev, and G. L. Heise
aN. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences,
4
7 Leninsky prosp., 119992 Moscow, Russian Federation.
Fax: +7 (095) 135 5328. E-mail: ving@cacr.ioc.ac.ru
bCambrex Corporation,
One Meadowlands Plaza, East Rutherford, NJ 07073, USA
Rhodium and iridium complexes of Schiff´s bases derived from (1R,2R)- and (1S,2S)-di-
i
aminocyclohexane catalyze asymmetric transfer hydrogenation of alkyl aryl ketones in Pr OH
at room temperature to give chiral secondary alcohols (up to 65% ee).
Key words: asymmetric hydrogenation of ketones, hydrogen transfer, catalysis, rhodium
complexes, iridium complexes, chiral Schiff´s bases, (1R,2R)- and (1S,2S)-diaminocyclohexane
derivatives.
i
Considerable progress has been recently achieved in
lysts in the hydrogenation of ketones 3 in Pr OH (Table 1)
is moderate but much higher than that of Ru catalysts,
for the latter it did not exceed 40% ee.9 The maximum
yield and the highest level of asymmetric induction in
the reduction of most of the ketones studied was pro-
vided by the Ir/1b system (see Table 1).
asymmetric transfer hydrogenation catalyzed by com-
i
plexes of transition metals (Rh, Ir, and Ru) in Pr OH or
in a mixture of HCOOH with Et N.1 Chiral bidentate
3
ligands such as 1,2-diamines, their N-acetyl derivatives,
and bisoxazolines are successively used in the prepara-
tion of catalysts for the reactions of this type.2
—8
How-
ever, the use of complexes with bidentate Schiff´s bases
for this purpose is scarcely reported in the literature and
only in a ruthenium-catalyzed reaction.9
Scheme 1
OH
The goal of this paper is to present the results of
[
M(COD)Cl] /1
2
i
asymmetric hydrogenation of ketones in Pr OH in the
Ar
Alk
presence of rhodium and iridium complexes with Schiff´s
bases, namely, (1R,2R)- and (1S,2S)-diaminocyclo-
hexane derivatives. The catalysts were prepared in situ by
the reaction of [M(COD)Cl]2 (M = Rh and Ir, and
COD is cycloocta-1,5-diene) with ligands 1 or 2.
O
i
(R)-4a—f
PrOH
Ar
Alk
KOH
OH
3a—f
[
M(COD)Cl] /2
2
Ar
Alk
(S)-4a—f
M = Rh, Ir
3
, 4
a
b
c
d
e
f
N
N
N
N
Ar
Alk
Ph Ph
Me Et
Ph
Pri
1-Naphthyl
Me
2-Naphthyl
Me
2-Fluorenyl
Me
Ar
Ar
Ar
Ar
(S,S)-1a—c
(R,R)-2a
Experimental
Ar = Ph (a), 2-MeOC H (b), 1-naphthyl (c)
6
4
Polarimetric measurements were carried out on a JASCO
Results and Discussion
DIP-360 instrument in 1-cm cells.
Commercial alkyl aryl ketones 3, (1S,2S)-diamino-
cyclohexane and its enantiomer (Aldrich), and [Rh(COD)Cl]2
and [Ir(COD)Cl]2 (Fluka) were used in the syntheses.
The stereochemistry of this reaction is shown in
Scheme 1. It is of note that the reaction catalyzed by
analogous ruthenium complexes yields the same stereoi-
somer, i.e., (S)-4 in the presence of ligands (R,R)-2.9
Enantioselectivities of the Rh- and Ir-containing cata-
(
1S,2S)-N,N´-Dibenzylidene-1,2-diaminocyclohexane (1a).
A solution of (1S,2S)-1,2-diaminocyclohexane (5.5 g, 50 mmol)
and benzaldehyde (11 g, 140 mmol) in anhydrous benzene
(250 mL) was refluxed with a Dean—Stark trap for 3 h.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 704—705, April, 2001.
066-5285/01/5004-734 $25.00 © 2001 Plenum Publishing Corporation
1

Asymmetric transfer hydrogenation of ketones
Russ.Chem.Bull., Int.Ed., Vol. 50, No. 4, April, 2001
735
Table 1. Yield (Y ) and enantiomeric excess (ee) of secondary alcohols 4 (%) in the asymmetric transfer hydrogenation of ketones
3
a—f in the presence of [M(COD)Cl] /1 and [M(COD)Cl] /2 as catalysts
2 2
M
Schiff´s
base
4a
4b
4c
4d
4e
4f
Y
ee
Y
ee
Y
ee
Y
ee
Y
ee
Y
ee
Rh
Rh
Rh
Rh
Ir
1a
2a
1b
1c
2a
1b
43
46
51
19
88
91
45 (R)
48 (S)
36 (R)
44 (R)
41 (S)
55 (R)
55
60
55
34
84
86
43 (R)
46 (S)
26 (R)
40 (R)
43 (S)
51 (R)
—
46
20
—
30
—
—
60
60
44
40
68
90
34 (R)
32 (S)
28 (R)
31 (R)
34 (S)
59 (R)
73
60
43
44
65
74
35 (R)
35 (S)
42 (R)
35 (R)
48 (S)
48 (R)
70
64
34
69
85
88
60 (R)
65 (S)
43 (R)
50 (R)
50 (S)
61 (R)
46 (S)
40 (R)
—
32 (S)
—
Ir
Benzene was evaporated, and the solid residue was suspended in
hexane, filtered off, and washed with hexane to decolorization.
The product was recrystallized from hexane (100 mL). The
white crystals were dried at 70 °Ñ in vacuo (1—2 Torr) to give
This work was financially supported by the Cam-
brex Co.
2
0
compound 1à, yield 8.5 g (61%), m.p. 98—99 °Ñ, [α]D +205
References
(
c 1, CHCl ).
3
Ligands 2a, 1b, and 1c were prepared in a similar manner.
1
2
. R. Noyori and S. Hashiguchi, Acc. Chem. Res., 1997, 30, 97.
. P. Gamez, F. Fache, P. Mangeney, and M. Lemaire,
Tetrahedron Lett., 1993, 34, 6897.
. K. Puntener, L. Schwink, and P. Knochel, Tetrahedron
Lett., 1996, 37, 8165.
(
1R,2R)-N,N´-Dibenzylidene-1,2-diaminocyclohexane (2a).
Yield 63%, m.p. 98—99 °Ñ (cf. Ref. 9: m.p. 99—100 °Ñ),
2
0
[
α]D –208 (c 1, CHCl ).
3
3
(
1S,2S)-N,N´-Bis(2-methoxybenzylidene)-1,2-diamino-
2
0
cyclohexane (1b). Yield 56%, m.p. 102—104 °Ñ, [α]D +68.4
c 0.5, MeOH) (cf. Ref. 9: m.p. 105—106 °C, [α]D –69.2
c 0.5, MeOH) for the (1R, 2R)-enantiomer).
2
5
4. S. Inoue, K. Nomura, S. Hashiguchi, R. Noyori, and
(
(
Y. Izawa, Chem. Lett., 1997, 957.
. P. Gamez, B. Dunjic, and M. Lemaire, J. Org. Chem., 1996,
61, 5196.
5
(
1S,2S)-N,N´-Bis(1-naphthylmethylidene)-1,2-diamino-
cyclohexane (1c). Yield 80%, m.p. 130—133 °Ñ, [α]D20 +233.5
2
5
6. A. Fujii, S. Hashiguchi, N. Uematsu, T. Ikariya, and
R. Noyori, J. Am. Chem. Soc., 1996, 118, 2521.
7. K. Mashita, T. Abe, and K. Tani, Chem. Lett., 1998,
1199; 1201.
(
(
c 0.25, CH Cl ) (cf. Ref. 9: m.p. 131—132 °C, [α]
D
–202
2
2
c 0.25, CH Cl ) for the (1R, 2R)-enantiomer).
2
2
The 1H NMR spectra of the ligands obtained coincide with
the published ones.9
Asymmetric transfer hydrogenation of ketones 3 (general
8
. D. Muller, G. Umbricht, B. Weber, and A. Pfaltz, Helv.
Chim. Acta, 1991, 74, 232.
. P. Krasik and H. Alper, Tetrahedron, 1994, 50, 4347.
procedure). A mixture of [M(COD)Cl]2 (M = Rh or Ir)
28.4 µmol) and a chiral ligand (62.5 µmol) was placed in a
9
(
1
0. M. G. Vinogradov, L. S. Gorshkova, V. A. Pavlov, O. V.
Mikhalev, G. V. Chel´tsova, I. V. Razmanov, V. A.
Ferapontov, O. R. Malyshev, and G. L. Heise, Izv. Akad.
Nauk, Ser. Khim., 2000, 459 [Russ. Chem. Bull., Int. Ed.,
2000, 49, 460].
flask equipped with a magnetic stirrer in an atmosphere of Ar. A
i
solution of KOH (0.196 mmol) in Pr OH (10 mL) was added
through a silicone septum by a syringe. The reaction mixture
was stirred for 1 h, and a solution of ketone 3 (0.625 mmol) in
Pr OH (10 mL) was added in the same manner. The resulting
i
solution was stirred at ∼ 20 °C for five days, neutralized with
HCl, passed through a 2-cm layer of activated carbon, and
analyzed by GLC or HPLC. For the detailed conditions of
chromatographic analyzes, see Ref. 10.
Received May 15, 2000;
in revised form December 22, 2000