Catalytic reduction of ketones and aldehydes using...

Details Catalytic reduction of ketones and aldehydes using... Catalytic reduction of ketones and aldehydes using...

2001-06-20

2002-10-08

Shippen, Michael L. (Department: 1621)

Organic compounds -- part of the class 532-570 series

Organic compounds

Heterocyclic carbon compounds containing a hetero ring...

C549S273000, C560S186000, C568S814000, C568S821000, C568S832000, C568S835000, C568S881000, C585S357000, C585S469000, C585S733000

Reexamination Certificate

active

06462206

ABSTRACT:

FIELD OF INVENTION
This invention relates to a method of reducing ketones and aldehydes to the corresponding alcohol or alkyl group, using H2 gas as the stoichiometric reductant, and organometallic ruthenium complexes as the catalysts.
BACKGROUND
The homogeneous catalyzed reduction of ketones and aldehydes to various products is an important synthetic reaction in industry. Ruthenium complexes are well known catalysts for the reduction of ketones and aldehydes to various end products. Often phosphorus-containing ligands are used to complex the ruthenium (U.S. Pat. No. 5,614,641, U.S. Pat. No. 4,418,227, and Ohkuma, et al.,
J. Amer. Chem. Soc
., 1998, 120, 1086). Typically, phosphorus-containing ligands are expensive, difficult to make and handle, and sensitive to oxygen.
Chinn, et al, (
Organometallics
1989, 8, 1824-1826) described the synthesis and spectroscopic properties of the unstable dihydrogen complex [Cp*Ru(CO)
2
(H
2
)]
+
which was found to decompose to {[Cp*Ru(CO)
2
]
2
(&mgr;-H)}
+
OTf
−
, where Cp* indicates a &eegr;
5
-C
5
Me
5
group. The dihydrogen complex is synthesized under mild conditions, has no need for oxygen sensitive ligands (e.g., triaryl phosphines, trialkyl phosphines) or nitrogen-based ligands, and is tolerant to acid and water. However, no mention is made of the catalytic activity of any of these complexes.
SUMMARY OF THE INVENTION
The invention is directed to a process for the reduction of a ketone or aldehyde, comprising contacting a compound of the formula R
1
—C(═O)—R
2
with hydrogen in the presence of a catalytically effective amount of a catalyst precursor having the formula {[CpM(CO)
2
]
2
(&mgr;-H)}
+
Q
−
, wherein M is selected from the group consisting of Ru and Fe, R
1
is selected from the group consisting of hydrogen, substituted and unsubstituted alkyl and aryl groups, R
2
is selected from the group consisting of substituted and unsubstituted alkyl and aryl groups; Cp is &eegr;
5
-C
5
R
5
wherein R is selected from the group consisting of hydrogen, substituted and unsubstituted C
1
-C
18
alkyl and aryl groups; and Q
−
is a non-coordinating or weakly coordinating non-reactive anion. R
1
and R
2
may form a ring together.
Preferably, M is Ru, Q
−
is OSO
2
CF
3
−
, R is selected from the group consisting of hydrogen and methyl, and the compound of the formula R
1
—C(═O)—R
2
is selected from the group consisting of cyclooctanone, levulinic acid, levulinic acid methyl ester, benzylacetone, 3-heptanone, 4-methoxy-acetoacetate, 3-pentanone and propanal.
Also preferably R
1
is selected from the group consisting of hydrogen and substituted and unsubstituted alkyl groups, R
2
is selected from the groups consisting of substituted and unsubstituted alkyl groups, and the reduction product is an alcohol.
In the case where R
1
and R
2
have not formed a ring, the process can further comprise the cyclizing of the alcohol to form the corresponding lactone.
The invention is further directed to a process to reduce a ketone or aldehyde to form a compound of the formula R
1
—CH
2
—R
2
, comprising contacting a compound of the formula R
1
—C(═O)—R
2
with hydrogen in the presence of a catalytically effective amount of a complex having the formula {[CpRu(CO)
2
]
2
(&mgr;-H)}
+
Q
−
, wherein R
1
is selected from the group consisting of hydrogen, substituted and unsubstituted alkyl and aryl groups; R
2
is selected from the group consisting of unsubstituted and substituted aryl groups, Cp is &eegr;
5
-C
5
R
5
wherein R is selected from the group consisting of hydrogen, and unsubstituted and substituted C
1
-C
18
alkyl and aryl groups; and Q
−
is a non-coordinating or weakly coordinating non-reactive anion. R
1
and R
2
may form a ring together.
Preferably Q
−
is OSO
2
CF
3
−
and R is selected from the group consisting of hydrogen and methyl, and the compound of formula R
1
—C(═O)—R
2
is selected from the group consisting of 1-acetonaphthalene and acetophenone.
DETAILED DESCRIPTION OF THE INVENTION
In the present description, “alkyl” means an alkyl group containing up to 18 carbon atoms. Common examples of such alkyl groups include methyl, ethyl, propyl, isopropyl, butyl, s-butyl, isobutyl, pentyl, neopentyl, hexyl, heptyl, isoheptyl, 2-ethylhexyl, cyclohexyl and octyl. The alkyl group may be linear, branched, or cyclic.
By “substituted” is meant the addition of one or more substituent groups to a compound or functional group. Said substituent groups do not cause the compound to be unstable or unsuitable for use in an intended reaction, and are inert under reaction conditions. Substituent groups which are generally useful include nitrile, ether, ester, halo, amino (including primary, secondary and tertiary amino), hydroxy, oxo, vinylidene or substituted vinylidene, carboxyl, silyl or substituted silyl, nitro, sulfinyl, and thioether. Highly basic substituents are generally not suitable in the process of present invention unless previously protonated with acid or protected by a suitable protecting group.
By “aryl” is meant an aromatic carbocyclic group having a single ring (e.g., phenyl), multiple rings (e.g., biphenyl), or multiple condensed rings in which at least one is aromatic, (e.g., 1,2,3,4-tetrahydronaphthyl, naphthyl, anthryl, or phenanthryl), which may be mono-, di-, or trisubstituted with halogen, lower alkyl, lower alkoxy, lower alkylthio, trifluoromethyl, lower acyloxy, aryl, heteroaryl, or hydroxy groups. By “aryl” is also meant heteroaryl groups where heteroaryl is defined as 5-, 6-, or 7-membered aromatic ring systems having at least one heteroatom selected from the group consisting of nitrogen, oxygen and sulfur. Examples of heteroaryl groups are pyridyl, pyrimidinyl, pyrrolyl, pyrazolyl, pyrazinyl, pyridazinyl, oxazolyl, furanyl, quinolinyl, isoquinolinyl, thiazolyl, and thienyl. Said heteroaryl groups may contain substituent groups including halogen, lower alkyl, lower alkoxy, lower alkylthio, trifluoromethyl, lower acyloxy, aryl, heteroaryl, and hydroxy.
The following definitions are used herein:
Ar′=3,5-bis(trifluoromethyl)phenyl
Cp*=&eegr;
5
-C
5
Me
5
HOTf=CF
3
SO
3
H
OTf
−
=OSO
2
CF
3
−
OTf=OSO
2
CF
3
The present invention provides a process to prepare an alcohol via the hydrogenation of a ketone or aldehyde by contacting a compound of the formula R
1
—C(═O)—R
2
with hydrogen in the presence of a catalytically effective amount of a catalyst precursor, to form an alcohol, wherein R
1
is selected from the group consisting of hydrogen, substituted and unsubstituted alkyl and aryl groups; R
2
is selected from the group consisting of substituted and unsubstituted alkyl and aryl groups; and R
1
and R
2
may form a ring together. The catalyst precursor is of the formula {[CpM(CO)
2
]
2
(&mgr;-H)}
+
Q
−
where Q
−
is a non-coordinating or weakly coordinating non-reactive anion, M is selected from the group consisting of Fe and Ru, and Cp is &eegr;
5
-C
5
R
5
wherein R is selected from the group consisting of hydrogen and substituted and unsubstituted C
1
-C
18
alkyl and aryl groups. Preferably Q
−
is OSO
2
CF
3
−
, R is hydrogen or methyl and M is Ru.
Preferred compounds of formula R
1
—C(═O)—R
2
include cyclooctanone, levulinic acid, levuliniic acid methyl ester, benzylacetone, 3-heptanone, 4-methoxyacetoacetate, 3-pentanone, and propanal.
By “alcohol” is meant a compound containing an alcohol functionality. By “ketone” it is meant a compound containing a ketone functionality. By “aldehyde” it is meant a compound containing an aldehyde functionality.
The invention also provides a process to cyclize the alcohol to form a corresponding lactone. This may occur spontaneously under the reaction conditions when the keto group of an ester or carboxylic acid is in the &ggr;, &dgr; or higher position relative to the carbonyl group of the reacting alde

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