Organic compounds -- part of the class 532-570 series – Organic compounds – Heavy metal containing
Reexamination Certificate
2000-01-28
2001-02-27
Vollano, Jean F. (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Heavy metal containing
C568S017000, C502S166000
Reexamination Certificate
active
06194593
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a 1,2-bis(dialkylphosphino) benzene derivative having an optical activity which is suitably useful as a ligand for an asymmetric catalyst for use in asymmetrical hydrogenation, and also to a process for producing such a benzene derivative. Further, the invention relates to a rhodium metal complex containing, as a ligand, such an optically active 1,2-bis-(dialkylphosphino) benzene derivative which is suitable as an asymmetric catalyst for use in asymmetrical hydrogenation.
The development of new chiral phosphine ligands has given a great impetus to studies on asymmetric syntheses using metal catalysts so that these studies have become rapidly progressive over the last 30 years. Most of these ligands are configured so as to have a center of asymmetry on a carbon skeleton, a phosphorus atom bonded to that skeleton and two aryl groups situated on this atom. Meanwhile, little has been studied regarding P-chiral phosphine ligands structured to have dialkyl and trialkyl groups attached thereto. This is due to the fact that the latter ligands are difficult to synthesize.
Recently, the present inventors have proposed a 1,2-bis-(akylmethylphosphino) ethane having a P-chiral trialkyl group and represented by the following general formula (3):
(where R denotes a cyclopentyl, cyclohexyl, tert-butyl, 1,1-diethylpropyl group or 1-adamantile) (J. Am. Chem. Soc., 120, 1635-1636, 1998). The ethane compound noted here permits a variety of &agr;, &bgr;-unsaturated &agr;-amino acids and their esters to be asymmetrically hydrogenated with high efficiency.
Nevertheless there still remains a demand for the development of other phosphine ligands which are optically active and particularly suitable as a ligand for use in an asymmetric catalyst in asymmetrical hydrogenation.
Accordingly, principal objects of the present invention are to provide a 1,2-bis(dialkylphosphino) benzene derivative possessing an optical activity and which is suitably useful as a ligand for an asymmetric catalyst in asymmetrical hydrogenation, a process for producing such a benzene derivative, and a rhodium metal complex containing, as a ligand, such a benzene derivative which is applicable as an asymmetric catalyst in asymmetrical hydrogenation.
SUMMARY OF THE INVENTION
As a result of the present inventors' intensive research conducted with the foregoing situation in mind, the present invention has been completed. More specifically, the invention provides a 1,2-bis(dialkylphosphino) benzene derivative having an optical activity represented by the following general formula (1):
(where R
1
denotes a straight or branched alkyl group having 2-6 carbon atoms, and each of the asterisks denotes an asymmetric phosphorus atom).
The invention also provides a process for the production of the above-specified 1,2-bis(dialkylphosphino) benzene derivative having an optical activity, which comprises: optically resolving a 1,2-bis(dialkylphosphinoyl) benzene compound by the use of benzoyl tartrate in optically active form, the benzene compound being represented by the following general formula (2):
(where R
1
is the same as defined above); and subsequently reducing the benzene compound, thus made optically active, with a reducing agent.
In addition, the invention provides a rhodium metal complex containing as a ligand the 1,2-bis(dialkylphosphino) benzene derivative having an optical activity represented by the above general formula (1).
DETAILED DESCRIPTION OF THE INVENTION
The substituting group R
1
in the formula (1) expressing the 1,2-bis(dialkylphosphino) benzene derivative of the present invention denotes a straight or branched alkyl group having 2-6 carbon atoms. Specific examples of the alkyl group include ethyl, isopropyl, n-propyl, isobutyl, n-butyl, sec-butyl, tert-butyl, isoheptyl, n-heptyl, isohexyl, n-hexyl, cyclopentyl, cyclohexyl and like groups.
The 1,2-bis(dialkyl-phosphino) benzene derivative of the formula (1) is exemplified by (R,R)-1,2-bis(ethylmethylphosphino) benzene, (S,S)-1,2-bis-(ethylmethylphosphino) benzene, (R,R)-1,2-bis(iso-propylmethyl-phosphino) benzene, (S,S)-1,2-bis(isopropyl-methyl-phosphino) benzene, (R,R)-1,2-bis(n-propylmethylphosphino)-benzene, (S,S)-1,2-bis(n-propylmethylphosphino) benzene, (R,R)-1,2-bis-(isobutylmethylphosphino) benzene, (S,S)-1,2-bis(isobutyl-methyl-phosphino) benzene, (R,R)-1,2-bis(n-butylmethyl-phosphino) benzene, (S,S)-1,2-bis(n-butylmethylphosphino) benzene, (R,R)-1,2-bis(sec-butylmethylphosphino) benzene, (S,S)-1,2-bis(sec-butylmethyl-phosphino) benzene, (R,R)-1,2-bis(tert-butylmethyl-phosphino) benzene, (S,S)-1,2-bis(tert-butylmethylphosphino) benzene, (R,R)-1,2-bis-iso-heptylmethyl-phosphino) benzene, (S,S)-1,2-bis(isoheptylmethyl-phosphino) benzene, (R,R)-1,2-bis(n-heptylmethylphosphino) benzene, (S,S)-1,2-bis(n-heptylmethyl-phosphino) benzene, (R,R)-1,2-bis-(isohexylmethylphosphino) benzene, (S,S)-1,2-bis(isohexyl-methyl-phosphino) benzene, (R,R)-1,2-bis(n-hexylmethyl-phosphino) benzene, (S,S)-1,2-bis(n-hexylmethylphosphino) benzene, (R,R)-1,2-bis(cyclo-pentylmethyl-phosphino) benzene, (S,S)-1,2-bis(cyclopentylmethyl-phosphino) benzene, (R,R)-1,2-bis(cyclohexylmethylphosphino) benzene, (S,S)-1,2-bis(cyclo-hexylmethylphosphino) benzene and the like.
The process of the present invention is described below.
According to the invention, the process for the production of the 1,2-bis(dialkylphosphino) benzene derivative of an optically active nature expressed by the formula (1) is constituted, for example, by a first step in which a 1,2-bis-(dialkylphosphinoyl) benzene compound of the formula (2) is subjected to optical resolution in the presence of optically active benzoyl tartrate so as to prepare a 1,2-bis(dialkyl-phosphinoyl) benzene of an optically active nature, and a second step in which the 1,2-bis-(dialkyl-phosphinoyl) benzene, thus made optically active, is then reduced with a reducing agent, thereby yielding the desired compound, i.e., the 1,2-bis(dialkyl-phosphino) benzene derivative expressed by the formula (1).
(First Step)
In the first step, the substituting group R
1
in the formula (2) expressing the 1,2-bis(dialkylphosphinoyl) benzene for use as a starting material is equivalent to the substituting group R
1
in the formula (1) expressing the desired compound, namely the 1,2-bis(dialkylphosphino) benzene derivative. The 1,2-bis- dialkyl-phosphinoyl) benzene of the formula (2) may be prepared in a conventional manner. For example, the starting material is easily obtainable in accordance with the following reaction formula (I):
Reaction Formula (I)
(where R
1
is the same as defined above).
To be more specific, 1,2-bis(phosphino) benzene (the compound (4) in the above reaction formula) is methylated at a temperature of −78° C. to room temperature and with use of solvents such as n-butylithium and methyl iodide so as to prepare 1,2-bis(methyl-phosphino) benzene (the compound (5)). Into a reactor are thereafter introduced the compound (5), ethyl ether and n-butyl-lithium, and reaction is carried out with gradual dropping of an alkyl bromide for several hours at a temperature of −10 to 0° C. to thereby obtain a 1,2-bis(alkylmethylphosphino) benzene (of the formula (6) in the above reaction formula). Next, the compound of the formula (6) is dissolved in methanol, followed by reaction with hydrogen peroxide for several hours at a temperature of 0° C. to provide a 1,2-bis-(alkylmethylphosphinoyl) benzene in racemic arrangement, that is, as a combination of a rac form of the formula (7) and a meso form of the formula (8). For convenience, the formulas (7) and (8) are consolidated herein as the general formula (2).
In order to effect optical resolution of the 1,2-bis(dialkyl-phosphinoyl) benzene of the formula (2), benzoyl tartrate in optically active form is used as a resolving agent. Here, both a (−) form and a (+) form of benzoyl tartrate are acceptable. The amount of the benzoyl tartrate to be used is usually in the range of 0.5-1.2 times per mol, preferably approximately 1.0 time p
Imamoto Tsuneo
Miura Tomoya
Yamada Hironari
Armstrong, Westerman Hattori, McLeland & Naughton
Nippon Chemical Industrial Co. Ltd.
Vollano Jean F.
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