Ruthenium catalysts and their use in the asymmetric hydrogenatio

Details Ruthenium catalysts and their use in the asymmetric hydrogenatio Ruthenium catalysts and their use in the asymmetric hydrogenatio

1997-07-10

1999-02-23

Geist, Gary

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

Organic compounds

Carbohydrates or derivatives

556 21, 560121, 560122, C07F 1500, C07C 6974

Patent

active

058746005

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

The present invention relates to the field of asymmetric hydrogenation in homogeneous conditions and, more particularly, to the use of novel Ru(II) chiral catalysts for the asymmetric hydrogenation of cyclopentenone derivatives having the general formula ##STR1## wherein R.sup.1 represents a linear or branched C.sub.1 to C.sub.4 alkyl radical and R.sup.2 represents a saturated or unsaturated, linear or branched, C.sub.1 to C.sub.8 hydrocarbon radical.
The compounds of formula (II) are substrates the asymmetric and stereospecific hydrogenation of which had proved heretofore impossible as a result of their weak donor capability and of their hindered structure, and this in spite of all the progress in homogeneous catalysis achieved in recent years.


PRIOR ART

A great number of chiral catalysts useful for asymmetric hydrogenations is in fact known at present. In the context of the present invention, we can cite in particular the efforts of two research groups which actively studied the synthesis of Ru(II) chiral catalysts, obtained from the Ru(II) !(COD=cyclo-1,5-octadiene).
Thus, J.-P. Genet and his collaborators have published work related to represents a bidentate ligand of the type of those currently known under abbreviated designations such as DIOP, CHIRAPHOS, PROPHOS, BDPP, CBD, NORPHOS, DEGUPHOS, BPPM, BINAP, R-DuPHOS (R=methyl or ethyl), BIPHEMP or yet DIPAMP (see, for example, J.-P. Genet et al., Tetrahedron: Asymmetry 1991, 2, 43). Such catalysts were obtained by heating the above-mentioned Ru(II) complex together with the appropriate diphosphine ligand, in a solvent such as hexane or toluene, such as to replace the cyclooctadiene with the chiral phosphine.
Upon subsequent work (see, for example, WO 91/02588; J.-P. Genet, Acros Organics Acta, 1994, 1, 1-8; J.-P. Genet et al., Tetrahedron : Asymmetry, 1994, 5, 665-690), these authors described the transformation of such catalysts via protonation by means of aqueous acids such as HBr, HCl, HF or HBF.sub.4, in strongly coordinating solvents, capable of playing a role in stabilizing the coordination structure around the metal, which structure, according to the same authors, is of the hexacoordinate type. This kind of catalysts, which can be prepared in situ, proved to be useful for the asymmetric hydrogenation, in protic or strongly electron-donating solvents (methanol, ethanol, THF, or their mixtures with other solvents), of substrates comprising carbonyl groups and acyclic ethylenic bonds.
Other studies (see, for example, F. Heiser et al., Tetrahedron: Asymmetry, 1991, 2, 51-62; EP 643 052; EP 398 132; EP 570 674) have resulted in reports of the use of catalysts prepared in situ for hydrogenating a variety of substrates, starting from the same ruthenium complex, but following a process according to which a mixture of said complex and an appropriate diphosphine ligand is treated with namely CF.sub.3 COOH, once again in an electron-donor solvent able to stabilize the coordinating structure of the metal.
These catalysts, and others obtained according to similar processes described in the cited references, reveal themselves very efficient in the asymmetric hydrogenation of various substrates, often good electron-donor substrates capable of coordinating the Ru(II), and are typically used with protic solvents, or mixtures of protic and aprotic solvents. However, they proved to be inefficient with regard to the hydrogenation of substrates (II) cited above, when prepared according to the prior art methods and used under the reported conditions. In fact, substrates (II) are weak electron-donors, when compared to the type of substrates described in the prior art, and the many attempts carried out heretofore in an effort to asymmetrically hydrogenate them had always proved fruitless.
It should be pointed out that, among the formula (II) substrates, methyl 3-oxo-2-pentyl-1-cyclopentene-1-acetate is particularly interesting in the context of the invention, inasmuch as its asymmetric hydrogenation could potentially provide, in a single step, the o

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