Heteroaromatic diphosphines as chiral ligands

Details Heteroaromatic diphosphines as chiral ligands Heteroaromatic diphosphines as chiral ligands

1996-12-23

1999-05-25

Geist, Gary

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

Organic compounds

Heterocyclic carbon compounds containing a hetero ring...

549 7, C07D33300, C07D27502

Patent

active

059070455

DESCRIPTION:

BRIEF SUMMARY
Object of the present invention are chiral diphosphines, complexes between said diphosphines and transition metals, and their utilization as chiral catalysts in stereoselective (sterocontrolled) reactions, such as, for instance, diastereo- and enantioselective reduction reactions in general, or asymmetric isomerization in general.
Another object of the present invention is a process for the preparation of said chiral diphosphines, as well as a process for the preparation of said chiral complexes and their utilization as catalysts in diastereo- and enantioselective reactions.
Further another object of the present invention are stereoselective processes, in particular diastereo- and enantioselective reductions in general, which utilize said chiral catalysts.


PRIOR ART

As is known, stereoselective reactions, in particular the reactions of sterocontrolled reduction, such as, for instance, diastereo- and enatioselective hydrogenations, are of great importance and have been studied for a long time; in fact, such reactions lead directly to the formation of optically active compounds which would be obtainable otherwise only as racemates, with the ensuing need of a subsequent separation of the enantiomers and the related drawbacks which sometimes are found in performing such separation, with the associated high probability of failing to obtain the pure enantiomeric forms; besides, in these cases a further drawback may arise from the presence of an unwished enantiomer, which must be reconverted or disposed of.
In general, the sterocontrolled reduction reactions realized by means of chiral calalysts allow to obtain the optically active reaction products, often also with good enantiomeric excesses.
For instance, the first enantioselective hydrogenation reaction of unsaturated compounds was carried out through the utilization of metal catalysts deposited on chiral supports and goes back to the thirties. Afterwards, homogeneous asymmetric hydrogenation reactions have been studied and described that had been realized by means of special chiral catalysts, constituted by complexes between transition metals and chiral phosphines which act as ligands towards the metal.
The literature reports on different types of chiral phosphines which can act as ligands and form chiral complexes with transition metals, such as, for instance, Ruthenium (Ru), Rhodium (Rh), Palladium (Pd), Iridium (Ir) and Platinum (Pt). In particular, chiral phosphines are characterized by one or two stereogenic atoms of phosphorus, which will have, in this case, three different substituents, such as, for instance, DIPAMP which (R,R) enantiomer has the following formula: ##STR1## D. et al., J. Am. Chem. Soc. 99, 5946(1977)!; phosphines are also described whose chirality is due to the presence of carbon-based stereocentres, such as for instance the compound known as CHIRAPHOS, which (S,S) enantiomer has the following formula: ##STR2## are reported whose chirality is due to the presence of an atropisomeric biaryl system, i.e. a system in which the rotation around the simple bond connecting two aryl groups is prevented. For example, WO 92/16536 discloses new racemic and optically active diphosphines, or chiral diphosphines, having a biphenyl structure. Said chiral phosphines are described as ligands in the preparation of complexes with group VIII metals, which complexes are useful as catalysts for asymmetrical hydrogenations and for enantioselective hydrogen shifts in prochiral allylic systems. The chirality of the described phosphines is due to the presence of the biphenyl structure which also renders the corresponding complexes suitable for being used as chiral catalysts.
EP 643065 also discloses a new diphosphine useful as catalyst for asymmetrical hydrogenations; the disclosed diphosphine is characterized by the presence of a biphenyl structure which is responsable for the chirality of the system.
Other diphosphines of this type are for instance BINAP, BIPHEMP or BICHEP, which (R) enantiomers have the following formulae: ##STR3## Helv. Chim. Acta 71, 897

REFERENCES:
Benincori, J. Chem Soc., Chem Comm, Diphenylphosphino-biheteroaryls issue 6, pp. 685-686, 1995.
Benincori, J Org Chem, "New Class of Chiral Diphophine Ligands for Highly Efficient Transition Metal-Catalyzed Stereoselective Reactions", 61, pp. 6244-6251, 1996.
Chemical Abstracts, vol. 089, No. 5, Jul. 31 1978, Columbus, Ohio.

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