Chiral aminophosphine ligands

New Chiral Aminophosphine Ligands Application to Catalytic Asymmetric C-C Bond Formation... 

Development of proline-derived chiral aminophosphine ligands for palladium-catalyzed asymmetric allylic alkylation 06Y628. 

A practical synthesis of new chiral aminophosphine ligands (37) based on the cam-phane scaffold bearing alkoxy groups has been accomplished. The application of these ligands in the Pd-catalysed allylic alkylation of ( )-l,3-diphenyl-2-propenyl acetate proceeded with excellent conversions and enantioselectivities of up to 91%. 

Although the vast majority of centrally chiral diphosphine ligands to be employed in enantioselective rhodium-catalyzed hydroborations possess -symmetry, there are a few examples of ( -symmetric diphosphine ligands. Buono prepared bis(aminophosphine) ligands 35-38,81 while Bianchini reported (R, i )-BDPBzP 39 (Figure 5).82... 

This Mulheim chemistry has been highlighted by the discovery of the highly enantioselective hydrovinylation of styrene to produce chiral 2-phenyl-1-butene in 95.2% ee for a 10 kg-scale reaction (Scheme 60) (132). The Ni catalyst is very reactive and contains the unique chiral dimeric aminophosphine ligand derived from (R)-myrtenal and (S)-1-phenylethylamine. Computer simulations suggest that in this chiral Ni complex, the phenyl substituent of the chiral phenylethyl group acts as a windshield wiper across the catalytically active metal center. This... 

Certain chiral phosphinite or aminophosphine ligands are also useful for amino acid synthesis. Hydrogenation with a CYCPHOS-Rh complex occurs rapidly to produce high optical yields. The efficacy of this reaction is ascribed to the flexibility of the ligand, which speeds the reaction and gives a fixed chelate ring conformation (26). 

The cyclic phosphinate (96) has been isolated from the reaction of dichloro(methyl)phosphine with the ethoxycarbonylimine derived from hexafluoroacetone. Treatment of trichloro(organo)phosphonium-hexafluorophosphate salts with dichloro(diethylamino)phosphine results in the halophosphonium salts (97). Some reactions of dichloro(-)menthylphosphine have been reported.As usual, nucleophilic displacement reactions of halogenophosphines have received attention as routes to new systems of interest as ligands.Of particular interest in this connection is a report of the synthesis of the phosphorus-functionalised calixarenes (98). Only one chlorine atom of dichloro(phenyl)-phosphine is replaced on treatment with an excess of dicyclohexylamine, enabling the stepwise synthesis of the chiral aminophosphines (99), described as air-stable solids. 

Another major contribution of polydentate ligands is the creation of a chiral pocket around the catalytic center providing, an appropriate chiral environment. The chiral pocket concept has been introduced by Trost for catalytic enantioselective allylic alkylation with the tetradentate aminophosphine ligand 33 [133]. The nucleophile fits into the chiral environment created by the chiral ligand and the allyl Pd intermediate. As a result, the enantiocontrol of the newly formed chiral center is very effective. In addition, the chiral control is likely to be efficient even at positions remote from the chiral ligand. That auxiliary has been widely... 

Brunei, J.-M., Buono, G. Enantioselective rhodium catalyzed hydroboration of olefins using chiral bis(aminophosphine) ligands. Tetrahedron Lett. 1999, 40, 3561-3564. 

Aminophosphines. - The bis(V-pyrrolidinyl)phosphines (139), prepared conventionally by treatment of the appropriate organodichlorophosphine with an excess of pyrrolidine, have proved to be unusually electron-rich <7-donor ligands when compared to either tris(V-pyrrolidinyl)phosphine, or trialkyl-and triaryl-phosphines. Full details of a route to the polycylic aminophos-phirane systems (140) have now appeared. The bis(aminophosphine) (141) has been prepared and used in the synthesis of macrocyclic metal complexes. Two new chiral aminophosphine systems (142) and (143) have been prepared by transamidation of related aryl bis(dimethylamino)phosphines with a chiral amine. The chiral aminophosphine (144) has been obtained from the reaction of chlorodiphenylphosphine with the methyl ester of alanine. A range of ether-functionalised aminophosphines (145) has also been prepared. 

Studies suggest that the mechanism of AHRs is quite similar to the achiral version, which includes the same fundamental steps in the catalytic cycles that we have seen already. The major difference is the presence of chiral bidentate ligands, such as bisphosphines [R2P-Y-PR2], phosphine-phosphites [R2P-Y-P(OR)2], bisphospites [(RO)2P-Y-P(OR)2], aminophosphines [R2N-Y-PR2], or diamines (such as (-)-sparteine), which we encountered earlier in Chapter 12. The bidentate variation of the cationic cycle, shown in Scheme 12.15b, seems to explain most aspects of the mechanism of AHR when X = OTf or I (in the presence of halide scavengers). Throughout the cycle, the ligand remains bidentate, and this factor seems to enhance enantioselectivity. The neutral cycle variant, which ought to be... 

Cyclic chiral aminophosphine and phosphinite ligands in enantioselective catalysis 03CCR(242)145. 

A novel class of complexes, Ir-(5 )-26a, with chiral spiro aminophosphine ligands was found to be effective catalyst for the asymmetric hydrogenation of a-substituted acrylic acids (Scheme 11) [62]. Under mild reaction conditions and at ambient pressure, various a-aryl and alkyl propionic acids were produced with extremely high efficiency (TONS up to 10 000 TOFs up to 6000h ) and excellent enantioselectivity (up to 99% ee). This reaction provides a practically useful method for the preparation of a-aryl propionic acids, a popular class of non-steroid anti-inflammtory reagents. 

The diastereoselective synthesis of a 7 -chirogenic p-aminophosphine ligand 300 by carbon-carbon bond formation of the ethano bridge in a 3 1 ratio via reaction of an a-metallated f -chiral phosphine borane (5)-297 with a benzaldimine was described. The major diastereoisomeric p-aminophosphine borane (Sp)-298 was separated and decomplexed into the corresponding p-aminophosphine (5p)-300 under neutral conditions and without epimerization by heating at reflux in EtOH (Scheme 100) [198]. 

Oliana M, King F, Horton PN, Hursthouse MB, Hii KK (2006) Practical synthesis of chiral vinylphosphine oxides by direct nucleophilic substitution. Stereodivergent synthesis of aminophosphine ligands. J Org Chem 71 2472-2479... 

Aminophosphines. The synthesis and use of aminophosphines as ligands have been reviewed. Raeemie ehlorophosphines of the type R R PCl have been shown to react stereoselectively with chiral amines (1-phenylethylamine or aminoacid esters) in the presence of triethylamine to give the diastereomerically enriched aminophosphines (137), which were isolated as diastereomerically pure crystalhne borane complexes. This approach has also been used in the synthesis of chiral t-butylphenylphosphine oxide, via the acid hydrolysis of an intermediate chiral aminophosphine. Among other new mon-oaminophosphines prepared by treatment of primary or secondary amines with ehlorophosphines in the presence of a base are the adenine derivatives (138), the phosphinoalkylaminophosphines (139), " the aminophosphine-phosphine... 

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