P-chiral phosphines

BisP ligands are highly active and enantioselective for the hydrogenation of many classes of substrates. As noted in the mechanistic discussion, studies on asymmetric hydrogenation by rhodium catalysts of terf-Bu-BisP have provided evidence that these reactions occur through the hydrogen-first pathway even though the complexes are cationic.  

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Two reports have been made of the preparation of P-chiral phosphine oxides through reaction of chiral f-butylphenylphosphine oxide treated with LDA and electrophiles. The electrophiles included aldehydes,355 ketones,355 and benzylic-type halides.356 Optically active a-hydroxyphosphonate products have also been generated from aldehydes and dialkyl phosphites using an asymmetric induction approach with LiAl-BINOL.357... 

Haynes, R.K., Lam, W.W.-L., and Yeung, L.-L., Stereoselective preparation of functionalized tertiary P-chiral phosphine oxides by nucleophilic addition of lithiated tert-butylphenylphosphine oxide to carbonyl compounds, Tetrahedron Lett., 37, 4729, 1996. 

Knowles et al. had shown that the use of the P-chiral monodentate CAMP gave rise to an e.e. of 88% [9] in the formation of N-acyl-phenylalanine. However, due to the superior results obtained using bidentate ligands and the difficult preparation of P-chiral phosphines, this route was rarely followed for a long time [10, 11]. 

Tris(trimethylsilyl)silane reacts with phosphine sulfides and phosphine selen-ides under free radical conditions to give the corresponding phosphines or, after treatment with BH3-THF, the corresponding phosphine-borane complex in good to excellent yields (Reaction 4.45) [82]. Stereochemical studies on P-chiral phosphine sulphides showed that these reductions proceed with retention of configuration. An example is given in Reaction (4.46). 

Addition of Hydrogen Phosphinates and Extension to Synthesis of P-Chiral Phosphinates. 50... 

In addition to nitrogen bases, the potential of chiral phosphanes as catalysts has also been assessed. Early work on the use of P-chiral phosphines in intramolecular... 

P-Chiral phosphine an p the corresponding racemic substrate (Figure 17).18 hpase-catalyzed optical resou rugosa (CRL) was used for the enantioselective... 

P-Chiral phosphine-borane compounds were synthesized through lipase-catalyzed optical resolution (Figure 17 (d)).18e Alkyl(l-hydroxymethyl)phosphine-boranes (up to ee 99% ) were obtained using lipase AK or CAL. 

A number of C2 symmetric diphosphine ligands with a ferrocenyl backbone (see Figure 15.5) have been described and tested with sometimes very good results. Interesting examples are f-binaphane (11),14 ferrotane (12),15 the sugar-based phospholane 13,16 the ferrocenyl bisphosphonite 14,17 and the P-chiral phosphine 15.18... 

Chemists who wish to prepare enantiomerically pure phosphines should consult the excellent review by Pietrusiewics and Zablocka,45 which gives examples of most of the P-chiral phosphines that have been made efficiently. In the last 10 years, a number of effective asymmetric syntheses of P-chiral phosphines have been developed. Prior to this, many of the chiral phosphines prepared were synthesized in racemic form and then resolved using stoichiometric amounts of a chiral organic compound or chiral palladium, platinum, or iron complexes. Although some interesting phosphines have been prepared by this method, they are not mentioned here as the experimental procedures are not in widespread use. 

Watanabe, T., Gridnev, I. D., Imamoto, T. Synthesis of a new enantiomerically pure P-chiral phosphine and its use in probing the mechanism of the Mitsunobu reaction. Chirality 2000,12, 346-351. 

As has been the pattern in recent years, there has been considerable interest in the synthesis and characterisation of phosphide reagents derived from metals other than lithium, sodium, and potassium, and also in studies of the structure of metallophosphides in the solid state. A new route to P-chiral phosphine-boranes of high enantiopurity is afforded by treatment of the borane complexes of methyl(phenyl)phosphine with a copper(I) reagent, giving the copper-phosphido intermediate (83), which, on subsequent treatment with an iodoarene in the presence of a palladium(O) catalyst, gives the related chiral t-phosphine-borane (84), with retention of configuration at phosphorus. Organophosphido systems... 

Phosphorylation of At2PH-BH3 with aryl halides proceeds under mild conditions using Pd-Cu catalyst and P-chiral phosphine-boranes of high enantiopurity are prepared by this method. As an effective ligand, MePPh2 is used with Pd(OAc)2. The phosphine-borane 50 was prepared in 68 % yield by phosphorylation of optically active (Sp)-methylphenylphosphine-borane (47) via 48 with the iodide 49 in the presence of the Pd(OAc)2-MePPh2 catalyst and Cul as a cocatalyst at 0°C for 3 days. The reaction proceeded with retention of stereochemistry and the asymmetrically substituted phosphine 51 with 99% ee was obtained [15]. 

Han [49] reported a diastereoselective method for the synthesis of P-chiral phosphine oxides. The sequential nucleophilic substitution of 1,3,2-... 

Dihydroboronium derivatives of t-Bu-BisP with different cotmter anions were prepared, as shown in Scheme 56. The reaction of BisP with BH2Br afforded the boronium salt 175 which possessed a bromide ion. The dihydroboronium derivative of (S,S)-l,2-bis(tert-butylmethylphosphino)ethane 175 (t-Bu-BisP ) was prepared by the reaction of t-Bu-BisP 174 with catecholborane and used as chiral diphosphine ligand precursor in Rh-catalyzed asymmetric hydrogenated of methyl (Z)-acetamidocinnamate to afford the hydrogenation product in up to 94% ee. Complexes of iron(III) and P-chiral phosphine oxides 176 are catalysts for the asymmetric Diels-Alder reaction of iV-acrylamide dienophiles [106]. 

The biocatalytic desymmetrization of various C2-symmetric tertiary phosphine oxides was used for the preparation of P-chiral phosphines. Mikolajczyk et al. [183-185] studied the desymmetrization of bis-functional phosphinates and phosphine oxides. The hydrolysis of prochiral bis(methoxycarbonylmethyl) phenylphosphine oxide 274 was carried out in phosphate buffer in the presence of... 

Ouchi Y, Morisaki Y, Chujo Y (2006) Synthesis of photraesponsive polymers having P-chiral phosphine in the main chain. Polym Preprints 47 708-709... 

Chen WP, Mbafor W, Roberts SM, Whittall J (2006) A very simple, highly stereoselective and modular synthesis of ferrocene-based P-chiral phosphine ligands. J Am Chem Soc 128 3922-3923... 

Yeo W-C, Chen S, Tan G-K, Leung P-H (2007) Synthesis of P-chiral phosphines via chiral metal template promoted asymmetric furan Diels-Alder reaction. J Organomet Chem 692 2539-2547... 

Leung PH, Siah SY, White AJP, Williams DJ (1998) Asymmetric syntheses, structures and reactions of palladium(II) complexes containing thiolato- and sulfinyl-substituted P chiral phosphines. J Chem Soc Dalton Trans 893-899... 

In essence, four types of Rh complexes have routinely been used as precursors for Rh-catalyzed hydrogenation reactions (see Fig. 3) neutral or cationic bis-diene (norbomadiene or 1,5-cyclooctadiene) Rh(l) complexes with CP or as anion, respectively, preformed diene-diphosphine complexes (see Fig. 1), mostly as anionic species and especially with air-sensitive ligands and/or P-chiral phosphines prone to racemization. Before the diene-diphosphine complexes become active catalysts, the diene has to be removed via hydrogenation. Depending on the diene and the ligand, this reaction can be rather slow, thereby leading to induction phases and/or decreased catalyst productivity for an overview, see Heller et al. [16]. The results presented show some clear trends as to which precursor type is most likely to be effective for a desired transformation ... 

The absolute configuration of P-chiral phosphines can be determined by special x-ray diffraction techniques (Chapter 14.2),... 

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