Chiral phosphane

Incorporation of a chiral phosphane allowed resolution of the complex 6 which was obtained in enantiomerically pure form. Reaction of 6 with 2,2-dimethylpropanal provided the adduct 7 as the sole observable aldol product13. Oxidation of the metal center of 7 with ferric chloride induced decomplexation via reductive elimination, to provide the enantiomerically pure cy-clobutanone 8. 

One of the limitations of the use of asymmetric catalysis comes from the difficulties of separating the chiral catalyst from the reaction medium and recycling it. Such systems are generally formed with chiral phosphane and/or... 

The stabilized anion 134 also attacks the terminal vinylic position of 131 exclusively to give cyclopropylideneethyl derivatives 135, which are synthetically useful building blocks [69], The use of chiral phosphanes as ligands leads to optically active methylenecyclopropane derivatives. (Scheme 47)... 

If chiral phosphanes (6) are employed, retention of configuration is observed (Scheme 3) (81TL3827). 

Wilson and Pasternak reported the first asymmetric Staudinger reaction (Scheme 4) where the chiral phosphane (7) reacts with the racemic azide (8) to afford diastereomeric iminophosphoranes in different quantities, giving after hydrolysis an amine in slight enatiomeric excess. Separation of the racemate seems to be kinetically controlled, but needs optimization (90MI1). 

Catalytic enantioselective synthesis of 4,4-dimethyl-l-phenyl-l,2-pentadiene from 4,4-dimethyl-1,2-pentadiene and iodobenzene using 0.4 to 1 mol % of palladium complexes containing chiral phosphane ligands as the catalyst for the enantioselective cross coupling134 is the only example of substoichiometric transition metal catalyzed enantioselective allene synthesis. 

Following the success with cobalt and rhodium, Shibata reported Ir(i)-based enantioselective catalytic reaction. Right after their observation that the efficiency of [IrCl(COD)]2-catalyzed PKR substantially increased by addition of a phosphane co-ligand, they moved directly to use chiral phosphanes and examined the enantioselectivity. " TON and TOE of the reaction were low and the number of examples was limited. Typically, the reaction required a fair amount of Ir(i) catalyst [IrCl(COD)]2 (0.1-0.15 equiv.) and (reaction time. However, this has remained as the best in terms of enantioselectivity to date. Moreover, this catalytic system provided the first asymmetric intermolecular reaction as well. 

The introduction of a sulfonate group by reaction with oleum is not limited to arylphosphanes. Tris(co-pbenylalkyl)phosphanes, P[(CH2) (C6H5)]3 (n = 1, 2, 3, and 6), can be sulfonated in the para position and to a lesser extent in the meta position (18). The technique of sulfonating water-insoluble ligand precursors can be applied to bidentate, polydentate, and chiral phosphanes (20-24) the compounds 1-3 are presented in Scheme 2 as examples. 

Another attempt to apply the oxo reaction to the synthesis of fine chemicals was made by the hydroformylation of styrene. The chiral catalyst, a rhodium complex of a surfactant phosphane 12, gave no optical induction (76). This result agrees with the known poor enantioselection ability of other complexes with monodentate chiral phosphanes. 

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... 

Dimethylselenoxid ist ein sehr mildes Oxygenierungsmittel fiir tert.-Phosphane, das im-mer dann vorteilhaft angewendet werden kann, wenn das Phosphan oxidationsempfindli-che Reste hat. Zudem bietet es den Vorteil, chirale Phosphane unter praktisch vollstandi-ger Inversion zu oxygenieren273. 

Letzteres Reagenz iiberfiihrt chirale tert.Phosphansulfide in chirale Phosphane, wie auch Lithiumaluminiumhydrid588 und Hexachlordisilan589 unter Retention der [Configuration am P-Atom. 

Substitution of one cyano group with a trifluoromethyl group and reaction with excess HFA lead to the formation of a chiral phosphane. The X-ray structure determination (79) shows only one enantiomer to be present in the... 

Considerable efforts have been made to develop asymmetrical variants of the classical Pauson-Khand reaction. Initial investigations have shown that compounds derived from cobalt complexes of type 1, in which a carbonyl ligand is replaced by a chiral phosphane (glyphos), react with high enantioselectivity [22], However, the procedure is too complex to be of preparative value. The concept of Kerr et al., who achieved significant enantioselectivities (max. 44 % ee) in intermolecular Pauson-Khand reactions by... 

Asymmetric reduction of a, /I-unsaturated esters, lactones or lactames can be effected with copper-hydride catalysts and chiral phosphanes such as various BINAP related compounds in excellent yields and enantioselectivities (equation 23). As the hydrosilane component, polymethylhydrosiloxane (PMHS) is frequently used for this reaction. 

It is known that chiral phosphanes are more pyramidal and that inversion is more difficult, usually requiring temperatures well over 100°C for racemization. " Alder... 

Monodentate phosphanes (PPhj, P(flTol), (TOTP), P(oPuryI)3 (TFP), PfCeFjXO Chiral phosphanes (see Table 3.8) Bromide as leaving group Stabilization of Pd Enaniioseleclive HR (Section 3.5) [Ilia] [21]... 

The asymmetric induction in the formation of 214 stems from an eiiantiodifferentiation of two double bonds. The intramolecular jr-enantiofacial discrimination (cf. Scheme 3-49 for the intermolecular version) has also been successful, as shown by the asymmetric construction of quaternary carbon centers in the preparation of spirooxindoles 217 from 216 (Scheme 3-51). It is amazing that each product enantiomer was obtained selectively by careful choice of reaction conditions and, remarkably, by applying exactly the same enantiomer of the chiral phosphane ligand [122]. 

Tripod Ligands with Chiral Phosphane Donors 301... 

Tripod ligands with chiral phosphane donors... 

Replacement of bis(l,2-diphenylphosphino)ethane by chiral phosphanes such as (— )-(25, 3 5)-bis(diphenylphosphino)butane or (- -)-(/ )- ,2-bis(diphenylphosphino)propane allows a highly enantioselective cobalt-catalyzed homo-Diels-Alder reaction (maximum 91% ee) between norbornadiene and monosubstituted alkynes. Similarly, the reaction of norbornadiene with phenylacetylene in the presence of catalytic amounts of tris(acetylacetonato)cobalt and (-l-)-bicyclo[2.2.1]hept-5-ene-2,3-diylbis(diphenylphosphane) leads quantitatively to the homo-Diels-Alder adduct with an ee of 98.4%. ... 

Similar reactions of norbornadiene with substituted buta-1,3-dienes in the presence of cobalt catalysts lead to the corresponding 1,4-adducts in 92-96% yield.In the presence of chiral phosphane ligands, this reaction has been brought about with up to 79% enantiomeric excess. The head-to-head dimer of norbornadiene, 1,2,4 5,6,8-dimethano-5-indacene (3, Binor-S ) was formed in quantitative yield on dimerizing norbornadiene with catalysts such as co-balt(II) bromide/triphenylphosphane, cobalt(ll) iodide/triphenylphosphane, or (triphenylphos-phanejrhodium chloride, in the presence of boron trifluoride-diethyl ether complex. ... 

An enantioselective version of the cyclopentaannulation via [3 + 2] cycloaddition has been developed using cyclopent-2-enone and several different methylenecyclopropanes. Whereas chiral phosphane ligands, such as menthyldiphenylphosphane (21), or the camphor-derived sultam 22 only result in enantiomeric excesses of 31% at a maximum in nickel(0)-catalyzed reactions, the enantioselectivity dramatically increases when the bidentate azaphospholene ligand 23 is employed. The yields, however, are relatively low due to the competing formation of alkylation products. ... 

Our patent department always considered our invention was the use of chiral phosphanes with rhodium but, of course, without finding PAMP and CAMP, we would have only had a new way of doing what had been done before. The lawyers... 

We have called these catalysts man-made but this is not strictly true. We have not violated the general principal that, if you want chiral molecules, you will have to get them with the assistance of previously formed natural products. Our asymmetry was obtained from the (-)-menthol used in the chiral phosphane synthesis, but being a catalyst, a small amount of (-)-menthol could lead to a large amount of chiral product. CAMP worked equally well for the L-dopa precursor (Fig. 2), and it made no difference whether the amine-blocking group was benzoyl or acetyl. 

---