Chiral phosphane ligands

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. 

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]. 

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. ... 

Amino acid derived chiral aminophosphane phosphinites (AMPP) such as Ephos, Proliphos, Glyphos and others1 " 128,195 constitute another new type of chiral phosphane ligand used in asymmetric hydroformylation with rhodium complexes 127,128 and platinum salts113. 

Several reviews discussing general aspects of this topic are available154- l 55,159. In the first applications the rhodium catalyst was attached to non-cross-linked polystyrene via chiral phosphane ligands such as Diop9. More efficiency is achieved with platinum catalysts attached to cross-linked polystyrene/ Diop systems138. 

A polymer-supported rhodium catalyst modified with Diop attached to non-cross-linked polystyrene, first used in the asymmetric hydroformylation of styrene, gives 95 % branched aldehyde, however with only 2% ee9. Further developments in the preparation and use of cross-linked polymers with attached chiral phosphane ligands (Diop, DIPHOL, BPPM) in rhodium- and platinum-catalyzed asymmetric hydroformylation have led to good to excellent results with respect to the asymmetric induction62-124 157,159 and arc described in Section 1.5.8 2.2.3.2. The results arc integrated in Table 4. 

Many other chiral phosphane ligands are used in asymmetric hydrocarboxylation. In the presence of NMDPP and trifluoroacetic acid in methanol carbomethoxylation of vinyl aromatics. in particular styrene, with palladium(0)bis(dibenzylidcncacetone) takes place with marked asymmetric induction (up to 52% cc) and high selectivities towards the branched product (94%)20. With other chiral ligands and other acids only smaller inductions are observed using the same catalytic system. With an increase in carbon monoxide pressure the asymmetric induction decreases. Involvement of the complex PdH(PR3),OCOCF3 is presumed20. 

Table 1, Examples of Chiral Phosphane Ligands for Enantioselective Hydrogenation...

A rhodium complex with chiral phosphane ligand was also intercalated into sodium hectorite by cation exchange (Sento et al. ). The intercalated compound was characterized by FTIR, XRD, and TEM and the basal spacing of the compound was estimated to be 2.29 nm. This novel het-erogenized eatalyst exhibited a characteristic chiral as well as size recognition of the substrate molecule (like the "Tailor-made compounds" method used earlier by Balandin in the hydrogenation of tripticene derivatives over Ni) and was used in enantioselective hydrogenation of the itaconates (methylene-succinic acid esters). 

Liu D, Zhang X (2005) Practical P-chiral phosphane ligand for Rh-catalyzed asymmetric hydrogenation. Eur J Org Chem 646-649... 

Recently, Darses et al. described for the first time a rhodium-catalyzed 1,4-addition of organoboranes to hindered MBH adducts, trisubstituted alkenes, to afford highly functionalized alkenes 483, via addition of organoboranes and p-hydroxy elimination (Scheme 3.213). Moreover, preliminary results showed that enantio-enriched products 484 were easily accessible by using a mono-substituted chiral diene 485 as ligand, while chiral phosphane ligands were completely ineffective. ... 

Shortly after this publication, Hayashi and coworkers [11] reported the first enantioselective variant of this transformation, achieving excellent yields and enantioselectivities. The use of the chiral phosphane ligand (S)-B1NAP (2,2 -bis(diphenylphosphino)-l,l -binaphthyl) along with RhfacacjfCjH lj makes the perfect catalyst - which is formed in situ to achieve >99% yield and... 

Scheme 7.7 Novel axially chiral phosphane ligand with a fluoroalcohol moiety and the proposed catalytic cycle in the arylation of aromatic aldehydes with boronic acids catalyzed by rhodium, as described by Amii and coworkers [13].

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