DIOP ligands, chiral palladium complexes

At best, the product has 26% op using zerovalent or divalent palladium complexes of (R,R)-Diop. Ligands which give rise to a more rigid chiral environment around the metal center, e.g., (l/ ,2/ )-bis(diphenylphosphano)cyclopentane, may lead to enhanced enantioselectivity. 

Using (/ ,/ )-Diop as the chiral auxiliary, the amount of chiral induction is not dependent on the temperature, but depends on the type of chiral ligand in the palladium complex and on the allenylmetal reagent. When magnesium or copper is present, a reversal of the configuration... 

Enantioselective allylations of prostereogenic enolates have been attempted using catalytic amounts of a palladium complex incorporating (5,5)-Diop as the chiral ligand. The reactions of ketone zinc enolate 2 with allyl chloride 17 and of the sodium enolate derived from aldehyde 5 with phenyl ether 423 yield 3 and 6 of low enantiomeric excess, respectively. 

The coordination chemistry of many chiral ligands is directed towards preparing complexes with catalytically useful metals, most notably late transition metals. Some Rh, Pd, Pt, and Ag complexes of Diop (149) (and also (150)) have been described,327,328,381,382 along with the use of palladium Diop complexes in asymmetric palladium catalysed cross-couplings383 and alkene hydrocyanation reactions. 

Olefin hydrocyanation using palladium catalysts has been less well studied than with nickel. Nevertheless, zerovalent complexes of palladium, particulrly triarylphosphite complexes, hydrocyanate a wide range of olefins in useful yields (see Table 1). Early work reported the merit of excess phosphorus ligand to promote the reaction, and further paralleling the observations with nickel, Lewis acids have been used to improve catalytic activity. However, addition of ZnClj fails to improve nitrile product yield . Asymmetric induction in hydrocyanation results in optical yields of 30% in the synthesis of exo-2-cyanonorbomane using the chiral ligand DIOP, and studies on the stereochemistry of HCN and DCN addition to terminal alkenes and a substituted cyclohexene with the same catalyst have been reported. ... 

In the TMM- Pd eycloaddition to cyclopentenone, a chiral product is formed. Reduction to the corresponding alcohol allows an ee determination to be carried out using chiral shift NMR techniques. The use of a chiral monophosphane (CAMP) or diphosphane (Diop) leads to the cycloadduct with a maximum of 7% ee72. This poor transfer of chirality from the palladium-bound ligand to the product is in accord with the proposed mechanism of the cycloaddition, which suggests addition of the TMM-Pd complex to the olefin from the face distal to the palladium species73. 

Chiral esters (133) have been produced from 7r-allylpalladium complexes derived from methyl 3-acetoxycyclohex-4-en-l-carboxylate, by reactions with malonate-type enolates (cf. ref. 152). The chiralty is introduced by complexation of the palladium with the optically-active ligand DIOP optical yields of (133) are between 16 and 46%. ... 

Consiglio and colleagues described the enantioselective version of bis-alk-oxycarbonylations of alkenes [25-27], Here, BQ was applied to reoxidize the palladium centre. As chiral ligands, DIOP, BINAP, and some other chiral phosphine ligands were tested. More recently, Chan s group succeeded in using modified dipyridylphosphine cationic Pd(II) complexes to obtain both good ee and chemoselectivity. ... 

The palladium(ii) acetylacetonate-tri phenyl phosphine catalysed reaction of butadiene with water and carbon dioxide in solvents such as t-butanol or acetone has been reported to give octa-2,7-dien-l-ol as the major product together with minor amounts of octa-l,7-dien-3-ol, 1,3,7-octatriene and octadienyl ethers. In contrast aqueous potassium tetrachloropalladate with excess diene leads to pale yellow solids which were polymeric. Decomposition of these complexes with dimethylglyoxime gave a mixture of 3-methyIbutenyl ethers, (Scheme 33). The use of (—)-2,2-dimethyl-4,5-bis(diphenylphosphinomethyl)-l,3-dioxolane (DIOP) as a chiral ligand... 

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