Chiral ligands BINOL

It may not be necessary to employ an optically pure chiral ligand (BINOL) for the preparation of the catalyst because a high degree of asymmetric amplification can be expected. 

Nitrile aldol reactions. P-Hydroxy nitriles are formed in the presence of CeCl3 7H20. Addition of a chiral ligand (BINOL) increases the diastereoselectivity. 

Derivatives of the chiral ligand binol have been introduced successfully to Ta chemistry by use of an amido precursor (Scheme 30).316... 

In spite of the prevailing application of homo- and heterobidentate chiral ligands, BINOL-derived monodentate phosphoramidites have been used in highly enantioselective rhodium-catalyzed hydrogenations (14,233). 

A remarkable change in reaction course is notable when changing the metal from aluminum to titanium for cydoaddition reactions using BINOL as the chiral ligand. When the chiral aluminum(III) catalyst is applied the cydoaddition product is the major product, whereas for the chiral titanium(IV) catalyst, the ene product is the major product. The reason for this significant change in reaction course is not fully understood. Maybe the glyoxylate coordinates to the former Le-... 

Similar reaction pathways were recently shown to be available to the widely used chiral ligand l,l -binaphthol (BINOL) (138).87 Irradiation of BINOL in aqueous acetonitrile initiated ESIPT to the 4 -, 5 -, and 7 -ring carbons to give biaryl quinone... 

Various chiral ligands with metal catalysts can be employed in the organosilane reduction of imines to amines. Many of these provide modest success. These include (oxazolino)diphenylphosphinoferrocene ligands with ruthenium,605 (—)-DIOP/Rh(I),606,607 3,3 -BINOL (l,l -bi-2-naphthol) and LiHMDS,608 and (S)-phenyl V-formylprolinamidc with trichlorosilane.609... 

In recent years, there is no doubt that BINOL is one of the most extensively studied motifs. Incorporating a chiral binol unit into the chiral or achiral backbone constitutes a straightforward way in which to generate new chiral ligands [109]. 

Zhang and Chan122 found that Hg-BINOL, (R)- or (S )-134, in which the naphthyl rings in the BINOL were partially hydrogenated,123 can give even better results in the diethylzinc reactions. Using (R)- or (5,)-134 as the chiral ligand, addition of diethylzinc to aromatic aldehydes proceeds smoothly with over 95% ee and, in most cases, quantitative conversion.122... 

Ti-BINOL-catalyzed reactions have been well established. When the Ti is replaced by Zr,92 the resulting complex 140 can also catalyze the addition of allyl-tributyltin to aldehydes (aldehydes allyl-tributyltin 140 = 1 2 0.2 mol ratio) in the presence of 4 A MS. Product l-alken-4-ols are obtained in good yield and high ee. The, Sz-face of the aldehyde is attacked if (S)-BINOL is used, and Re-face attack takes place when (K)-BINOL is used as the chiral ligand. For Zr complex-catalyzed reactions, the reaction proceeds much faster, although the... 

In 2001, Scettri and coworkers could show that titanium-catalyzed asymmetric sulfoxidation with a tertiary furyl hydroperoxide 188a can be achieved under catalytic conditions by a modification of Uemura s approach employing (R)-BINOL as chiral ligand (equation 57). Under these conditions sulfoxides could be isolated in medium to good... 

Chiral aluminium complexes have been used as catalysts for inverse electron-demand 1,3-dipolar cycloadditions of alkenes with nitrones, and the first contribution to this field was pubhshed in 1999 (344). The chiral AlMe-BEMOL (BINOL = 2,2 -bis(diphenylphosphino)-l,l -binaphthyl) complexes 235 were excellent catalysts for the reaction between nitrone 225a and vinyl ethers 232 (Scheme 12.68). The diastereo- and enantioselectivities are highly dependent on the chiral ligand. An exo/endo ratio of 73 27 was observed, and the exo-product was... 

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