BINAP derivatives

A number of chiral ketones have been developed that are capable of enantiose-lective epoxidation via dioxirane intermediates.104 Scheme 12.13 shows the structures of some chiral ketones that have been used as catalysts for enantioselective epoxidation. The BINAP-derived ketone shown in Entry 1, as well as its halogenated derivatives, have shown good enantioselectivity toward di- and trisubstituted alkenes. 

In asymmetric reactions, chiral phosphine ligands such as BINAP derivatives are used as effective chiral ligands in silver complexes. In particular, an Agr-BINAP complex activates aldehydes and imines effectively and asymmetric allylations,220-222 aldol reactions 223 and Mannich-type reactions224 proceed in high yield with high selectivity (Scheme 51). 

Polymerization of a BINAP derivative (Figure 14) followed by complexation with [ RuC12 (benzene) 2] afforded a catalyst showing high enantioselectivities for the hydrogenation of various substrates such as dehydroaminoacids, ketoesters, olefins, and ketones.135 The catalyst may be re-used four times with negligible loss of enantioselectivity and activity. 

A fluorous version of the chiral bis-phosphine BINAP has been developed for asymmetric Heck reactions [5], Several fluorous-derivatized binaphthols and BINAP derivatives have been reported, (Scheme 10.4) [6], The silane spacer group present in one of the ligands was used to maximize the percentage fluorine on the molecule. Even so, the partition coefficient1 between FC-72 (see Chapter 3) and benzene was only 2.85, and not surprisingly, the reuse of the catalyst was poor. 

The BINAP derivative of the ort/io-cyclometallated iridium catalyst has been characterized by single crystal X-ray diffraction analysis [280]. Remarkably, although the reaction sequence depends upon oxidation of either the reactant alcohol or isopropanol, the enantiomeric purity of the homoallylic alcohol product... 

Figure 5.33 Schematic illustration of the immobilization of bisphosporylated-BINAP derivatives, [Rh(C0D) (Na2P03)2-BINAP ] and [Ru(p-cymene) (Na2P03)2-BINAP Cl], within a polyelectrolyte. (Redrawn from Kockritz et al. [200].)...

The eclipsed tetra-BINAP porphyrin 171 was conveniently synthesized by condensation of the meso-tetrakis(2,6-dihydroxyphenyl)porphyrin 173 with the (S)-BINAP derivative 174 in the presence of K2C03. After removal of the staggered isomer iron was inserted by addition of Fe(CO)5/I2, and the resulting Fe(III)-complex 171 was used as a catalyst (0.2%) to epoxidize a series of six styrene derivatives in the presence of an excess of PhIO. In every case the corresponding (R)-epoxides were preferentially formed in yields up to 72%. The best ee-values were obtained for the electron deficient substrates 2-nitrostyrene (80% ee) and pentafluorostyrene (74% ee), [114],... 

Chiral palladium complexes have been employed as enantio- and diastereo-selective catalysts of a Mannich-type addition of /3-kclo esters to aldimines and imino esters, q. in a strategy which activates both reactants 28 anti-Selective direct enantioselective Mannich reactions use a BINAP-derived axi- ally chiral aminosulfonamide as organocatalyst.29... 

A short review reports high ees in the alkynylation of aromatic aldehydes, using BINAP derivatives bearing amino alcohol ligands.209... 

BINAP-derived 1,2-amino alcohols catalyse the enantioselective phenylalkynylation and phenylation of aromatic aldehydes by zinc reagents.243... 

Indeed, the mechanism of these (salen)Mn catalysts activity is still of considerable controversy. Katsuki, for instance, who has focused recently on the reactivity of binap-derived catalysts (e.g., 6) with various cu-olefins [95SL827] as well as cyclic trisubstituted olefins [95SL197], maintains that all observations can be rationalized solely on the basis of steric and electronic steering of the substrate during the approach to the catalyst. According to... 

Although carbohydrates are cheap and readily available chiral compounds, their application in stereoselective synthesis was for a long time limited to ex-chiral-pool syntheses [3]. They have been considered too complex compared to other chiral auxiliaries, for example a-pinene in borane-chemistry [4] or BINAP-derivatives in reduction chemistry [5]. However, it has been shown during the past few years that carbohydrates can be successfully applied as stereodifferentiating tools in many different reaction types such as aldol- [6], hydrogenation- [7], carbonyl addition- [8], Michael- [9], Diels-Alder- [10], hetero-Diels-Alder [11], and rearrangement reactions [12]. 

Numerous groups have used the BINAP/Pd- and DPPF/Pd-based reaction protocols for the arylation of cyclic secondary amines. Independently, Ward and Farina [31] as well as Willoughby and Chapman [32] disclosed that the palladium-catalyzed arylation reaction could be effected on resin-bound amines, Eq. (7). Both groups reported that while the (o-tol)3P-based catalysts were often inferior to the BINAP-based system, using DPPF as ligand often resulted in comparable yields and reaction rates. They also observed that BINAP-derived catalysts usually yielded smaller amounts of reduced arene by-products. 

Table 3 Comparison of the chiral poisoning strategy to the traditional use of chiral resolved BINAP derivative...

This system for the asymmetric hydrogenation of ketones has been employed in the asyimnetric activation using a racemic BINAP derivative. Combination of RuCl2[(5)-Xyl-BINAP](dmf) (Xyl = 3,5-C6H3-Me2) and (5,5)-DPEN gave the precatalyst RuCl2[( 8)-Xyl-BlNAP][(5, 5 )-DPEN], which exhibited 99% enantioselectivity in the reduction of 1-acetylnaphthone to the (f )-alcohol (equation 10). 

A Ru complex with a BINAP derivative covalently bonded to an aminomethylated polystyrene resin is also usable, though both the rate and enantioselectivity are decreased [57]. 2,3-Dimethylenesuccinic acid is hydrogenated by an (R)-BINAP-Ru complex at 3 atm of H2 to give a 98.8 1.2 mixture of (2S,3S)-dimethylsuccinic acid with 96% e.e. and the meso isomer [58]. 

Scheme 5.2.86 Enantioselective propargylation of 389 using BINAP-derived catalyst...

When asymmetric reduction of the ketone of an enone such as 39 is wanted, the catalyst must be further modified14 by using the very crowded BINAP derivative XYLBINAP 41 and the diamine additive DAIPEN 42. The results are then excellent but this example makes the point that it is essential to follow closely related examples when attempting the asymmetric reduction of any but the simplest alkene. 

Mono- and bisphosphorylated BINAP derivatives of composition 24 have been reported quite recently. The sodium salts of the phosphonic acid derivatives are soluble in water [30]. 

Asymmetric hydrogenation. Hydrogenation of the a-substituted /8-kcto ester 2 with a Ru(ll) catalyst coupled with (R)-l provides the desired /8-hydroxy ester 3 in 90% ec but with only moderate. vyrr-selectivity (74% de). Hydrogenation with high cnantio-and diastereosclectivity can be achieved using a BINAP derivative in which the phenyl... 

Excellent results were also reported recently by Maruoka and coworkers by using 50% aqueous NaOH in toluene and a (5)-BINAP-derived C2-symmetric ammonium catalyst 14 [64]. The steric and/or electronic properties of this new class of catalysts can be finely tuned in order to improve reactivity and enantioselectivity. The N-spiro structure along with their high lipophilicity make such catalysts much more reactive than the traditional PTC catalysts, e.g., Bu4N+Br, in otherwise identical conditions [65]. Excellent ees are usually obtained in short reaction times with 1 % of catalyst only moreover, they should be more stable under basic conditions than ammonium salt derived from Cinchona alkaloids since they do not undergo Hofmann elimination resulting from lack of yS-hydrogens. However, they are not as easily prepared as Cinchona ammonium catalysts and are expected to be quite expensive since they are not derived from the chiral pool. On... 

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