BINAP in asymmetric hydrogenation

In 1992, Takaya et al. reported on the use of a chiral diphosphite derived from bisnaphthol in the asymmetric hydroformylation of vinyl acetate [11], but the enantioselectivity achieved was only 50%. They noted that diphosphites led to more stable hydroformylation catalysts than diphosphines. This observation prompted Takaya, Nozaki et al. to synthesize the chiral phosphine-phosphite ligands (R,S)- and (R,R)-BINAPHOS (24, figure 17), which were expected to combine the high enantioselectivity obtained with diphosphines such as BINAP in asymmetric hydrogenation, with the apparently efficient coordination of the phosphite moiety [38]. Indeed, the Rh(I) complex of Ci-symmetric (R,S)-BINAPHOS provided much higher enantioselectivities than either C2 symmetric diphosphine ligands or diphosphite ligands, viz. more than 90% ee for a wide variety of both functionalized and internal aUcenes [38,39,40,41]. 

Reaction Characteristics of Immobilized Ru-BINAP Catalysts in Asymmetric Hydrogenation of Dimethyl itaconate... 

The BINAP system of general structure 111 can be used in asymmetric hydrogenations the compound in which Ar = S.S-MejCgHj, R1 = R2 = 4-MeOCgH4,... 

Mikami et al. also reported the activation of a racemic catalyst in Ru-BINAP-catalyzed asymmetric hydrogenation (Scheme 9.22) [40]. The combination of racemic RuCl2[( )-39] and... 

Another Ru(BINAP)-catalyzed asymmetric hydrogenation that has been performed at manufacturing scale involves the reduction of a functionalized ketone. The reduction of hydroxyacetone catalyzed by [NH2Et2]+[ RuCl(p-tol-BINAP) 2 (li-CI)3 (39) proceeds in 94% ee (Scheme 12.11).46 The chiral diol (40) is incorporated into the synthesis of levofloxacin (41), a quinolinecarboxylic acid that exhibits marked antibacterial activity. Current production of 40 is 40 tons per year by Takasago International Corp.46... 

Two interesting reports by Chan and co-workers of dendritic core-functionalized Ru-BINAP (BINAP = 2,2/-bis(diphenylphosphino)-l,l/-binaphthyl) catalysts, which were employed in asymmetric hydrogenations and which were fully recoverable, have appeared recently [40,41]. In particular, such dendrimers containing long alkyl chains in the periphery were synthesized and... 

Mainly the hydrogenations are mediated through a platinum-group-metal-catalysed reaction with chiral ligands bound to the metal. Koten and coworkers210 proposed the use of Ru- and Rh-containing catalysts immobilised on silica in asymmetric hydrogenation. As a chiral compound, they used BINAP (2,2 -bis(diphenylphosphino)-1,1 -binaphthyl) (Scheme 4). 

For the influence of trace amount of acid in the ruthenium (II)-BINAP catalysed asymmetric hydrogenation, see S. A. King, A. S. Thompson,... 

Asymmetric hydrogenation was boosted towards synthetic applications with the preparation of binap 15 by Noyori et al. [55] (Scheme 10). This diphosphine is a good ligand of rhodium, but it was some ruthenium/binap complexes which have found spectacular applications (from 1986 up to now) in asymmetric hydrogenation of many types of unsaturated substrates (C=C or C=0 double bonds). Some examples are listed in Scheme 10. Another important development generated by binap was the isomerization of allylamines into enamines catalyzed by cationic rhodium/binap complexes [57]. This reaction has been applied since 1985 in Japan at the Takasago Company for the synthesis of (-)-menthol (Scheme 10). 

In the study of Ru-BINAP catalyzed asymmetric hydrogenation of geraniol 10, a striking isomerization to y-geraniol 11 was observed, Eq. (5) [24]. The reaction is noteworthy in that it promotes the olefin migration from an inner to an exo position. Originally the presence of 11 was supposed to be an intermediate... 

Very recently, Fan et al. [13] reported on the use of a water-soluble PEO-substitut-ed first- and second-generation Frechet-type dendrimer with a chiral BINOL (1,1 -bi-2-naphthol) unit in catalysis. The enantiomeric excess in asymmetric hydrogenation of 2-[p-(2-methylpropyl)phenyl]acrylic acid with [RuCl(BINAP)(cymene)]Cl in an aqueous system was reported to increase upon addition of the dendritic... 

Cyclopentadienyl groups can be incorporated in a manner similar to that shown in equation (4) for phosphines. Metallocene derivatives see Metallocene Complexes, in turn, can be incorporated into these modified polymers. Also, chiral phosphines such as DIOP and BINAP have been immobilized on polymers to be used in asymmetric hydrogenation catalysis and related reactions. ... 

Dendrimer based-BINAP polymers have been prepared from 124. A series of soluble dendritic mono-BINAP ligands with Frechet-type polyether wedges like 127 and dendritic poly-BlNAP ligands like 128 have been reported Ruthenium complexes of both classes of dendrimer were prepared and found to be comparable both in catalytic activity and enatioselectivity as homogeneous BINAP analogs in asymmetric hydrogenation reactions. 

Substituted acrylates (which resemble the enamide substrates employed In asymmetric hydrogenation) may be deracemized by reduction with an optically active catalyst, especially DIPAMPRh. Selectivity ratios of 12 1 to 22 1 have been obtained for a variety of reactants with compounds of reasonable volatility, separation of starting material and product may be effected by preparative GLC. Recovered starting material can then be reduced with an achiral catalyst to give the optically pure anti product. Examples of kinetic resolutions by this method are given in Table II. More recently very successful kinetic resolutions of allylic alcohols have been carried out with Ru(BINAP) catalysts. 

Among the vast number of chiral homogeneous catalysts, rhodium(I) and ruthenium(II) diphosphane complexes revealed to be the most efficient ones in asymmetric hydrogenation of functionalized olefins of practical importance. In certain cases described below (including also the BINAP-containing systems), enzyme-like enantioselectivities matching the requirements of natural product synthesis were reported. 

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