Ruthenium complexes enantiomeric resolution

Rhodium and ruthenium complexes of CHIRAPHOS are also useful for the asymmetric hydrogenation of p-keto esters. Dynamic kinetic resolution of racemic 2-acylamino-3-oxobutyrates was performed by hydrogenation using ((5,5)-CHIRAPHOS)RuBr2 (eq 3). The product yields and enantiomeric excesses were dependent upon solvent, ligand, and the ratio of substrate to catalyst. Under optimum conditions a 97 3 mixture of syn and anti p-hydroxy esters was formed, which was converted to o-threonine (85% ee) and D-allothreonine (99% ee) by hydrolysis and reaction with propylene oxide. 

The mechanism of the Arbuzov rearrangement of (allyloxy)phosphines PhJP-(0C3H5)34 (n = 0-2) at room temperature catalysed by [CpRu(AN>3]PF4 has been investigated. A new procedure has been developed for the preparation of enantiomerically pure sulphoxides and ruthenium complexes such as [CpRu((X>)(FI%3)(t-BuMeSO)]SbF4 by a combination of asymmetric oxidations of dialkylsulphides and metal resolution of the products. The Diels Alder reaction of coordinated dienophiles in [CpRu(dnq]p)3 (dienophile)JPF( have been investigated for a range of complexes. ... 

Racemization of the remnant substrate in a DKR process can be performed either spontaneously or by the employment of a chemo- or biocatalyst, which must be compatible with the reaction conditions used for the KR reaction. In the case of sec-alcohols, most of successful DKRs have been carried out by the use of ruthenium complex catalysts, soluble in the organic reaction media, which promote racemization through redox processes. The first examples describe the resolution of 1-phenylethanol (rac-1) by the combination of a rhodium catalyst (Rh2(OAc) ) with Pseudomonas fluorescens lipase [22], although more effective results were afforded by Backvall and coworkers [23], who developed the DKR of the same substrate and derivatives catalyzed by Candida antarctica lipase (CALB) and a ruthenium complex (Shvo s catalyst, 2 (Figure 14.2)), affording excellent conversions and enantiomeric excess (ee) values [24]. 

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