Ruthenium catalysts racemic compounds

Takasago Perfumery Ltd. manufactures optically pure (Jl)-muscone from the racemic compound by way of its silyl enol ether which is dehydrosUylated with palladium acetate to the pure (Z)-enone. [202] The enantioselective hydrogenation with ruthenium-BINAP catalysts finally gives the enantiomericaUy pure product. [203]... 

Immobilized and reusable ruthenium catalyst 13 oxovanadium compounds 14 and 15 as catalysts for the racemization of allylic alcohols. 

The method is not restricted to secondary aryl alcohols and very good results were also obtained for secondary diols [39], a- and S-hydroxyalkylphosphonates [40], 2-hydroxyalkyl sulfones [41], allylic alcohols [42], S-halo alcohols [43], aromatic chlorohydrins [44], functionalized y-hydroxy amides [45], 1,2-diarylethanols [46], and primary amines [47]. Recently, the synthetic potential of this method was expanded by application of an air-stable and recyclable racemization catalyst that is applicable to alcohol DKR at room temperature [48]. The catalyst type is not limited to organometallic ruthenium compounds. Recent report indicates that the in situ racemization of amines with thiyl radicals can also be combined with enzymatic acylation of amines [49]. It is clear that, in the future, other types of catalytic racemization processes will be used together with enzymatic processes. 

The asymmetric arylation or alkylation of racemic secondary phosphines catalyzed by chiral Lewis acids in many cases led to the formation of enantiomerically enriched tertiary phosphines [120-129]. Chiral complexes of ruthenium, platinum, and palladium were used. For example, chiral complex Pt(Me-Duphos)(Ph)Br catalyzed asymmetric alkylation of secondary phosphines by various RCH2X (X=C1, Br, I) compounds with formation of tertiary phosphines (or their boranes) 200 in good yields and with 50-93% ee [121]. The enantioselective alkylation of secondary phosphines 201 with benzyl halogenides catalyzed by complexes [RuH (/-Pr-PHOX 203)2] led to the formation of tertiary phosphines 202 with 57-95% ee [123, 125]. Catalyst [(R)-Difluorophos 204)(dmpe]Ru(H)][BPh4] was effective at asymmetric alkylation of secmidaiy phosphines with benzyl bromides, whereas (R)-MeOBiPHEP 205/dmpe was more effective in the case of benzyl chlorides (Schemes 65, 66, and 67) [125—127]. 

Enantioselective cyclopropanation is currently being explored. The ruthenium complex shown previously in Figure 7 also reacts with EDA and styrene to afford a transxis ratio of 4 1, with 46% ee of the trans isomer. The cis isomer is nearly racemic (<10% ee). The use of four-substituted stjrrene derivatives dramatically increases the diastereoisomeric excess of the trans isomer, with 4-fluorostyrene giving an 11 1 ratio, with 50% ee (74). Conversely, as shown in Figure 21, the porphyrin-like [RuCl(PNNP)]+ precatalyst reacts with EDA/ styrene to afford the cis isomer at a ratio of 10 1, with an enantiomeric excess of 87% (76). These types of ruthenium complexes have also been described as epoxi-dation catalysts above clearly there are mechanistic similarities between the oxo-and carbene- intermediates, which could help elucidate the reasons behind such variable enantioselectivity. Other ruthenium complexes that catalyze cyclopropanation include CpRu(II) catalysts, arene ruthenium complexes, and ruthenium-salen complexes. Cp Ru(cod)Cl is also known to catalyze the related reaction of diazo compounds with alkynes, affording the corresponding 1,3-diene (Figure 22) (77). 

All methyl isomers of norbornene, 1-, 2-, 5-, and 7-methylnorbornene have been reacted in the presence of catalysts based on tungsten, rhenium, ruthenium, osmium and iridium compounds [7]. The polymers corresponded to ring-opened products having various microstructures. Racemic mixtures or pure enantiomers have been used as starting materials. Differences in reactivities as a function of the methyl position (1, 2, 5 or 7) and steric configuration (endo-exo and syn-anti) have been reported. 

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