TolBINAP

Jessop and co-workers studied asymmetric hydrogenation reactions with the catalyst complex Ru(OAc)2(tolBINAP) dissolved in [BMIM][PFg]. In both reactions under investigation - the hydrogenation of tiglic acid (Scheme 5.2.10) and the hydrogenation of the precursor of the anti-inflammatory dmg ibuprofen (Scheme 5.2.11) - no CO2 was present during the catalytic transformation. However, SCCO2 was used in both cases to extract the reaction products from the reaction mixture when the reaction was complete. 

The first application involving a catalytic reaction in an ionic liquid and a subsequent extraction step with SCCO2 was reported by Jessop et al. in 2001 [9]. These authors described two different asymmetric hydrogenation reactions using [Ru(OAc)2(tolBINAP)] as catalyst dissolved in the ionic liquid [BMIM][PFg]. In the asymmetric hydrogenation of tiglic acid (Scheme 5.4-1), the reaction was carried out in a [BMIM][PF6]/water biphasic mixture with excellent yield and selectivity. When the reaction was complete, the product was isolated by SCCO2 extraction without contamination either by catalyst or by ionic liquid. 

Enantioselective hydroxylation of the double bond in C=N nitrones with diphenylsilane, using RU2CI4-I(S)-(—)-p-tolbinap 2(NEh) [p-tolbinap = 2, 2 -bis(di-p-tolylphosphino)-1,1 -binaphthyl] as a catalyst at 0°C, gives the corresponding optically active /V,N -disubstituted hydroxylamines (482). 

An ( )-TolBINAP-Ir complex with a protic amine such as benzylzmine as the additive has been applied for the hydrogenation of 2-phenyl-3,4,5,6-tetrahydropyridine, and enantioselectivity up to 90% ee is obtained.314 An ortho-metallated Ir dihydrid complex has been used in the hydrogenation of 2-methylquinoxaline, and enantiopurity up to 90% ee has been obtained for the 2-methyl-1,2,3,4-tetrahydroquinoxaline product (Scheme 16).327... 

In order to establish the industrial application, [Rh(BINAP)2]C104 was developed as a new catalyst, which has excellent thermal stability allowing multiple repetition of the catalyst recovery. A further improvement of the catalyst was accomplished by the use of [Rh(TolBINAP)2]Cl04, which possessed a better solubility in organic solvents and achieved even higher optical yields (>98% ee) for the isomerization of allylamines such as geranylamine and nerylamine.15... 

Metal-catalyzed C-H bond formation through isomerization, especially asymmetric variant of that, is highly useful in organic synthesis. The most successful example is no doubt the enantioselective isomerization of allylamines catalyzed by Rh(i)/TolBINAP complex, which was applied to the industrial synthesis of (—)-menthol. A highly enantioselective isomerization of allylic alcohols was also developed using Rh(l)/phosphaferrocene complex. Despite these successful examples, an enantioselective isomerization of unfunctionalized alkenes and metal-catalyzed isomerization of acetylenic triple bonds has not been extensively studied. Future developments of new catalysts and ligands for these reactions will enhance the synthetic utility of the metal-catalyzed isomerization reaction. 

Fig. 32.30 Rapid hydrogenation of acetophenone catalyzed by the TolBINAP/DPEN-Ru complex.

Fig. 32.32 Proposed catalytic cycle of hydrogenation of simple ketones with the TolBINAP/DPEN-Ru catalyst.

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