Hydrogenation Rh-catalyzed

The first successful hydrogenation reactions in ionic liquids were studied by the groups of de Souza [45] and Chauvin [46] in 1995. De Souza et al. investigated the Rh-catalyzed hydrogenation of cyclohexene in l-n-butyl-3-methylimidazolium ([BMIM]) tetrafluoroborate. Chauvin et al. dissolved the cationic Osborn complex [Rh(nbd)(PPh3)2][PFg] (nbd = norbornadiene) in ionic liquids with weakly coordinating anions (e.g., [PFg] , [BFJ , and [SbF ] ) and used the obtained ionic catalyst solutions for the biphasic hydrogenation of 1-pentene as seen in Scheme 5.2-7. 

The results clearly show that these novel ligands are able to form a suitable asymmetric enviromnent around the metal resulting in high asymmetric induction. Their catalytic potential has been demonstrated in the highly enantioselective Rh-catalyzed hydrogenation of itaconates and a-enamides and Ru-catalyzed hydrogenation of p-functionalized ketone. 

Table 3 Rh-catalyzed hydrogenative aldol cyclization of aldo-enonesa...

Table6 Highly syn-diastereoselective intermolecular Rh-catalyzed hydrogenative aldol coupling of vinyl ketones through the tri-2-furylphosphine effect3...

Scheme 5 Intermolecular Rh-catalyzed hydrogenative aldol coupling under an atmosphere of deuterium...

The coupling of enals and glyoxals was realized by hydrogen-mediated reaction with the cationic Rh complex and PI13P [35]. The intermediate aldehyde enolates derived via Rh-catalyzed hydrogenation were trapped with glyoxals to form (l-hydroxy-y-kclo-aldchydes, which were treated sequentially with hydrazine to give pyridazines in a one-pot transformation to provide, for example, a 62% yield of 72 (Scheme 21). 

A C2-symmetric bisphosphane FerroPhos has been developed by Kang and is found to be efficient for the Rh-catalyzed hydrogenation of a-dehydroamino acid derivatives.86,863 Knochel has independently reported a class of FERRIPHOS (MandyPhos) with similar structural features. All these ligands have provided excellent... 

Hydrogenation of ct-dehydroamino acid derivatives has been a typical reaction to test the efficiency of new chiral phosphorus ligands. Indeed, a number of chiral phosphorus ligands with great structural diversity are found to be effective for the Rh-catalyzed hydrogenation of a-dehydroamino acid derivatives. Since (Z)-2-(acetamido)cinnamic... 

The fundamental discovery by Burk et al. that the analogous trans-2,5-disub-stituted phospholanes formed a more rigid steric environment led to the introduction of the DuPhos and BPE ligand classes (Fig. 24.1) [8-13]. Subsequently, these ligands have been successfully employed in numerous enantiomeric catalytic systems [4 a, 5], the most fruitful and prolific being Rh-catalyzed hydrogenations. The reduction of N-substituted a- and /1-debydroarnino acid derivatives,... 

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