Heterogeneous asymmetric catalysis hydrogenation

Chiral PCPs can be used for heterogeneous asymmetric catalysis.43,52 162 164 167 The chiral porous ZrIV phosphonate with Run-binap fragments (binap = 2,2 -bis(diphenylphosphanyl)-1,1 -binaphthyl) has a permanent porosity, and shows asymmetric catalytic activity in the hydrogenation of (3-keto esters with enantiomeric excess values of up to 95%.162... 

Another well-known example of catalytic asymmetric hydrogenation is the synthesis of L-Dopa (an anti-Parkinson drug) developed by Monsanto [315], which is schematically reported in Figure 2.56, where the role of the chiral phosphine ligand is also highlighted. Various attempts have been also reported to use heterogeneous asymmetric catalysis (cinchonine modified Pd/C) to produce L-Dopa, although the results are still unsatisfactory [316]. 

A spectacular, site-isolation effect in heterogeneous asymmetric catalysis was first reported by Pugin et al. The asymmetric hydrogenation of imine 1 is important for the commercial production of fS -metolachlor, a herbicide presently produced at >10000 tons per year. In this reaction, whereas homogeneous Ir-BPPM (2) catalyst prepared with [Ir(COD)Cl]2 was deactivated after 26% conversion (turnover frequency (TOP) min = 0), the covalently immobilized Ir catalysts, Si-PPM (3)-Ir, were much more active and productive (TOP min = up to 5.1 Scheme 2.1)... 

Felfoldi, K., Balazsik, K., Bartok, M. (2003) Heterogeneous asymmetric catalysis. Part 32. High enantioselectivities in the hydrogenation of activated ketones on cinchona alkaloid modified Platinum-alumina catalysts, J. Mo/. Catal. A. Chem. 202, 163-170. 

The enantioselective hydrogenation of prochiral substances bearing an activated group, such as an ester, an acid or an amide, is often an important step in the industrial synthesis of fine and pharmaceutical products. In addition to the hydrogenation of /5-ketoesters into optically pure products with Raney nickel modified by tartaric acid [117], the asymmetric reduction of a-ketoesters on heterogeneous platinum catalysts modified by cinchona alkaloids (cinchonidine and cinchonine) was reported for the first time by Orito and coworkers [118-121]. Asymmetric catalysis on solid surfaces remains a very important research area for a better mechanistic understanding of the interaction between the substrate, the modifier and the catalyst [122-125], although excellent results in terms of enantiomeric excesses (up to 97%) have been obtained in the reduction of ethyl pyruvate under optimum reaction conditions with these Pt/cinchona systems [126-128],... 

The desire to produce enantiomerically pure pharmaceuticals and other fine chemicals has advanced the field of asymmetric catalytic technologies. Since the independent discoveries of Knowles and Homer [1,2] the number of innovative asymmetric catalysis for hydrogenation and other reactions has mushroomed. Initially, nature was the sole provider of enantiomeric and diastereoisomeric compounds these form what is known as the chiral pool. This pool is comprised of relatively inexpensive, readily available, optically active natural products, such as carbohydrates, hydroxy acids, and amino acids, that can be used as starting materials for asymmetric synthesis [3,4]. Before 1968, early attempts to mimic nature s biocatalysis through noble metal asymmetric catalysis primarily focused on a heterogeneous catalyst that used chiral supports [5] such as quartz, natural fibers, and polypeptides. An alternative strategy was hydrogenation of substrates modified by a chiral auxiliary [6]. 

This book contains many publications which represent analyses of the steps of elaboration of effective heterogeneous enantioselective hydrogenation catalysts, of their significant role in the theory of catalysis, and of their role in the practice of asymmetric catalysis. In addition to reviewing the first works on catal Tic hydrogenation of C=C double bond in prochiral compounds on metal catalysts supported on chiral carriers, which admittedly have only historical interest, the Chapters 1-3 review data on asymmetric adsorption of enantiomers and separation of racemic mixtures on organic and inorganic adsorbents. 

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