Dihydroxylation catalysts, aldol reactions

Precursor of Useful Chiral Ligands. OPEN is widely used for the preparation of chiral ligands. Organometallic compounds with these ligands act as useful reagents or catalysts in asymmetric induction reactions such as dihydroxylation of olefins, transfer hydrogenation of ketones and imines, Diels-Alder and aldol reactions, desymmetrization of meso-diols to produce chiral oxazolidinones, epoxidation of simple olefins, benzylic hydroxylation, and borohydride reduction of ketones, imines, and a,p-unsaturated carboxylates. ... 

In a simplified catalytic cycle, reversible coordination of the dienophile to the Lewis acid (LA) activates the substrate toward diene cycloaddition. In the catalyst turnover event, the Lewis acid-product complex dissociate to reveal the de-complexed cycloadduct and regenerated catalyst (Scheme 2). While this catalytic cycle neglects issues of product inhibition and nonproductive catalyst binding for dienophiles having more than one Lewis basic site, the gross features of this process are less convoluted than many other enantioselective reactions e.g., olefin dihydroxylation, aldol reactions), a fact which may provide insight as to why this process is frequently used as a test reaction for new Lewis acid catalysts. 

The rapid evolution of catalytic reaction methods for enantioselective aldol additions affords newer processes that are increasingly practical in their execution for a broad range of substrates prescribing minuscule amounts of catalyst. However, when compared to other catalytic asymmetric processes such as hydrogenation, dihydroxylation, and epoxidation it is evident that there is much room for further optimization. Without doubt, discovery and innovation in this area of C-C bond-forming reactions will lead to the development of catalysts and processes indispensable to the synthesis of optically active, stereochemically complex structures with applications in materials science and medicine. 

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