Asymmetric hydrogenation alkenes

Regioselective hydroamidation of 1-alkynylphosphine sulfides provided (E)-2-amino-l-thiophosphinyl-l-alkenes. Asymmetric hydrogenation led to the corresponding saturated derivative (Scheme 25). ... 

In 1968,Horner et al. [22] and Knowles and Sabacky [23] independently demonstrated that low but definite enantiomeric excesses (up to 15% ee) were produced in the rhodium-catalyzed asymmetric hydrogenation of simple alkenes using methylpropylphenylphosphine 7 as chiral ligand (Scheme 1). 

In 2004, Bolm et al. reported the use of chiral iridium complexes with chelating phosphinyl-imidazolylidene ligands in asymmetric hydrogenation of functionalized and simple alkenes with up to 89% ee [17]. These complexes were synthesized from the planar chiral [2.2]paracyclophane-based imida-zolium salts 74a-c with an imidazolylidenyl and a diphenylphosphino substituent in pseudo ortho positions of the [2.2]paracyclophane (Scheme 48). Treatment of 74a-c with t-BuOLi or t-BuOK in THF and subsequent reaction of the in situ formed carbenes with [Ir(cod)Cl]2 followed by anion exchange with NaBARF afforded complexes (Rp)-75a-c in 54-91% yield. The chela-... 

A breakthrough in iron-catalyzed asymmetric epoxidation of aromatic alkenes using hydrogen peroxide has been reported by our group in 2008. Good to excellent isolated yields of aromatic epoxides are obtained with ee-values up to 97% for stilbene derivatives using diphenylethylenediamines 9 as ligands (Scheme 5) [45, 46]. 

Experimental evidence of the —S03" H0Si— interaction have been obtained from IR, Rh K-edge EXAFS, and CP MAS 3 IP NMR studies. These supported catalysts have been tested for the hydrogenation and hydroformylation of alkenes. No Rh leaching was observed.128-130 An extension to the immobilization of chiral metal complexes for asymmetric hydrogenation is reported below. 

Asymmetry in metal-alkene coordination plays a critical role in asymmetric catalysis, with implications far beyond the scope of the present treatment. An instructive example is provided by catalytic asymmetric hydrogenation of enamides,... 

Following Wilkinson s discovery of [RhCl(PPh3)3] as an homogeneous hydrogenation catalyst for unhindered alkenes [14b, 35], and the development of methods to prepare chiral phosphines by Mislow [36] and Horner [37], Knowles [38] and Horner [15, 39] each showed that, with the use of optically active tertiary phosphines as ligands in complexes of rhodium, the enantioselective asymmetric hydrogenation of prochiral C=C double bonds is possible (Scheme 1.8). 

Related catalytic enantioselective processes Although great progress has been achieved in the area of metal-catalyzed hydrogenation reactions [124], examples of catalytic asymmetric hydrogenations of tetrasubstituted alkenes are rare. One other example, reported by Pfaltz and co-workers, is depicted in Eq. 6.26 (81 % ee, absolute stereochemistry of the product not determined) [125],... 

Buchwald et al. realized asymmetric hydrogenation of tetrasubstituted alkenes with a cationic zirconocene catalyst prepared by the protonolysis method (Scheme 8.53). The reactions were quite slow with these highly substituted alkenes, but some very good enantiomeric excesses were obtained [96],... 

The broad range of alkenes undergoing asymmetric hydrogenation using ruthenium-based systems as catalysts has attracted the attention of chemists engaged in the synthesis of chiral biologically active natural products (Scheme 13)[60] and other pharmaceuticals (Scheme 14)[61]. a, (3-Unsaturated phosphoric acids and esters have also proved to be suitable substrates for Ru(II)-catalysed asymmetric hydrogenation [62]. 

A more versatile method to use organic polymers in enantioselective catalysis is to employ these as catalytic supports for chiral ligands. This approach has been primarily applied in reactions as asymmetric hydrogenation of prochiral alkenes, asymmetric reduction of ketone and 1,2-additions to carbonyl groups. Later work has included additional studies dealing with Lewis acid-catalyzed Diels-Alder reactions, asymmetric epoxidation, and asymmetric dihydroxylation reactions. Enantioselective catalysis using polymer-supported catalysts is covered rather recently in a review by Bergbreiter [257],... 

As recently recognized by the Nobel Chemistry award committee, the conceptualization, development, and commercial application of enantioselective, homogeneous hydrogenation of alkenes represents a landmark achievement in modem chemistry. Further elaboration of asymmetric hydrogenation catalysts by Noyori, Burk, and others has created a robust and technologically important set of catalytic asymmetric synthetic techniques. As frequently occurs in science, these new technologies have spawned new areas of fundamental research. Soon after the development of... 

The hydroformylation reaction ( oxo reaction ) of alkenes with hydrogen and carbon monoxide is established as an important industrial tool for the production of aldehydes ( oxo aldehydes ) and products derived there from [1-6]. This method also leads to synthetically useful aldehydes and more recently is widely applied in the synthesis of more complex target molecules [7-15,17], including stereoselective and asymmetric syntheses [18-22]. 

Figure 4.10. Asymmetric hydrogenation via major and minor alkene complex intermediate only...

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