Imines metallated chiral

Asymmetric catalytic reduction reactions represent one of the most efficient and convenient methods to prepare a wide range of enantiomerically pure compounds (i.e. a-amino acids can be prepared from a-enamides, alcohols from ketones and amines from oximes or imines). The chirality transfer can be accomplished by different types of chiral catalysts metallic catalysts are very efficient for the hydrogenation of olefins, some ketones and oximes, while nonmetallic catalysts provide a complementary method for ketone and oxime hydrogenation. 

C. Reduction of Imines with Chiral Metal Hydride Reagents. 112... 

Since then, efficient catalytic asymmetric methods have been developed for the addition of silyl enol ethers or silyl ketene acetals to imines with chiral metal catalysts [29-34], Recently, direct catalytic asymmetric Mannich reactions which do not require preformation of enolate equivalents have appeared. 

Another important means of mediation of metal-free catalytic enantioselective Mannich-type reactions is via electrophilic activation of the preformed imines by chiral Bronstedt acids [7, 8, 46], By using this strategy Terada and coworkers performed chiral phosphoric acid-catalyzed direct asymmetric Mannich-type reactions between Boc-protected imines and acetoacetone that furnished aryl /3-amino... 

Chiral oxazolidines 6, or mixtures with their corresponding imines 7, are obtained in quantitative yield from acid-catalyzed condensation of methyl ketones and ( + )- or ( )-2-amino-l-phcnylpropanol (norephedrine, 5) with azeotropic removal of water. Metalation of these chiral oxazolidines (or their imine mixtures) using lithium diisopropylamide generates lithioazaeno-lates which, upon treatment with tin(II) chloride, are converted to cyclic tin(II) azaenolates. After enantioselective reaction with a variety of aldehydes at 0°C and hydrolysis, ft-hydroxy ketones 8 are obtained in 58-86% op4. 

The synthesis of sulfoximides and sulfimides has attracted considerable attention in recent years due to the potential utility of these compounds as efficient auxiliaries and chiral ligands in asymmetric synthesis (reviews [86-88]). Transition metal-catalyzed nitrene transfer to sulfoxides and sulfides is an efficient and straightforward way to synthesize sulfoximides and sulfimides, respectively. Bach and coworkers reported the first iron-catalyzed imination of sulfur compounds with FeCl2 as catalyst and B0CN3 as nitrene source. Various sulfoxides and sulfides were... 

So far, there is only one report describing the use of chiral NHC-metal complexes in catalytic asymmetric arylation of imines. This was achieved by using C -symmetric cationic NHC-Pd diaquo complex 20 (Scheme 7.6) [38]. The arylation of a variety of A-tosylimines with different arylboronic acids was carried out under mild conditions. The presence of electron-withdrawing or electron-donating substituents on both partners did not seem to affect the reaction and the corresponding chiral diarylamines were obtained in good to excellent yields and high enantiomeric excess. 

Scheme 5-47 Asymmetric hydrophosphonylation of a cyclic imine catalyzed by heterobimetallic rare earth/alkali metal/BI-NOL complexes or by chiral titanium alkoxide complexes...

The discussion of the activation of bonds containing a group 15 element is continued in chapter five. D.K. Wicht and D.S. Glueck discuss the addition of phosphines, R2P-H, phosphites, (R0)2P(=0)H, and phosphine oxides R2P(=0)H to unsaturated substrates. Although the addition of P-H bonds can be sometimes achieved directly, the transition metal-catalyzed reaction is usually faster and may proceed with a different stereochemistry. As in hydrosilylations, palladium and platinum complexes are frequently employed as catalyst precursors for P-H additions to unsaturated hydrocarbons, but (chiral) lanthanide complexes were used with great success for the (enantioselective) addition to heteropolar double bond systems, such as aldehydes and imines whereby pharmaceutically valuable a-hydroxy or a-amino phosphonates were obtained efficiently. 

The interpretation and prediction of the relationship between the configuration of the newly formed chiral center and the configuration of the amine is usually based on steric differentiation of the two faces of the imine anion. Most imine anions that show high stereoselectivity incorporate a substituent that can engage the metal cation in a... 

Other supramolecular structures such as catenanes and rotaxanes can be formed using zinc as a template ion for example, a benzylic imine catenate formed by Leigh et a/.288 The reversible five-component assembly of a [2]catenane from a chiral metallomacrocycle and a dinaphtho-crown ether has been achieved. Zinc is used as the metal component and drives assembly via the coordination to a bipyridyl unit 7r interactions between the aromatic components are also... 

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