Scandium complexes with 2 2 -bipyridine

In recent years, many chiral catalysts for the enantioselective synthesis of optical active 1,5-dicarbonyl compounds have been developed, such as chiral crown ethers with potassium salt bases and chiral palladium complexes, including bimetallic systems. Nakajima and coworkers reported on enantioselective Michael reactions of S-keto esters to a,/3-unsaturated carbonyl compounds in the presence of a chiral biquinoline N,N dioxide-scandium complex, which catalyzed the additions in high yields and with enan-tioselectivities up to 84% ee . Kobayashi and coworkers found that the combination of Sc(OTf)3 with the chiral bipyridine ligand 149 (equation 41) was also effective as a chiral catalyst for asymmetric Michael additions of 1,3-dicarbonyl compounds 147 to a,/3-unsaturated ketones 148. The corresponding Michael adducts 150 were obtained in good to high yields with excellent enantiomeric excesses in most cases (Table 10). 

The scandium diene complex reacts with PhCN via initial nitrile insertion into the Sc-diene bond to give a dimeric r/2-imido species, but with a 2,2 -bipyridine under elimination of the free diene (Scheme 71). The latter reaction... 

Scandium trifiate was found to be an effective catalyst for the aldol reactions of silyl enol ethers with aldehydes in aqueous solvent/micellar systems (205). While the reactions proceeded sluggishly in water, remarkable enhancement of the reactivity was observed in the presence of a small amount of a surfactant (206). In related asymmetric version, scandium trifiate (Sc(OTf)3) catalyzed asymmetric aldol of formaldehyde (hydroxymethylation) could be conducted with highly enantioselectively in the presence of chiral bipyridine based ligand (Scheme 53) (207). A significant progress was also made by Feng and co-workers recently a C-2-symmetric iV,iV -dioxide-Sc(III) complex has been developed to asymmetric catalytic aldol reaction of a-ketoesters and diazoacetate... 

Catalytic enantioselective addition of amines to wiayo-epoxides can be realized by employing a scandium bipyridine complex in 100% water (Scheme 31). Chiral jS-amino alcohols were prepared in mostly high yields with excellent enantioselectivities (Scheme 31). It is noted that the use of water as a solvent gave a higher yield and enantioselec-tivity than the use of dichloromethane as a solvent. ... 

Kobayashi developed an operationally simple, enantioselective addition of aromatic amines to meso-epoxides using a scandium/chiral bipyridine complex in water so that /3-aminoalcohols could be obtained in high yields and with ee sup to 96% (Scheme 8.19). °... 

Using same strategy, a catalytic, enantioselective addition of amines to meso-epoxides was established employing a scandium-bipyridine complex in emulsion (Scheme 8.12). In this work, Kobayashi and coworkers demonstrated that high yields and excellent enantioselectivities could be achieved using an amphiphilic Lewis acid combined with chiral Hgand as the catalyst in water. This work offered a green method for the synthesis of a-amino alcohols, which are important... 

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