Chiral ligands design

Fig. 2.11 Chiral ligand designs in Rh catalysts for the enantioselective hydrosilylation of carbonyl compounds...

Figure 9.4 A modular approach to chiral ligand design using metal-directed heteroleptic self-assembly of chiral bidentate SALs 5 and bimetallic catalysts 6 incorporating both structural (Ms) and catalytic metals (M ).

The number of chiral ligands designed for bidentate attachment to copper has grown rapidly during the 1990s, but only three have shown substantial promise Katsuki s chiral bipyrid-ines 13 [48], Fu s C2-symmetric bisazaferrocene 14 [49], and chiral 1,2-diamine 15 [50]. 

The sugar-derived chiral ligands designed by the Dieguez/Ruiz/Claver group... 

Lee JY, Miller JJ, Hamilton SS, Sigman MS. Stereochemical diversity in chiral ligand design discovery and optimization of catalysts for the enantioselective addition of allylic halides to aldehydes. Org. Lett. 2005 7 1837 1839. 

The use of metal catalysts for the synthesis of chiral cyanohydrins has also witnessed impressive developments (163, 164). In 1991, Oguni reported that the combination of Schiff base 261 with Ti(Oi-Pr)4 promotes the addition of TMSCN to aldehydes to give optically active adducts (20-96% ee. Equation 20) [172]. Incorporation of substituted salicylaldehydes as the corresponding Schiff bases in chiral ligand design has generally proven fruitful in a wide range of transformations. 

We therefore prepared a new chiral ligand, (l ,J )-isopropylidene-2,2 -bis[4-(o-hy-droxybenzyl)oxazoline)], hereafter designated J ,J -BOX/o-HOBn. To our delight, the copper(II) complex catalyst prepared from J ,J -BOX/o-HOBn ligand and Cu(OTf)2 was quite effective (Scheme 7.45). Especially, the reaction of O-benzylhydroxylamine with l-crotonoyl-3-isopropyl-2-imidazolidinone in dichloromethane (0.15 m) at -40°C in the presence of J ,J -BOX/o-HOBn-Cu(OTf)2 (10 mol%) provided the maximum enantioselectivity of 94% ee. 

Fig. 2.1 Chiral NHC ligand designs used in the Rh-catalysed enantioselective hydrogenation of...

The MOP range of ligands designed by Hayashi has proved remarkably useful for asymmetric hydrosilylation reactions.59 MOP ligands are a series of enantiomerically pure monophosphine ligands whose chirality is due to 1,1 -binaphthyl axial chirality. 

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