Tridentate bis-oxazoline ligand

SCHEME 12.21. The application of tridentate bis(oxazoline) ligands 26 in the NHK allylation and crotylation of benzaldehyde. 

McManus HA, Cozzi P-G, Guiry PJ. Application of tridentate bis(oxazoline) ligands in catalytic asymmetric Nozaki-Hiyama allylation and crotylation an example of high enan-tioselection with a non-symmetric bis(oxazoline) ligand. Adv. Synth. Catal. 2006 348 551-558. 

McManus HA, Guiry PJ. Coupling of bulky, electron-deficient partners in aryl amination in the preparation of tridentate bis (oxazoline) ligands for asymmetric synthesis. J. Org. Chem. 2002 67 8566-8573. 

The C2-symmetric bifunctional tridentate bis(thiazoline) 222 has been shown to promote the zinc(II)-catalyzed asymmetric Michael addition of nitroalkanes to nitroalkenes in high enantioselectivity <06JA7418>. The corresponding bis(oxazoline) ligand provides comparable enantioselectivity but higher product yield. The same bis(thiazoline) ligand has also been evaluated in the enantioselective Friedel-Crafts alkylation of indoles, but the enantioselectivity is moderate <06OL2115>. 

A series of chiral C2-symmetric tridentate bis(oxazoline) 110, 112 and bis(thiazoline) 111, in which a diphenylamine unit links the two chiral ox-azolines, was used for a more practical and efficient catalytic asymmetric alkylation of indoles with nitroalkenes (Scheme 31) [104], The alkylation of indole with frarzs-P-nitrostyrene in toluene at room temperature has been accomplished with 110d-Zn(OTf)2 or 113-Zn(OTf)2 as the catalyst. The obtained results show that the NH group in ligands 110-112 is crucial. Indole... 

The concept developed for the asymmetric Sn-catalyzed aldol reaction with chiral Ar,AT-ligand by Mukaiyama and co-workers was further extended by Evans and co-workers with bidentate bis(oxazoline) and tridentate pyridylbis(oxazoline) ligands (186). After a survey of ligand architecture, the best level of asymmetric induction was exhibited by [Sn(S,S)-pybox](OTf)2 138 for the Mukaiyamai aldol reaction of substituted silylketene acetal and methyl pyruvate. Noteworthy, the... 

Bis(oxazoline)pyridine (Pybox) and terpyridine (terpy) belong to the family of tridentate ligands that are often excluded from the discussions on pincer chemistry. However, recent studies have shown that in some cases they are redox-active [52, 53] and exhibit properties closely resembling those of pincer ligands. Thus, cross-coupling reactions catalyzed by nickel complexes containing these ligands are also discussed in this chapter. 

Nakada et al. developed a tridentate C2-symmetric bis (oxazolinyl)carbazole ligand 15 and proposed that this tridentate ligand would provide enhanced enantioselectivities as a result of stabilization of the allyl-Cr(lll)-ligand complex because of the presence of a o-bond with the carbazole nitrogen and two coordination bonds to the oxazoline nitrogens, which leaves a vacant coordination site at which an aldehyde can bind. ... 

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