Multidentate chiral ligands

Carbonyls. The title compound is widely used as an oxophilic Lewis acid, efficiently increasing the reactivity of carbonyl groups toward the additions of many nucleophiles. a-Dicarbonyls are particularly effective substrates for this kind of activation. A catalytic amount of In(OTf)3 combined with a multidentate chiral ligand allows nucleophiles, such as allylstannanes (eq 23), electron-rich... 

Macropolycyclic ligands, 2,942 classification, 2,917 metal complexes binding sites, 2, 922 cavity size, 2,924 chirality, 2, 924 conformation, 2,923 dimensionality, 2, 924 electronic effects, 2, 922 shaping groups, 2,923 structural effects, 2,922 molecular cation complexes, 2,947 molecular neutral complexes, 2,952 multidentate, 2,915-953 nomenclature, 2,920 Macro tetrolide actins metal complexes, 2,973 Macrotricycles anionic complexes, 2,951 cylindrical... 

Another class of ligands for ATH is represented by multidentate Schiff bases and their derivatives. Zassinovich and Mestroni reported on the effective reduction of alkyl aryl ketones catalyzed by a series of lr(l) complexes with chiral bidentate pyridylaldimines, of the form [lr(cod)(NNR )]C104 (76a-f see Scheme 4.31). It was observed that both the activity and selectivity depended heavily on the nature of the subshtuents at the chiral center of the ligand, and also at the prochiral center of the substrate. Optical yields of up to 50% (R-isomer) at 100% conversion were obtained in the ATH of BuC(0)Ph and PhCH2C(0)Ph using [lr(cod)(PPEl)]C104 as the precatalyst (0.1% mol, 83 °C, PrOH, KOH) [66]. 

Benzoyl formate decarboxylase from Pseudomonas putida has been used to synthesize chiral 2-hydroxy ketones and bis(a-hydroxy) ketones, which find their use as pharmaceutical intermediates and as new multidentate ligands for asymmetric transition metal catalysis, respectively.272 273 Combining this decarboxylase activity with AdH has allowed all the stereoisomers of 1 -phenyl-propane- 1,2-diol to be synthesized.274... 

Introduction of chirality in ancillary groups often acts by steric repulsion between different ligands, but the podates form an important exception. These multidentate ligands have two or more ligating strands attached to a template, and if this is chiral. 

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