Asymmetric Transition-Metal Catalyzed Reactions

Quinap (95) in a number of mutually unrelated transition-metal-catalyzed asymmetric reactions.50 Thus, 105 added to tert-butyl acrylate 106 using silver acetate and PINAP ligand 96, under the conditions described in Scheme 2.25, to provide the desired product 109 in excellent enantioselectivity and yield (see Scheme 2.6 and Table 2.5). Notably, the reaction required only 3 mol% of catalyst for complete conversion at -40°C within 36 h. 

Chiral phosphine ligands are the chiral auxiliaries extensively studied for transition metal-catalyzed asymmetric reactions. Most of the ligands were originally designed for asymmetric hydrogenation, but they also worked well in the conjugate addition of organoboronic acids to electron-deficient alkenes.951,952 The rhodium(i) complexes of 496-503953-966 have been successfully utilized for these asymmetric reactions (Scheme 37). 

The reaction is catalyzed by transition metal complexes coordinated with phosphine ligands. Since chiral phosphine ligands are the chiral auxiliaries most extensively studied for transition metal catalyzed asymmetric reactions, one can use the accumulated knowledge of the chiral phosphine ligands for the asymmetric reaction. The asymmetric 1,4-addition of aryl- and 1-alkenylboronic acids to enones proceeded with high enantioselectivity in the presence of a chiral phosphine-rhodium catalyst (Table 2). 

Enantiomerically pure phosphines are frequently employed as ligands in transition-metal-catalyzed asymmetric reactions. For this reason, various methods have been designed for their preparation.1 Many of them involve the use of borane adducts of trivalent phosphorus compounds,2 in which the borane moiety mainly acts as a protecting group. These Lewis adducts are easily prepared and stable to air, and several methods have been designed to cleave them. 

Hayashi, T. Chiral Monodentate Phosphine Ligand MOP for Transition Metal-Catalyzed Asymmetric Reactions, Acc. Chem. Res. 2000,33,354-362. 

Probably the most important class of planar-chiral ferrocenes accessible by the techniques delineated above is that of chelating ligands for transition-metal-catalyzed asymmetric reactions [1]. Progress in this area is characterized, among others, by ligands of type 16 [14], 17 [15], and 18 [16]. 

The concept of C2-symmetric ligands has widely been recognized as an ideal design of asymmetric ligands, which include DIOP, chiraphos, and BINAP. These ligands have been applied to a variety of transition metal-catalyzed asymmetric reactions and have been fairly successful. However, this situation is not always applied to rr-allylpalla-dium-mediated asymmetric allylic substitutions. In the reaction, which has been the most frequently examined asymmetric reaction catalyzed by 7r-allylpalladium complexes, two factors need to be controlled for the sake of high stereoselectivity. One is... 

For the last few years, enormous success has been achieved in the asynunetric synthesis of organophosphorus compounds, primarily for phosphine ligands for transition metal-catalyzed asymmetric reactions, and many articles devoted to the synthesis of chiral organophosphorus compounds have been published. It is therefore interesting to analyze and systematize the data dedicated to asynunetric synthesis of F-chiral organophosphorus compounds that have been published over the last 5-10 years. 

Nemoto T (2008) Transition metal-catalyzed asymmetric reactions using P-chirogenic diaminophosphine oxides DIAPHOXs. Chem Pharm Bull 56 1213-1228... 

Recently, a new family of axially chiral diphosphine, SEGPHOS, based on a bis(l,3-benzodioxol), was synthesized and is used in several transition metal catalyzed asymmetric reactions (see the next section). 

Functionalization of Azaferrocene Catalysts. Chiral azaferrocenes are highly useful in enantioselective acylation as nucleophilic catalysts, and in transition metal-catalyzed asymmetric reactions as chiral ligands. Enantioselective lithiation of an azaferrocene moiety followed by functionalization with (TMS0)2 resulted in a lateral hydroxyl-substituted product with excellent optical purity, but in poor yield (eq 7). The low yield was attributed to the poor reactivity of (TMSO)2 toward the labile azaferrocene substrate. 

Xie J-H, Zhou Q-L. Chiral diphosphine and monodentate phosphorus ligands on a spiro scaffold for transition-metal-catalyzed asymmetric reactions. Acc. Chem. Res. 2008 41(5) 581-593. 

Hayashi T (2000) Chiral monodentate phosphine ligand MOP for transition-metal-catalyzed asymmetric reactions. Acc Chem Res 33 354—362 and references therein... 

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