Phosphoramidites. as ligands

Phosphoramidites as Ligands for the ir-Catalyzed Allylic Substitution 9.2.4.1 Survey... 

Allyl carbonate 81 reacts with primary and secondary amines 82 to afford branched aUylic amination products 83 under the influence of a [IrCl(cod)]2/ P(OPh)3 catalyst (Equation 10.17) [38]. In this reaction, alcohols such as ethanol and methanol proved to be the best solvents, while both intermolecular and intramolecular enantioselective aUylic aminations were reported by using chiral phosphoramidites as ligands [39]. The aUylic amination of (Zj-2-noneyl carbonate 85 with 82 in the presence of [IrCl(cod)]2 and P(OPh)3 afforded Z-linear aUylic amines (Equation 10.18) [38]. In this reaction, the Z-geometry of 85 was completely retained. 

Membered cyclic phosphoramidites as ligands in catalytic asymmetric conjugate addition 00ACR346. 

Terminal alkynes react similarly with alkenyl isocyanates. In the presence of chiral phosphoramidites as ligands the corresponding cycloadducts are obtained. For example, from the alkenyl isocyanate 197 and the heterocyclic alkyne 198 the cycloadducts 199 and 200 are obtained in 85 % yield (91 % e,e) . 

Scheme 7.9. Copper-catalyzed 1,4-addition to cyclohexenone and chalcone, with phosphoramidites as chiral ligands.

Cationic nickel catalysts with monodentate phosphoramidites and Wilke s azaphosp-holene as ligands have been shown to be highly regio- and enantio-selective catalysts for the cycloisomerization of diethyl diallylmalonate (Scheme 78).120... 

Phosphoramidites, a ligand class that has only recently been introduced into asymmetric hydrogenation, in the form of hybrid chelate ligands [29], induce excellent enantioselectivity as monodentate ligands. Thus de Vries, Feringa, and co-workers could reduce standard substrates in >96% ee with a rhodium complex based upon the binaphtholphosphoramidite 3d, once the solvent and reaction temperature had been optimized [30],... 

It is evident from the previous examples that most copper catalysts have been applied only to simple, unsubstituted Michael acceptors so far. Only very recently, chiral, substituted cyclohex-2-enones were used as substrates for copper-catalyzed enantioselective 1,4-additions with phosphoramidites as the chiral ligand. Thus, highly enantioselective kinetic resolutions of several 4- or 5-substituted cyclohex-2-enones were reported by Feringa and co-workers.236,236a In contrast to these Michael acceptors, the corresponding 6-substituted cyclohex-2-enones possess a stereogenic center which can be... 

Although the polymerized or linked monodentate phosphoramidites are no longer monodentate phosphorus ligands, the nature of their coordination to the central metal of the catalysts resembles to that of the monodentated phosphoramidites. The catalysts are not chelate complexes like those with bidentate ligands. So it is suitable to discuss the polymerized or linked phosphoramidites as monodentate phosphorus ligands. 

The MonoPhos family of ligands for the reduction of C-C double bonds, including enamides, is based on the 2,2-bisnaphthol (BINOL) backbone. These phosphoramidite ligands are comparatively inexpensive to prepare compared to bisphosphine ligands. For enamide reductions with MonoPhos (20) as ligand, it was found that the reaction is strongly solvent dependent. Very good enantioselectivities were obtained in nonprotic solvents. - ... 

Besides phosphines and phosphites preferentially used as ligands in hydro-formylation, phosphoramidites have also been proposed. Phosphoramidites (sometimes also called phosphoroamidites) are a class of organic phosphorus compounds derived from phosphites in which the P-OR groups have been replaced by P-NR2 groups (Figure 2.31). Three different P-substituents produce a chiral (stereogenic) phosphorus atom. Phosphoramidites play a crucial role in the synthesis of nucleic acids [1] and have also been frequently considered as mono- or bidentate ligands in transition-metal catalysis [2]. 

Scheme 5 Cu-catalysed asymmetric phosphoramidite as chiral ligand L4...

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