Phosphoroamidite ligands

Bidentate Diphosphinite, Phosphite-Phosphinite, Diphosphite and Phosphine-Phosphoroamidite Ligands... 

Fig. 15 Phosphine-phosphoroamidite ligands 16-18. Summary of the best results obtained in the Ir-catalyzed hydrogenation quinolines using ligand 18...

A set of novel phosphine-phosphoroamidite ligands 16-18 (Fig. 15) possessing two elements of chirality have been prepared through a modular synthetic approach and successfully applied in the Ir-catalyzed asymmetric hydrogenation of... 

E. Raluy, O. Pamies, M. Dieguez, S. Rosset, and A. Alexakis, Sugar-based phosphite and phosphoroamidite ligands for the Cu-catalyzed asymmetric 1,4-addition to enones. Tetrahedron Asymmetry, 20 (2009) 2167—2172. 

Recently, Zhang and coworkers developed a new phosphine-phosphoroamidite ligand based on BINAPFIOS (Figure 3.13). This ligand provided excellent enantios-electivities (up to 99%) in the Rh-catalyzed hydroformylation of vinyl arenes and vinyl acetate [39]. 

For unsubstituted cyclic enones, 4,4-substituted and 2-substituted cychc enones, the use of Cu-precursors modified with biaryl phosphoroamidite ligands has been widely studied (Fig. 1). In general, two sets of conditions have been found to be optimal for the 1,4-addition of trialkylaluminum reagents, the choice of which depends on the solvent and the copper source used. Thus, while copper thiophene... 

Biaryl-based phosphoroamidite ligands provide optimum results (conversions and enantioselectivities) for the less hindered 6- and 7-membered substrates (i.e.,... 

A -phosphine (SimplePhos) ligands provide similar levels of enantioselectivity than those observed with phosphoroamidite ligands for simple trisubstituted enones [23, 34, 35]. However, the scope of this type of ligands is higher, because they also facilitate the highly enantioselective 1,4-addition of trialkylaluminum species to more challenging hindered substrates (i.e. = Bu Fig. 3) and 3-aryl-... 

Scheme 11 Representative results for the conjugate addition of trialkylaluminum to alkyl-substituted linear enones using phosphoroamidite ligand L2...

Binol-derived phosphoroamidite PipPhos (19) has been successfully used as a ligand for the Ir-catalyzed asymmetric hydrogenation of 2- and 2,6-substituted quinolines [39], 2- and 2,6-substituted quinoxalines [40], and IV-aryl imines [41] (Fig. 16). 

In situ-generated iridium complexes containing bulky 3,3 -substituted H8-phosphoroamidites 20 as ligands catalyzed the asymmetric hydrogenation of... 

Stereochemical studies on the formation of chiral internucleotide linkages using the phosphoroamidite approach which are relevant to the mechanism of the activation process have been initiated by Stec and Zon [15]. When tetra-zole was used as the activator, however, complete epimerization at the phosphorus centre was observed and this was explained by the rapid and multiple ligand exchange at the intermediate tetrazolide. In spite of these early discouraging observations highly promising results have been recently disclosed. 

Example 7 the bis(2,4-dinitrophenyl)phosphoroamidite which can be prepared by a standard procedure reacts with alcohols in a non-selective way which leads to a mixture of products [28]. From a mechanistic point of view this result is consistent with spontaneous displacement of a 2,4-dinitro-phenoxy group in the reaction with alcohol which liberates free DNP. The latter activates the amino group allowing further ligand exchange. However if phosphitylation by the bis(2,4-dinitrophenyl)phosphoroamidite is performed in the presence of one equivalent of triethylamine, high chemoselec-tivity is observed, and the nucleoside (2,4-dinitrophenyl)phosphoramidite is formed in over 92% yield. 

Phosphoroamidites of protected D-fructosamine derivatives 101 have been prepared as chiral ligands for coordination to Ni(II) and Cu(II), and the resulting complexes were employed as catalysts for asymmetric dialkylzinc and trialkylaluminum addition reactions with carbonyls " and enones. " ... 

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]. 

Magre M, Mazuela J, Dieguez M, Panties O, Alexakis A (2012) Furanoside phosphite-phosphoroamidite and diphosphoroamidite ligands applied to asymmetric Cu-catalyzed allylic substitution reactions. Tetrahedron Asymmetry 23 67-71... 

Biaryl phosphoroamidite Fig. 1 Most representative ligand types... 

Fig. 3 Representative results for the addition of trialkylaluminuni reagents to tiisubstituted cyclic enones using biaryl-based phosphoroamidite and iV-phosphine ligands...

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