Chirality transfer phosphite ligands

Chiral thioureas have been synthesized and used as ligands for the asymmetric hydroformylation of styrene catalyzed by rhodium(I) complexes. The best results were obtained with /V-phenyl-TV -OS )-(l-phenylethyl)thiourea associated with a cationic rhodium(I) precursor, and asymmetric induction of 40% was then achieved.387,388 Chiral polyether-phosphite ligands derived from (5)-binaphthol were prepared and combined with [Rh(cod)2]BF4. These systems showed high activity, chemo- and regio-selectivity for the catalytic enantioselective hydroformylation of styrene in thermoregulated phase-transfer conditions. Ee values of up to 25% were obtained and recycling was possible without loss of enantioselectivity.389... 

The X-ray analysis of the crystal stracture of Rh-(5)-18a showed that two coordinating Spiro phosphite ligands (S )-18a create an effective asymmetric enviromnent around the Rh (Figure 9). The rigid chiral pocket may be the reason for its highly efficient chiral induction in the addition reactions. It can be seen from the model that the transfer of the... 

The use of copper catalysts based on chiral phosphorus ligands to assist 1,4-additions of dialkylzinc reagents has in recent years produced major breakthroughs, with excellent enantioselectivities. A number of monodentate and bidentate phos-phoramidites, phosphites, phosphonites, and phosphines are now available as chiral ligands for alkyl transfer to a variety of cyclic and acyclic enones. So far. 

While alkyl halides are typically employed as an electrophile for this transformation, Takemoto developed palladium-catalyzed asymmetric allylic alkylation of 1 using allylic acetates and chiral phase-transfer catalyst 4k, as depicted in Scheme 2.5 [ 2 3 ]. The choice of triphenyl phosphite [(PhO)3P] as an achiral palladium ligand was crucial to achieve high enantioselectivity. 

To further understand the role of chirality at the bridge and axial chirality at the phosphite moiety in transferring the chiral information to the product outcome, ligands 35 and 36 were studied (Figure 3.8) [25]. Ligand 35, which has an R)-binaphthyl in the bridge, provides an ee of 83% R). This value is close to that of (R,S)-BINAPHOS (94% R) ee), suggesting that, in the formation of the Rh complex, the... 

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