Ligand chiral sulfoxide

There are several efficient methods available for the synthesis of homochiral sulfoxides [3], such as asymmetric oxidation, optical resolution (chemical or bio-catalytic) and nucleophilic substitution on chiral sulfinates (the Andersen synthesis). The asymmetric oxidation process, in particular, has received much attention recently. The first practical example of asymmetric oxidation based on a modified Sharpless epoxidation reagent was first reported by Kagan [4] and Modena [5] independently. With further improvement on the oxidant and the chiral ligand, chiral sulfoxides of >95% ee can be routinely prepared by these asymmetric oxidation methods. Nonetheless, of these methods, the Andersen synthesis [6] is still one of the most widely used and reliable synthetic route to homochiral sulfoxides. Clean inversion takes place at the stereogenic sulfur center of the sulfinate in the Andersen synthesis. Therefore, the key advantage of the Andersen approach is that the absolute configuration of the resulting sulfoxide is well defined provided the absolute stereochemistry of the sulfinate is known. 

On the other hand, James reported, in 1976, the use of a chiral sulfoxide as a ligand of ruthenium for the asymmetric hydrogenation of itaconic acid, providing a low enantioselectivity of 12% ee (Scheme 8.23). ... 

In addition, Rowlands has involved chiral sulfoxide-containing ligands for the catalytic addition of McsSiCN to aldehydes. " The ligand structure was based on a phenolic oxazoline scaffold with introduction of the sulfur substituent via cysteine derivatives. The best enantioselectivities of up to 61% ee were obtained with the bulkiest tert-butyl substituted ligand (Scheme 10.42). The effect of the sulfoxide configuration was studied, showing that the use of... 

Structural Identification of a Palladium Complex with a Chiral Sulfoxide Ligand... 

Ruthenium and Rhodium Hydrides Containing Chiral Phosphine or Chiral Sulfoxide Ligands, and Catalytic Asymmetric Hydrogenation... 

This chapter reports principally on studies with ruthenium chiral phosphine and chiral sulfoxide complexes and their use for catalytic hydrogenation. We have used the familiar diop ligand, [2R,3R-(—)-2,3-Oisopropylidene-2,3-dihydroxy-l,4-bis(diphenylphosphino) butane] (7) a related chiral chelating sulfoxide ligand dios, the bis(methyl sulfinyl)butane analog (21) (S,R S,S)-(+)-2-meth-ylbutyl methyl sulfoxide(MBMSO), chiral in the alkyl group and R-(+)-methyl para-tolyl sulfoxide(MPTSO), chiral at sulfur. Preliminary data on some corresponding Rh(I) complexes are presented also. 

Complexes Containing Chiral Sulfoxides. The blue solutions obtained by refluxing RuCl3 3H20 in polar solvents under H2 have provided a useful route to Ru(II) complexes (43,44). As described in the experimental section, treatment of such methanolic solutions with monodentate sulfoxides (Rudigand = 1 2) yielded the trimeric [RuC L ta species (where L = chiral ligands MBMSO and MPTSO) and a polymeric complex [RuC L ln (where L is racemic methyl phenyl sulfoxide). 

With Chiral Sulfoxide/metal Complexes Certain chiral hydroxysulfoxide and bis-sulfoxide are found useful as chiral ligands for the enantioselective Diels-Alder addition of acryloyl... 

Bolm et al. reported the first planar chiral NHC at the beginning of 2002 [87]. The synthetic strategy is based on an oriented ortho-metallation starting from a chiral sulfoxide, followed by the conversion of the sulfoxy group to a hydroxymethyl unit. The imidazole ring is then linked to this intermediate with the aid of W,AT-carbonyl diimidazole and subsequently quarter nized with methyl iodide to give the imidazolium ligand precursor of the carbene 41 (Scheme 31). 

When (R)-binaphtol 3.7 (R = H) is used as a titanium ligand, the catalytic asymmetric oxidation of arylmethylsulfides by fe/7-BuOOH in the presence of water in CCI4 leads to (i )-sulfbxides [815, 947, 1514], In tins reaction, the initial oxidation of the sulfide into the chiral sulfoxide takes place with a moderate ee (= 50%). This step is fbllowed by further oxidation of the sulfoxides with kinetic resolution ( 1.6) [815, 1514]. To observe a high enantiomeric excess (> 90%), it is necessary to oxidize the minor (S)-enantiomer into the corresponding sulfone, and the chemical yield of the sulfoxide is in the 45 - 65% range. 

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