Chiral carbohydrate derivatives

Only a few reactions with bidentate ligands have been described. 32, reacting with the chiral carbohydrate derivative phenyl-4,6-o-(R)-benzylidene -2,3, 0-bis(diphenyl-phosphino-/ -D-glucopyranoside) (Ph-/ -glup), gave the compound [TcBr(CO)3 (Ph-/Tglup)] (56) in 53% yield. The complex was characterized by elemental analysis and i.r. spectroscopy [71]. Furthermore, reaction with dithio-... 

Roberts and co-workers have employed a number of chiral carbohydrate-derived thiols as polarity reversal catalysts in the radical hydrosilylation of electron-rich prochiral alkenes [68-70]. In these thiols, the SH group is attached to the anomeric carbon atom. Scheme 21 demonstrates the non-catalyzed reaction and in step b, the hydrogen atom transfer from the silane... 

Reactions of alkenes such as 120 with a-chloronitrosoalkanes of type 119 proceed under very mild conditions and result in the formation of nitrones 121 that can be easily hydrolyzed into hydroxylamines 122 (equation 86) . Chiral carbohydrate-derived a-chloronitrosoalkenes 123 possess enhanced reactivity and produce good stereoselectivity in reaction with prochiral alkenes such as 124 (equation 87) . ... 

Schumacher, R, Reissig, H U, Stereoselective cyclopropanation of chiral carbohydrate-derived enol ethers, Synlett, 1121-1122, 1996. 

Similar conversions in the presence of chiral carbohydrate-derived pbosphonites lead predominantly to the weso-product16. Conversion of isoprene in the presence of a chiral 1,4-diazadiene iron(II) complex provides (—)-(/ )-l,7-dimethyl-l,5-cyclooctadiene in 90% yield and 61 % ee17. 

Besides monoallylethers of chiral alcohols, allylglycosides bearing a free alcohol functionality have been applied in asymmetric syntheses of enantiomerically pure cyclopropanemethanols with success." The cleavage of the chiral carbohydrate-derived auxiliary was achieved by treatment of the cycloadducts with a. Tf20, pyridine b. DMF/H2O, pyridine, whereas for the compounds derived from 57 a. Tf20, BU4NI and b. nBuLi were applied. 

Chiral carbohydrate-derived 1-alkoxy-1,3-dienes have been intensively examined in asymmetric Diels-Alder reactions with quinones. Moderate selectivities were observed. However, in water as solvent high endo selectivities were obtained at room... 

ASYMMETRIC DOMINO REACTIONS USING CHIRAL CARBOHYDRATE DERIVATIVES 3... 

In spite of the explosive development of asymmetric domino processes including multicomponent reactions, domino reactions involving chiral carbohydrate derivatives still remain rare in the literature. It is particularly true with regard to carbohydrate-derived organocatalysts. This section highlights several important works dealing with stereocontrolled domino reactions of chiral carbohydrate derivatives in a first part, and a rare enantioselective domino reaction catalyzed by a chiral carbohydrate derivative in a second part. It must be noted that all the discussed domino reactions are multicomponent ones. 

Stereocontrolled Domino Reactions of Chiral Carbohydrate Derivatives... 

SCHEME 1.2 Three-component Ugi reactions of chiral carbohydrate-derived amines. 

SCHEME 13 Three-component Passerini reaction of chiral carbohydrate-derived aldehydes. 

Recently, Oukani et al. (2013) also investigated the 1,3-dipolar cycloaddition reaction of chiral carbohydrate derived a,p-unsaturated esters and nitrones, which were derived from threitol under microwave irradiation for the synthesis of long chain sugars with nine contiguous chiral centers. 

Scheme 18.14). Upon treatment of ketones or aldehydes with 62, condensation reactions lead to the formation of nitrones including 63 [71, 72]. Such nitrones were observed to participate in dipolar cycloadditions with olefin 64 and to furnish the corresponding isoxazolidines (cf. 65) in a diastereoselective manner. Facile removal of the chiral carbohydrate-derived auxiliary was effected upon exposure of the adduct to acidic hydrolysis, providing the chiral isoxazolidine 66 (> 90% ee). 

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