Polymer supports osmium tetroxide

Polymer-supported osmium tetroxide j sodium periodate Oxo compds. from ethylene derivs. 

Polymer-supported osmium tetroxide jiQXi-butyl hydroperoxide j -... 

Polymer-supported [e.g. 8, 9] and silica-supported [10] cinchona alkaloids have been used in the asymmetric dihydroxylation of alkenes using osmium tetroxide. Enantiomeric excesses >90% have been achieved for diols derived from styrene derivatives. 

Other functionalized supports that are able to serve in the asymmetric dihydroxylation of alkenes were reported by the groups of Sharpless (catalyst 25) [88], Sal-vadori (catalyst 26) [89-91] and Cmdden (catalyst 27) (Scheme 4.13) [92]. Commonly, the oxidations were carried out using K3Fe(CN)g as secondary oxidant in acetone/water or tert-butyl alcohol/water as solvents. For reasons of comparison, the dihydroxylation of trons-stilbene is depicted in Scheme 4.13. The polymeric catalysts could be reused but had to be regenerated after each experiment by treatment with small amounts of osmium tetroxide. A systematic study on the role of the polymeric support and the influence of the alkoxy or aryloxy group in the C-9 position of the immobilized cinchona alkaloids was conducted by Salvadori and coworkers [89-91]. Co-polymerization of a dihydroquinidine phthalazine derivative with hydroxyethylmethacrylate and ethylene glycol dimethacrylate afforded a functionalized polymer (26) with better swelling properties in polar solvents and hence improved performance in the dihydroxylation process [90]. 

This asymmetric dihydroxylation problem was first solved by the use of cinchona alkaloid esters (5 and 6 R = P-CIC6H4) together with a catalytic amount of osmium tetroxide [86]. The alkaloid esters act as pseudoenantiomeric ligands (Scheme 8) [87-91], They can also be supported on a polymer [92,93],... 

An alternative way to use the polymer support is to microcapsulate the catalyst Kobayashi developed a microcapsulated osmium tetroxide using phenoxyethoxy-methyl-polystyrene, and applied this to the asymmetric dihydroxylation of olefins in water (Scheme 3.34) [64]. The reaction proceeded smoothly in water with cata-... 

Immobilization of Osmium Tetroxide onto Ionic Polymer Support. The incorporation of OSO4 onto short-length PEGy-lated (PEG Poly(ethylene glycol)) ionic polymers was achieved by Janda and coworkers. Immobilized OSO4 exhibited excellent catalytic performance and recyclability in the AD reaction. The high recyclability could be attributed to the interaction between the induced dipole of OSO4 and the ions of the polymeric scaffolds in a manner similar to ionic liquids. Moreover, Os-bounded... 

Since excellent results were obtained in the asymmetric aminohydroxylation in homogeneous phase by Sharpless [169], heterogeneous systems appeared to be of great interest. Nandanan has reported the first heterogeneous osmium tetroxide-catalyzed asymmetric aminohydroxylation of various olefins using polymer-supported bisdehydroquinine ligand 273 (Scheme 111) [170]. When chloramine T was used as nitogen source, yields and ee were moderate with all olefins. 

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