Dihydroxylation osmium-catalysed

The systematic study of the origins of high enantioselectivity in the osmium-catalysed dihydroxylation carried out by the Sharpless group has led to defining certain crucial features and ruled out other mechanistic proposals478-481. Thus, the dihydroxylation has been... 

Osmium-catalysed dihydroxylation has been reviewed with emphasis on the use of new reoxidants and recycling of the catalysts.44 Various aspects of asymmetric dihydroxylation of alkenes by osmium complexes, including the mechanism, acceleration by chiral ligands 45 and development of novel asymmetric dihydroxylation processes,46 has been reviewed. Two reviews on the recent developments in osmium-catalysed asymmetric aminohydroxylation of alkenes have appeared. Factors responsible for chemo-, enantio- and regio-selectivities have been discussed.47,48 Osmium tetraoxide oxidizes unactivated alkanes in aqueous base. Isobutane is oxidized to r-butyl alcohol, cyclohexane to a mixture of adipate and succinate, toluene to benzoate, and both ethane and propane to acetate in low yields. The data are consistent with a concerted 3 + 2 mechanism, analogous to that proposed for alkane oxidation by Ru04, and for alkene oxidations by 0s04.49... 

A variation within the osmium-catalysed asymmetric dihydroxylation (AD) of alkenes has been described that yields cyclic boronic esters from alkenes in a straightforward manner. A protocol based on the Sharpless AD conditions (for enantiose-lective oxidation of prochiral olefins) has been developed that gives cyclic boronic esters, rather than free diols, with excellent enantiomeric excesses. Some of the... 

Asymmetric, osmium-catalysed dihydroxylation of 1,1-disubstituted and 1,3-disub stituted allenes has been employed to synthesize chiral a-hydroxy ketones, a,a - (g) Dihydroxy ketones were obtained from 1,3-disubstituted allenes with high enantio-... 

Osmium-catalysed dihydroxylation of olefins is a powerful route towards enantioselective introduction of chiral centers into organic substrates [82]. Its importance is remarkable because of its common use in organic and natural product synthesis, due to its ability to introduce two vicinal functional groups into hydrocarbons with no functional groups [83]. Prof. Sharpless received the 2001 Nobel Prize in chemistry for his development of asymmetric catalytic oxidation reactions of alkenes, including his outstanding achievements in the osmium asymmetric dihydroxylation of olefins. 

Another method that has successfully been developed recently by Sharpless is the osmium-catalysed asymmetric dihydroxylation (AD) [10] (Scheme 5). 

Treatment of the D-arabino- and D-xylo-furanosides 1 and 2 with DAST afforded the deoxyfluoro derivatives 3 and 4 in the former case, whereas the latter gave the anhydro-sugar 5 and the deoxyfluoro compound 6 (Scheme 1). Osmium tetroxide-catalysed dihydroxylation of the chiral unsaturated derivative 7 led to the synthesis of 2-deoxy-2-fluoro-D-xylose and -L-lyxose." 1,2,5-Tri-deoxy-2-fluoro-1,5-imino-D-glucitol and 1,2,5-trideoxy-1 -fluoro-2,5-imino-D-... 

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