Osmium tetraoxide

The oxidation of alkenes with osmium tetraoxide gives excellent yields of vicinal diols. However, this reagent is both expensive and highly toxic. Therefore, it is used only in small-scale laboratory syntheses, not in industrial processes. Osmium tetraoxide can, however, be used in a catalytic process in which the oxidizing agent is recycled. For example, hydrogen peroxide can be used to oxidize the reduced osmium back to osmium tetraoxide, which continues to oxidize the alkene to a diol. This process allows the reaction to be carried out with only a small amount of the toxic OsO. A similar result can be obtained with A methylmorpholine-A -oxide (NMNO). 

The above reaction shows that the oxygen atoms add to the same face of the double bond. Thus, OsO forms vicinal diols by syn addition. 

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In the laboratory vicinal diols are normally prepared from alkenes using the reagent osmium tetraoxide (OSO4) Osmium tetraoxide reacts rapidly with alkenes to give cyclic osmate esters... 

Because osmium tetraoxide is regenerated m this step alkenes can be converted to vie mal diols using only catalytic amounts of osmium tetraoxide which is both toxic and expensive The entire process is performed m a single operation by simply allowing a solution of the alkene and tert butyl hydroperoxide m tert butyl alcohol containing a small amount of osmium tetraoxide and base to stand for several hours... 

Section 15 5 Osmium tetraoxide is a key reactant m the conversion of alkenes to vie mal diols... 

From acrolein by oxidation with sodium chlorate and osmium tetraoxide. Neuberg, Biochem. Z. 255, i (1932). 

Overall, the reaction leads to addition of two hydroxyl groups to the double bond and is refened to as hydroxylation. Both oxygens of the diol come from osmium tetraoxide via the cyclic osmate ester. The reaction of OSO4 with the alkene is a syn addition, and the conversion of the cyclic osmate to the diol involves cleavage of the bonds between oxygen and osmium. Thus, both hydroxyl groups of the diol become attached to the sfflne face of the double bond syn hydroxylation of the alkene is observed. 

The blends are frozen in liquid nitrogen and then microtomed and stained with osmium tetraoxide, which stains only unsaturated elastomers. 

The masked propargylic anfz-l,3-diols obtained in these reactions are useful precursors to more functionalized systems. Lindlar reduction of alkyne 171 generated the (Z)-allylic diol 172, which underwent diastereoselective osmium tetraoxide-catalyzed dihydroxylation to provide the partially protected tetraol 173 (Scheme 28). The propargylic anfz-l,3-dioxane 175,obtained in 88% yield from... 

Hydroxylation of 16 with osmium tetraoxide and hydrogen peroxide, followed by acetylation, gave 5a-carba-/ -DL-gulopyranose pentaacetate... 

When 35 was heated in acetic acid containing hydrogen bromide, the tribromide 46 was obtained as a single product in 74% yield. Debromina-tion of 46 with zinc dust in acetic acid furnished the cyclohexene derivative 47, which was converted into compound 48 by osmium tetraoxide hydroxyl-ation and acetylation. The substitution reaction of 48 with acetate ions provided carba-a-DL-glucopyranose pentaacetate (49), which gave the carba-sugar 50 on hydrolysis. ... 

Analogously, for preparation of racemic carba-a-glucopyranose 49 from 52, esterification of (—)-52 furnished the ester 95, which was transformed into compound 96 by debromination with zinc dust and acetic acid. Stereoselective hydroxylation of 96 with osmium tetraoxide and hydrogen peroxide, followed by acetylation, gave compound 97. Lithium aluminum hydride reduction of 97, and acetylation of the product, gave pentaacetate 98, which was converted into 99 by hydrolysis. ... 

Starting from 149, novel carba-sugar pentaacetates of the P-L-allo (168) and a-u-manno (171) configuration have been synthesized. Reduction of 149 with diisobutylaluminum hydride (DIBAL-H) and acetylation gave a mixture of acetates 162 and 163. Hydroxylation of the mixture with osmium tetraoxide and hydrogen peroxide provided compounds 164 and 165 in the ratio of 9 1. Hydrolysis of 164 gave compound 166, which was transformed into 168 by a reaction analogous to that employed in the preparation of 157 from 153. 

Vinyl acetate had been hydroxylated by treatment with excess hydrogen peroxide in presence of osmium tetraoxide catalyst. An explosion occurred while excess vinyl acetate and solvent were being removed by vacuum distillation. This was attributed to the presence of peracetic acid, formed by interaction of excess hydrogen peroxide with acetic acid produced by hydrolysis of the vinyl acetate. 

An initial osmium tetraoxide/olefin complex (in Scheme 21) is not generally disputed and is considered a donor/acceptor complex between an alkene as electron donor and 0s04 as an electron acceptor (with a reversible reduction potential E ed = —0.06 V versus SEC),217 e.g.,... 

Donor-acceptor complexes. A colorless hexane (or dichloromethane) solution of osmium tetraoxide upon exposure to benzene turns yellow instantaneously owing to the formation of a donor/acceptor complex,218 i.e.. 

Oxidation of alkenes with osmium tetraoxide is much more moderate than similar oxidations with permanganate. This makes OSO4 a very reliable reagent for cis dihydroxylation. 

The effect of an ally lie hydroxy group was first observed in divinylglycol (1,5-hexadiene-cA-3,4-diol and 1.5-hexadiene-/raw.v-3,4-diol). It was shown that the hydroxy substitutions directed the addition of the osmium tetraoxide to syn addition, so that the cA-diol yielded allitol (all cA-hexaol) and the iraws-diol yielded mannitol42. The oxidation of the dienol 35 yielded a lactone ring 36 by cA-dihydroxylation and transesterification... 

Osmic Acid Anhydride Osmium Oxide Osmium Tetraoxide Osmium Tetroxide OU1 Dry Agent ... 

Also fifteen years of painstaking work and the gradual improvement of the system, the Sharpless team announced that asymmetric dihydroxylation (AD) of nearly every type of alkene can be accomplished using osmium tetraoxide, a co-oxidant such as potassium ferricyanide, the crucial chiral ligand based on a dihydroquinidine (DHQD) (21) or dihydroquinine (DHQ) (22) and metha-nesulfonamide to increase the rate of hydrolysis of intermediate osmate esters 1811. 

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