Osmium 6 2+, reaction with acetone

Chlorothionitrene complex, osmium, 37 262 Chloro(trifluoromethyl) peroxide, 16 144 Chlorotrimethylsilane, reaction with hexafluoro-acetone, 30 225... 

Sable and coworkers also synthesized all four of the predicted racemic forms of cyclopentanetetrol (131-134), and the meso diastereomer (130). The all-cfs, meso isomer is unknown. cis-Hydroxylation of the enediols (136 and 137) is effected with permanganate or with silver chlorate-osmium tetroxide Irans-hydroxylation is caused by peroxybenzoic acid. Ihe epoxy group enters ds to the neighboring, free hydroxyl group in the intermediates (136-A, 136-B, and 137-A), according to Henbest s rule. However, prior reaction of the diol structure in the intermediate (136-A) with acetone caused the epoxide group to enter trana,... 

Treatment of a solution of 19 in acetone - water with N- methyl morpholine N- oxide and Osmium tetroxide will give the single cis diol which can be cleaved by reaction with lead tetraacetate in benzene to give the sensitive dialdehyde 20. Treatment of 20 with benzylammonium trifluoroacetate in benzene and refluxing will give the alpha,beta unsaturated aldehyde 21. 

Os(NH3)6] condenses with acetone in a redox-catalyzed coordinated ligand reaction, impelled by the Os(II)-imine intermediate being strongly stabilized by TT-bonding. Indeed one of the most distinctive features of the chemistry of osmium(II) is its unusually high tendency to 7r-bond. This has a large effect on reactivity, manifested in the various substitution and tautomerization reactions of [Os(NH3)5L] complexes discussed in this section. Kinetic parameters for reactions of the L = 17 -arene series have been conveniently assembled. ... 

Because osmium tetroxide is expensive, and its vapors are toxic, alternate methods have been explored for effecting vic-glycol formation. In the aliphatic series, olefins can be hydroxylated with hydrogen peroxide with the use of only a catalytic amount of osmium tetroxide. Anhydrous conditions are not necessary 30% hydrogen peroxide in acetone or acetone-ether is satisfactory. The intermediate osmate ester is presumably cleaved by peroxide to the glycol with regeneration of osmium tetroxide. When this reaction was tried on a A -steroid, the product isolated was the 20-ketone ... 

Syn-hydroxylation of alkenes is also effected by a catalytic amount of osmium tetroxide in the presence of hydrogen peroxide. Originally developed by Milas, the reaction can be performed with aqueous hydrogen peroxide in solvents such as acetone or diethyl ether.58 Allyl alcohol is quantitatively hydroxylated in water (Eq. 3.12).59... 

The /3-electrophilic additions of pentaamineosmium(ll) complexes bearing various 4,5-tf -coordinated pyrroles to carbonyl compounds have been reported by Harman and co-workers (Scheme 78). 1 1-Methylpyrrole complex, when reacted with benzaldehyde or its dimethylacetal in the presence of /-butyldimethylsilyl triflate (TBSOTf), afforded the corresponding aldol adduct 177 as a 1 1 ratio of diastereoisomers. Pyrrole, 1-methylpyrrole, or 2,5-dimethylpyr-role osmium complexes reacted with an excess of acetone in the presence of TBSOTf to give the O-silylated 377-pyrrolium aldol adducts 178, which may serve as intermediates for various other reactions. 

Reaction of (-)-a-pinene (1) with stoich. RuO /CCl gave a ketoaldehyde (2), probably via a Ru(VI) diester (4). If the reaction is performed using RuO in acetone rather than CCl, the a-ketol (3) is the main product. It is likely that a Ru(VI) diester (4) is involved such a species was isolated and both H and NMR data suggest the structure shown in (Fig. 3.8). An X-ray crystal structure determination was carried out on the osmium analogue of (4) [178]. 

Sodium Salt (54)3717a,20 20,21-Bismethylenedioxy-1, 2 -dihydroxypregn-4-ene-3, l-dione (53).37 A solution of 100 g of 17a,20 20,21-bismethylene-dioxypregna-l,4-diene-3,ll-dione (prednisone BMD) (52) in 720 ml of pyridine is cooled to 5° and treated with a solution of 69.9 g of osmium tetroxide in 408 ml of pyridine. The mixture, which turns black within 5 min is allowed to stand at room temperature for five days and then is added with stirring to 13.4 liters of petroleum ether. The crude osmate ester is isolated by filtration and washed with petroleum ether to remove most of the residual pyridine. The crude product is dissolved in 8 liters of dioxane and kept in an ice bath while a slow stream of hydrogen sulfide is bubbled through the reaction mixture. The precipitated osmium sulfide is removed by filtration, and the filtrate is concentrated to dryness in vacuo. The residual foam is dissolved in 2 liters of acetone, decolorized with activated carbon, filtered and concentrated to a volume of 1 liter. Addition of 1 liter of Skellysolve B affords 38 g of diol (53) A OH 236 mfi (e 14,100). 

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