Dienes osmium tetroxide

Dehydration of cortisone (198) affords the diene 199. This is then converted to ketal 200. The selectivity is due to hindrance about both the 11- and 20-carbonyl groups. The shift of the double bond to the 5,6-position is characteristic of that particular enone. Treatment of protected diene 200 with osmium tetroxide results in selective oxidation of the conjugated double bond at C-16,17 to afford the cis-diol (201). Reduction of the ketone at C-ll (202) followed by hydrolysis of the ketal function gives the intermediate 203. Selenium dioxide has been... 

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). 

The classical diene synthesis has been used for building the six-membered ring in the preparation of a/to-inositol by Criegee and Becher.36 trans, trans-Diacetoxybutadiene (XVI) and vinylene carbonate (XVII) condensed at 205-210° to an addition product (XVIII). Hydroxylation of this compound by osmium tetroxide, followed by hydrolysis, gave aWo-inositol the bulky osmium tetroxide approaches from the unhindered side of the molecule and the other possible product of the hydroxylation, m-inositol, is not formed.4 trans-Hydroxy 1 ation of XVIII would give epi-inositol. 

CXXXI. Its properties are those to be expected of such a structure for example, the UV-spectrum shows absorption at 224 m/u. (e = 14000) corresponding to one diene chromophore in the C4o-molecule, and oxidation by osmium tetroxide-sodium chlorate followed by periodate fission gives both acetaldehyde and formaldehyde. The Hofmann degradation can be completed by treatment of descurarine with alkali to yield the ditertiary ether base CXXVIII (129). 

We now turn to the stereochemistry governed by a ring system, and we shall look at both nucleophilic and electrophilic attack, since usually they have similar stereochemical preferences rather than contrasting preferences. In addition to several reactions that are straightforwardly electrophilic attack, we shall see several which can be described as electrophilic in nature, like the reactions of alkenes with osmium tetroxide, with peracids, with some 1,3-dipoles, and with boranes, and of dienes with dienophiles in Diels-Alder reactions. Some of these reactions are pericyclic, the pericyclic nature of which we shall meet in Chapter 6. For now, it is only their diastereoselectivity that will concern us. 

Permanganate oxidation of 1,5-dienes to prepare f r-2,5-disubstituted tetrahydrofurans is a well-known procedure (Equation 80). The introduction of asymmetric oxidation methodology has revived interest in this area. Sharpless-Katsuki epoxidation has found widespread application in the catalytic enantioselective synthesis of optically active tetrahydrofurans and the desymmetrization of w ro-tetrahydrofurans <2001COR663>. A general stereoselective route for the synthesis of f-tetrahydrofurans from 1,5-dienes has been developed which uses catalytic amounts of osmium tetroxide and trimethyl amine oxide as a stoichiometric oxidant in the presence of camphorsulfonic acid <2003AGE948>. 

With careful choice of reagent and reaction conditions, alkenes containing other functionalities can be selectively hydroxylated without complicating side reactions. For example, the oxidation may be carried out in the presence of ester, ether, sulfide, carboxylic acid, acetal, carbonyl, halo, alcohol and aryl groups. Regioselective hydroxylation is also possible in dienes in which one center is electron poor, and some selectivity is also found between isolated double bonds. For example, syn hydroxylation of diene (5) with a catalytic amount of osmium tetroxide and N-methylmorpholine N-oxide as the secondary oxidant gives diol (6) in 46% yield, and phase transfer catalyzed permanganate oxidation of diene (7) affords diol (8) in 83% yield. 

Dienes may be hydroxylated at one or at both double bonds, depending on the amount of oxidants used. Cyclopentadiene, on treatment with an excess of hydrogen peroxide and osmium tetroxide as a catalyst in tert-butyl alcohol, gives a mixture of 21% of 3,5-cyclopentenediol and 61% of 1,2,3,4-cyclopentanetetrol [152. ... 

Osmium tetroxide. 13,222-225 236-240 18,265-267 19, 241-2-Chemoselective dihydroxyletm allylic alcohols are preferentially d nonconjugated dienes is favored.-Asymmetric dihydroxylaiiomt. both ends, producing major product Another type of polymer-bound Dl... 

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