Osmium tetroxide oxidant

The double bonds of avermectins react with y -chloroperbenzoic acid to give 3,4-, 8,9-, and 14,15-epoxides. The 8,9-epoxide is the primary product and can be isolated in good yield (45). The 8,9-epoxide was opened by aqueous acids to the 8,9-diol (46). The 3,4-diol can be obtained readily and regiospecificaHy by osmium tetroxide oxidation. Neither peracids nor OsO will attack the 22,23-double bond. 

Osmium Tetroxide Oxidation of a A -Cyanopregnene 20-Cyano-21-hydroxy-5j5-pregn-17(20)-ene-3,l l-dione21-methyl ether (8 g) isdissolved in 100 ml of benzene and 8 ml of pyridine. After the addition of 9.6 g of osmium tetroxide, the reaction mixture is stoppered and allowed to stand at room temperature for 5 days. The mixture is stirred for 24 hr with 160 ml of chloroform, 200 ml of methanol and 280 ml of an aqueous solution... 

Osmium tetroxide oxidations can be highly enantioselective in the presence of chiral ligands. The most highly developed ligands are derived from the cinchona alkaloids dihydroquinine (DHQ) and dihydroquinidine (DHQD).45 The most effective... 

Potassium permanganate or osmium tetroxide oxidize alkenes to furnish 1,2-diols (glycols). 

Osmium tetroxide oxidation of (- )-( )-cyclooctene (6) afforded the ( + )-diol 7 whose absolute configuration was related to that of (+ )-tartaric acid (9) via the (+)-dimethoxy derivative 8. The (R)-configuration assigned by this correlation has been confirmed by a number of direct or indirect approaches. 

The (+ )-enantiomer 31 which has the highest optical rotation ([a]D + 171°) so far recorded, was reported to be formed by reductive elimination9 31 of (—)-32 using NaH-DMF. Osmium tetroxide oxidation discriminated the two unsaturated centers in (—)-31, yielding the unsaturated ( + )-ds-diol 33 whose conversion into ( + )-(lS,2S)-34 established the (R)-configuration of (—)-3132). 

CATALYTIC OSMIUM TETROXIDE OXIDATION OF OLEFINS cis-1,2-CYCLOHEX ANEDIOL... 

Osmium tetroxide, 58, 45, 51 OSMIUM TETROXIDE, OXIDATION OF OLEFINS, 58,43... 

Organometallic reagents and catalysts continue to be of considerable importance, as illustrated in several procedures CAR-BENE GENERATION BY a-ELIMINATION WITH LITHIUM 2,2,6,6-TETRAMETHYLPIPERIDIDE l-ETHOXY-2-p-TOL-YLCYCLOPROPANE CATALYTIC OSMIUM TETROXIDE OXIDATION OF OLEFINS PREPARATION OF cis-1,2-CYCLOHEXANEDIOL COPPER CATALYZED ARYLA-TION OF /3-DICARBONYL COMPOUNDS 2-(l-ACETYL-2-OXOPROPYL)BENZOIC ACID and PHOSPHINE-NICKEL COMPLEX CATALYZED CROSS-COUPLING OF GRIG-NARD REAGENTS WITH ARYL AND ALKENYL HALIDES 1,2-DIBUTYLBENZENE. 

The results of the DFT-calculations on the osmium tetroxide oxidation of alkenes are described in detail in Section 2.1. 

Osmium tetroxide oxidizes olefins as well as enamines, furnishing the corresponding diol derivatives, as shown in an example (Scheme 65) concerning a Vinca alkaloid analogue88. 

Straightforward is the stereoselective introduction of two oxygen functionalities onto carbon-carbon double bonds, as represented by the Sharpless epoxidation4 or osmium tetroxide oxidation of allyl alcohols.5 An alternative route may be envisioned by anti-Markovnikov hydration of enol ether derivatives, as in the present method, but such an approach has so far been rarely studied. The only other reported method is hydroboration which affords syn/anti ratios in the range of 83/17 to 3/97 in essentially the same systems as those examined in this procedure. The method described here is a highly stereoselective route to 2,3-syn isomers of 1,2,3-triol skeletons from a-hydroxy enol ethers. 

Although known for almost forty years, and in spite of a total synthesis of its racemate, the stereochemistry of doisynolic acid has remained in doubt. This problem has now been settled by a stepwise chemical conversion (Scheme 23) of 14)5-oestrone methyl ether (339), prepared from natural oestrone (114a), into c/s-doisynolic acid methyl ether (342). Osmium tetroxide oxidation of the enol acetate corresponding to (339) provided 16a-hydroxy-14)S-oestrone methyl ether. Subsequent periodic acid oxidation afforded the lactol (340), which upon treatment with diazomethane gave the aldehydo-ester (341). Electrochemical reduction of the aldehyde (341) afforded a methyl ester which by alkaline hydrolysis provided (-f )-ds-doisynolic acid 3-methyl ether (342), thus defining its complete stereochemistry. ... 

Sodium permanganate and, especially, osmium tetroxide oxidize sulfoxides to sulfones but do not oxidize sulfides [837]. When a mixture of equimolar amounts of diphenyl sulfide, diphenyl sulfoxide, and osmium tetroxide is refluxed in ether for 48 h, the sulfoxide is oxidized in 96% yield to the sulfone, whereas the sulfide is completely recovered [837], Certain unsaturated sulfoxides treated with a catalytic amount of osmium tetroxide and trimethylamine oxide as a reoxidant are not only oxidized to sulfones but also hydroxylated at the double bond. The sulfoxide group exerts a steric influence in the hydroxylation two stereoisomers of a sulfoxide yield, by syn hydroxylation, two different stereoisomeric diols (equation 580) [1102]. 

Lemieux-Johnson oxidation, see Periodate-Osmium tetroxide oxidation. 

Periodate-osmium tetroxide oxidation (Lemieux-Johnson). - The reagent, periodate catalyzed by osmium tetroxide, operates as follows. Osmium tetroxide adds to a double bond to form an osmate ester, and this is oxidized by periodate with cleavage to carbonyl compounds and regeneration of osmium tetroxide. Discovery of the... 

The ortho ester 681 of menthane-3,8,9-triol has been isolated from Mentha piperita and synthesized from (- )-isopulegol (169). Osmium tetroxide oxidation... 

Among these extensive studies, the first total synthesis of ( )-pan-cratistatin (211) has been reported (J49) (Scheme 20). Tricyclic 1,2-dihydroxy-5-lactone 214 was converted into vicinal acetoxy-bromo-5-lactone 215 in 88% yield along with the regioisomers. Osmium tetroxide oxidation of 215, followed by introduction of a double bond and selective protection of the hydroxyl groups, gave the corresponding allylic alcohol... 

Periodate-Osmium tetroxide oxidation [1, 812-813, after citation of ref. 22]. A British group has reported two cases where cleavage of an exocyclic methylene group is effected more cleanly by this reagent than by ozonolysis.22 ... 

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