Osmium tetroxide with chlorates

During the induced reduction of chlorate a considerable oxygen effect was observed. The air oxidation of arsenic(ril) is also an induced reaction, the extent of which decreases with increasing acid concentration and is increased by decreasing the rate of primary reaction. The induced oxidation caused by air also can be observed during the osmium tetroxide-catalyzed chlorate-arsenic(III) reaction. 

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). 

Diarylacetylenes are converted in 55-90% yields into a-diketones by refluxing for 2-7 h with thallium trinitrate in glyme solutions containing perchloric acid [413. Other oxidants capable of achieving the same oxidation are ozone [84], selenium dioxide [509], zinc dichromate [660], molybdenum peroxo complex with HMPA [534], potassium permanganate in buffered solutions [848, 856, 864,1117], zinc permanganate [898], osmium tetroxide with potassium chlorate [717], ruthenium tetroxide and sodium hypochlorite or periodate [938], dimethyl sulfoxide and iV-bromosuccin-imide [997], and iodosobenzene in the presence of a ruthenium catalyst [787] (equation 143). 

Hydroxylation at double bonds of unsaturated carboxylic acids is accomplished stereoselectively by the same reagents as those used to hy-droxylate alkenes. syn Hydroxylation is carried out with potassium permanganate [101] or osmium tetroxide with hydrogen peroxide [130], sodium chlorate [310, 715], potassium chlorate [715], or silver chlorate [310] as reoxidant, anti Hydroxylation is achieved with peroxyacids, such as peroxybenzoic acid [310] or peroxyformic acid, prepared in situ from hydrogen peroxide and formic acid [101] (equation 472). 

Syn-Dihydroxylation. When the reaction was first discovered, the syn-dihydroxylation of alkenes was carried out by using a stoichiometric amount of osmium tetroxide in dry organic solvent.56 Hoffman made the observation that alkenes could react with chlorate salts as the primary oxidants together with a catalytic quantity of osmium tetroxide, yielding syn-vicinal diols (Eq. 3.11). This catalytic reaction is usually carried out in an aqueous and tetrahydrofuran solvent mixture, and silver or barium chlorate generally give better yields.57... 

In addition to the two types of products formed by osmium tetroxide in Scheme 9 is its action on 5,10-diacetoxy-2-methyl-2//-naphtho[2,3-6]pyran (172) in conjunction with sodium chlorate at room temperature to give a mixture of stereoisomeric chromanones (173) (78CB1285). 

Inclusion in the reaction of a cooxidant serves to return the osmium to the osmium tetroxide level of oxidation and allows for the use of osmium in catalytic amounts. Various cooxidants have been used for this purpose historically, the application of sodium or potassium chlorate in this regard was first reported by Hofmann [7]. Milas and co-workers [8,9] introduced the use of hydrogen peroxide in f-butyl alcohol as an alternative to the metal chlorates. Although catalytic cis dihydroxylation by using perchlorates or hydrogen peroxide usually gives good yields of diols, it is difficult to avoid overoxidation, which with some types of olefins becomes a serious limitation to the method. Superior cooxidants that minimize overoxidation are alkaline t-butylhydroperoxide, introduced by Sharpless and Akashi [10], and tertiary amine oxides such as A - rn e t h y I rn o r p h o I i n e - A - o x i d e (NMO), introduced by VanRheenen, Kelly, and Cha (the Upjohn process) [11], A new, important addition to this list of cooxidants is potassium ferricyanide, introduced by Minato, Yamamoto, and Tsuji in 1990 [12]. 

Osmium tetroxide catalytically assists the oxidation of certain oxidisable substances. For example,8 a mixture of 15 grams of arsenic with 10 grams of potassium chlorate in 50 e.c. of water remains unaltered even after addition of a few drops of dilute sulphuric acid. Upon introducing a trace of osmium tetroxide (c. 0-015 gram) in solution, the temperature immediately rises, the arsenic being rapidly oxidised to... 

From the mechanism shown in Scheme 7.23, we would expect the dihydroxylation with syn-selectivity. The cyclic intermediate may be isolated in the osmium reaction, which is formed by the cycloaddition of OSO4 to the alkene. Since osmium tetroxide is highly toxic and very expensive, the reaction is performed using a catalytic amount of osmium tetroxide and an oxidizing agent such as TBHP, sodium chlorate, potassium ferricyanide or NMO, which regenerates osmium tetroxide. For example, Upjohn dihydroxylation allows the syn-selective preparation of 1,2-diols from alkenes by the use of catalytic amount of OSO4 and a stoichiometric amount of an oxidant such as NMO. 

For the oxidation of alkenes, osmium tetroxide is used either stoichiometrically, when the alkene is precious or only small scale operation is required, or catalytically with a range of secondary oxidants which include metal chlorates, hydrogen peroxide, f-butyl hydroperoxide and N-methylmorpholine A -oxide. The osmium tetroxide//V-methylmorpholine A -oxide combination is probably the most general and effective procedure which is currently available for the syn hydroxylation of alkenes, although tetrasubstituted alkenes may be resistant to oxidation. For hindered alkenes, use of the related oxidant trimethylamine A -oxide in the presence of pyridine appears advantageous. When r-butyl hydroperoxide is used as a cooxidant, problems of overoxidation are avoided which occasionally occur with the catalytic procedures using metal chlorates or hydrogen peroxide. Further, in the presence of tetraethylam-monium hydroxide hydroxylation of tetrasubstituted alkenes is possible, but the alkaline conditions clearly limit the application. 

Oxidation. As one step in the synthesis of furaneol (3, a flavor principle of pineapples and strawberries), Buchi et a . wished to effect hydroxylation of 2,5-dimethyl-2,5-dimethoxy-2,5-dihydrofurane (1). They tried oxidation of(1 15.8 mmole) with potassium chlorate (22.8 mmole) and osmium tetroxide (0.3 mmole) in aqueous letrahydro-furane containing sodium bicarbonate at 30° for 63 hr. however, the expected diol... 

W. S. Johnson, M. Neeman, S. P. Birkeland, and N. A. Fedoruk. Am. Soc., 84. 989 (1962) Osmium tetroxlde-Barium chlorate. For the hydroxylation of (1), an intermediate in the synthesis of reserpine-type alkaloids, a Czech group found that use of barium chlorate with osmium tetroxide, taken in catalytic amount rather than in equivalent amount, gave improved yields of the diol (2). The starting material (1) was shaken... 

In investigating the synthesis of diterpene alkaloids, Wiesner et al.1 1 have used the combination of sodium chlorate with a catalytic amount of osmium tetroxide, for example ... 

Posternak prepared five ortlio-tetrol diastereoisomers (54, 55, 56, 60, and 61) by the appropriate cis or trans hydroxylation of ds- or trans-S-cyclohexene-l,2-diol (58 or 59). cis-Hydroxylation may be effected with permanganate or with silver chlorate-osmium tetroxide Imns-hydroxy-lation with a peroxy acid, or with silver benzoate-iodine (the Provost reagent). ... 

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,... 

Other epoxidizing reagents which have been proposed but have not been extensively employed with olefinic acids include r-butyl hydroperoxide and transition metal salts, hydrogen peroxide and isocyanate, sodium chlorate and osmium tetroxide, iodine and silver oxide and hydrogen peroxide and ortho esters. 

P-DL-ribopyranoside from furfuryl alcohol have been described. cis-Hydroxyl-ation of the enones (4) and (5) with silver chlorate-osmium tetroxide gave methyl... 

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