Osmium tetroxide oxidation of olefins

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. 

Van Rheenan, V. Kelly, R. C. Cha, D. Y. An Improved Catalytic Osmium Tetroxide Oxidation of Olefins to cif-1,2-Glycols using Tertiary Amine Oxides as the Oxidant Tetrahedron Lett. 1976, 17, 1973-1976. 

Preparation of cis-Diols by Catalytic Oxidation of Olefins with Osmium Tetroxide... 

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]. 

A second class of reactions of this kind are ones involving cycloaddition to double bonds. The Diels-Alder reaction can be regarded as an example if we are concerned primarily with the fate of the dienophile. It is generally believed that various oxidations of olefins, e.g. by osmium tetroxide, also take place in this way, i.e. 

It has been known for decades that osmium tetroxide catalyzes the H2O2 oxidation of olefins to c -l,2-diols but the cost, toxicity and volatility of OSO4 have limited its use to the organic research laboratory. Industrial interest was aroused in the 1990 s by i) the invention of a system for vicinal hydro-xylation using an electrochemical device as the ultimate oxidant and ii) the discovery of conditions to carry out the reaction enantioselectively, mainly by Sharpless and his group. The reaction is currently carried out by Chirex to... 

Osmium tetroxide is very expensive and very toxic which made using it quite unattractive. For a long time, many people who used osmium tetroxide to convert olefins to diols—and this was long before enantioselective dihydroxylations came on the scene—used the Upjohn procedure.20 This process used catalytic amounts of osmium tetroxide, NMO (/V-methylmorpholine /V-oxidc) 87 as the stoichiometric oxidant, and one solvent phase. The solvent was water, acetone and tert-butyl alcohol. The osmate ester 86 was hydrolysed under these conditions and the osmium (VI) species was reoxidised to 0s04 by NMO. 

Oxidation of olefins by hydrogen peroxide and catalytic amounts of osmium tetroxide is effected in anhydrous tert-butyl alcohol (Milas reagent139), ether,122 aqueous methanol,140 or acetone.141 Also, tert-butyl hydroxyperoxide may be used in place of hydrogen peroxide.142... 

Oxidation of olefins. The relative rate of oxidation of a double bond with this reagent decreases with increasing alkyl substitution. Such selectivity is unusual. Thus the rate of oxidation of a double bond with osmium tetroxide or ruthenium tetroxide increases with alkyl substitution. 

The osmium-tetroxide-catalyzed oxidation of olefin is well known. 

Many steroidal A -olefins have been protected as the dibromide during reactions of other parts of the molecule with ozone [3], chromium trioxide [4-8], potassium permanganate [9], and osmium tetroxide [9]. Other olefins have been protected in this way from oxidation [10-12] addition reactions [13], catalytic reduction [14, 15] and hydrogenolysis [16]. 

The osmium-catalyzed dihydroxylation reaction, that is, the addition of osmium tetr-oxide to alkenes producing a vicinal diol, is one of the most selective and reliable of organic transformations. Work by Sharpless, Fokin, and coworkers has revealed that electron-deficient alkenes can be converted to the corresponding diols much more efficiently when the pH of the reaction medium is maintained on the acidic side [199]. One of the most useful additives in this context has proved to be citric acid (2 equivalents), which, in combination with 4-methylmorpholine N-oxide (NMO) as a reoxidant for osmium(VI) and potassium osmate [K20s02(0H)4] (0.2 mol%) as a stable, non-volatile substitute for osmium tetroxide, allows the conversion of many olefinic substrates to their corresponding diols at ambient temperatures. In specific cases, such as with extremely electron-deficient alkenes (Scheme 6.96), the reaction has to be carried out under microwave irradiation at 120 °C, to produce in the illustrated case an 81% isolated yield of the pure diol [199]. 

In summary, the reaction of osmium tetroxide with alkenes is a reliable and selective transformation. Chiral diamines and cinchona alkakoid are most frequently used as chiral auxiliaries. Complexes derived from osmium tetroxide with diamines do not undergo catalytic turnover, whereas dihydroquinidine and dihydroquinine derivatives have been found to be very effective catalysts for the oxidation of a variety of alkenes. OsC>4 can be used catalytically in the presence of a secondary oxygen donor (e.g., H202, TBHP, A -methylmorpholine-/V-oxide, sodium periodate, 02, sodium hypochlorite, potassium ferricyanide). Furthermore, a remarkable rate enhancement occurs with the addition of a nucleophilic ligand such as pyridine or a tertiary amine. Table 4-11 lists the preferred chiral ligands for the dihydroxylation of a variety of olefins.61 Table 4-12 lists the recommended ligands for each class of olefins. 

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