Alcohols, oxidizing reagents alkenes

Selenium dioxide is a useful reagent for allylic oxidation of alkenes. The products can include enones, allylic alcohols, or allylic esters, depending on the reaction conditions. The mechanism consists of three essential steps (a) an electrophilic ene reaction with Se02, (b) a [2,3]-sigmatropic rearrangement that restores the original location of the double bond, and (c) solvolysis of the resulting selenium ester.183... 

Using dicyclohexyl-18-crown-6 it is possible to dissolve potassium hydroxide in benzene at a concentration which exceeds 0.15 mol dm-3 (Pedersen, 1967). The free OH- has been shown to be an excellent reagent for ester hydrolysis under such conditions. The related solubilization of potassium permanganate in benzene, to yield purple benzene , enables oxidations to be performed in this solvent (Hiraoka, 1982). Thus, it is possible to oxidize a range of alkenes, alcohols, aldehydes, and alkylbenzenes under mild conditions using this solubilized reagent. For example, purple benzene will oxidize many alkenes or alcohols virtually instantaneously at room temperature to yield the corresponding carboxylic acids in near-quantitative yields (Sam Simmons, 1972). 

Asymmetric epoxidation of olefins is an effective approach for the synthesis of enan-tiomerically enriched epoxides. A variety of efficient methods have been developed [1, 2], including Sharpless epoxidation of allylic alcohols [3, 4], metal-catalyzed epoxidation of unfunctionalized olefins [5-10], and nucleophilic epoxidation of electron-deficient olefins [11-14], Dioxiranes and oxazirdinium salts have been proven to be effective oxidation reagents [15-21], Chiral dioxiranes [22-28] and oxaziridinium salts [19] generated in situ with Oxone from ketones and iminium salts, respectively, have been extensively investigated in numerous laboratories and have been shown to be useful toward the asymmetric epoxidation of alkenes. In these epoxidation reactions, only a catalytic amount of ketone or iminium salt is required since they are regenerated upon epoxidation of alkenes (Scheme 1). 

Notes A useful reagent in that one can titrate the oxidation. Primary alcohols are converted to acids secondary alcohols to ketones alkenes and alkynes are resistant. Related reagents ... 

Some reagents, such as Se02 (the best oxidant for allylic hydroxylation) and palladium(II) (best known for oxidation of alkenes to allylic alcohols and carbonyl compounds), can be used in the formation of cc,p-unsaturated carbonyl compounds under special reaction conditions.671,692... 

Freshly prepared Mn02 is a useful reagent in organic chemistry and has been used in a large variety of oxidative transformations.311 These reactions involve the allylic oxidation of alkene to a,/3-unsaturated carbonyl compounds, the transformation of methylarenes to benzaldehyde and benzoic acid derivatives, the oxidation of secondary methylene groups to ketones, and the oxidation of alcohols to carbonyl compounds.311 The yields are generally fair to good. 

Among the other reagents listed, activated Mn02 is specific for the oxidation of allylic and ben/ylie alcohols.22 KM11O4 is used for the oxidation of alkenes to diols.23 Ceriv(lV) ammonium nitrate (CAN) accomplishes oxidative cleavage of the PMB protecting group. 

Sometimes, alcohols can direct the oxidation of alkenes, resulting in highly stereoselective formation of tetrahydrofurans by the action of Collins reagent. Thus, 1,2-diols can form cyclic chromate esters that can intramole-cularly oxidize alkenes, positioned so as to allow the operation of five-membered cyclic transition states.119... 

Modern variations include the in situ, and thus catalytic, use of this high-valent selective reagent, not only for alcohols but also for ethers (see later). Ru(VII) (perruthenate) in the compounds tetra-n-butylammonium perruthenate (TBAP) and tetra-n-propylammonium perruthenate (TPAP) has found wide application in alcohol oxidation. Ru-oxo complexes with valence states of IV to VI are key intermediates in, for example, the selective oxygen transfer to alkenes, leading to epoxides. On the other hand 16-electron Ru(II) complexes can be used to catalyse hydrogen transfer thus these are excellent catalysts for oxidative dehydrogenation of alcohols. A separate section is included to describe the different mechanisms in more detail. 

The BH3 THF reagent is the form of borane commonly used in organic reactions. BH3 adds to the double bond of an alkene to give an alkylborane. Basic hydrogen peroxide oxidizes the alkylborane to an alcohol. In effect, hydroboration-oxidation converts alkenes to alcohols by adding water across the double bond, with anti-Markovnikov orientation. 

In all of the above processes, the organoaluminum compounds serve as cocatalysts that activate a transition metal for the desired organic transformations. There are several important processes that do not involve transition metals and in which the organoaluminum reagents acts as a catalyst or stoichiometric reagent. The two most important of these are the formation of fatty alcohols and terminal alkenes from ethylene. These capitalize on the Aufbau reaction for formation of alkyl chains that can reach to C200, but the commercially important alkyls are those from C14 to C20 Oxidation of the aluminum alkyl followed by acidic hydrolysis yields predominately C14 to C20 alcohols and alumina (equation 36). The alcohols are converted to... 

Oxidation of alcohols and aldehydes. Primary alcohols and aldehydes are oxidized to the corresponding acids in good yield by this reagent, which can be used in catalytic amounts in the presence of excess oxidant for regeneration. Secondary alcohols afford ketones alkenes and tertiary alcohols do not react. ... 

An easily prepared acetonitrile complex of hypofluorous acid (HOF-CH3CN) serves an excellent reagent for the oxidation of alkenes with pendant alcohol or carboxylic acid functionalities <1996TL531>. 

Chromium, trioxobisfpyridine)- Collins reagent, CrO)Py2, CrOy 2Py) allylic oxidation of alkenes, 116,120 oxn. of prim, alcohols, 125 oxn. of sec. alcohols (selective), 135 Chugaev pyrolysis of thioesters, 138,140-141 Cinchona alkaloids pr., 290... 

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