Alkenes to 1,2-diols

In Section 11-7C we described the use of permanganate for the oxidation of alkenes to 1,2-diols. How is it possible to control this reaction so that it will... 

Aldehydes and ketones often can be prepared by oxidation of alkenes to 1,2-diols (Sections 11-7C and 11-7D), followed by oxidative cleavage of the 1,2-diols with lead tetraethanoate or sodium periodate. For example,... 

The conversion of alkenes to 1,2-diols by osmium tetroxide is also an olefin addition reaction. In this case a hydroxy group is added to each carbon of the olefin group, and the addition is termed an oxidative addition since the diol product is at a higher oxidation level than the alkene reactant. Oxidation of the carbon atoms of the alkene takes place in the first step, which is the reaction with 0s04 to produce the intermediate osmate ester. 

Platinum(II), for example, K2PtClt, in an aqueous medium in the presence of 02, oxidizes ethane selectively to ethanol and ethylene glycol, whereas metallic Pt is required for the further oxidation of alcohols to carboxylic acids. Platinum metal also catalyzes the oxidation of alkenes to 1,2-diols. The presence of CO prevents further oxidation of the alcohol products.155... 

Sato et al. have rcporied the oxidation of alkenes to 1,2-diols using H2O2 as oxidant in the presence of resin-supported sulfonic acid in aqueous medium... 

In this section, permanganate [principally potassium permanganate (KMnOq)] will be used to oxidize alkenes to 1,2-diols. It is apparent from preceding discussions that alkenes can donate an electron pair to an electrophilic center. The structure of permanganate (MnOq", 239) is best viewed as the 1,3-dipolar molecule (b O and an negative O). Reaction occurs between an alkene, which donates electrons to the electrophilic oxygen of the dipole. As the Jt-bond breaks, positive character develops on one carbon, which is attacked by... 

For applications to organic chemistry, osmium tetroxide is most often used in neutral, aqueous media and the primary use is for the conversion of alkenes to 1,2-diols. 

Alkenes have been oxidized to 1,2-diols (>90%) by catalytic amounts of the ammonium periodate in the presence of osmium, and stoichiometric amounts of the periodate cleave the diols to produce the dicarbonyl derivatives (>80%) [23,30]. The procedure appears, however, to be less effective than with the quaternary ammonium permanganate. 

Alkenes from 1,2-diols (7, 385-386). An efficient synthesis of (S)-(—)-y-methoxymethyl-a, /J-butenolide (3) from (+)-5-0-methyl-D-ribonolactone (1) involves conversion to the cyclic orthoformate 2 followed by pyrolysis to give 3 in 66.5% overall yield.1 In this case, the Corey-Winter reaction and the Hanessian route (8,192) were... 

The introduction of oxygen atoms into unsaturated organic molecules via dihydroxylation reactions leads to 1,2-diols. 1,2-Diols can be synthesized by the reaction of alkenes either with peracids via corresponding epoxides and subsequent hydrolysis or with OSO4, KMn04, RUO4 and Cr(VI) compounds. 

We have seen that alkenes can be oxidized to 1,2-diols and that 1,2-diols can be further oxidized to aldehydes and ketones (Sections 20.6 and 20.7, respectively). Alternatively, alkenes can be directly oxidized to aldehydes and ketones by ozone (O3). When an alkene is treated with ozone at low temperatures, the double bond breaks and the carbons that were doubly bonded to each other find themselves doubly bonded to oxygens instead. This oxidation reaction is known as ozonolysis. 

We have seen that alkenes are oxidized to 1,2-diols by a basic solution of potassium permanganate at room temperature or below, and the 1,2-diols can subsequently be cleaved by periodic acid to form aldehydes and/or ketones (Sections 20.6 and 20.7). If, however, the basic solution of potassium permanganate is heated or if the solution is acidic, the reaction will not stop at the diol. Instead, the alkene will be cleaved, and the reaction products will be ketones and carboxylic acids. If the reaction is carried out under basic conditions, any carboxylic acid product will be in its basic form (RCOO ) if the reaction is carried out under acidic conditions, any carboxylic acid product will be in its acidic form (RCOOH) (Section 1.20). Terminal alkenes form CO2 as a product. 

Primary alcohols are oxidized to carboxylic acids by chromium-containing reagents and to aldehydes by PCC or a Swem oxidation. Secondary alcohols are oxidized to ketones. Tollens reagent can oxidize only aldehydes. A peroxyacid oxidizes an aldehyde to a carboxylic acid, a ketone to an ester (in a Baeyer-Villiger oxidation), and an alkene to an epoxide. Alkenes are oxidized to 1,2-diols by potassium permanganate (KMn04) in a cold basic solution or by osmium tetroxide (OSO4). 

An alternative route to 1,2-diols reacts alkenes with a mixture of silver carboxylate and iodine rather than with peroxides. Prevost found that silver benzoate and iodide converted styrene to 1,2-dibenzoate 272, which could be saponified to the l,2-diol. 358 xhe transformation is called the Prevost reaction.3 6 This... 

A PS-peroxyselenic acid (29) was prepared by treatment of PS-mercury(II) chloride (30) with selenium dioxide followed by 30% hydrogen peroxide (Scheme 10). In a triphase system, consi ting of (29) (1.5 mol %), 1.5-1.8 equivalents of 30% aqueous hydrogen peroxide and dichloromethane, alkenes were oxidized to 1,2-diols, and ketones to esters or lactones. The polymeric seleninic acid (31) could be reoxidized to the PS-peroxyseleninic acid (29) and recycled with no apparent loss of activity. 

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