Hydroxylation of olefins

Long chain aliphatic v/c-diols and their derivatives have properties which make them useful as modifiers in protective coatings, plastics, lubricants, waxes, emulsifiers and textile finishing agents. 

There are very few examples of direct hydroxylation of olefins using hydrogen peroxide, since these methods are limited to polymer applications or derivatization of natural products. Vinyl monomers have been hydroxy-lated in an alcoholic medium using acidic hydrogen peroxide 111 normally the acid is methanesulfonic. Natural rubber has also been hydroxylated, and simultaneously depolymerized by employing a hydrogen peroxide/UV system.112 The product distribution can be altered by varying the irradiation time. 

There have been attempts to lower the formic acid and hydrogen peroxide consumption.114-116 However, to date there has been limited success, the main reason being that the in situ performic acid can quickly decompose to water and carbon dioxide. 

Peracetic acid has also been used117 and the procedure is similar to that outlined for performic, except that it is often necessary to add sulfuric acid in 

The peracid methods invariably open the epoxide with reversion of configuration, i.e. trans-diol formation. Aryl substituents, however, are converted to the cw-diols with retention of configuration.118-120 Olefins which have been hydroxylated by means of in situ percarboxylic acid techniques include cyclohexene (65-73%),121 dodecane (91 %)122 and oleic acid (99%).123 Chlorestrol has been frans-hydroxylated with performic acid in high yield (91%).124 

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Amino-Hydroxylation. A related reaction to asymmetric dihydroxylation is the asymmetric amino-hydroxylation of olefins, forming v/c-ami noalcohols. The vic-hydroxyamino group is found in many biologically important molecules, such as the (3-amino acid 3.10 (the side-chain of taxol). In the mid-1970s, Sharpless76 reported that the trihydrate of N-chloro-p-toluenesulfonamide sodium salt (chloramine-T) reacts with olefins in the presence of a catalytic amount of osmium tetroxide to produce vicinal hydroxyl p-toluenesulfonamides (Eq. 3.16). Aminohydroxylation was also promoted by palladium.77... 

Osmium(VIII) tetraoxide (0s04) is an effective reagent for the cis hydroxylation of olefins under stoichiometric conditions as well as in a variety of catalytic variants.213 Under both catalytic and stoichiometric conditions, the critical step is the formation of an osmium(VI) cycloadduct, the formation of which is dramatically accelerated in the presence of amine bases such as pyridine,214 i.e.,... 

Se02 has also been used to carry out allylic hydroxylation of olefines and in this connection the following points are guiding factors. 

Interestingly, the first examples of catalytic oxygen transfer involved the so-called Milas reagents,4 formed by mixing heterogeneous metal oxide catalysts with a solution of hydrogen peroxide in tert-butanol. These reagents were used for the vicinal hydroxylation of olefins (reaction 10). 

The hydroxylation of olefins can be considered as the addition of hydrogen peroxide across a double bond to produce a vicinal diol. Where the epoxide is formed as an intermediate, the diol product is usually trans with respect to the olefin (Figure 3.23). 

Peracid methods are a popular choice for hydroxylation of olefins and generally more forcing conditions are required compared with epoxidation. Performic and peracetic acids are usually employed. A convenient and efficient method is to dissolve the olefin in an excess of the carboxylic acid and to slowly add the hydrogen peroxide to the mixture.113 When formic acid is employed, the acidity is usually sufficient to effect hydroxylation via the hydroxyformate (Figure 3.24). 

Figure 3.25 Hydroxylation of olefins to vic-diols using in situ formed peracetic acid.

Metal silicalite catalysts based on ZSM-5 zeolite type materials have been used for the hydroxylation of olefins. The silicalites need to contain a certain amount of A102 units to be active.136... 

Oxidation systems based on osmium have been extensively researched for the hydroxylation of olefins. Hydrogen peroxide/Os04 (Milas reagent) will hydro-... 

Enantiomeric purities ranging from 20 to 80% have been reported for the acid-promoted asymmetric oxidation of sulfides to sulfoxides by binaphthyl-derived oxaziridines has been described <2007T6232>. A novel amino hydroxylation of olefins has been developed using /ra t-2-phenylsulfonyl-3-phenyloxaziridine 33 <2007JA1866>. The reaction, which is catalyzed by copper(ll) salts, affords good yields of the product. Oxidation of aldimines to oxaziridines using alumina-supported M0O3 catalyst and anhydrous /-butyl hydroperoxide (TBHP) has been described. Yields are excellent. 

We may also note that acetonium or benzonium bridged ions are intermediates in the hydroxylation of olefinic bonds with iodine and silver acetate or benzoate (see p. 99). 

Hydroxylation of olefins. Lloyd et al. have described two active catalyst solutions for hydroxylation of olefins using potassium osmate. One (catalyst A) is prepared using hydrogen peroxide as oxidant and acetic acid lo neutralize the potassium osmate solution. In the other (catalyst B) sodium chlorate (1, 10S6-I0S8) is used as oxidant. 

AUyUc hydroxylation. From investigations of his own and analysis of the literature, Guillemonat" proposed the following rules regarding the allylic hydroxylation of olefins by selenium dioxide ... 

Woodward and Brutcher developed a procedure for the cis-hydroxylation of olefins which combines halogenation with acetolysis in wet acetic acid. Thus the synthetic intermediate (1) on treatment in acetic acid with iodine (1.05 equiv.). 

Milas hydroxylation of olefins. Formation of cw-glycols by reaction of alkenes with hydrogen peroxide and either a catalytic amount of osmium, vanadium, or chromium oxide or UV light. 

Prevost reaction. Hydroxylation of olefins with iodine and silver benzoate in an anhydrous solvent to give trans-glycols. 

The second method uses the pregnane derivative XI as a starting material. This compound, on hydroxylation with osmium tetroxide, afforded the diol Xlla. This diol was then converted to the androstane analogue X. The same approach was independently published also by Hondo and Mori (3). As a by-product of hydroxylation of olefin XI with osmium tetroxide, we obtained 2B,3B-diol XIV and, from this, the lactone XV. However, when we treated XII (a corresponding diacetate, respectively) with trifluoroperacetic acid we found that oxidation of the side chain surprisingly proceeded much faster than oxidation of the B ring. Thus we obtained not only compound X but also an intermediate, compound XHIb, and on hydrolysis compound Xllla, that is the androstane analogue of castasterone ... 

Recently we found that Re207 catalysed the hydroxylation of olefins by H202, if appropriate solvents like 1,4-dioxane or trialkylphosphate are applied and if the reaction takes place at higher temperatures [57] ... 

Aryl pinacols are readily obtained from the photolysis of substituted benzophenones in isopropyl alcohol. Photochemical coupling of benzophenones in isopropyl alcohol has even been reported to occur in direct sunlight.7 It is known however, that some aryl ketones do not give the pinacol from photolysis in isopropyl alcohol.8 Nevertheless, aryl pinacols have also been prepared from electrochemical reduction,9 hydroxylation of olefins,10 photoreduction of ketones by amines,11 metal reduction,12 and by other routes.13 The phenanthrene ring system has often been... 

Hydroxylation of olefins by hydrogen peroxide in the presence of osmium tetroxide leads to cis-glycols because a cyclic osmic ester is formed as intermediate and the cis-glycol is formed by hydrolysis of that intermediate. Other catalysts afford fraws-hydroxylation, which occurs by way of an intermediate epoxide.138... 

The catalytic hydroxylation of olefins with was first reported by Milas in 1936 [3, 4] and studied in more detail by Mugdan and Young a few years later... 

Acetal formation is a characteristic property of aldehydes. It is.the addition of two alcohol molecules to the carbonyl carbon under acidic conditions. Acetals are stable to the hydroxylation of olefins by neutral permanganate in alkaline condition. It can be converted back to aldehyde by acid-catalyzed hydrolysis. However, the double bond has to be masked before the acetal formation. This can be done simply by hydrohalogenation which does not affect the aldehyde. Dehydrohalogenation can be accomplished by elimination after the formation of acetal. 

Fig. 7 Poly(ethylene glycol)-immobilized ligands PEG5000-supported proline (62 or 63) for aldol and iminoaldol reactions [186] PEGsooo-supported BINAP 64 for Rh(I) and Ru(II) asymmetric hydrogenations [187] and PEGsooo-supported alkaloid 65 for asymmetric di-hydroxylation of olefins [188]...

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