Diols, from olefin oxidation

The asymmetric oxidation of organic compounds, especially the epoxidation, dihydroxylation, aminohydroxylation, aziridination, and related reactions have been extensively studied and found widespread applications in the asymmetric synthesis of many important compounds. Like many other asymmetric reactions discussed in other chapters of this book, oxidation systems have been developed and extended steadily over the years in order to attain high stereoselectivity. This chapter on oxidation is organized into several key topics. The first section covers the formation of epoxides from allylic alcohols or their derivatives and the corresponding ring-opening reactions of the thus formed 2,3-epoxy alcohols. The second part deals with dihydroxylation reactions, which can provide diols from olefins. The third section delineates the recently discovered aminohydroxylation of olefins. The fourth topic involves the oxidation of unfunc-tionalized olefins. The chapter ends with a discussion of the oxidation of eno-lates and asymmetric aziridination reactions. 

In conclusion, the chiral salen Co(III) complexes immobilized on Si-MCM-41 colud be synthesized by multi-grafting method. The asymmetric synthesis of diols from terminal olefins was applied with success using a hybrid catalyst of Ti-MCM-41/chiral Co(III) salen complexes. The olefins are readily oxidized to racemic epoxides over Ti-MCM-41 in the presence of oxidants such as TBHP, and then these synthesized diols are generated sequentially by epoxide hydrolysis on the salen Co(lll) complexes. This catalytic system may provide a direct approach to the synthesis of enantioselective diols from olefins. 

The combination of A -bromoacetamidc, silver acetate, and dry acetic acid has been shown to be superior to Woodward s procedure for the rfy-hydroxylation of olefins. Work up of the reaction mixture is simply effected by hydrolysis of the dioxolenium ion, followed by cleavage of the hydroxyacetate intermediate with lithium aluminium hydride. The use of a co-oxidant, such as sodium chlorate or hydrogen peroxide, allows the addition of catalytic quantities of osmium tetroxide to prepare c/y-diols from olefins. However the reaction is often complicated by further oxidation of the glycol to the a-ketol. The use of tertiary amine A -oxides, particularly A -methylmorpholine A -oxide, prevents this oxidation and gives higher yields of the desired product (Table 6). Another variation on this theme employs... 

The 1,2-diol is liberated easily from cyclic osmate ester by either reductive or oxidative hydrolysis.213 Importantly, the ligand acceleration has been utilized extensively for the production of chiral 1,2-diols from (achiral) olefins using optically active amine bases (such as L = dihydroquinidine, dihydroquinine and various chiral diamine ligands).215... 

N-methylmorpholine (NMM) and the cheaper oxidant H202 rather than stoichiometric amounts of NMO (Scheme 5.11) [55]. In this process, NMM is reoxidized into NMO by H202 together with tungsten catalyst. LDH-PdOsW asymmetrically catalyzed a one-pot synthesis of chiral diols from aryl halides and olefins (Figure 5.10). 

Already in the first reports on olefin oxidation with the MTO/H2O2 system [3], it was noted that the formation of diols from the desired epoxides, caused by the Br0nsted acidity of the system, is a major drawback of this system. The solution for this problem was found in the same report by the addition of a nitrogen base. This method has been explored extensively since and has become an important factor in the MTO-catalyzed olefin epoxidation. 

We recently immobilized an Os compound as a surface-bound, highly substituted diolate complex (391). It is well-known that the hydrolytic release of a diol from an Os-diolate complex becomes increasingly difficult with increasing substitution (392). Under well-defined conditions (e.g., with NMO as the oxidant in CH2Q2-/-BUOII), tetrasubstituted diols and Os do not dissociate. Although the Os is bound on one side by the surface-anchored tetrasubstituted diolate, it is catalytically active on the other side. Most olefins can be dihydroxylated in very high yields with a stoichiometric amount of NMO (391) ... 

As shown, osmium tetroxide bearing the chiral ligand interacts with the olefin to give an Os(VI) ester, which upon hydrolysis releases the chiral diol. The actual oxidant is the metal itself that reduces from Os(VIII) to Os(VI). This reaction was known since the 1930 s and in this respeet it resembles the Wacker system where ethylene is oxidized to acetaldehyde with reduction of Pd(II) to... 

The metabolic oxidation of otefinic carbon-carbon double bonds leads to the corresponding epoxide (or oxiranc). Epoxides derived from olefins generally tend to be somewhat more stable than the arene oxides formed from aromatic-compounds. A few epoxides arc stable enough to be direclly mcasurable in biological fluids (e.g.. plasma, urine). Like their arene oxide counterparts, epoxides- are susceptible to cnz.ymatic hydration by epoxide hydra.se to form lran,s-. 2-dihydrodiols (al.so called 1,2-diols or 1.2-dihydroxy com-... 

From 2, it was concluded that the ferryl complex is the catalytically active species. Observation 1 suggested that 80% of the epoxide product in the aerobic reaction is derived from a carbon-based radical, which is quenched by O2 (autoxidation), and this is known to produce epoxide in reactions with cyclooc-tene (325). Methanol (observation 3) is known to quench radicals. The fact that the diols formed are a mixture of cis and trans products (observation 1 this is very unusual in iron-catalyzed olefin oxidations) suggested that the diol results from the capture of OH radicals by the putative carbon-based radical. 

Once the osmium( VI) glycolate (5.08) is formed, the catalytic cycle is completed by reoxidation with the stoichiometric oxidant followed by hydrolysis (Figure 5.2). Water is required to hberate the diol from the osmium and methanesulfonamide is often used as an additive, especially when using internal olefins, to increase the rate of this hydrolysis. It has been found that the rate of osmium glycolate hydrolysis is also enhanced under basic conditions. As the basicity of the AD reaction mixture decreases during the reaction, the maintenance of a constant pH of ca. 12, using an automatic titrator, leads to improvement in the reaction rate allowing the methanesulfonamide to be omitted. ... 

The exo-olefin is a precursor to a variety of chain-end-functionalized polymers via postpolymerization reaaions as shown in Scheme 37. Hydroxy-functionalized PIB has been utilized as a precursor for the preparation of RAFT macromo-lecular CTAs and carboxylic acid end-fimctionalized polymers. Telechelic PIB diols have been prepared using p-dicumyl chloride/BCU initiator system followed by dehydro-chlorination, hydroboration, and alkaline peroxide oxidation. Aldehyde end-fiinctionalized PIBs have been used to prepare carboxyl- and hydroxyl-terminated poly-mers. Carboxylic acid-functionalized PIBs have also been prepared from the oxidation of the methyl ketone-functionalized PIBs." The hydroxyl-functionalized PIBs have also been used to prepare methacrylate macromonomers by their reaction with methacryloyl chloride in the presence of triethylamine. The homopolymerization and copolymerization of these maaomonomers with methyl methacrylate were also reported. Cyanoacrylate-funaionalized PIBs prepared via the hydroxyl-functionalized PIB were also reported by Kennedy et al. ... 

Intermolecular Additions of Alcohois and Carboxylates The intermolecular oxidations of olefins with alcohols as nucleophile typically generate ketals, whereas the palladium-catalyzed oxidations of olefins with carboxylic acids as nucleophile generates vinylic or allylic carboxylates. As a result, many of the oxidations with alcohols have been conducted with diols to generate stable cyclic acetal products. Both types of oxidations have been conducted on large industrial scale, and vinyl acetate is produced from the oxidative reaction of ethylene with acetic acid in the gas phase over a supported palladium catalyst. ... 

Table 6 Yields of ch-diols obtained from olefins using various oxidants...

Homologous oxidation products of certain olefins have been isolated this evidence indicates that at least two routes of attack on the olefin molecule are possible. Bruyn (1954) isolated n-hexadecanediol-1,2 as a product of n-hexadecene-1 oxidation by the yeast Candida lipolytica. The primary attack in this case is at the double bond. Isotopic oxygen experiments with this system have not been reported. It may be surmized that the diol oxygen originates from O. The second route of olefin oxidation occurs on the terminal methyl carbon of the saturated end of the molecule, catalyzed by the ester bacterium of Stewart et al. (1960). Terminal hydroperoxide formation similar to that occurring during alkane oxidation undoubtedly occurs here since the double bond remains intact and appears in the alcohol moiety of the final ester product. It is too early to say if the above two mechanisms are characteristic of yeasts and bacteria, respectively. (See the Addendum.)... 

Despite the dominance of dihydroxylation reactions employing Os(VlIl) for the production of vicinal diols, alternatives have been utilized in asymmetric syntheses. The best known of these is perhaps Woodward s modification [205] of the Prevost reaction [206]. This classic oxidation is known to generally yield anti-1,2-diacetates from olefinic substrates [207]. Woodward s key modification involves the inclusion of water in the reaction mixture. The intermediate iodo-acetate 303 undergoes hydrolytic cleavage... 

Oxidation. Olefins in general can be oxidized by a variety of reagents ranging from oxygen itself to ozone (qv), hydroperoxides, nitric acid (qv), etc. In some sequences, oxidation is carried out to create a stable product such as 1,2-diols or glycols, aldehydes, ketones, or carboxyUc acids. In other... 

High-valent ruthenium oxides (e. g., Ru04) are powerful oxidants and react readily with olefins, mostly resulting in cleavage of the double bond [132]. If reactions are performed with very short reaction times (0.5 min.) at 0 °C it is possible to control the reactivity better and thereby to obtain ds-diols. On the other hand, the use of less reactive, low-valent ruthenium complexes in combination with various terminal oxidants for the preparation of epoxides from simple olefins has been described [133]. In the more successful earlier cases, ruthenium porphyrins were used as catalysts, especially in combination with N-oxides as terminal oxidants [134, 135, 136]. Two examples are shown in Scheme 6.20, terminal olefins being oxidized in the presence of catalytic amounts of Ru-porphyrins 25 and 26 with the sterically hindered 2,6-dichloropyridine N-oxide (2,6-DCPNO) as oxidant. The use... 

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