Aldehydes alkene oxidation

We ve already discussed two methods of aldehyde synthesis oxidation of primary alcohols and oxidative cleavage of alkenes. 

Effective catalysts for heterogeneous oxidations using 02 are mainly Pt and Pd with some activity by Ir70 and Ru.71 Much work has gone into alcohol oxidations that are dehydrogenations to ketones or aldehydes. Also, oxygen may be inserted at allylic positions of alkenes and these may be dehydrogenated to ketones or aldehydes.72 In the case of aldehydes, additional oxidation may be accomplished to produce acids.72,73... 

Co-containing POMs have been found to be among the most efficient catalysts for homogeneous aerobic oxidation and co-oxidation processes [91-93]. This prompted many researchers to design solid Co-POM-containing materials [78,94-100]. Thus, various Co-POMs have been deposited on cotton cloth [94] and silica [100], datively [95] or electrostatically [96,97] bonded to NH2-modified silica surfaces (vide infra) as well as intercalated in LDHs [78,98,99]. The resulting materials were successfully used for aerobic oxidation of aldehydes, alkenes, alkanes, alcohols and some other organic substrates. 

As shown by their redox potentials oxoruthenium(IV) species containing polypyridyl ligands are strong oxidants and they oxidize a variety of substrates. The complex [Ru(0)(bpy)2(py)] has also been used electrocatalytically for the oxidation of alcohols, aldehydes, alkenes, and aromatics." Electrocatalytic oxidation has also been performed on this complex that has been incorporated into poly-4-vinylpyridine. ... 

The catalytic preparation of esters and amides under mild and waste free reaction conditions using readily available starting materials is a desirable goal. The first redox process of this type using heterocyclic carbenes was reported by Castells and co-workers in 1977 in which aldehydes were oxidized to esters in one-pot in the presence of nitrobenzene [104], Furfural 169 is converted into methyl 2-furoate 170 in 79% yield Eq. 15. Nitrobenzene is the presumed stoichiometric oxidant for the oxidation of the nucleophilic alkene XXX to the acyl azolium XXXI by successive electron transfer events. The authors observe nitrosobenzene as a stoichiometric byproduct. This type of reactivity is also observed when cyanide is used as the catalyst. Miyashita has expanded the scope of this transformation using imida-zolylidene carbenes [105-107]. 

Abstract This chapter covers one of the most important areas of Ru-catalysed oxidative chemistry. First, alkene oxidations are covered in which the double bond is not cleaved (3.1) epoxidation, cis-dihydroxylation, ketohydroxylation and miscellaneous non-cleavage reactions follow. The second section (3.2) concerns reactions in which C=C bond cleavage does occur (oxidation of alkenes to aldehydes, ketones or carboxylic acids), followed by a short survey of other alkene cleavage oxidations. Section 3.3 covers arene oxidations, and finally, in section 3.4, the corresponding topics for aUcyne oxidations are considered, most being cleavage reactions. 

Alkenes are directly oxidized to aldehydes and/or ketones by ozone (O3) at low temperatures (—78 °C) in methylene chloride, followed by the reductive work-up. For example, 2-methyl-2-butene reacts with O3, followed by a reductive work-up to yield acetone and acetaldehyde. This reducing agent prevents aldehyde from oxidation to carboxylic acid. 

Selenium dioxide is a most useful reagent for the oxidation of ketones or aldehydes to a-dicarbonyl compounds along with a,)3-unsaturated carbonyl compounds as by-products.291,293 The carbonyl compound probably reacts in its enol form in a way similar to that of alkene oxidation (equation 130).358... 

Similar reaction pathways have also been found for the oxidation of dimethyl sulfide to dimethyl sulfoxide and dimethyl sulfoxide to dimethyl sulfone by [Ru(bpy)2(py)(0)]2+ with respective rate constants of 17.1 and 0.13 M l s"1 in MeCN at 298 K (48). The complex [Ru(bpy)2 (py)(0)]2+ has also been used electrocatalytically for the oxidation of alcohols, aldehydes, alkenes, and aromatics (23, 49). The kinetics of oxidation of formic acid/formate ion by [Ru(bpy)2(py)(0)]2 +, with a large kinetic isotope effect [ HC02-/ADCo2- = 19 (25°C, /r = 1.0 M)], has been reported (50). A two-electron hydride transfer has been suggested for the oxidation of HC02 by [Ru(bpy)2(py)(0)]2+. A similar mechanism has also been suggested for the oxidation of alcohols (51) and aromatics (52) by [Ru(bpy)2(py)(0)]2+ and other related Ru(IV) oxo complexes (28,... 

Aldehydes The oxidative breakdown of polyunsaturated fatty acids generates a number of aldehydes, which are highly bioactive and well characterized molecules. Aldehydes are longer-lived than free radicals, and are able to attack targets extra or intracellularly (for review see Esterbauer et al., 1991). Among the different aldehydes formed during lipid and LDL oxidation, malondialdehyde and 4-hydroxyl alkenals, in particular 4-hydroxynonenal (4-HNE), have been intensively studied. 4-HNE results from the oxidation of arachidonic acid and, to a lesser extent, linoleic acid (Esterbauer et al., 1991). 4-HNE and related hydroxyalkenals react rapidly... 

We have already encountered three methods for preparing carboxylic acids (1) oxidation of alcohols and aldehydes, (2) oxidative cleavage of alkenes and alkynes, and (3) severe side-chain oxidation of alkylbenzenes. 

We ve a) ready discussed two of tha best methods of aldehyde syritheais oxidation of primary alcohola and oxid ative cleavage of alkenes. Let a review briefly. 

Other related reactions of these high-valent species include cyclopropanation of alkenes, oxidation of benzyltrialkylstannanes, dehydration of aldoximes, and olefination of aldehydes and ketones. Mechanisms... 

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. ... 

Now the aldehyde is oxidized to an add and the acid chloride does an intramolecular, Lewis-ac . -catalysed, aliphatic Friedel-Crafts reaction on the vinyl silane. Notice attack at the ipso carbon give a stable P-sUyl cation intermediate and that this vinyl silane has to react with inversion as frans-alkene is impossible in the ring. 

The (3-methyl homoallylic alcohol moiety of both anti- and 5yn-configurations is a characteristic structural element of a number of macrolides and polyether antibiotics. Reactions of crotylmetal (2-butenylmetal) reagents with carbonyl substrates provide access to acyclic stereo- and enantioselective syntheses of p-methyl homoallylic alcohols. The alkene moiety of these alcohols can be further elaborated into aldehydes by oxidative cleavage of the double bond, leading to aldol-type products. 

Oxidations. Alcohols undergo rapid oxidation when exposed to PhI(0Ac)2-Alj03 (with microwave irradiation) or PhlCOAc) with catalytic amount of TEMPO. The latter procedure is mild and selective. Primary alcohols can be converted to aldehydes without oxidizing secondary alcohols. (Z)-Allylic alcohols give (Z)-enals, 1,3-diols afford 3-ketols, and cholesterol is oxidized to the 5-en-one without migration of the double bond. Tertiary cyclopropanols fragment to release carboxylic acid and alkene moieties. ... 

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