Cleavage reactions alkenes

Reaction of triethylsilyl hydrotrfoxide with electron-rich olefins to gh/e dioxetanes that react IntrarTMlecularly with a keto group in the presence of t-txrtyidimethyl silyl triflateto afford 1,2,4 Inoxanes also oxydatnre cleavage ol alkenes Also used in cleavage ol olefins... 

Methods of synthesis for carboxylic acids include (1) oxidation of alkyl-benzenes, (2) oxidative cleavage of alkenes, (3) oxidation of primary alcohols or aldehydes, (4) hydrolysis of nitriles, and (5) reaction of Grignard reagents with CO2 (carboxylation). General reactions of carboxylic acids include (1) loss of the acidic proton, (2) nucleophilic acyl substitution at the carbonyl group, (3) substitution on the a carbon, and (4) reduction. 

This reaction is reversible and suitable p-hydroxy alkenes can be cleaved by heat (17-34). There is evidence that the cleavage reaction occurs by a cyclic mechanism (p. 1351), and, by the principle of microscopic reversibility, the addition mechanism should be cyclic too. Note that this reaction is an oxygen analog of the ene... 

The oxidative cleavage of alkenes is a common reaction usually achieved by ozonolysis or the use of potassium permanganate. An example of NHC-coordina(ed Ru complex (31) capable of catalysing the oxidative cleavage of alkenes was reported by Peris and co-workers (Table 10.9) [44]. Despite a relatively limited substrate scope, this reaction reveals an intriguing reactivity of ruthenium and will surely see further elaboration. 

The oxidative cleavage of C=C bond is a common type of reaction encountered in organic synthesis and has played a historical role in the structural elucidation of organic compounds. There are two main conventional methods to oxidatively cleave a C=C bond (1) via ozonol-ysis and (2) via oxidation with high-valent transition-metal oxidizing reagents. A more recent method developed is via the osmium oxide catalyzed periodate oxidative cleavage of alkenes. All these methods can occur under aqueous conditions. 

New photochemical cleavage reactions of ortho-substituted C=C double bonds were reported by introducing a 2-nitrophenyl group to the double bond104. Photolysis of 1-(2-nitrophenyl)-l-alkenes 174 in methylene chloride solution without oxygen affords aryl... 

The synthesis of polyhalide salts, R4NX , used in electrophilic substitution reactions, are described in Chapter 2 and H-bonded complexed salts with the free acid, R4NHX2, which are used for example in acid-catalysed cleavage reactions and in electrophilic addition reactions with alkenes, are often produced in situ [33], although the fluorides are obtained by modification of method I.I.I.B. [19, 34], The in situ formation of such salts can inhibit normal nucleophilic reactions [35, 36]. Quaternary ammonium chlorometallates have been synthesized from quaternary ammonium chlorides and transition metal chlorides, such as IrClj and PtCl4, and are highly efficient catalysts for phase-transfer reactions and for metal complex promoted reactions [37]. 

Beckmann fragmentation is frequently applied to cyclic oximes resulting in a ring-cleavage reaction. Normally, a nitrile-alkene compound is obtained from the oxime and further transformation is usual. 

By far the most commonly used - though not the most environmentally friendly -solvent is CCl (or more usually water-CCl ). In a classic paper Sharpless et al. showed that oxidation reactions of RuO (and other some Ru-based oxidants) were accelerated by addition of a little acetonitrile to the conventional water-CCl biphasic mixture. It was suggested that the CH3CN might function as a mild donor stabilising a lower oxidation state carboxylato Ru species which could be involved in the catalytic process [260]. A comparative study of CCl, acetone, ethyl acetate, cyclohexane and acetone for cleavage of alkenes and alkynes by RuClg/aq. IO(OH)3/solvent showed that cyclohexane was the most effective [216]. Other solvents sometimes... 

There is a rich chemistry of alkene and alkyne oxidation by RuO. The main application lies in alkene cleavage, bnt there is growing interest in cw-dihydroxylation by the reagent. In the sections below we first consider oxidations which do not sever the C=C bond (epoxidation, ctT-dihydroxylation, ketohydroxylation), and then alkene cleavage reactions. 

This is one of the most important applications for RuO. Oxidative cleavage of alkenes and alkynes by a variety of reagents has been reviewed [30, 35, 50, 60, 68-71]. The gentler cleavage reactions of alkenes to aldehydes or ketones are considered first (Table 3.3), then the commoner cases of cleavage to carboxylic acids (Table 3.6). 

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. 

Ruthenium complexes catalyse the two main oxidative reactions for alkenes those in which oxygen atoms or hydroxyl groups span the erstwhile double bond without C=C rupture (e.g. epoxidation, ctT-dihydroxylation, ketohydroxylation), and cleavage reactions in which the C=C bond is broken. Although RuO has recently been shown to be effective for c/x-dihydroxylation and ketohdroxylation, epoxidations are in general effected by Ru complexes of lower oxidation states, while RuO excels at cleavage reactions. 

Photolysis of 2-oxetanones gives decarboxylative cleavage to alkenes, similar to pyrolysis, but subsequent photoaddition reactions of the alkene product may lead to complex reaction mixtures. A very useful example of 2-oxetanone photolysis is that of 5-oxabicyclo[2.2.0]oct-2-en-6-one, the photoisomer of a-pyrone when it was irradiated in a argon matrix at 80 K, carbon dioxide and cyclobutadiene were formed (equation 7) (73JA1337). 

Notes For organic chemists the major use of this oxidizing agent is in the cleavage of alkene bonds. This can be followed by either oxidative or reductive workups. The reaction can be run in a number of common solvents. 

Formation of C8 alkanes in the alkylation of isobutane even when it reacts with propene or pentenes is explained by the ready formation of isobutylene in the systems (by olefin oligomerization-cleavage reaction) (Scheme 5.2). Hydrogen transfer converting an alkane to an alkene is also a side reaction of acid-catalyzed alkylations. Isobutylene thus formed may participate in alkylation Cg alkanes, therefore, are formed via the isobutylene-isobutane alkylation. 

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