Alkenes and cycloalkenes

The oxidation of alkenes and cycloalkenes may affect the double bonds, the rest of the molecule, or both. Also included in this section are aromatic hydrocarbons containing double bonds in their side chains. Compounds containing double bonds and other functional groups, such as hydroxyl, carbonyl, or carboxyl, will be discussed in the appropriate sections, such as unsaturated alcohols, aldehydes, ketones, acids, and esters. 

The simplest imaginable case of oxidation of a double bond is the industrial production of ethylene oxide from ethylene and oxygen in the presence of silver oxide on alumina at 270 °C [1098], 

In the laboratory, epoxidations of alkenes are usually accomplished by hydrogen peroxide or its derivatives. Hydrogen peroxide is applied in an alkaline medium so that it reacts as an anion (equation 54) [138, 142, 143, 146, 147, 148, 1099]. 

In the presence of a nitrile, alkaline hydrogen peroxide forms per-oxycarboximidic acid, which, in the presence of an alkene, gives an epoxide and a carboxamide (equation 55) [129], 

The most popular derivatives of hydrogen peroxide used for epoxi-dation are organic peroxy acids (equation 56) peroxyacetic [250, 251], pcroxytrifluoroacetic [283, 287], peroxybenzoic [295, 296, 297, 300], m-chloroperoxybenzoic [315, 316], p-nitroperoxybenzoic [328], peroxy-phthalic [330], peroxymaleic [338], and peroxylauric [174]. 

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Oxidative reactions frequently represent a convenient preparative route to synthetic intermediates and end products This chapter includes oxidations of alkanes and cycloalkanes, alkenes and cycloalkenes, dienes, aromatic fluorocarbons, alcohols, phenols, ethers, aldehydes and ketones, carboxylic acids, nitrogen compounds, and organophosphorus, -sulfur, -selenium, -iodine, and -boron compounds... 

It can be concluded that the metathesis reaction of acyclic alkenes and cycloalkenes proceeds via the rupture and formation of carbon-carbon double bonds, i.e. that the metathesis of alkenes is a true transalkylidenation reaction. 

H risson and Chauvin (88) examined the metathesis between acyclic alkenes and cycloalkenes (telomerization) in the presence of two other tungsten-based catalysts, namely WOCl4-Sn(n-C4He)4 and WOCI4-... 

From studies of the telomerization between 1-alkenes and cycloalkenes another interesting result emerged. The expected triads were observed, but within each triad the ratio of the products varied between 1 10 1 and 1 20 1 (88). This is not consistent with the scheme of H6risson and Chauvin. However, with the scheme of Calderon, this can be explained if... 

The hydroalumination of alkenes with BujAlCl catalyzed by Cp2ZrCl2 produces higher dialkylaluminum chlorides, which cannot be prepared by non-catalytic hydroalumination (Scheme 2-12) [63-65]. Terminal alkenes, internal linear alkenes and cycloalkenes can serve as substrates at reaction temperatures increasing in this order. 1,5-Dienes react to give cyclized products. 

Cycloaddition with nitrile oxides occur with compounds of practically any type with a C=C bond alkenes and cycloalkenes, their functional derivatives, dienes and trienes with isolated, conjugated or cumulated double bonds, some aromatic compounds, unsaturated and aromatic heterocycles, and fullerenes. The content of this subsection is classified according to the mentioned types of dipolarophiles. Problems of relative reactivities of dienophiles and dipoles, regio- and stereoselectivity of nitrile oxide cycloadditions were considered in detail by Jaeger and... 

The optimized protocol has also been applied to a wide range of open-chain and cyclic dienes (for selected examples, see Table 11.11) [113], The latter generally give higher yields than non-terminal alkenes and cycloalkenes, except for strained ones such as JV-benzyl-pyrroline, cyclopentene, and norbornene (Table 11.10, entries 20—22). 

Isolated double bonds in alkenes and cycloalkenes are best reduced by catalytic hydrogenation. Addition of hydrogen is very easy and takes place at room temperature and atmospheric pressure over almost any noble metal catalyst, over Raney nickel, and over nickel catalysts prepared in special ways such as P-1 nickel [13] or complex catalysts, referred to as Nic [49]. 

The reduction of an isolated carbon-carbon double bond by other methods is exceptional. Occasionally an isolated double bond has been reduced elec-Irolylicolly 344 and by dissolving melols. Sodium under special conditions -using tert-butyl alcohol and hexamethylphosphoramide as solvents - reduces alkenes and cycloalkenes in 40-100% yields [345. 3-Methylenecholestane, for example, afforded 3-methylcholestane in 74% yield on heating for 2 hours at 55-57° with lithium in ethylenediamine [346]. 

Alkenes and cycloalkenes are commonly termed olefins in the refining industry. These double-bonded compounds are rarely found in crude oil. Olefins appear in finished products as a result of cracking and other refining processes. 

On a similar note, a series of bridgehead alkenes and -cycloalkenes have been reported to undergo cycloadditions with l,l-dichloro-2,2-difluoroethene (12) to give the corresponding dichlorodifluorocyelobutanes.s... 

Branched alkenes and cycloalkenes react more readily. The hydrofluorinations may be carried out advantageously with 70 % hydrogen fluoride/pyridine (Olah s reagent) using tetrahydro-furan as a solvent,10,31 but a homogeneous system forms in this case. Therefore, the workup procedure was carried out by quenching the reaction mixture with ice water and neutralization with sodium hydrogen carbonate hydrofluorinations of various alkenes in this way are described in ref 40. 

The substitution of chlorine for fluorine atoms at C = C bonds in polyhalogcnated alkenes and cycloalkenes facilitates the addition reaction. 

Internal alkenes and cycloalkenes react much more slowly. If double-bond migration, however, can lead to an isomeric terminal olefin, slow transformation to the terminally substituted alkylsilane is possible.401,423 126 All three isomeric... 

Further studies with other alkenes and cycloalkenes proved the general nature of the reaction. 474 475 B2F4 is less reactive but forms more stable products.474... 

The reaction is also called hydrocarboxylation. According to a later modification, the alkene first reacts with carbon monoxide in the presence of the acid to form an acyl cation, which then is hydrolyzed with water to give the carboxylic acid.97 The advantage of this two-step synthesis is that it requires only medium pressure (100 atm). Aqueous HF (85-95%) gave good results in the carboxylation of alkenes and cycloalkenes.98 Phosphoric acid is also effective in the carboxylation of terminal alkenes and isobutylene, but it causes substantial oligomerization as well.99 100 Neocarboxylic acids are manufactured industrially with this process (see Section 7.2.4). The addition may also be performed with formic acid as the source of CO (Koch-Haaf reaction).101 102 The mechanism involves carbocation formation via protonation of the alkene97 103 [Eq. (7.10)]. It then reacts with carbon monoxide... 

The stereochemistry of addition depends largely on the structure of the alkene, but for simple alkenes and cycloalkenes, addition occurs predominantly in an antarafacial manner. For example, hydrogen bromide reacts with 1,2-dimethylcyclohexene to give the antarafacial addition product ... 

This reaction works well for simple alkenes and cycloalkenes. Attempts to add hydrazoic acid to di-arylalkenes in the presence of sulfuric acid, however, leads to considerable decomposition due to Schmidt rearrangement.260... 

Transfer of carbene 3a from 19 to a variety of alkenes and cycloalkenes has been achieved under catalysis by copper(I) chloride74,79 - 82. However, with the exception of cyclohexene69,70 (72% yield), only moderate yields could be obtained. In all cases, the cyclopropanation was stereospecific with respect to the double bond configuration of the alkene and gave the sterically less crowded cyclopropane diastereomer in excess. As in the photochemical cyclopropanation, the formal carbene dimer trans-1,2-bis(trimethylsilyl)ethene is often formed as the major by-product. Cyclopropanation of fraws-but-2-ene with 19 with copper(II) chloride as catalyst was found to be even less... 

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