Alkenes aldehydes and ketones

A variety of double bonds give reactions corresponding to the pattern of the ene reaction. Those that have been studied from a mechanistic and synthetic perspective include alkenes, aldehydes and ketones, imines and iminium ions, triazoline-2,5-diones, nitroso compounds, and singlet oxygen, 10=0. After a mechanistic overview of the reaction, we concentrate on the carbon-carbon bond-forming reactions. The important and well-studied reaction with 10=0 is discussed in Section 12.3.2. 

Alcohols can be made from monohaloalkanes, alkenes, aldehydes and ketones. 

Heats of formation are calculated as a sum of the bond energies and other stabilizing and destabilizing (e.g., strain) increments for the structure. MM4 calculations include terms for contributions of higher-energy conformations. For a set of hydrocarbons ranging from methane and ethane to adamantane and bicyclo[2.2.2]octane, the heats of formation are calculated with a standard deviation of 0.353 kcal/mol. The MM4 system has also been applied to alkenes, ° aldehydes, and ketones. ... 

Let s now take a look at some examples of oxidation-reduction reactions that take place on carbon. You have seen these reactions in previous chapters. Notice that in each of the following reactions, the product has more C—H bonds than the reactant has The alkene, aldehyde, and ketone, therefore, are being reduced (Sections 4.11, 18.5, and 15.15). Hydrogen, sodium borohydride, and hydrazine are the reducing agents. 

Gladysz has investigated the solution behaviour and configurational stability of these chiral rhenium complexes further, he extensively studied the chiral recognition process that results from the enantioface binding of alkenes, aldehydes and ketones on these rhenium chiral Lewis acids 3.7 and/or 3.8. There is a huge body of papers and reviews on this chemistry, and the reader may consult the referenced review. ... 

Gladysz et al. have investigated the kinetic and thermodynamic binding selectivities of f Ti-ligands (re-ligands = alkenes, aldehydes and ketones) to the rhenium Lewis acids 3.7 and 3.8. ° The studies with monosubstituted alkenes and the dichloromethane... 

Br0nsted-Lowry acids and bases (Chapter 6, Sections 6.2-6.4) Lewis bases and Lewis acids (Chapter 6, Section 6.5) the acid-base properties of alcohols, alkenes, aldehydes, and ketones (Chapter 6, Sections 6.3-6.S)... 

Other imaginative uses of rare earths include the reduction of alkenes, aldehydes and ketones with intermetalhc compounds containing absorbed hydrogen, viz. LaNijHg (Imamoto et al., 1984d). The use of duPont s Nafion polymer as a support for Cr(III) and Ce(IV) reagents useful in the oxidation of alcohols has also been reported (Kanemoto et al., 1984). Such conversions also involved the use of t-butylhydroperoxide or sodium bromate as cooxidant. 

Hydrides are available in many molecular sizes and possessing different reactivities. LiAIH reduces most unsaturated groups except alkenes and alkynes. NaBH is less reactive and reduces only aldehydes and ketones, but usually no carboxylic acids or esters (N.G. Gaylord, 1956 A. Haj6s, 1979). 

The final step can involve introduction of the amino group or of the carbonyl group. o-Nitrobenzyl aldehydes and ketones are useful intermediates which undergo cyclization and aromatization upon reduction. The carbonyl group can also be introduced by oxidation of alcohols or alkenes or by ozonolysis. There are also examples of preparing indoles from o-aminophcnyl-acetonitriles by partial reduction of the cyano group. 

Ozonolysis has both synthetic and analytical applications m organic chemistry In synthesis ozonolysis of alkenes provides a method for the preparation of aldehydes and ketones... 

The most obvious way to reduce an aldehyde or a ketone to an alcohol is by hydro genation of the carbon-oxygen double bond Like the hydrogenation of alkenes the reac tion IS exothermic but exceedingly slow m the absence of a catalyst Finely divided metals such as platinum palladium nickel and ruthenium are effective catalysts for the hydrogenation of aldehydes and ketones Aldehydes yield primary alcohols... 

The carbonyl carbon of a ketone bears two electron releasing alkyl groups an aldehyde carbonyl group has only one Just as a disubstituted double bond m an alkene is more stable than a monosubstituted double bond a ketone carbonyl is more stable than an aldehyde carbonyl We 11 see later m this chapter that structural effects on the relative stability of carbonyl groups m aldehydes and ketones are an important factor m then rel ative reactivity... 

In general aldehydes and ketones have higher boiling points than alkenes because they are more polar and the dipole-dipole attractive forces between molecules are stronger But they have lower boiling points than alcohols because unlike alcohols two carbonyl groups can t form hydrogen bonds to each other... 

The carbonyl oxygen of aldehydes and ketones can form hydrogen bonds with the pro tons of OH groups This makes them more soluble m water than alkenes but less solu ble than alcohols... 

Many aldehydes and ketones are made m the laboratory from alkenes alkynes arenes and alcohols by reactions that you already know about and are summarized m Table 17 1... 

The Wittig reaction uses phosphorus ylides (called Wittig reagents) to convert aldehydes and ketones to alkenes... 

The Wittig reaction (Sections 17 12-17 13) Reaction of a phosphorus ylide with aldehydes and ketones leads to the formation of an alkene A versa tile method for the regiospecific prepa ration of alkenes... 

AUylic organoboranes react via cyclic transition states not only with aldehydes and ketones, but also with alkynes, aHenes, and electron-rich or strained alkenes. Bicyclic stmctures, which can be further transformed into boraadamantanes, are obtained from triaHyl- or tricrotylborane and alkynes (323,438,439). 

By-Products. Almost all commercial manufacture of pyridine compounds involves the concomitant manufacture of various side products. Liquid- and vapor-phase synthesis of pyridines from ammonia and aldehydes or ketones produces pyridine or an alkylated pyridine as a primary product, as well as isomeric aLkylpyridines and higher substituted aLkylpyridines, along with their isomers. Furthermore, self-condensation of aldehydes and ketones can produce substituted ben2enes. Condensation of ammonia with the aldehydes can produce certain alkyl or unsaturated nitrile side products. Lasdy, self-condensation of the aldehydes and ketones, perhaps with reduction, can lead to alkanes and alkenes. 

In 1959 Carboni and Lindsay first reported the cycloaddition reaction between 1,2,4,5-tetrazines and alkynes or alkenes (59JA4342) and this reaction type has become a useful synthetic approach to pyridazines. In general, the reaction proceeds between 1,2,4,5-tetrazines with strongly electrophilic substituents at positions 3 and 6 (alkoxycarbonyl, carboxamido, trifluoromethyl, aryl, heteroaryl, etc.) and a variety of alkenes and alkynes, enol ethers, ketene acetals, enol esters, enamines (78HC(33)1073) or even with aldehydes and ketones (79JOC629). With alkenes 1,4-dihydropyridazines (172) are first formed, which in most cases are not isolated but are oxidized further to pyridazines (173). These are obtained directly from alkynes which are, however, less reactive in these cycloaddition reactions. In general, the overall reaction which is presented in Scheme 96 is strongly... 

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... 

The carbonyl group makes aldehydes and ketones rather polar molecules, with dipole moments that are substantially higher than alkenes. 

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