Ketones, conjugated => alkenes

An important cyclization procedure involves acid-catalyzed addition of diene-ketones such as 58, where one conjugated alkene adds to the other conjugated alkene to form cyclopentenones (59). This is called the Nazarov cyclization Cyclization can also give the nonconjugated five-membered ring. ... 

Simvastatin, a conjugated alkene, can polymerise as a result of peroxyl radical addition. The peroxide-linked oligomers can be subsequently cleaved to produce epoxides, which in turn degrade to form ketones and alcohols [69]. Inclusion of vitamin E (a-tocopherol) into formulations was found to inhibit chain-oxidation of simvastatin, lovastatin and other structurally related statins. 

The reactivity profiles of the boronate complexes are also diverse.43 For example, the lithium methyl-trialkylboronates (75) are inert, but the more reactive copper(I) methyltrialkylboronates (76) afford conjugate adducts with acrylonitrile and ethyl acrylate (Scheme 16).44 In contrast, the lithium alkynylboronates (77) are alkylated by powerful acceptors, such as alkylideneacetoacetates, alkylidene-malonates and a-nitroethylene, to afford the intermediate vinylboranes (78) to (80), which on oxidation (peracids) or protonolysis yield the corresponding ketones or alkenes, respectively (Scheme 17).45a Similarly, titanium tetrachloride-catalyzed alkynylboronate (77) additions to methyl vinyl ketone afford 1,5-diketones (81).4Sb Mechanistically, the alkynylboronate additions proceed by initial 3-attack of the electrophile and simultaneous alkyl migration from boron to the a-carbon. 

Heating IBX with aldehydes and ketones, results in the introduction of conjugated alkenes in a highly efficient way.103 This reaction, similar to the reaction of IBX with X-acyl and /V - a I k o x y c ar b o n y I a n i I i n e s. usually operates under different experimental conditions than the oxidation of alcohols ... 

The new ketone can be used to add the ester group regioselectively to the less hindered side (though this is not important) and the ketone is reduced to a mixture of epimers of the alcohol 73. Tosylation and elimination give the conjugated alkene by the ElcB mechanism so that the stereochemistry of the OTs group is irrelevant. Deprotection gives juvabione 65. 

The Cp2TiCl/H20 combination can also be used for the chemoselective reduction of aromatic ketones. The reaction discriminates between ketones and alkenes, between ketones and esters and, remarkably, between conjugated and non-conjugated ketones [80]. There is strong evidence that this reduction proceeds via ketyl-type radicals, which are finally reduced by H-atom transfer from 42 [81]. Under dry conditions, titanium-promoted ketyl radicals from aromatic ketones can be used for intermolecular and intramolecular cross-coupling of ketones [82], Thus, depending on whether water is added or not, complementary and versatile synthetic procedure protocols are available. 

The indium hydride compound, generated in situ from sodium borohydride and a catalytic amount of indium(m) chloride, selectively reduces carbon-carbon double bonds in conjugated alkenes such as a,a-dicyano olefins, a,/3-unsaturated nitriles, cyano esters, cyanophosphonates, diesters, and ketones (Scheme 107).372 This combined reagent system in acetonitrile reduces exclusively the a,/3-carbon-carbon double bond in a,/3,7,<5-unsaturated diaryl ketones, dicarboxylic esters, cyano esters, and dicyano compounds (Scheme 108).373... 

The reaction of alkenes with iodosobenzene in acetic acid in the presence of sodium azide offers a simple and high yield route to 1,2-diazides (Table 3)76. a-Azido ketones are side products or the exclusive product from the reaction with conjugated alkenes. Allylic azides or oxonitriles, resulting from oxidative cleavage of the C-C double bond, are alternatively obtained from trisubstituted steroid alkenes77. 

Ion 36 can either lose a proton or combine with chloride ion. If it loses a proton, the product is an unsaturated ketone the mechanism is similar to the tetrahedral mechanism of Chapter 10, but with the charges reversed. If it combines with chloride, the product is a (3-halo ketone, which can be isolated, so that the result is addition to the double bond (see 15-47). On the other hand, the 3-halo ketone may, under the conditions of the reaction, lose HCl to give the unsaturated ketone, this time by an addition-elimination mechanism. In the case of unsymmetrical alkenes, the more stable alkene is formed (the more highly substituted and/or conjugated alkene, following Markovnikov s rule, see p. 1019). Anhydrides and carboxylic acids (the latter with a proton acid such as anhydrous HF, H2SO4, or polyphospho-ric acid as a catalyst) are sometimes used instead of acyl halides. With some sub-... 

As we know, an alkene in which the carbon-carbon double bond is conjugated with an aromatic ring is particularly stable (Sec. 12.17) in those cases where elimination of water from the aldol product can form such a conjugated alkene, the unsaturated aldehyde or ketone is the product actually isolated from the reaction. For example ... 

The reaction of a silylacetate derivative with an aldehyde or ketone was initially studied by Rathke and Yamamoto. Rathke and coworicers studied the addition of the lithium anion of r-butyl (trimethylsi-lyl)acetate (340) with a variety of aldehydes and ketones (equation 78). The anion can be formed directly from the silyl compound on treatment with LDA. The reaction proceeded to give the conjugated alkenes in excellent yields. Unsaturated compounds reacted via 1,2-addition. No discussion of alkene geometry was present. In the Yamamoto work, the ethyl (trimethylsilyl)acetate derivative (342) was used in a variety of reactions with aldehydes and ketones (equation 79). The anion was formed wiA dicyclohexyl-amide in THF. It was stated in the experimental section that the ( ) (Z) ratios of alkenes were dependent on the reaction conditions. In all the examples presented in this work, the ( )-isomer was predominantly formed. 

The stabilization of benzylic radical and cation makes homolytic or heterolytic fragmentation at the benzylic position a common occurrence in the photochemistry of these derivatives C-H and C-C fragmentation take place (Scheme 4.29). An example of the first case is the oxidation of the alcohol function to ketone in the anthistaminic drug terfenadine (44 dehydration to form a conjugated alkene also takes place, Scheme 4.30) (Chen et al., 1986). Another is the oxidation of a CH2 to... 

Although the final yields of ketone are not high, i.e. they range from 50 to 67%, the reaction is very useful because it can be carried out on substrates with several other functional groups. For example, the reaction is successful when acetals, thioacetals, lactones, non-conjugated alkenes, epoxides, alcohols, and secondary bromides are present in the alkyne. 

Aromatic compounds > conjugated alkenes > alicyclic compounds > organic sulfides > unbranched hydrocarbons > mercaptans > ketones > amines > esters > ethers > carboxylic acids > branched hydrocarbons > alcohols... 

The methodology described above allows the asymmetric epoxidation of allylic alcohols or cis-substituted conjugated alkenes and the resolution of terminal epoxides. The asymmetric synthesis of trans-di- and trisubstituted epoxides can be achieved with the dioxirane formed from the fructose-derived ketone 64, developed by Shi and co-workers. The oxidizing agent potassium peroxomonosulfate... 

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