Diketones olefinic ketones

Addition of alkyllithium to cyclobutanones and transmetallation with VO(OEt)Cl2 is considered to give a similar alkoxide intermediates, which are converted to either the y-chloroketones 239 or the olefinic ketone 240 depending on the substituent of cyclobutanones. Deprotonation of the cationic species, formed by further oxidation of the radical intermediate, leads to 240. The oxovanadium compound also induces tandem nucleophilic addition of silyl enol ethers and oxidative ring-opening transformation to produce 6-chloro-l,3-diketones and 2-tetrahydrofurylidene ketones. (Scheme 95)... 

One or both carbonyls in /3-diketones can be reduced, as well as the carbonyl function in acyl cyanides (210). Similar treatment of a,/3-unsat-urated ketones and aldehydes can lead to the saturated carbonyl products via selective reduction of the olefinic bond (207, 208, 210) see Eq. (51) in Section III,A,4. Some terpenes (a- and /3-ionone, pulegone) were reduced in this way (208). Platinum(II) phosphine complexes have been used for the hydrosilylation of saturated ketones and could be used for the reduction (211). 

Permanganate oxidations may be used for the direct conversion of olefins to a-hydroxy ketones and 1,2-diketones in moderate yields usually under acidic conditions.562"566... 

Fig (14) Olefin (107) has been converted to cyclic ether (114) by standard reactions. Its transformation to enone (115) is accomplished by annelation with methyl vinyl ketone and heating the resulting diketone with sodium hydride in dimethoxyethane. The ketoester (116) is subjected to Grignard reaction with methyllithium, aromatization and methylation to obtain the cyclic ether (117). Its transformation to phenolic ester (119) has been achieved by reduction, oxidation and esterification and deoxygenation. 

Moreno-Manas et al. [98] reported on a similar effect of triphenylphosphine for the Michael addition of active methylene compounds to n-acceptor olefins such as methyl vinyl ketone, acrylonitrile, and 2-vinylpyridine and dialkyl azodi-carboxylates. They compared the reactivity of RuH2(PPh3)4, RuCl2(PPh3)3, and PPh3 and concluded that for /5-diketones, ketoesters, and ketoamides, triphenylphosphine released from the ruthenium complexes contributes totally or partially to the catalysis. 

Preussomerin I 697 and ( )-preussomerin G 698 were obtained from 620 with a five- and six-steps sequence in 15% and 12% overall yield, respectively, through modifications of substituents of the dioxocin ring. Thus, attack of lithium methoxide from the less hindered face of the enone 620, followed by protection of the phenolic oxygen as its methyl ether provided the methoxy adduct 692. The ketone 693 was obtained through a benzylic bromination-solvolysis-oxidation protocol, which required only a single purification. The C(2)-C(3) olefin was introduced by selective silylation of the C-l carbonyl of diketone 693 and oxidation of the silyl enol ether with Pd(OAc)2. Enone... 

The simplest ggwi-dizincio alkane bis(iodozincio)methane [CH2(Znl)2] reacts with aldehydes, and with ketones in presence of a suitable activator or catalyst, to produce the corresponding olefinated compounds in good yields (equation 80). It has been shown that the nucleophihcity of the zinc atom in CH2(ZnI)2 can be enhanced by coordination of a heteroatom from a ligand or a solvent. Substrates which contain a suitably placed donor atom also lead to activation. For example, 1,2-diketones see Diketones) suchasbenzil (PhCO-COPh) undergo efi cient [2- -l] cycloaddition reactions with CH2(ZnI)2 (equation 81). The reaction is stereoselective, leading only to m-diol derivatives. 

If the reaction between enol silyl ethers and a,/ -unsaturated ketones is attempted in the presence of a titanium Lewis acid, the mode of the reaction switches to 1,4-addition with reference to the unsaturated ketone [109-113]. The reaction of an enol silyl ether is shown in Eq. (30) [114]. Ketene silyl acetals react with a,j8-unsaturated ketones in similar 1,4-fashion, as exemplified in Eq. (31) [115]. Acrylic esters, which often tend to polymerize, are also acceptable substrates for a, -unsaturated carbonyl compounds [111]. A difluoroenol silyl ether participated in this cationic reaction (Eq. 32) [116], and an olefinic acetal can be used in place of the parent a-methylene ketone [111] to give the 1,5-diketone in good yield (Eq. 33) [117]. More results from titanium-catalyzed 1,4-addition of enol silyl ethers and silyl ketene acetals to a,f -unsaturated carbonyl compounds are summarized in Table 4. 

Common colored compounds include nitro and nitroso compounds (yellow), a-diketones (yellow), quinones (yellow to red), azo compounds (yellow to red), and polyconjugated olefins and ketones (yellow to red). Phenols and amines are often brown to dark-purple because of traces of air oxidation products. 

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