Ketones, conjugated, from

Oxidations - 3,5-Dinitroperbenzoic acid is a stable storable peracid equivalent in activity to trlfluoroperacetic acid. A full paper has appeared which gives the experimental details for the a-hydroxylation of carbonyl compounds by treatment of the anions of enol silanes with Mo05 HMPA (MOOPH). Anions from carboxylic esters (LiN(iPr)2>LDA -78°C) can be efficiently, regiospecifically chlorinated or brominated by treatment with respectively CCl or CBr. Treatment of enol silanes from conjugated ketones with m-chloroperbenzolc acid (MCPBA) followed by removal of silicon affords the a-hydroxyketones. ... 

Catalysis of Ring Formation. 1,2,4-Triazole can induce the formation of isoxazole rings from conjugated ketones and hydrox-ylamine (eq 5). ... 

Aldol condensation offers an effective route to a p unsaturated aldehydes and ketones These compounds have some interesting properties that result from conjugation of the carbon-carbon double bond with the carbonyl group As shown m Figure 18 6 the rr systems of the carbon-carbon and carbon-oxygen double bonds overlap to form an extended rr system that permits increased electron delocalization... 

These are usually obtained from the isomeric conjugated ketone, and are sometimes useful as intermediates, offering an alternative to enol derivatives. They may also be formed as a result of double bond introduction or by oxidation of homoallylic alcohols if so the conditions must be mild because they generally represent a less stable isomer. 

TMM cycloadditions to cyclic and conjugated ketones have also been reported (Scheme 2.22) [31]. The steric nature of the substrate does play a critical role in determining product formation. Thus the cyclic ketone (73) produced 55% yield of the tetrahydrofuran, but no cycloadduct could be obtained from the cyclic ketone (74). The enone (75) gave only carbonyl cycloaddition, whereas enone (76) yielded only olefin adduct. Interestingly, both modes of cycloaddition were observed with the enone (77). The ynone (78) also cycloadds exclusively at the carbonyl function [34]. 

Related compounds have been generated from BocRNCH2SnR 3 and s-butyllithium/ CuCN which also added to conjugated ketones. Other amino-cuprates are known to give conjugate addition reactions... 

Aziridines can be prepared directly from double-bond compounds by photolysis or thermolysis of a mixture of the substrate and an azide. The reaction has been carried out with R = aryl, cyano, EtOOC, and RSO2, as well as other groups. The reaction can take place by at least two pathways. In one, the azide is converted to a nitrene, which adds to the double bond in a manner analogous to that of carbene addition (15-62). Reaction of NsONHC02Et/ CuO [Ns = A(/7-toluenesulfonyl-inimo)] and a conjugated ketone, for example, leads to the A-carboethoxy aziridine derivative.Calcium oxide has also been used to generate the nitrene.Other specialized reagents have also been used." ... 

A particularly important example of the intramolecular aldol reaction is the Robinson annulation, a procedure that constructs a new six-membered ring from a ketone.171 The reaction sequence starts with conjugate addition of the enolate to methyl... 

Various diorganozinc compounds (ZnR2 R = Me, Et, Pr, Pr1, Buc, Ph) reacted with o-quinones by two mechanisms, namely (i) a single-electron transfer from ZnR2 to the quinone to yield, after hydrolysis, alkyl(phenyl)oxyphenols, and (ii) a polar 1,2- and 1,4-addition of ZnR2 similar to those of conjugated ketones.201 Diorganozinc compounds with low ionization potentials favor a polar mechanism. 

Aryl vinyl ketones are produced thermally from the corresponding quaternary ammonium salts via Hofmann elimination. However, the conjugated ketones are heat-sensitive and polymerization is difficult to avoid. Traditional preparations afforded only moderate yields. Microwave conditions were established for Hofmann eliminations, performed essentially quantitatively, by batch or continuous processes. 

Five-membered ring compounds are obtained from conjugated bisallenes under a variety of conditions. Whereas oxidation with m-chloroperbenzoic acid (MCPBA) provides ketones of type 323 [137], carbonylation by iron pentacarbonyl in THF at 50 °C leads to the symmetrical dialkylidene cyclopentenones 326 [45]. With phosphi-nidene complexes such as 325, biallenyls react in a stepwise process that eventually leads to adducts such as 327 [138], mimicking the behavior of singlet carbenes [139]. 

A difference in the reactivities and selectivities between tetra-n-butylammonium borohydride and sodium borohydride in the reduction of conjugated ketones is well illustrated with A1-9 2-octalone (Scheme 11.3) [17], Reduction with the sodium salt in tetrahydrofuran is relatively slow and produces the allylic alcohol (1) and the saturated alcohol (2) in a 1.2 1 ratio whereas, in contrast, tetra-n-butylammonium borohydride produces the non-conjugated alcohol (3) (50%) and the saturated alcohol (2) (47%), with minor amounts of the ketone (4), and the allylic alcohol (1) [16]. It has been proposed that (3) results from an initial unprecedented formation of a dienolate anion and its subsequent reduction. 

Hydride ion transfer from formic acid and its salts finds widespread application in the reduction of organic substrates, but limited use has been made of the procedure under phase-transfer catalytic conditions. However in the presence of a ruthenium complex catalyst, it is possible to selectively reduce the C=C bonds of conjugated ketones with sodium formate [11], The rate of reduction is fastest with tetrahexyl-ammonium hydrogensulphate and Aliquat the complete reduction of chalcone being effected within one hour, whereas with benzyltriethylammonium chloride only ca. 15% reduction is observed after two hours under similar conditions. 

Base removes a proton from adjacent to a carbonyl group. We can use a general to represent the base however, we could use hydroxide, since that is released upon dissolving sodium carbonate in water. It does not matter which a-position we choose they are actually all equivalent in this symmetrical substrate. The nucleophilic attack of the enolate anion onto the second carbonyl is followed by base-initiated dehydration, so that a favourable conjugated ketone is the product. As you can see, the size of the ring systems is automatically defined by the reaction. 

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