Ketocarboxylic acids ketones, cyclic

The butylated /J-ketoester C of Figure 13.26 is not the final synthetic target of the acetoacetic ester synthesis of methyl ketones. In that context, the /J-ketoester C is converted into the corresponding /J-ketocarhoxylic acid via acid-catalyzed hydrolysis (Figure 13.27 for the mechanism, see Figure 6.22). This /i-ketocarboxylic acid is then heated either in the same pot or after isolation to effect decarboxylation. The /f-ketocarboxylic acid decarboxylates via a cyclic six-membered transition state in which three valence electron pairs are shifted at the same time. The reaction product is an enol, which isomerizes immediately to a ketone (to phenyl methyl ketone in the specific example shown). 

Cyclic ketones also can be cleaved by oxidation with KMn04 (Figure 17.33). Under these conditions, 1, -ketocarboxylic acids or 1, -dicarboxylic acids are formed. The mechanism of this reaction is not known in detail. It is known only that KMn04 serves as a three-electron oxidizing reagent and that it is reduced to Mn02. 

P-ketocarboxylic acid esters 43, 727 ketones, cyclic 44, 928 p-ketothiolic acid esters 43, 727 y-lactones 43,215... 

Ketocarboxylic acid esters from cyclic ketones s. 17, 194 Nitric acid... 

Ketocarboxylic acid esters from cyclic ketones... 

Sodium carbonate Cyclic ketocarboxylic acid esters from N-nitroso-a-oxo-N-heterocyclics Ring expansion of cyclic ketones... 

Cyclic ketones from cyclic -ketocarboxylic acid esters COOR H... 

Ketones from y -ketocarboxylic acid esters with protection of the keto group as cyclic ketal Decarboxylation with cleavage of ketals... 

We mentioned that by mixing vinyl epoxides and zerovalent palladium, the alcoholate formed was usually sufficiently basic to deprotonate the pronucleophile entity. In some cases, especially with ketones, low reactivity and yields were reported (Table To overcome the problem of the weak basicity of the alcoholate, silyl enol ethers, keto adds, or preformed lithium enolates have successfully been employed.f f" f f /3-Keto acids are masked enolates via the decarboxylation of the intermediary Tr-allylpalladium ]3-ketocarboxylate complexes. The main limitation of the use of keto adds as pronucleophiles seems to be their low reactivity toward the hindered cyclic vinyl epoxides. In these cases, the cationic n-allylpalladium complex undergoes ]S-elimination. Indeed, the reaction between benzoyl acetic acid and cyclobutadiene monoxide in the presence of Pd(PPh3>4 gives only the corresponding cyclopentanone and acetophenone as the... 

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