Enols as intermediates

We have already seen that exchange of hydrogen for deuterium, movement of double bonds into conjugation, and racemization can occur with enols or enolates as intermediates. These are chemical reactions of a sort, but it is time to look at some reactions that make significant changes to the carbonyl compound. 

Copper(I)-catalysed conjugate additions to zirconocene are supposed to have zirconium enolates as intermediates, which can be oxidized with A-halosuccinimides (equation 45)" . 

When phenylacetaldehyde (C6H5CH2CHO) is dissolved in D2O with added DCI, the hydrogen atoms a to the carbonyl are gradually replaced by deuterium atoms. Write a mechanism for this process that involves enols as intermediates. 

Among other studies of the decarboxylation of malonic acids is the interesting discovery that racemic methyl propionate is obtained from methyl hydrogen ethylmalonate this racemization is most simply interpreted as arising through formation of an enol or enolate as intermediate. 

The four most common methods for the synthesis of late transition metal enolates are oxidative addition to halocarbonyl compoxmds, ligand metathesis with main group enolates or silyl enol ethers, nucleophilic addition of anionic metal complexes to halocarbonyl electrophiles, and insertion of an a,3-imsaturated carbonyl compoimd into a metal hydride. Examples of these synthetic routes are shown in Equation 3.47-Equation 3.50. Equation 3.47 shows the synthesis of a palladium enolate complex by oxidative addition of ClCHjC(0)CHj to Pd(PPh3), Equation 3.48 shows the synthesis of a palladium enolate complex by the addition of a potassium enolate to an aryl Pd(II) halide complex, and Equation 3.49 shows the synthesis of the C-bound W(II) enolate complex in Figure 3.7 by the addition of Na[( n -C5R5)(CO)jW] to the a-halocarbonyl compound. Finally, Equation 3.50 shows the synthesis of a rhodium enolate complex by insertion of but-l-en-3-one into a rhodium hydride. This last route has also been used to prepare enolates as intermediates in reductive aldol processes. - ... 

Formation of keto-enols as intermediates in many organic reactions is known to be vigorously catalyzed in the basic environment and effectively hindered in the acidic one. The ethanol-aqueous environment, most often utilized in our experiments with the APAs, can rightfully be described as ampholytic. It seems that ampholytic environment combined with certain growth of viscosity of the APA solutions (in comparison with that of the pure solvents) [8] sufficiently M-fils the requirements for oscillatory transenantiomerization of the chiral analytes discussed. 

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