Dieckmann reaction mechanism

The mechanism of the Claisen and Dieckmann reactions is the ordinary tetrahedral mechanism,1694 with one molecule of ester being converted to a nucleophile by the base and the other serving as the substrate. 

The mechanism of the Dieckmann reaction is exactly the same as the mechanism of an inter-molecular Claisen reaction. It is illustrated in Mechanism 24.5 for the formation of a six-membered ring. 

Hromatka, O., Binder, D., Eichinger, K. Mechanism of the Dieckmann-reaction of methyl-3-(methoxycarbonylmethylthio)propionic acid methyl ester. Monatsh. Chem. 1973, 104,1520-1525. 

The mechanism of this reaction is closely similar to that described for the Claisen and Dieckmann reactions. The a-protons are acidic, the resulting anion being stabilized by conjugation to the cyanide, and the anion can then act as a nucleophile towards a second molecule of the cyanide. The resulting imine can then rearrange to the enamine and this results in the reaction being driven towards completion (Scheme 83). 

Interestingly ketones can be carbonylated. Reaction of cyclohexanone with CO in MeOH using PdCh and CuCb as catalysts under mild conditions afforded dimethyl pimelate (474) and methyl 6-chlorohexanoate (475) in good yields. Mechanism of the carbonylation is not clear. Dimethyl pimelate (474) is formed by methanolysis (retro-Dieckmann reaction) of methyl cyclohexanonecarboxylate (478) promoted by CuCF and acid. Methyl cyclohexanonecarboxylate (478) may be formed by methoxypalladation of the enolate 476 to form Pd enolate 477, followed by CO insertion. Chlorination of cyclohexanone with CuCl2 gives 2-chlorocyclohexanone 480 which is converted to 475 [197]. 

The mechanism involves a Michael reaction followed by a Dieckmann reaction (intramolecular Claisen), all base promoted. Loss of the ester group begins with an add-catalyzed hydrolysis, followed by decarboxylation of the resulting carboxylic acid. Finally, a Robinson annulation with methyl vinyl ketone affords the final product. 

The mechanism of the Fiesselmann reaction between methylthioglycolate and a,P-acetylenic esters proceeds via consecutive base-catalyzed 1,4-conjugate addition reactions to form thioacetal Enolate formation, as a result of treatment with a stronger base, causes a Dieckmann condensation to occur providing ketone 8. Elimination of methylthioglycolate and tautomerization driven by aromaticity provides the 3-hydroxy thiophene dicarboxylate 9. 

Intramolecular Claisen condensations, called Dieckmann condensations, are ringclosing reactions that yield 2-cyclopentanone carboxylic esters (Figure 10.52) or 2-cyclohexanone carboxylic esters. The mechanism of the Dieckmann condensation is, of course, identical to the mechanism of the Claisen condensation (Figure 10.51). To ensure that the Dieckmann condensation goes to completion, the presence of a stoichiometric amount of base is required. As before, the neutral /3-ketoester (B in Figure... 

Key Mechanism 22-12 The Claisen Ester Condensation 1071 22-13 The Dieckmann Condensation A Claisen Cyclization 1074 22-14 Crossed Claisen Condensations 1074 22-15 Syntheses Using /3-Dicarbonyl Compounds 1077 22-16 The Malonic Ester Synthesis 1079 22-17 The Acetoacetic Ester Synthesis 1082 22-18 Conjugate Additions The Michael Reaction 1085 Mechanism 22-13 1,2-Addition and 1,4-Addition (Conjugate Addition) 1085... 

The mechanism of the Dieckmann cyclization, shown in Figure 23.6 (p. 954), is analogous to that of the Claisen reaction. One of the two ester groups is converted into an enolate ion, which then carries out a nucleophilic acyl substitution on the second ester group at the other end of the molecule. A cyclic /S-keto ester product results. 

Bagavant, G., Thaoker, M. R., Raich, N. K. Mechanism of the Dieckmann-Komppa reaction of diethyl oxalate with diethyl oxydiacetate. 

To most organic chemists the term Claisen condensation implies the self-condensation of esters in the presence of sodium ethoxide to give 0-ketoesters. A Dieckmann condensation is a special Claisen condensation in which an ester of a dibasic acid undergoes intramolecular condensation to produce a cyclic jS-ketoester. From the point of view of mechanism, however, this idea of a Claisen condensation is perhaps unnecessarily limited, for there are a number of extremely closely related reactions which involve compounds other than esters, and bases other than sodium ethoxide. In all these transformations, the essential feature of the reaction is the addition of a carbanion to a carbonyl group, followed by the loss of a negative ion from the seat of reaction. 

It has been suggested that autoxidation of saturated fatty acids and aldehydes occurs through a free-radical mechanism (13, 14). Supporting evidence of a radical chain mechanism was provided by Palamand and Dieckmann (15) who studied the autoxidation of hexanal. The reaction involves peroxycarboxylic acid as an intermediate (16) and probably proceeds via the mechanism shown in Figure 1. 

The mechanism of the Dieckmaim condensation is the same as the mechanism of the Claisen condensation. The only difference between the two reactions is that the attacking enolate and the carbonyl group undergoing nucleophilic attack are in different molecules in the Claisen condensation, but are in the same molecule in the Dieckmaim condensation. The Dieckmann condensation, like the Claisen condensation, is driven... 

Keto esters are capable of undergoing cyclization reactions similar to the Dieckmann condensation. Write a mechanism for the following reaction. 

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