Reaction and Mechanism of Dieckmann reaction

About Dieckmann reaction

intramolecular Claisen condensation in dibasic acid esters is called the Dieckmann reaction. The resulting products are invariably cyclic 13-ketone derivatives. The condensing bases may be sodium, sodium ethoxide, sodium hydride, potassium t-butoxide, etc.

The reaction best proceeds with dibasic acid esters having 6, 7 or 8 carbon atoms which give stable rings with s, 6, or  7 carbons .  Yields for rings of 9 to 12 carbons are very low. High-dilution technique is used for the formation of large-size rings.

Reaction Mechanism of Dieckmann reaction

The mechanism of the reaction is similar to that of Claisen condensation.

The base abstracts a proton from one of the a-carbons. The resulting carbanion then attacks the carbonyl carbon of the other ester group. Subsequent expulsion of the alkoxide ion gives the cyclic ketone derivative.The compound on hydrolysis and decarboxylation gives cyclic ketone,Esters of acids tower than adipic acid undergo more of intermolecular condensation with subsequent cyclisation. Thµs, ethyl succinate gives cyclohexandione derivative. This may be due to reasons of stability of six-membered rings.

Applications and extension of Dieckmann reaction

The reaction affords a useful route for the synthesis of cyclopentanone and cyclohexanone derivatives. Some examples are given for illustration.

The reaction has been used to buildup five- or six-membered rings in the synthesis of various natural products. The general process is given below.

Synthesis of steroid