Write the mechanism for the reaction of a 1,7-diester with an alkoxide ion to form a cyclic $\mathbf{\beta }$-keto ester.

The reaction in which the addition of a base to a diester causes the diester to undergo an intramolecular Claisen condensation,resulting in the formation of a five-membered ring beta-keto ester, such an intramolecular Claisen condensation is called a Dieckmann condensation.

The reaction of 1,7-diester with an alkoxide ion to form a cyclic $\mathrm{\beta }$-keto ester is done by Dieckmann condensation.

In the first step, the base removes a proton from an alpha-carbon of a 1,7-diester, creating an enolate ion. The base employed corresponds to the leaving group of the ester. In the second step, the enolate ion adds to a second carbonyl carbon of the same 1,7-diester. In the last step, the pie bond re-forms, eliminating an alkoxide ion and resulting in the formation of cyclic ester shown as follows:

Formation of cyclic ester