What carboxylic acid would be formed if the malonic ester synthesis (alkylation of diethyl malonate followed by hydrolysis with acidic workup and decarboxylation) were carried out with one equivalent of malonic ester, one equivalent of 1,5-dibromopentane, and two equivalents of hydroxide as the base

The malonic ester synthesis is often used to form different types of carboxilic acid. In this case, we have excess of base, so we can expect a ring formed in the molecule.

In the first step, the base substract the more acidic hydrogen of the ester. In the next step we have the ester reacting with the dibromopentane. Then, in the next step, the excess of base will substract again the acidic hydrogen remaining of the carbon, and then, will promove a Sn2 reaction with the bromine in the pentane (That it was previously attached to the molecule). In this step, a ring id formed. Then, the hydrolisis with acid, will form carboxilic acid in both sides of the molecule, and finally the decarboxilation in heat will separate the molecule and formed the cyclohexilic acid.

The picture below shows the mechanism