Chapter 21, Problem 60DSP

Interpretation Introduction

Interpretation:

The structure of the lactone formed as the final product in the given reaction and havinga molecular formula ${\text{C}}_{\text{12}}{\text{H}}_{\text{16}}{\text{O}}_{\text{2}}$, is to be determined.

Concept Introduction:

Carboxylic acids in presence of the reagent $\text{NaH, THF followed by LDA}$ yields anacid dianions in which the negative charge resides on both the oxygen atoms in the original carboxylic acid.

However, the dianion formed has carbanionic character and it can potentially act as anucleophile to create a new carbon-carbon single bond.

The reactions of dianions with epoxides generate a hydroxyl acid. The carbon atom in the dianion attacks on the less hindered carbon atom of the epoxide to yield a hydroxy acid derivative. Thus, there will be a new carbon-carbon single bond formed between the carbon atom in the dianion and the less hindered carbon atom in the epoxide.

The hydroxy acid generated can be then cyclized to yield a lactone, this creates a new carbon-oxygen single bond between carbonyl carbon in the carboxylic acid group and the oxygen atom in the epoxide.