Chapter 20, Problem 20.24P

Interpretation Introduction

Interpretation:

A synthetic route is to be proposed for the given transformation.

Concept introduction:

An organometallic compound has a polar covalent $\text{C-M}$ bond. For example, the Grignard reagent ($\text{RMgX}$) has a polar R-Mg bond, and alkyllithium ($\text{RLi}$) has a polar covalent $\text{C-Li}$ bond. Since carbon is bonded with an electropositive element, carbon possesses the partial negative charge and acts as the nucleophile as well as the base. Thus, it is used to the new $\text{C-C}$ bond formation with electrophilic carbon. The nucleophilic part (${\text{R}}^{\text{-}}$) of the Grignard reagent shows a nucleophilic addition reaction with electrophilic carbon of the carbonyl compounds. In case of an ester, the Grignard reagent adds twice to the carbonyl carbon to form the tertiary alcohol. In the first addition, the corresponding ketone will be formed. Due to electrophilic carbonyl carbon, second addition takes place to form the tertiary alcohol on workup step. Since the $\text{HO}$ group of the carboxylic acid is not a good leaving group, it is converted to a good leaving group by treating it with diazomethane, which produces a methyl ester.