Chapter 18, Problem 18.72P

Interpretation Introduction

(a)

Interpretation:

The detailed mechanism for the given equation of cross aldol reaction using a weak base such as pyridine is to be drawn.

Concept introduction:

Like aldehyde or ketone, the diethyl malonate having $\text{α}$ hydrogen can be converted to a good nucleophile by reacting it with a weak base. The diethyl malonate, in the presence of a base, undergoes deprotonation at the $\text{α}$ carbon (the carbon between two carbonyl groups) and forms stabilized carbanion, which can be resonance stabilized by both carbonyl groups. The carbanion undergoes nucleophilic addition reaction with polar $\text{π}$ bonds like aldehyde or ketone, similar to crossed aldol reaction.

Interpretation Introduction

(b)

Interpretation:

Why a relatively weak base can be used in the given crossed aldol reaction of diethyl malonate it is to be explained.

Concept introduction:

Like aldehyde or ketone, the diethyl malonate having $\text{α}$ hydrogen can be converted to a good nucleophile by reacting it with a weak base. The diethyl malonate, in the presence of a base, undergoes deprotonation at the $\text{α}$ carbon (the carbon between two carbonyl groups) and forms stabilized carbanion, which can be resonance stabilized by both carbonyl groups. The carbanion undergoes nucleophilic addition reaction with polar $\text{π}$ bonds like aldehyde or ketone, similar to crossed aldol reaction.