Chapter 18.12, Problem 24P

(a)

Interpretation Introduction

Interpretation: The given following compounds has to be prepared using an aldol addition in the first step.

Concept introduction: If two different carbonyl compound used in an aldol addition, known as a crossed-aldol reaction.  If the two carbonyl compounds contain alpha carbon then four products are formed because two different enolate ion is formed.

If both carbonyl compounds have alpha hydrogens, primarily only one product is formed if LDA is used to remove the alpha hydrogen from carbonyl carbon that is needed for the enolate ion.

Because LDA is a strong base, all of the carbonyl carbon is converted to the enolate ion, so none of the carbonyl carbon is left behind to react with enolate ion.  Therefore, the second carbonyl compound is added slowly.

(b)

Interpretation Introduction

Interpretation: The given following compounds has to be prepared using an aldol addition in the first step

Concept introduction: If two different carbonyl compound used in an aldol addition, known as a crossed-aldol reaction.  If the two carbonyl compounds contain alpha carbon then four products are formed because two different enolate ion is formed.

If both carbonyl compounds have alpha hydrogens, primarily only one product is formed if LDA is used to remove the alpha hydrogen from carbonyl carbon that is needed for the enolate ion.

Because LDA is a strong base, all of the carbonyl carbon is converted to the enolate ion, so none of the carbonyl carbon is left behind to react with enolate ion.  Therefore, the second carbonyl compound is added slowly.

(c)

Interpretation Introduction

Interpretation: The given following compounds has to be prepared using an aldol addition in the first step.

Concept introduction: If two different carbonyl compound used in an aldol addition, known as a crossed-aldol reaction.  If the two carbonyl compounds contain alpha carbon then four products are formed because two different enolate ion is formed.

If both carbonyl compounds have alpha hydrogens, primarily only one product is formed if LDA is used to remove the alpha hydrogen from carbonyl carbon that is needed for the enolate ion.

Because LDA is a strong base, all of the carbonyl carbon is converted to the enolate ion, so none of the carbonyl carbon is left behind to react with enolate ion.  Therefore, the second carbonyl compound is added slowly.

(d)

Interpretation Introduction

Interpretation: The given following compounds has to be prepared using an aldol addition in the first step.

Concept introduction: If two different carbonyl compound used in an aldol addition, known as a crossed-aldol reaction.  If the two carbonyl compounds contain alpha carbon then four products are formed because two different enolate ion is formed.

If both carbonyl compounds have alpha hydrogens, primarily only one product is formed if LDA is used to remove the alpha hydrogen from carbonyl carbon that is needed for the enolate ion.

Because LDA is a strong base, all of the carbonyl carbon is converted to the enolate ion, so none of the carbonyl carbon is left behind to react with enolate ion.  Therefore, the second carbonyl compound is added slowly.