Chapter 13, Problem 13.9P

Interpretation Introduction

(a)

Interpretation:

How the given transform would appear in a synthesis is to be shown.

Concept introduction:

A synthetic trap is a synthesis which prevents the reaction from occurring in the forward direction as planned. This occurs mainly because the reactant molecule contains multiple functional groups which interfere in the desired mechanism. However, even when there is only one functional group, a synthetic trap can still arise if a reaction takes place at two or more sites within that functional group. In such cases, regiochemistry is an issue. Regiochemistry is the specific region in the given molecule at which the reaction takes place selectively. We can choose a synthesis according to the regioselectivities of the functional group transformation reactions.

The alkylation at alpha carbon atoms in ketones is regioselective, and we can control the regioselectivity by using appropriate reagents and the sequence in which the reagents are used. The choice of base dictates which alpha carbon undergoes reaction. A very strong base such as LDA leads to alkylation at the less substituted alpha carbon atom whereas a moderately strong base such as tert-butoxide anion leads to alkylation at the more substituted alpha carbon atom. The alkylation occurs using an alkyl halide as an alkylating group.

Interpretation Introduction

(b)

Interpretation:

How the given transform would appear in a synthesis is to be shown.

Concept introduction:

A synthetic trap is a synthesis which prevents the reaction from occurring in the forward direction as planned. This occurs mainly because the reactant molecule contains multiple functional groups which interfere in the desired mechanism. However, even when there is only one functional group, a synthetic trap can still arise if a reaction takes place at two or more sites within that functional group. In such cases, regiochemistry is an issue. Regiochemistry is the specific region in the given molecule at which the reaction takes place selectively. We can choose a synthesis according to the regioselectivities of the functional group transformation reactions.

The alkylation at the alpha carbon atoms in ketones is regioselective, and we can control the regioselectivity using appropriate reagents, and the sequence in which the reagents are used. The choice of base dictates which alpha carbon undergoes a reaction. A very strong base such as LDA leads to alkylation at the less substituted alpha carbon atom. whereas a moderately strong base such as tert-butoxide anion leads to alkylation at the more substituted alpha carbon atom. The alkylation occurs using an alkyl halide as an alkylating group.