Question

Predict the major products of the following reactions.

a)

Short answer

a)

b)

c)

Step-by-step solution

Alkylation of enolate ions

Bases like sodium hydroxide or alkoxide ion cannot be used to generate enolates as these bases cause side reactions with the alkyl halide.

Predicting the major products of the reaction

(a) The product formed on treating pentan-3-one with LDA and ${\mathrm{CH}}_2-{\mathrm{CHCH}}_2\mathrm{BR}$ is oct-7-en-3-one. The reaction is given as follows:

Product formed in reaction (a)

Alkylation of enolate ions 

Lithium diisopropyl amide (LDA) is used for the alkylation of enolate ions as it is a strong base and transforms the ketone to an enolate.

Predicting the major products of the reaction 

The reaction of the given compound with LDA and CH₃CH₂Br is 2-ethyloctahydronaphthalen-1(2H)-one. The reaction is given below:

Product of reaction (b)

Alkylation of enolate ions 

When enolates are alkylated directly with LDA, it produces the best yields when one kind of alpha hydrogen is substituted by an alkyl group. Aldehydes are not good for direct alkylation as they lead to side reactions

Predicting the major products of the reaction 

(c) The given compound reacts with LDA and to form a product where the methyl group is attached to the five-membered ring. The reaction is given below:

Product formed in reaction (c)