Question

Draw the aromatic compound formed in the following reaction sequence:

Answer 1

Concepts and reason

In the reaction, a ketone is first reacting with LDA (lithium diisopropylamide) a base and the product of the reaction reacts with benzyl bromide in second step. In second step, final product in obtained.

Fundamentals

This method is used for the alkylation of the α-carbon of the carbonyl compound and it is one of the method used for forming carbon-carbon single bond. In this reaction, the first step is abstraction of a proton from a α-carbon of the carbonyl compound with base, that is, LDA. The hydrogen presents at α-carbon is acidic because the negative charged formed after removal of proton are delocalized and delocalization increases the stability of the compound.

The species formed after removal of proton is known as lithium enolate ion. In the second step, the lithium enolate ion act as a nucleophile which reacts with alkyl halide and final an α-alkylated product is obtained.

The general reaction mechanism for the reaction is as follows:

Abstract the proton from the α-carbon of acetophenone from base LDA and lithium enolate ion is formed.

The reaction is as follows:

The negative charge formed in α-carbon which is stable by delocalization, attack the benzyl chloride and obtained the final α-alkylated product and lithium bromide as side product.

The reaction is as follows:

Ans: