91Ó°ÊÓ

(a) Sodium triacetoxy borohydride NaBH(OAc)₃, can reduce aldehyde in presence of ketone because it is a weak reduction agent.

(b) Aldehydes are more electrophilic than the ketones. In order for a ketone to react with a grignard reagent in presence of an aldehyde, the aldehyde group must be protected first forming an acetal. Then the acetal can react with grignard reagent followed by hydrolysis to give the desired product.

(c) In the second step of the last step, three process takes place which are, hydrolysis of an acetal, hydrolysis of Grignard reagent, and dehydration.

(d) Ketone between two methyl groups becomes less reactive due to the steric hindrance of the metyl groups. The more reactive ketone is protected first and then the reduction reaction takes palce followed by the hydrolysis of the acetal.

(e) A ketone must be protected before the grignard reagent is made. Otherwise the Grignard reagent will react with carbonyl group of another Grignard reagent.

(f) Before substitution of bromine, ketone must be protected else the nucleophile would react with more electrophilic carbonyl group.