Question

Design a stepwise synthesis to convert cyclopentanone and 4-bromobutanal to hydroxy aldehyde A.

Short answer

Carbonyl compounds are protected by forming either open or closed acetals by reacting with suitable alcohol.

4-bromobutanal reacts with ethylene glycol to form a ring acetal. This would protect the carbonyl group increasing the chemoselectivity of the halide ion.

Protection of carbonyl compound

Step-by-step solution

Acetal formation

Carbonyl compounds are protected by forming either open or closed acetals by reacting with suitable alcohol.

4-bromobutanal reacts with ethylene glycol to form a ring acetal. This would protect the carbonyl group increasing the chemoselectivity of the halide ion.

Protection of carbonyl compound

Organometallic compound

The compound would react with magnesium to form the corresponding Grignard reagent (RMgX).

Formation of Grignard reagent

Nucleophilic reaction

The Grignard reagent would attack the carbonyl carbon and is hydrolyzed to form the corresponding alcohol.

Nucleophilic addition

Deprotection

The compound is protonated in order to deprotect the carbonyl group giving the required product A.

Deprotection to form A