Question

Devise a synthesis of each compound from ethanol as the only source of carbon atoms. You may use any other organic or inorganic reagents you choose.

Short answer

a.

b.

Step-by-step solution

Acetal

Acetals are diether compounds produced by the reaction of a protonated aldehyde and ketones with two equivalents of alcohol. The protonated hydroxyl group of the hemiacetal is dehydrated to form the carbocation. This is attacked by the alcohol, followed by deprotonation to give the acetal.

Acetal formation

Consider the formation of the given acetal from ethanol,

a) But-2-one is protonated followed by nucleophilic attack by a molecule of ethanol. The proton transfer followed by dehydration would form the protonated ether. Another molecule of ethanol attacks the cation to undergo deprotonation to give the acetal.

Formation of open acetal using ethanol

b) Ethanol is dehydrated to form ethene that is oxidized into ethylene oxide. This undergoes acidic hydrolysis to form ethylene glycol, which is treated with propan-2-yneol in the presence of tosyl hydroxide to form the required product.

Synthesis of b.