To practice working through the early parts of a multistep synthesis, devise syntheses of

(a) pentan-3-one from alcohols containing no more than three carbon atoms.

(b) 3-ethylpentan-2-one from compounds containing no more than three carbon atoms.

It is carried out by more than one step and forms multiple intermediate compounds. It is the process were the complex product is formed from multiple steps using readily available compounds.

(a) When propanol is treated with 1 equivalent of NaOCl, it forms propanal. Aldehydes, when reacted with Grignard reagent, form secondary alcohol. Therefore, propanal reacts with ethyl magnesium bromide followed by hydrolysis from pentan-3-ol. Pentan-3-ol is treated with NaOCl and HOAc to form pentan-3-one.

Formation of pentan-3-one

(b) When propanoyl chloride is treated with ethyl magnesium bromide followed by hydrolysis form 3-ethyl-pentan-3-ol. 3-ethyl-pentan-3-ol treated with sulphuric acid undergoes dehydration to form 3-ethyl-pentan-2-ene, which on further reaction with BH₃. THF and H₂O₂, HO^- form 3-ethyl-pentan-2-ol. 3-ethyl-pentan-2-ol treated with NaOCl and HOAc forms 3-ethylpentan-2-one.

Formation of 3-ethylpentan-2-one