Chapter 22, Problem 22.53P

Interpretation Introduction

Interpretation:

Compounds A-G in the given synthesis scheme are to be identified.

Concept introduction:

The missing compounds in a given synthesis scheme can be identified on the basis of functional group transformation reactions and the reactions in which a new carbon-carbon bond is formed.

Benzene undergoes aromatic electrophilic substitution with molecular bromine in the presence of a Lewis acid such as ${\text{FeBr}}_3$ to yield bromobenzene. Grignard reagents are prepared from corresponding aryl or alkyl halides when treated with the magnesium metal in the presence of dry ether as a solvent. This generates a carbon nucleophile. These serve as good nucleophiles and attack the least substituted carbon atom of the epoxide in the nucleophilic substitution reaction. The alkoxide ion thus formed is protonated using the acidic work-up to yield an alcohol. Primary alcohols undergo oxidation to yield an aldehyde using the oxidizing agent PCC.

Alcohols are converted into their corresponding alkyl bromides using the reagent ${\text{PBr}}_3$ via an ${\text{S}}_{\text{N}}\text{2}$ reaction. Alkyl bromides are used in the synthesis of Wittig reagents, which in turn are used to form alkenes when treated with a carbonyl compound.