Electrophilic Aromatic Substitution: Multi-Step Synthesis

Suggest a synthetic scheme for the conversion shown on the left. Work each problem backwards, and draw the structures of the two intermediates required for the conversion, and the reaction conditions necessary for each step.
Click the mouse on the buttons to view the synthetic logic for each step, the structures of the intermediates and the solution to the problem.

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Working backwards, this molecule is a brominated carboxylic acid, and we must begin with benzene. A benzene carboxylic acid can be formed by permanganate oxidation of an alkyl group attached to the ring; any alkyl group containing at least one benzylic hydrogen will work.

Working backwards, this molecule is a brominated carboxylic acid, and we must begin with benzene. A benzene carboxylic acid can be formed by permanganate oxidation of an alkyl group attached to the ring. A methyl group is shown above, but any alkyl group containing at least one benzylic hydrogen would also work. Next, suggest a synthesis of 4-bromotoluene.

Since we are beginning with benzene, both the bromine and the methyl group must be introduced separately. Since they are both (ortho) and para-directing, either can be done first; suggest a synthesis of 4-bromotoluene beginning with toluene.

Since we are beginning with benzene, both the bromine and the methyl group must be introduced separately. Since they are both (ortho) and para-directing, either can be done first; next, suggest a synthesis of toluene beginning with benzene.

Benzene is first methylated by reaction with CH₃Cl in the presence of AlCl₃. In a second step, toluene is brominated to give 4-bromotoluene, which is oxidized to the carboxylic acid by reaction with hot neutral MnO₄^-.