Show how you would use the Friedel–Crafts acylation, Clemmensen reduction, and/or Gatterman–Koch synthesis to prepare the following compounds:
a.

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Step 1: Begin with Friedel–Crafts acylation to introduce the acyl group onto the benzene ring. Use benzene as the starting material and react it with isobutyryl chloride (CH3CH(CH3)COCl) in the presence of a Lewis acid catalyst such as AlCl3. This will yield isobutyl phenyl ketone (Ph-C=O-CH2CH(CH3)2).

Step 2: Perform a Clemmensen reduction to convert the ketone group into a methylene group. React the isobutyl phenyl ketone with zinc amalgam (Zn(Hg)) and concentrated hydrochloric acid (HCl). This will reduce the carbonyl group to a CH2 group, forming isobutylbenzene.

Step 3: Verify the structure of the final product, isobutylbenzene, to ensure the correct substitution pattern on the benzene ring. The structure should have a benzene ring attached to a CH2 group, which is further connected to CH(CH3)2.

Step 4: If using Gatterman–Koch synthesis, note that this method is typically used for introducing a formyl group (-CHO) onto the benzene ring. It is not directly applicable for synthesizing isobutylbenzene but could be used in a different synthetic route if needed.

Step 5: Ensure all reagents and conditions are appropriate for each step, and confirm the reaction mechanisms align with the desired transformations. Friedel–Crafts acylation and Clemmensen reduction are the most direct methods for this synthesis.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Friedel–Crafts Acylation

Friedel–Crafts acylation is an electrophilic aromatic substitution reaction that introduces an acyl group into an aromatic ring. This reaction typically uses an acyl chloride and a Lewis acid catalyst, such as AlCl3, to form a ketone. The resulting acylated aromatic compound can serve as a precursor for further transformations, making it essential for synthesizing complex organic molecules.

Clemmensen Reduction

The Clemmensen reduction is a chemical reaction that reduces carbonyl groups (ketones or aldehydes) to alkanes using zinc amalgam and hydrochloric acid. This method is particularly useful for converting acylated aromatic compounds into their corresponding alkylated derivatives, allowing for the removal of the carbonyl functionality while preserving the aromatic system.

Gatterman–Koch Synthesis

The Gatterman–Koch synthesis is a method for synthesizing aromatic aldehydes from aromatic compounds using carbon monoxide and hydrochloric acid in the presence of a Lewis acid catalyst. This reaction is significant for introducing carbonyl functionalities into aromatic systems, which can then be further manipulated in organic synthesis, such as in the preparation of ketones or other derivatives.

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