When we cannot use Friedel-Crafts acylation to insert alkyl group?

Question

Questions:

1. Show a probable synthethic pathway to obtain the first molecule, I.
2. Will the same strategy be used to insert the alkyl group for J. Explain.

My answers (please tell me if there is any incorrect answer):

1. Friedel-Crafts acylation -> Clemmenson reduction -> Nitration -> Reduction of Nitro Benzene

2. No, to insert alkyl group for molecule J, it must undergo Friedel-Crafts alkylation. In Friedel-Crafts alkylation, there is carbocation rearrangement to ensure the carbocation is stable and tertiary. In J, the carbon that will directly attach to benzene is already stable, so the C(CH3)3 substituent will attach directly to benzene. (I'm not sure what to explain more)

Is this correct for alkylation step in J?

My questions:

• For no. 2, is it true if we say that, in this case, no rearrangement will occur in Friedel-Crafts Alkylation step because the carbocation is tertiary and stable so it can proceed with this step (Friedel-Crafts Alkylation). Is it possible that rearrangement will not occur in Friedel-Crafts Alkylation?
• Why we cannot use Friedel-Crafts acylation to insert alkyl group in J? I am confused, if we use (CH3)3Cl, there will be no carbocation rearrangement, but why the question asked about acylation, I think it is not possible to undergo acylation step because there is no carbocation rearrangement, so the substituent attached to J will be CH3CH2CH2???

Answer 1

tBu-benzene is prepared exactly as you describe, see this preparation here. Follow this by nitration and reduction.

There is no obviously comparable strategy of acylation that can compete with this. Making a tBu group from acetophenone is not straightforward and is illogical when there is a perfectly good direct route.

Answer 2

If a Friedel-Crafts reaction is made with $\ce{CH3-CH2-CH2-Cl}$ and $\ce{AlCl3}$, isopropyl benzene will be obtained, and not propylbenzene, because n-propyl cation may isomerize into isopropyl cation. That is why $\ce{CH3-CH2-CO-Cl}$ should be used instead. And -CO- is reduced later on.