[Carcul]

Show how you could synthesize aniline from cyclopentanone in only four steps.

(Source: created by Carcul)

[Yggdrasil]

Please read our Forum Rules.  Before we will help, you must show your attempt at answering the problem first.

[Carcul]

Hi Yggdrasil. Thanks, I have already read the forum rules. Read carefully my post: I created the problem, so I now perfectly how to solve it. I just posted it as an exercise because I thought it could be interesting.

Regards, Carcul

[Borek]

I created the problem

Everybody can tell such a story and I can assure you that we have seen it done here before. As long as we don't know you we are assuiming you are troubled by the question and you don't know how/where to start. Try to look at the situation from our point of view and it will become obvious.

[Congenial]

Hi Yggdrasil. Thanks, I have already read the forum rules. Read carefully my post: I created the problem, so I now perfectly how to solve it. I just posted it as an exercise because I thought it could be interesting.

Regards, Carcul

I think two steps is enough. One step for ring enlargement, one step for aromatization. Could you show us your route?

[movies]

I can't figure this one out, so I would love to know the answer as well.

[Carcul]

I think two steps is enough.

Explain those two steps in detail, if you don't mind. Thanks

[Borek]

Geez. You show first... no you show first... I though it is played mostly in kindergartens

[AhmedEzatAlzawalaty]

here u are the synthesis i could make, but could u tell me what ar these four steps u are talking about?

[Dan]

Excuse my ignorance, but how does that first step work? I can't see the rearrangement.

Instead of the grignard, you could use diazomethane for the ring expansion.

For step 2, I assume you mean H₃PO₄.

[Carcul]

I also don't see how that rearrangement would work. I know that Grignard Reagents sometimes allow unexpected conversions, but I don't see one of those here.

Instead of the grignard, you could use diazomethane for the ring expansion.

That's not also a good choice, because in the reaction of ketones with diazomethane there is always some considerable amont of epoxide as by-product. A much better choice would be the following sequence:

1) Reaction of cyclopentanone with NaCN/H+, to obtain the cyanohydrin.
2) Redution of cyano group (for example, with H2/metal catalyst) to obtain beta-aminoalcohol.
3) Treatment with NaNO2/HCl: this will diazotate the amino group, followed by rearrangement with ring expansion.

However, for the present problem this sequence is not needed (as expected, since it envolves three steps).

but could u tell me what ar these four steps u are talking about?

Ok, as an hint, here is the first step. The rest I will leave to you.

Step 1. Conversion to an enamine by reaction with pyrrolidine (for example) in the presence of a small amount of acid as catalyst.

[Custos]

Ok, as an hint, here is the first step. The rest I will leave to you.

Step 1. Conversion to an enamine by reaction with pyrrolidine (for example) in the presence of a small amount of acid as catalyst.

This seems a bit pointless, because you would never bother to make aniline from cyclopentanone. But as a thought exercise, I would try the following - make the enol ether (trimethylorthoformate, pTSOH), then do a dibromocarbene addition to the double bond. Under the right conditions the bicyclic intermediate would collapse directly to the bromocyclohexenone in one step. Then to get to aniline is all pretty much downhill - heating to high temperature in ammonia, maybe with a little silver nitrate, would probably do it.