Show how you would accomplish each conversion using an enamine...

Question

Show how you would accomplish each conversion using an enamine synthesis with pyrrolidine as the secondary amine.

(a) cyclopentanone → 2-allylcyclopentanone

(b) pentan-3-one → 2-methyl-1-phenylpentan-3-one

Accepted Answer

All right. Hello everyone. So this question is asking us to propose the plausible synthesis for the given transformations through the synthesis of enemy with pip pyridine as the secondary ami. Now, before we go ahead and talk about each specific synthesis for parts one and two, let's briefly talk about a general scheme of the reaction itself. So, piperidine, if you recall is a secondary amine in which the nitrogen or the amino group is part of a six member ring. And so here, both of our starting materials are notably ketones. And even though we're going to discuss both reactions in greater detail in a moment, both of these are examples of alpha alky reactions using an enemy intermediate. So lets go ahead and talk about a general scheme starting off with acetone here as my generic ketone. So in this particular case, we have a generic ketone and a secondary amine like the piperidine we were given. So when combining these two starting materials together, the resulting intermediate is an enemy and this is done in the presence of some acid. So as a result of this step, we're going to have a single bond between the initial carbon carbon and the nitrogen of the secondary of meat. Instead, there's going to be a pi bond in between the initial carbon carbon and the carbon next to it. Now, it's worth mentioning that this reaction is going to result in the net loss of water. However, in any case, in our enemy intermediate, the alpha carbon, which if you recall is the carbon atom next to the car bono carbon is now going to be nucleic. This is going to lead us into the next step of the synthesis, which is in an sn two type reaction with an cul hide or between an cul hide and the alpha carbon of the enemy. So that is going to establish a new carbon carbon bond between the alpha position of the enemy and the R group of the all kill hide. However, as a result of this, the pi electrons in between the two carbons of the enemy are now going to be present in between carbon and nitrogen. This gives nitrogen a positive charge. So now this gives rise to the last step of the synthesis, which is the hydrolysis of the enemy intermediate. So here in the presence of aqueous acid, our enemy is going to be replaced with a key to once more this time with the new R group from the O hide. And so with this context in mind, we can go ahead and discuss discuss each of these individual reactions. All right. So starting off with part one here, we have cyclohexane known as the starting material and two propal cyclohexane, one known as the intended product. And so our starting material is a ketone inside of a six carbon ring. Whereas our product still has our ketone inside of that six carbon ring. But this time, there's an extra three carbon chain branching off of the alpha position relative to the carbon. And so with this, we can see that it is the three carbon chain that must be the R group from the OK, hide. So attaching a halogen, let's say bromine to that Ocu group will give us one Bromma propane as one of our reagents for the synthesis. So let's go ahead and draw that. So first, we have cyclohexane reacting with piperidine to produce our and a mean intermediate. This is done in the presence of acid H A and water is ultimately lost. And so this gives us our enemy intermediate. And so it is this enemy intermediate that's going to undergo SN two and then hydrolysis right afterwards. So here I'm going to combine those two steps in the same reaction. Arrow. So on top of the arrow for step one of the sequence, we have the addition of one bromo propane. And then in the second step, we have the addition of aqueous acid for the hydrolysis portion. And from there, we have our target product and part one is complete. So now we can go ahead and talk about part two. The starting material for part two is hecan three own and the target product is three methyl one phenol hecan 40. So for part two, our starting material is hecan 30, which is a six carbon parent chain with the car bono on position three of the chain. The target product is three methyl one fenny hep tan 40. So we have a seven carbon parent chain with a benzene ring attached to carbon one of the chain, the car bal attached to position four and a methyl group branching off carbon number three. And so once again, here we have another example of the alpha Oculus of our starting ketone. So here I always advise to try your best to find the carbon chain of the starting material. And by doing so counting the methyl substituent as well. We can see the six carbons from our hexane 30 and so are substituent. Is this additional two carbon chain with the benzene ring branching off of that as well? And so from here, let's go ahead and start with our synthesis because I am starting to run out of space. So for the first step, we have our original ketone and piperidine. So our enemy is synthesized in the presence of some acid water is ultimately lost and we have our enemy. And so from here, it's a or it is an additional SN two reaction followed by our acid hydrolysis. All right. So I was able to clear up some space. So I'm actually going to draw this going downwards. So first in the S and two reaction, we can add a halogen like bromine to the art group that was added, two are starting material. So here's our additional two carbon chain with our benzene ring branching off of that. And then in the second step of the sequence, we proceed with hydrolysis using some aqueous acid and there you have it. So this completes our final answer for part one and two. And with that being said, thank you so very much for watching. And I hope you found this helpful.

Show how you would accomplish each conversion using an enamine synthesis with pyrrolidine as the secondary amine.
(a) cyclopentanone → 2-allylcyclopentanone
(b) pentan-3-one → 2-methyl-1-phenylpentan-3-one

Key Concepts

Enamine Synthesis

Alkylation of Enamines

Reactivity of Carbonyl Compounds

Watch next