Show how Diels–Alder reactions might be used to synthesize the...

Question

Show how Diels–Alder reactions might be used to synthesize the following compounds.

(g)

(h)

Accepted Answer

All right. Hello everyone. So this question is asking us to provide the deals all the reaction that would produce the compound shown below. So up on the screen here are the two target products for this question. Now, one thing to recall about deals older is that it can otherwise be described as a four and two cyclo addition. And it's a four and two cycle addition between two components, two reagents. One of them is a conjugated dying and the other is a dien ahi. Now, in this context, the Diop file is an alkin or an alky that has high affinity for the conjugated dying, hence its name. And so deals older is the combination of four atoms from the dying, combining with two of the dienno to produce a six membered ring, considering the structures of both target products, there is a six member ring present at the center of both structures. And what's also notable is that both of these double bonds, excuse me, both of these rings have a double bond inside of them that's indicative of a deal's older product. So here after you've located the, the double bond inside of those six membered rings, the pi bond, excuse me, the signal bond that's directly adjacent to it came from the dying of a. It may not always be a sigma bond if the dienno was an all kind. But the main point is that the bond across from it, across from the double bond of the six member ring came from the dienno file. And so to separate the dying from the Diop all you have to do now is separate those two carbons from the bond you just identified from its neighbors, so to speak. So with that in mind, let's start with part one. And after creating that split, separating the diane from the Diop file, everything to the left of the split came from the dying and everything to the right came from the Dyno. So here it's also important to recognize that in retro synthetic questions like this one pi bonds must be added to the reagents because we're moving backwards in this case. So for example, let's start with the structure of the dying, which is to the left of the split that I just drew considering that there is a one carbon bridge that one carbon at the very top of the structure of the target product must have come from the dying itself. So when drawing this reagent separately, it should have two pi bonds indicative of a conjugated dying then, so our bromine substituents are going to remain attached. It's worth mentioning that substituents retain their configuration after a deals alder reaction. So that's important to recognize too. All right. So here's our diane and now the diana file is essentially whatever is on the other side of the split that you just dr So in this particular case, that's a five carbon ring, another one actually. So on that five carbon ring, I have bromine atoms, one on two adjacent carbons. But recall that pi bonds must be added. This is because during the deals, all the reaction, one pi bond from the Diop is converted into a signal bond. So now I must add that double bond back to the structure of the Diop. Now, if you've identified the bond of the Diop and that's actually a double bond, that means the Diano must have been an all kind. So always just add a double bond or Pyon, I should say. All right. So here are the reagents and for deals alder recall that that's usually done in the presence of heat just to speed up the reaction. And now we can move on to part two. So part two is a similar principle, we've identified the bond that came from the Diop. So our task is to separate those two carbons from the remaining carbons of the Deal's alder ring. So first, the single carbon that's bridging on top of the deal's, all the ring must have come from the dying. So the dying in actuality must have been a five carbon ring. And once again, I need to add a double bond to show that it was a conjugated dying in the beginning though. We still have bromine substituents on every carpet. So I'm just going to add that. But our dienno file is pretty interesting because looking at the left side of the split, the dyno is itself a six membered ring with a single carbon bridge. So here's our six carbon ring and we have one carbon above that or above the ring. Now, the structure of the Diop must have one additional pipe on added. So I'm going to do that and there's already a pi bond present in the ring. So I'm going to add that as well and this is done in the presence of heat and there you have it. So here I went ahead and just drew the two reagents that will produce the products labeled one and two, the two sets of reagents. And so with that being said, thank you so very much for watching and I hope you found this helpful.

Show how Diels–Alder reactions might be used to synthesize the following compounds.
(g)
(h)

Key Concepts

Diels–Alder Reaction

Conjugated Dienes

Stereochemistry in Diels–Alder Reactions

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