An important variation of the Diels–Alder reaction is intr...

Question

An important variation of the Diels–Alder reaction is intramolecular, in which the diene and the dienophile are connected. This type of Diels–Alder reaction makes two new rings. Draw the compound produced in each of these examples; try to predict stereochemistry (using models will help). In some cases, Lewis acid catalysts are used; that can be ignored for this problem.
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Accepted Answer

All right. Hello everyone. So this question says that the intra molecular deals all the reaction is a notable version of such a reaction in which the dying and the dienno are in the same molecule. This type of Deal's older reaction forms two new rings. If the following molecules undergo deals alter reactions, draw the compound produced including its stereo chemistry. Note that Lewis asked catalysts are utilized. However, we will ignore this in this case. And here we're given two starting materials reacting in the presence of heat. So just for a moment, I'm going to go ahead and scroll down here to make some space for a few notes regarding the deal's older reaction. First off deals all the reactions can be referred to as the four and two cyclo addition. Now the four and two cyclo addition refers to the fact that four carbons from a conjugated dien combined with two carbons from a dienno file to produce a six member ring. Now, in this context, a Diop refers to an alkene or an al kine that is electron deficient. The mechanism itself is concerted and it's important to recognize that the dying in question must be able to exist in the S sis configuration. What that means is that the two py bonds of the dyne should be pointing in the same direction. Now, because steel's older is a sin addition, the configuration of any substituents, whether that's cis or trans is going to be retained in the structure of the final product. So let's say for example, that the Dian Ahi in question has two substituents that are trans to each other in the structure of the final product, they're going to remain trans to each other. So that's not going to change. On that note, it's also worth mentioning that if the starting material is a chiral and the product produced is Cairo, the net product is actually going to be a recce mixture. So now that we have a few more notes about the deal's older reaction, I'm going to go ahead and scroll up here to talk about the mechanism and therefore the products starting off with part one. Now, for part one in the center of the starting material, we can see that there is a system with three total pie bots, two of them are conjugated with each other and the other one is on the other side. So the four carbons from this conjugated diane combine with two more from the Diop the isolated py bond can be referred to as a dienno because it's an all keen with an electron withdrawing nitro substituent, excuse me, natural group So now let's talk about the mechanism. Now, once again, the mechanism is concerted, which means that everything is happening at the same time. So first, we can have the pi electrons in between carbons one and two, establishing a new bond with carbon number six. This forces the pi electrons in between carbons five and six to connect or establish a bond with carbon four. And then the pi electrons in between carbons three and four are forced to move in between carbons two and three. Now this gives us the six member ring that is characteristic of deals older. But because this is an intra molecular reaction, we end up closing two rings instead. So in the center of the structure is a six member ring characteristic of deals older this time with a pie bond in between carbons two and three. So at this point, we have to take into consideration the stereo chemistry of any substituents. The five member ring that is branching off of carbons two and three is going to remain a chiral because carbons two and three are still sp two hybrids. And so from here, we have to look at the configuration of the substituents breaking off of the Diop because they're on the same side of the double wand, they should be cy to each other in the final product, which is also going to be a reca mixture because now these carbons are chiral. So this means that one in an tumor is going to have both substituents of the Diop on a wedge and the other, an anime is going to have both substituents from the dienno on a dash. So from here, let's go ahead and talk about part two. So now we're go for part two, we're going to proceed the same way as we did. For part one, we're going to identify the four carbons from the conjugated dying and the two from the dienno file labeled five and six as for the mechanism that's going to proceed the same way as well. So eventually two pi bonds are converted into Sigal bonds. So here we have our six member ring and we're still going to have a pi bond in between carbons two and three. So carpets two and three happen to both have all cocky substituents, but stereo chemistry is not a concern for them because carbon two and three are still sp two hybridized. But now carbons five and six from the Diop both have substituents that are on the same side of the double bond relative to each other, meaning that our product is still going to be a reca mixture and those substituents are going to remain sis to each other. So for one in numer, both substituents are going to be on a wedge and on a dash for the other. Now there is another methyl group that's depicted on a dash towards the left side of the structure, but that's going to to remain the same for both stereo isomers because it's not involved in the deal's older reaction. And there you have it. Now, just a quick correction for part two. Part two is not necessarily going to be a reca mixture because these two compounds are diserio mires and not enantiomer. So part one was a reca mixture, but part two is simply a mixture of stereo isomers. And so with that being said, if you watch this video all the way through, thank you so very much and I hope you found this helpful.

Key Concepts

Diels–Alder Reaction

Intramolecular Reactions

Stereochemistry

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