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.
(d)

(d)

Accepted Answer

All right. Hello everyone. So this question says that an important type of the deals alder reaction is the intra molecular reaction where the dyane and diana are connected together. This deals all the reaction result in the formation of two new rinks, determine the product for the intra molecular gels alder reaction for the compound. Given below. For this problem, the use of le acid catalysts can be disregarded. All right. So first, just taking a moment to analyze what we're given here, we can see that towards the bottom of the structure is a conjugated dyne and towards the top of the structure is a Diop recall it in the context of deals older, a Diop describes an allen or an all kind that has high affinity for the conjugated dyane. Hence the name. So with that in mind, deals alder can otherwise be described as a four and two cyclo edition. This is because four atoms more specifically four carbons from the conjugated dyane combine with two from the Diop to create a six member ring. So the formation of this new six member ring is actually going to create two rings given our starting material due to the presence of our substituents here. And so now that there's more context on what type of reaction we're dealing with. Let's just talk about a few notes about stereo chemistry. Now recall that deals all the reaction is sin addition and this is true for both the dying and Diop. So the Diop is going to add to one face of the dying and the dying adds to one face of the dienno. So all that is to say that the stereo chemistry of existing substituents is preserved. It's going to stay the same because that sin edition doesn't give substituents the chance to alter their positions. Now, one more thing to consider here is known as the endo rule for Dio's older and to talk about the endo rule, I very quickly want to point out something about the Diop. The dianno happens to have an electron withdrawing substituent, which is a car bomb. Now, the endo rule is relevant for Diano files that contain pi bonds in their electron withdrawing groups. And that's true for the car bono in this case. So when you have a pi bond on the electron withdrawing substituent, that pi bond is going to gravitate towards the central atoms of the dying as it gravitates towards those central atoms, it's going to approach what's known as the endo position. And as we move through drawing the product for this reaction, we will talk more about how to illustrate that endo rule But for now, let's talk briefly about the mechanism and for the mechanism, I'm going to go ahead and label these carbons. We have four from the conjugated dying and two more from the Diop that I'm labeling five and six. Now the mechanism is concerted, which means everything is happening at the same time. So while the pi bond between carbons five and six moves to carbon four, the pi bond between carbons three and four moves in between carbons two and three. This forces the pi bonds in between carbons one and two to attack carbon six. And so the bottom line here is that two pi bonds of the original three are converted into sign bonds to establish this new ring. Now, the formation of this new ring is going to establish a second ring because of the additional carbons that are in between the dying and Diop. So now let's go ahead and illustrate, illustrate our new ring, I should say. Now for a question like this, I like to go ahead and start by drawing out what's not going to change, what did not participate in the reaction. So to do that, I'm actually going to draw the second ring that formed as a result of deals alder. So here's our new five membered ring with our additional substituents. Now, when it comes to drawing out the ring, it's important to be careful of any existing substituents and their stereo chemistry, their arrangement. So considering the dienno for a second, the Diana has two substituents on either side of the double bond, those substituents are trans to each other. So according to our sin edition here, those trans substituents are going to remain trans to each other. So to illustrate the fact that they're going to remain trans to each other, the new sigma bond in between carbons five and six is going to be depicted on a wedge, excuse me, on a dash on a dash. And so here considering also the substituents of the dying, the substituents of the dying are on the same face of the six membered ring. And so to illustrate that point, the new signal bond in between carbons three and four is going to be depicted on in which and our all kind here is also going to be on a wedge recall that now there should be a pi bond in between positions two and three of the new six member group. And so my remaining substituent is my car on the meth group that's towards the left side of the structure should be depicted on a dash. So let me just fix that, but there you have it, notice how the methyl group branching off of carbon number two is not depicted on a wedge or a dash because carbon two remained sp two hybridized after the reaction. But with that being said, thank you so very much for watching and I hope you found this helpful.

Key Concepts

Diels–Alder Reaction

Intramolecular Reactions

Stereochemistry

Watch next