Diels-Alder Retrosynthesis

in this video, I'm gonna walk you guys through a technique that you might need to use for deals. Elder problems. So sometimes your professor, your textbook your online homework is gonna ask you to do a deal's elder retro synthesis. That means that you're gonna be given the final cycle ization product, and then you're gonna be asked which dying and which Diana file were required to make this six member ring in the first place. Now, it turns out this is a really easy type of question to answer if you just have the right technique, and that's what I'm here to show you. So here's an example which Diane and Diana file would you use to synthesize the following compound. Okay, It's really easy get lost in these types of questions because as college students, we hate doing stuff that we haven't been taught to do explicitly. Right. And this is a backwards question. You have to think backwards. So I'm gonna teach you guys how to think already tell you guys how toe think forwards, and I'm gonna teach you guys how to think backwards as well. Well, the first thing that you guys want to notice what this product is that there's a certain, like, kind of, like landmark that you're always going to be able to find on these products because you know about the mechanism and the mechanism, remember, Always makes a double bond between the second and the third carbon. Remember me showing you guys that? So that means the first thing you want to do is you want to find that landmark, and you want to kind of orient yourself on that because that's going to provide the structure for the rest of the molecule. So the first thing I want to do is identify Where was that new double bond? That new double bond is right here. Okay, That means that this must have been my second and my third carbon. Okay, which means that that must have been where my dying waas. Okay, so my first step is always to find the original dying. And the way you do that is by identifying the double bond and then saying, Well, this must have been the dying to begin with this Muslim in my one. And this What must have been my four. Okay, now that I have that dying I understand the mechanism better. I know that the dying must have reacted with a dying of file. And remember that the dying always creates two new bonds to the Diana file. So the next step is gonna be to cross out the new bonds because I know that my dying must have made to bonds. So here's my dying once again. Okay? And it made to new bonds. I'm gonna cross these out because I know that they didn't used to exist. Okay, so after I've crossed them out, that means that whatever is attached on the other side must have been the dying a file. So in my next step, I isolate the Diana file and guess how you do that really easy. All you do is you take your exes, right? You still have your dying, and you just cross a line right through them. So I'm gonna just chop it off right there, right through the excess. And what we see is that now we have a dying on one side and something on the other. The other side must have had a double bond in order to react in the first place. Okay, so basically we're making those three double bonds that we started with. So the answer for this question would be that I start off with a dying that looked like this. Ah, 13 dying holds like this. Plus, I started off with a Diana file that looked like this. Okay, And now that we figured that out, isn't it crazy to see how actually, it was a diamond ization? This is a molecule that reacted with itself through deals alder, but it wouldn't have been obvious unless you use a system to figure it out. Okay, so I know this is a new skill. I know that I might be making it look too easy. So let's test out our skills on this example. Go ahead for the following two problems. Try to figure them out. We'll do them one at a time. Go ahead and do a right now and then I'll help you guys and show you the answer.

So, guys, this was again just a three step process. And you always start by finding the original dying, which must have been right here because this double bond comes from the original dying. If that's the original dying, that means the new bonds were these two right here. Which means that when I isolate the Diana file, I'm gonna chop right through both of those exes. Okay, Now, notice that this question did include stereo chemistry. So in order to get this question right, you needed to include the stereo chemistry. So let's go ahead and draw both of these components. I would have a dying that looked like this. Okay? With the two metals coming off of it, and I would have a Diana file that is a double bond, right? Because it must have been a double bond, but notice that you can't really see that. Sorry. It must have been a double bond, right? But noticed that my substitute Wint's r cist to each other on the ring notice that they're both facing up. That means that that original dying a fought Diana file must have had sis groups. So this is your answer. You must have had a dying that looked like that with the two are groups. And then a cyst, the whole bond die in a file. All right, Awesome. So go ahead and work on the next one, and then I'll show you guys the answer.

All right. So do the limited space. Once again, I'm gonna take myself out of the video. Don't miss me too much right here. Okay? So let's go ahead and do this one once again. It was pretty easy to identify the dying. It was right next to the double bond. So we know that that is the dying. But notice that I gave you guys a bridge compound this time, so it's a little bit more challenging. So you have to take out the new bonds in this next step. And I really hope you guys didn't cross out the bridge because that just doesn't make any sense. You guys know that the bridge has to do with extra carbons That must have been on the dying to begin with. So, actually, the bonds that we wanna cross out are the ones that go to the rest of this ring. Okay? Meaning that when we go to separate this, we're separating the dying and the dying. A file that means that my original Diana file must have had a double bond here. But it means that my dying had extra carbons. Right? So how big of a molecule was the original. Dying how big? It was a ring, Right? Because we know that rings meek bridges, right? We kind of went over that extensively. So the question is, how big is that ring? And you're just gonna draw it exactly the way it is we're gonna draw. Let me use red. We're going to show that the dying must have been a six member ID ring because I've got double bond, double bond. But then I've got thes 12 extra carbons that didn't even wanna be there. That air now. Here. Okay, so we had a six member ring that formed a to carbon bridge. And then my Diana file is pretty straightforward. Guys, it's just gonna be this ring. Oops. And really, you don't have to worry about CIS and trans here because a ring is always gonna be CIS and trans What? Wow, that was really unclear what I meant to say. Let me just come back in. You don't have to worry about drawing my Diana file as like, a sister trans ring, because rings are always gonna be on one side of the molecule there automatically, sis, because they're small. So don't worry about that this is the right answer. So if you just have this Diana file with this six member dying, you got the question, right? Okay. Awesome. So I hope that that skill might help you on the exam. Maybe get you a few more points. Um, let's go ahead and move on to the next topic.