Sharpless Epoxidation

So now I want to talk about a former up oxidation that has some pretty interesting advantage is the name of this reaction is the Sharpless asymmetric approximation. So the whole point of this reaction is that it's a form of approximation that is in Nancy O selective. What that means is that it's gonna generate on Lee one of the two possible any Ann Summers in excess. In fact, it's almost going perfectly select one and in humor over another. Okay, now, in order to do this, we're gonna use, um, pretty weird molecules, some pretty weird re agents that overall, I would just ask you to recognize more than memorize, Okay, because most professors aren't going to get into the nitty gritty of memorizing every single letter off these re agents. They just want you to know what this direction is about. Okay, so the way this direction works is that it's going to convert a little alcohol's. Okay, that means it's an alcohol that has a CH two and then a double bond. A little is a position that says that you're next to a double bond not directly attached to one, and then it's going to generate a certain a pox side based on the type of tar trait that is used. Okay, so these tar traits are basically, um, functional groups that have different Kyrill centers. Okay. And what you're gonna find is that there's three different possibilities of types of tar traits that I could use in this reaction. I could use the s s. I could use the r r. We're talking about thes Kyle centers right here. Okay, so both of them are s that's considered a positive tar trade. Okay. And positive. You remember if you see a little positive sign inside of brackets, what that's talking about is the optical activity. Okay, so what that's saying is that the Cairo centers are s and s. When you run it through a polar emitter, it's gonna rotate light clockwise, okay? And that's what the positive means. Okay, Well, the Ananta more of that would mean that both karl centers are opposite. So if you haven't are are tar trait. Okay, that's gonna be a negative rotation. And the reason is because remember that the Anant humor of any Carl center or of any kind of molecule will always have the opposite. configuration the opposite rotation, but of the other configuration. Okay, So, for example, if it was positive 20 degrees, that it would be a negative 20 degrees rotation with the with the negative D t Okay. And then finally, we have an r and An S or an s and m R. Okay, this is actually a me so d t so this one would be actually since me. So this one, I have no optical activity. Oops. I'm just gonna write no optical activity. Okay, This is going back to our Chire ality chapter. We talked about miso compounds and how they don't rotate plane polarized light, so it's impossible to assign a plus or minus toe me so because it's not gonna rotate it all. Okay, so this is interesting. We're talking about Kyle Centers. You're like, OK, this sounds a lot like Cairo ality, but what does this have to do with the pox side? Well, it turns out that you can predict the direction that the epoxy is gonna form from what type of any interior you're using. Okay, so it turns out that the positive DT the positive tar treat, the one that has the positive rotation of light is going to attack from above. Okay, it's going to an anti Oh, selectively Pick the top part of a double bond toe. Add in a park side. Okay, then we've got the negative one. The negative one is gonna be the opposite. So it's gonna pick. It's gonna attack from below. Okay? And we would expect the one from below to now form of Parkside below the double bond. Okay, so we've got positive is up. Negative is down. That's really easy. Right? Then you got me. So what do you think about me? So? Well, Miss a would just be both okay. And the reason that missile is both is because this would be non an anti. Oh, selective. Okay. Why? Because it doesn't have a preference of top or bottom. So it's just gonna be a 50 50% 50% chance. Okay, So really, we don't really care about the missile one so much, and we're not gonna use that one synthetically or we're gonna use is positive DT and negative de et as our catalysts toe form the upwards of Parkside and the downwards of Parkside. Okay,

So now you're probably wondering. OK, Johnny, how does this actually look in a reaction? Well, here's the general reaction. Okay, so here as you'll notice, I have an a little alcohol. This is my alot alcohol right here. The reason to call it a will is because it is next to a double bond. It has a seed, Xu, and then it has an Ohh. Okay, so this is a Lilic. That's a position word. Okay, so you have in a Lilic. Ohh. And when we react it with a peroxide, this is the oxidizing agent. That's what's gonna make the the oh, and then a titanium catalysts. Okay, don't worry too much about the titanium catalyst. You'll just see that there's t I there that stands for titanium, the titanium catalysts. And then we use one of the tart treats either negative or positive. Okay? And when you put all those things together, what you're gonna wind up getting is Thea Parkside in the place that you want it. So if I want my a pox sides face down, then I would use if I wanted to be below the plane. Then I would use a negative tar trait. Okay, A negative charge rate is going to attack from the bottom of the Dole bond and is going to give me my a pox side at the bottom. Now, obviously, that means if the epoxy is facing towards the bottom, then my other substitutes must be forced up. Right? Cool. So so far, I know these regions air super confusing. Okay. But really, I'm not asking much from you. I'm not asking you to memorize them. I'm just saying, Hey, can you remember that the positive tar trait ads from the top and the bottom the negative Tartarus ads from the bottom is that cool so far?

All right. So I just want to add one more little twist to it to make sure that you always get these questions right. If you want to make sure that your alcohol is oriented correctly so that you always predict the right product, you always want to draw the alcohol on the bottom, right corner off the double bond. Okay, now you're going to notice is that in some textbooks, they don't use the bottom right corner. Some textbooks, they use the top right corner. Some textbooks, they tell you other directions. But go ahead and use mine. Just because the fact that it doesn't matter which corner you use as long as you're consistent and that's gonna be the one that translates to the pattern that I told you about working. Okay, so if you wanted another way, that's fine. But honestly, most people really don't understand startup oxidation. So I think this where it works really well. So we always put this what I'm saying. If you have your alcohol oriented wherever you always make sure that it has to be at the bottom right corner. Why? Because once it's at the bottom right corner. Now you're double bond is oriented correctly. So now when you look at your DT, you say, Okay, Is this a positive tar trait or a negative tar trait? Positive. That means that my a pox I should form above this double bond. That's exactly we did. So you form Europe oxide and notice that whatever is in the front, whatever's facing towards the front here, let's say this is your line. Whatever facing towards the front goes on a wedge, okay. And whatever was facing towards the back goes on a dash. So that means the Brahmin and the metal group going to dash the alcohol and the h go on the wedge. Ideally, your alcohol should always be going on the wedge. Right? Because you always want to face your alcohol towards the front or down and everything else we're supposed to go. Okay, so in this case, I would get in the Parkside above the plane. So in a park side, exactly facing up. Okay. Because it's a positive d a t d t. So I'm just gonna give us an example. How about if we had used just us consider it looks like negative tar trait. Then what would the answer look like? Okay, I'm just gonna tell you right now, all of these wedges and dashes don't change, because that has to do with how the dull bond is oriented. The dull bond is going to stay the same. So I would want to do the same thing of how they're oriented on watches and dash is the only thing is that if we use negative d t actually gonna put it over here So you guys can see if we use negative de et tar treat instead. Then what I would get is in a park side facing down, okay? And then all these groups where they are, where they're at. So that means that I would have my ohh facing towards the front. I would have my h facing towards the front. Okay, then I would get my metal in the back, and I would get my bro Ming in the back. Okay? And the reason that makes sense is once again think that this double bond is exactly the way it looks. And you just popping in a pox side right at the bottom. So that means that everything stays in the same place that it was originally same with the positive tar trait. Okay, so, guys, I hope that that made sense. Really? A lot of professors don't ask for a lot from Sharpless approximation. It is a newer reaction discovered in the past 2030 years. Okay, so there isn't a whole lot to know. I would just suggest knowing this trick, and it could maybe get you some points in the test. So anyway, that's it for now. Let's go ahead and move on to the next topic.