Another group used to protect alcohols are silyl chlorides, namely TBDMS.
Mechanism of Silyl Ether Protecting Groups.
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alcohol's air so reactive that sometimes we want to react with another part of the molecule without actually interfering with the alcohol. And this is a situation where you want to use a protecting group. Okay, so now I want to talk about a type of protecting group called a syllable ether protecting group. Okay, so just you guys know on there are too many ways to protect alcohol's. You can use a t beautiful either protecting group or a silo ether protecting group. You may have to learn one or both of these for your professor. I'm only gonna include the ones that your professor needs. Okay. So if you're watching this video and fits in your playlist, that means you're Professor wants you to know this one. All right, So, sill Oh, ethers. I know they sound weird, but it just means that it's something made with silicon. Okay, It's a molecules made of silicon. It looks a lot like an ether, except instead of it. Oh, it's gonna have an S I a silicon. Okay. And these were used to protect. Remember that the definition of protecting group isn't that you can put on the molecule, protect and then take it off later. Okay? So just you know, there's this weird re agent called t b d m s o k t b d m s. You absolutely do not need to know what it stands for. What you do need to know is that it's the most common silla chloride used in organic chemistry. One to make a civil either. Okay, so just you guys know this is the structure T b d m s. Okay. And I would advise knowing what the structure looks like. Why? Because you need to know the mechanism for this. Okay, So how does this work? Well, basically, what I want to do is let's say that I'm trying to react to this alcohol. Hey, light. Okay, But we know that some re agents that react with alcohol highlights also react with alcohols. Okay. For example, strong bases, strong basis Could do elimination on Ah, Kyohei light. But they could also deep protein eight and alcohol. So how do we protect that? Well, what we could do is you could expose the alcohol toe a sill. Oh, chloride. What's gonna wind up happening is that this silicon has a pretty strong die poll pulling away from it. So there's gonna be a partial positive charge right there. You can use your alcohol to attack that silicon, but now silicon is just like carbon. It's It's actually right under carbon in the periodic table. So silicon once have four bonds. Okay? Right now, by adding that bonds of silicon were making five. So if we make a bond, we have to break upon. Is there an easy bond here to break? Hell, yeah. We could break off chlorine and cause it to kick out as a leaving group. What that's going to give us is a molecule that looks like this where nothing's happened to my alcohol. Hey, light yet. But now I have Oh, s I with, um, the two methyl groups and the tribunal group. Cool so far. Okay, We've also got the h that's still present and a positive charge. Okay, What we can now do is we can use the chlorine that got kicked off two D protein e. Okay. And we're gonna wind up getting is we're gonna wind up getting each cl okay because of the fact that we are deep rotating with cl and we're gonna get are protected alcohol case we got. Oh, then you got s I metal metal t beautiful. Okay, Now, the reason that this is helpful is because now forward exposes to re agent that reacts normally with alcohol. This thing will not react with alcohol. This is a NRI active, which is the entire point off a silo ether. This thing isn't gonna do anything, okay? It's not gonna react with anything. So what that means is that now, in the next step, there's another step that I'm going to skip here. We could do whatever we want to this part of the molecule. Okay? We could wreck this with a strong base we could react it with, I don't know, a nuclear file. Whatever. And we would Onley react with this. Onley reacts with target with the target functional groups, and it would not react with the civil either. Okay, so now that's great. We can do whatever we want to the alcohol. Hey, lied. But what happens when we want to get that alcohol back? Because that's the whole point of a protecting group is you want to make sure you could take the silicon off and get the H back on. Okay, well, then we're gonna use another re agent, And that re agent is kind of weird. It's a nitrogen with four beauty groups. Okay, So just if you guys want to see what that looks like, could be a nitrogen with four beautiful groups. Okay? 12 three, four. Okay, that's gonna give it a positive charge, and then you're gonna have a negative f associated with that. Okay? And what's gonna happen is that the flooring from that molecule can wind up kicking out. So this is after I've done my reaction to the bro. Mean Okay. Now, in my last step, I'm gonna deep protect. This is the protecting step. This protect one is protect than two is react. You do your actual reaction. Okay, then three is deep. Protect? Yeah, And when you deep protect, the way that the mechanism goes for that is that your f negative is gonna wind up coming over here and attacking that silicon, okay? And then kicking out. Oh, because the fact that you can't make that many bonds silk and you can only make four. So now we're going to get is something looks like this. Where now? I still you know, let's say that I reacted with that. Um, let's say that I reacted with the alcohol light and I did some kind of s and two. So now I have a nuclear file here. Okay. Notice that I'm doing is I'm saying that some kind of reaction took place where I had a broken before, and now I have something else. Okay, Well, now, in this last step, what I would get is Oh, negative. Okay, So what can we do to make an alcohol? Remember, there's HCL around. Where did that hcl come from? The HCL came from the cl earlier that deep throat nated the h. So now my alcohol My Ohh! I'm sorry. My own negative is gonna deport Nate the HCL and what I get as my final product is my alcohol once again. Okay. Now, the reason this is so helpful is because now notice that I can target a specific, functional group. If I wouldn't have protected and be protected, then maybe my nuclear file would have actually reacted with the O. H. Okay, But since I protected it with a civil either Now I can do whatever I want to the other part of the molecule, and then I can be protected and get that alcohol back. Okay, so it's very, very useful reaction. It's one that your professor may want you to know. Okay. So what I want us to do now is trying to do this yourself, draw the whole mechanism, trying to predict what's gonna happen here, notice that it's really the same thing we're gonna protect. What are you protecting? The alcohol, right? Then you're gonna react. This is up to you. You have to figure out what that reaction is, and then you're going to deep protect. Okay? What I'm interested in is that you can draw that mechanism and figure out what the final product is. All right? So go ahead and try to do that, and then I'll jump in. I'll show you guys how to solve it.
TBDMS stands for 'tert-butyldimethylsilyl'. A few variations of this are:1) TBDMS ether and 2) TBDMS-Cl (seen above). Both can be used to protect alcohols.
Predict the product of the following reaction.
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Alright, guys. So I'm gonna go ahead and draw the mechanism for this, and I am going abbreviate a few steps because this doesn't save draw the whole mechanism. It says predict the products. Okay, so what I'm gonna do is going to kind of simplify stuff so that you guys can get the point. We're not gonna draw every single step. Okay, So in the protect in the protection step, we know that my t b d M s. Wow, man, I'm dyslexic here, okay? T v d m s is going to react with the Ohh. Okay, so I just know that my oh is gonna grab T v d m s and what I'm gonna wind up getting is a protected version of the alcohol that looks like this. Okay, now, if I wanted to draw that whole thing out, I could That just stands for the oxygen attached to the Silla either. Is that cool? Awesome. Okay, so now that I've got that, what does that mean? It's protected now. Nothing can react with the O and the T v d m s on it. So now I can do my actual reaction. Well, do you know what kind of reaction this would be. It would be a reaction of my double bond with HBR. This is gonna be a hydro geology nation. This is the most basic edition reaction. So I go ahead and I grabbed my age Kick out the br What I wind up getting if something looks like this o t b d m s. Wow, I keep doing them first. And now I'm gonna have a carbon cat ion right here. Okay, According to Mark Avnet, college rule. Okay, so now what's gonna happen? Well, actually, this is a carbon cat I in that wants to shift. So you really have to do the whole reaction. We're gonna want to do a shift here. What kind of shift? I hydride shift. Why? Because there's, ah, hydrate in the position that is more stable. Okay, so I go ahead and I do an age shift. I've got an age here. It moves over, and what I wind up getting is O T B Wait D m s with now Carbo Catalan here. Okay, Now that Carvell Catalan is actually stable. So now I can react with the b r negative an attack Okay. What that's going to give me is O T B D m s and my bro. Mean right here. Okay, so now I've got the actual target molecule. I reacted the one with the HPR. I got my alcohol. Hey, lied. But I don't want to end up with O T B D m s. What? What the heck is that? You want to take it off? Okay, so the last step, we use f negative, Remember? F negative is the thing that attacks to attack kick out the oh, and then HCL will protein eat it? Okay, so we wind up getting at the end of this. I don't have a whole lot of them too, right? So I'm gonna try toe try to fit in here. I'm sorry. My head's in the way, too, but what we're gonna wind up doing, I'm gonna I'm gonna draw it up here, Okay? If you guys don't mind, we're going to get is something? Looks like this. Ohh. Metal br like that. Okay, this is our final product because we're regenerating the alcohol, and we reacted with the double bond and we got our halogen. Okay, so this would be the final answer to this question, and it used the method of protection reaction on deep protection. So it's always gonna be kind of the the method that we use. I hope that made sense. Let me know if you have any questions, but if not, let's go ahead and move on.