Using an appropriate tosylate intermediate, synthesize the fol...

Question

Using an appropriate tosylate intermediate, synthesize the following molecules starting from the appropriate alcohol.

(a)

Accepted Answer

Hi, everybody. Welcome back. Let's take a look at our next problem starting with alcohol and using an appropriate tosylate intermediate, synthesize. The following molecule are molecules of cyclohexane. And if I number the carbons in my double bond, one and two, carbon, one has a methyl group and then carbon four in the ring has an azide substituent. So we know we need to start with alcohol. Uh Let's recall what Azide nasi group is. It says it's N three. So we have three nitrogens. The central nitrogen has a double bonds to nitrogens on either side and the central nitrogen has a positive charge. So no lone pairs while the outer nitrogens have negative charges, meaning they each have two lone pairs. And one thing to note is that this is a strong Nile, as you can see by that negative charge. So we need to start with an al alcohol and then we're putting on a group that's a strong nucleo when it's by itself. So we'll be looking for a substitution reaction. Now, we're told right here, we're going to use a tosylate intermediate. So let's think about what a and why would we be using a tosylate intermediate. Well, we have an alcohol that also has a double bond. So we can't use any of our acid catalyze reactions. Usually we'd use an acid to proton our alcohol and make it a good leaving group because we have an acid sensitive molecule that double bond may react with the acid instead of the alcohol that we want. So we need to avoid using things like hydrochloric acid or anything like that. So let's look at our original molecule, we'll draw our six carbon ring put on the double bond in the methyl group and on carbon four where the azide group is, we have an alcohol. So we need a tosylate intermediate. So what that would look like? Let's recall our, what our tassel group is. Put that up top, we'd have a sulfur which will bond to our, our group. The sulfur has two oxygens bound to it by double bonds. And then it has a benzene ring with a methyl group attached. That's what makes it a tassel group. So a toss intermediate for this straw ring. Again, we have the oxygen from the alcohol group and that will be bound to that electro pilic sulfur. So our sulfur then still has those two oxygens with double bonds and then it's benzene ring with the methyl group or we can just call it a Taine substituent and converting our alcohol to this tussle intermediate has converted it into a good leaving group again, alcohol is a poor leaving group. Um But without the issue of causing cross reactivity with that do carbon carbon double bond. So now we need to replace that oxygen from the alcohol with the azide. We already know our azides, a strong nuclei. So we can have that come in here to do the substitution reaction. So let's put that down here. N three, I won't draw out the whole molecule. I'm just gonna show that there's a pair of electrons here that can react, it's negatively charged strong nuclei file. So we're going to have an SN two substitution reaction. That's all right, SN two. So that lone pair on the aide can come up and go to that carbon on our intermediate. And then the electrons from the co bond will go on to our tosylate and then we'll generate our desired product. Draw an arrow back to the original drawing that was provided to me. But this is sort of showing us intermediate. But we also need to think about what, what reagent will we use? We've just shown the group here. Well, what we'd probably use here is to or excuse me, TSCL or Tossy chloride, which has a chloride on this molecule. So we've got the chloride bound to the sulfur. So to show our more complete synthesis, again, we'll use Tassel chloride. So I'm going to draw that molecule here over our arrow. So chlorine sulfur, draw the two oxygens and my toluene here. And so the lone pair on my alcohol or one of the lone pairs I should say is going to attack that electro pilic sulfur on my tossy chloride that will then make the electrons between the chlorine sulfur bond go to the chloride that forms my tosylate intermediate. Though I'm just going to erase this drawing I did earlier because I do need to show one additional step in here, which is the dep protonation of that oxygen because we've still got hydrogen there if you can see. So let me just add that and step in really quickly. So you can see the first molecule I actually generate when the oxygen formed that bond with the sulfur, I now have a positive charge my oxygen, which it doesn't like. Now I did generate a chlorine on the last step that could deproteinate this. But it's also important because I'm about to generate a proton. I don't want any acid in the solution or it's going to react with that double bond. So I need to have a base, I need to be on a basic solution along with my tossy chloride to prevent any acid from forming. So an example of a base might be triamine. So et three N or purine something like that. So this base you'll have some electrons and it can come over and react with that hydrogen. Its electrons will go on to the oxygen and then I'll generate that intermediate that I drew earlier, now my oxygen is neutral. Again, it's happy. But now with that toss intermediate, that can be a good leaving group unlike alcohol. So again, I want to replace it with the azide. So I've got my N three minus. Now, this is a negative ion. So I need a counter ion. So how about sodium azide? So that will dissociate and the electrons on that azide can then perform that sn two reactions a strong nuclei. So those electrons can come on over to this carbon and the co bond will break those electrons will come to the oxygen. And again, I will generate my final product. So now I have my synthesis. So I had to add Tossy chloride. Put that there and a bass to prevent the formation of acid, I formed my fossil intermediate write that under there converting the alcohol into a good leaving group and having that base to prevent any acid from forming. And then I reacted it with sodium azide to act as a nucleo file and put that N three group onto the molecule, substituting it for the alcohol group that had formed that tosylate. See you in the next video.

Using an appropriate tosylate intermediate, synthesize the following molecules starting from the appropriate alcohol.
(a)

Key Concepts

Tosylate Formation

Nucleophilic Substitution Mechanisms

Stereochemistry in Organic Reactions

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