Suggest a synthetic scheme, involving a protecting group, to g...

Question

Suggest a synthetic scheme, involving a protecting group, to generate the molecule shown starting with the molecule at the left.

(a) Chemical reaction scheme showing conversion of an alkyne to a ketone with an isopropyl group.

Accepted Answer

All right. Hi, everyone. So this question is asking us to provide a synthetic scheme to form the product from the given starting molecule include a protecting group in the scheme. So our starting material here is four methyl hept six iron to own. And our final product is excuse me, 46 time metal hept 620. So when it comes to synthetic schemes like this, the first thing I always check for is whether or not the carbon chain has been modified somehow, has it increased or has it de decreased? And when I consider that when I go ahead and I consider that what I'll notice here is that the starting material actually has one less carbon than the final product. So somehow some way, right, we have to add one more carbon by the time we get to our given product. And what I also want to mention is that at the end of the carbon chain in our product on the right side, right? We have this a key specifically a terminal ay. And the reason why I want to bring this up is because recall that there is a way to extend a carbon chain by adding an all keen to the end of it. And that is going to be via the witted reaction. So, somehow some way, right, we have to get to a witted reaction to make sure that this carbon chain increases. So here let's go ahead and actually start by examining our all kinds because wi reactions, wooded reactions are generally used with compound or compounds that contain car bottles. So if we convert this all kind here into either an aldehyde or a ketone, we can go ahead and proceed with a witted reaction. So that's her first step or rather, that's the first component of our plan. But the question does mention to include a protecting group and we do have this kone to the very left side of the starting material. No, because we're going for a witted reaction and our strutting material already has a car bono which is a ketone. We have to make sure that we go ahead and be protected, right. So before we do anything, our first step is always going to be protection to make sure that there are no unwanted side reactions and their side products. So our first step is going to be protection with ethylene glycol in the presence of sulfuric acid. The convert are starting ketone into an ace because we recall that aces are the protecting groups of aldehydes and ketones. So by having this acetal, we are in less danger of having any unexpected side reaction. So now we can go ahead and convert our all kind into a car bal. But what I want to point out here is that the terminal all keen in our final product, it's actually in between, right, it's actually in the middle of this carbon chain. And because it's in the middle of that carbon chain or rather within the carbon chain, it looks strikingly similar to a ketone, which means that are all kind must be converted into a ketone. So that's why our next step is going to be the acid catalyzed hydration of the all kind to install hydroxy group on the more substituted position, which will therefore convert it into the keto form or a ketone. So here we have HGSO four reacting with H two. So four in the presence of water to go ahead and produce our car bal, right. So here, like I said previously, because we're doing acid catalyzed hydration, a hydroxy group would be installed on the more substituted carbon of the all kind. However, keto anal organization will form or rather will take place and that is going to result in the formation of a key tone as opposed to an Enel. So its at this point that we can go ahead and proceed with our witt reaction because we do have a an unprotected carbonel group. So now we can go ahead and proceed. So now we can go ahead and react our unprotected car bal with a trenny phosphine elide. So that's ph three p and this phosphorus is double bound to one C two. Because here, our goal is to only ex or rather extend our carbon chain by one, right. So that's why I only have one carbon in my Trenny phosphine elite. So that is going to extend the carbon chain by only one. So instead of having a key toone there, on the right side, we have a terminal alkene instead. And last, but not least we're almost there, right? Because at this point, we've gone ahead and converted our all kind into a terminal. All keen after extending the carbon chain by just one. So our final step, if the first step was protection, our final step is going to be the protection. So our final step is going to be acidic hydrolysis with H two. So four and water to go ahead and remove the aceta. So with that, we end up with our final product which is 46 methyl hept 16 to 0 and there you have it. So let's go ahead and recap the steps. The first was protection, right by converting our car bono here into an acetal. And then after protection, we proceeded with acid catalyzed hydration of the all kind to yield the corresponding keto product. And then that kone was converted into and all keen using a wi reaction followed by the protection to remove our ace to and generate our final product. So with that being said, if you stuck around to the end, thank you so very much for watching. And I hope we found this helpful.

Suggest a synthetic scheme, involving a protecting group, to generate the molecule shown starting with the molecule at the left.
(a)

Key Concepts

Protecting Groups

Synthetic Scheme

Functional Group Transformation

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