Show how Wittig reactions might be used to synthesize the foll...

Question

Show how Wittig reactions might be used to synthesize the following compounds. In each case, start with an alkyl halide and a ketone or an aldehyde.

(a) Ph–CH=C(CH₃)₂

(b) Ph–C(CH₃)=CH₂

Accepted Answer

Hey everyone and welcome back device a synthesis for the following al Kane's using the Wittig reaction starting with an alcohol. Hey light and a key zone or an AL to hide because we're dealing with a Wittig reaction. The easiest way is to start with problem number one by identifying our double bond, we noticed that we have only one double bond. Let's ignore the double bonds within the benzene ring definitely. We cannot perform the Wittig reaction within an aromatic system. So we're thinking about this double bond only and we are going to separate the result on fragments. First of all, we can throw our six member ring. Now we are going to create that carbon carbon bond. We understand that we have that hydrogen and there is this double bond over here. Now the remaining part on the right hand side corresponds to double bond With two ethyl substitutions. Okay, and now when we have separated the two fragments, we just want to think about the assignment of our carbonell compound and our phosphorus Allied. So let's suppose that for the purposes of this problem we are going to choose our carbonell compound for the second fragment. So let's just add oxygen. Right, so we got our key tone. Well done. Now the world last thing for us is to get an elk kill. Hey light. Okay and essentially we have to keep in mind that for if we assign the auction over here then here we are signing our phosphorus Allied. Now if we have our kids zone, we are good. We just want to think about the formation of that prosperous allied first of all keep in mind that we control its restaurants form so that we can essentially break that pipe on. And another form of this alliance would correspond to the following phosphorus has four bonds positive charge. Carbon has a negative charge. Now essentially remember that to form this Allied your world last step is a deep rotation step at this carbon to get that negative charge. So that means if we go from right to left we're going to use a strong base such as normal visa lithium two d. Protein it a structure. So we simply need to add one hydrogen here and we will get the corresponding structure for the previous steps we have our six member ring. Then we have our siege two groups. We can just say that this is our carbon with two hydrogen and this carbon is wanted to p P. H three which still has that formal positive charge. Now the world last thing for us is to think about the formation of this structure And you may recall that we have must have a good leaving group bonded to that carbon that carbon will be attacked by try final foss fine. And we are done. We can throw our alcohol. Hey light let's suppose that we are choosing our bromo substitute as a good leaving group. So essentially let's draw it out let's keep in mind that the nuclear file that we're using for this essence. Your reaction is try final pass fine. And on that carbon we are going to bond romaine because it's a good leaving group. So phosphorus attacks we have the loss of the leaving group. We're forming our fragment, treating it with normal B cell lithium D. Protein. Ating that carbon we have residents the two fragments combined basically our allied with our key tones to give us our found product. So we can clearly see how the reaction sequence looks like. We got our alcohol daylight. We got our key tone. So if we draw the reaction sequence we may start by drawing Benzel bromide because that's what we have. We may draw siege to br that's pencil bromide. Our starting L kill hey light. It would actually be more accurate to say that this is ariel hey light but that's perfectly fine. And now we need several steps if we read from right to left. The first step was the addition of try fennel fosse finn. The second step was addition of normal bees. A lithium. Here we are getting our allied and when we get our allied we just need to treat it with the key tone. So we can start by drawing the carbonell group. And let's add to ethel substitue ints. That's it. This is how we get our product. We can label this is our final answer to the first part. And moving on to the second part we can start by breaking our double bond Once again, we only have one double bond that we can break. And we have to draw two fragments. Let's see that. So, first of all, we are going to start by drawing this fragment. So that would be carbon bonded to two hydrogen and then having a double bond. Okay, so first of all, we have our carbon monitor to high pigeons. And now for the remaining fragment we had our benzene ring. And let's see what the remaining substitutes were. So we have our carbon with a double bond and then with apropos substitute print. I'm sorry that would be an ethyl substitution. Right? We have CS two CS 3. So carbon and then this ethyl group. So now we're going to draw carbon this ethyl group. So that ceased to C three. Right? And then here we have the remaining fragment of our double bond. We simply want to assign our carbon ill first. So we have two possibilities here let's suppose that the second fragment is our carbon eels. We once again get our kids on well done. And we just want to form Our Allied for the remaining one. We once again understand that we control its resonance form and we get the following. Now two hydrogen atoms. Carbon has a negative charge. We already understand that this form will be formed during the D. Protein nation using normal Visa lithium. So we have to add hodge in here to get the structure. And we get the following. So basically Carbon with three hydrogen atoms or basically a metal group. Right? And how to get this one. We want to replace phosphorus with a good leaving group. So we can say what if we simply use of course the nuclear file will be tried fennel fosse fine for this essence to reaction. And we noticed that we just need to replace phosphorus with a good leaving group. We have our methyl group CH three and we can just replace it with our bromo substitution. Right? Because it's a good leaving group. So we clearly see how the synthesis would look like try final fosse fine would essentially attack our electro Felix center followed by the loss of the leaving group. We would form our fragment from here. We were D. Protein ate it. We get our allies, we treat it with the key zone and we get our product. So we are ready to draw the final sequence. Starting with no more methane. That would be C three. We are going to get the following sequence. The first two steps will be exactly the same as before. Number one edition of Try Fennel. That's fine. Number two additional of normal Visa lithium. So just as we had these steps before to form our allied and number three addition of the key tone for the key. It's only half hour. Benzene ring. Now we're drawing our carbonell group and then let's troll that ethel wanted to that carbon. Okay, so we got our key tone and this would summarize our steps. This is how we get our final product. So let's write down product and let's label this reaction sequences our final answer. So we have our answers. This is the answer to party. Going back, we see the answer to part one. We can summarize that. The first two steps are exactly the same. We are going to get our daylight out of an al kill Hey light in this case that's errol hey light right for number one for the second one we have our L kill hey light. The first two steps allow us to get the required a light and then we're treating it with a carbon compound in each case. That's a key tone and we get our products based on what we got. We may conclude that the correct answer to the multiple choice question is D However, if you have any questions, don't hesitate to leave a comment down below. Thank you for watching

Show how Wittig reactions might be used to synthesize the following compounds. In each case, start with an alkyl halide and a ketone or an aldehyde.
(a) Ph–CH=C(CH₃)₂
(b) Ph–C(CH₃)=CH₂

Key Concepts

Wittig Reaction

Phosphonium Ylide

Alkyl Halides

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