Develop syntheses for the following compounds, using acetylene...

Question

Develop syntheses for the following compounds, using acetylene and compounds containing no more than four carbon atoms as your organic starting materials.

(b) cis-1-ethyl-2-methylcyclopropane

Accepted Answer

All right. Hi, everyone. So this question is asking us to develop a synthesis for cis one Isobel two Isopto cyclopropane use acetylene as the starting material and other organic compounds containing no more than five carbon atoms. So let's go ahead and start by drawing out the intended synthesis here. Our starting material is acetylene, otherwise known as ethane. So here we have only two carbons in total with a triple bond in between them. So acetylene is being converted into cis one Isobel two Isopto cyclopropane. So that's a three carbon ring with an Isobel substituent on carbon number one and an iso penal substituent on carbon number two. Now, because the cis configuration is being specified, these two substituents should be on the same side. So I'm going to draw them both on a wedge. So branching off of carbon number one of the cyclopropane ring is an additional three carbons with a metal substituent on the second position of the substituent itself. That's the Isobel group. So on carbon number two, the iso penal substituent is a full carbon chain with a methyl group on the third carbon of the substituent, that's the opal group. So In addition to there being a new cyclopropane ring, the carbon chain has also been extended because we have new all kill substituents on either side of it. So in this particular case, we have to not only extend the carbon chain from Celine, we also have to somehow introduce a three carbon ring. Now recall that one of the most common ways to create a cyclopropane ring is villa and or but before we go ahead and reduce the all kind down to an all keen, let's go ahead and extend the carbon chain by adding the iso butyl and isol penal substituents because recall that acetylene is an example of a terminal all kind whose proton is relatively acidic. So by detonating the terminal all kind, the acetyl ion that results from that is a suitable nucleo file for SN two, which is a convenient way to extend a carbon chain. So the corresponding cul halides necessary to extend the carbon chain are going to be based off of the new substituents that we see in the structure of the final product. So for example, if we take the iso beetle group and attach a halogen in this case, bromine to the position that's attached to the cycle propane ring. One of the ocho halides necessary is one bromo two methyl propane. So with the iso penal group, we can do the same thing and that gives us one brom three methyl butane. So with this in mind lets go ahead and begin our sequence starting off with acetylene. Our first step is to add a strong base to go ahead and detonate our terminal all kind here and produce the acetyl ion. So here we can use one equivalent of sodium amide that's nanh two. This produces a negative charge on one side and therefore, are a see a light ion from there. We can go ahead and set up an sn two reaction to install one of our Ocu groups using the Ocu hate lights that we discussed previously. Now, in this particular case, either of the two oy hide can be added. There's really no preference. But for the sake of discussion, let's go ahead and install the ISO beo group first. So the Ocu hide that I'm adding in this particular step is one bromo two methyl propane. So now the negatively charged carbon atom of the acetyl ion is going to replace Bromine on the o high light, which has now extended the carbon chain by adding our Isobel substituent. From here, we can repeat the same process, recreate an acetyl ion on the other side by adding one more equivalent of sodium amide. This creates another acetyl ion that can then be used for an additional SN two reaction. So for the next two reaction, we're going to add a remaining oy Halide, which is one bromo three methyl butane, this installs the iso penal group on the other side. All right, So at this point, our carbon chain has been extended, our intended substituents have since been added via the S and two reactions described earlier. So now, now we have to go ahead and reduce the all kind down to an all keen to then proceed with the addition or the rather the formation of the cyclopropane ring. Now, because our intended final product is in the cis configuration, meaning the Ocu groups are in the same or rather on the same side, we want this reduction to produce the corresponding sis. OK. So to make this possible, we're going to reduce our alk line here with hydrogen gas and Lin Lars catalyst. This reduces the triple bond down to a double bond and the corresponding keen is going to be in the cis configuration. And so from here, the last step of the synthesis is to go ahead and produce our cyclopropane ring and therefore produce our intended product. Now, in this particular case, when it comes to producing a cyclopropane ring from an alkene, the appropriate reagents are going to be CH two I two in the presence of zinc and copper, one chloride. And by setting up our cyclopropane nation like this, we've ensured that the reaction is going to preserve the cy configuration that we set up when reducing our all kind down to a CIS OK. So here an additional carbon is added across the Aine itself, creating a cyclopropane ring and our other och substituents are going to be on the same side relative to each other. Now, keep in mind that the two substituents could have also been depicted on a dash. The main point was that they were both on the same side, but there you have it. So now we've completed our reaction sequence. But in this particular case, I'm going to go ahead and revise some of these steps so they can go ahead and match your answer choices. So namely, I'm going to go ahead and create skeletal structures by removing the carbon atoms that were previously shown for illustrative purposes. So namely the ones of the all kind and subsequent acetyl ions and here you have it now we have the completed reaction sequence. And so with that being said, if you watch this video all the way through, thank you so very much. And I hope you found this hopeful.

Develop syntheses for the following compounds, using acetylene and compounds containing no more than four carbon atoms as your organic starting materials.
(b) cis-1-ethyl-2-methylcyclopropane

Key Concepts

Acetylene as a Building Block

Cyclopropane Structure and Reactivity

Stereochemistry in Organic Synthesis

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